Petroleum Hydrocarbon Pollution and Sustainable Uses of Indigene Absorbents for Spill Removal from the Environment—A Review

Abstract

Petroleum hydrocarbon pollution is a serious environmental and human health problem. In recent decades, the impact of this substance has been profound and persistent, affecting the balance of aquatic and terrestrial ecosystems and leading to significant physical and psychosocial effects among the population. Natural sources (crude oil, natural gas, forest fires, and volcanic eruptions) and anthropogenic (road traffic, smoking, pesticide use, oil drilling, underground water leaks, improper oil spills, industrial and mining waste water washing, etc.), the molar weight of the hydrocarbon, and the physicochemical properties are important factors in determining the degree of pollution. The effects of pollution on the environment consist of altering the fundamental structures for sustaining life (infertile lands, climate change, and loss of biodiversity). In terms of human health, diseases of the following systems occur: respiratory (asthma, bronchitis), cardiovascular (stroke, heart attack), pulmonary (infections, cancer), and premature death. To reduce contamination, sustainable intervention must be carried out in the early stages of the pollution-control process. These include physical techniques (isolation, soil vapor extraction, solvent extraction, soil washing), chemical techniques (dispersants–surfactants, chemical oxidation, solidification/stabilization, thermal desorption), biological techniques (bioremediation, phytoremediation), and indigenous absorbents (peat, straw, wood sawdust, natural zeolites, clays, hemp fibers, granular slag, Adabline II OS). Due to the significant environmental consequences, decisions regarding the treatment of contaminated sites should be made by environmental experts, who must consider factors such as treatment costs, environmental protection regulations, resource recovery, and social implications. Public awareness is also crucial, as citizens need to understand the severity of the issue. They must address the sources of pollution to develop sustainable solutions for ecosystem decontamination. By protecting the environment, we are also safeguarding human nature.

1. Introduction

This review is based on the identification study of specialized literature using electronic databases, PubMed, Web of Science, and Scopus, Figure 1. The search terms were petroleum hydrocarbon pollution, impact of petroleum hydrocarbons on the environment and human health, remediation techniques of petroleum hydrocarbons, and absorbent remediation of petroleum hydrocarbons. The relevance of the studied topic was assessed through a review of original full-text articles published in English over the past 10 years. The data extracted from these relevant sources helped enhance both the structure of the review and the conceptual clarity of the figures and key ideas related to the research topic. These criteria ensure that the study remain up-to-date with a thorough review of detailed methodologies and results. The selected studies focused on the impact of petroleum hydrocarbons and the applications of indigenous absorbents for environmental decontaminations. The screening process involved several exclusion criteria, including duplicate records, articles available only as abstracts, letters, interviews, retracted publications, editorials, proceedings, and data papers. Additionally, the publication title and research not relevant to the subject area were excluded. The structure of the review was further refined by analyzing the citations referenced within the selected paper.

The presence of hydrocarbons in the environment is becoming a global concern. They are a group of hazardous pollutants that include volatile, semi-volatile, and non-volatile organic compounds [1]. In recent years, pollution has become so strong that the impact on the environment is profound and persistent, with effects on the ecological balance and terrestrial and aquatic ecosystems, but also on human health. The interaction of hydrocarbons with living systems has transformed their quality, natural composition, and fundamental role in sustaining life. In other words, these substances build up in organisms and are eventually passed on to humans via the food chain, leading to poisoning and severe, irreversible effects [2,3]. They also disrupt natural environments—such as water and soil—through physicochemical and biological reactions that alter their internal structure and ecological functions. These pollutants can accumulate in the atmosphere, be deposited on urban roads, and reach the sewage system by being washed on the road infrastructure. Beaches and sea surfaces are also affected due to accidental spills, spills, and uncontrolled elimination processes [3]. Persistent contamination has very serious consequences on ecosystems and living things and disproportionately affects certain geographical areas depending on the proximity to polluting sources and the physicochemical characteristics of the environment [4].

Petroleum hydrocarbons are complex organic compounds primarily composed of carbon and hydrogen atoms, though they may also include elements such as oxygen, sulfur, and nitrogen [5]. Based on the types of chemical bonds they contain, they are divided into three main categories, as illustrated in Figure 2.

Saturated hydrocarbons, paraffins, have only single bonds in their molecules, for example alkanes (ethane, propane, etc.) and cycloalkanes (cyclohexane, cyclopentane). Unsaturated hydrocarbons, olefins, include alkenes that contain one double bond in their molecule (ethene, propene), alkadienes that contain two double bonds in their molecule (butadiene, propadiene), and alkynes that contain one triple bond in their molecule (acetylene, ethyne, propyne). Aromatic hydrocarbons such as arenes have a cyclic structure with six carbon atoms with alternating single and double bonds (benzene, naphthalene, toluene, etc.) [6,7].

The scope and severity of petroleum hydrocarbon pollution depend on their sources. These sources fall into two main categories: natural and anthropogenic, as illustrated in Figure 3. Distinguishing between the two is crucial for developing effective strategies for pollution prevention and control.

Natural sources such as crude oil and natural gases (methane, ethane, butane) produce contamination slowly and over time, which allows the environment to interact and gradually respond to the toxicological effects. They are also generated from forest fires and volcanic eruptions that release significant quantities of polycyclic aromatic hydrocarbons into the atmosphere [8,9]. The degree of pollution depends on the content and family of hydrocarbons, the molecular weight, and the life cycle of the exposed ecosystem [10]. In contrast, due to the intensification of socio-industrial activities, wastewater, and sewage, the development of road infrastructure based on fossil fuels, the use of pesticides and fertilizers in agriculture, oil drilling processes, oil spills in the sea or in inland waters, leaks from underground pipelines, improper storage of oil residues, washing of contaminated industrial equipment, and losses from refining facilities, pollution is much deeper and more concentrated [11,12]. Accidents or negligence often occur that cause severe contamination in a short time that does not allow the environment to manifest itself and alters the metabolic activity of microorganisms [13,14].

This review is organized to address the origins of petroleum hydrocarbon pollution, its impacts on ecosystems and human health, and the various remediation strategies employed—namely physical, chemical, and biological methods. Also, the review aims to assess the viability of natural indigenous materials as sustainable alternatives for the decontamination of petroleum hydrocarbons, highlighting their biodegradability, practicality, rapid action, environmental friendliness, and cost-effectiveness compared to synthetic products. However, several research gaps remain that require further investigation. These include determining the most effective type and dosage of absorbent, optimal contact time, the specific properties and concentrations of hydrocarbons, and the characteristics of the contaminated soil or water matrix. Moreover, the lack of standardized guidelines for indigenous absorbent materials creates uncertainty about their efficacy and hinders their integration into formal remediation practices. Additionally, in outdoor or poorly insulated settings, fluctuating environmental conditions—such as temperature, humidity, atmospheric pressure, and wind—can alter hydrocarbon behavior by accelerating processes like evaporation, dispersion, or oxidation, thereby influencing the overall effectiveness of the absorbents. Future research will consider these gaps.

2. The Impact of Petroleum Hydrocarbons

2.1. On Aquatic Ecosystems

Aquatic ecosystems are among the most vulnerable, especially those located near heavily trafficked maritime routes, oil ports, or offshore drilling platforms. Oil spills from ships or wells can contaminate vast water areas, creating a viscous film on the sea surface that hinders gas exchange between the atmosphere and the water. Over time, this can lead to the suffocation of marine life by obstructing phytoplankton photosynthesis and reducing water oxygenation [15].

Lakes, ponds, and marshes located near refineries, fuel deposits, or oil transport routes are also highly vulnerable, as the limited water movement in this environment allows hydrocarbons to accumulate persistently in the upper layers. Water quality is compromised, disrupting the structure and functions of the freshwater trophic network. Gas exchange is exhibited, leading to an imbalance in living systems and a decline in biodiversity [16,17]. In addition, there is a significant risk of drinking water contamination, making it unsafe for human consumption. Understanding the sources and environmental consequences of oil pollution is essential for developing effective management strategies.

2.2. On Terrestrial Ecosystems

Soil contamination with petroleum hydrocarbons has had significant impacts on terrestrial ecosystems. The extent of the damages largely depends on the soil’s characteristics and the properties of the hydrocarbons involved. Hydrocarbons penetrate clay soils with difficulty but tend to remain on the surface and on vegetation for a long time. The specialized literature demonstrates the presence of hydrocarbons in the street dust and the particulate matters from air PM2.5 and PM1, which, through chemical reactions with other chemical compounds, lead to the formation of tropospheric ozone and photochemical smog [18]. In this way, the soil loses its fertility and productivity, and the processes of mineralization, germination, and humification are interrupted, leading to a hostile soil [19,20,21]. Hydrocarbon degradation is slow due to low oxygenation. Vegetable species are the first affected by blocking the functions of photosynthesis. On the other hand, hydrocarbons can penetrate groundwater by contaminating underground drinking water reserves and communities that consume it.

The release into the environment affects the physicochemical and biological processes of living organisms, with impacts ranging from subcellular damage to mass mortality in exposed populations. The vulnerability of the affected systems depends on the amount and concentration of pollutants released into the environment, as well as their capacity to tolerate pollution and regenerate. When the environmental impact is severe, human health is similarly affected.

It is important to note that once petroleum hydrocarbons enter the environment, they do not remain permanently inactive or stable. Under the influence of extreme weather events such as strong wind, floods, drought, and frost and thaw cycles, they can become reactivated posing a renewed risk to ecosystems and human health. To prevent this, contaminated sites should be regularly assessed and intervention measures must be adapted to current climatic conditions.

2.3. On Human Health

Human exposure to these substances affects their interaction within the body, leading to a wide range of health conditions. The type of hydrocarbon, along with the duration and level of exposure, determines whether the effects are acute or chronic. Health impacts are often not immediately apparent but may develop over time, resulting in irreversible damage or even death. Accordingly, Figure 4a illustrates the pathways of hydrocarbon exposure and absorption, while Figure 4b highlights the short- and long-term effects on the human body.

Figure 4a illustrates inhalation as the primary and most common route of petroleum hydrocarbon entry into the human body. The most at-risk groups include workers in areas affected by discharges or near industrial zones, residents of cities with heavy traffic, agricultural workers exposed to pesticides and fertilizers, individuals who smoke excessively, car mechanics, miners, and vendors working in public spaces [22]. After the inhalation of hydrocarbons such as benzene, toluene, xylene, and PAH, they are rapidly absorbed through the respiratory system and can lead to irritation of the nasal and ocular mucous membranes, as well as symptoms like headaches, dizziness, nausea, neurological disorders, central nervous system damage, and elevated blood pressure [23,24,25,26]. Ingestion is another route of exposure, which can occur through the consumption of contaminated food, such as polluted drinking water, fish and seafood, or other affected products. The daily accumulation of hydrocarbons in the human body can occur as a result of road traffic emissions, even during routine activities such as walking through the city, waiting at bus stops, or engaging in conversations outdoors. In such case, the digestive system is affected. Symptoms such as diarrhea, headaches, fatigue, and vomiting appear at short-term exposure. Long-term exposure leads to renal and liver changes, central nervous system lesions, cardiovascular disease, pulmonary disease, osteoporosis, chronic bronchitis, mutagenic effects, cancer, and death [27].

Skin and eye contact can occur through the direct handling of contaminated materials or even through passive exposure. Common modern examples include smoking, applying insecticides, and burning plants, where toxic substances are absorbed both through the respiratory system and the skin’s pores. Short-term can cause skin and eye irritation, dermatitis, and allergic reactions [27]. Direct contact to crude oil or heavy petroleum products may result in more severe health effects, including damage to internal organs and skin cancer, and even skin burns are produced [28].

In addition to direct physical effects, significant psychosocial risks must also be considered. Major oil spills can cause these within affected communities, often resulting from job loss, forced displacement, and uncertainty about the declining the quality of life. These situations have a profound impact on health, leading to chronic psychological stress, anxiety, and depression. Neglecting these effects in post-pollution interventions can have serious long-term implications.

Given the harmful effects of petroleum hydrocarbon pollution on the environment and human health, it is vital to develop effective mitigation strategies. The continuous monitoring of air quality and drinking water is equally important to protect public health. Furthermore, raising public awareness and supplying protective equipment to workers can help reduce the negative effects on ecosystems and human well-being. The effective prevention of hydrocarbon and other hazardous substance pollution requires the implementation of well-planned strategies and thorough risk assessments. Addressing the threats posed by hydrocarbon contamination demands a comprehensive and sustainable approach. Early and efficient intervention is critical. One accessible, rapid, and direct remediation method involves using materials capable of absorbing and retaining liquid pollutants, thereby minimizing the environmental impact.

3. Techniques and Methods of Environmental Depollution with Hydrocarbons

Conventional absorption and decontamination methods have been employed to remove petroleum hydrocarbons from the environment, as illustrated in Figure 5. Their effectiveness depends on factors such as the type of contamination (water or soil), the nature of the hydrocarbons, and the environmental conditions like wind and temperature. Table 1 provides examples of these methods along with their advantages and remediation costs [29,30].

Temperature influences both the viscosity of hydrocarbons and the absorbent material’s capacity to retain them. At lower temperatures, hydrocarbons become more viscous, making them harder to absorb as they penetrate the absorbent structure more slowly. In contrast, higher temperatures reduce viscosity, allowing for more efficient absorption. However, elevated temperatures also promote the volatilization of lighter hydrocarbon fractions, which decreases the quantity available for absorption while increasing the risk of air pollution. Jha and colleagues evaluated the sorption capacities of rice husk, wheat straw, and sawdust at various dosages over 24 h, using a shaking speed of 125 rpm and temperatures of 20, 25, 30, and 35 °C. Their findings show that rice husk consistently exhibited the highest sorption capacity across all temperatures, peaking between 25 and 30 °C, with a decline observed at 35 °C. In contrast, the oil sorption capacities of wheat straw and sawdust remained stable across the tested temperature range [31]. Yu et al. investigate the influence of temperature on the adsorption performance of petroleum hydrocarbons [32]. Their experiments reveal that when the temperature is below 180 °C, the n-alkane content in the raffinate of the reaction system gradually decreases as the adsorption temperature rises. This indicates that the adsorption performance improves with increasing temperatures [32].

Air humidity and the presence of water in the substrate affect absorption, particularly when using hydrophilic materials or hydrophobic materials that have not been adequately treated. Dry plant-based absorbents may become more effective after a period of acclimatization, during which their ability to expand is activated. Cho et al. assessed toluene adsorption efficiency under elevated temperatures (40–50 °C) and varying humidity levels (28–83 g H₂O/kg-dry air) [33]. Their results indicate that the amount of toluene adsorbed decreases as both the temperature and humidity increase [33].

Wind can speed up the evaporation of volatile hydrocarbons, thereby decreasing the amount available for physical absorption. However, in the case of lightweight granular materials, wind may also cause dispersion, making it difficult to maintain control over the treatment area. In such situations, denser materials or those that are mechanically compacted are more suitable. Avram and colleagues demonstrated in their study that, in November, wind speeds of approximately 2.14 m/s are sufficient to lift granular materials from street dust into the atmosphere [34].

The nature of the contaminated substrate—such as soil, sand, gravel, or stagnant/flowing water—significantly influences the initial behavior of hydrocarbons and dictates the choice of absorbent materials. For example, permeable substrates like sand allow hydrocarbons to quickly seep downward, necessitating absorbents capable of deep penetration and layered application. In contrast, on compacted soil, hydrocarbons tend to remain on the surface, forming dense films that can block absorbent penetration unless the material is applied evenly or activated through pressure [35].

Figure 5. Techniques and methods for petroleum hydrocarbon removal [23,30,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52].

Figure 5. Techniques and methods for petroleum hydrocarbon removal [23,30,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52].

Table 1. Advantages of the methods used.

Depollution Techniques/Cost	Methods Examples	Advantages/Benefits	Clean-Up Efficiency	References
Physical 50–330 US $/tons	Isolation	-uses physical and mechanical barriers (skimmers, containment booms, pump and treat, excavation), -effective and acceptable management remedial option.	-no limit to the contaminant concentration that can be contained in any given site	[23,30,36]
	Soil vapor extraction	-remove the volatile (VOC) and semi-volatile organic compound (SVOC), -low-cost, -high-efficiency remediation method, -used in the remediation of volatile petroleum hydrocarbon-contaminated sites, -low energy consumption, -controllable secondary pollution.	-73% of VOC concentration in soil after four-year treatment	[30,36,37,38]
	Soil extraction, solvent extraction	-useful to identify the composition of soil contamination, -efficient in removing hydrophobic organic contaminants from soils.	-90% of naphthene aromatics, polar aromatics -60% of nC7-asphaltenes	[36,39,40]
	Soil washing or soil flushing	-flexible application, -simple operation, -short duration, -low cost, -high removal efficiency.	-97% of total petroleum hydrocarbons -73% of benzo(a)pyrene	[36,41,42]
Chemical 19–940 US $/tons	Dispersing agents	-fast treatment, -low toxicity, -accelerate natural biodegradation, -increase bioavailability, -may prevent the oil from stranding and reaching the shore, -act by lowering the interfacial tension between oil and water.	-89.2%, 61.9%, and 28.6% of phenanthrene, pyrene, and benzo [a] pyrene when surfactants were combined with Phanerochaete sordida	[40,43,44,45,46]
	Chemical oxidation	-is a rapid process, -can be applied in all-weather situations.	-from 47.32% to 78.06% at 10% (v/v) H2O2 in the conventional Fenton process -78.2% and 72.64% within 72 h for the ultrasonically/thermally activated persulfate (“US/Heat/PS”) and thermally activated persulfate (“Heat/PS”) systems -sandy soil using continuous ozone injection of 94% in 14 h	[40,41,43,44,47,48,49]
	Solidification/stabilization	-minimal input of energy, -less atmospheric emissions.	-petroleum-contaminated soils can be stabilized and solidify using Portland cement, gypsum, silicates, carbon, phosphates, sulfur-based binders, and organo-clays that can serve as a construction material	[36,49]
	Thermal desorption	-short treatment period, -high efficiency, -high safety, -lack of secondary pollution, -non-combustion technology, -remove the most volatile and semi-volatile organic contaminants from soil.	-93.44% to 96.91% within 20 min, at temperatures between 200 and 300 °C from contaminated soil -89% within just 30 min from marine sediment	[30,50,51,52]
Biological 5–266 US $/tons	Bioremediation	-low cost, -no side effects, -transforms chemical compounds into harmless final products, -efficient method for detoxifying and mineralizing toxic pollutants.	-92% and 100% of phenanthrene and fluoranthene were degraded after 168 h -100% of pyrene after 24 h	[30,36,43,47,52]
	Phytoremediation	-green plants are used that act as filters or traps in the tissue, -convert the contaminants into less toxic and less persistent in the environments, -eco-friendly, -cost-effective, -remediates large contaminated areas, -easily implemented on-site, -a significant restorative effect, -highly sustainable approach.	-85.9% and 79.1% of phenanthrene and pyrene removal with V. spiralis -63.2% of petroleum from contaminated soil with Mirabilis jalapa L.	[30,36,40,43,44,47]

Table 1. Advantages of the methods used.

Depollution Techniques/Cost	Methods Examples	Advantages/Benefits	Clean-Up Efficiency	References
Physical 50–330 US $/tons	Isolation	-uses physical and mechanical barriers (skimmers, containment booms, pump and treat, excavation), -effective and acceptable management remedial option.	-no limit to the contaminant concentration that can be contained in any given site	[23,30,36]
	Soil vapor extraction	-remove the volatile (VOC) and semi-volatile organic compound (SVOC), -low-cost, -high-efficiency remediation method, -used in the remediation of volatile petroleum hydrocarbon-contaminated sites, -low energy consumption, -controllable secondary pollution.	-73% of VOC concentration in soil after four-year treatment	[30,36,37,38]
	Soil extraction, solvent extraction	-useful to identify the composition of soil contamination, -efficient in removing hydrophobic organic contaminants from soils.	-90% of naphthene aromatics, polar aromatics -60% of nC7-asphaltenes	[36,39,40]
	Soil washing or soil flushing	-flexible application, -simple operation, -short duration, -low cost, -high removal efficiency.	-97% of total petroleum hydrocarbons -73% of benzo(a)pyrene	[36,41,42]
Chemical 19–940 US $/tons	Dispersing agents	-fast treatment, -low toxicity, -accelerate natural biodegradation, -increase bioavailability, -may prevent the oil from stranding and reaching the shore, -act by lowering the interfacial tension between oil and water.	-89.2%, 61.9%, and 28.6% of phenanthrene, pyrene, and benzo [a] pyrene when surfactants were combined with Phanerochaete sordida	[40,43,44,45,46]
	Chemical oxidation	-is a rapid process, -can be applied in all-weather situations.	-from 47.32% to 78.06% at 10% (v/v) H2O2 in the conventional Fenton process -78.2% and 72.64% within 72 h for the ultrasonically/thermally activated persulfate (“US/Heat/PS”) and thermally activated persulfate (“Heat/PS”) systems -sandy soil using continuous ozone injection of 94% in 14 h	[40,41,43,44,47,48,49]
	Solidification/stabilization	-minimal input of energy, -less atmospheric emissions.	-petroleum-contaminated soils can be stabilized and solidify using Portland cement, gypsum, silicates, carbon, phosphates, sulfur-based binders, and organo-clays that can serve as a construction material	[36,49]
	Thermal desorption	-short treatment period, -high efficiency, -high safety, -lack of secondary pollution, -non-combustion technology, -remove the most volatile and semi-volatile organic contaminants from soil.	-93.44% to 96.91% within 20 min, at temperatures between 200 and 300 °C from contaminated soil -89% within just 30 min from marine sediment	[30,50,51,52]
Biological 5–266 US $/tons	Bioremediation	-low cost, -no side effects, -transforms chemical compounds into harmless final products, -efficient method for detoxifying and mineralizing toxic pollutants.	-92% and 100% of phenanthrene and fluoranthene were degraded after 168 h -100% of pyrene after 24 h	[30,36,43,47,52]
	Phytoremediation	-green plants are used that act as filters or traps in the tissue, -convert the contaminants into less toxic and less persistent in the environments, -eco-friendly, -cost-effective, -remediates large contaminated areas, -easily implemented on-site, -a significant restorative effect, -highly sustainable approach.	-85.9% and 79.1% of phenanthrene and pyrene removal with V. spiralis -63.2% of petroleum from contaminated soil with Mirabilis jalapa L.	[30,36,40,43,44,47]

In terms of the specific performance, bioremediation shows the highest petroleum hydrocarbon absorption efficiency, ranging from 97% to 100%, followed closely by soil washing at 97% and thermal desorption at 93–96%. When it comes to cost, biological methods are generally more economical, with expenses ranging between 5 and 266 US $/ton comparing it with physical, 50–330 US $/tons, and chemical ones, 19–940 US $/tons [29].

Physical techniques rely on mechanical and physical processes to collect, separate, or retain hydrocarbons from the contaminated environment. These methods are rapid and particularly effective during the emergency response phase, though they do not always result in complete remediation. In terms of cleanup efficiency, there is no specific limit to the concentration of contaminants that can be managed at a given site [36]. Skimmers are used as mechanical barriers to remove oil stains from the surface of the sea [36]. Cao and his collaborators, LaBianca et al., used the soil vapor extraction method for the in situ remediation of contaminated soil, groundwater, and areas affected by volatile organic compounds [37,38]. The method is simple and cost-effective, has low energy consumption, has control over secondary pollution, and has high remediation efficiency of 73% of the VOC concentration in soil after a four-year treatment [37,38]. Solvent extraction is an effective method for removing harmful chemicals from soil, utilizing solvents such as hexane, dichloromethane, or acetone to dissolve hydrocarbons [39,40]. This technique has achieved the removal of approximately 90% of naphthenic and polar aromatics, as well as around 60% of nC7-asphaltenes [39]. Another example is emptying or pumping in the case of large oil accumulation, both on the ground and in water pools. A mechanical action is the excavation followed by its transport to specialized treatment stations, which allows the complete removal of the affected layer in cases of deep or persistent pollution [41]. Zoghi and Mafigholami demonstrate that the soil washing method involves the use of water or solvents capable of extracting contaminants, separating them, and eliminating the contaminated solution [42]. The method offers flexible application, is easy to operate, and is characterized by low cost, a short implementation time, and high contaminant removal efficiency—eliminating 97% of total petroleum hydrocarbons and 73% of benzo(a)pyrene [42]. Other actions are cutting and removing contaminated vegetation, burning or suctioning into tanks, and washing with high pressure water [43].

Chemical techniques are applied in several ways, but physical and biological methods are not sufficient. Their efficiency is significant in reducing the impact of pollution, but they must be applied in correlation with physical and biological methods. Chemical compounds such as surfactants, solvents, and oxidizing agents are used [44]. Surfactants act by reducing the surface tension between oil and water [45,46]. These are used in the case of marine spills and have the role of fragmenting the formed film into small droplets, dispersing it in the water mass for biodegradation [44,45,46]. The method is rapid, involves low toxicity, increases bioavailability, and prevents the spilled oil from reaching the shore. A cleanup efficiency of approximately 89.2% for phenanthrene, 61.9% for pyrene, and 28.6% for benzo[a]pyrene was achieved when surfactants were combined with Phanerochaete sordida [40].

Chemical oxidation is a rapid method that can be applied in any weather condition. It significantly reduces contaminants in a short time and does not require the use of excavation. Chemical oxidation remediates soils contaminated with polycyclic aromatic hydrocarbons using oxidizing substances such as ozone, hydrogen peroxide—H₂O₂, potassium permanganate—KMnO₄, and dichromate [41,43,44,45,46,47,48]. These substances have the role of degrading hydrocarbons into less harmful compounds that are more easily assimilated by organisms in soil or water. The chemical structure and therefore the behavior in the environment are modified. The chemical structure of the contaminants is altered, which consequently changes their behavior in the environment. Notable pollutant-removal efficiencies have been reported: between 47.32% and 78.06% using 10% (v/v) H₂O₂ in the conventional Fenton process; 78.2% and 72.64% within 72 h using ultrasonically/thermally activated persulfate (“US/Heat/PS”) and thermally activated persulfate (“Heat/PS”) systems, respectively; and up to 94% removal within 14 h through continuous ozone injection [40,41,49]. Another chemical method is solidification/stabilization, which reduces harmful contaminants by capturing them or simply transforming them into less toxic substances. The contaminated material is mixed with stabilizing agents that change the properties and reactivity of the contaminants. It is a method that requires minimal energy consumption and has low atmospheric emissions. This method can stabilize and solidify petroleum-contaminated soil using materials such as Portland cement, gypsum, silicates, and organo-clays, allowing the treated soil to be repurposed as a construction material [36,49,50].

Thermal desorption is a chemical technique that uses temperature to separate semi-volatile and volatile contaminants, PAHs, from the environment. The advantages of the method are a short treatment time, high efficiency, no secondary pollution, and safety, and it is a combustion-free technology [51,52]. Falciglia and colleagues demonstrated, in their study, that at a temperature of 200 °C, petroleum hydrocarbons were removed from contaminated marine sediment with an efficiency of 89% within just 30 min. On the other hand, Xue and colleagues [52] applied electromagnetic induction heating and found that within 20 min, at temperatures between 200 and 300 °C, petroleum hydrocarbons were removed from contaminated soil with an efficiency ranging from 93.44% to 96.91%.

Biological techniques such as bioremediation provide an ecological, cost-effective, side-effect-free, and effective method for detoxifying and mineralizing toxic pollutants [53]. Bioremediation uses microorganisms, plants, or enzymes to degrade and transform toxic compounds into harmless substances, such as carbon dioxide and water [54,55,56]. Bioremediation can be used effectively in both soils and freshwater or marine waters and contributes to the long-term restoration of environmental quality. It is an invasive and cost-effective method for the recovery of contaminated sites [43]. An optimal effect requires a rigorous selection of the bacterial strain and careful monitoring with sampling and analysis of the composition of the soil and water. The density of bacterial populations is determined, and the parameters of temperature, pH, and dissolved oxygen are taken into account. Yemele and collaborators [47], in their systematic review, emphasized that the degradation of phenanthrene, fluoranthene, and pyrene is influenced by the cell density of microalgae. After 168 h of exposure at a cell density of 2.5 × 10⁵ cells bead⁻¹, 92% of phenanthrene and 100% of fluoranthene were degraded. Pyrene was degraded at 100% after 24 h.

Phytoremediation is a method that uses green plants to clean contaminated environments. Plants act as filters, absorbing pollutants and accumulating them in their tissues and transforming them into less harmful substances. The method is ecological, is easy to implement, is effective in remediating contaminated areas, and has low cost [36,40,43,44,47]. Yemele and colleagues reported [47], in their review, that the plant Vallisneria spiralis effectively removed approximately 85.9% of phenanthrene and 79.1% of pyrene. Elijah reported in his review that the use of Mirabilis jalapa L. demonstrated a petroleum-removal efficiency of approximately 63.2% from contaminated soil. The selection of appropriate techniques and methods for treating contaminated sites should be carried out by environmental specialists, considering factors such as the type and concentration of pollutants, treatment costs, environmental protection regulations, potential for resource recovery, and the social impact [55].

4. The Use of Absorbent Materials in Environmental Decontamination

In recent years, there has been growing interest in the use of indigenous materials, (see Figure 6) for the control and remediation of environmental pollution [57,58]. These natural, cheap, and locally available materials often originate from plant waste (such as sawdust, straw, peat, tree bark, reed fluff, hemp, eucalyptus, and cotton), industrial byproducts (like granular slag and power plant ash), or minerals (including zeolites and clays). They possess a strong affinity for absorbing, capturing, and distributing pollutants within their structure [58].

Romania possesses significant natural resources of this kind, and their extraction does not require highly advanced technologies. In

Table 2. Natural local absorbents from Romania.

Local Absorbents	Locality, County, Country	Cost/Kg	Applications
Zeolite (Clinoptilolite)	Rupea, Brasov, Romania https://zeolitesproduction.com/despre-noi/ (accessed on 20 August 2025) Campulung, Maramures, Romania https://www.zeolitnatural.ro/ (accessed on 20 August 2025)	13.85 Euro/10 kg 19.40 Euro RON/25 kg	-Absorbent material for accidental pollution -Decontamination of radioactive waters -Substrate for ponds
Clay (Kaolinite)	Suncuius, Bihor, Romania	7.91 Euro RON/kg	-traditional building ceramics
Clay (Bentonite)	Orasu Nou, Satu Mare, Romania https://bentoflux.ro/?_gl=1%2A7e25qo%2A_up%2AMQ..%2A_gs%2AMQ..&gclid=EAIaIQobChMIzavxttuljwMV3ZqDBx2IsjvVEAAYASAAEgIVlPD_BwE&gbraid=0AAAAApO0EjTEyOaxc1rzz_Q4bD4lVScRh (accessed on 20 August 2025)	14.25 Euro/30 kg	-Removing contamination from liquids
Sawdust	Woodworking industry, Romania, (Satu Mare, Romania) https://www.bio-combustibil.ro/tocatura-lemn/ (accessed on 21 August 2025) https://www.erdholz.ro/produse-proprii/ (accessed on 21 August 2025)	465 Euro/1000 kg 19.79 Euro/1000 kg	-Absorbent material for environmental pollution
Straw	Agriculture, Romania https://tbmenergy.ro/produs/baloti-de-paie/ (accessed on 21 August 2025)	0.59–5.94 Euro/bale	-Absorbent material for environmental pollution
Peat	Forest, Romania	4.94 Euro/50 L	-Absorbent material for environmental pollution
Wool	Sheep farmers, Romania	0.20–1 Euro/kg	-Absorbent material for environmental pollution

, some examples of natural absorbents from Romania are highlighted.

Overall costs are mainly influenced by processes such as grinding, drying, granule classification, and transportation. The production costs of plant-based materials such as sawdust and straw, as well as textile fibers like hemp and wool, are generally low. These materials are typically by-products of other industries—such as wood processing, agriculture, and textile manufacturing—which ensures consistent availability at minimal expense. In the case of locally sourced mineral materials, extraction and processing costs are somewhat higher but remain affordable within a regional context. Overall costs are mainly influenced by processes such as grinding, drying, granule classification, and transportation.

The bioremediation of oil-contaminated ecosystems is designed to remove pollutants as quickly and efficiently as possible. The choice of bioremediation materials in the decontamination process is made according to clear criteria, namely the following:

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Absorption capacity highlights the efficiency in retaining petroleum substances; the more porous, fibrous, or irregular the absorbent material is, the better it will absorb the pollutant.

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Excellent hydrophobicity and oleophilicity [59], which means that the chosen material will retain oils and hydrocarbons more effectively.

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Retention capacity—highlights the volume of liquid that can be stored after handwashing.

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High biodegradability—compared to absorbent materials made from polymers that require limited storage and disposal, indigenous products decompose quickly after use without leaving any traces of toxic residues. Thus, they are ideal sources for interventions in sensitive areas such as deltas, reserves, and protected areas.

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Reduced acquisition and transportation costs [59] influence the economic sustainability of the intervention, especially in the case of large or repeated spills. This is a strategic criterion that influences the response capacity, logistical efficiency, sustainability of the intervention, and even the overall success of the decontamination process.

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Adaptation to real environmental conditions means that an indigenous material that comes from the same environment in which they are used will be compatible from a physico-chemical point of view. Some absorbents may perform well in the laboratory but lose their effectiveness in the presence of weather conditions (wind, low temperature).

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Social acceptability involves participation in greening activities, educational projects, or volunteering actions of willing local communities in which these indigenous materials are involved.

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Immediate accessibility in the event of accidental oil spills; materials can be immediately collected and distributed within hours compared to imported products where distribution would take days or weeks.

4.1. Vegetable Absorbents

Straw and vegetable wastes such as dried leaves, stalks, stalks, and grain fibers are crop residues generated as by-products of cereal crop cultivation [60]. These biological materials are commonly used for water absorption in both rural and urban areas. Their hollow, tubular structure, rich in cellulose, hemicellulose, and lignin [61], enables them to effectively retain liquid hydrocarbons. To enhance post-remediation quality, studies have shown that adding wheat straw to oil-contaminated agricultural soil promotes plant growth and improve soil oxygenation [62]. Alotaibi and collaborators demonstrated that wheat straw stimulates soil microbial respiration and accelerates the mineralization of organic carbon. Another study found that mixing biochar derived from straw and sawdust with soil contaminated by polycyclic aromatic hydrocarbons resulted in effective soil decontamination and a reduction in PAH levels [63,64]. Additionally, biochar enhances soil fertility and aids in hydrocarbon remediation through surface adsorption. Rice straw and sawdust have also been reported to improve soil porosity and water retention capacity [65]. Although the availability of these plant materials is seasonal, they offer a practical, rapid, eco-friendly, and cost-effective alternative to synthetic products. Their use supports the cleanup and restoration of environmental functions impacted by petroleum hydrocarbon pollution and promotes the development of remediation strategies in communities with limited financial resources.

Wood sawdust is commonly used for treating oil-contaminated waters. Its effectiveness varies based on the type of wood (softwoods like pine and fir typically offer higher absorption than hardwood such as oak and beech), as well as the particle size and moisture content, with dryer sawdust exhibiting greater absorption efficiency. Mkheidze and his collaborators demonstrated, in their research, that there is a correlation between the particle size and sorption capacity. Thus, the smaller the sawdust particles, the greater the crude oil absorption process and the higher the specific surface area [66]. Sawdust is an affordable, economical, efficient, and low-density absorbent [67,68]. Due to its porous structure, carboxyl and hydroxyl groups, and biodegradable nature, sawdust can extract volatile and semi-volatile fractions of hydrocarbons and heavy metals [67,69]. Sawdust is biodegradable and can be integrated into the composting process if it has been used to absorb less toxic light petroleum fractions. This means that microorganisms can degrade the retained hydrocarbons and contribute to the bioremediation of the site.

Peat is a natural absorbent formed through the partial decomposition of mosses, grasses, shrubs, or trees in moist environments. Its composition includes lignin, cellulose, and fulvic and humic acids, which contain functional groups such as carboxylic, phenolic, and hydroxyl. Peat’s porous structure offers a large surface area, giving it a high capacity for hydrocarbon absorption. Additionally, its strong buoyancy allows it to float on water, making recovery easier. Thanks to its excellent oil-retention properties, peat minimizes the risk of secondary pollution during the cleanup process [70]. According to the literature, peat can be even more effective when converted into biochar [71,72]. Margenot and collaborators found that peat-based biochar exhibits greater porosity, a higher cation exchange capacity, and enhanced sorption properties compared to raw peat [72]. In a study by Paulauskienė, T. and Jucikė, I., the absorption capacity of straw and peat and their mixture was evaluated for crude oil and diesel oil spilled in water. The results showed that the straw–peat mixture absorbed significantly more crude oil and diesel than either material used alone [73].

A sustainable and eco-friendly solution involves using natural textile fibers like hemp and wool. These plant- and animal-based fibers offer effective physicochemical properties for hydrocarbons retention. Hemp, in a particular, has a porous, durable, and hydrophobic structure that enables it to rapidly absorb liquid hydrocarbons. When utilized in forms such as canvas, felt, twine, or loose fibers, its active surface area is significantly increased, enhancing its absorption efficiency. The main components of hemp are cellulose, hemicellulose, and lignin, but also small amounts of proteins, lipids, waxes, and other extracts with ecological, economic, and social benefits [74]. Untreated wool is a natural absorbent with hydrophobic and hydrophilic properties, which means that it attracts non-polar organic substances and oils but repels water. It has the capacity to retain volatile organic compounds, and it is biodegradable, being decomposed by microorganisms without leaving behind toxic residues. Hemp and wool prove to be efficient, ecological, and sustainable absorbent materials that offer performance comparable to synthetic materials.

In addition to these discussed absorbents, the literature highlights many types of absorbents used in environmental decontamination with hydrocarbons, namely cotton fibers [59,75,76], corn stalks [77], nettle [78], and orange and banana peels [59,79]. Although each sorbent has its own characteristics, it is very important to take into account the above-mentioned criteria and the type of oil/hydrocarbon that needs to be absorbed.

4.2. Mineral Absorbents

The absorption process is the most economical and feasible method, and minerals such as clays, zeolites, granular slag, and fly ash are the most common materials used. These are natural raw materials used in the form of powder or granules where the particle size varies from a few nm to a few mm [76].

Zeolites are a family of alkali and alkaline earth metal aluminosilicates, formed by tetrahedral units of aluminum (AlO₄)³⁻ and silicon (SiO₄)⁴⁻ linked together by common oxygen atoms [76,80,81]. The crystalline structure gives them exceptional adsorption properties and high cation exchange capacity and catalysis, which makes them materials frequently used in the purification and decontamination processes of aquatic and terrestrial ecosystems. The internal structure contains channels and cavities inside which water molecules and cations such as Na⁺, K⁺, Ca²⁺, and Mg²⁺ are located, which can be substituted by other cations [82]. According to the literature, zeolites are most frequently reported in the effort to eliminate oil spills. Among the natural zeolites, the most widely used is clinoptilolite due to its abundance and ion exchange, while synthetic zeolites include fly ash [83,84]. Unique properties such as size, porosity, and thermal and chemical stability make them effective in reducing concentrations of organic contaminants such as VOCs, PAHs, and other petroleum derivatives [85]. Hoghia et al. demonstrated in their research that zeolites with small particle sizes (<10 µm) have a higher adsorption capacity than zeolites with a particle size of 1–3 mm [81]. The large specific surface area and porosity allow them to capture and retain contaminants in cavities. Zeolites can be reused after regeneration and represent an efficient and long-lasting solution in terms of hydrocarbon capture, offering a balance among performance, technique, and sustainability, being a viable choice for environmental interventions.

Clays are natural materials formed from hydrated aluminum silicates with a lamellar structure (composed of layered sheets with interlamellar spaces). This structure gives them a large specific surface area, which allows them to interact efficiently with hydrocarbon molecules. The substitution of inorganic cations with organic cations and surface acidity can lead to the improvement of clay material in terms of the absorption of toxic substances and stimulation of biodegradation [86,87,88]. Their retention capacity increases depending on the degree of fineness of the particles (the finer they are, the more efficient the interaction), the mineralogical composition (smectic clays, such as montmorillonite, have a higher ion exchange capacity), and the humidity and pH of the environment.

An example of an effective clay is bentonite, which is mainly composed of montmorillonite. It functions as a molecular sponge, allowing pollutants to be fixed in the crystal lattice through Van der Waals attraction mechanisms, electrostatic forces, and weak hydrogen bonds.

The negative charge, due to isomorphic substitutions in the tetrahedral and octahedral bentonite layer, is balanced by the presence of Na⁺, K⁺, and Ca²⁺ cations that give affinity for aromatic hydrocarbons and catalyze the transformations [89]. Both clays and bentonites are used either individually or in mixtures (powder, granules) in contaminated soils or as barrier layers in landfills. They are environmentally friendly, non-toxic, and low-cost materials, which makes them useful in environmental decontamination. However, studies show that due to the negative charge, clay cannot absorb organic compounds. In this regard, clay must be modified with surfactants to convert its hydrophilic properties into hydrophobic ones [90,91]. Their use valorizes mineral resources and contributes to the development of sustainable depollution technologies with minimal impact on the environment.

Another source of clay matter consists of sedimentary deposits within Transylvania Basin (Romania), rich in kaolinite with traces of muscovite. They are easy to be exploited and almost ready for use. Some of our research reveals their nanostructural constituents of fine lamellas of kaolinite around 40 nm and muscovite around 60 nm [92,93]. These can be easily observed through atomic force microscopy (AFM) investigations, and a relevant example is presented in Figure 7.

The fine interlocking of the kaolinite and muscovite nanoparticles ensures a high specific surface, which ensures an optimal site for liquid absorption. The fact is confirmed by literature on aqueous dispersions [94,95]. The hydrophilic behavior of clays must be adjusted via fluoridation or silanization to turn them into a hydrophobic state able to absorb petroleum spills [96,97].

Fly ash from coal combustion in power plants and used in construction or as a stabilizing agent can also be used as an absorbent material due to its fine particle size distribution, porous structure, and large surface area available for adsorption [98,99,100]. Ash particles function as a microfilter that captures organic molecules on the surface or in internal cavities. Its characteristics depend on the type of coal and the burning conditions.

Metal slag, (steel slag) obtained from the processing of metals in mining operations and steelmaking processes [101], has a coarse and porous structure and can be used in areas near mines [102]. To increase efficiency, slag can be used in a mixture with other natural materials such as sawdust or peat.

4.3. Synthetic Absorbents

Synthetic absorbents include polymers such as polypropylene, polyethylene, polyacrylate, polystyrene, and polyurethane. These materials possess oleophilic and hydrophobic properties, a low bulk density, strong mechanical resistance, good buoyancy, and a high absorption capacity [76,103,104]. They are among the most commonly used sorbents for oil spill cleanup. However, their effectiveness is limited by factors such as low oil retention, high cost, and poor recyclability [105,106].

Once used, any absorbent material can become a potential pollutant if not managed in accordance with environmental principles. These materials must not be discarded in nature or left to degrade without control. Proper collection, transport, and treatment are essential to prevent environmental harm and to maintain a simple, sustainable decontamination process. If not handled responsibly, used absorbents can become sources of secondary pollution. Therefore, every stage of the decontamination process, from the initial application to the final disposal or neutralization of used absorbent materials, must be carefully planned to prevent the spread of contamination from one area to another.

The use of locally sourced absorbents has contributed to reducing the environmental impact, supporting the principles of the circular economy and contemporary sustainability policies. These natural materials are particularly suitable for ecological emergencies or for equipping local response teams, as they provide an effective and cost-efficient solution.

5. Conclusions and Perspectives

This research focused on two main scientific directions related to petroleum hydrocarbons. The first part explored fundamental aspects in the context of increasing emissions from both natural sources (such as crude oil, natural gas, volcanic eruptions, fires) and human activities (socio-industrial activities, oil extraction and processing and fossil fuels, underground leaks, maritime and land transport, pesticide use in agriculture, smoking). Whether in the raw form (crude oil) or processed (diesel, gasoline, industrial oils), petroleum hydrocarbons infiltrate the environment, disrupting the ecological balance of aquatic and terrestrial ecosystems and posing risks to human health.

The second part of the study focuses on techniques and methods used for the environmental decontamination of petroleum hydrocarbons. It explores a range of approaches, including physical techniques (such as isolation through physical and mechanical actions, soil vapor extraction, solvent extraction, and soil washing), chemical methods (including dispersants, chemical oxidation, thermal desorption, and solidification/stabilization), biological methods (such as bioremediation and phytoremediation), and the use of locally available natural absorbents. These methods were assessed based on their efficiency, conditions of application, environmental impact, and potential for broader implementation.

The integration of natural indigenous absorbents (straw, sawdust, natural hemp and wool textile fibers, cotton, nettle, reed), minerals (clays, zeolites, industrial slag), and synthetics (polypropylene, polyethylene, polyurethane, polystyrene, and polyacrylate) can become a new and innovative way of interacting with the environment. The efficiency, feasibility, and applicability of these solutions in combating petroleum hydrocarbon pollution have been highlighted. Indigenous absorbents represent a viable, ecological, and efficient alternative to standardized commercial solutions and provide a solid basis for further research and expansion of the applicability in various contamination scenarios.

A key research perspective on this topic is the field application of natural absorbent materials, as only a limited number of studies have explored this area. Most existing research has been conducted under controlled laboratory conditions, where efficiency tends to be higher. However, in real-world environments, various external factors can significantly influence performance.

A practical approach involves developing pilot projects supported by public or European funding sources, such as Start-Up Nation, PNRR, the Environmental Fund Administration, or other programs focused on environmental innovation. Additionally, forming partnerships with local authorities, universities, municipalities, or NGOs—who can act as co-financiers or direct beneficiaries—can enhance both the eligibility and long-term sustainability of these initiatives.

Integrating indigenous absorbents into national and local plans through regulatory measures is essential. The standardization and certification of these materials are critical steps toward promoting their wider adopting international, economic, and operational levels.