Emerging Pollutants as Chemical Additives in the Petroleum Industry: A Review of Functional Uses, Environmental Challenges and Sustainable Control Strategies

Abstract

Emerging pollutants (EPs) associated with the petroleum industry present considerable challenges to environmental management and sustainable development. To support sustainable development and improve the control of EPs in the petroleum industry, this review systematically examines the functional uses of EPs as chemical additives across the entire petroleum supply chain—from extraction and transportation to refining and product blending. It also summarizes the environmental emissions, health impacts, mitigation strategies, and current regulatory frameworks of EPs. In addition, some challenges have been found, namely unclear data on EPs in chemical additives, insufficient attention to high-risk areas, undefined health risks of mixing EPs, lack of green assessment of alternative technologies, and regional policy disparities, which collectively hinder the effective prevention and management ofEPs. In response, we propose future perspectives including enhanced screening and substitution of high-EP-risk additives, development of source-specific fingerprinting techniques, expanded monitoring of mixed contaminants and understudied regions, accelerated deployment of green technologies, and strengthened global cooperation under sustainability-oriented governance frameworks. This study underscores the necessity of integrated, science-based approaches to align petroleum industry practices with global sustainability goals. This review underscores the critical need for a proactive and integrated approach toward the sustainable development of the petroleum industry through the control of and reduction in EPs.

1. Introduction

Emerging pollutants (EPs) are pollutants that have been recently recognized and pose potential risks to ecological systems and human health. To date, a wide range of EPs, including persistent organic pollutants (POPs), endocrine-disrupting compounds (EDCs), antibiotics, and microplastics (MPs) [1], have been identified and detected worldwide across various environmental matrices [2,3,4,5,6,7]. Despite growing concern, effective prevention and control of EPs are still challenging due to regulatory deficiencies and inadequate management strategies [8,9]. While the proliferation and usage of synthetic chemicals have been well recognized as an important source of EPs in the environment, the occurrence and transformation pathways of EPs within industrial supply chains have received comparatively little attention. This gap represents a major obstacle to effective management of EPs discharges into the environment.

Among major industrial sectors, the petroleum industry serves as a backbone of global energy and raw material supply [10,11]. It was estimated that global oil supply reached a record high of approximately 103 million barrels per day in 2024 and is projected to increase in the forthcoming years [12]. Therefore, in order to reduce the negative impact of petroleum on the environment, the industry is working towards green and sustainable development [13,14]. Previous studies have frequently detected EPs in oilfields [15] and petroleum refineries [16], suggesting a potential association between the petroleum industry and EPs generation, emission, and use. Additionally, it is well known that the industrial process, from oil extraction to refining and processing, involves the extensive use of synthetic chemicals [17,18,19]. These chemicals are often characterized by substantial amounts of consumption, diverse physicochemical properties, and frequent formulation as multi-component mixtures, and thus increase the risk of EPs entering the petroleum product chain.

Consequently, to better understand the potential sources of EPs within the petroleum industry, this review systematically examines the chemicals used throughout the entire supply chain from oil extraction to refining and blending, and identifies those with potential to generate or transform into EPs. Based on the results of examination and identification, the review further collates the ecological and environmental hazards associated with them to support their harmfulness. In order to further control the EPs in the petroleum industry, relevant reduction pathways and control policies are also summarized. This analysis is anticipated to play a pivotal role in elucidating the origins of EPs within the petroleum industry sector and facilitating effective source control measures.

2. Functional Uses of EPs

2.1. Oilfield Chemicals

The utilization of oilfield chemicals is widespread in oil extraction, primarily to address chemical-related issues during oilfield drilling, oil recovery, and enhanced oil recovery [20,21,22,23]. The complex composition of oilfield chemicals, combined with variations in reservoir characteristics, geology, and extraction conditions across different oilfields, results in significant differences in their practical application [24]. Consequently, the risk of introducing EPs exhibits considerable variation between different oilfields.

As shown in

Table 1. Functional uses of EPs in oilfields.

Number	Group	Application	Chemicals	Major EPs
C-1-1	Oil well drilling	Filtration reducer	Polyacrylamide	PFAS
C-1-2		Shale inhibitor	Polymer Cationic surfactant	PFAS
C-2-1	Oil recovery	Oil well acidifier	Inorganic acid Potential acid	HHCs
C-2-2		Thickener	Polyacrylamide Surfactant	PFAS
C-2-3		Retarder	Surfactant (soluble in acid) Polymer	PFAS
C-2-4		Fracturing agent	Emulsion fracturing agent Foam fracturing agent	PFAS
C-2-5		Foaming agent	Surfactant	PFAS AP
C-2-6		Defoamer	Surfactant	AP
C-2-7		Oil well water-plugging agent	Surfactant	PFAS
C-2-8		Tracer	Tracer	HHCs
C-3-1	Chemical oil displacement agent	Polymer oil-displacing agent	Modified polyacrylamide	PFAS
C-3-2		Surfactant oil-displacing agent	Highly chemically resistant surfactant	PFAS

, a comprehensive review of the extant literature reveals that the oilfield chemicals may potentially introduce EPs, including alkylphenol ethoxylates (APEO), alkylphenol (AP) [25,26], halogenated hydrocarbons (HHCs) [27], per- and polyfluorinated compounds (PFAS) and their modified polymer materials [22].

2.1.1. Oil Well Drilling

Drilling, the foundational step in oil and gas extraction, requires specialized drilling fluids to meet the demands of the process [28]. Synthetic polymer materials, principally polyacrylamide and its modifiers, function as drilling fluid treatment agents. These materials are primarily utilized as a filtration reducer and shale inhibitor in drilling fluid treatments [29,30]. To enhance the thermal, saline, high-valent ion, and shear resistance of polyacrylamide, modification strategies frequently involve incorporating sulfonate groups, reinforcing stabilizing moieties, and introducing hydrophobic associations [31]. PFAS find wide application in polyacrylamide modification owing to their high surface activity, excellent thermal and chemical stability, and amphiphobic properties [32,33]. As shown in Figure 1, Wenxin et al. synthesized a fluorocarbon-containing hydrophobic monomer (FC-137) with perfluorooctanoic acid (PFOA), N,N-dimethylpropy-lenediamine (HNB), allyl chloride (AC), and prepared a fluorocarbon hydrophobically associative polyelectrolytes (FCPAM) by radical aqueous solution level polymerization [34].

2.1.2. Oil Well Acidifier

The permeability of the formation has been demonstrated to exert a significant influence on the efficiency of oil recovery. The process of acidizing an oil well has been shown to result in a substantial increase in its permeability [35,36]. In addition to the direct acid addition methods (e.g., the addition of hydrochloric or hydrofluoric acid), the potential acid methods are also effective [37]. The potential acid methods, including halogenated hydrocarbons, halogenated salts, and low-molecular-weight esters, can form acids under specific conditions. This capacity can hinder the reaction rate between acids and formations, as well as the corrosion of metals. Notably, such potential acid methods have advantages for high-depth wells [37].

HHCs, including tetrachloromethane, tetrachloroethane, and tetrafluoroethylene, undergo hydrolysis under specific downhole conditions, generating acids such as hydrogen chloride (HCl) or hydrofluoric acid (HF). This hydrolysis occurs at temperatures between 120 °C and 370 °C under downhole conditions, with the specific reaction mechanism detailed in Figure 2. Incomplete hydrolysis of HHCs in oil wells leaves residual compounds that partition into crude oil, enabling their migration through the petroleum production stream.

2.1.3. Chemical Oil Displacement Agent

Numerous chemical agents enhance oil recovery during secondary and tertiary extraction by improving the wave volume and oil repellent efficiency, thereby increasing recoverable reserves [38,39]. Surfactants represent the most prevalent additives, functioning as demulsifiers, fracturing fluid additives, water-blocking agents, and foaming agents [40]. Following application, residual surfactants migrate into extracted crude oil, produced wastewater, and subsurface formations. Ultimately, these compounds enter environmental compartments via industrial discharge or migration through petroleum chains.

• Fluorocarbon Surfactants

In the context of the progressively intricate geological characteristics of oil reservoirs and the escalating depth of burial, the high-temperature and high-salt oil recovery conditions impose stringent demands on surfactants. The remarkable properties of fluorocarbon surfactants render them efficacious in reducing interfacial tension, even under conditions of concentrated acid and high salt [41,42]. Consequently, fluorocarbon surfactants have the capacity to enhance the permeability of the formation, elevate the fluidity of crude oil, and function as an oil repellent. Moreover, they exhibit resistance to strong acids, thereby serving as an auxiliary agent. Additionally, they are capable of generating more stable foams, rendering them suitable for use as a foaming agent [22]. There are five common types of fluorocarbon surfactants (Figure 3): (1) fluorinated nonionic surfactants [43,44]; (2) fluorinated anionic surfactants [45,46]; (3) fluorinated cationic surfactants [47,48]; (4) fluorinated zwitterionic surfactants [49]; (5) fluorinated gemini surfactants [50,51].

2.

Alkylphenol Ethoxylate Surfactants

Prevalent nonionic surfactant ethers represent prevalent nonionic surfactants utilized in the petroleum industry [52]. Octylphenol ethoxylates (OPEOs) and nonylphenol ethoxylates (NPEOs) are the most common of alkylphenol ethoxylates (APEOs). The typical structure of NPEOs is shown in Figure 4.

Table 2. Index and application of common nonylphenol ethoxylates.

Number	Phenotype	Solubility	Major Applications
NPE-4	Colorless or yellowish transparent oily liquid	Oil-soluble	Polymeric emulsifiers, industrial emulsifiers, metal degreasers, and cleaning agents
NPE-7	Colorless or yellowish transparent oily liquid	Water-soluble	Industrial emulsifier, wetting agent
NPE-9	Colorless, transparent oily liquid	Water-soluble	Antistatic agent, cleaning agent
NPE-10	Colorless, transparent oily liquid	Water-soluble	Emulsifier, detergent
NPE-15	White paste	Water-soluble	Emulsifier, high temperature dispersant, detergent
NPE-40	White wax	Water-soluble	Emulsifier, dispersant, viscosity reducer

enumerates a number of common nonylphenol ethoxylates that have a wide range of applications in crude oil treatment, especially in crude oil demulsification. Nonylphenol ethoxylates have demonstrated substantial environmental toxicity, and their utilization has been restricted in both domestic and international contexts [52,53].

In practical applications, different kinds of surfactants are always mixed in order to enhance application effects. The composition of a high-temperature acidizing co-discharge agent (HC 2-1) developed by Sun et al. includes the following components: 20% fluorocarbon anionic surfactant (FX-2), 70% polyoxyethylene alkylphenol ether phosphate salts (AP-4), 5% polyoxyethylene alkyl phenol phosphate salts and hydrocarbon cationic surfactants (BCDMACl), and 5% co-surfactant, in addition to other components [54]. The deployment of surfactant formulations in oilfields introduces complex mixtures of EPs, significantly complicating source control strategies for them.

2.2. Oil Transportation Chemicals

Furthermore, the transportation of crude oil requires the use of a considerable amount of chemicals. A variety of issues, such as high water content in crude oil, wax formation, and solidification, can significantly affect oil and gas gathering and transportation processes [55]. In order to improve the flowability of crude oil, chemical emulsifiers, viscosity reducers, wax cleaners, and wax preventive agents are widely used to prevent wax deposition, solidification, and blockages. Additionally, chemical emulsion breakers are frequently employed to mitigate the impact of high water content on subsequent processes. As listed in

Table 3. Functional uses of EPs in crude oil gathering and transportation.

Number	Group	Application	Chemicals	Major EPs
S-1-1	Improving crude oil liquidity	Polymer viscosity reducer	Modified polyacrylamide	PFAS
S-1-2		Surface-active viscosity reducer	surfactant	PFAS
S-1-3		Mixed-type viscosity reducer	/	/
S-2-1	Paraffin wax remover and inhibitor	Paraffin wax remover	Organic Solvent	HHCs
S-2-2		Paraffin wax inhibitor	Polycyclic aromatic hydrocarbons Surfactants Polymer agents	PFAS AP
S-3-1	Crude oil demulsifier	W/O demulsifier	Sulfonate Phenolic resins Polyoxyethylene ether Phenolamine Resins	PFOS NP
S-3-2		O/W demulsifier	Polymer Emulsion Breaker Macromolecule emulsion breakers	NP

, PFAS, AP, and HHCs may be introduced into crude oil gathering and transportation, primarily through viscosity reducers, wax-cleaning and wax-preventing agents, and W/O-type emulsion breakers [56].

2.2.1. Viscosity Reducer

Thickened oil is characterized by its high viscosity and density, which complicate its extraction and transportation [57]. The primary component of emulsifying viscosity-reducing agent is a surfactant, which facilitates the transformation of water-in-oil (W/O) emulsions in to oil-in-water (O/W) emulsions, where water forms the external phase, thereby significantly reducing the viscosity of the thickened oil [58]. In practical applications, in addition to surfactants, fluorocarbon-based compounds, hydrocarbon-based compounds, and polyoxyethylene ether are often employed to achieve optimal high-temperature and salt resistance, reduce cost, and enhance viscosity reduction, respectively [59]. As a result, the compounded viscosity reducer will also be a common introduction pathway for a variety of EPs.

2.2.2. Paraffin Wax Inhibitor and Remover

The presence of paraffin wax in crude oil has been identified as a primary factor influencing its fluidity. A significant amount of paraffin wax precipitation has been shown to directly impact the fluidity of crude oil, thereby influencing the selection of optimal pipeline routes [55]. Polycyclic aromatic hydrocarbons (PAHs) are commonly used as paraffin wax inhibitors. Their solubility in crude oil is lower than that of paraffin wax, thus enabling them to act as the crystal nuclei for paraffin wax precipitation. Consequently, paraffin wax undergoes nucleation on PAH substrates, forming microcrystalline structures rather than macrocrystalline aggregates. Micron paraffin wax crystals remain suspended in crude oil flow streams, effectively mitigating large-scale agglomeration that would otherwise precipitate deposition, induced flow restrictions. Since most PAH congeners are well-known carcinogens, their injection into oil wells through annular piping and subsequent extraction and transportation with crude oil could introduce a category of EPs into the downstream petroleum production chain. Besides PAHs, alkylphenol ethoxylates are also frequently utilized as an oil-soluble antifouling agent that prevents the formation of wax precipitation, a process that may also introduce nonylphenols into the petroleum production.

Conversely, paraffin wax removers are primarily employed to dissolve condensed paraffin wax, thereby preventing clogging. HHCs, including carbon tetrachloride, were extensively used in the early history of oilfields due to their high solubility and effective paraffin wax remover properties. However, their use has since been prohibited due to their inherent toxicity and adverse effects on subsequent processing operations. Other low-toxicity organic solvents, such as switchable polarity solvents (SPSs) composed of dipropylamine (DPA), ethylbutylamine (EBA), and dibutylamine (DBA), remain in use due to their demonstrated performance efficacy [60].

2.2.3. Crude Oil Demulsifier

Crude oil dewatering constitutes a pivotal step in the processes of gathering and transportation. A portion of the water contained in crude oil exists in a dispersed state as liquid droplets, thereby forming W/O emulsions [61]. During the three stages of oil recovery, the high-water content necessitates the injection of chemicals that alter the complex composition of the extractive fluid and lead to the formation of O/W emulsified crude oil. These alterations can also result in more complex emulsions, such as “oil-in-water-in-oil -O/W/O” or “water-in-oil-in-water -W/O/W”, collectively referred to as multiple emulsions [61]. The presence of high-water content in crude oil has been demonstrated to exert adverse effects on post-processing operations and to increase the energy load required for transportation. The challenge of eliminating water from crude oil is compounded by the fact that a portion of the water exists in the form of a stable emulsion, rendering conventional settling methods ineffective. Consequently, additional techniques are needed to disrupt the emulsification process, such as the addition of chemicals.

Phenolic resin and phenol amine resin are a prevalent class of W/O-type emulsified crude oil emulsion breakers. Phenolic resin demulsifiers are predominantly block polyether derived from the copolymerization of alkylphenol formaldehyde resin with ethylene oxide and propylene oxide [62]. The alkylphenols utilized primarily include butylphenol, nonylphenol, and dodecyl phenol. The predominant structures observed are the three-segment block polyether (AF-type) and two-segment block polyether (AP-type), as shown in Figure 5.

2.2.4. Anti-Corrosion Lining

Critical petroleum infrastructure materials also release EPs during degradation. Polytetrafluoroethylene (PTFE) is extensively used in equipment such as piping, tanks, seals, and linings where chemical stability is required [63]. PTFE can leach PFOA and its degraded short-chain perfluorinated compounds during high-temperature processing or seal failure. Furthermore, petroleum operations utilize extensive mechanical equipment, such as drilling rigs, pumps, and transformers. Lubricants and functional chemicals associated with these systems introduce additional EPs into production streams, highlighting a critical research gap that warrants urgent investigation.

2.3. Petroleum Refining Chemicals

Chemicals used in oil refining and petrochemical processes mainly include catalysts, additives, and solvents. These substances play a key role in enhancing refining efficiency, protecting equipment, and separating impurities. However, they also serve as important vehicles for EPs to enter the petroleum industry chain. In the context of refinery additives, PFAS and NP act as surfactants and surfactant precursors, consistent with their historical applications in oil extraction and crude oil transportation. These compounds are predominantly utilized as corrosion inhibitors, defoamers, and demulsifiers, as summarized in

Table 4. Functional uses of EPs in refining additives.

Number	Group	Application	Chemicals	Major EPs
L-0-1	Universal agent	Corrosion inhibitor	Surfactant	PFAS
L-0-2		Defoaming agent	Surfactant	PFAS
L-1-1	Oil Processing	Crude Oil Demulsifies	Sulfonate and other anionic types Polyether type	NP
L-2-1	Oil Distillation	Crude oil distillation enhancer	Aromatic concentrates Surfactant Complex activator	PFAS NP

.

As shown in

Table 5. Functional uses of EPs in chemical additives.

Number	Application	Chemicals	Major EPs
H-1	Emulsifier	Nonylphenol polyoxyethylene ether sulfate amine salt Nonylphenol polyoxyethylene ether carboxylate salt Betaine amphoteric surfactants	PFOA NP
H-2	Dispersant	PFOA	PFOA
H-3	Polymerization terminator	Bisphenol A Hydroquinone	BPA
H-4	Polymerization inhibitor	Hydroquinone NP	NP
H-5	Antioxidant	Bisphenol A phosphite	BPA
H-6	Antistatic agent	Perfluorobutanesulfonates Salicylates Bisphenol A Bis(salicylate) Benzophenones	PFAS BPA

, multiple factors contribute to the presence of EPs in chemical auxiliaries. In addition to PFAS and NP, other well-known endocrine disruptors such as bisphenol A (BPA) are also prevalent EPs.

Solvents function as the primary medium for various processes in oil refining, including separation, reaction, and processing. The following are examples of common solvents: (1) hydrocarbons (propane, hexane, benzene, etc.); (2) halogenated hydrocarbons (dichloromethane, trichloromethane, tetrachloroethylene, chloro-benzene, etc.); (3) alcohol-based solvents (methanol, ethylene glycol, etc.); (4) phenols (phenol, p-tert-butylphenol, etc.); (5) ethers (dimethyl ether, tetrahydrofuran, etc.); (6) organic acids and anhydrides (formic acid, etc.); (7) esters (ethyl acetate, dimethyl carbonate, etc.); and (8) amines. Organic solvents are widely used in the refining sector, including the solvent extraction processes [64]. Because these solvents are employed in large quantities, they serve as a major source of volatile organic compounds (VOCs) such as dichloromethane and trichloromethane, and warrant further attention.

2.4. Petroleum Product Additives

Petroleum product additives are chemicals that are added to oil products according to a certain dosage in order to strengthen or give them new properties. The amount of additives ranges from a few parts per million to 20% (mass fraction) or more [65,66,67].

Table 6. Functional uses of EPs in product chemical additives.

Number	Group	Application	Chemicals	Major EPs
T-1-1	Lubricant Additives	Detergents and dispersants	Alkyl phenate Sulfurized alkyl phenate Alkyl salicylate	APs
T-1-2		Extreme-pressure antiwear agent	Chlorine-based extreme-pressure antiwear agent	SCCPs
T-1-3		Pour point depressant	Alkylphenol	APs
T-2-1	Fuel Additives	Antioxidant and anti-gum agent	Alkylphenol	APs
T-2-2		Antistatic agent	Perfluorobutyl sulfonate	PFAS
T-2-3		Antiwear agent	Chlorine-based antiwear agent	SCCPs PCPs
T-2-4		Oxidizer	Tritolyl phosphate
T-2-5		Detergents and dispersants	Alkyl phenol salts and their derivatives	APs

presents a comprehensive list of EPs that may be introduced in common additives, as classified according to the standard. Among the various product additives, short-chain chlorinated paraffins (SCCPs), pentachlorophenol (PCP), and APs have emerged as the most prevalent contaminants, with the potential for facile introduction into the environment.

2.4.1. Detergents and Dispersants

The primary function of detergents and dispersants in lubricant additives is to neutralize acids, inhibit the formation of high-temperature deposits, and effectively suspend and disperse sludge, ash, metals, and other substances to maintain the stability of lubricant performance [68]. Alkylphenol salts, sulfated alkylphenol salts, and alkyl salicylates are three common types of detergent dispersants [69,70] (Figure 6). Calcium alkylphenol is one of the most prevalent scavenging and dispersing agents. It is frequently incorporated into gasoline and diesel engine oils with the purpose of neutralizing corrosive acids, regulating carbon buildup, and preventing the gelling of engine piston rings. Representative grades include LZ692. Alkylphenol sulfide salt introduces sulfur, thereby enhancing the polarity of alkylphenol salts and consequently improving their antioxidant and corrosion resistance. Notable grades include LZ115A and LZ6500. Alkyl salicylates enhance molecular polarity by introducing carboxyl groups to alkylphenols and transferring metals from hydroxyl groups to carboxyl groups, thereby improving their working efficiency under high-temperature conditions. Common grades include OSCA420 and InfineumC9372, among others. Phenolic cleaners and dispersants composed primarily of alkylphenol have extensive utilization, thereby markedly elevating the probability of nonylphenol contamination.

2.4.2. Extreme-Pressure Wear Agents

The utilization of extreme-pressure wear agents has been demonstrated to enhance oil lubrication performance, mitigate wear of machine components, conserve energy, and prolong the operational lifespan of machinery. Chlorine-series extruded antiwear agents react with the metal surface through chemical adsorption, thereby generating a protective film. These agents demonstrate both antiwear and extreme-pressure effects, and they are typically added at concentrations ranging from 1% to 10%. Common varieties of chlorine series extreme-pressure antiwear agents include chlorinated paraffins, pentachlorophenol, and chlorinated alkyl phenols, among others [71]. The most prevalent chlorine-containing compound is chlorinated paraffin (T301), which is distinguished by its affordability and high activity. Furthermore, a variety of chlorinated paraffins, including CW60 and CW35, are frequently employed. Cyclic chlorinated compounds, exemplified by PCP, are frequently employed due to their stabilizing properties and demonstrated corrosion resistance. Short-chained chlorinated paraffins and PCP have been included in the list of emerging pollutants under key control, and medium-chained chlorinated paraffins have gradually received research attention. Consequently, the utilization of chlorinated extreme-pressure antiwear agents has emerged as a pivotal element in facilitating the integration of SCCPs and PCPs within the petroleum industry supply chain.

2.5. Auxiliary Equipment Chemicals

Beyond synthetic chemicals used throughout petroleum extraction and refining, ancillary operations, such as water treatment and firefighting, introduce additional EPs. Firefighting agents constitute significant pathways for introducing EPs, mainly PFAS, through direct release, wastewater migration, and environmental transformation. Petroleum facilities primarily experience Class B fires (involving flammable liquids), necessitating foam-based suppression systems. Fluorocarbon surfactants serve as essential functional components in these firefighting foams [72]. While historically reliant on perfluorooctanesulfonic acid (PFOS) agent, its incorporation into firefighting formulations has been progressively prohibited due to mounting evidence of its environmental persistence and ecotoxicity. Aqueous film-forming foam (AFFF), fluoroprotein foam (FP), and film-forming fluoroprotein foam (FFFP) represent prevalent PFOS alternatives whose formulations are engineered to minimize environmental impacts [73,74].

During fire incidents or training exercises, applied agents can seep into soils containing unrecovered oil–water emulsions. Resulting wastewater enters treatment systems, while residual foam in pipelines is transported via oil-drainage networks and stormwater to discharge points. Legacy fluorinated agents persist in environmental matrices and products.

2.6. Summary of the Entire Chain

APs/APEOs (e.g., NP/NPEO and OP/OPEO) have been identified as the primary EPs in the petroleum industry. It is predominantly utilized in the synthesis of nonionic surfactants, phenolic resins, and acylphenol salts. The utilization of AP and its derivatives extends to a wide range of applications as emulsifiers, demulsifiers, detergents, and dispersants in petroleum processing.

PFASs, used as fluorocarbon surfactants, possess advantageous properties that have led to their extensive utilization in the domains of the extraction and transportation of petroleum. In most cases, PFASs are utilized in conjunction with other surfactants to achieve enhanced chemical properties.

Halogenated chemicals, which have the potential to introduce EPs, boast a wide range of applications. HHCs represent a prevalent category of chemical additives, exhibiting applications in two distinct domains. Primarily, they function as effective acids during the process of well acidization. Additionally, their solvency properties render them valuable in diverse phases of the petroleum industry. SSCPs and PCPs are primarily found in petroleum product additives. These additives are utilized to enhance the extreme-pressure antiwear capability of oils.

In addition to chemicals directly associated with the oil chain, auxiliary chemicals employed in the oil industry may also introduce EPs. Of particular interest are firefighting foams and corrosion-resistant linings. The utilization of the chemical properties of PFAS by both chemicals results in a significantly higher potential for PFAS introduction.

However, as shown in Figure 7, it must be acknowledged that the practical application of chemical additives is highly complex. Different processes and equipment entail specific requirements, which may introduce distinct EPs. Furthermore, characterizing the types and concentrations of EPs in these additives remains challenging. Commercial products typically lack detailed composition disclosure, and companies often lack the necessary instrumental analytical capabilities. Therefore, comprehensive and detailed investigations are essential to reduce the use of EPs at the source.

3. Environmental Concentrations

3.1. Petroleum Extraction

A mounting body of monitoring evidence has confirmed the presence of EPs in oilfield wastes. The presence of PFAS and AP/APEO in produced water (PW), drill cuttings, and slurry, ranging from nanograms per liter (ng/L) to micrograms per liter (μg/L), underscores their significant release from operational activities. Halogenated hydrocarbons such as dichloromethane constitute a component of fugitive VOC emissions from oilfield operations.

Oilfield produced water (PW) is a major waste stream generated during petroleum extraction [75]. Relevant studies indicate that the extraction from a conventional well requires approximately 8000~100,000 m³ of water and hydraulic fracturing fluid per operation [76]. Annual PW generation reaches approximately 3200~4000 million m³ in the United States [75,77], while discharges total around 8.56 million m³ in China [78] and approximately 130 million m³ in Norway [79]. Due to its intimate contact with both crude oil and chemical additives, PW contains residual compounds that make its chemical composition a valuable medium for characterizing oilfield-specific pollutants [76]. Boitsov et al. detected 52 APs, including NP, in the PW from nine oil wells in the Norwegian North Sea [80]. Zhang et al. identified C₁~C₃ APs in PW from oilfields in the Qaidam Basin, China, although specific concentration data were not provided [81]. In a study conducted in Wyoming, USA, McLaughlin et al. reported the presence of NPEOs at all sampled PW discharge points, with measured concentrations of 2.7 μg/L, 1.7 μg/L, and 3.8 μg/L, respectively [82]. Similarly, research by Akyon et al. confirmed the occurrence of NPEOs in PW from the Bakken and Utica oilfields [83]. These findings demonstrate that AP/APEO-based EPs have been widely detected in oilfields across geographically diverse regions, and multiple studies have documented their clear association with surfactant applications within oilfield operations [84,85]. In addition, analysis of PW from offshore oilfields in China (Bohai Sea, East China Sea, and South China Sea) revealed the presence of multiple PFAS. The measured concentrations of ΣPFAS ranged from 81.9 to 2090 ng/L, with a median value of 299 ng/L [86].

In addition to PW, drill cuttings and slurry generated during drilling and extraction operations represent the primary forms of hazardous waste associated with oilfield production [87,88]. However, research on EPs in such waste remains relatively scarce. Although Costa et al. summarized common contaminant types in drill cuttings, HHCs were often quantified only as part of total organic carbon (TOC), lacking well-defined concentration profiles [89]. Moreover, the widespread use of solvents such as dichloromethane and trichloromethane in chemical analysis further complicates the isolation and determination of HHCs in drill cuttings [89]. The study by Wang et al. on offshore oilfields also included an examination of drill cuttings and sludge. Their results revealed significant contamination, with ΣPFAS concentrations ranging from 1049 to 3473 ng/g (median: 1295 ng/g), dominated by medium- and long-chain PFAS [86].

The release of applied EPs into the environment contributes to localized contamination near oilfields (

Table 7. Concentration of EPs in different environmental media in oilfields.

Location	Media	Types of EPs	Concentration	References
North Sea Oilfield, Norway	Sediment	AP/APEOs	4.1–137,000 μg/g	[91]
Daqing Oilfield, China	Surface water	ΣPFASs	560–5000 ng/L	[92]
Dagang Oilfield, China	Surface water	ΣPFASs (C ≥ 4)	201–12,036 ng/L	[93]
	Sediment	ΣPFASs (C ≥ 4)	4.65–87.4 ng/g
	Soil	ΣPFASs (C ≥ 4)	2.57–32.3 ng/g
Bohai Sea oilfields, China	Receiving water	ΣPFASs (C ≥ 4)	46.2–99.7 ng/L	[86]

). The persistence of certain compounds, particularly PFAS, further intensifies pollution levels in these areas. These EPs may further pose risks to living organisms through pathways such as environmental exposure, posing potential threats to both ecosystem integrity and public health [90].

Mclaren et al. investigated the occurrence of AP/APEOs in sediments from the North Sea oilfields and reported total concentrations ranging from 4.1 μg/g to 137,000 μg/g [91]. Their findings revealed a positive correlation between AP/APEO concentrations and both proximity to operational wells and the duration of oilfield activities, with higher levels detected closer to wellheads and in areas with longer production histories [91]. Besides, Xu et al. identified a novel polyfluoroalkyl benzenesulfonic acid, sodium p-perfluorous nonenoxybenzenesulfonate (OBS), in waters around the Daqing Oilfield in China, where concentrations reached 3200 ng/L near long-producing wells and demonstrated a clear positive correlation between OBS levels and oil production history, with significantly higher contributions to ΣPFASs in older oilfield areas (up to 69%) [92]. In a broader assessment, Meng et al. conducted a comprehensive survey of 26 PFASs in multimedia environments within the Dagang Oilfield, China, which confirmed the widespread presence of both legacy compounds (PFOA and PFOS) and emerging alternatives such as OBS and 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB). The study identified total petroleum hydrocarbons (TPH) as a significant predictor of PFAS contamination, with OBS and 6:2 FTAB levels positively correlated with TPH concentrations [93]. Contrastingly, Wang et al. reported that the maximum concentration of ΣPFASs in oilfield receiving waters reached 99.7 ng/L, which aligned with background levels in the adjacent marine area and suggested the potential role of high oceanic assimilative capacity in mitigating detectable contamination [86].

3.2. Petroleum Refining and Chemical Production

Upon transportation to refineries and petrochemical complexes for processing, crude oil itself can act as a notable vector for introducing EPs into industrial facilities. For instance, Yao et al. detected 20 PFAS in crude oil, among which OBS was the most abundant with a concentration of 634 ng/L, followed by PFOA (359 ng/L), PFOS (185 ng/L), and 6:2 FTAB (141 ng/L) [15]. In addition to this inherent input, various EPs, including APs, PFAS, SCCPs, and HHCs, are intentionally employed during refining operations, further amplifying their prevalence in adjacent environmental compartments. Against this backdrop of dual contamination pathways, the following section examines the documented occurrence and distribution of EPs in environments surrounding petroleum refineries and chemical plants.

Reinikainen et al. detected high concentrations of PFAS in water bodies near a site impacted by aqueous film-forming foam (AFFF) at the Neste Corporation refinery in Finland. The most prevalent compounds were perfluorononanoic acid (PFNA) (2700 ng/L), PFOS (2500 ng/L), and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) (1700 ng/L). Various perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) were also identified in downstream water samples, indicating significant environmental risk [94]. In a separate study, Zhao et al. employed the total oxidizable precursor (TOP) assay and non-target high-resolution mass spectrometry to identify 34 PFAS compounds in soil from a refinery in southwestern China, 23 of which were novel structures. PFCAs, PFSAs, and GenX were identified as major contaminants. Additionally, hexafluoroisopropanol (HFIP), a precursor to perfluoroacetic acid, was detected at concentrations up to 657 ng/g (dry weight) [16]. Further supporting the widespread occurrence of PFAS contamination, PFOS and PFOA have been detected in downstream water samples near the Suncor refinery in Colorado, groundwater adjacent to the Flint Hills Resources refinery in Alaska, and the Marathon Petroleum facility in Michigan, as well as in samples from a former refinery site in Philadelphia, Pennsylvania [95]. In addition to PFAS, Huang et al. detected SCCPs at concentrations ranging from 37.5 to 995.7 ng/g dry weight in soil samples from the Yangkou Chemical Industrial Park in Jiangsu, China [96]. Similarly, Li et al. reported substantial levels of SCCPs in wastewater from a treatment plant near a typical petrochemical park in Eastern China [97]. Both studies attributed the source of these SCCPs to petrochemical activities. These findings underscore a clear link between petroleum industrial activities and EP emissions. However, it remains uncertain whether such contamination originates primarily from incoming crude oil or from intentionally added chemicals during refining, highlighting a critical need for further source-apportionment studies.

4. Ecological and Health Risks

4.1. Alkylphenols

Alkylphenols (APs), as typical EDCs and POPs, have attracted significant scientific interest due to their extensive environmental and health risks, which span from macroscopic ecological disruption to molecular-level toxicity [98]. In environmental systems, APEOs used in petroleum industries can undergo partial degradation; however, their transformation products, such as NP and OP, often exhibit greater ecological toxicity, environmental persistence, and bioaccumulation potential than their parent compounds [99]. For instance, NP demonstrates high affinity for organic phases, leading to its accumulation in sediments, biological lipids, and sewage sludge, thereby forming long-term contaminant reservoirs [98,100,101]. The widespread detection of AP/APEOs near oil wells has established these compounds as ongoing sources of ecosystem exposure.

At the ecological level, APs are particularly notorious for their endocrine-disrupting effects, posing severe threats to aquatic organisms [98,102]. NP and OP demonstrated significant embryotoxic and genotoxic effects of sea urchin, causing reduced fertilization, mitotic disruption, and skeletal malformations at concentrations as low as 0.937 μg/L and 4.685 μg/L, respectively, indicating considerable ecological risk at the population level [103]. Their half-maximal effect concentrations (EC₅₀) can be as low as the ng/L range, and chronic exposure to concentrations ranging from ng/L to mg/L has been shown to cause skewed sex ratios, impaired gonadal development, and reduced reproductive fitness [104,105]. Furthermore, these compounds can undergo trophic transfer and biomagnification, leading to their accumulation at considerable concentrations in top predators and endangering the structure and functional stability of ecosystems [106,107,108]. Additionally, APs adsorbed in sediments and sludge can be continuously released through desorption and resuspension processes, resulting in secondary contamination risks and prolonging environmental exposure [109,110,111].

APs, particularly NP and OP, have been extensively studied for their impacts on human health, with a broad consensus established regarding their adverse health effects [112,113,114]. ADMET predictions indicated high epithelial absorption and plasma bioavailability of 4-OP, consistent with its detection in human tissues and fluids [115,116], and moderate blood–brain barrier penetration, aligning with evidence of neuroaccumulation and damage [117]. APs also exhibited high skin sensitization potential [118]. In HepG2 liver cells, APs inhibited S-phase entry and induced apoptosis via caspase-3 activation and chromatin fragmentation [119,120], consistent with broader findings of liver accumulation and metabolic disruption [121]. Overall, APs exert multifaceted health-relevant effects, including tissue-specific cytotoxicity, organelle stress, apoptotic and autophagic dysregulation, and oxidative imbalance, underscoring their potential risk to human health upon exposure.

4.2. Per- and Polyfluoroalkyl Substances

On a global scale, Per- and polyfluoroalkyl substances (PFASs) contamination is pervasive, with detections documented even in remote polar regions and deep-sea organisms [122,123]. This is due to their extreme environmental persistence, long-range transport potential, and bioaccumulate capacity [42]. These factors underline the extensive environmental and health risks posed by PFAS.

Ecotoxicity of PFAS has been confirmed across multiple species. In aquatic organisms such as fish and invertebrates, PFAS exposure can lead to developmental abnormalities, oxidative stress, and immunosuppression [124]. PFAS also exhibit acute toxicity within the μg/L to mg/L range in algae, crustaceans, and fish, while chronic exposure to concentrations as low as ng/L may impair reproduction and disrupt population structures [125]. Furthermore, PFAS enter food webs through ingestion and particle adsorption, and can biomagnify across trophic levels [126,127]. It is noteworthy that the environmental behavior and ecological risks of PFAS vary considerably with chemical structure. While earlier studies predominantly focused on long-chain compounds such as PFOA and PFOS [128], recent research is increasingly addressing the potential hazards of short-chain alternatives (e.g., PFBS [129]) and other substitutes (e.g., OBS [130], GenX [131], and F-53B [132]).

Extensive studies demonstrate that PFASs pose multifaceted risks to human health through molecular and metabolic disruption. PFAS, including legacy compounds and newer alternatives such as OBS and 6:2 Cl-PFESA, readily incorporate into phospholipid bilayers, altering membrane structure and dynamics, with alternatives often exhibiting stronger effects than PFOS [133]. In silico and experimental analyses reveal that numerous PFAS interact strongly with human androgen receptors (HARs), leading to antiandrogenic effects—such as inhibition of HAR transactivation and downregulation of genes including PSA and FKBP5—with some alternatives being more potent than legacy compounds [134]. Metabolomic profiling shows that PFOA disrupts inflammatory and metabolic pathways in lung, liver, and intestinal cells, though nutrients like vitamin B6 and arginine may mitigate some inflammatory responses [135]. PFAS also affect steroidogenesis and fatty acid metabolism in Leydig cells, impairing male reproductive health [136]. Activation of the Nrf2-ARE pathway by long-chain PFAS like PFDA indicates oxidative stress mechanisms, with sulfonated PFAS showing synergistic toxicity in mixtures [137]. Epidemiological studies associate prenatal PFAS exposure with reduced birth weight, altered ponderal indices, and disrupted neonatal estrogen levels, particularly with elevated estrone, estradiol, and estriol linked to 6:2 Cl-PFESA and other PFAS [138]. These findings underscore the potential of PFAS to disrupt endocrine, metabolic, and developmental processes in humans.

4.3. Halogenated Hydrocarbons

Halogenated hydrocarbons (HHCs) pose multi-scale environmental and health risks, originating from their stable carbon-halogen bonds, pronounced persistence, and complex congener-specific properties, leading to detrimental effects from global pollution to intracellular disruption [139,140].

Highly chlorinated HHCs, such as polychlorinated biphenyls (PCBs), tend to adsorb onto particles and accumulate in sediments and biological lipids [141,142]. In contrast, lightly chlorinated or volatile HHCs, including DCM and TCM, are more likely to remain in the atmosphere and aqueous phases, enabling long-range transport via global air and ocean currents [143,144]. Due to their high volatility, typical HHCs, such as DCM and TCM, readily evaporate into the atmosphere, where they participate in photochemical reactions contributing to ozone formation and secondary aerosol production [145,146]. Ecologically, these compounds exhibit both acute and chronic toxicity to aquatic organisms such as fish and invertebrates, inducing neurotoxicity, hepatic enzyme induction, and reproductive abnormalities [147,148,149].

In terms of human health, HHCs pose significant risks to human health, with carcinogenicity being one of the most well-documented adverse effects [150]. Zhang et al. assessed the carcinogenic risk of halogenated hydrocarbons (HHCs) in the atmosphere near Beijing, and their study indicated that HHCs pose a carcinogenic risk to humans during heavy pollution episodes [151]. Vinyl chloride monomer, a kind of HHCs, was established causative agent of hepatic angiosarcoma [152]. Furthermore, HHCs exert various adverse effects on multiple organs and cellular systems in humans. Epidemiological studies have consistently associated long-term HHC exposure with liver damage (e.g., steatosis from chloroform [153]) and renal dysfunction (e.g., tubular necrosis from carbon tetrachloride [154]).

4.4. Short-Chain Chlorinated Paraffins

Short-chain chlorinated paraffins (SCCPs) pose substantial environmental and health risks due to their high stability, complex congener composition, and significant bioaccumulation potential [155]. Ecologically, SCCPs exhibit considerable toxicity to both aquatic and soil organisms [156,157]. SCCPs can transfer through food webs, where concentrations in liver and adipose tissue can exceed environmental background levels by several orders of magnitude, thereby threatening population survival and ecological balance [158,159,160]. With regard to human health, following exposure, SCCPs accumulate mainly in adipose tissue, the liver, and blood [161,162]. Their high lipophilicity and metabolic resistance lead to prolonged retention, with half-lives ranging from several days to months [163]. Continuous exposure can result in steadily increasing body burdens [163].

At the human cellular and molecular level, SCCPs exert multiple mechanisms of toxicity. Studies indicate that environmentally relevant doses of SCCPs disrupt glucose homeostasis and induce insulin resistance through macrophage-mediated inflammation and NF-kappa B activation [164]. Additionally, SCCPs trigger microglial activation and lipid metabolic shifts in neural cells, potentially impairing neurogenesis [165]. SCCPs activate nuclear receptors such as CAR and AhR in HepG2 cells, leading to perturbations in xenobiotic metabolism pathways [166]. Further immunotoxicity studies in macrophages suggest that SCCPs promote proliferation and alter immune function through the β₂-AR/AMPK/NF-kappa B axis [167]. These findings collectively underscore the multipath endocrine, metabolic, neural, and immunomodulatory disruptions induced by SCCPs, highlighting the need for further investigation into chronic exposure and gender-specific effects. However, systematic epidemiological evidence in human populations remains limited and warrants further investigation.

5. Mitigation Strategies

5.1. Green Oil Recovery Technologies

The development of green oil recovery technologies has consistently focused on synergistically enhancing crude oil recovery while reducing environmental impact. Gas injection technologies, for instance, are increasingly aligned with green objectives: CO₂ flooding can enhance oil recovery by 10–20% while simultaneously enabling carbon sequestration, offering dual benefits of emission reduction and production increase [168,169,170]; nitrogen and flue gas flooding also demonstrate strong applicability in high-pressure, high-viscosity reservoirs with minimal environmental risk [171]. Microbial enhanced oil recovery (MEOR) represents another major green approach, wherein injected bacteria (e.g., pseudoxanthomonas [172]) capable of producing biosurfactants, gases, or polymers, become activated in situ to reduce oil viscosity, improve mobility ratios, and increase recovery rates, all with excellent ecological compatibility [173,174]. Low-salinity water flooding modifies rock wettability by adjusting the ionic composition of injected water, improving recovery rates in many sandstone reservoirs, with the notable advantages of requiring no chemical additives, operational simplicity, and low cost [175]. Nanofluid flooding has also shown considerable promise; materials such as lipophilic silica nanoparticles [176] and graphene oxide [177] can modify interfacial properties and fluid behavior at very low concentrations (typically below 0.1 wt%), effectively controlling emulsification and adjusting wettability, while also being recyclable and minimally toxic [178,179]. Furthermore, several physically enhanced oil recovery methods, including ultrasonic extraction [176] and microwave heating [180], enhance oil mobility through physical field effects, proving particularly suitable for heavy oil reservoirs and sensitive formations. In summary, green oil recovery technologies not only enhance crude oil recovery through diverse mechanisms but also advance the transition toward cleaner, more efficient, and low-carbon oil extraction. Future research should focus on the integrated application of multiple green technologies, the development of smart materials, and systematic lifecycle environmental assessments.

5.2. Green Surfactants

Although various methods can reduce chemical usage, surfactants remain integral to multiple stages of petroleum operations. Early widely used surfactants such as NPEO, PFOA, and PFOS have been confirmed to pose significant health hazards, leading to the emergence of substitutes including OPEO and OBS [181,182]. However, these alternatives still share structural similarities with conventional surfactants and continue to exhibit comparable environmental and health risks. Consequently, there is growing interest in developing new substitutes for AP/APEO and PFAS. Recent years have seen major breakthroughs in the development and application of green surfactants, whose environmental friendliness and high performance have been thoroughly validated across various segments of the petroleum industry. These novel green surfactants are primarily derived from renewable resources—such as bio-based betaines [183], methyl ester sulfonates (MESs) [184], alkyl polyglucosides (APGs) [185], sophorolipids [186], rhamnolipids [187], and tunable ester-based quaternary ammonium salts [188,189]—and not only exhibit high interfacial activity but also demonstrate excellent biodegradability and low ecotoxicity, enabling rapid decomposition in natural environments without causing persistent pollution. In oilfield extraction, they are widely used as chemical driving agents. For example, bio-based betaines can reduce oil–water interfacial tension to low levels, significantly improving microscopic displacement efficiency and increasing recovery rates, while their good biocompatibility greatly reduces challenges in flowback water treatment and groundwater contamination risks [190,191]. In petroleum transportation, natural surfactants based on phospholipids or sugar esters are used for heavy oil emulsification and viscosity reduction, decreasing pipeline transportation viscosity while avoiding traditional toxic solvents. Additionally, categories such as sucrose esters and microbial lipopeptides are replacing toxic demulsifiers in oily wastewater treatment, effectively achieving flotation separation without secondary pollution [192,193]. Green surfactants are continually advancing toward higher performance, lower cost, and better adaptability to extreme reservoir conditions (e.g., high temperature and salinity). Future integration with nanotechnology and synthetic biology is expected to further promote the green transformation of the entire petroleum industry value chain.

5.3. Green Solvents

Progress in green solvents, particularly in replacing DCM and TCM in the petrochemical industry, has become a crucial direction for achieving cleaner processes and greener products [194,195]. To address the environmental issues associated with traditional solvents, green solvent systems aim to eliminate hazards at the source and have diversified in development and application. Bio-based solvents (e.g., ethyl lactate [196,197], soybean oil-derived methyl esters [198], and limonene extracts) not only offer dissolution capabilities comparable to those of conventional halogenated solvents but also feature low ecotoxicity and rapid biodegradability, having already been industry applied in equipment cleaning and lubricant extraction [199]. Ionic liquids (ILs) are used in desulfurization [200], aromatics extraction [201], and catalyst recovery [202] due to their negligible vapor pressure and tunable dissolution selectivity, achieving near-zero emissions during solvent use [203]. Deep eutectic solvents (DESs), composed of natural components like choline chloride and urea, demonstrate high efficiency and recyclability in oil desulfurization and phenol extraction, significantly reducing toxic residues in wastewater [204,205,206]. Supercritical carbon dioxide (scCO₂), as a widely valued physical alternative, is extensively used for heavy oil viscosity reduction, residue deasphalting, and precision cleaning under mild critical conditions, replacing many processes that previously relied on TCM and leaving no solvent residue after separation [207]. These green solvents not only markedly reduce the impact on human health and the environment but also decrease material consumption and waste generation through closed-loop circulation design and solvent recovery technologies. Although challenges remain in cost control, process compatibility, and stability under extreme conditions, green solvents have become a key technical pillar for the sustainable development of the petrochemical industry due to their environmental friendliness, safety, and ease of integration. Future trends will emphasize intelligent solvent design, full lifecycle assessment, and deeper integration with green processing technologies.

6. Global Governance Frameworks

Globally, the Stockholm Convention on Persistent Organic Pollutants (the Stockholm Convention), adopted in May 2001, serves as the cornerstone international policy for controlling POPs, a part of EPs. Based on scientific assessment and the precautionary principle, the Stockholm Convention updates its list of controlled substances. Compounds listed in Annex A are targeted for complete elimination by Parties, while those in Annex B are subject to strict restrictions. PFAS, as a major class of POPs, are tightly regulated: PFOS was listed in Annex B in 2009; PFOA was added to Annex A in 2019; and PFHxS followed in Annex A in 2022 [208]. SCCPs were also listed in Annex A in 2017 [209]. Although AP/APEOs have not yet been fully incorporated into the Stockholm Convention, they are regulated in numerous countries. Additionally, many HHCs fall under the regulation of the Montreal Protocol on Substances that Deplete the Ozone Layer [210]. Together, these international conventions form a comprehensive global network for chemical management across the lifecycle. They establish differentiated obligations for Parties and have effectively curbed the cross-border threats of toxic pollutants to ecosystems and public health.

The European Union (EU) is the most proactive region in managing EPs. The Water Framework Directive, adopted in 2000, aims to safeguard drinking water and aquatic ecosystems in Europe, requiring member states to develop river basin management plans [211]. In 2006, the EU introduced the REACH Regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals), which systematically monitors and restricts chemical usage. Key milestones include the restriction of NPEO in textiles and leather under Directive 2003/53/EC (later integrated into REACH Annex XVII), the addition of NP to Annex XVII in 2016, the addition of PFOA in 2017, and the comprehensive ban on SCCPs via regulation (EU) 2019/1021 in 2019 [212,213]. In 2023, the European Union Chemicals Agency submitted a landmark proposal to restrict the entire class of PFAS (approximately 10,000 substances), with an updated version released in August 2025, marking a significant escalation in PFAS regulation.

In the United States, the EPA included NP and NPEO in its Chemicals of Concern list in 2010 and issued an assessment in 2014, though no federal ban was established. The Unregulated Contaminant Monitoring Rule (UCMR) guides nationwide monitoring of EPs in drinking water. PFAS were incorporated into the fifth UCMR in 2021, and in 2023, the EPA set a stringent limit of 4 ng/L for both PFOA and PFOS in drinking water. Endocrine disruptor screening and prioritization of contaminants such as microplastics and pesticides further illustrate the country’s evolving regulatory focus [214].

China has rapidly advanced its management of EPs in recent years. The national Action Plan on Emerging Pollutants Management (the Action Plan) was released in 2022, followed by the List of Key Emerging Pollutants for Control in 2023, which prioritizes substances including PFOA, PFOS, PFHxS, SCCPs, NP, DCM, and TCM. Supporting legislation, such as the draft Hazardous Chemicals Safety Law and the Technical Framework for Chemical Risk Assessment and Control (2024), underscores China’s commitment to a systematic and legally grounded approach. Industries, including petrochemicals, are accelerating efforts to control emerging pollutant emissions [215].

Globally, chemical management is characterized by increasingly stringent measures. The EU leads with precautionary and class-based regulation through REACH; the US employs monitoring-driven and incremental regulatory enhancements under the UCMR; and China employs a dynamic, list-based strategy for high-efficiency control. Overall, control policies continue to tighten worldwide, expanding in scope from individual substances to homologous groups and even entire classes (e.g., PFAS). Regulatory tools have also evolved from bans and concentration limits to include transparency mechanisms and supply chain due diligence. While international conventions provide a foundational framework, the EU, the US, and China are emerging as regulatory poles shaping global standards, collectively steering chemical governance toward greater safety and prevention.

7. Conclusions and Future Perspectives

This review systematically identifies the application of EPs as chemical additives across various stages of the petroleum industry, summarizes their emission levels and environmental occurrence, and associated ecological and health risks. Mitigation and regulatory measures are also outlined. Based on the above analysis, the following conclusions can be drawn:

EPs such as AP/APEOs, PFAS, HHCs, SCCPs, BPA, and PCPs have been identified as commonly used synthetic chemicals. Among them, AP/APEOs, PFAS, and HHCs are widely used in the whole industry chain based on their surface activity or solubility, while SCCPs, BPA, and PCPs are often added as specific performance additives to products. However, commercial confidentiality concerning additive compositions significantly obstructs accurate source tracing and risk assessment, while significant variations in chemicals used across different regions, extraction periods, and refining technologies further complicate the identification of EPs concentrations and species in the petroleum industry.

Although the pollution characteristics of EPs have been extensively studied across various environmental media, investigations specifically targeting on petroleum industry remain comparatively limited. Studies have confirmed the presence of diverse EPs in surface water, soil, and sediment near oilfields or refineries, with preliminary evidence indicating a connection to the use of synthetic chemicals with EPs. Significantly, existing research has been concentrated in only a few countries and regions (e.g., Norway, China, and the United States), leaving considerable geographical knowledge gaps. Furthermore, studies focusing on petroleum transportation remain relatively scarce, which constrains a comprehensive understanding of the cross-regional transport of EPs.

The environmental and health risks of various EPs have been relatively well-documented, covering impacts from aquatic ecosystems to human health, and highlighting concerns such as endocrine disruption, environmental persistence, specific toxicities, and human health effects. However, petroleum industrial practices often release EPs as complex mixtures—particularly through the use of multi-component additives—leading to combined environmental exposure. Despite this reality, the health implications of such mixture exposures remain poorly characterized. There is an urgent need for further toxicological and epidemiological research to clarify the additive, synergistic, or antagonistic interactions among mixing EPs in mediating adverse health outcomes.

From a sustainability perspective, source control represents the most effective strategy for reducing EPs in the petroleum industry. Minimizing chemical additive use, adopting green extraction technologies, and transitioning to environmentally benign alternatives (e.g., bio-based surfactants and ionic liquids) are essential steps. Nevertheless, comprehensive environmental and health assessments of these alternatives are imperative to avoid meaningless or negative substitutions.

International chemical management has increasingly prioritized the control of EPs through global frameworks such as the Stockholm Convention. Regional-specific policies, including the REACH system in the EU, the UCMR in the US, and the Action Plan in China, have further strengthened the management of regional EPs. However, divergent approaches across nations and regions have resulted in significant disparities in the management of pollutants, including EPs. Against the backdrop of economic globalization, it is crucial to regulate the global transportation of EPs through coordinated policy interventions, highlighting the need for more integrated and harmonized global efforts.

Controlling EPs in the petroleum industry is crucial for sustainable development. Source control reduces environmental and health risks, while policy-driven strategies promote a transition to green and circular economies. Based on the conclusions presented above, the following future perspectives are proposed:

(1)

Screen chemical additives for EPs. Petrochemical enterprises should utilize advanced analytical methods to identify and quantify EPs in chemical additives, facilitating targeted substitution or phase-out to support sustainable production practices.

(2)

Develop pollutant fingerprinting techniques for source apportionment. Characteristic EPs should be identified based on operational profiles of petrochemical facilities to enhance traceability and support region-specific pollution control strategies.

(3)

Expand comprehensive monitoring programs. Research should prioritize mixed contamination of multiple EPs beyond conventional single target, and extend to under-represented regions (e.g., the Middle East) and processes (e.g., transportation) to enable full life-cycle assessment.

(4)

Track the global transport of EPs via the petroleum trade. Studies should focus on residual EPs in petroleum and assess their movement along international trade routes to improve understanding of transboundary pollution and inform global sustainability initiatives.

(5)

Enhance assessment of combined toxicity and health impacts. Mixture toxicity studies of complex chemical additives are essential to accurately evaluate ecological and health risks, supporting science-based and sustainable management decisions.

(6)

Accelerate green petrochemical technology deployment. Reducing chemical input through alternative technologies (e.g., CO₂-enhanced oil recovery) can significantly lower the use of EPs, contributing to cleaner and more sustainable industrial operations.

(7)

Promote the development and assessment of green substitutes. Replacement of EPs with safe substitutes is key to sustainable source control; however, comprehensive environmental and health assessments of substitutes must be conducted to avoid regrettable substitutions.

(8)

Strengthen international cooperation under sustainability frameworks. As petroleum is a globally traded commodity, coordinated efforts under conventions such as the Stockholm Convention are essential to advance equitable and effective global pollution control and sustainable industry practices.