Temporal and Spatial Comparison of Mercury Bioaccumulation in the Lower Trophic Levels of a Post-glacial Lake Food Web.

Total mercury (Hg) concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotopes were quantified among aquatic invertebrate and sediment samples collected from Keuka Lake in New York's Finger Lakes region to evaluate temporal and spatial variability in Hg bioaccumulation and trophic ecology among these lower trophic levels. Hg concentrations ranged from 6.3 to 158.8 ng/g (dry wt) across dreissenid mussel, zooplankton, and juvenile (< 10 mm) and adult (≥ 10 mm) mysid shrimp (Mysis diluviana) samples. Hg concentrations were higher in samples collected from the western basin in 2015 relative to those for samples collected from this basin in 2022 (p < 0.001). While no specific mechanisms could be identified to explain this difference, higher δ15N values for zooplankton collected in 2015 support conclusions regarding the role of zooplankton trophic status on Hg concentrations in these populations. Spatial patterns in Hg concentrations were of generally low variability among samples collected from the lake's east, west and south basins in 2022. Trophic positions as inferred by δ15N were represented by adult mysids > juvenile mysids > large zooplankton (≥ 500 µm) > dreissenid mussels ≥ small zooplankton (64-500 µm). Differences were evident among the regression slopes describing the relationships between sample Hg concentrations and δ15N values across the lake's three basins (p = 0.028). However, this was primarily attributed to high δ15N values measured in dreissenid mussels collected from the south basin in 2022. Biota sediment accumulation factors ranged from 0.2 to 2.3 and were highest for adult M. diluviana but mysid δ13C values generally supported a pelagic pathway of Hg exposure relative to benthic sediments. Overall, these results provide additional support regarding the contributions of lower trophic levels to Hg biomagnification in aquatic food-webs.

Spatial Comparison of Persistent Organic Pollutants in the Boardman River Following Impoundment Removal and Channel Restoration.

Semi-permeable membrane devices (SPMDs) were used to quantify dissolved concentrations of persistent organic pollutants (POPs) along a 40-km reach of the Boardman River in Traverse City, Michigan that has recently undergone dam and impoundment pond sediment removal. Concentrations of polychlorinated biphenyls (ΣPCBs; 7.7-65.0 pg/L), dichloro-diphenyl-trichloroethane and metabolites (ΣDDTs; 7.6-202.5 pg/L) and cyclodiene compounds (3.7-220.7 pg/L) were below regulatory guidelines considered to pose chronic risks to aquatic health. POP concentrations estimated from SPMD monitoring were not representative of potential residual contamination from legacy sediment impoundments. Spatial patterns in POP profiles were present among the different deployment sites and were reflective of differences in land-use patterns along the rural to urban gradient of the monitored area of the river. These results represent baseline POP data prior to the removal of remaining dam infrastructure in the Boardman River. Overall, this study supports the utility of SPMDs for monitoring trace environmental contamination and helps assess the efficacy of environmental remediation for mitigating legacy pollutant releases following dam and impoundment pond sediment removal.

Implications of population connectivity studies for the design of marine protected areas in the deep sea: An example of a demosponge from the Clarion-Clipperton Zone.

The abyssal demosponge Plenaster craigi inhabits the Clarion-Clipperton Zone (CCZ) in the northeast Pacific, a region with abundant seafloor polymetallic nodules with potential mining interest. Since P. craigi is a very abundant encrusting sponge on nodules, understanding its genetic diversity and connectivity could provide important insights into extinction risks and design of marine protected areas. Our main aim was to assess the effectiveness of the Area of Particular Environmental Interest 6 (APEI-6) as a potential genetic reservoir for three adjacent mining exploration contract areas (UK-1A, UK-1B and OMS-1A). As in many other sponges, COI showed extremely low variability even for samples ~900 km apart. Conversely, the 168 individuals of P. craigi, genotyped for 11 microsatellite markers, provided strong genetic structure at large geographical scales not explained by isolation by distance (IBD). Interestingly, we detected molecular affinities between samples from APEI-6 and UK-1A, despite being separated ~800 km. Although our migration analysis inferred very little progeny dispersal of individuals between areas, the major differentiation of OMS-1A from the other areas might be explained by the occurrence of predominantly northeasterly transport predicted by the HYCOM hydrodynamic model. Our study suggests that although APEI-6 does serve a conservation role, with species connectivity to the exploration areas, it is on its own inadequate as a propagule source for P. craigi for the entire eastern portion of the CCZ. Our new data suggest that an APEI located to the east and/or the south of the UK-1, OMS-1, BGR, TOML and NORI areas would be highly valuable.

Polychlorinated Biphenyl Bioaccumulation Patterns Among Lake Erie Lower Trophic Level Consumers Reflect Species Ecologies.

Polychlorinated biphenyl (PCB) concentrations were quantified in lower trophic level consumers of the Lake Erie western basin food web to assess the capacity of PCBs to discriminate among trophically similar species inhabiting different compartments of the same ecosystem. Zooplankton were characterized by higher proportions of less chlorinated and hydrophobic homologs relative to zebra mussel (Dreissena polymorpha), mayfly (Hexagenia limbata) and emerald shiner (Notropis atherinoides) samples. PCB biota-sediment accumulation factors (BSAF) differed significantly among species with zebra mussels and emerald shiners having the highest BSAFs. Principal components analysis of sample PCB profiles reflected the contrasting pelagic and benthic habitats occupied by filter-feeding zooplankton and zebra mussel samples. Benthic mayfly PCB profiles were characterized by increasingly hydrophobic (logK OW ≥ 6.9) congeners with more variable emerald shiner profiles reflecting the greater mobility and extent of spatial habitat integration achieved by this secondary consumer. These results contribute to growing evidence for the use of PCBs as ecological tracers in aquatic ecosystems.

Ecological Implications of Steady State and Nonsteady State Bioaccumulation Models.

Accurate predictions on the bioaccumulation of persistent organic pollutants (POPs) are critical for hazard and ecosystem health assessments. Aquatic systems are influenced by multiple stressors including climate change and species invasions and it is important to be able to predict variability in POP concentrations in changing environments. Current steady state bioaccumulation models simplify POP bioaccumulation dynamics, assuming that pollutant uptake and elimination processes become balanced over an organism's lifespan. These models do not consider the complexity of dynamic variables such as temperature and growth rates which are known to have the potential to regulate bioaccumulation in aquatic organisms. We contrast a steady state (SS) bioaccumulation model with a dynamic nonsteady state (NSS) model and a no elimination (NE) model. We demonstrate that both the NSS and the NE models are superior at predicting both average concentrations as well as variation in POPs among individuals. This comparison demonstrates that temporal drivers, such as environmental fluctuations in temperature, growth dynamics, and modified food-web structure strongly determine contaminant concentrations and variability in a changing environment. These results support the recommendation of the future development of more dynamic, nonsteady state bioaccumulation models to predict hazard and risk assessments in the Anthropocene.

PCB Food Web Dynamics Quantify Nutrient and Energy Flow in Aquatic Ecosystems.

Measuring in situ nutrient and energy flows in spatially and temporally complex aquatic ecosystems represents a major ecological challenge. Food web structure, energy and nutrient budgets are difficult to measure, and it is becoming more important to quantify both energy and nutrient flow to determine how food web processes and structure are being modified by multiple stressors. We propose that polychlorinated biphenyl (PCB) congeners represent an ideal tracer to quantify in situ energy and nutrient flow between trophic levels. Here, we demonstrate how an understanding of PCB congener bioaccumulation dynamics provides multiple direct measurements of energy and nutrient flow in aquatic food webs. To demonstrate this novel approach, we quantified nitrogen (N), phosphorus (P) and caloric turnover rates for Lake Huron lake trout, and reveal how these processes are regulated by both growth rate and fish life history. Although minimal nutrient recycling was observed in young growing fish, slow growing, older lake trout (>5 yr) recycled an average of 482 Tonnes·yr(-1) of N, 45 Tonnes·yr(-1) of P and assimilated 22 TJ yr(-1) of energy. Compared to total P loading rates of 590 Tonnes·yr(-1), the recycling of primarily bioavailable nutrients by fish plays an important role regulating the nutrient states of oligotrophic lakes.

Bioamplification as a bioaccumulation mechanism for persistent organic pollutants (POPs) in wildlife.

Persistent organic pollutant bioaccumulation models have generally been formulated to predict bioconcentration and biomagnification. A third bioaccumulation process that can mediate chemical fugacity in an organism is bioamplification.Bioamplification occurs when an organism loses body weight and the chemical partitioning capacity occurs at a rate that is faster than the chemical can be eliminated.Although bioamplification has not been widely recognized as a bioaccumulation process, the potential consequences of this process are significant. Bioamplification causes an increase in chemical fugacity in the animal's tissues and results in there distribution of contaminants from inert storage sites to more toxicologically sensitive tissues. By reviewing laboratory and field studies, we have shown in this paper that bioamplification occurs across taxonomic groups that include, invertebrates,amphibians, fishes, birds, and mammals. Two case studies are presented, and constitute multi-life stage non-steady state bioaccumulation models calibrated for yellow perch and herring gulls. These case studies were used to demonstrate that bioamplification is predicted to occur under realistic scenarios of animal growth and seasonal weight loss. Bioamplification greatly enhances POP concentrations and chemical fugacities during critical physiological and behavioral events in an animal's life history, e.g., embryo development, juvenile stages, metamorphosis, reproduction, migration, overwintering, hibernation, and disease. Consequently,understanding the dynamics of bioamplification, and how different life history scenario scan alter tissue residues, may be helpful and important in assessing wildlife hazards and risks.

Low concentrations of contaminants in an invasive cyprinid, the rudd, in a Great Lakes Area of Concern.

The invasive, omnivorous rudd Scardinius erythrophthalmus is abundant in the upper Niagara River, a Great Lakes Area of Concern. Invasive species can alter trophic and contaminant pathways, but complex ontogenetic and seasonal diet shifts by rudds make it difficult to predict their chemical burdens relative to other fishes. We quantified concentrations of chemical residues in rudds and compared them to six fish species from various trophic levels. Rudds contained low concentrations of total dichlorodiphenyltrichloroethane (mean = 0.02 µg/g), Hg (mean = 0.03 µg/g), and polychlorinated biphenyls (mean = 0.06 µg/g); these concentrations were among the lowest for all species examined. Concentrations of aldrin, heptachlor, hexachlorobenzene, total hexachlorocyclohexanes, mirex, and total chlordanes were less than the method detection limit for all rudds examined. If reducing rudd biomass is determined to be beneficial, resource managers could consider targeted harvest, given the low concentrations of contaminant in rudds and their susceptibility to capture.

Pacific salmon as vectors of environmental contaminants: An experimental test confirms synoptic surveys in natural streams.

Pacific salmon transfer large quantities of material to tributaries during their spawning migrations, including carcass tissue and labile nutrients but also persistent organic pollutants (POPs) and heavy metals. We conducted a Before-After-Control-Intervention experiment by adding salmon carcasses and eggs to a Michigan (USA) stream that had never received inputs from non-native salmon to understand the bioaccumulation and persistence of biotransported contaminants. Our experimental outcomes were compared to previous studies using meta-analysis. Coincident with the introduction of salmon, the PCB and DDE burden of resident trout significantly increased. However, we did not observe changes in total mercury (Hg). Two years after the salmon addition experiment concluded, resident trout POP concentrations had returned to pre-addition levels, with no difference between the treatment and control reaches. Analysis of effect sizes suggested that the contaminant response observed in our experiment is consistent with field survey observations. Our study suggested that the consumption of salmon eggs drove the increase in POP burden of resident trout while Hg bioaccumulation was influenced by watershed sources. Critically, our study suggests that ecosystems are capable of quickly recovering from POP inputs from species migrations if contaminant sources are removed.

Soluble P-Selectin and von Willebrand Factor Rise in Healthy Volunteers Following Non-exertional Ascent to High Altitude.

Reduced oxygen tensions experienced at high altitudes are thought to predispose to thrombosis, yet there are few studies linking hypoxia, platelet activation, and thrombosis. Reports of platelet phenotypes in hypoxia are inconsistent, perhaps due to differing degrees of hypoxia experienced and the duration of exposure. This study aimed to investigate the relationship between soluble P-selectin, a marker of platelet activation, and von Willebrand factor (vWF) on exposure to hypoxia. We measured plasma concentrations of P-selectin and vWF in sixteen healthy volunteers before, during and after the APEX 2 expedition. APEX 2 consisted of a non-exertional ascent to 5,200 m, followed by 7 consecutive days at high altitude. We showed that high altitude significantly increased mean plasma P-selectin and vWF compared to pre-expedition levels. Both plasma marker levels returned to baseline post-expedition. We found a strong positive correlation between vWF and P-selectin, but no association between P-selectin and platelet count. Our results are consistent with previous work showing evidence of platelet activation at high altitude and demonstrate that the rise in P-selectin is not simply due to an increase in platelet count. As vWF and P-selectin could be derived from either platelets or endothelial cells, further work assessing more specific markers of endothelial activation is proposed to provide insight into the source of these potential pro-thrombotic biomarkers at altitude.

Regional variation in mercury bioaccumulation among NW Atlantic Golden (Lopholatilus chamaeleonticeps) and Blueline (Caulolatilus microps) Tilefish.

Mercury (Hg) concentrations in fishes from the NW Atlantic Ocean pose concern due to the importance of this region to U.S. fisheries harvest. In this study, total Hg (THg) concentrations and nitrogen stable isotope (δ15N) values were quantified in muscle tissues sampled from Golden (Lopholatilus chamaeleonticeps) and Blueline (Caulolatilus microps) Tilefish collected during a fishery-independent survey conducted in the NW Atlantic to compare bioaccumulation patterns between these species. Total Hg concentrations averaged (±SD) 0.4 ± 0.4 µg/g dry weight (d.w.) for L. chamaeleonticeps and 1.1 ± 0.7 µg/g d.w. for C. microps with <2% of all sampled fish, those >70 cm fork length, exceeding the most restrictive USEPA regulatory guidelines for human consumption (THg > 0.46 µg/g w.w.), when converted to wet weight concentrations. The THg concentrations reported here for individuals from the NW Atlantic stock are comparable to those reported for similarly sized individuals collected from the SW Atlantic stock but notably lower than those reported for Gulf of Mexico L. chamaeleonticeps, indicating different Hg exposure and assimilation kinetics for fish from the NW Atlantic, and highlights the broad geographic variability of Hg bioaccumulation among Tilefish stocks. Caulolatilus microps had higher δ15N values relative to L. chamaeleonticeps and a pattern of decreasing THg concentrations was also present from south to north across the study range. It is concluded that this trophic difference and spatial pattern in Tilefish THg concentrations emphasizes the habitat and resource partitioning mechanisms described for these sympatric species that permits their coexistence in the continental shelf environment. Importantly, regional variability in THg concentrations accentuate the possible roles of fine-scale biotic and abiotic processes that can act to regulate Hg bioaccumulation among individuals and species.

Adaptive Manufacturing for Healthcare During the COVID-19 Emergency and Beyond.

During the COVID-19 pandemic, global health services have faced unprecedented demands. Many key workers in health and social care have experienced crippling shortages of personal protective equipment, and clinical engineers in hospitals have been severely stretched due to insufficient supplies of medical devices and equipment. Many engineers who normally work in other sectors have been redeployed to address the crisis, and they have rapidly improvised solutions to some of the challenges that emerged, using a combination of low-tech and cutting-edge methods. Much publicity has been given to efforts to design new ventilator systems and the production of 3D-printed face shields, but many other devices and systems have been developed or explored. This paper presents a description of efforts to reverse engineer or redesign critical parts, specifically a manifold for an anaesthesia station, a leak port, plasticware for COVID-19 testing, and a syringe pump lock box. The insights obtained from these projects were used to develop a product lifecycle management system based on Aras Innovator, which could with further work be deployed to facilitate future rapid response manufacturing of bespoke hardware for healthcare. The lessons learned could inform plans to exploit distributed manufacturing to secure back-up supply chains for future emergency situations. If applied generally, the concept of distributed manufacturing could give rise to "21st century cottage industries" or "nanofactories," where high-tech goods are produced locally in small batches.

Neutrophils Fuel Effective Immune Responses through Gluconeogenesis and Glycogenesis.

Neutrophils can function and survive in injured and infected tissues, where oxygen and metabolic substrates are limited. Using radioactive flux assays and LC-MS tracing with U-13C glucose, glutamine, and pyruvate, we observe that neutrophils require the generation of intracellular glycogen stores by gluconeogenesis and glycogenesis for effective survival and bacterial killing. These metabolic adaptations are dynamic, with net increases in glycogen stores observed following LPS challenge or altitude-induced hypoxia. Neutrophils from patients with chronic obstructive pulmonary disease have reduced glycogen cycling, resulting in impaired function. Metabolic specialization of neutrophils may therefore underpin disease pathology and allow selective therapeutic targeting.

Variable vitellogenin response of Japanese medaka (Oryzias latipes) to weekly estrogen exposure.

Japanese medaka (Oryzias latipes) is a valuable model organism in reproductive and developmental toxicity testing. The purpose of this experiment is to assess the response of medaka to aquatic estrogen exposure over the course of 1 year. Each week, three pairs of adult male medaka were exposed separately for 4 days (100% static renewal daily) to 17beta-estradiol at a nominal level of 25 microg/l, with a fourth pair of fish exposed separately to an ethanol control. Vitellogenin (VTG) induction was observed each week, with hepatic and plasma VTG levels significantly higher (P < 0.001) than reported for ethanol control specimens. A significant (P < 0.001) increasing trend was observed for plasma VTG results over the duration of the study, whereas a decreasing trend (P = 0.030) of hepatic VTG was evident. A Durbin-Watson test, however, did not demonstrate any serial autocorrelation of hepatic (d = 1.180) or plasma (d = 1.311) VTG levels over the duration of the study. Time-series transformations of the hepatic and plasma VTG data did not reveal any significant seasonal or behavioral patterns. However, significant intermittent peaks in VTG production were observed in both tissue types during the study. These data indicate that some consideration must be taken to time long-term medaka exposures (>20 weeks) in order to eliminate any influence of cyclic changes on plasma VTG response. Alternatively, hepatic cytosolic measurement of VTG appears to show a more sensitive response to aquatic estrogen exposure.

Basin-Specific Pollutant Bioaccumulation Patterns Define Lake Huron Forage Fish.

The Lake Huron ecosystem is unique among the Laurentian Great Lakes (USA/Canada) in that its surface area encompasses 3 distinct basins. This ecosystem recently experienced significant ecological restructuring characterized by changes in primary production, species dominance and abundances, and top predator energy dynamics. However, much of the evidence for this restructuring has been largely derived from biomonitoring data obtained from long-term sampling of the lake's Main Basin. We examined polychlorinated biphenyl (PCB) concentrations and the stable isotopes of carbon (δ13 C) and nitrogen (δ15 N) in rainbow smelt (Osmerus mordax), bloater (Coregonus hoyi), and round goby (Neogobius melanostomus) to determine spatial variability in these environmental markers as indicators of the ubiquity of trophic restructuring throughout Lake Huron. Stable isotopes indicated that North Channel fish occupied trophic positions between 0.5 and 1.0 lower relative to Main Basin and Georgian Bay conspecifics, respectively. Sum PCB concentrations for 41 congeners were highest for fish from the Main Basin (27.5 ± 3.0 ng g-1 wet wt) and Georgian Bay (26.3 ± 3.4 ng g-1 wet wt) relative to North Channel (13.6 ± 1.2 ng g-1 wet wt) fish. Discriminant functions analysis demonstrated basin-specific PCB congener profiles with individual species also having distinct profiles dependent on their basin of collection. These bioaccumulation patterns among Lake Huron forage fish mirror those reported for lake trout in this lake and indicate that the degree of food-web ecological restructuring in Lake Huron is not equivalent across the basins. Specifically, basin-specific PCB congener profiles demonstrated that differences among Lake Huron secondary and top predator consumer species are likely dictated by cross-basin differences in zooplankton community ecology and trophodynamics that can regulate the efficiencies of prey energy transfer and PCB congener bioaccumulation patterns in aquatic food webs. Environ Toxicol Chem 2020;39:1712-1723. © 2020 SETAC.

Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration.

Benthic environmental impact assessments and monitoring programs accompanying offshore hydrocarbon industry activities result in large collections of benthic organisms. Such collections offer great potential for systematics, biodiversity and biogeography research, but these opportunities are only rarely realised. In recent decades, the hydrocarbon industry has started exploration activities in offshore waters off the Falkland Islands. A large collection of ca. 25,000 polychaete (Annelida) specimens, representing some 233 morphological species was processed at the Natural History Museum, London. Taxonomic assessment led to recognition of many polychaete species that are new to science. The existing taxonomic literature for the region is outdated and many species in existing literature are likely misidentifications. Initially, an online taxonomic guide (http://falklands.myspecies.info) was created, to provide a single taxonomic source for 191 polychaete species to standardise identification across different environmental contractors working in Falkland Islands. Here, this effort is continued to make data available for 18,015 specimens through publication of raw biodiversity data, checklist with links to online taxonomic information and formal descriptions of five new species. New species were chosen across different families to highlight the taxonomic novelty of this area: Apistobranchus jasoni Neal & Paterson, sp. nov. (Apistobranchidae), Leitoscoloplos olei Neal & Paterson, sp. nov. (Orbiniidae), Prosphaerosyllis modinouae Neal & Paterson, sp. nov. (Syllidae) and Aphelochaeta falklandica Paterson & Neal, sp. nov., and Dodecaceria saeria Paterson & Neal, sp. nov. (both Cirratulidae). The potential of the Falkland Islands material to provide up to date informationfor known species described in the literature is also highlighted by publishing images and redescription of Harmothoe anderssoni Bergström, 1916 and Aphelochaeta longisetosa (Hartmann-Schröder, 1965). Biodiversity and abundance data are made available through a DarwinCore database, including material collected from 83 stations at Sea Lion developmental oil field in North Falklands Basin and voucher specimens' data collected from exploratory oil wells in East Falklands Basin.

Hypoxia Modulates Platelet Purinergic Signalling Pathways.

BACKGROUND: Hypoxia resulting from ascent to high-altitude or pathological states at sea level is known to increase platelet reactivity. Previous work from our group has suggested that this may be adenosine diphosphate (ADP)-specific. Given the clinical importance of drugs targeting ADP pathways, research into the impact of hypoxia on platelet ADP pathways is highly important. METHODS: Optimul aggregometry was performed on plasma from 29 lowland residents ascending to 4,700 m, allowing systematic assessment of platelet reactivity in response to several platelet agonists. Aggregometry was also performed in response to ADP in the presence of inhibitors of the two main ADP receptors, P2Y1 and P2Y12 (MRS2500 and cangrelor, respectively). Phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a key determinant of platelet aggregation, was analysed using the VASPFix assay. RESULTS: Hypobaric hypoxia significantly reduced the ability of a fixed concentration of cangrelor to inhibit ADP-induced aggregation and increased basal VASP phosphorylation. However, in the absence of P2Y receptor inhibitors, we did not find evidence of increased platelet sensitivity to any of the agonists tested and found reduced sensitivity to thrombin receptor-activating peptide-6 amide. CONCLUSION: Our results provide evidence of increased P2Y1 receptor activity at high altitude and suggest down-regulation of the P2Y12 pathway through increased VASP phosphorylation. These changes in ADP pathway activity are of potential therapeutic significance to high-altitude sojourners and hypoxic sea level patients prescribed platelet inhibitors and warrant further investigation.

Pesticides related to land use in watersheds of the Great Lakes basin.

In this study, we evaluated the distribution and concentrations of a range of neonicotinoid insecticides (NNIs) and other insecticides, fungicides, biocides and selected herbicides in watersheds that drain into the lower Great Lakes in Ontario, Canada. Polar Organic Chemical Integrative Samplers (POCIS) were deployed in 18 watersheds during late May to late June of 2016. Grab samples were also collected in 7 of these watersheds. There was generally good agreement between the time-weighted average concentrations of pesticides estimated from the POCIS and the concentrations detected in grab samples. The NNIs, thiamethoxam, clothianidin and imidacloprid, were present in several watersheds at concentrations that exceeded the Canadian Water Quality Guideline for imidacloprid of 0.23 µg/L. The new generation insecticides, flonicamid and flupyradifurone were also detected in some watersheds, which is the first report of these pesticides in the peer-reviewed literature. Atrazine, 2,4-D, dicamba, carbendazim, thiophanate methyl and several azole-based fungicides were also widely detected. Discriminant Function Analysis (DFA) indicated that a high proportion (i.e. >80%) of the watersheds could be discriminated from each other on the basis of the pattern of pesticides detected in surface waters, and the proportion of field crops in the watershed.

Importance of growth rate on mercury and polychlorinated biphenyl bioaccumulation in fish.

To evaluate the effect of fish growth on mercury (Hg) and polychlorinated biphenyl (PCB) bioaccumulation, a non-steady-state toxicokinetic model, combined with a Wisconsin bioenergetics model, was developed to simulate Hg and PCB bioaccumulation in bluegill (Lepomis macrochirus). The model was validated by comparing observed with predicted Hg and PCB 180 concentrations across 5 age classes from 5 different waterbodies across North America. The non-steady-state model generated accurate predictions for Hg and PCB bioaccumulation in 3 of 5 waterbodies: Apsey Lake (ON, Canada), Sharbot Lake (ON, Canada), and Stonelick Lake (OH, USA). The poor performance of the model for the Detroit River (MI, USA/ON, Canada) and Lake Hartwell (GA/SC, USA), which are 2 well-known contaminated sites with possibly high heterogeneity in spatial contamination, was attributed to changes in feeding behavior and/or prey contamination. Model simulations indicate that growth dilution is a major component of contaminant bioaccumulation patterns in fish, especially during early life stages, and was predicted to be more important for hydrophobic PCBs than for Hg. Simulations that considered tissue-specific growth provided some improvement in model performance particularly for PCBs in fish populations that exhibited changes in their whole-body lipid content with age. Higher variation in lipid growth compared with that of lean dry protein was also observed between different bluegill populations, which partially explains the greater variation in PCB bioaccumulation slopes compared with Hg across sampling sites. Environ Toxicol Chem 2018;37:1655-1667. © 2018 SETAC.