A food web bioaccumulation model for the accumulation of per- and polyfluoroalkyl substances (PFAS) in fish: how important is renal elimination?

Per- and polyfluoroalkyl substances (PFAS) are a large class of highly fluorinated anthropogenic chemicals. Some PFAS bioaccumulate in aquatic food webs, thereby posing risks for seafood consumers. Existing models for persistent organic pollutants (POPs) perform poorly for ionizable PFAS. Here we adapt a well-established food web bioaccumulation model for neutral POPs to predict the bioaccumulation behavior of six perfluoroalkyl acids (PFAAs) and two perfluoroalkyl ether acids (HFPO-DA, 9-Cl-PF3ONS) produced as PFAA replacements. The new model includes sorption to blood plasma proteins and phospholipids, empirically parameterized membrane transport, and renal elimination for PFAAs. Improved performance relative to prior models without these updates is shown by comparing simulations to field and lab measurements. PFAS with eight or more perfluorinated carbons (ηpfc ≥ 8, i.e., C8 perfluorosulfonic acid, C10-C11 perfluorocarboxylic acid, 9-Cl-PF3ONS) are often the most abundant in aquatic food webs. The new model reproduces their observed bioaccumulation potential within a factor of two for >80% of fish species, indicating its readiness to support development of fish consumption advisories for these compounds. Results suggest bioaccumulation of ηpfc ≥ 8 PFAS is primarily driven by phospholipid partitioning, and that renal elimination is negligible for these compounds. However, specific protein binding mechanisms are important for reproducing the observed tissue concentrations of many shorter-chain PFAAs, including protein transporter-mediated renal elimination. Additional data on protein-binding and membrane transport mechanisms for PFAS are needed to better understand the biological behavior of shorter-chain PFAAs and their alternatives.

Applicability of Equilibrium Sampling in Informing Tissue Residues and Dietary Risks of Legacy and Current-Use Organic Chemicals in Aquaculture.

Equilibrium sampling based on silicone polydimethylsiloxane (PDMS) has been used to determine the concentrations of freely dissolved hydrophobic organic compounds (HOCs) and assess the thermodynamic potentials for bioaccumulation of these compounds in the aquatic environment. This allows the use of PDMS-based sampling techniques in assisting conventional sampling and extraction methods for the determination of the concentrations of HOCs in aquaculture products. The present study is an ex situ demonstration of how well PDMS can inform the tissue residues and dietary risks of legacy or current-use organic chemicals in aquaculture species from farm ponds in eastern China. For legacy contaminants such as polybrominated diphenyl ethers (PBDEs, n = 10), good agreement between the predicted concentrations based on PDMS and the measured lipid-normalized concentrations was observed for 60% of the studied biota, including both pelagic and benthic species. For pesticides currently used, such as pyrethroid (PE) (n = 4) and organophosphate pesticides (OPPs, n = 7), the measured tissue residues were consistently higher than those predicted by PDMS, possibly caused by the continuous input from the surroundings. For the organochlorine pesticides (OCPs, n = 5), the only detected chemical was also underestimated. Adjusted by ingestion rates of aquaculture products and toxicology data, the target hazard quotients of these chemicals predicted from PDMS were generally comparable to those derived from measured concentrations in tissue because of the predominance of PBDEs. Overall, PDMS-based equilibrium sampling offered an alternative approach for the prediction of tissue residues and dietary risks of PBDEs. Moreover, it should be applied with caution for PEs, OPPs, and OCPs. Improving the application of PDMS for these chemicals in farm ponds warrants future study. Environ Toxicol Chem 2021;40:79-87. © 2020 SETAC.

Bioaccumulation behaviour of pharmaceuticals and personal care products in a constructed wetland.

Pharmaceuticals and personal care products (PPCPs) is an important class of environmental contaminants and has gained increasing concerns in recent years. The bioaccumulation behaviour of PPCPs in wetland plants is not well understood. In the present study we report results of a field investigation to assess the bioaccumulation behaviour and phytoremediation efficacy of several PPCPs in Lorong Halus Wetland, a large-scale constructed wetland system in Singapore, constructed for the treatment of landfill leachate. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) based methods were employed to quantify concentrations of target PPCPs in leachate and flowing water, as well as wetland plants (roots and shoots), at different locations in the wetland system. The results indicated the presence of several PPCPs in leachate, water and vegetation in the wetland. Bioconcentration factors (BCFs) in the dominant wetland plant, Typha angustifolia, ranged between approximately 60 and 2000. Results indicated that Cattail Typha angustifolia was capable of remediating PPCPs to various extends, with bioconcentration factors ranging up to 2000. The suitability for phytoremediation depends on the physical chemical properties such as hydrophilicity and lipophilicity of these PPCPs.

Partitioning and Bioaccumulation of Legacy and Emerging Hydrophobic Organic Chemicals in Mangrove Ecosystems.

Knowledge regarding partitioning behavior and bioaccumulation potential of environmental contaminants is important for ecological and human health risk assessment. While a range of models are available to describe bioaccumulation potential of hydrophobic organic chemicals (HOCs) in temperate aquatic food webs, their applicability to tropical systems still needs to be validated. The present study involved field investigations to assess the occurrence, partitioning, and bioaccumulation behavior of several legacy and emerging HOCs in mangrove ecosystems in Singapore. Concentrations of synthetic musk fragrance compounds, methyl triclosan (MTCS), polychlorinated biphenyls, organochlorine pesticides, and polycyclic aromatic hydrocarbons were measured in mangrove sediments, clams, and caged mussels. Freely dissolved concentrations of the HOCs in water were determined using silicone rubber passive samplers. Results showed that polycyclic musks and MTCS are present in mangrove ecosystems and can accumulate in the tissues of mollusks. The generated HOC concentration data for mangrove water, sediments, and biota samples was further utilized to evaluate water-sediment partitioning (e.g., Koc values) and bioaccumulation behavior (e.g., BAF and BSAF values). Overall, the empirical models fit reasonably well with the data obtained for this ecosystem, supporting the concept that general models are applicable to predict the behavior of legacy and emerging HOCs in mangrove ecosystems.

Assessing pH-dependent toxicity of fluoxetine in embryonic zebrafish using mass spectrometry-based metabolomics.

While it is well known that fluoxetine is more toxic to aquatic organisms at high pH, the metabolic dysregulations related to observed pH-dependent effects are still poorly understood. In the present study, we utilized a gas chromatography mass spectrometry (GC-MS) based metabolomics approach to assess metabolomic profile changes in developing zebrafish embryos following exposure (2 hpf-96 hpf) to different concentrations of fluoxetine at three environmentally relevant pH values (7.0, 8.0, and 9.0). Multivariate data analyses and pathway analyses were used to assess metabolomic profile changes and elicit important biochemical information regarding pH-dependent toxicity of fluoxetine. Overall, the affected biochemical functions related to fluoxetine exposure included amino acid metabolism, energy metabolism, nitrogenous waste excretion and osmolyte functions. While fluoxetine exposure (56 µg/L, 70 µg/L and 500 µg/L) caused no significant changes at pH 7, 500 µg/L and 70 µg/L fluoxetine was differentiated from the controls at pH 8 and pH 9 respectively. Three, eight and seven metabolites were identified as the most adversely affected at pH 7, 8 and 9, respectively. The altered metabolites associated with fluoxetine toxicity at high pH included urea, glycine and d-glucose 6-phosphate. Exposure to 70 µg/L fluoxetine, did not cause significant metabolomic profile changes at pH 7, However, the results indicate that this exposure concentration at pH and 9 can cause significant metabolic dysregulation related to apoptosis and oxidative stress. Increasing aqueous pH progressively enhanced fluoxetine induced toxicity for the 70 µg/L exposure group. The observed impacts included higher energy consumption at pH 7, a breakdown of reserve energy to supplement energy demand at pH 8 and impaired lipid metabolism at pH 9. This study provides important information regarding molecular-level effects related to pH-dependent exposure of fluoxetine in embryonic zebrafish.

Metabolomic profiling of zebrafish (Danio rerio) embryos exposed to the antibacterial agent triclosan.

Triclosan, a widely used antibacterial and antifungal agent, is ubiquitously detected in the natural environment. There is increasing evidence that triclosan can produce cytotoxic, genotoxic, and endocrine disruptor effects in aquatic biota, including algae, crustaceans, and fish. Metabolomics can provide important information regarding molecular-level effects and toxicity of xenobiotic chemicals in aquatic organisms. The aim of the present study was to assess the toxicity of triclosan in developing zebrafish (Danio rerio) embryos using gas chromatography-mass spectrometry (GC-MS)-based metabolomics. The embryos were exposed to a wide range of triclosan concentrations (10 ng/L-500 µg/L). Endogenous metabolites were extracted using acetonitrile:isopropanol:water (3:3:2, v/v/v). Derivatization of metabolites was performed prior to identification and quantification via GC-MS analysis. A total of 29 metabolites were positively identified in embryos. Univariate (one-way analysis of variance) and multivariate (principal components analysis and projection to latent structure-discriminant analysis) analyses were employed to determine metabolic profile changes in triclosan-exposed embryos. Eight metabolites were significantly altered (p < 0.05) in embryos exposed to triclosan (urea, citric acid, D-(+)-galactose, D-glucose, stearic acid, L-proline, phenylalanine, and L-glutamic acid). The results suggest that triclosan exposure can result in impairment of several pathways in developing zebrafish embryos, with implications for energy metabolism and amino acid metabolism, as well as nitrogen metabolism and gill function. These findings will benefit future risk assessments of triclosan and other contaminants of emerging concern. Environ Toxicol Chem 2019;38:240-249. © 2018 SETAC.

Development and evaluation of a mechanistic model to assess the fate and removal efficiency of hydrophobic organic contaminants in horizontal subsurface flow treatment wetlands.

A mechanistic model for assessing the fate and removal efficiency of hydrophobic organic contaminants in horizontal subsurface flow treatment wetlands was developed and evaluated using empirical concentration data from Singapore's Lorong Halus Treatment Wetland. This treatment wetland consists of a series of horizontal subsurface flow reed beds. The model, calibrated for the Lorong Halus Treatment Wetland, provided an adequate description of the concentrations of nine neutral organic substances in water, rhizomes and emergent vegetation in the wetland. The model was applied to investigate the sensitivity of the contaminant removal efficiency to environmental conditions and physicochemical properties of contaminants that enter the wetland. The water-budget of the wetland was found to exhibit an important influence on both the mass-removal efficiency and reduction of contaminant concentrations that can be achieved through wetland treatment. The model illustrated that removal pathways of organic contaminants in the wetland varied as a function of the properties of the contaminants. The mass-removal efficiency of the treatment wetland was greatest for chemicals with a log KOW between 3.0 and 5.0 and log KAW > -1.0. Removal of contaminants through volatilization was found to be greatest for substances with a log KOW between 3 and 5 and log KAW > 0. Transpiration flux in vegetation was found to be most important for substances with a log KOW between 4.5 and 5.5 and a log KAW between -5.0 and 0.0. Biotransformation rates of the contaminants in the wetland media play a crucial role in the removal of contaminants from wastewater. The model provides a tool for assessing the removal capacity of treatment wetlands for neutral organic contaminants and evaluating trade-offs in the design and operation of a horizontal subsurface flow treatment wetland.

Assessing bioaccumulation behaviour of hydrophobic organic contaminants in a tropical urban catchment.

The bioaccumulation behaviour of halogenated flame retardant (HFRs), synthetic musks (SMs), organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in plankton, invertebrates and fish was assessed in an urban catchment in Singapore which is a tropical island country highly populated. The studied contaminants ranged widely in physical-chemical properties, with KOW values ranging between approximately 103-1011. BDE-47 and dechlorane plus (DPs) were the predominant HFRs, while galaxolide (HHCB) and tonalide (AHTN) were the predominant synthetic musk compounds in biota from the studied freshwater system. Concentrations of organochlorine contaminants such as chlordanes, DDE, DDD, PCB 138 and PCB 153 were generally higher than those of the HFRs and SMs. On a wet weight basis, bioaccumulation factors (BAFs) of the current use HFRs were in some cases higher than the bioaccumulation criteria value of 5000 L/kg wet weight. Conversely, BAFs of SMs were found to be less than the 5000 L/kg guideline. Lipid adjusted BAFs (L/kg lipid) of the studied contaminants varied among the different aquatic species, which is likely due to organism trophic level and metabolic transformation capacity differences. BAFs were highly correlated with the chemical KOW values. For fish, log BAFs of the studied contaminants increased with increasing log KOW, between a log KOW range of approximately 3-7, after which BAFs subsequently decreased. A similar relationship was observed for BAFs in the studied invertebrates. For plankton, a simple linear regression was observed between log BAF and log KOW over the target analyte KOW range (log KOW's between 3-11). Predicted BAF values derived from a mechanistic bioaccumulation model for hydrophobic organic contaminants were generally consistent with the observed BAFs. However, in some cases the model substantially overestimated bioaccumulation potential based on the chemical's hydrophobicity, which may be due to a high degree of biotransformation of those compounds. The study provides important information regarding bioaccumulation potential of several emerging organic contaminants of concern.

Human exposure to trace elements in central Cambodia: Influence of seasonal hydrology and food-chain bioaccumulation behaviour.

Exposure to mercury and other trace elements remains an important public health concern, worldwide. The present study involved a comprehensive field study to determine concentrations of fourteen trace elements (Al, As, Cr, Co, Cd, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn) in surface water and different fish species from Tonlé Sap Lake in central Cambodia, during both the dry and wet seasons. Total arsenic (tAs) and Mn in surface water during the dry season exceeded WHO drinking water guidelines. Total mercury (tHg) concentrations (µg/g wet wt.) in fish during the wet season (GM = 0.055; CI95 = 0.01-0.26) were approximately 15 times higher (P < 0.05) compared to those during the dry season (GM = 0.0035; CI95 = 0.0004-0.033). Mean target hazard quotients (THQs) for inorganic arsenic (iAs), methyl mercury (MeHg), Mn and Pb were > 1, with estimated maximum values greatly exceeding 1. Mean THQs of Zn, Cd, Ni and Se were very near 1, with estimated maximum values exceeding 1. The MeHg THQ (min-max range: 0.16-9.09) during the wet season was 7 times higher than in the dry season (min-max range: 0.05-1.35). Concentrations of Hg and other trace elements varied widely between fish species. The findings suggest that exposure of some trace elements via water and food is of concern in this region. High consumption rates of fish and rice key factors related to trace element exposure. Seasonal hydrology and species-specific bioaccumulation behaviour in the Tonlé Sap Lake watershed also play an important role. The generated information will be useful to better mitigate trace element exposure in this region.

Sorption and bioaccumulation behavior of multi-class hydrophobic organic contaminants in a tropical marine food web.

While numerous studies have demonstrated the environmental behavior of legacy persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), information regarding sorption and bioaccumulation potential of other widely used organic chemicals such as halogenated flame retardants (HFRs) is limited. This study involved a comprehensive field investigation of multi-class hydrophobic organic contaminants (HOCs) in environmental media and fish in Singapore Strait, an important tropical maritime strait in Southeast Asia. In total, 90 HOCs were analyzed, including HFRs, synthetic musks, PCBs, OCPs, as well as triclosan and methyl triclosan. The results show that the organic carbon normalized sediment-seawater distribution ratios (CSED/CWD) of the studied compounds are comparable to the organic carbon-water partition coefficients (KOC), over a log KOC range of approximately 4-11. The observed species-specific bioaccumulation factors (BAFs), biota-sediment accumulation factors (BSAFs), organism-environment media fugacity ratios (fFISH/fWD and fFISH/fSED) and trophic magnification factors (TMFs) indicate that legacy POPs and PBDE 47 show bioaccumulation behavior in this tropical marine ecosystem, while triclosan, tonalide, dodecachlorodimethanodibenzocyclooctane stereoisomers (DDC-COs), and hexabromocyclododecanes (HBCDDs) do not. Methyl triclosan and galaxolide exhibit moderate biomagnification. Tetrabromobisphenol A (TBBPA) and 1,2-bis (2,4,6-tribromophenoxy)ethane (BTBPE) were detected in environmental media but not in any of the organisms, suggesting low bioaccumulation potential of these flame retardants. The apparently low bioaccumulation potential of the studied HFRs and synthetic musks is likely because of metabolic transformation and/or reduced bioavailability due to the hydrophobic nature of these compounds.

Assessing biological effects of fluoxetine in developing zebrafish embryos using gas chromatography-mass spectrometry based metabolomics.

Continuous low-dose exposure of pharmaceutically active compounds (PhACs) in aquatic ecosystems is a concern worldwide. In this study, we utilized a gas chromatography mass spectrometry (GC-MS) based metabolomics approach to assess endogenous metabolite changes in developing zebrafish embryos exposed to different concentrations of the widely used antidepressant, fluoxetine. Embryos were exposed from 2 h post fertilization (hpf) until 96 hpf. Using the Fiehn GC-MS library, a total of 31 metabolites were positively identified in embryos. Statistical analyses revealed significant dysregulation of 11 metabolites in fluoxetine exposed embryos. Metabolite classes that were significantly altered included, amino acids, monosaccharides, glycerophosphates, fatty acids, carboxylic acid derivatives and sugars. Concentrations of amino acids, maltose, d-malic acid, 3-phosphoglycerate and d-glucose were significantly reduced in exposed embryos. Conversely, concentrations of citric acid were in some cases significantly elevated in exposed embryos. Metabolic pathway analysis revealed perturbation of five main pathways, including (i) alanine, aspartate and glutamate metabolism, (ii) phenylalanine, tyrosine and tryptophan biosynthesis, (iii) phenylalanine metabolism. (iv) tyrosine metabolism and (v) starch and sucrose metabolism. The results indicate fluoxetine exposure causes perturbation of energy and amino acid metabolism, which may adversely impact embryogenesis due to depletion of energy reserves during this period. Also, the observed alterations in aspartic acid, phenylalanine and tyrosine in fluoxetine exposed embryos suggests potential disruption of normal neurobehavioral and liver function. The results further demonstrate that GC-MS based metabolomics is an effective approach for assessing toxicodynamics and threshold effect levels of environmental pollutants in aquatic organisms.

Occurrence and distribution of halogenated flame retardants in an urban watershed: Comparison to polychlorinated biphenyls and organochlorine pesticides.

Due to restrictions on polybrominated diphenyl ethers (PBDEs), market demand for alternative flame retardants is projected to increase, worldwide. Information regarding the environmental behavior of these compounds is limited. The present study involved field measurements of several alternative halogenated flame retardants (HFRs), along with PBDEs and legacy persistent organic pollutants (POPs) in surface water, bottom sediments and suspended particulate matter (SPM) within a highly urbanized watershed in Singapore. Several alternative HFRs were detected in water and sediments. Dechlornane Plus stereoisomers (syn- and anti-DP) were detected in all samples, exhibiting relatively high concentrations in water, sediments and SPM. The maximum syn-DP concentrations in water, sediments and SPM were 24.30 ng/L, 2.48 ng/g dry wt. and 7774 ng/g dry wt., respectively. 1,2-Bis(2,4,6-tribromophenoxy) ethane (BTBPE), pentabromotoluene (PBT), hexabromobenzene (HxBBz) and tetrabromoethylcyclohexane (TBECH) were routinely detected. PBDE concentrations were relatively low and often non-detectable. Polychlorinated biphenyl (PCB) concentrations ranged from 0.017 to 8.37 ng/L in water, 9.86-27.92 ng/g dry wt. in SPM, and 6.48-212.3 ng/g dry wt. in sediments. Congener and isomer patterns suggested no recent inputs of PBDEs or dichlorodiphenyltrichloroethane (DDT). Rainfall was found to be an important factor influencing temporal and spatial patterns of DPs, BTBPE, PBDEs and some organochlorines in surface water. Land use index was found to be important for several organochlorines, but not HFRs. The observed sediment-water partitioning behavior of the studied HFRs and legacy POPs was highly dependent on chemical hydrophobicity. The data demonstrate that the studied HFRs have a relatively high affinity for SPM and bottom sediments. For example, the log KOC,OBS for TBECH, syn-DP and anti-DP and BTBPE in bottom sediments ranged between 8.1 and 9.6. The findings will aid future studies regarding fate, transport and bioaccumulation of these current-use contaminants of concern.

Bioaccumulation Behavior of Pharmaceuticals and Personal Care Products in Adult Zebrafish (Danio rerio): Influence of Physical-Chemical Properties and Biotransformation.

The factors influencing bioaccumulation of pharmaceuticals and personal care products (PPCPs) in aquatic organisms are not well understood. The present study involved a comprehensive laboratory investigation to assess the bioaccumulation behavior of several PPCPs in adult zebrafish (Danio rerio). The studied PPCPs included several ionogenic organic compounds (IOCs) such as weak acids and weak bases. Experiments involved two exposure groups (high and low) and a control group, with a 6 day aqueous exposure, followed by a 7 day depuration phase under flow-through conditions. Uptake rate constants (ku) ranged between 0.19 and 8610 L·kg-1·d-1, while depuration rate constants (kd) ranged between 0.14 and 5.14 d-1 in different fish tissues. Steady-state bioconcentration factor (BCFss) values varied widely among the studied PPCPs, ranging from 0.09 to 6,460. In many cases, BCFss values of individual PPCPs differed substantially among different fish tissues. Positive linear relationships were observed between log BCFss values and physical-chemical properties such as octanol-water distribution coefficients (log Dow), membrane-water distribution coefficients (log Dmw), albumin-water distribution coefficients (log DBSAw), and muscle protein-water distribution coefficients (log Dmpw), indicating the importance of lipid-, phospholipid-, and protein-water partitioning. The results also showed that for many PPCPs, the estimated whole-body metabolism rate constant (km) values were comparable to the observed depuration rate (kd), indicating that metabolism plays a major role in the overall elimination of these compounds in zebrafish. An exception was sertraline, which exhibited a kd value (0.4-0.5 d-1) that was much higher than the estimated whole-body km (0.03 d-1). Overall, the results help to better understand the influence of physical-chemical properties and biotransformation on bioaccumulation behavior of these contaminants of concern in aquatic organisms.

Occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland in Singapore.

This study involved a field-based investigation to assess the occurrence, distribution and bioaccumulation behaviour of hydrophobic organic contaminants in a large-scale constructed wetland. Samples of raw leachate, water and wetland plants, Typha angustifolia, were collected for chemical analysis. Target contaminants included polychlorinated biphenyls (PCBs), organochlorine pesticides (OCP), as well as several halogenated flame retardants (HFRs) and personal care products (triclosan and synthetic musks). In addition to PCBs and OCPs, synthetic musks, triclosan (TCS) and dechlorane plus stereoisomers (syn- and anti-DPs) were frequently detected. Root concentration factors (log RCF L/kg wet weight) of the various contaminants ranged between 3.0 and 7.9. Leaf concentration factors (log LCF L/kg wet weight) ranged between 2.4 and 8.2. syn- and anti-DPs exhibited the greatest RCF and LCF values. A strong linear relationship was observed between log RCF and octanol-water partition coefficient (log KOW). Translocation factors (log TFs) were negatively correlated with log KOW. The results demonstrate that more hydrophobic compounds exhibit higher degrees of partitioning into plant roots and are less effectively transported from roots to plant leaves. Methyl triclosan (MTCS) and 2,8-dichlorodibenzo-p-dioxin (DCDD), TCS degradation products, exhibited relatively high concentrations in roots and leaves., highlighting the importance of degradation/biotransformation. The results further suggest that Typha angustifolia in this constructed wetland can aid the removal of hydrophobic organic contaminants present in this landfill leachate. The findings will aid future investigations regarding the fate and bioaccumulation of hydrophobic organic contaminants in constructed wetlands.

Chlorinated Polyfluoroalkyl Ether Sulfonic Acids in Matched Maternal, Cord, and Placenta Samples: A Study of Transplacental Transfer.

Currently, information regarding concentrations of chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) in human placenta does not exist. The main objective of this study was to assess the occurrence and distribution of two Cl-PFESAs, 6:2 Cl-PFESA and 8:2 Cl-PFESA, in maternal serum, umbilical cord serum, and placenta to better assess the transport pathways related to human prenatal exposure. The widely studied perfluorooctanesulfonate (PFOS) was studied for comparison. This study was a hospital-based survey involving quantitative determination of Cl-PFESA and PFOS concentrations in maternal serum (n = 32), cord serum (n = 32), and placenta (n = 32) samples from women in Wuhan, China. The results indicate that Cl-PFESAs can efficiently be transported across placenta, with median exposure levels of 0.60 and 0.01 ng/mL for 6:2 Cl-PFESA and 8:2 Cl-PFESA in the cord sera, respectively. Concentrations of the target compounds in maternal sera, cord sera, and placentas decreased in the following order: PFOS > 6:2 Cl-PFESA > 8:2 Cl-PFESA. Similar patterns were observed in maternal sera, cord sera, and placentas for Cl-PFESAs, with concentrations decreasing in the following order: maternal sera > cord sera > placentas. Significant correlations were observed among 6:2 Cl-PFESA, 8:2 Cl-PFESA, and PFOS concentrations in the maternal serum, cord serum, and placenta samples (r > 0.7; p < 0.001). The median value of RCM (ratio of cord serum to maternal serum concentration) of 6:2 Cl-PFESA was 0.403, indicating a relatively high (∼40%) placental transfer efficiency. 8:2 Cl-PFESA was transported across placenta to a greater extent than 6:2 Cl-PFESA was, likely because of its higher hydrophobicity and lower plasma protein binding affinity. To the best of our knowledge, this is the first study to report the occurrence and distribution of 6:2 Cl-PFESA and 8:2 Cl-PFESA in human placenta. The findings improve our understanding of the mechanisms of transplacental transfer and neonatal exposure to these important PFOS alternatives.

Isomer-Specific Transplacental Transfer of Perfluoroalkyl Acids: Results from a Survey of Paired Maternal, Cord Sera, and Placentas.

Currently, information regarding isomer-specific concentrations of PFHxS, PFOS, and PFOA in human placenta, and corresponding placental-maternal ratios (RPM) of these compounds does not exist. The objective of the present study was to assess the occurrence, and distribution of different PFHxS, PFOS, and PFOA isomers in maternal serum, umbilical cord serum, and placenta to gain a better understanding of transplacental transport efficiency and prenatal exposure risks. The study involved quantitative determination of isomer-specific concentrations of PFHxS, PFOS, and PFOA in samples of maternal serum (n = 32), cord serum (n = 32), and placenta (n = 32) from pregnant women in Wuhan, China. The results indicate that both linear and branched PFHxS, PFOS and PFOA can be efficiently transported across the placenta, with exposure levels ordered maternal serum > cord serum > placenta. For PFOS isomers, the concentration ratios between cord serum and maternal serum (RCM) were ordered n < iso < 4m < (3 + 5)m < 1m < ∑m2. The RPM values exhibited a similar trend for branched PFOS isomers: iso < 4m ≈ (3 + 5)m < 1m ≈ ∑m2. Conversely, PFOA isomers did not exhibit an obvious structure-activity relationship for RCM and RPM. n-PFHxS transported across the placenta to a greater extent than br-PFHxS. To the best of our knowledge, this is the first study to report the occurrence of PFHxS, PFOS, and PFOA isomers in human placenta. Further, RPM values of these compounds are reported here for the first time. The findings help to better understand the mechanisms of the placental transfer and neonatal exposure to these important contaminants of concern.

Stable nitrogen and carbon isotopes in sediments and biota from three tropical marine food webs: Application to chemical bioaccumulation assessment.

Studies of trophodynamics and contaminant bioaccumulation in tropical marine ecosystems are limited. The present study employed stable isotope and trace contaminant analysis to assess sources of primary productivity, trophic interactions, and chemical bioaccumulation behavior in 2 mangrove food webs and 1 offshore coastal marine food web in Singapore. Samples of sediment, phytoplankton, mangrove leaves, clams, snails, crabs, worms, prawns, and fishes were analyzed for stable carbon and nitrogen isotope values, as well as concentrations of persistent organic pollutants. In the mangrove food webs, consumers exhibited similar δ13 C values, probably because of the well-mixed nature of these systems. However, the 2 primary consumers (common nerite and rodong snail) exhibited distinct δ13 C values (-21.6‰ vs -17.7‰), indicating different carbon sources. Fish from Singapore Strait exhibited similar δ13 C values, indicating common carbon sources in this offshore marine food web. The highest trophic level was found in glass perchlet (trophic level = 3.3) and tilapia (trophic level = 3.4) in the 2 mangrove food webs and grunter (trophic level = 3.7) in the Singapore Strait food web. Concentrations of polychlorinated biphenyl (PCB 153) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) concentrations ranged from 0.9 to 84.6 ng/g lipid weight and from <0.2 to 267.4 ng/g lipid weight, respectively. The trophic magnification factors of PCB 153 and p,p'-DDE ranged between 1.63 and 4.62, indicating biomagnification in these tropical marine food webs. The findings provide important information that will aid future chemical bioaccumulation assessment initiatives. Environ Toxicol Chem 2017;36:2521-2532. © 2017 SETAC.

Occurrence and distribution of synthetic musks, triclosan and methyl triclosan in a tropical urban catchment: Influence of land-use proximity, rainfall and physicochemical properties.

This study involved a comprehensive thirteen month survey of synthetic musks, triclosan (TCS) and methyl triclosan (MTCS) in surface water, as well as suspended particular matter (SPM) and bottom sediments in a tropical urban catchment in Singapore. The polycyclic musk, Galaxolide (HHCB), exhibited the highest concentration among musk compounds, ranging from 5.16 to 42.9ng/L in surface water, 11.0 to 108ng/g dry wt. in sediments and 44.1 to 81.3ng/g dry wt. in SPM. Concentrations of musk ketone, the dominant nitroaromatic musk, ranged from 0.08 to 6.45ng/L in water, 0.082 to 0.72ng/g dry wt. in sediments and 1.75 to 5.50ng/g dry wt. in SPM. Concentrations of MTCS ranged from 0.0056 to 5.6ng/L in water, 0.01 to 0.17ng/g dry wt. in bottom sediments and 0.75 to 2.81ng/g dry wt. in SPM. These concentrations are below predicted no-effect concentrations (PNEC). Principal components analysis (PCA) results showed that synthetic musk concentrations were positively correlated, indicating common source emissions. Rainfall amount and land-use index were found to be key determinants of hydrophobic organic contaminant concentrations in this catchment. Concentrations of TCS and its methylated degradation product, MTCS, were also positively correlated. However, the relative composition of MTCS to total triclosans was relatively low in water (2.8±2.5%) and bottom sediments (0.3±0.1%), suggesting only minor transformation of TCS to MTCS. The organic carbon-water distribution ratio, log Koc (observed), ranged between 3.8 and 5.4 for musks, TCS and MTCS, indicating relatively strong partitioning from dissolved to solid phases. These field-derived log Koc (observed) values are comparable to estimated values based on physicochemical properties. The results provide insight into the occurrence, transport pathways and exposure risks of synthetic musks, triclosan and methyl triclosan in this tropical catchment.

Multi-tool assessment of trace metals in mangroves combining sediment and clam sampling, DGT passive samplers and caged mussels.

The rapid loss of mangroves globally has triggered a call for a better understanding of this habitat, including its dynamics and the threats it is exposed to. The present paper reports the study of trace metals at nine mangrove sites in Singapore in 2012/2013, using the simultaneous application of various tools, namely sediment analyses, the technique of diffusive gradients in thin-films (DGT) and caged/native bivalves (for both chemical and biomarker analyses). DGT devices were successfully deployed over 28days in tropical mangrove waters, and the concentration measured with DGT showed significant correlation with the accumulation for Cu, Zn and Cd in caged mussels, and Cu for native clams, supporting the relevance of DGT to predict metal bioaccumulation. Concentrations in mangrove sediment are reported for As, Cd, Co, Cr, Cu, Ni, Pb and Zn. Sediment levels on a dry weight (dw) basis of Cu (ND-219.5µg/g dw) and Zn (ND-502µg/g dw) exceeded general sediment quality criteria at two sites. Most notably for these two metals, investigations based on the four tools (DGT, sediments, caged mussels and clams) were all able to segregate sites above and below the sediment quality guideline. This was further supported by a range of significant linear correlations between the measurements obtained with the various tools. The present findings support that these monitoring tools are comparable in the field to provide a time-integrated assessment of metals such as Cu and Zn.

Occurrence and distribution of bacteria indicators, chemical tracers and pathogenic vibrios in Singapore coastal waters.

Water quality in Singapore's coastal area was evaluated with microbial indicators, pathogenic vibrios, chemical tracers and physico-chemical parameters. Sampling sites were grouped into two clusters (coastal sites at (i) northern and (ii) southern part of Singapore). The coastal sites located at northern part of Singapore along the Johor Straits exhibited greater pollution. Principal component analysis revealed that sampling sites at Johor Straits have greater loading on carbamazepine, while turbidity poses greater influence on sampling sites at Singapore Straits. Detection of pathogenic vibrios was also more prominent at Johor Straits than the Singapore Straits. This study examined the spatial variations in Singapore's coastal water quality and provided the baseline information for health risk assessment and future pollution management.