Bioconcentration, biotransformation and elimination of pyrene in the arctic crustacean Gammarus setosus (Amphipoda) at two temperatures

Microbial machinery dealing diverse aromatic compounds: Decoded from pelagic sediment ecogenomics in the gulfs of Kathiawar Peninsula and Arabian Sea

Aromatic hydrocarbons are persistent pollutants in aquatic systems as endocrine disruptors, significantly impacting natural ecosystems and human health. Microbes perform as natural bioremediators to remove and regulate aromatic hydrocarbons in the marine ecosystem. The present study focuses upon the comparative diversity and abundance of various hydrocarbon-degrading enzymes and their pathways from deep sediments along the Gulf of Kathiawar Peninsula and Arabian Sea, India. The elucidation of large number of degradation pathways in the study area under the presence of a wide range of pollutants whose fate needs to be addressed. Sediment core samples were collected, and the whole microbiome was sequenced. Analysis of the predicted ORFs (open reading frames) against the AromaDeg database revealed 2946 aromatic hydrocarbon-degrading enzyme sequences. Statistical analysis portrayed that the Gulfs were more diverse in degradation pathways compared to the open sea, with the Gulf of Kutch being more prosperous and more diverse than the Gulf of Cambay. The vast majority of the annotated ORFs belonged to groups of dioxygenases that included catechol, gentisate, and benzene dioxygenases, along with Rieske (2Fe-2S) and vicinal oxygen chelate (VOC) family proteins. From the sampling sites, only 960 of the total predicted genes were given taxonomic annotations, which mention the presence of many under-explored marine microorganism-derived hydrocarbon degrading genes and pathways. Through the present study, we tried to unveil the array of catabolic pathways of aromatic hydrocarbon degradation and genes from a marine ecosystem that upholds economic and ecological significance in India. Thus, this study provides vast opportunities and strategies for microbial resource recovery in marine ecosystems, which can be investigated to explore aromatic hydrocarbon degradation and their potential mechanisms under various oxic or anoxic environments. Future studies should focus on aromatic hydrocarbon degradation by considering degradation pathways, biochemical analysis, enzymatic, metabolic, and genetic systems, and regulations.

Increased daily temperature fluctuations exacerbate the toxicity of phenanthrene in Enchytraeus albidus (Enchytraeidae)

Temperature variability in soils is expected to increase due to the more frequent occurrence of heat waves, putting species under thermal stress. In addition, organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) are released into the environment due to anthropogenic activities. Both stressors negatively impact terrestrial organisms and may interact with each other. Here, we subjected the soil living enchytraeid, Enchytraeus albidus, to combined exposure to phenanthrene (PHE; 0, 10, 20, 40, and 80 mg kg^-1 dry soil) and a range of temperature treatments (constant temperature (CT): 10, 15 and 20 °C; different mean temperature with the same daily temperature fluctuation (DTF-5): 10 ± 5, 15 ± 5 and 20 ± 5 °C; daily temperature fluctuation with the same mean, but different amplitudes (DTF-A): 20, 20 ± 2, 20 ± 5 and 20 ± 7 °C). We measured internal PHE concentration in adults and found that an increase in mean temperature significantly increased the internal PHE concentration. The production of juveniles was measured using a standardized test. We found a synergistic interaction between the temperature amplitude (DTF-A treatments) and PHE on the reproduction of E. albidus. The EC₅₀ of reproduction decreased with increasing amplitude. These results show that the negative effects of PHE on E. albidus can be magnified if stressful temperatures are reached (although briefly) during diurnal fluctuations of soil temperature. Our results highlight the importance and inclusion of extreme thermal events in the risk assessment of pollutants.

Changes in metabolic profiles of amphipods Allorchestes compressa after acute exposures to copper, pyrene, and their mixtures

Amphipods are ideal indicators for biomonitoring and ecotoxicological studies of environmental contaminants because they are extensively distributed in aquatic environments, are easy to collect and are important in nutrient cycling. Marine amphipods (Allorchestes compressa) were exposed to two concentrations of copper and pyrene, and their mixtures, for 24 and 48 h. Changes in polar metabolites were assessed using Gas Chromatography Mass Spectrometry (GC-MS)-based untargeted metabolomics. Generally, limited metabolite changes were observed for copper and pyrene single exposures (eight and two significant metabolites, respectively), while 28 metabolites had changed following exposures to mixtures. Furthermore, changes were mainly observed after 24 h but had seemingly returned to control levels after 48 h. Multiple types of metabolites were affected including amino acids, Tricarboxylic acid (TCA) cycle intermediates, sugars, fatty acids, and hormones. This study highlights the sensitivity of metabolomics in assessing the impacts of low concentrations of chemicals compared to traditional ecotoxicological endpoints.

Modeling Time-Dependent Aquatic Toxicity of Hydrocarbons: Role of Organism Weight, Temperature, and Substance Hydrophobicity

Oil spill exposures are highly dynamic and are not comparable to laboratory exposures used in standard toxicity tests. Toxicokinetic-toxicodynamic (TKTD) models allow translation of effects observed in the laboratory to the field. To improve TKTD model calibration, new and previously published data from 148 tests were analyzed to estimate rates characterizing the time course of toxicity for 10 fish and 42 invertebrate species across 37 hydrocarbons. A key parameter in the TKTD model is the first-order rate that incorporates passive elimination, biotransformation, and damage repair processes. The results indicated that temperature (4-26 °C), organism size (0.0001-10 g), and substance log octanol-water partition coefficient (2-6) had limited influence on this parameter, which exhibited a 5th to 95th percentile range of 0.2-2.5 day^-1 (median 0.7 day^-1 ). A species sensitivity distribution approach is proposed to quantify the variability of this parameter across taxa, with further studies needed for aliphatic hydrocarbons and plant species. Study findings allow existing oil spill models to be refined to improve effect predictions. Environ Toxicol Chem 2022;41:3070-3083. © 2022 ExxonMobil Biomedical Science Inc. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Determination of In Vivo Biotransformation Kinetics Using Early-Time Biota Concentrations

Technical challenges have hampered the characterization of biotransformation kinetics-a critical link in understanding and predicting the toxicokinetics and ecotoxicology of organic compounds. A shortcut approach to characterize the in vivo biotransformation rate constant (k_M ) with incomplete pathway or metabolite details was proposed. The value of k_M can be derived as 2tln1fPC(t)) , with f_PC (t) being the molar equivalent fraction of the parent compound (PC) at an early time t in both constant exposure and decay source chemical uptake scenarios. The approximation-based k_M values agreed well with k_M values derived from rigorous fitting or toxicokinetic modeling (n = 42, root mean square error = 0.30) with accuracy exceeding those of typical toxicokinetic or partitioning models. The method is accurate when sampling time is adequately resolved (i.e., t < ln(2)/k_M ) but will likely produce biased k_M values with improper time-averaging. The approximate equation yields consistent theoretical expectations for fast and slow biotransformation reactions and is fully compatible with standard bioaccumulation and toxicity testing protocols. The simplification strategy circumvents statistical complications and numerical issues inherent in regressing or modeling the toxicokinetics of multimetabolite systems and may be adapted to similar problems at other physiological scales or ecotoxicological contexts. The method can help advance interspecies comparison of chemical metabolism and support the development of in vitro-in vivo extrapolations and in silico models needed for building next-generation ecological and health risk-assessment practices. Environ Toxicol Chem 2022;41:148-158. © 2021 SETAC.

The added value of Bayesian inference for estimating biotransformation rates of organic contaminants in aquatic invertebrates

Toxicokinetic (TK) models refer to the process of contaminant bioaccumulation as a balance between rate of uptake from different sources (e.g., water or food), and rate of elimination via different processes such as excretion, growth and/or biotransformation. Biotransformation can considerably modify the fate of chemicals in an organism, especially their bioavailability, residence time, and toxicity. Invertebrate models generally neglect this process as they assume a low metabolic activity. However, some species such as Gammarus sp. amphipods are able to metabolize a vast range of organic compounds. Some recent TK models include biotransformation, but they prove limited for estimating related parameters by giving negative values and/or large uncertainties for biotransformation rate(s). Here we propose a generic TK model accounting for biotransformation using a Bayesian framework for simultaneously estimating the parameters. We illustrated the added value of our method by fitting this generic TK model to 22 published datasets of several benthic invertebrate species exposed to different chemicals. All parameters are estimated simultaneously for all datasets and showed narrow estimates. Furthermore, the median model predictions and their 95% credibility intervals showed that the model confidently fitted the data. In most cases the uncertainties around biotransformation rate(s) were reduced in comparison to the original studies. From a methodology standpoint, this paper reflects that Bayesian inference has real added value for simultaneously estimating all TK parameters for parent chemicals and their metabolite(s) based on all available data, while accounting for different types of data and the correlation between parameters. Bayesian inference was able to overcome the limits of previous methods, since no parameters were fixed and no irrelevant negative values were obtained. Moreover, the 95% credibility intervals around model predictions, which are core uncertainties for Environmental Risk Assessment, were easily acquired.

Temperature-Dependent Toxicokinetics of Phenanthrene in Enchytraeus albidus (Oligochaeta)

Although the toxicokinetics of organic pollutants in soil invertebrates under optimal and constant temperature has been widely reported, their uptake, elimination, and bioaccumulation under suboptimal temperatures, and especially daily fluctuating temperature (FT) regimes have received only little research attention. In this study, the uptake, elimination, and bioaccumulation of phenanthrene (PHE) in Enchytraeus albidus (Oligochaeta) under different constant temperatures, and an FT regime were investigated in a natural soil. In general, the PHE concentrations in worm tissues reached steady state within 14 days at different temperatures. The uptake (k_u) and elimination (k_e) rate constants and the bioaccumulation increased with increasing temperature likely because of an increased diffusivity of PHE into the worms and an increased metabolic rate. Interestingly, the bioaccumulation factor of PHE in E. albidus showed a positive relationship with temperature because the slope of the k_u-temperature relationship was larger than that of the k_e-temperature relationship. Further, the uptake and elimination rate constants were larger under the FT regime than at the constant average of the fluctuating temperature. These findings suggest that, climatic conditions, especially daily fluctuating temperatures, should be considered for the assessment of the toxicokinetics of organic pollutants in terrestrial organisms.

In vitro-in vivo and cross-life stage extrapolation of uptake and biotransformation of benzo[a]pyrene in the fathead minnow (Pimephales promelas)

Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransformed and have not been validated against early-life stages (ELS) that are often considered the most sensitive to the exposure to contaminants. To address these uncertainties, TK models were parameterized for the rapidly biotransformed chemical benzo[a]pyrene (B[a]P) in embryo-larval and adult life stages of fathead minnows. Biotransformation of B[a]P was determined through measurements of in vitro clearance. Using in vitro-in vivo extrapolation, in vitro clearance was integrated into a multi-compartment TK model for adult fish and a one-compartment model for ELS. Model predictions were validated using measurements of B[a]P metabolites from in vivo flow-through exposures to graded concentrations of water-borne B[a]P. Significantly greater amounts of B[a]P metabolites were observed with exposure to greater concentrations of parent compound in both life stages. However, when assessing biotransformation capacity, no differences in phase I or phase II biotransformation were observed with greater exposures to B[a]P. Results of modelling suggested that biotransformation of B[a]P can be successfully implemented into in silico models to accurately predict life stage-specific abundances of B[a]P metabolites in either whole-body larvae or the bile of adult fish. Models developed increase the scope of applications in which TK models can be used to support environmental risk assessments.

Implications of Trophic Variability for Modeling Biomagnification of POPs in Marine Food Webs in the Svalbard Archipelago

The occurrence of persistent organic pollutants (POPs) in the Arctic has been of constant concern, as these chemicals cause reproductive effects and mortality in organisms. The Arctic acts as a chemical sink, which makes this system an interesting case for bioaccumulation studies. However, as conducting empirical studies for all Arctic species and POPs individually is unfeasible, in silico methods have been developed. Existing bioaccumulation models are predominately validated for temperate food chains, and do not account for a large variation in trophic levels. This study applies Monte Carlo simulations to account for variability in trophic ecology on Svalbard when predicting bioaccumulation of POPs using the optimal modeling for ecotoxicological applications (OMEGA) bioaccumulation model. Trophic magnification factors (TMFs) were calculated accordingly. Comparing our model results with monitored POP residues in biota revealed that, on average, all predictions fell within a factor 6 of the monitored POP residues in biota. Trophic variability did not affect model performance tremendously, with up to a 25% variability in performance metrics. To our knowledge, we were the first to include trophic variability in predicting biomagnification in Arctic ecosystems using a mechanistic biomagnification model. However, considerable amounts of data are required to quantify the implications of trophic variability on biomagnification of POPs in Arctic food webs.

First evidence of microplastics ingestion in benthic amphipods from Svalbard

The present paper provides the first record of ingestion of microplastics in natural context by Gammarus setosus from Svalbard Archipelago. The plastic particles were identified both by Nile Red staining and Micro FT-IR spectroscopy. The species studied ingests microplastic particles in natural conditions if present in its habitat, probably mistaking them as food. The microplastic particles ingested may be available for uptake to predators that consume this Arctic amphipod, producing consequences to the food web.

A Bayesian framework for estimating parameters of a generic toxicokinetic model for the bioaccumulation of organic chemicals by benthic invertebrates: Proof of concept with PCB153 and two freshwater species

Toxicokinetic (TK) models are relevant and widely used to predict chemical concentrations in biological organisms. The importance of dietary uptake for aquatic invertebrates has been increasingly assessed in recent years. However, the model parameters are estimated on limited specific laboratory data sets that are bounded by several uncertainties. The aim of this study was to implement a Bayesian framework for simultaneously estimating the parameters of a generic TK model for benthic invertebrate species from all data collected. We illustrate our approach on the bioaccumulation of PCB153 by two species with different life traits and therefore exposure routes: Chironomus riparius larvae exposed to spiked sediment for 7 days and Gammarus fossarum exposed to spiked sediment and/or leaves for 7 days and then transferred to a clean media for 7 more days. The TK models assuming first-order kinetics were fitted to the data using Bayesian inference. The median model predictions and their 95% credibility intervals showed that the model fit the data well. From a methodological point of view, this paper illustrates that simultaneously estimating all model parameters from all available data by Bayesian inference, while considering the correlation between parameters and different types of data, is a real added value for TK modeling. Moreover, we demonstrated the ability of a generic TK model considering uptake and elimination routes as modules to add according to the availability of the data measured. From an ecotoxicological point of view, we show differences in PCB153 bioaccumulation between chironomids and gammarids, explained by the different life traits of these two organisms.

Biomarker responses and biotransformation capacity in Arctic and temperate benthic species exposed to polycyclic aromatic hydrocarbons

Monitoring parameters for the assessment of oil and gas related contaminants and their biological effects need validation before application in the Arctic. For such monitoring purposes, we evaluated the potential use of three biomarkers (acetylcholinesterase, acyl-CoA oxidase and glutathione S-transferase) for application to an Arctic bivalve (Astarte borealis) and determined the body residue of pyrene and two pyrene metabolites (1-hydroxypyrene and pyrene-1-glucuronide) in Arctic benthic species (bivalve: Macoma calcarea; polychaete: Nephtys ciliata) and temperate benthic species (bivalve: Limecola balthica; polychaete: Alitta virens) in order to establish the potential of polycyclic aromatic hydrocarbons (PAHs) metabolite profiles as biomarkers of exposure in such species. Experimental PAH exposure levels were probably too low (0.2-1.7 mg/kg dry weight in sediment) to induce or inhibit biomarker responses in A. borealis. Concentrations of pyrene and pyrene metabolites varied between species, although no consistent patterns could be established among taxonomic groups and locations. Metabolites made up to 79% of the total pyrene concentrations, indicating that basal metabolic activity is affecting pyrene kinetics even at low concentrations in all species. This indicates that Arctic and temperate species could show similar metabolism patterns of PAHs, although more insight into the effects of confounding factors is needed.

Bioaccumulation of polycyclic aromatic hydrocarbons by arctic and temperate benthic species

Increasing oil and gas activities may substantially increase chemical stress to benthic ecosystems in the Arctic, and it is necessary to evaluate such environmental risks in these systems. Risk assessment procedures for oil-related compounds (e.g., polycyclic aromatic hydrocarbons [PAHs]) should address differences in exposure between Arctic and temperate benthos. We compare for the first time the bioaccumulation of PAHs by Arctic benthic invertebrate species with that of temperate species, based on their biota-sediment accumulation factors (BSAFs). Measured PAH BSAFs were generally higher in temperate bivalves (Limecola balthica) than in Arctic bivalves (Macoma calcarea), whereas BSAFs in Arctic polychaetes (Nephtys ciliata) were higher than in temperate polychaetes (Alitta virens). Differences in measured BSAFs were explained by species-specific feeding modes and traits. However, modeled BSAFs revealed that steady state was not likely to be reached in the 28-d tests for all PAHs and organisms. Due to the low numbers of individuals, most species-specific parameters were too uncertain to reveal differences between Arctic and temperate species. The results of the present study suggest that data from temperate species could be used as a surrogate for Arctic species in risk assessment. Environ Toxicol Chem 2019;38:883-895. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Concentrations of polycyclic aromatic hydrocarbons and trace elements in Arctic soils: A case-study in Svalbard

A combined assessment on the levels and distribution profiles of polycyclic aromatic hydrocarbons (PAHs) and trace elements in soils from Pyramiden (Central Spitsbergen, Svalbard Archipelago) is here reported. As previously stated, long-range atmospheric transport, coal deposits and previous mining extractions, as well as the stack emissions of two operative power plants at this settlement are considered as potential sources of pollution. Eight top-layer soil samples were collected and analysed for the 16 US EPA priority PAHs and for 15 trace elements (As, Be, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sn, Tl, V and Zn) during late summer of 2014. The highest levels of PAHs and trace elements were found in sampling sites located near two power plants, and at downwind from these sites. The current PAH concentrations were even higher than typical threshold values. The determination of the pyrogenic molecular diagnostic ratios (MDRs) in most samples revealed that fossil fuel burning might be heavily contributing to the PAHs levels. Two different indices, the Pollution Load Index (PLI) and the Geoaccumulation Index (Igeo), were determined for assessing soil samples with respect to trace elements pollution. Samples collected close to the power plants were found to be slightly and moderately polluted with zinc (Zn) and mercury (Hg), respectively. The Spearman correlation showed significant correlations between the concentrations of 16 PAHs and some trace elements (Pb, V, Hg, Cu, Zn, Sn, Be) with the organic matter content, indicating that soil properties play a key role for pollutant retention in the Arctic soils. Furthermore, the correlations between ∑16 PAHs and some trace elements (e.g., Hg, Pb, Zn and Cu) suggest that the main source of contamination is probably pyrogenic, although the biogenic and petrogenic origin of PAHs should not be disregarded according to the local geology.

Comparative Studies on the Toxicokinetics of Benzo[a]pyrene in Pinctada martensii and Perna viridis

Research on the kinetics of Benzo[a]pyrene (B[a]P) bioaccumulation in the clam Pinctada martensii and mussel Perna viridis showed that the initial rate of uptake was directly related to the PAH concentrations in the ambient environment. The uptake and depuration rate constants were different at the four B[a]P exposure levels, which indicated that the toxicokinetic rate constants mainly depended on the exposure levels of pollutants to the environment. In addition, the uptake rate constants of B[a]P were higher than the depuration rate constants in the entire experiment. The comparison demonstrated that mussels release B[a]P more rapidly than clams. The bioconcentration factors (BCFs) of B[a]P varied from 3335 to 12892 in the clam and 2373-6235 in the mussel. These findings on the bioaccumulation kinetics for petroleum hydrocarbons, in association with the critical body residue, will be valuable when choosing sensitive organisms to assess the potential ecotoxicological risk to the marine environment.