Nano- and Microplastics in Single-Use Plastic Water Bottles: A Review of Occurrence, Health Risks, and Regulatory Needs

Abstract

Nano- and microplastics (NMPs), which are ubiquitous environmental pollutants, are commonly found in single-use plastic water bottles. They originate primarily from the bottle material itself with the amount increasing through mechanical wear. This review synthesizes current scientific knowledge on the occurrence, health risks, and regulatory considerations concerning NMPs in single-use plastic water bottles. The review revealed that concentrations vary widely, leading to potential human exposure risks. Ingested NMPs can induce oxidative stress, inflammation, disruption of gut microbiota and potential bioaccumulation. Current health risk assessments are challenged by inconsistent methods and lack of standardized reference materials. While regulatory frameworks addressing NMP contamination are developing globally, they lack consistency and legally enforceable limits. Standardized detection and monitoring are emerging priorities, but legally enforceable limits and comprehensive policies are underdeveloped. This review highlights an urgent need for consistent regulations, standardized analysis methods, and research that examines realistic human exposure and toxicological impacts. To safeguard consumer health amidst escalating plastic utilization, it is essential for policymakers, researchers, industry, and public health stakeholders to coordinate their efforts to mitigate NMP contamination in single-use plastic water bottles.

1. Introduction

The escalating production and consumption of plastics have led to their pervasive presence across global ecosystems, resulting in widespread environmental contamination by nano and microplastics (NMPs) [1,2,3]. These minute plastic fragments are generally defined by their size: microplastics are particles smaller than 5 mm, while nanoplastics are less than 100 nm [4]. Both are now recognized as emerging environmental pollutants, leading to significant attention directed towards their occurrence in drinking water sources [5,6].

The ubiquitous nature of NMPs in bottled water raises considerable concerns regarding their potential health impacts and necessitates a thorough examination of their origins, characteristics, and implications for public health [7,8]. It examines the presence and nature of these particles and pinpoints their main sources and how they spread. It then assesses current evidence regarding the potential risks they pose to human health. Furthermore, the review critically analyzes the current state of regulatory frameworks and highlights the pressing needs for standardized methodologies and policy interventions to address this growing environmental and public health challenge.

2. Literature Search Methodology

A structured literature search was conducted to identify peer-reviewed studies relevant to nano- and microplastics (NMPs) in drinking water, with emphasis on single-use plastic bottled water. Searches were performed in PubMed/MEDLINE, Scopus, Web of Science, ScienceDirect, Google Scholar, EMBASE, and EBSCOHost. Where applicable, platform-specific indexing terms were used alongside free-text keywords. Search queries combined core concepts using Boolean logic. Key concepts included: (i) NMPs (“microplastics” OR “nanoplastics”); (ii) drinking water exposure (“single-use plastic water bottles” OR “bottled water” OR “drinking water” OR “tap water”); (iii) occurrence metrics (“occurrence” OR “presence” OR “contamination” OR “abundance”); (iv) health outcomes (“health risks” OR “human health effects” OR “toxicity” OR “carcinogenicity” OR “immune disorders” OR “neurotoxicity” OR “reproductive issues” OR “respiratory diseases”); and (v) governance responses (“regulatory needs” OR “policy” OR “management” OR “standardization”). The review prioritized publications from 2015–2025 to reflect the rapid growth of NMP research in recent years.

Eligible records included English-language original studies and evidence syntheses (systematic reviews, meta-analyses, and narrative reviews). Selected articles reported on nanomaterial/microplastic (NMP) occurrence in drinking water (bottled, tap, or other sources) and/or evaluated related human health implications and policy considerations. Studies were excluded if they addressed plastic waste or pollution without analyzing micro-/nanoplastics in drinking water, or if they were not peer-reviewed. Articles focused solely on manufacturing or engineering topics without a direct link to NMP occurrence, health effects, or regulation in drinking water were also excluded. Titles and abstracts were screened independently by two reviewers. Any disagreements were resolved through discussion and, when needed, adjudication by a third reviewer. Full texts of potentially eligible studies were then evaluated against the criteria. Data were extracted on reported concentrations, polymer composition, particle size ranges, likely contamination sources, health-effect findings, and regulatory or policy recommendations.

3. Occurrence and Characteristics of NMPs in Bottled Water

NMPs are ubiquitous contaminants identified in various environmental settings, including aquatic and terrestrial environments. Their occurrences in drinking water and beverages are frequent [1,7], with bottled drinking water samples consistently showing microplastic contamination [8]. This is a particular concern, highlighting how a broad range of products meant for consumption are contaminated.

3.1. Definitional Framework of Microplastics and Nanoplastics

As plastic pollution grows globally, scientists have established precise definitions for microplastics (MPs) and nanoplastics (NPs) based on their size and how they interact with living organisms [9]. These pollutants now contaminate the entire biosphere, from the deep sea to human organs, posing severe risks to the environment and human health [9]. A thorough understanding of their characteristics is essential for tackling the challenges they present.

Microplastics are solid plastic pieces between 100 nanometers and 5 mm, commonly extending down to about 1 micrometer (µm) [10,11]. These particles originate from two main pathways: primary sources, which are deliberately manufactured (e.g., industrial abrasives), and secondary sources, resulting from the gradual breakdown of existing plastic waste (e.g., plastic bags, synthetic textiles) [12]. They exist in diverse physical forms such as fibers, fragments, films, pellets, beads, and foams which vary in shape, density, and surface properties [1,9]. Common polymer types are polyethylene terephthalate (PETE), polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC) [8].

Nanoplastics are plastic particles generally defined as being smaller than 1 micrometer (µm), though some classifications refine this range to between 1 and 100 nanometers to align with standard nanomaterial definitions [13,14]. These particles are especially concerning because their minute size allows them to easily penetrate biological barriers, move into tissues, and interact with cells and their components [15]. NPs originate from two primary sources: they are either intentionally engineered for industrial use or created naturally when plastic waste in the environment breaks down [16,17]. While current methods can readily detect MPs, reliably analyzing NPs is considerably more challenging because of their diminutive size [18].

3.2. Concentration Ranges and Variability

The concentration of NMPs in bottled water shows considerable variation, influenced by the manufacturing processes, types of packaging, and analytical methods used across different studies, brands, and countries [1]. Studies have reported a wide range of concentrations, spanning from as low as a few tens to as high as hundreds of particles per liter [19]. For example, a study in Indonesia found concentrations of 7043 to 8339 particles/L in bottled water in Indonesia [20]. Another study reported an average of 10.4 microplastic particles per liter for those greater than 100 µm, which increased to 325 particles per liter when including the 6.5 to 100 µm size range [8]. High variability can also be observed even among bottles from the same manufacturing batch. This indicates that standard manufacturing tolerances inherently contribute to these differences [21]. Nanoplastics, which vary in particle size from 58 to 255 nanometers, have also been detected in a range of concentrations [1].

NMPs in bottled water exhibit a wide range of sizes and diverse morphologies [8,20,22]. Studies consistently report a high proportion of smaller particles, with up to 95% of detected microplastics often falling between 6.5 and 100 µm [8,23]. Commonly identified shapes of NMPs include fragments, fibers, pellets/granules, beads, and films [8,20,22]. Fragments are typically irregular shards, whereas fibers are thin, thread-like particles that are often observed to be dominant [20,22]. Granules predominated in some analyses using specific detection methods [24].

3.3. Physical and Chemical Characteristics

NMPs consist of synthetic polymers that do not easily dissolve in water and remain in the environment for long periods without breaking down [25]. These materials often retain hazardous production additives, such as phthalates and bisphenol A, while simultaneously absorbing external environmental pollutants including heavy metals, organic toxins, and pathogens onto their surfaces [26,27]. They pose risks of both physical and chemical contamination because they can transport pathogens and hazardous chemicals [28]. Subsequent ingestion or inhalation of these contaminated materials may then lead to toxicological effects [27]. The vast diversity of polymer types, sizes, shapes, and surface characteristics makes comprehensive analysis difficult [9].

The chemical composition of NMPs in bottled water largely reflects the materials used in the manufacturing of bottles and their caps [5,8].

Table 1. Polymer composition of NMPs in bottled water.

Polymer Type	Common Sources	Detection Frequency	Percentage	Notes	References
PET (Polyethylene Terephthalate)	Bottle bodies		Up to 42% of MPs; 28.57% in samples	Main material for single-use bottles	[8,20,29]
PE (Polyethylene)	Bottle caps, packaging		35.71% in samples	Includes low- and high-density polyethylene	[19,29]
PP (Polypropylene)	Bottle caps, additives		14.28% in samples	Used in caps and certain plastic components	[8,20,29]
PS (Polystyrene)	Packaging, other contaminants		14.28% in samples	Less common but detected	[29,32]
PVC (Polyvinyl Chloride)	Contaminants		7.14% in samples	Identified in some studies	[29,33]
PC (Polycarbonate)	Some water bottles, feeding bottles	Detected in specific bottle types		Primarily in reusable or specialized bottles	[30,34]
PPSU (Polyphenylene Sulfone)	Feeding bottles	Detected in specific bottle types		Used in infant feeding bottles	[30,35]

presents the identified synthetic polymers. Polyethylene terephthalate (PET) and polypropylene (PP) are the most identified polymer types because they are typically used to manufacture bottle bodies and caps, respectively [8,20,29]. Aliyu et al. [19] and Osoro et al. [29] indicate that polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC) are also commonly encountered. Polyphenylene sulfone (PPSU) resins and polycarbonate (PC) have also been identified in feeding bottles [30]. Some studies have also identified cellulose-based polymers, which generally originate from natural textiles instead of the plastic packaging material itself [31].

4. Sources and Pathways of Contamination

NMP contamination in bottled water is a multifaceted issue stemming from various stages, including raw material acquisition, production, packaging, storage, and consumer use [6,36].

4.1. Raw Water Source

Raw water sources can be a pathway for NMP contamination in bottled drinking water [6]. NMPs are widespread across diverse ecosystems, appearing frequently in freshwater sources such as rivers, lakes, and groundwater [37]. Karst aquifers, which supply about 25% of global drinking water, are susceptible to contamination from surface pollutants [38]. NMPs have been found in springs and wells within karst aquifers, often alongside other contaminants like phosphate, chloride, and triclosan, suggesting septic effluent as a source [38]. Freshwater studies report a wide range of NMP particle concentrations, varying from undetectable (0 particles/L) to a high of approximately 1000 particles/L [39]. Raw water contains varying levels of NMPs, most composed of polyethylene (PE), polyethylene terephthalate (PET), and polypropylene [40,41]. Drinking water treatment plants (DWTPs) can significantly reduce the high concentrations of microplastics (MPs) often found in raw water sources [42].

4.2. Production and Bottling Process

The bottling process introduces NMP contamination into bottled water products as plastic bottles shed micro-particles that contaminate the water inside [8]. NMP concentrations in bottled water have been noted to rise following industrial cleaning and filling processes [43]. For example, Weisser et al., [43], observed that the bottle-capping process caused microplastic concentrations to surge from less than 1 MP/L to 317 ± 257 MP/L. NMPs are detected in water from all types of bottles, including single-use and reusable PET bottles, as well as glass bottles. Research by Duda and Petka [44] found that glass bottles averaged 6292 microplastics per liter (±10,521), more than double the 2649 particles per liter (±2857) found in PET bottles. However, high standard deviations in both categories indicate a wide range of contamination levels across individual samples. While PET is the standard polymer for plastic bottles, glass bottle components such as liners and seals often incorporate different polymers like polyethylene or styrene-butadiene copolymers [45]. These findings suggest that microparticles may be released directly from the packaging [46].

Water particulate levels can be affected by gas injections, thermal fluctuations, and light exposure [47]. Furthermore, NMP contamination and introduction in bottled water can result from substandard manufacturing practices, including improperly sterilized containers, air pollution during the filling process, and inadequate lid sealing [48]. The diverse ranges of plastic particles found in bottled water suggest distinct origins of contamination that occur at different stages of the water production process. For instance, larger PET and PE particles might be freshly released from packaging during transport or storage. In contrast, polymers like PA, PP, PS, and PVC are likely introduced earlier, either during production or from the water source itself [49].

4.3. Packaging Material Degradation

Degradation of packaging materials, especially plastic bottles, is a major cause of NMP contamination in bottled drinking water [50]. Both PET bottles and PP caps are prone to mechanical stress and material degradation [51]. Research indicates that PET plastics contain various chemical additives, impurities, and degradation byproducts, with potential contaminants that can leach into bottled water [52]. Phthalates also known as plasticizers, which are chemicals added to plastics to make them more flexible and durable, can leach from packaging into water over time, especially when exposed to heat [53]. Although studies suggest that contamination from plastic bottles alone may not be harmful, experts still recommend minimizing their use because of the widespread nature of microplastics from other sources [54].

The degradation of packaging materials can introduce plastic particles into water. Research shows that NMPs found in bottled water match the materials used to make the packaging, specifically PET from the bottles and PP from the caps [8]. Similarly, some studies have also found various polymers, such as polyethylene or styrene-butadiene-copolymer, in glass bottles [27]. This suggests that contamination is not limited solely to plastic packaging. Although polypropylene (PP) and polycarbonate (PC) are present in various water bottles and their breakdown results in NMP, fewer microparticles tend to be released by high quality plastic and glass bottles [30]. Song et al. [30] indicates that additives like calcium stearate and silicone that are present in the plastic can also contribute to the released microparticles. These degradations of plastics vary in scale, from large pieces (macro) down to microscopic fragments (nano) [55].

4.4. Storage Conditions and Environmental Factors

Storage conditions and environmental factors significantly influence the level of NMP contamination in bottled drinking water [56]. Environmental factors accelerate the degradation of plastics into progressively smaller fragments, specifically NMPs. Exposure to elements such as sunlight, temperature fluctuations, and physical stress hastens this process [57]. Higher temperatures and longer storage periods accelerate the migration of chemicals, such as antimony, from PET plastics into bottled water [58]. While UV-ray irradiation alone did not increase antimony release after 14 days, prolonged exposure to direct sunlight and high temperatures caused antimony levels in bottled water to rise, occasionally exceeding safety limits [59]. Plastic bottles that have been refilled exhibit different concentrations of microplastics based on how they are stored (e.g., in shade, cooled, or frozen). Of these conditions, storage in the shade results in the highest concentration of microplastics [60]. This longer storage durations can lead to increased microplastic content due to continuous degradation [20].

4.5. Handling and Use Patterns

The usage and handling patterns of plastic water bottles can contribute to NMP contamination of the water they contain [61]. The screw cap system used on reusable plastic bottles is one potential source of microplastics [62]. Repeatedly opening and closing a plastic bottle cap can cause PET plastic particles to break off [63]. Mechanical stress, like crushing the bottle or exposing it to heat, contributes to the release of plastic particles [63]. A preliminary study found that opening a reusable PET bottle with a polypropylene (PP) cap and polyethylene (PE) seal released an average of 131 (±25) microplastic particles per liter [62]. This number increased to 242 ± 64 MPP/L after 11 openings and closings, primarily due to a significant increase in PP particles [62]. The abrasion between the bottle cap and bottleneck can contribute significantly to NMP contamination in bottled water [21].

Metal bottle caps contribute to microplastic pollution because their polyester-based coatings degrade into microscopic plastic particles [64]. Chaïb et al., [64] indicated that microplastic concentrations in glass bottles are approximately 50 times higher than in plastic bottles, likely because plastic bottles use caps that lack the specific paint found on glass bottle closures. Furthermore, metal caps stored post-production can scrape against each other, leading to bits of plastic from these scratches ending up in the bottled water. This suggests that metal bottle caps can also be a direct source of NMPs. In addition to abrasion caused by wear and tear, microplastics can be released due to physical degradation from normal use and exposure to environmental factors [65]. Frequent reuse of single-use plastic bottles increases the likelihood of NMP contamination originating specifically from the bottleneck–cap system [62].

4.6. Global Bottled Water Consumption

Bottled water consumption varies significantly by country, influenced by consumer concerns over tap water safety, ease of access, and cultural habits [1,66,67]. These consumption rates directly determine the level of human exposure to NMPs in bottled water. Widespread bottled water consumption is driven by the perception that it is safer and purer than tap water, even in high-income regions where public supplies meet rigorous quality standards [68,69]. Furthermore, the portability of bottled water makes it the ideal choice for busy, on-the-go lifestyles [68,70]. Rising disposable incomes in emerging economies and rapid urbanization are key drivers of demand, fundamentally shifting consumer needs [68,71]. Finally, consumption can be driven by a lack of trust in public water systems, particularly in countries with poor infrastructure where bottled water often serves as the main source of drinking water [72,73].

While varied regional research and reporting methods make compiling global data on bottled water consumption per capita difficult, available data and projections indicate significant consumption patterns worldwide [74,75].

Figure 1 illustrates the lifecycle of a single-use polyethylene terephthalate water bottle, emphasizing the cumulative nature of contamination that leads to human exposure upon consumption. It highlights the primary sources and pathways through which nano- and microplastic particles contaminate the bottled water. NMPs originate from the water sources to the manufacturing of PET resin pellets and subsequent molding of bottle preform and final container. Particle generation can also occur during the processes of washing the bottle, filling it with treated water, and sealing it. Environmental factors like fluctuating temperatures, UV light exposure, and physical agitation during storage and transit may hasten degradation, resulting in particles leaching into the water. The physical act of opening the cap, handling the bottle and repeated temperature changes continue to shed NMPs.

5. Analytical Techniques for Detection and Quantification

Accurate identification and quantification of NMPs in bottled water are crucial for assessing exposure and health risks [5,79,80]. However, challenges exist due to the minute size, low mass, and heterogeneity of these particles [4,81]. A variety of analytical techniques are employed, each with specific advantages and limitations [5,82].

5.1. Sample Preparation

Effective sample preparation is fundamental for isolating NMPs from the water matrix and minimizing contamination [4]. Filtration is often the initial step, employing membrane filters typically sized at 0.45 µm to effectively capture microplastics [83]. Digestion protocols, often involving hydrogen peroxide (H₂O₂) or Fenton reagent, are used to remove organic matter that can interfere with analysis, ensuring plastics remain unaltered [24,84]. Strict contamination control measures, including the use of blanks and controlled laboratory environments, are essential throughout the process [85,86].

5.2. Instrumentation and Detection Limits

5.2.1. Microscopy Techniques

Optical microscopy, often paired with Nile Red staining, provides an efficient method for the visual detection, quantification, and morphological characterization of microplastics (ranging from a few micrometers to 5 mm) [8,24,87]. However, its limited resolution makes it unsuitable for detecting smaller NPs [5]. Conversely, Scanning Electron Microscopy (SEM) provides superior, high-resolution insights into particle morphology at the nanometer scale [24,88]. In contrast to the wide field of view provided by optical microscopy, SEM is limited by demanding sample preparation and reduced throughput capabilities [84].

5.2.2. Spectroscopic Methods

Chemical identification of microplastics is primarily achieved through Fourier-Transform Infrared (FTIR) and Raman spectroscopy, both of which correlate unique spectral signatures with established polymer libraries [5,8,22]. While Micro-FTIR can analyze particles down to approximately 1 µm [85], Raman spectroscopy offers higher resolution for sub-micrometer levels [85,89,90]. When combined with Laser-Induced Breakdown Spectroscopy (LIBS), Raman spectroscopy enhances the discrimination of polymers such as PET, PE, PS, PP, and PVC [29]. Surface-Enhanced Raman Spectroscopy (SERS) provides an advanced, high-sensitivity alternative capable of detecting trace NPs as small as 50 nm with high precision [23].

5.2.3. Thermal Analysis

Pyrolysis Gas Chromatography–Mass Spectrometry (Pyrolysis GC-MS): This technique involves the thermal degradation of plastic polymers into specific monomer units or characteristic fragments. These resulting components are subsequently identified and quantified using Gas Chromatography–Mass Spectrometry (GC-MS) [91]. It provides a mass-based quantification specific to the polymer content, but it does not provide details regarding the particles’ size or shape [91].

5.2.4. Advanced and Integrated Approaches

To enhance analysis, artificial intelligence (AI) is increasingly integrated with microscopy for automated, consistent quantitative particle analysis [92,93,94]. Emerging techniques like electrophoresis and quartz crystal microbalance (QCM) show potential for detecting nanoplastics in water by sensing minute mass changes upon electrode adhesion [95]. Finally, low-cost smartphone-based microscopy systems are being developed to enable preliminary screening of microplastics as small as 20 μm (µm) [96].

Table 2. Analytical techniques for NMP detection in bottled water.

Analytical Technique	Sample Preparation	Instrumentation	Detection Limits/Size Range	Advantages	Limitations	References
Optical Microscopy (Digital/Fluorescence)	Filtration (0.45–1 µm); Nile Red staining	Optical/Fluorescence microscope	~1 µm to 5 mm	Visual identification, counting, morphology	Limited resolution for NPs; potential misidentification	[5]
Scanning Electron Microscopy (SEM)	Filtration; drying; (optional) conductive coating	SEM	Nanometer scale (tens of nm)	High-resolution morphology, surface details	Time-consuming; complex preparation; low throughput	[24,84]
FTIR Spectroscopy (Micro-FTIR)	Filtration; organic matter digestion	FTIR spectrometer; micro-FTIR	Down to ~1 µm	Polymer identification	Lower spatial resolution than Raman for very small particles	[5,85]
Raman Spectroscopy (Micro-Raman)	Filtration; organic matter digestion	Raman microscope	Down to ~1 µm or smaller	Polymer identification; higher spatial resolution	Can be affected by fluorescence interference; cost; time-efficiency	[29,85]
LIBS (Laser-Induced Breakdown Spectroscopy)	Filtration	LIBS system (often with Raman)	Microplastic scale	Enhances polymer discrimination	Primarily elemental analysis, needs integration for organic polymers	[29,97]
Pyrolysis-GC-MS	Thermal degradation of isolated particles	Pyrolyzer coupled to GC-MS	Mass-based quantification of specific polymers	Accurate polymer-specific quantification	No information on particle size, shape, or number	[91,98]
SERS (Surface-Enhanced Raman Spectroscopy)	Specialized sample prep for SERS substrate	SERS-active substrate, Raman spectrometer	Down to 50 nm	High sensitivity for trace nanoplastics	Requires specialized substrates; still developing for complex samples	[23,99,100]

outlines various instrumental methods used for qualitative and quantitative analysis of NMP contamination and detection limits. The information can be used to compare the efficacy and applicability of different methodologies for monitoring NMP levels in alignment with potential regulatory requirements.

5.3. Comparative Approaches to Analyzing NMPs in Bottled and Alternative Water Sources

Analyzing NMPs in bottled water requires specialized protocols and faces unique challenges that differ from those used for tap, surface, or groundwater [45]. While identification methods generally rely on filtration and spectroscopy, the specific approach is tailored to the sample’s complexity, anticipated concentration levels, and potential contaminants [27,101]. International standards like ISO 24187 harmonize methodologies by providing clear guidelines for analyzing NMPs across different environmental matrices [102].

Bottled water contains higher concentrations of NMPs than tap water, largely because the bottling process and materials (specifically PET bottles and polypropylene caps) shed plastic particles directly into the water [8,27,49]. Studies indicate that bottled water contains an average of 325 plastic NMPs per liter, with NPs being the primary contaminant, comprising roughly 90% of the total count [8]. Studies indicate that the degradation from washing and reusing bottles releases more microplastics than the original manufacturing process [27]. To avoid contamination from the packaging itself, bottled water protocols often require analyzing the entire container’s contents, whereas environmental or tap water sampling typically uses large volume filtration [85,103].

Despite these differences, strict contamination measures must be applied to all water samples to account for airborne NMPs in the laboratory [104]. Once particles are isolated, spectroscopic methods like µ-FTIR and Raman are universally applied for polymer identification, regardless of the water source [27]. A lack of standardized methods makes it difficult to compare research findings across the field [105]. To address this, international initiatives like ISO 16094 are standardizing microplastic analysis in water by establishing unified protocols for sampling, filtration, contamination control, and reporting [106].

A comparative overview of the approaches to quantify and characterize NMPs in bottled versus alternative water sources is summarized in

Table 3. Comparative Analytical Approaches for Assessing NMPs in Bottled and Alternative Drinking Water Sources.

Aspect	Bottled Water Analysis	Other Water Source Analysis (Tap, Surface, Groundwater)	References
Sample Collection	To eliminate subsampling errors, entire bottle units are analyzed across multiple brands. Comprehensive studies involve collecting small-volume samples across a high number of bottles.	Requires large-volume sampling (grab/filter) for low-concentration or heterogeneous samples. Water is sampled across all supply points including treatment plants, distribution networks, and natural sources.	[101,107]
Matrix Complexity	The primary concern is contamination from the plastic packaging and bottling process itself, rather than environmental debris	More complex, natural matrices contain high levels of inorganic sediments, organic matter, and biological organisms. These interfering substances require specific removal steps.	[8,101]
Sample Preparation	Focus is on minimizing physical degradation and chemical alteration of microplastics. Filtration usually employs membranes with small pore sizes (e.g., 0.2–0.45 µm). Digestion of organic matter is less common but can involve mild treatments if necessary. Gentle drying (below 40 °C) is crucial to prevent plastic degradation.	Rigorous pretreatment is often necessary to remove complex matrices, using methods like wet peroxide oxidation or hydrochloric acid digestion to break down organic and inorganic components. High temperatures (>60 °C) are typically avoided to prevent MP damage. Filtration typically uses pore sizes appropriate for the target particle range, often 0.22–0.45 µm.	[101]
Contamination Control	Widespread microplastic contamination requires strict laboratory control measures. This includes using glass or metal equipment, filtering all reagents, working in laminar flow hoods, wearing cotton lab coats, and conducting numerous field and procedural blanks.	Stringent contamination control is essential, as the environmental sampling equipment and process can introduce additional pollutants. Field blanks are essential to account for airborne contamination during collection.	[101]
Analytical Techniques	Employs highly sensitive spectroscopic methods such as micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) and micro-Raman Spectroscopy (μ-Raman) to identify polymer types and count particles down to 1 µm or smaller. Pyrolysis-Gas Chromatography–Mass Spectrometry (Py-GC/MS) is used for mass quantification of polymer types, often without providing particle size information.	Uses similar advanced spectroscopic and mass spectrometry techniques (μ-FTIR, μ-Raman, Py-GC/MS). However, the focus may be on a broader size range, and challenges arise from distinguishing microplastics from natural particles after digestion. Visual identification under a microscope is often a preliminary step, followed by chemical confirmation.	[85,101]
Detection Limits	Quantifying microplastics down to 1 µm or smaller requires sensitive detection, especially when assessing potential health impacts.	Detection limits vary based on instrument capabilities and matrix complexity, with some studies focusing on particles greater than 10 µm or even 50 µm. The presence of smaller particles is often noted to be significantly higher.	[101]
Reporting Standards	Comprehensive reporting includes bottle brand, packaging material, volume, production dates, and specific details on analytical methods and contamination controls. Results quantify findings as particle concentration (particles per liter) and specify the individual polymer types identified	Reporting includes sampling location, environmental conditions, raw water quality, water treatment efficiency, and detailed characterization of identified microplastics (size, shape, color, polymer type). The lack of standardized reporting contributes to difficulty in comparing studies.	[101]

. The table highlights key disparities in, and limitations of, current detection methods.

6. Adverse Health Risks and Dose–Response Relationships

The widespread exposure to NMPs has spurred extensive research into their potential health impacts, revealing a growing body of evidence for adverse effects in various biological systems [108,109]. However, establishing definitive dose–response relationships and human safety thresholds remains a significant challenge due to methodological limitations and the complexity of plastic particles [27,109].

6.1. Observed Effects on Animal Studies

Animal studies have demonstrated that NMPs can impact multiple systems, often at doses higher than typical human environmental exposure [27,110]. These particles trigger the production of reactive oxygen species (ROS) inside cells, leading to oxidative stress and cellular damage [111,112]. This process disrupts tissue integrity and impairs overall biological function. Furthermore, smaller particles, particularly NPs, move beyond the initial point of contact, translocating from exposure organs to other parts of the body [15].

Ingested particles can cause physical irritation and chronic inflammation in the gastrointestinal tract. Specifically, studies in mice demonstrate that polystyrene microplastics disrupt gut microbiota balance and impair intestinal barrier function [27,113]. Inhaling NMPs poses a significant respiratory risk. Research has identified these particles within human lung tissue, while animal studies demonstrate that exposure can trigger lung injury, elevate inflammatory cytokines, and activate cellular stress pathways [112,114].

In the cardiovascular system, NMPs have been found in arterial tissues and atherosclerotic plaques, where their presence is linked to a higher risk of major adverse cardiovascular events (MACE) [115]. Additionally, animal research indicates that these particles cause pathological damage, oxidative stress, and disruptions to cardiac metabolism [116,117]. NMPs also disrupt metabolic and endocrine functions by interfering with hormonal balance. Animal studies indicate that these disruptions including exposure during pregnancy can lead to accelerated weight gain, insulin resistance, abnormal lipid metabolism, and restricted fetal growth [118,119]. Finally, NMP exposure can have significant impacts on the neuroendocrine system. This exposure leads to an increase in both neuronal membrane damage and DNA damage within the affected cells [120].

6.2. Limited Human Data and Accumulation

While animal studies strongly indicate potential effects of NMPs, a clear understanding of their direct impact on human health and the precise dose–response relationships has yet to be established [1,121,122]. However, NMPs have been detected across a range of human biological systems, including the digestive tract (feces), the circulatory system (blood), and the respiratory system (lung tissue) [113]. A recent prospective study identified NMPs within surgically removed carotid plaques, linking their presence to an increased risk of major cardiovascular events [123]. The presence of these plastic particles was linked to an increased risk of primary endpoint cardiovascular events [113]. Due to their microscopic size, NPs can easily penetrate human tissues and organs, increasing the risk of long-term health complications [124].

Many current environmental studies fail to assess the actual physiological consequences [125]. Consequently, there is no definitive evidence that microplastics in drinking water pose a human health risk at current exposure levels, as the danger they present remains significantly lower than that of known waterborne pathogens [126]. Research involving high-concentration laboratory experiments suggests that microplastics can trigger cellular damage, inflammation, and oxidative stress [127]. Ingesting microplastics can result in physical harm, including the obstruction of the digestive tract, which may cause malnutrition or starvation in aquatic organisms and accumulation within internal tissues [128,129]. Beyond physical harm, NMPs can carry toxins by leaching their own chemical additives or absorbing pollutants from the environment, both of which are released once ingested [130].

6.3. Human Exposure Levels

Human exposure to NMPs via the consumption of bottled water can be significant. The degree of this exposure depends on individual consumption habits and geographical location [1,83,131,132]. The estimated annual intake of microplastics from drinking water per person is highly variable, potentially ranging from a few hundred to several million particles [83,133]. Children typically ingest more microplastics than adults on a body weight normalized basis, a phenomenon attributed to their comparatively higher water intake relative to their smaller body mass [19,24,132]. For example, Alva-Rojas et al., [24] estimated that, per kilogram of body weight, the exposure to microplastics in children and infants is 3 to 5 times higher than that in adults. This increased risk is driven by frequent hand-to-mouth behaviors, higher ingestion of plastics from bottles and teethers, and greater inhalation of dust from floor play, all exacerbated by their small body mass [30]. In another study, Mohamad Nor et al. [132] estimated that adults ingest a median of 883 particles per person per day. These particles, specifically those ranging from 1 to 10 µm in size, could potentially build up to a total accumulation of approximately 50,100 particles per person in body tissue by the age of 70.

6.4. Cellular and Systemic Effects

Ingested NMPs can cause various biological effects, impacting organisms at scales ranging from individual cells to entire systems [2,42,127]. At the cellular level, NMPs have been shown to initiate oxidative stress, which causes cell damage and inflammatory reactions [42,127]. They can also cause cytotoxicity and genotoxicity, affecting DNA and cellular viability [76]. Studies have shown that microplastics may disrupt the metabolic system, alter the balance of gut bacteria (microflora), and lead to problems with normal gastrointestinal function [134,135]. Systemically, NMPs have been linked to disruptions in hepatic (liver), cardiopulmonary (heart and lung), and immune systems, and can degrade reproductive health [127,136]. Toxicological studies have observed an increase in various inflammatory outcomes, including interleukins, tumor necrosis factors, chemokines, and interferons, associated with exposure to microplastics [137].

6.5. Bioaccumulation and Translocation

Their small size may allow NPs to penetrate biological barriers like the intestinal wall and spread throughout tissues and organs [55,138]. While the full extent of bioaccumulation in humans is still being studied, evidence from animal models suggests that a marginal fraction of ingested microplastics can be absorbed [7,132]. Following ingestion, NMPs have been observed adhering to the external carapaces and appendages of zooplanktons. These particles can also be egested in fecal pellets [139]. Consequently, concerns exist regarding the long-term accumulation of these substances within the human body [132].

6.6. Vector Effect of Contaminants

NMPs can act as vectors for other environmental pollutants [42,140]. Their surface properties facilitate the binding and retention of heavy metals, endocrine-disrupting chemicals (EDCs), antibiotics, and persistent organic pollutants [42,55]. These adsorbed chemicals, such as phthalates, can leach from the microplastics upon ingestion, potentially acting as endocrine disruptors and impacting reproductive health [42]. The concurrent intake of microplastics and other contaminants can produce varied hazards through complex interactions. A notable example is the co-exposure of mice to polystyrene microplastics and epoxiconazole, which causes significantly greater tissue damage and metabolic disruption than exposure to either substance individually [141,142].

6.7. Absence of Established Safety Thresholds

Although evidence of harmful effects is accumulating, the actual risks of NMPs are still unknown. This is due to the absence of standardized methods for measuring them in biological tissue and the lack of defined safe exposure limits [143]. Consequently, there are currently no established international or national guidelines, recommendations, or mandatory limits defining what constitutes a safe level of NMP intake [15,105]. Regulatory scientists continue to face challenges because of the uncertainty in testing methods and the vast diversity among plastic particles [105]. These difficulties are compounded by dose–response challenges. Animal studies often use exposure levels far higher than typical environmental concentrations, making it difficult to extrapolate the risk to humans [109]. Furthermore, research is difficult to interpret because the particles found in tissue samples are often larger than those scientifically proven to pass through biological barriers [15,144].

6.8. Current Understanding of Microplastic Exposure Health Risks

Scientists have yet to establish specific intake thresholds or reference doses that link microplastic consumption to defined health risks [42]. Observed harm often results from concentrations orders of magnitude greater than what people encounter in daily life [145]. This gap underscores the urgent need for standardized research and toxicological assessments to define dose–response relationships and guide public health policy.

While bottled water is a notable source of microplastic ingestion, its overall impact on human health varies. This significance depends on individual consumption patterns, the safety of local tap water, and the amount of microplastics encountered through food and air [1]. Heavy bottled water drinkers ingest roughly 90,000 microplastic particles annually, compared to only 4000 for those who drink tap water [146]. However, recent research indicates the actual concentration may be significantly higher [147].

NNP ingestion varies greatly by region; for example, Indonesia’s widespread bottled water use results in >700,000 particles annually, unlike areas with reliable, safe tap water where intake is significantly lower [20,148]. These figures should be considered alongside a wider range of exposures beyond bottled water. For example, an average person also takes an estimated 39,000 to 52,000 NMP annually through food plus contributions from inhalation and tap water sources [1,147]. It is therefore difficult to determine exactly how much bottled water contributes to total NMP intake. This complexity is worsened by the fact that different studies offer widely inconsistent estimates of daily liquid consumption.

Table 4. Health effects from oral exposure to NMPs (toxicological studies).

Endpoint/Effect	Study Models	Key Findings	References
Oxidative Stress	Human-derived cells, Rodent models, In vivo animal studies	NMPs induce reactive oxygen species generation, leading to cellular damage	[42,137,149,150]
Inflammatory Responses	Human-derived cells, Rodent models, Systematic reviews	Increase in interleukins, TNF-α, chemokines, indicating immune activation.	[2,42,151]
Cytotoxicity	Human-derived cells, In vivo animal studies	Direct cell damage and death observed, especially with smaller particles	[152,153,154]
Genotoxicity	Lung epithelial cells (in vitro)	DNA damage detected, suggesting mutagenic potential	[155]
Gut Microbiota Dysbiosis	Rodent models, In vivo animal studies	Alterations in gut microbial composition and function, impacting gut health	[2,42,135,156]
Gastrointestinal Dysfunction	Rodent models	Interference with gut barrier function and overall GI health	[2,42,157,158]
Hepatotoxicity	Rodent models (liver)	Liver damage, dysfunction, and metabolic disorders	[42,134,141,159]
Reproductive Toxicity	Rodent models	Impaired reproductive health, potential endocrine disruption from leached additives	[42,160,161]
Immunotoxicity	Rodent models, In vivo animal studies	Disruption of immune system function	[42,137,162]
Neurotoxicity	Rodent models	Potential for behavioral changes and neurological impacts	[42,163,164]
Systemic Accumulation	In vivo animal studies	NMPs cross biological barriers and accumulate in various organs	[55,132,138,165]
Vector for Pollutants	In vivo animal studies	NMPs absorb and carry other toxic chemicals, amplifying combined effects	[42,55,141,166]

Note: The analysis reported in this table utilized commercially available PET fragments and PS pearls as reference materials. However, these synthetic standards may not accurately mimic the environmental degradation processes, chemical interactions, or microbial colonization typically observed in natural microplastic pollutants. Therefore, applying these controlled laboratory results to real-world ecosystems should be approached with caution.

presents a summary of in vivo and in vitro toxicological studies regarding the adverse health outcomes associated with oral ingestion of NMPs.

6.9. Knowledge Gaps and Uncertainties in Health Assessment

Despite the growing body of evidence, significant knowledge gaps and uncertainties remain in comprehensively assessing the health risks of NMPs from bottled water [131,167].

Table 5. Key knowledge gaps and uncertainties in NMP health risk assessment.

Knowledge Gap	Description	Impact on Risk Assessment	References
Standardized Analytical Methods	Lack of consistent, sensitive methods for detecting and characterizing diverse NMPs (especially nanoplastics)	Limits accurate exposure quantification and comparability across studies	[4,76,168,169]
Environmentally Realistic Toxicological Data	Most studies use high doses of pristine polystyrene, not reflecting complex environmental NMPs	Difficult to extrapolate findings to real-world human exposure levels and diverse NMP types	[7,170]
Bioaccumulation & Biodistribution Mechanisms	Incomplete understanding of how NMPs translocate across biological barriers (e.g., intestinal lining, placenta) and their fate in the body	Hinders understanding of internal exposure and long-term accumulation	[55,171,172]
Long-Term Effects of Chronic Exposure	Limited research on chronic low-dose ingestion of NMPs over a human lifespan	Unknown long-term health consequences, especially for chronic diseases	[173]
Vulnerable Populations	Insufficient focus on specific risks for infants, children, pregnant women, and individuals with pre-existing conditions	Health impacts on susceptible groups are poorly understood	[174]
Role as Contaminant Vectors	The full extent of NMPs acting as carriers for chemicals and microbes, and their combined toxic effects, is not fully elucidated	Underestimates potential composite health risks	[42,175,176]
Physicochemical Properties	Variability in particle size, shape, polymer type, surface charge, and aging state significantly influences toxicity, but these are not consistently studied	Makes it challenging to generalize toxicological findings	[76,177,178]

summarizes the key knowledge gaps and uncertainties in the health risk assessment of NMPs. The table highlights critical data deficiencies identified in the risk assessment process, variability in exposure scenarios across different occupational and general populations, and the challenges associated with extrapolating data from animal studies to human health outcomes. The table specifically addresses the impact of these gaps on accurate dose response modeling and the setting of robust safety margins.

7. Overview of Current Regulatory Environment and Necessary Actions

The regulatory environment for NMPs in bottled water is in its early stages and inconsistent worldwide. This situation directly exemplifies both the emerging nature of scientific knowledge and the challenges inherent in establishing enforceable regulations and standards [179,180,181].

7.1. Current Regulatory Status

Currently, there are no universally accepted, enforceable regulatory limits for NMP concentrations in bottled water [182]. International bodies acknowledge the issue but often lack specific directives. NMPs are especially concerning because their microscopic size allows them to penetrate tissues and organs, potentially transporting toxic synthetic chemicals directly into cells throughout the body [183]. These particles can disrupt cellular functions and release harmful additives used in plastic manufacturing such as bisphenols, phthalates, flame retardants, PFAS, and heavy metals which act as endocrine disruptors [1,184]. Ingestion is considered a primary exposure route for NMPs, as recent studies consistently detect these particles in a wide variety of foods and beverages [16]. It is estimated that individuals ingest between 220,000 and 1.2 million NMP particles annually through drinking water [185]. Despite these challenges, the World Health Organization (WHO) remains committed to eliminating waterborne pathogens and chemicals that pose serious, immediate threats to health, particularly those that cause fatal diarrhea. [186]. Because of insufficient evidence to suggest that the levels of NMPs found in drinking water pose a human health concern, WHO concluded that current evidence is insufficient to suggest a widespread human health risk, though data remains limited [126]. However, the WHO advocates for expanded research to better assess human health risks from NMPs [187]. Key priorities include establishing standardized measurement methods and investigating NMPs’ sources and prevalence and the effectiveness of removal treatments [188].

7.2. International and National Initiatives

Despite the lack of specific limits, there is a growing trend towards regulatory development and monitoring. Organizations like the International Bottled Water Association (IBWA) and the European Union (EU) have established quality standards for bottled water even though they lack specific permissible limits for NMPs [179]. The EU has taken steps towards harmonizing measurement methodologies for microplastic detection in drinking water among member states, indicating a move towards consistent monitoring [179]. Further, the European Food Safety Authority (EFSA) is evaluating the latest scientific data on microplastics, with a formal opinion scheduled for release in late 2027 [189].

In the United States, states such as California are proactively implementing measures and developing regulations to monitor and reduce microplastic contamination in public drinking water supplies. California’s Senate Bill 1422 (SB 1422) required the State Water Board to develop a comprehensive microplastics program, including: a definition for microplastics in drinking water, a standard testing methodology, and a four-year testing and public reporting requirement by 1 July 2021 (California State Water Resources). This state-led initiative allows for consistent data collection and a better scientific understanding of the issue, which will inform and support the development of federal standards [179]. Further, seven governors have petitioned the U.S. EPA to include NMPs in the 2027 Unregulated Contaminant Monitoring Rule (UCMR), a move that could lead to future federal regulations.

India, recognizing microplastic pollution as an emerging contaminant of concern, has also begun to formulate regulatory frameworks to control it [181]. Canada regulates microplastics primarily at the provincial level, which results in the absence of a consistent federal standard [179]. Thus, there is a clear need for increased understanding regarding the dangers posed by microplastics, alongside the implementation of regulatory measures to ensure consumer safety.

7.3. Standardization Challenges and Policy Recommendations

A key impediment to regulation is the lack of standardized, validated analytical methodologies for NMP detection and quantification [4,76,163]. Methodological variability across studies makes data comparison and synthesis challenging, directly impacting the ability to set health-based thresholds [4]. European consensus papers provide guidance aimed at harmonizing the analysis of microplastic particles in clean waters, including bottled water [85]. Policy initiatives are increasingly prioritizing a reduction in single-use plastics and the advancement of sustainable alternatives [190,191]. Recommendations include implementing standardized analytical methods, strengthening regulatory frameworks with permissible NMP limits, promoting sustainable packaging, enhancing public awareness, and investing in advanced water treatment technologies [76,191]. There is an urgent need for multi-disciplinary approaches to investigate the interactions between NMPs and human health, guiding future studies and informing public health strategies [127]. This scenario underscores the pressing necessity for a globally coordinated initiative aimed at establishing consistent definitions, standardized detection methods, risk-based regulatory limits, and mandatory standards to effectively safeguard consumer health.

7.4. Future Directions

To effectively mitigate the potential risks posed by NMPs in bottled water, several urgent actions are required. The first step is to establish internationally recognized, validated protocols for detecting and characterizing diverse, NMP particles [4,76,163]. These efforts must be supported by future toxicological and epidemiological studies that focus on environmentally relevant exposure doses, complex mixtures, and long-term health outcomes in vulnerable populations [7,139]. Furthermore, international and national bodies should establish enforceable regulatory limits based on robust scientific evidence, complemented by consistent monitoring programs [76,182]. To reduce contamination at the source, policymakers and industry should accelerate the transition to sustainable packaging, while investing in improved water treatment technologies capable of effective NMP removal [76,191,192]. Finally, enhanced public awareness campaigns are essential to inform consumers about NMP risks and encourage alternatives to single-use plastic bottles [6,193,194].

7.5. Promotion of Sustainable Practices and Public Awareness

To combat NMP contamination, policymakers and industry must accelerate the transition to sustainable packaging, reduce single-use plastic consumption, and invest in advanced waste management and water treatment technologies [76,191]. Furthermore, public awareness campaigns are essential to educate consumers on the sources and health risks of NMPs, while highlighting the benefits of alternatives to single-use plastic bottles [6,193,194].

8. Challenges and Uncertainties in Quantifying the Human Health Risks of MNPs

Establishing the health risks of NMPs is difficult because the links between exposure, absorption, biological impact, and resulting damage all remain uncertain [195]. A major challenge is that NMPs are not a uniform substance [196]. Instead, they constitute a diverse, evolving mixture of materials that vary widely in polymer type, particle shape (fibers, fragments, spheres), size, and surface chemistry, all of which change further due to aging and weathering [197]. These properties determine how substances are transported, taken up, and cleared; consequently, they dictate whether dose–response relationships can be accurately estimated and compared between studies [198].

8.1. Analytical and Methodological Challenges

The most immediate barrier to quantified risk lies in measurement [105]. Detecting and characterizing NMPs, especially NPs in environmental samples and biological matrices, is difficult at the concentrations relevant to human exposure [199]. Inconsistent results often stem from low particle abundance, strong background interference, and contamination during sample collection and processing [9]. Sample preparation can introduce inaccuracies by fragmenting plastics or losing specific particles [200], while airborne fibers and plastic labware may artificially inflate counts [201]. These issues introduce substantial variability across different research settings, thereby devaluing the exposure estimates essential to robust risk assessment.

Measuring dose is also complicated by heterogeneity, which makes it difficult to establish a consistent standard for what is being measured [202]. Analytical challenges intensify for particles smaller than one micrometer, as validated, standardized methods for NPs remain limited compared to those for microplastics [9]. Yet NPs warrant greater concern because their small size increases the likelihood of them invading individual cells and migrating across bodily barriers [203]. Methodological inconsistency specifically regarding varying particle sizes, concentrations, exposure durations, biological models, and unreported crucial characteristics like surface charge or contaminants further limits study comparability [204]. Limited reference materials present a critical constraint in microplastic research [205]. Most experiments use clean polystyrene spheres for simplicity, overlooking the varied and weathered polymers found in real environmental conditions. Without standardized protocols and representative materials, it is difficult to synthesize data quantitatively or generate stable effect estimates through meta-analyses.

8.2. Uncertainties in Health Impact and Risk Assessment

The scarcity of human-specific evidence compounds existing uncertainty. Ethical constraints prohibit controlled human exposure experiments [206]; consequently, evidence is derived from a combination of observational epidemiology, biomarker data, and preclinical animal or in vitro studies. Nevertheless, accurate epidemiological assessment depends on reliable exposure data and the mitigation of confounding from correlated stressors like ambient air pollution, diet, and occupational factors [207]. Exposure misclassification resulting from measurement inconsistency or lower detection limits attenuates associations, reducing statistical power and complicating interpretation. Therefore, while studies suggest links between NMP exposure and health, a direct causal relationship in humans is currently considered emerging rather than proven.

In parallel, key knowledge gaps persist about NMP fate in the human body. Key parameters including exposure doses, barrier crossing efficiency, tissue distribution, and the kinetics of accumulation versus clearance remain poorly defined, particularly for NPs [208]. The lack of robust internal-dose data makes it difficult to establish exposure-dose conversion factors and identify the target-organ doses required for dose–response modeling. Experts call for more long-term, low-dose research [209] because it captures the chronic exposure people face. These studies are challenging, however, because they demand steady tracking over long periods.

8.3. Complex Mechanisms of Toxicity

Quantified risk is further complicated by the mechanistic complexity of NMPs, which may exert effects through both direct particle interactions and associated chemicals. Direct pathways can manifest through membrane interactions [210], inflammatory signaling [211], oxidative stress [212], mitochondrial dysfunction [213], and either cytotoxic [214] or genotoxic responses [214]. Plastics contain additives with known biological effects [215], such as endocrine disruption [216]. Additionally, plastic particles can absorb and transport co-contaminants, including metals and persistent organic pollutants [217]. The situation presents a ‘mixture problem’ where toxicological responses may stem from the polymer matrix, its additives, or sorbed contaminants. These components may interact to produce effects that are synergistic (greater than the sum of their parts) or antagonistic (less than expected). The tendency for diverse biological pathways to yield identical clinical endpoints complicates the isolation of NMP-specific effects. Accurate attribution requires precisely characterized materials and robust experimental controls. The wide range of potential health risks including respiratory and gut inflammation, microbiome changes, metabolic and liver issues, neurotoxicity, hormonal disruption, and cancer heighten concern but makes the evidence base feel fragmented [218]. Varying thresholds, timelines, and affected groups across health domains make it difficult to establish a single, universal risk estimate.

8.4. Inadequate Risk Assessment Models

Current risk assessment frameworks struggle to model the diverse physical characteristics and broad, multi-pathway nature of NMP exposure. Simplified models based on average ingestion rates often fail to account for specific particle characteristics [219]. These factors, including shape and surface chemistry, dictate the particle’s behavior regarding bodily deposition, tissue uptake, and resulting toxicological effects [218]. Thus, this limits the accuracy of their dose–response predictions. While frameworks accounting for sensitive life stages, mixture effects, and population heterogeneity are still emerging, case-by-case assessment of every NMP variant remains practically unfeasible [175].

Advancing quantified health risk assessments requires standardized measurement protocols, precise exposure monitoring, representative reference materials, and a clearer understanding of how external exposure translates to internal dosage. To create reliable risk estimates for policy and regulation, these technological advances must be integrated with study designs that focus on human biology and toxicology that accounts for chemical mixtures.

9. Conclusions

Evidence summarized in this review indicates the ubiquitous presence of NMPs in single-use water bottles and highlights the significant, yet often underestimated, pathway to human exposure through daily water consumption. NMPs, predominantly composed of PET, PE, and PP, are introduced into bottled water through a complex interplay of factors, including material degradation, mechanical abrasion during bottling and cap usage, and environmental conditions during storage. These factors contribute to the release of tiny particles into the water, a process that can be influenced by the storage conditions after bottling. Concentrations differ significantly between regions and brands influenced by analytical methods and the minimum detectable particle size. Nanoplastics, with their minute dimensions, present a specific challenge to detection.

The review determined that ingested NMPs can induce a range of adverse cellular and systemic effects. They include oxidative stress, inflammatory responses, cytotoxicity, genotoxicity, and disruption of gut microbiota and other organ systems. Nanoplastics can translocate across biological barriers more easily, posing potentially greater risks to human health. These risks are especially pronounced for vulnerable populations like infants and children, who demonstrate higher exposure levels per body weight. Furthermore, NMPs can act as vectors for other harmful chemical pollutants and pathogens, amplifying their toxicological impact.

It should, however, be noted that critical knowledge gaps persist, impeding a definitive assessment of human health risks. These include the lack of standardized and sensitive analytical methods, particularly for nanoplastics; and the reliance on high-dose, non-environmentally realistic exposures in toxicological studies. This study recommends the universal adoption of ISO 16094, recognizing it as the premier global standard for microplastic analysis. This initiative will establish a unified international framework to identify and quantify microplastics. There is also an incomplete understanding of NMP biodistribution, long term chronic effects, and interactions with the complex human biological system. These challenges are worsened by a global regulatory environment that is still developing and is not consistent across borders. While international bodies mostly agree on the problem, they have not created binding rules or standardized monitoring methods. Addressing these challenges requires an integrated, multidisciplinary approach involving collaboration among governments, scientific communities, industry, and the public. By closing the knowledge gaps and implementing robust regulatory and preventive measures, society can work towards safeguarding public health and the environment. These efforts are vital for effective protection because they will directly address the widespread problem of NMPs found in bottled water.