The leaching of additive-derived flame retardants (FRs) from plastics in avian digestive fluids: The significant risk of highly lipophilic FRs

In silico degradation of fluoroquinolones by a microalgae-based constructed wetland system

Fluoroquinolone antibiotics (FQs) have been used worldwide due to their extended antimicrobial spectrum. However, the overuse of FQs leads to frequent detection in the environment and cannot be efficiently removed. Microalgae-based constructed wetland systems have been proven to be a relatively proper method to treat FQs, mainly by microalgae, plants, microorganisms, and sediments. To improve the removal efficiency of microalgae-constructed wetland, a systematic molecular design, screening, functional, and risk evaluation method was developed using three-dimensional quantitative structure-activity relationship models, molecular dynamics simulation, molecular docking, and TOPKAT approaches. Five designed ciprofloxacin alternatives with improved bactericidal effects and lower human health risks were found to be more easily degraded by microalgae (16.11-167.88 %), plants (6.72-58.86 %), microorganisms (9.10-15.02 %), and sediments (435.83 %-1763.51 %) compared with ciprofloxacin. According to the mechanism analysis, the removal effect of the FQs can be affected via changes in the number, bond energy, and molecular descriptors of favorable and unfavorable amino acids. To the best of our knowledge, this is the first comprehensive study of improving the microalgae, plants, microorganisms, and sediment removal efficiency of FQs in constructed wetlands, which provides theoretical support for the treatment of FQ pollution.

Desorption of Polycyclic Aromatic Hydrocarbons from Microplastics in Human Gastrointestinal Fluid Simulants-Implications for Exposure Assessment

Microplastics have been detected in various food types, suggesting inevitable human exposure. A major fraction may originate from aerial deposition and could be contaminated by ubiquitous pollutants such as polycyclic aromatic hydrocarbons (PAHs). While data on the sorption of pollutants to microplastics are abundant, the subsequent desorption in the gastrointestinal tract (GIT) is less understood. This prompted us to systematically investigate the release of microplastics-sorbed PAHs at realistic loadings (44-95 ng/mg) utilizing a physiology-based in vitro model comprising digestion in simulated saliva, gastric, and small and large intestinal fluids. Using benzo[a]pyrene as a representative PAH, desorption from different microplastics based on low density polyethylene (LDPE), thermoplastic polyurethanes (TPUs), and polyamides (PAs) was investigated consecutively in all four GIT fluid simulants. The cumulative relative desorption (CRD) of benzo[a]pyrene was negligible in saliva simulant but increased from gastric (4 ± 1% - 15 ± 4%) to large intestinal fluid simulant (21 ± 1% - 29 ± 6%), depending on the polymer type. CRDs were comparable for ten different microplastics in the small intestinal fluid simulant, except for a polydisperse PA-6 variant (1-10 μm), which showed an exceptionally high release (51 ± 8%). Nevertheless, the estimated contribution of microplastics-sorbed PAHs to total human PAH dietary intake was very low (≤0.1%). Our study provides a systematic data set on the desorption of PAHs from microplastics in GIT fluid simulants.

Leaching kinetics and bioaccumulation potential of additive-derived organophosphate esters in microplastics

Considerable research has been conducted to evaluate microplastics (MPs) as vehicles for the transfer of hazardous pollutants in organisms. However, little effort has been devoted to the chemical release of hazardous additive-derived pollutants from MPs in gut simulations. This study looked at the leaching kinetics of organophosphate esters (OPFRs) from polypropylene (PP) and polystyrene (PS) MPs in the presence of gut surfactants, specifically sodium taurocholate, at two biologically relevant temperatures for marine organisms. Diffusion coefficients of OPFRs ranged from 1.71 × 10-20 to 4.04 × 10-18 m2 s-1 in PP and 2.91 × 10-18 to 1.51 × 10-15 m2 s-1 in PS. The accumulation factors for OPFRs in biota-plastic and biota-sediment interactions ranged from 1.52 × 10-3-69.1 and 0.02-0.7, respectively. Based on B3LYP/6-31G (d,p) calculations, the biodynamic model analysis revealed a slight increase in the bioaccumulation of OPFRs at a minor dose of 0.05% MPs. However, at higher concentrations (0.5% and 5% MPs), there was a decrease in bioaccumulation compared to the lower concentration for most OPFR compounds. In general, the ingestion of PE MPs notably contributed to the bioaccumulation of OPFRs in lugworms, whereas the contribution of PP and PS MPs was minimal. This could vary among sites exhibiting varying levels of MP concentrations or MPs displaying stronger affinities towards chemicals.

Effect of particle size and environmental conditions on the release of di(2-ethylhexyl) phthalate from microplastics

The extensive use and improper handling of plastics have caused extensive microplastic (MP) pollution in terrestrial environments. Di(2-ethylhexyl) phthalate (DEHP), the main additive used in plastics, is toxic to organisms and may pose risks to human and animal reproductive functions. However, research on the release behavior of DEHP from MPs is scarce. In this study, the effects of particle size and environmental conditions (temperature, pH, ionic strength, and cation type) on DEHP release from polylactide (PLA), polystyrene (PS), and polyvinyl chloride (PVC) MPs were determined by performing leaching experiments. The results showed that when particle size decreased, the content of DEHP in the MPs and the amount of released DEHP increased though increasing specific surface area. An increase in temperature also promoted DEHP release; when the temperature increased from 15 °C to 45 °C, the amount of DEHP released from PLA, PS, and PVC increased by 38.4%, 71.0%, and 109%, respectively. The lower the crystallinity, the greater the increase in the amount of DEHP released. Ionic strength inhibited the release of DEHP from MPs. When Na+ concentration increased from 0 to 200 mM, the amount of DEHP released from PLA, PS, and PVC decreased by 27.4%, 41.6%, and 35.3%, respectively. The effect of Ca2+ on DEHP release from MPs was greater than that of Na+. In addition, the process of DEHP release from MPs fit well with a pseudo-first-order kinetic model. The results of this study provide a theoretical basis for managing and controlling the risks associated with plastic wastes.

Insight into Bioaccumulation of Decabromodiphenyl Ethane in Eisenia fetida Increased by Microplastics

The rise of electronics inevitably induced the co-pollution of novel brominated flame retardants (NBFRs) and microplastics (MPs). However, studies on how they interact to influence their bioavailability are scarce. Here, we explored the influence mechanism of acrylonitrile butadiene styrene (ABS)-MPs on the bioaccumulation of decabromodiphenyl ethane (DBDPE) in soil-earthworm microcosms. The influence exhibited a temporal pattern characterized by short-term inhibition and long-term promotion. After 28 days of exposure, DBDPE bioaccumulation in a co-exposure (10 mg kg-1 DBDPE accompanied by 1000 mg kg-1 ABS-MPs) was 2.61 times higher than that in a separate exposure. The adsorption process in the soil, intestines, and mucus introduced DBDPE-carried MPs, which had a higher concentration of DBDPE than the surrounding soil and directly affected the bioavailability of DBDPE. MP-pre-exposure (100, 1000, and 10000 mg kg-1) reduced epidermal soundness, mucus secretion, and worm cast production. This eventually promoted the contact between earthworm and soil particles and enhanced the DBDPE of earthworm tissue by 6%-61% in the next DBDPE-postexposure period, confirming that MPs increased DBDPE bioaccumulation indirectly by impairing the earthworm health. This study indicates that MPs promoted DBDPE bioaccumulation via adsorption and self-toxicity, providing new insight into the combined risk of MPs and NBFRs.

A critical review of microplastics toxicity and potential adverse outcome pathway in human gastrointestinal tract following oral exposure

Microplastics (MPs) are typically produced via environmental degradation of larger plastics, where they enter the human food chain. MPs are complex materials containing chemical and physical characteristics that can potentially affect their hazard and exposure. These physical properties can be altered by environmental exposure potentially altering any risk assessment conducted on the primary material. We conducted a literature review using an Adverse Outcome Pathway (AOP)-based approach from Molecular Initiating Event (MIE) to cell effect event to identify multiple knowledge gaps that affect MPs hazard assessment. There is some convergence of key biological events but could relate to most lying along well-established biological effector pathways such as apoptosis which can respond to many MIEs. In contrast, MIEs of chemicals will be via protein interaction. As MPs may occur in the lumen of the alimentary canal for example to the mucus, therefore, not requiring translocation of MPs across the epithelial membrane. At the other end of the AOP, currently it is not possible to identify a single adverse outcome at the organ level. This work did establish a clear need to understand both external and internal exposure (resulting from translocation) and develop hazard data at both levels to inform on risk assessments.

How Digestive Processes Can Affect the Bioavailability of PCBs Associated with Microplastics: A Modeling Study Supported by Empirical Data

The transfer kinetics of plastic-associated chemicals during intestinal digestive processes is unknown. Here, we assessed whether digestive processes affect chemical exchange kinetics on microplastics, using an in vitro gut fluid digestive model mimicking the human upper intestinal tract. Chemical exchange kinetics of microplastics were measured for 10 polychlorinated biphenyls (PCBs) as proxies for the broad class of hydrophobic organic chemicals. Following earlier studies, olive oil was used as a proxy for digestible food, under high and low digestive enzyme activities. The micelle-water and oil-water partition coefficients of the 10 PCBs were also determined to evaluate the relative contribution of each gut component to sorb PCBs. A new biphasic and reversible chemical exchange model, which included the digestion process, fitted well to the empirical data. We demonstrate that the digestive processes that break down contaminated food can lead to a substantial increase in chemical concentration in microplastics by a factor of 10-20, thereby reducing the overall chemical bioavailability in the gastrointestinal tract when compared to a scenario without microplastics. Higher enzyme activities result in more chemicals being released by the digested food, thereby resulting in higher chemical concentrations in the microplastics. While the model-calibrated kinetic parameters are specific to the studied scenario, we argue that the mechanism of the reduced bioavailability of chemicals and the modeling tool developed have generic relevance. These digestive processes should be considered when assessing the risks of microplastics to humans and also biomagnification in aquatic food webs.

Organophosphate flame retardants and plastics in soil from an abandoned e-waste recycling site: significant ecological risks derived from plastic debris

The distribution of 9 organophosphate flame retardants (OPFRs) was determined in plastic debris and soil samples separated from twenty soil samples collected from an abandoned e-waste recycling area. Tris-(chloroisopropyl) phosphate (TCPP) and triphenyl phosphate (TPhP) were the main chemicals, with median concentrations of 124-1930 ng/g and 143-1170 ng/g in soil, and 712-803 ng/g and 600-953 ng/g in plastics, respectively. Plastics contributed less than 10% of the total OPFR mass in bulk soil samples. No apparent OPFR distribution trend was observed in different sizes of plastics and soil. The ecological risks of plastics and OPFRs were estimated by the species sensitivity distributions (SSDs) method, which resulted in lower predicted no-effect concentrations (PNECs) of TPhP and decabromodiphenyl ether 209 (BDE 209) than the standard values derived from limited toxicity tests. In addition, the PNEC of polyethene (PE) was lower than the plastic concentration in the soil of a previous study. TPhP and BDE 209 had high ecological risks with risk quotients (RQs) > 0.1, and RQ of TPhP was among the highest values in literature.

Polylactic acid microplastics induce higher biotoxicity of decabromodiphenyl ethane on earthworms (Eisenia fetida) compared to polyethylene and polypropylene microplastics

Decabromodiphenyl ethane (DBDPE) and microplastics (MPs), such as fossil-based polymers polyethylene (PE), polypropylene (PP), and bio-based plastics polylactic acid (PLA) are abundant in e-waste dismantling areas. However, the information on the effects of DBDPE combined with MPs (DBDPE-MPs) on earthworms is still limited. In this study, we explored the impacts of DBDPE-MPs on neurotoxic biomarkers, tissue damage, and transcriptomics of Eisenia fetida by simulating different exposure patterns of 10 mg kg^-1 DBDPE and 10 mg kg^-1 DBDPE-MPs (PLA, PP, and PE). Results showed that the activities of acetylcholinesterase, Na⁺/K⁺-ATPase, Ca²⁺/Mg²⁺-ATPase, carboxylate enzyme, and the contents of calcium and glutamate were significantly stimulated. DBDPE-MP co-exposure caused more severe damage to the epidermis, muscles, and tissues. Transcriptomic analysis revealed that differentially expressed genes (DEGs) of DBDPE-MPs were mainly related to inflammation, the immune system, digestive system, endocrine system, and metabolism. DBDPE and PP-MPs had similar influences on immunity and metabolism. However, DBDPE-PLA and DBDPE-PE further affected the endocrine system and signaling pathways. Specific DEGs showed that detoxification systems in the case of MPs were significantly upregulated. The study indicated that MPs exacerbated DBDPE toxicity in the nervous system, epidermis, and gene regulation of E. fetida, helping to assess the ecological risks of e-wastes and microplastics in soil.

High accumulation of microplastic fibers in fish hindgut induces an enhancement of triphenyl phosphate hydroxylation

Fiber shedding from artificial textiles is among the primary sources of pervasive microplastics in various aquatic habitats. To avoid molten drop burning, triphenyl phosphate (TPhP), a typical flame retardant additive, is commonly incorporated into textile fibers. However, the role of microplastic fibers (MFs) as a vehicle for TPhP remains largely unknown. In this study, we investigated the effects of MFs on the bioaccumulation and metabolism of TPhP in zebrafish. We applied the compound spinning technique for a non-disruptive in situ measurement of fluorescent MFs in fish, and the desorption electrospray ionization mass spectrometry (DESI-MS) to display the tissue distribution of TPhP and its metabolites vividly. Laboratory results showed that ingested MFs did not change the TPhP distribution in fish; however, they statistically increased the metabolite p-OH-TPhP concentration in the fish hindgut, which was probably because the high accumulation of MFs there enhanced the TPhP hydroxylation. Field investigation further supported the lab-based analyses. Higher concentrations of MFs did cause a higher ratio of [p-OH-TPhP]/[TPhP] in the wild fish gut, particularly in the hindgut. Collectively, our results demonstrated that MFs can change the distribution and bioavailability of TPhP metabolites, which was confirmed by both laboratory and fieldwork. Therefore, the ingestion of MFs can indirectly but substantially influence the bioaccumulation and biotransformation of co-existing pollutants.

Dietary microplastics: Occurrence, exposure and health implications

The increasing use of plastic materials generates an enormous amount of waste. In the aquatic environment, a significant part of this waste is present in the form of microplastics (MPs)- particles with a diameter of between 0.1 μm and 5 mm. The arrival of these small plastics in the food chain has been recently documented. MPs have been reported in fishery products, drinking water and sea salt among other foods. Their intestinal absorption is considered limited due to their size, however, they contain a mixture of chemicals intentionally added during their manufacture, which could cross the intestinal barrier. Currently there are not enough data to allow an accurate assessment of the risk associated with dietary exposure to MPs. The lack of robust methodologies is undoubtedly one of the main problems. There is limited information on occurrence in dietary sources (drinking water and food), human intake, toxicokinetics and long term toxicity of these contaminants. The present review describes the studies published so far and points to the need for improved knowledge in order to have a more accurate view of the problems posed by MPs.

Dibutyl phthalate release from polyvinyl chloride microplastics: Influence of plastic properties and environmental factors

In recent years, great efforts have been made to understand the capacity of microplastics to adsorb environmental pollutants; however, relatively little is known about the ability of microplastics to release inherent additives into peripheral environments. In this study, we investigated the leaching behavior of phthalate plasticizer from polyvinyl chloride (PVC) microplastics, in aqueous solutions relevant to aquatic and soil environments. It was found that plastic properties, such as particle size, plasticizer content and aging of plastics had a great effect on the leaching of dibutyl phthalate (DnBP). Phthalate release was generally higher in smaller particles and particles with higher phthalate content. Whereas, plastic aging caused by solar irradiation could either enhance phthalate release by increasing plastic hydrophilicity or decrease the leaching by reducing readily available fractions of phthalate. Regarding environmental factors, solution pH (3-9) and ionic strength (0-0.2 M NaCl) were found to have minor effect on phthalate release, while fulvic acid (0-200 mg/L) greatly promoted the release by improving phthalate solubility and solution-plastic affinity. Interestingly, we found that more DnBP was leached out when fulvic acid and NaCl coexisted, and the results from dissolved organic carbon (DOC) and three-dimensional fluorescence spectroscopy analyzes suggested that the leaching of other fulvic acid-like additives might have played a role. These findings would be helpful for predicting the potential of microplastics to release toxic additives under different environmental conditions.

First study on the presence of plastic additives in loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea

Loggerhead turtles (Caretta caretta) voluntarily ingest floating plastic debris and hence are chronically exposed to plastic additives, but very little is known about the levels of these compounds in their tissues. This work studied the presence of organophosphate esters (OPEs) on sea turtles collected from two different areas in the western Mediterranean, some of their prey and some floating plastic debris. OPEs were detected in all the samples analysed and ∑OPEs ranged from 12.5 to 384 ng/g wet weight (ww) in the turtles from the Catalan coasts, with a mean value of 21.6 ng/g ww, and from 6.08 to 100 ng/g ww in the turtles the Balearic Islands, with a mean value of 37.9 ng/g ww. Differences in ∑OPEs were statistically significant, but turtles from the two regions did not differ in their OPE profiles. As per turtle's prey, ∑OPEs ranged from 4.55 to 90.5 ng/g ww. Finally, marine plastic litter showed ∑OPEs concentrations between 10.9 and 868 ng/g. Although most compounds were present in both potential sources of contamination, prey and plastic debris, the OPE profiles in loggerhead turtles and these sources were different. Some OPEs, such as tris(2-isopropylphenyl) phosphate (T2IPPP), tripropyl phosphate (TPP) and tris(2-butoxyethyl) phosphate (TBOEP), were detected in plastic debris and turtle muscle but not in their prey, thus suggesting that ingestion of plastic debris was their main source. Contrarily, the levels of triethyl phosphate (TEP), diphenyl cresyl phosphate (DCP), 2-isopropylphenyl diphenyl phosphate (2IPPDPP) and 4-isopropylphenyl diphenyl phosphate (4IPPDPP) in turtle muscle were much higher than in jellyfish, their main prey, thus indicating a biomagnification potential. Regular ingestion of plastic debris and contamination from their prey may explain why ∑OPEs in loggerhead turtles is much higher than the values reported previously for teleost fishes and marine mammals from the western Mediterranean.

Leaching and extraction of additives from plastic pollution to inform environmental risk: A multidisciplinary review of analytical approaches

Plastic pollution is prevalent worldwide and has been highlighted as an issue of global concern due to its harmful impacts on wildlife. The extent and mechanism by which plastic pollution effects organisms is poorly understood, especially for microplastics. One proposed mechanism by which plastics may exert a harmful effect is through the leaching of additives. To determine the risk to wildlife, the chemical identity and exposure to additives must be established. However, there are few reports with disparate experimental approaches. In contrast, a breadth of knowledge on additive release from plastics is held within the food, pharmaceutical and medical, construction, and waste management industries. This includes standardised methods to perform migration, extraction, and leaching studies. This review provides an overview of the approaches and methods used to characterise additives and their leaching behaviour from plastic pollution. The limitations of these methods are highlighted and compared with industry standardised approaches. Furthermore, an overview of the analytical strategies for the identification and quantification of additives is presented. This work provides a basis for refining current leaching approaches and analytical methods with a view towards understanding the risk of plastic pollution.

Pollution of plastic debris and halogenated flame retardants (HFRs) in soil from an abandoned e-waste recycling site: Do plastics contribute to (HFRs) in soil?

Electronic waste (e-waste) recycling site may be a "hotspot" for pollution of plastic debris, which has not been well studied. Eighteen halogenated flame retardants (HFRs) were measured in plastics and soil separated from twenty soil samples, respectively, from an abandoned e-waste recycling site. Abundances and concentrations of plastic debris ranged from 600 to 14,200 particles/kg and 0.24-153 mg/g, respectively, which were at the high end in literature. Blue, black, and red were main plastic colors, and acrylonitrile-butadiene-styrene (ABS) was the main type of plastics. Polybrominated diphenyl ether (PBDE) 209 was the main chemical, with median concentrations of 6.22-40.6 μg/g in soil and 28.1-47.2 μg/g in plastics, respectively. Contributions of HFRs in plastics were less than 10% in total HFR masses in bulk soil samples. Exposure values to HFRs from plastics via soil ingestion and dermal contact with soil were generally two orders of magnitude lower than those from soil. The results indicate that plastics in soil have little contribution to total HFR burden in soil and human exposure risks to HFRs in this study. However, ecological risks of plastics to terrestrial wildlife in e-waste sites should be paid attention.

Interspecies comparisons of brominated flame retardants in relation to foraging ecology and behaviour of gulls frequenting a UK landfill

This study quantifies and compares concentrations and profiles of legacy and alternative (alt-) brominated flame retardants (BFRs) in the eggs of three gull (Laridae) species of international/UK conservation concern - great black-backed gulls (Larus marinus; n = 7), European herring gulls (L. argentatus; n = 16) and lesser black-backed gulls (L. fuscus; n = 11) in relation to their foraging ecology and behaviour in order to investigate potential exposure pathways at a remote landfill in western Scotland, UK. Egg concentrations of sum (∑) polybrominated diphenyl ethers (∑₈PBDEs) in all three species exceeded those for most reported avian species using landfill, except for those in North America. Despite relatively high detection frequencies of ∑hexabromocyclododecanes (∑₃HBCDDs) (94-100%), concentrations of ∑₈PBDEs exceeded ∑₃HBCDDs and ∑₅alt-BFRs, with ∑₈PBDE levels similar in all three species. Egg carbon isotopic (δ¹³C) values highlighted a greater marine dietary input in great black-backed gulls that was consistent with their higher BDE-47 levels; otherwise, dietary tracers were minimally correlated with measured BFRs. ∑₃HBCDD egg concentrations of herring gulls markedly exceeded those reported elsewhere in Europe. Decabromodiphenylethane (DBDPE) was the only alt-BFR detected (6-14% detection rate), in a single egg of each species. The great black-backed gull egg contained the highest concentration of DBDPE measured in biota to date globally and provides strong evidence for its emerging environmental presence as a BDE-209 replacement in UK wildlife. Correlations between δ¹³C (dietary source) and some measured BFRs in eggs suggest multiple routes of BFR exposure for gulls frequenting landfill through their diet, behaviour, preening, dermal exposure and likely inhalation. The frequent use of landfill by herring gulls and their increased egg BFR burdens suggest that this species may be an important bioindicator of BFR emissions from such sites.

Inhalation bioaccessibility and health risk assessment of flame retardants in indoor dust from Vietnamese e-waste-dismantling workshops

Although bioaccessibility testing is applied worldwide for appropriate chemical risk assessment, few studies have focused on the bioaccessibility of flame retardants (FRs), especially inhalation exposure. This study assessed inhalation exposure to FRs in indoor dust by workers at e-waste-dismantling workshops in northern Vietnam, by using modified simulated epithelial lung fluid (SELF) and artificial lysosomal fluid (ALF). The average mass concentrations of FRs were 130,000 ng/g for workplace dust (n = 3), 140,000 ng/g for floor dust (n = 3), and 74,000 ng/g for settled dust (n = 2), whereas the average bioaccessible concentrations of FRs were 1900, 1400, and 270 ng/g in the SELF condition and 2600, 770, and 490 ng/g in the ALF condition, respectively. Results clearly indicate that the bioaccessible concentrations of FRs are markedly lower than their mass concentrations. Tris(2-chloroethyl) phosphate (TCEP, ~19%), tris(2-chloroisopropyl) phosphate (TCIPP, ~35%), and tris(1,3-dichloroisopropyl) phosphate (TDCIPP, ~22%) showed comparably high bioaccessibility in both SELF and ALF conditions. In contrast, the bioaccessibility of tetrabromobisphenol A (TBBPA, ~20%) was high in the SELF condition, but not in the ALF condition. With regard to the test compounds' physicochemical properties, the inhalation bioaccessibility of FRs in both conditions increased as molecular weight or octanol-water partition coefficient decreased, and it decreased as water solubility decreased. Health risk assessment clearly indicated that the hazard quotient of FRs via inhalation exposure for workers in the e-waste-dismantling workshops was less than 1, suggesting that the inhalation exposure to FRs during indoor dismantling of e-waste at this site was negligible based on the current methodology of non-cancer health risk assessment used in this study.

Microplastics and associated contaminants in the aquatic environment: A review on their ecotoxicological effects, trophic transfer, and potential impacts to human health

The microplastic pollution and related ecological impacts in the aquatic environment have attracted global attention over the past decade. Microplastics can be ingested by aquatic organisms from different trophic levels either directly or indirectly, and transferred along aquatic food chains, causing different impacts on life activities of aquatic organisms. In addition, microplastics can adsorb various environmental chemical contaminants and release toxic plastic additives, thereby serving as a sink and source of these associated chemical contaminants and potentially changing their toxicity, bioavailability, and fate. However, knowledge regarding the potential risks of microplastics and associated chemical contaminants (e.g., hydrophobic organic contaminants, heavy metals, plastic additives) on diverse organisms, especially top predators, remains to be explored. Herein, this review describes the effects of microplastics on typical aquatic organisms from different trophic levels, and systematically summarizes the combined effects of microplastics and associated contaminants on aquatic biota. Furthermore, we highlight the research progress on trophic transfer of microplastics and associated contaminants along aquatic food chain. Finally, potential human health concerns about microplastics via the food chain and dietary exposure are discussed. This work is expected to provide a meaningful perspective for better understanding the potential impacts of microplastics and associated contaminants on aquatic ecology and human health.

Release kinetics as a key linkage between the occurrence of flame retardants in microplastics and their risk to the environment and ecosystem: A critical review

The widely occurring debris of plastic materials, particularly microplastics, can be an important source of flame retardants, which are one of the main groups of chemicals added in the production of plastics from polymers. This review provides an overview on the use of flame retardants in plastic manufacturing, the kinetics of their releases from microplastics, the factors affecting their releases, and the potential environmental and ecosystem risk of the released flame retardants. The releases of flame retardants from microplastics typically involve three major steps: internal diffusion, mass transfer across the plastic-medium boundary layer, and diffusion in the environmental medium, while the overall mass transfer rate is commonly controlled by diffusion within the plastic matrix. The overall release rates of additive flame retardants from microplastics, which are dependent on the particle's geometry, can often be described by the Fick's Law. The physicochemical properties of flame retardant and plastic matrix, and ambient temperature all affect the release rate, which can be predicted with empirical and semi-empirical models. Weathering of microplastics, which reduces their particle sizes and likely disrupts their polymeric structures, can greatly accelerate the releases of flame retardants. Flame retardants could also be released directly from the microplastics ingested by aquatic organisms and seabirds, with physical and chemical digestion in the bodies significantly enhancing their release rates. Limited by the extremely slow diffusion in plastic matrices, the fluxes of flame retardants released from microplastics are very low, and are unlikely to pose significant risk to the ecosystem in general. More research is needed to characterize the mechanical, chemical, and biological processes that degrade microplastics and accelerate the releases of flame retardants and to model their release kinetics from microplastics, while efforts should also be made to develop environmentally benign flame retardants to ultimately minimize their risk to the environment and ecosystem.

Tris(2-chloroethyl) phosphate, a pervasive flame retardant: critical perspective on its emissions into the environment and human toxicity

Regulations and the voluntary activities of manufacturers have led to a market shift in the use of flame retardants (FRs). Accordingly, organophosphate ester flame retardants (OPFRs) have emerged as a replacement for polybrominated diphenyl ethers (PBDEs). One of the widely used OPFRs is tris(2-chloroethyl) phosphate (TCEP), the considerable usage of which has reached 1.0 Mt globally. High concentrations of TCEP in indoor dust (∼2.0 × 105 ng g-1), its detection in nearly all foodstuffs (max. concentration of ∼30-300 ng g-1 or ng L-1), human body burden, and toxicological properties as revealed by meta-analysis make TCEP hard to distinguish from traditional FRs, and this situation requires researchers to rethink whether or not TCEP is an appropriate choice as a new FR. However, there are many unresolved issues, which may impede global health agencies in framing stringent regulations and manufacturers considering the meticulous use of TCEP. Therefore, the aim of the present review is to highlight the factors that influence TCEP emissions from its sources, its bioaccessibility, threat of trophic transfer, and toxicogenomics in order to provide better insight into its emergence as an FR. Finally, remediation strategies for dealing with TCEP emissions, and future research directions are addressed.

Analytical methods and environmental processes of nanoplastics

The degradation of plastic debris may result in the generation of nanoplastics (NPs). Their high specific surface area for the sorption of organic pollutions and toxic heavy metals and possible transfer between organisms at different nutrient levels make the study of NPs an urgent priority. However, there is very limited understanding on the occurrence, distribution, abundant, and fate of NPs in the environment, partially due to the lack of suitable techniques for the separation and identification of NPs from complex environmental matrices. In this review, we first overviewed the state-of-the-art methods for the extraction, separation, identification and quantification of NPs in the environment. Some of them have been successfully applied for the field determination of NPs, while some are borrowed from the detection of microplastics or engineered nanomaterials. Then the possible fate and transport of NPs in the environment are thoroughly described. Although great efforts have been made during the recent years, large knowledge gaps still exist, such as the relatively high detection limit of existing method failing to detect ultralow masses of NPs in the environment, and spherical polystyrene NP models failing to represent the various compositions of NPs with different irregular shapes, which needs further investigation.

Leaching of brominated flame retardants (BFRs) from BFRs-incorporated plastics in digestive fluids and the influence of bird diets

Leaching kinetics of additive-derived brominated flame retardants (BFRs) in different sizes (100 μm-2 mm) of acrylonitrile-butadiene-styrene copolymer (ABS) plastics were investigated in water, simulated gastric fluids, and simulated gastrointestinal fluids. The influences of bird diets (fish, clam, and rice) on the leaching of BFRs from plastics were also explored. The leaching kinetics of BFRs were best fitted with the second-order diffusion model. The leaching rates of BFRs increased for the less lipophilic BFRs in finer sizes of ABS. The log-transformed leached proportions of BFRs at equilibrium were significantly correlated with logK_OW of BFRs (p < 0.05). BFRs migrated from ABS to digestive fluids and diet residues at equilibrium, since elevated concentrations of BFRs were observed in diet residues than virgin diet samples. Leached proportions of BFRs in gut fluids from mixture of ABS and diets were lower than those from only ABS. The logK_OW of BFRs and the migration proportions of BFRs from ABS to digestive fluids and diet residues were fitted with linear regression analysis. The results indicate that more lipophilic BFRs are preferentially leached from BFRs-incorporated plastics into fluids and are further adsorbed by diet residues.

Occurrence of organic pollutants in plastics on beach: Stranded foams can be sources of pollutants in islands

Increasing amount of plastic debris stranded on beach can introduce many foreign substances, including organic pollutants into island ecosystems. In the present study, stranded foams were collected from an island located in South China Sea, to investigate the levels and profiles of several flame retardants (FRs) and plasticizers, including polybrominated diphenyl ethers (PBDEs), organophosphate esters (OPEs), emerging brominated FRs, and dechlorane plus (DP). The concentrations of PBDEs and OPEs in plastic debris ranged from not detected (ND, <0.60 ng/g) to 0.46 mg/g and from ND (<0.70 ng/g) to 17.3 mg/g, respectively. The high levels of PBDEs and OPEs were expected as the fact that PBDEs and OPEs were incorporated additives in plastics. OPEs were the main chemicals in most of foams. Brominated FRs dominated in some samples. Core and surface parts in foams had similar composition profiles of pollutants. Significantly higher concentrations of tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPHP) were observed in surface samples than core samples (p < .05). TCEP and TPHP in foam surface seem to be from both incorporated additives and adsorbed chemicals from environmental matrices. The density of pollutants introduced by stranded foams in sampling area was estimated in comparison with air deposition of pollutants. The high loading of pollutants in stranded foams indicates that foams can be potential sources for organic pollutants, especially incorporated plastic additives, in islands.