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.

The potential for artificial intelligence to predict clinical outcomes in patients who have acquired acute kidney injury during the perioperative period.

Acute kidney injury (AKI) is a common medical problem in hospitalised patients worldwide that may result in negative physiological, social and economic consequences. Amongst patients admitted to ICU with AKI, over 40% have had either elective or emergency surgery prior to admission. Predicting outcomes after AKI is difficult and the decision on whom to initiate RRT with a goal of renal recovery or predict a long-term survival benefit still poses a challenge for acute care physicians. With the increasing use of electronic healthcare records, artificial intelligence may allow postoperative AKI prognostication and aid clinical management. Patients will benefit if the data can be readily accessed andregulatory, ethical and human factors challenges can be overcome.

Transepithelial nasal potential difference in patients with, and at risk of acute respiratory distress syndrome.

BACKGROUND: Impaired alveolar fluid clearance, determined in part by alveolar sodium transport, is associated with acute respiratory distress syndrome (ARDS). Nasal sodium transport may reflect alveolar transport. The primary objective of this prospective, observational study was to determine if reduced nasal sodium transport, as measured by nasal potential difference (NPD), was predictive of the development of and outcome from ARDS. METHODS: NPD was measured in 15 healthy controls and in 88 patients: 40 mechanically ventilated patients defined as 'at-risk' for ARDS, 61 mechanically ventilated patients with ARDS (13 who were previously included in the 'at-risk' group) and 8 ARDS survivors on the ward. RESULTS: In at-risk subjects, maximum NPD (mNPD) was greater in those who developed ARDS (difference -8.4 mV; 95% CI -13.8 to -3.7; p=0.005) and increased mNPD predicted the development of ARDS before its onset (area under the curve (AUC) 0.75; 95% CI 0.59 to 0.89). In the ARDS group, mNPD was not significantly different for survivors and non-survivors (p=0.076), and mNPD was a modest predictor of death (AUC 0.60; 95% CI 0.45 to 0.75). mNPD was greater in subjects with ARDS (-30.8 mV) than in at-risk subjects (-24.2 mV) and controls (-19.9 mV) (p<0.001). NPD values were not significantly different for survivors and controls (p=0.18). CONCLUSIONS: Increased NPD predicts the development of ARDS in at-risk subjects but does not predict mortality. NPD increases before ARDS develops, is greater during ARDS, but is not significantly different for controls and survivors. These results may reflect the upregulated sodium transport necessary for alveolar fluid clearance in ARDS. NPD may be useful as a biomarker of endogenous mechanisms to stimulate sodium transport. Larger studies are now needed to confirm these associations and predictive performance.

Strategic resources for assessing PFAS ecological risks at AFFF sites.

The use of aqueous film forming foam (AFFF) in the United States has caused concern about the potential effects of per- and polyfluoroalkyl substances (PFAS) on ecological resources. Moreover, the limited availability of scientific information and a lack of guidance have collectively resulted in significant challenges for ecological risk assessors supporting site-specific investigations and management decisions at PFAS-impacted sites. To address these needs, the environmental science and technology program of the Department of Defense (DoD), the Strategic Environmental Research and Development Program (SERDP), began funding four desktop review projects in 2018. Project teams were tasked with developing strategic guidance for assessing ecological risk at AFFF-impacted DoD sites. The projects focused specifically on ecological risk assessment practices for threatened and endangered (T&E) species; however, the recommendations and approaches presented in the projects are also applicable and adaptable to common species. The present review provides risk assessors and site managers an overview of how the resources provided in these projects can support ecological-risk-based management decisions at AFFF and other PFAS-impacted sites. Additionally, we synthesize perspectives offered by the four projects on a path forward for PFAS ecological risk assessment, including research needs that we recommend should be prioritized by the scientific community. Integr Environ Assess Manag 2021;17:746-752. © 2021 SETAC.

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.

PFAS Exposure Pathways for Humans and Wildlife: A Synthesis of Current Knowledge and Key Gaps in Understanding.

We synthesize current understanding of the magnitudes and methods for assessing human and wildlife exposures to poly- and perfluoroalkyl substances (PFAS). Most human exposure assessments have focused on 2 to 5 legacy PFAS, and wildlife assessments are typically limited to targeted PFAS (up to ~30 substances). However, shifts in chemical production are occurring rapidly, and targeted methods for detecting PFAS have not kept pace with these changes. Total fluorine measurements complemented by suspect screening using high-resolution mass spectrometry are thus emerging as essential tools for PFAS exposure assessment. Such methods enable researchers to better understand contributions from precursor compounds that degrade into terminal perfluoroalkyl acids. Available data suggest that diet is the major human exposure pathway for some PFAS, but there is large variability across populations and PFAS compounds. Additional data on total fluorine in exposure media and the fraction of unidentified organofluorine are needed. Drinking water has been established as the major exposure source in contaminated communities. As water supplies are remediated, for the general population, exposures from dust, personal care products, indoor environments, and other sources may be more important. A major challenge for exposure assessments is the lack of statistically representative population surveys. For wildlife, bioaccumulation processes differ substantially between PFAS and neutral lipophilic organic compounds, prompting a reevaluation of traditional bioaccumulation metrics. There is evidence that both phospholipids and proteins are important for the tissue partitioning and accumulation of PFAS. New mechanistic models for PFAS bioaccumulation are being developed that will assist in wildlife risk evaluations. Environ Toxicol Chem 2021;40:631-657. © 2020 SETAC.

Effect of Ultraviolet C Disinfection Treatment on the Nanomechanical and Topographic Properties of N95 Respirator Filtration Microfibers.

Ultraviolet germicidal irradiation (UVGI) N95 filtering facepiece respirator (FFR) treatment is considered an effective decontamination approach to address the supply shortage of N95 FFRs during the ongoing Covid-19 pandemic. In this study, we investigated the nanomechanical and topographic properties of filtration fibers that have been exposed to different doses of UVC radiation. UVC exposure was shown to decrease both Young's modulus (E), hardness (H) and fiber width, as measured on individual polypropylene (PP) fibers. Our results also show that the PP microfiber layer loses its strength when N95 respirators are exposed to an accumulated UVC dose during the process of decontamination, and the PP fiber width also exhibits a logarithmic decrease during UVC exposure. The nanoscale measurement results on individual fibers suggest that maximum cycles of UVC disinfection treatment should be limited due to excessive accumulated dose, which has the potential to decrease the fiber breaking strength.

Effects of Anticholinesterase Reversal Under General Anesthesia on Postoperative Cardiovascular Complications: A Retrospective Cohort Study.

BACKGROUND: The anticholinesterase neostigmine and the muscarinic inhibitor glycopyrrolate are frequently coadministered for the reversal of neuromuscular blockade. This practice can precipitate severe bradycardia or tachycardia, but whether it affects the incidence of cardiovascular complications remains unclear. We hypothesized that anticholinesterase reversal with neostigmine and glycopyrrolate versus no anticholinesterase reversal increases the risk of postoperative cardiovascular complications among adult patients undergoing noncardiac surgery with general anesthesia. METHODS: We conducted a prespecified retrospective analysis of hospital registry data from a major health care network for patients undergoing surgery with general anesthesia from January 2007 to December 2015. The primary outcome was a composite of cardiac dysrhythmia, acute heart failure, transient ischemic attack, ischemic stroke, and acute myocardial infarction within 30 days after surgery. We performed sensitivity analyses in subgroups and propensity score adjustment and explored the association between exposure and outcome in subgroups of patients with high risk of cardiovascular complications. RESULTS: Of the 98,147 cases receiving neuromuscular blockade, 73,181 (74.6%) received neostigmine and glycopyrrolate, while 24,966 (25.4%) did not. A total of 5612 patients (7.7%) in the anticholinesterase reversal group and 1651 (6.6%) in the control group (P < .001) experienced the primary outcome. After adjustment for clinical covariates, neostigmine and glycopyrrolate exposure was significantly associated in a dose-dependent fashion (P for trend <.001, respectively) with tachycardia (adjusted odds ratio = 2.1 [95% CI, 1.97-2.23]; P < .001) and bradycardia (adjusted odds ratio = 2.84 [95% CI, 2.49-3.24]; P < .001) but not with postoperative cardiovascular complications (adjusted odds ratio = 1.03 [95% CI, 0.97-1.1]; P = .33). We identified a significant effect modification of anticholinesterase reversal by high age, high-risk surgery, and history of atrial fibrillation (P for interaction = .002, .001, and .02, respectively). By using linear combinations of main effect and exposure-risk interaction terms, we detected significant associations between anticholinesterase reversal and cardiovascular complications toward a higher vulnerability in these patient subgroups. CONCLUSIONS: Neuromuscular blockade reversal with neostigmine and glycopyrrolate was associated with an increased incidence of intraoperative tachycardia and bradycardia but not with 30-day postoperative cardiovascular complications. Exploratory analyses suggest that a high postoperative cardiovascular complication risk profile may modify the effects of anticholinesterase reversal toward clinical relevance.

Extended Indications for Extracorporeal Membrane Oxygenation in the Operating Room.

BACKGROUND: The use of extracorporeal life support (ECLS) for cardiorespiratory support is increasing. Traditional absolute contraindications are currently deemed relative contraindications. Extracorporeal life support is now considered for a wider cohort of patients on a case-by-case basis. METHOD: We performed a review of the literature and examined current Extracorporeal Life Support Organization guidelines that support the use of ECLS in the operating room, based on the underlying pathology and surgical procedure proposed. We discuss specific surgical populations and different modes of ECLS and cannulation strategies. RESULTS: Based on the available literature, veno-venous extracorporeal membrane oxygenation (ECMO) can be used for the management of complex tracheobronchial and lung surgery, both in the elective and in the emergent setting. Elective veno-arterial (V-A) ECMO for cardiocirculatory support should be considered in high-risk patients undergoing ventricular tachycardia ablation. Extracorporeal life support should be considered as a potential life-saving intervention in almost all parturients with severe respiratory failure or refractory cardiogenic shock. V-A ECMO should be considered in unanticipated intraoperative cardiac arrest in patients without preexisting end-organ failure. CONCLUSION: As the number of indications for ECLS in the operating room is growing, anesthesiology and surgical staff should become familiar with the perioperative management of patients on ECLS.

Evaluation of qSOFA as a Predictor of Mortality Among ICU Patients With Positive Clinical Cultures-A Retrospective Cohort Study.

OBJECTIVE: To compare the discriminative value of the quick-sequential organ failure assessment score (qSOFA) to SOFA in a critically ill population, in which a microbial pathogen was isolated within 48 hours of admission to intensive care. DESIGN: Retrospective cohort study. SETTING: Academic tertiary referral center from July 2008 to June 2017. PATIENTS: Hospitalized patients admitted to intensive care unit. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The primary outcome was in-hospital mortality for all patients with confirmed positive microbiological cultures within 48 hours of admission to intensive care unit (ICU). Subgroup analysis was performed on patients with pathogenic bacteremia or positive cultures in cerebrospinal fluid. Of the 11 415 patients analyzed with positive microbiology specimens within 48 hours of admission, 2933 (25.7%) had a qSOFA ≥2. Of these, 16.6% reached the primary outcome of in-hospital mortality. Unsurprisingly, the discriminative value of qSOFA on admission was significantly worse than that of SOFA (0.73 vs 0.76; P = .0004), despite observing a significant association between qSOFA category and in-hospital mortality (P < .0001). In secondary analyses, similar observations were found using qSOFA within 6 and 24 hours of ICU admission. When analysis was focused on patients with pathogenic bacteremia or positive cerebrospinal fluid (CSF) cultures (n = 1646), there was no significant difference between the discriminative value of qSOFA and SOFA (0.75 vs 0.78; P = .17). CONCLUSIONS: Quick-sequential organ failure assessment score at admission was not superior to SOFA in predicting in-hospital mortality in patients with positive clinical cultures within 48 hours of admission to ICU. Quick-sequential organ failure assessment score at admission to the ICU was associated with mortality and showed reasonable calibration and discrimination. When the analysis was focused on patients with pathogenic bacteremia or positive CSF cultures, qSOFA performed similarly to SOFA in discriminatory those who will die from sepsis.

The Effects of Postoperative Residual Neuromuscular Blockade on Hospital Costs and Intensive Care Unit Admission: A Population-Based Cohort Study.

BACKGROUND: Postoperative residual neuromuscular blockade continues to be a frequent occurrence with a reported incidence rate of up to 64%. However, the effect of postoperative residual neuromuscular blockade on health care utilization remains unclear. We conducted a retrospective cohort study to investigate the effects of postoperative residual neuromuscular blockade on hospital costs (primary outcome), intensive care unit admission rate, and hospital length of stay (secondary outcomes). METHODS: We performed a prespecified secondary analysis of data obtained in 2233 adult patients undergoing surgery under general anesthesia. Postoperative residual neuromuscular blockade was defined as a train-of-four ratio <0.9 in the postanesthesia care unit (PACU). Our confounder model adjusted for a variety of patient, surgical, and anesthesia-related factors. We fitted truncated negative binomial regression models for hospital cost and hospital length of stay analyses and a logistic regression model for our intensive care unit admission analysis. RESULTS: Overall, 457 (20.5%) patients in our cohort had residual neuromuscular blockade on admission to the PACU. Postoperative residual neuromuscular blockade was not independently associated with increased hospital costs (adjusted incidence rate ratio, 1.04, CI, 0.98-1.11; P = .22). There were significantly higher odds of intensive care unit admission in those with postoperative residual neuromuscular blockade compared to those without (adjusted odds ratio, 3.03, CI, 1.33-6.87; P < .01). Further, we found a trend toward increased hospital length of stay in patients with postoperative residual neuromuscular blockade (adjusted incidence rate ratio, 1.09; P = .06). Sensitivity analysis using the same model in the day of surgery admissions and ambulatory surgery confirmed our findings. CONCLUSIONS: Postoperative residual neuromuscular blockade at PACU admission was not significantly associated with increased hospital costs, but was associated with higher rates of intensive care unit admission. These findings support the view that clinicians should continue to work to reduce the rate of postoperative residual neuromuscular blockade.

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.