Critical Body Residue Research Articles

Assessing chronic effects of chemical pollution on biodiversity using mean species abundance relationships.

Since chemical pollution poses a persistent threat to freshwater ecosystems and biodiversity, innovative methodologies are required to address the ecological risks associated with such pollutants. This study predicts the long-term impacts of chemicals based on an equation that describes the time-dependency of the median lethal and effect concentration (L(E)C50) with the Critical Body Residue concept. This way, the methodology can predict Species Sensitivity Distributions (SSDs) for any given time point. The methodology was extended to predict the Mean Species Abundance Relationships (MSAR) as an indicator of biodiversity. To test and validate the methodology, data from a case study with six freshwater arthropods exposed short- and long-term to imidacloprid was used. The potentially affected fraction of species (PAF) and its opposite (1-PAF) was used to validate the MSAR framework itself. The accuracy of the predicted chronic median lethal concentration (LC50) values was species-dependent. However, except for one species, all predicted chronic LC50 values were within the 95% Confidence Intervals (CIs) of the fits based on only acute data. The mean differences between the predicted and calculated MSARs were between 2% and 6%. The predicted MSARs generally underestimated the impact of imidacloprid. However, all predicted MSARs were either similar or lower than the calculated 1-PAF, and their CIs covered the calculated MSARs. Thus, the study found that the presented methodology is useful for predicting the long-term effects of chemical pollutants.

Temperate Versus Arctic: Unraveling the Effects of Temperature on Oil Toxicity in Gammarids.

Shipping activities are increasing with sea ice receding in the Arctic, leading to higher risks of accidents and oil spills. Because Arctic toxicity data are limited, oil spill risk assessments for the Arctic are challenging to conduct. In the present study, we tested if acute oil toxicity metrics obtained at temperate conditions reflect those at Arctic conditions. The effects of temperature (4 °C, 12 °C, and 20 °C) on the median lethal concentration (LC50) and the critical body residue (CBR) of the temperate invertebrate Gammarus locusta exposed to water accommodated fractions of a fuel oil were determined. Both toxicity metrics decreased with increasing temperature. In addition, data for the temperate G. locusta were compared to data obtained for Arctic Gammarus species at 4 °C. The LC50 for the Arctic Gammarus sp. was a factor of 3 higher than that for the temperate G. locusta at 4 °C, but its CBR was similar, although both the exposure time and concentration were extended to reach lethality. Probably, this was a result of the larger size and higher weight and total lipid content of Arctic gammarids compared to the temperate gammarids. Taken together, the present data support the use of temperate acute oil toxicity data as a basis for assessing risks in the Arctic region, provided that the effects of temperature on oil fate and functional traits (e.g., body size and lipid content) of test species are considered. As such, using the CBR as a toxicity metric is beneficial because it is independent of functional traits, despite its temperature dependency. To the best of our knowledge, the present study is the first to report CBRs for oil. Environ Toxicol Chem 2024;43:1627-1637. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

QSAR assessment of aquatic toxicity potential of diverse agrochemicals

ABSTRACT The fast-increasing number of commercially produced chemicals challenges the experimental ecotoxicity assessment methods, which are costly, time-consuming, and dependent on the sacrifice of animals. In this regard, Quantitative Structure-Property/Activity Relationships (QSPR/QSAR) have led the way in developing ecotoxicity assessment models. In this study, QSAR models have been developed using the pEC50 values of 82 diverse agrochemicals or agro-molecules against a planktonic crustacean Daphnia magna with easily interpretable 2D descriptors. Moreover, a link among octanol-water partition coefficient (KOW), bio-concentration factor (BCF), and critical body residue (CBR) has been addressed, and their imputation for the prediction of the toxicity endpoint (EC50) has been done with an objective of the advanced exploration of several ecotoxicological parameters for toxic chemicals. The developed partial least squares (PLS) models were validated rigorously and proved to be robust, sound, and immensely well-predictive. The final Daphnia toxicity model derived from experimental derived properties along with computed descriptors emerged better in statistical quality and predictivity than those obtained solely from computed descriptors. Additionally, the pEC50 and other important properties (log KOW, log BCF, and log CBR) for a set of external agro-molecules, not employed in model development, were predicted to show the predictive ability of the models.

Toxicological risk of mercury for fish and invertebrate prey in the Arctic.

We assessed the risks of mercury (Hg) to Arctic marine and freshwater fish by compiling published muscle Hg concentrations and information on tissue concentrations associated with adverse effects. The assessment included 333 groups of fish representing 35 genera and 14,002 individuals sampled from sites across the circumpolar Arctic. Mean or median Hg concentrations in fish muscle varied widely from 0.005 μg/g ww to a maximum of 2.2 μg/g ww. Results indicate that most (n = 139 of 333 or ~ 42%) Arctic fish are not at risk for Hg toxicity, based on the large number of fish mean or median muscle Hg concentrations below 0.1 μg/g ww. A smaller number of the identified groups (n = 76 of 333 or ~ 23%) of Arctic fish had mean or median Hg concentrations consistent with moderate (0.3-0.5 μg/g ww), high (0.5-2 μg/g ww), and severe risk (≥2 μg/g ww). Most of the fish with Hg concentrations in these risk categories were long-lived predators (e.g., non-anadromous Arctic char, northern pike, lake trout, Greenland halibut, Greenland shark). We also, for the first time, conducted a risk assessment of Arctic marine and freshwater invertebrates to evaluate the potential for Hg effects at lower trophic levels and to support risk assessment for Arctic fish. The vast majority (90%) of site-specific Hg or methylmercury (MeHg) concentrations in taxa of marine and freshwater invertebrates (n = 321) were < 0.5 μg/g dw, which is well below critical body residues of Hg in aquatic invertebrates associated with acute and sublethal effects determined in laboratory dosing studies. As the screening-level approach we carried out in the present study is not indicative of actual effects, more studies which directly evaluate the effects of Hg exposure in Arctic fish species are needed. The information here will be of use to Article 22 (Effectiveness Evaluation) of the Minamata Convention.

The impact of exposure timing on embryo mortality and the partitioning of PAHs when cod eggs are exposed to dispersed and dissolved crude oil

During sub-sea oil spills to the marine environment, oil droplets will rise towards the sea surface at a rate determined by their density and diameter as well as the vertical turbulence in the water. Micro-droplets (< 50 µm) are expected to have prolonged residence times in the water column. If present, pelagic fish eggs may thus be exposed to dispersed oil from subsurface oil spills for days, and the contribution of these micro-droplets to toxicity is not well known. The purpose of this work was to investigate to what extent timing of exposure and the presence of oil micro droplets affects PAH uptake and survival of pelagic Atlantic cod eggs. A single batch of eggs was separated in two groups and exposed to dispersions and corresponding water-soluble fraction at 3–7 days (Early exposure) and 9–13 days (Late exposure) post fertilization. Partitioning of PAHs between crude oil microdroplets, water and eggs was estimated as well as the contribution of oil droplets to PAH body residue and acute and delayed mortality. Timing of oil exposure clearly affects both the mortality rate and the timing of mortality. Even though the body residue of PAHs were lower when embryos were exposed in the later embryonic stage, mortality rate increased relative to the early exposure indicating that critical body residue threshold is stage specific. Although our results suggest that the dissolved fraction is the dominating driver for toxicity in cod embryos exposed to oil dispersions, crude oil micro droplets contribute to increased mortality as well.

Sensitivity of Freshwater Australian Bass (Macquaria novemaculeata) and Silver Perch (Bidyanus bidyanus) to Waterborne Antimony: Exposure–Dose–Response Characteristics and Ion Homeostasis

We conducted acute toxicity studies using semi-static protocols to examine the lethal responses of Australian bass and silver perch exposed to antimony (Sb) oxidation states in Sb(III) (10.5-30.5mg L-1) and Sb(V) (95.9-258.7mg L-1). Bioavailability and the effects of Sb on body ion regulation (Na, Ca, Mg, and K) were also investigated. Antimony species-specific effects were observed with exposure to both Sb oxidation states. Median lethal concentrations (LC50s) for Sb(III) were 13.6 and 18mg L-1 for Australian bass and silver perch, respectively, and the LC50 for Sb(V) in Australian bass was 165.3mg L-1. The LC50 could not be calculated for silver perch exposed to Sb(V) as the maximum exposure concentrations produced 40% mortality but a larger-than value of > 258.7mg L-1 was estimated. Relative median potency values derived from the LC50s were 0.1 Sb(III) and 12.2 and 16.6 Sb(V) for Australian bass and silver perch, respectively, demonstrating greater toxicity of Sb(III) to both fish species. Antimony uptake in fish was observed. Median critical body residue (CBR50) values of 77.7 and 26.6mgkg-1 for Sb(III) were estimated for Australian bass and silver perch, respectively, and 628.1mgkg-1 for Sb(V) in Australian bass. Bioconcentration factors (BCFs) for both Sb(III) and Sb(V) did not change with exposure but the greater BCFs for fish exposed to Sb(III) indicate that it is more bioavailable than Sb(V) in acute exposure. No effects on whole-body Na, Ca, Mg, or K ions were observed with fish exposure to either Sb species.

Evaluation of modes of action of pesticides to Daphnia magna based on QSAR, excess toxicity and critical body residues

Agricultural pesticides serve as effective controls of unwanted weeds and pests. However, these same chemicals can exert toxic effects in non-target organisms. To determine chemical modes of action, the toxicity ratio (TR) and critical body residues (CBRs) of 57 pesticides were calculated for Daphnia magna. Results showed that the CBR values of inert compounds were close to a constant while the CBR values of pesticides varied over a wider range. Although herbicides are categorized as specifically-acting compounds to plants, herbicides did not exhibit excess toxicity to Daphnia magna and were categorized as inert compounds with an average logTR = 0.41, which was less than a threshold of one. Conversely, fungicides and insecticides exhibited strong potential for toxic effects to Daphnia magna with an average logTR >2. Many of these chemicals act via disruption of the nervous, respiratory, or reproductive system, with high ligand-receptor binding activity which leads to higher toxicity for Daphnia magna. Molecular docking using acetylcholinesterase revealed that fungicides and insecticides bind more easily with the biological macromolecule when compared with inert compounds. Quantitative structure-activity relationship (QSAR) analysis revealed that the toxicity of fungicides was mainly dependent upon the heat of formation and polar surface area, while the toxicity of insecticides was more related to hydrogen-bond properties. This comprehensive analysis reveals that there are specific differences in toxic mechanisms between fungicides and insecticides. These results are useful for determining relative risk associated with pesticide exposure to aquatic crustaceans, such as Daphnia magna.

Relationship among the acute toxicity, critical body residue, and bioconcentration of ortho-dinitrobenzene in zebrafish (Danio rerio) based on toxicokinetics.

The internal critical concentration represented by the critical body residue (CBR) is an ideal indicator for reflecting the toxicity of a chemical. Although some authors have realized that the CBR50 can be calculated from the LC50 via the bioconcentration factor (BCF), the effects of exposure time and exposure concentration on the relationship between the LC50 and CBR50 have not been investigated to date. In this paper, the LC50 and CBR50 of ortho-dinitrobenzene in zebrafish were experimentally determined and their relationship was investigated. The results showed that ortho-dinitrobenzene exhibited excess toxicity and cannot completely be identified as a reactive compound based on toxic ratio. Comparison of the measured CBR50 and the CBR50 calculated from the LC50 via the BCF showed that there was a 0.46 log unit difference. Investigation of the relationship between the concentration in fish calculated by the toxicokinetic model and exposure time showed that the bio-uptake of fish was fast and reached a steady state in the toxicity test, indicating that the difference in CBR50 values could not be attributed to the different exposure times used in toxicity and BCF assays. On the other hand, investigation of the measured bioconcentration ratio (BCR) showed that the BCR (or BCFapp) decreased with increasing exposure concentration. Compared with the CBR50 calculated from the LC50 via the BCF, the CBR50 calculated from the LC50 via the BCFapp is close to the measured CBR50, suggesting that the difference in CBR50 values is attributed to the different exposure concentrations used in the BCF and toxicity assays.

Assessment of potential mercury toxicity to native invertebrates in a high-gradient stream.

This study evaluated potential effects of mercury (Hg) on benthic macroinvertebrates in the South River, Virginia, USA. The study used a multiple lines of evidence approach, including spatially and temporally matched sediment chemistry, biological, and toxicological information (Sediment Quality Triad), exposure and effect analysis in bulk and interstitial sediment and interstitial water, and critical body residue analysis. Ten-day Chironomus dilutus and Hyalella azteca toxicity tests established site-specific no-effect concentrations (NOEC) at 18.9 μg/g total Hg (THg) and 102 ng/g methylmercury (MeHg). However, the benthic community at these locations was impaired, with lower mayfly and caddisfly composition. Few locations had concentrations of THg and MeHg that exceeded the NOEC in bulk or interstitial sediment. The THg concentrations in interstitial water were far below concentrations expected to reduce survival in benthic invertebrates, and only a low percentage of samples exceeded sublethal (growth) low-effect concentrations (LOEC) for THg or MeHg. The THg concentrations in invertebrate tissue did not exceed the NOEC or LOEC in the South River, and MeHg concentrations exceeded the LOEC at all locations, including those with no evidence of benthic impairment, illustrating the uncertainty associated with this line of evidence. Finally, statistical modeling that evaluated diversity of sensitive invertebrate species as a function of Hg exposure, geomorphological parameters, and physicochemical variables indicated that physicochemical and geomorphological parameters were most predictive of benthic community; where Hg was indicated, we were unable to distinguish between models with or without interstitial water Hg. Overall, the lines of evidence indicate that Hg, while clearly toxic to invertebrates at sufficiently high exposure concentrations, is not negatively impacting invertebrate communities in the South River. This study illustrates the difficulty of assessing risks to invertebrates using traditional tools of risk assessment and identifies critical gaps in knowledge that complicate the management of Hg risk. Integr Environ Assess Manag 2019;00:000-000. © 2019 SETAC.

Benzo(a)pyrene inhibits the accumulation and toxicity of cadmium in subcellular fractions of Eisenia fetida

Cadmium (Cd) and benzo [a]pyrene (BaP) often co-occur in the environment, and the critical body residue of organisms is used as an indicator of the toxic effects of contaminants. However, little is known about their distributions and toxicities when pollution of Cd and BaP are combined. Semi-static solution culture experiment was used to study the impacts of BaP on the subcellular distribution of the toxic metal Cd in the earthworm Eisenia fetida. We explored the mechanisms by which this organism responds to combined exposure to these pollutants by measuring the protein content of each of three subcellular fractions, as well as acetylcholinesterase (AChE) and glutathione S-transferase (GST) activities. The subcellular partitioning of Cd was heterogeneous and Cd mainly accumulated in the cytosolic fraction (Fraction C), which was previously reported to be involved in metal immobilization. In Fraction C, Cd accumulation was correlated with the external concentration to which the earthworm had been exposed; however, in the presence of BaP, Cd accumulation was inhibited and plateaued at high external Cd concentrations. A principal component analysis revealed that this decreased Cd accumulation might be caused by increases in GST activity, which likely increased the excretion of Cd. BaP was also found to stimulate protein biosynthesis and upregulate AChE and GST activities in the debris fraction (Fraction E), indicating other potential detoxification mechanisms in this fraction. Granule fraction (Fraction D) had a lower protein content, AChE and GST activities than the other subcellular fractions, supporting previous findings that Fraction D is largely inert.

Investigation on the relationship between critical body residue and bioconcentration in zebrafish based on bio-uptake kinetics for five nitro-aromatics

It is well known that the critical body residue (CBR) can be estimated via bioconcentration factor (BCF). However, the relationship between CBR and BCF in zebrafish has not been carried out based on bio-uptake kinetics for nitro-aromatics. In this paper, the time-variable concentrations and CBRs in zebrafish were determined for five nitro substituted benzenes. The result shows that CBR values can well be calculated from the BCF and external critical concentrations (LC50). Although CBRs measured from 5 h exposure period are greater than the CBRs obtained from 96 h for the five nitro-aromatics, no significant difference was observed, indicating that the CBR approach is a truer measure of chemical levels in exposed organisms and an ideal indicator to reflect the toxicity of a chemical. The bio-uptake can well be described by first-order kinetics and reach steady-state within 48 h. Almost same BCF values are obtained from the ratio of concentration in the fish (Cf) and in the water (Cw) at apparent steady-state and the ratio of the rate constants of uptake (k1) and depuration (k2) assuming first-order kinetics. The toxicity ratio (TR) can reflect the difference of internal critical concentrations and be used to identify mode of action.

Spatiotemporal heterogeneity of antibiotic pollution and ecological risk assessment in Taihu Lake Basin, China

Natural lakes play a vital role as receiving system of a cocktail of antibiotics (ABs) which have triggered a major health concern. The comparisons of ABs concentrations have been substantially implemented throughout the worldwide range. However, from lake management, the questions are not yet adequately solved: “when and where does the overall pollution level of ABs present more serious, and what AB species dominate”. In this study, we detected 22 ABs in water column and sediment bottom in Taihu Lake Basin in January, April, July and October in 2017. Non-metric multi-dimensional scaling (NMDS) was applied to characterize spatiotemporal dissimilarity of ABs concentrations. Combined with a method of summed standardized concentrations, analysis of variance was applied to evaluate the overall pollution level of ABs at different sites and time periods, instead of, traditionally, a comparison of concentration. The results showed that 90% CI of Macrolides, Sulfonamides, Tetracyclines and Quinolones were 0.020–5.646, 0.040–7.887, 0.100–13.308 and 0.130–9.631 ng/L in water column, respectively; and 0.005–1.532, 0.002–0.120, 0.010–0.902 and 0.006–3.972 μg/kg in sediment, respectively. ABs concentrations approximately presented spatial homogeneity in the whole basin which included all main inflow rivers, outflow rivers and the lake body itself. Species composition was seasonally distinct and the overall pollution level was significantly lower in autumn. A critical body residue analysis showed that ABs concentrations presented a neglectable cumulative risk for fish species. This research added to the body of knowledge to develop pollution management strategies on point and non-point source loads for Taihu Lake Basin, and also the methodology provided reference for spatiotemporal characterization of dissolved pollutant in other water bodies.

Immunologic, reproductive, and carcinogenic risk assessment from POP exposure in East Greenland polar bears (Ursus maritimus) during 1983–2013

Polar bears (Ursus maritimus) are among the world's highest trophic level marine predators and as such have some of the highest tissue concentrations of organohalogen contaminants (OHCs) among Arctic biota. In this paper we present the results of a three decade (1983–2013) risk assessment of OHC exposure and effects on reproduction, immunity, and cancer (genotoxicity) in polar bears from Central East Greenland. Risk of adverse effects are evaluated using a risk quotient (RQ) approach with derivation from measured OHC concentrations in polar bear tissue and critical body residues (CBR) extrapolated for polar bears using physiologically-based pharmacokinetic modelling (PBPK). The additive RQs for all OHCs in polar bears were above the threshold for all effect categories (RQ > 1) in every year, suggesting this population has been at significant and continuous risk of contaminant-mediated effects for over three decades. RQs peaked in 1983 (RQ > 58) and again in 2013 (RQ > 50) after a period of decline. These trends follow ΣPCB levels during that time, and contributed almost all of the risk to immune, reproductive, and carcinogenic effects (71–99% of total RQ). The recent spike in RQs suggests a major shift in polar bear contaminant exposure from climate related changes in food composition and hereby the increased risk of adverse health effects. In the context of lifetime exposure ΣPCB and PFOS levels showed the interactive importance of year of birth, age, and emission history. In conclusion, the results indicate that East Greenland polar bears have been exposed to OHC levels over the period of 1983–2013 that potentially and continuously affected individual and theoretically also population health, with a peaking risk in the more recent years.

The chemical exposure toxicity space (CETS) model: Displaying exposure time, aqueous and organic concentration, activity, and onset of toxicity.

A 1‐compartment toxicokinetic model is used to characterize the chemical exposure toxicity space (CETS), providing a novel graphic tool that can aid in the design of aquatic toxicity tests for fish and for interpreting their results. The graph depicts the solution to the differential equation describing the uptake kinetics of a chemical by a modeled fish under conventional bioassay conditions. The model relates the exposure concentration in the water to a dimensionless time and the onset of toxicity as determined by an estimated or assumed critical body residue or incipient lethal aqueous concentration. These concentration graphs are specific to each chemical and exposure and organism parameters and clearly demonstrate differences in toxicity between chemicals and how factors such as hydrophobicity influence the toxic endpoint. The CETS plots can also be used to assess bioconcentration test conditions to ensure that concentrations are well below toxic levels. Illustrative applications are presented using a recent set of high‐quality toxicity data. Conversion of concentrations to chemical activities in the plots enables results for different baseline toxicants to be superimposed. For chemicals that have different modes of toxic action, the increased toxicity then becomes apparent. Implications for design and interpretation of aquatic toxicity tests are discussed. The model, and pictorial visualization of the time‐course of aquatic toxicity tests, may contribute to improvements in test design, implementation, and interpretation, and to reduced animal usage. Environ Toxicol Chem 2017;36:1389–1396. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Bioaccumulation of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and hexachlorobenzene by three Arctic benthic species from Kongsfjorden (Svalbard, Norway)

The predicted expansion of oil and gas (O&G) activities in the Arctic urges for a better understanding of impacts of these activities in this region. Here we investigated the influence of location, feeding strategy and animal size on the bioaccumulation of Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs) and Hexachlorobenzene (HCB) by three Arctic benthic species in Kongsfjorden (Svalbard, Norway). No toxicity was expected based on biota PAH critical body residues. Biota PCB levels were mainly below limit of detection, whereas samples were moderately polluted by HCB. PAH concentrations in biota and Biota Sediment Accumulation Factors (BSAFs) were generally higher in Blomstrandhalvøya than in Ny-Ålesund, which was explained by a higher abundance of black carbon in Ny-Ålesund harbour. BSAFs differed significantly among species and stations. We conclude that contaminant body residues are a less variable and more straightforward monitoring parameter than sediment concentrations or BSAFs in Arctic benthos.

A fugacity-based toxicokinetic model for narcotic organic chemicals in fish.

A novel dynamic fugacity-based model is described, developed, and tested that simulates the uptake of narcotic organic chemicals in fish from water as occurs in aquatic bioconcentration and toxicity tests. The physiologically based toxicokinetic model treats the time course of chemical distribution in 4 compartments (tissue groups) in the fish, including the liver, in which biotransformation may occur. In addition to calculating bioconcentration and toxicokinetics, 5 possible toxic endpoints are defined corresponding to chemical concentration, fugacity, or activity reaching a critical value that causes 50% mortality. The mathematical description of multicompartment uptake is simplified by expressing the equations in the fugacity format. The model is parameterized and tested against reported empirical data for the bioconcentration of pentachloroethane in rainbow trout and for uptake and mortality from aquatic exposures to naphthalene and 1,2,4-trichlorobenzene in fathead minnows. Model performance is evaluated, and it is concluded that with suitable parameterization it has potential for application for assessment of both bioconcentration and toxicity expressed as median lethal concentrations, critical body residues, and chemical activity as a function of time to death.

Discrimination of excess toxicity from baseline level for ionizable compounds: Effect of pH.

The toxic effect can be affected by pH in water through affecting the degree of ionization of ionizable compounds. Wrong classification of mode of action can be made from the apparent toxicities. In this paper, the toxicity data of 61 compounds to Daphnia magna determined at three pH values were used to investigate the effect of pH on the discrimination of excess toxicity. The results show that the apparent toxicities are significantly less than the baseline level. Analysis on the effect of pH on bioconcentration factor (BCF) shows that the log BCF values are significantly over-estimated for the strongly ionizable compounds, leading to the apparent toxicities greatly less than the baseline toxicities and the toxic ratios greatly less than zero. A theoretical equation between the apparent toxicities and pH has been developed basing on the critical body residue (CBR). The apparent toxicities are non-linearly related to pH, but linearly to fraction of unionized form. The determined apparent toxicities are well fitted with the toxicities predicted by the equation. The toxicities in the unionized form calculated from the equation are close to, or greater than the baseline level for almost all the strongly ionizable compounds, which are very different from the apparent toxicities. The studied ionizable compounds can be either classified as baseline, less inert or reactive compounds in D. magna toxicity. Some ionizable compounds do not exhibit excess toxicity at a certain pH, due not to their poor reactivity with target molecules, but because of the ionization in water.

Risk evaluation of the Arctic environmental POP exposure based on critical body residue and critical daily dose using captive Greenland sledge dogs (Canis familiaris) as surrogate species

The risk from POP (persistent organic pollutant) exposure and subsequent reproductive, immunotoxic and liver histopathological effects was evaluated in a classical parallel trial on Greenland sledge dogs (Canis familiaris) fed contaminated minke whale (Balaenoptera acutorostrata) blubber. First the critical body residues (CBRs) were estimated using the physiologically-based pharmacokinetic (PBPK) model for seven POP compounds based on rat critical daily doses (CDDs). These were then compared with the actual daily oral POP doses (DD) and body residues (BR) in the sledge dogs by calculating risk quotients (RQDD: DD/CDD; RQBR: BR/CBR; ≥1 indicates risk). The results showed that risk quotients for reproductive, immunotoxic and liver histopathological effects were significantly lowest in the control group (p<0.01) while risk quotients based on daily doses (RQDD) were significantly lower than RQs based on body residues (RQBR) (all p<0.01). RQBR in the exposed group ranged from 1.0–12 for reproductive and immunotoxic effects while those for liver histopathological effects ranged from 0.7–3.0. PCBs (polychlorinated biphenyls) and chlordanes were the dominant driver behind high immune and reproductive RQs while dieldrin was the most important factor behind RQs for liver histopathology. Principal component analyses and Spearman rank correlation analyses showed that complement and cellular immune parameters were significantly negative correlated with RQBR (all p<0.05) while logistic regression showed that RQDD had a significant effect on the number of born cups (p=0.03). No significantly relations were found between RQs and hormone concentrations, number of gestations, antibody titres or liver histopathology. These results confirm previous studies showing that POP exposure negatively impacts steroid hormones, various immune parameters, as well as liver histopathology in sledge dogs. It is also clear that RQBR is the best reflector of health effects from POP exposure and that it is especially accurate in predicting immune and reproductive effects. We recommend that PBPK modelled (CBR) and RQBR should be used in the assessment of POP exposure and health effects in Arctic top predators.

Re-analysis of narcotic critical body residue data using the equilibrium distribution concept and refined partition coefficients.

Narcosis occurs as a result of the accumulation of chemicals in the phospholipid membrane. The toxic threshold concentration in the membrane is thought to be relatively constant across different chemicals and species. Hence, estimating chemical concentrations in the membrane is expected to reduce the variability of narcotic critical body residue (CBR) data. In this study, a high quality CBR dataset for three aquatic species reported recently in the literature was evaluated with the internal equilibrium distribution concept. The raw wet-weight-based CBR values were converted to membrane-weight-based CBR values by assuming that the chemical is distributed in storage lipids, membranes, proteins, and water according to the respective equilibrium partition coefficients. Several sets of partition coefficients were compared for this analysis. The results were consistent with the notion that the use of a structural protein instead of serum albumin as a surrogate for the body protein fraction could reduce the variability of CBRs. Partition coefficients predicted by polyparameter linear free energy relationships (PP-LFERs) reduced the variability of CBRs as much as or even more than experimental partition coefficients did. It is suggested that CBR data for chemicals with larger structural diversity and biological species with more distinct compositions are needed to evaluate further the equilibrium distribution concept and the constant membrane threshold hypothesis.

Mercury tissue residue approach in Chironomus riparius: Involvement of toxicokinetics and comparison of subcellular fractionation methods

Along with the growing body of evidence that total internal concentration is not a good indicator of toxicity, the Critical Body Residue (CBR) approach recently evolved into the Tissue Residue Approach (TRA) which considers the biologically active portion of metal that is available to contribute to the toxicity at sites of toxic action. For that purpose, we examined total mercury (Hg) bioaccumulation and subcellular fractionation kinetics in fourth stage larvae of the midge Chironomus riparius during a four-day laboratory exposure to Hg-spiked sediments and water. The debris (including exoskeleton, gut contents and cellular debris), granule and organelle fractions accounted only for about 10% of the Hg taken up, whereas Hg concentrations in the entire cytosolic fraction rapidly increased to approach steady-state. Within this fraction, Hg compartmentalization to metallothionein-like proteins (MTLP) and heat-sensitive proteins (HSP), consisting mostly of enzymes, was assessed in a comparative manner by two methodologies based on heat-treatment and centrifugation (HT&C method) or size exclusion chromatography separation (SECS method). The low Hg recoveries obtained with the HT&C method prevented accurate analysis of the cytosolic Hg fractionation by this approach. According to the SECS methodology, the Hg-bound MTLP fraction increased linearly over the exposure duration and sequestered a third of the Hg flux entering the cytosol. In contrast, the HSP fraction progressively saturated leading to Hg excretion and physiological impairments. This work highlights several methodological and biological aspects to improve our understanding of Hg toxicological bioavailability in aquatic invertebrates.