Parameter uncertainty in modeling bioaccumulation factors of fish

The effect of microplastics on the depuration of hydrophobic organic contaminants in Daphnia magna: A quantitative model analysis

Microplastics are emerging pollutants that can absorb large amounts of hydrophobic organic contaminants (HOCs). However, no biodynamic model has yet been proposed to estimate their effects on HOC depuration in aquatic organisms, where the HOC concentrations are time-varying. In this work, a microplastic-inclusive biodynamic model was developed to estimate the depuration of HOCs via ingestion of microplastics. Several key parameters of the model were redefined to determine the dynamic HOC concentrations. Through the parameterized model, the relative contributions of dermal and intestinal pathways can be distinguished. Moreover, the model was verified and the vector effect of microplastics was confirmed by studying the depuration of polychlorinated biphenyl (PCB) in Daphnia magna (D. magna) with different sizes of polystyrene (PS) microplastics. The results showed that microplastics contributed to the elimination kinetics of PCBs because of the fugacity gradient between the ingested microplastics and the biota lipids, especially for the less hydrophobic PCBs. The intestinal elimination pathway via microplastics would promote overall PCB elimination, contributing 37-41 % and 29-35 % to the total flux in the 100 nm and 2 μm polystyrene (PS) microplastic suspensions, respectively. Furthermore, the contribution of microplastic uptake to total HOC elimination increased with decreasing microplastic size in water, suggesting that microplastics may protect organisms from HOC risks. In conclusion, this work demonstrated that the proposed biodynamic model is capable of estimating the dynamic depuration of HOCs for aquatic organisms. The results can shed light on a better understanding of the vector effects of microplastics.

Collection of human and environmental data on pesticide use in Europe and Argentina: Field study protocol for the SPRINT project

Current farm systems rely on the use of Plant Protection Products (PPP) to secure high productivity and control threats to the quality of the crops. However, PPP use may have considerable impacts on human health and the environment. A study protocol is presented aiming to determine the occurrence and levels of PPP residues in plants (crops), animals (livestock), humans and other non-target species (ecosystem representatives) for exposure modelling and impact assessment. To achieve this, we designed a cross-sectional study to compare conventional and organic farm systems across Europe. Environmental and biological samples were/are being/will be collected during the 2021 growing season, at 10 case study sites in Europe covering a range of climate zones and crops. An additional study site in Argentina will inform the impact of PPP use on growing soybean which is an important European protein-source in animal feed. We will study the impact of PPP mixtures using an integrated risk assessment methodology. The fate of PPP in environmental media (soil, water and air) and in the homes of farmers will be monitored. This will be complemented by biomonitoring to estimate PPP uptake by humans and farm animals (cow, goat, sheep and chicken), and by collection of samples from non-target species (earthworms, fish, aquatic and terrestrial macroinvertebrates, bats, and farm cats). We will use data on PPP residues in environmental and biological matrices to estimate exposures by modelling. These exposure estimates together with health and toxicity data will be used to predict the impact of PPP use on environment, plant, animal and human health. The outcome of this study will then be integrated with socio-economic information leading to an overall assessment used to identify transition pathways towards more sustainable plant protection and inform decision makers, practitioners and other stakeholders regarding farming practices and land use policy.

A New Approach to Quantifying Bioaccumulation of Elements in Biological Processes

Simple Summary

The bioaccumulation of elements (e.g., heavy metals) in living organisms (e.g., animals) is vitally important from at least two points of view: the growth and development of the organisms themselves and remediation of the polluted environment. So far, bioaccumulation has been characterized by the bioaccumulation factor (BAF), which is the ratio between the concentration of elements in the organism to the concentration in the matrix (water, soil, etc.). This factor is a good measure of bioaccumulation in ecosystems in which an organism lives from the beginning of their lives to the moment of investigation. However, especially in laboratory experiments, when organisms at a given stage of development are introduced to the system and contain some non-zero concentration of an element, the BAF can lead to misinterpretation. Therefore, we propose a new measure called the bioaccumulation index (BAI), which is the relative increase in the concentration of a given element in the organism to its initial concentration after the experiment. We proved, on the basis of data published by other authors, that the BAI was much more valid for the interpretation of bioaccumulation in these cases.

Abstract

Bioaccumulation, expressed as the bioaccumulation factor (BAF), is a phenomenon widely investigated in the natural environment and at laboratory scale. However, the BAF is more suitable for ecological studies, while in small-scale experiments it has limitations, which are discussed in this article. We propose a new indicator, the bioaccumulation index (BAI). The BAI takes into account the initial load of test elements, which are added to the experimental system together with the biomass of the organism. This offers the opportunity to explore the phenomena related to the bioaccumulation and, contrary to the BAF, can also reveal the dilution of element concentration in the organism. The BAF can overestimate bioaccumulation, and in an extremal situation, when the dilution of element concentration during organism growth occurs, the BAF may produce completely opposite results to the BAI. In one of the examples presented in this work (Tschirner and Simon, 2015), the concentration of phosphorous in fly larvae was lower after the experiment than in the younger larvae before the experiment. Because the phosphorous concentration in the feed was low, the BAF indicated a high bioaccumulation of this element (BAF = 14.85). In contrast, the BAI showed element dilution, which is a more realistic situation (BAI = −0.32). By taking more data into account, the BAI seems to be more valid in determining bioaccumulation, especially in the context of entomoremediation research.

Joint effect of nanoplastics and humic acid on the uptake of PAHs for Daphnia magna: A model study

Nanoplastics (NPs) are emerging pollutants which can adsorb large amounts of hydrophobic organic compounds (HOCs) and be ingested by aquatic organisms. NPs interact with dissolved organic matter (DOM) and result in significant impacts on the bioaccumulation of HOCs in the actual environment. For the first time, the joint effects of two complex matrices on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) to Daphnia magna (D. magna) were studied by modeling calculation. The complex matrices, nano-sized polystyrene (PS) and/or humic acid (HA), were under environmentally realistic concentrations. A biodynamic model was modified and the uptake fluxes from all exposure pathways were quantified using the experimental data. A flux estimation showed that the bioaccumulation amounts at equilibrium were mostly dependent on dermal uptake (≥99.3 % of the total). The PS matrix would retard the intestinal uptake process in D. magna, especially for the less hydrophobic PAHs; while the HA or the HA-PS matrix would facilitate the mass transfer of PAHs from the matrix to lipids in the gut. Moreover, the biota matrix accumulation factor (BMAF) were calculated to verify the biodynamic model. This work is helpful to clarify the bioaccumulation effects of PAHs in complex environmental systems.

Estimating microplastic-bound intake of hydrophobic organic chemicals by fish using measured desorption rates to artificial gut fluid

One of the most important concerns about marine microplastics is their role in delivery of chemical contaminants to biota. The contribution of microplastic ingestion to the overall uptake of five hydrophobic organic chemicals (HOCs) [α-, β-, and γ-hexachlorocyclohexanes (HCHs), pentachlorobenzene (PeCB), and hexachlorobenzene (HeCB)] by fish is evaluated in this study. Partition coefficients of all five HOCs between surfactant micelles and simulated intestinal fluid (SIF), as well as between protein and SIF, were experimentally determined. Desorption of model HOCs from a polyethylene film into an artificial gut solution was measured to estimate the fraction of HOCs that can be absorbed from microplastics during their gut retention time. Monte-Carlo simulation (n = 100,000) showed that the uptake via microplastic ingestion will be negligible for HCHs as compared to uptake via other exposure routes, water ventilation and food ingestion. On the other hand, microplastic ingestion might increase the total uptake rate of PeCB and HeCB due to their accelerated desorption from microplastics into the artificial gut solution under the model scenario, assuming an extremely high intake of microplastics. However, the steady-state bioaccumulation factor was predicted to decrease with increasing ingestion of microplastics, showing a dilution effect by microplastic ingestion. Results indicate that HOCs that are close to be at phase equilibrium between microplastics and environmental media are not likely to be further accumulated via ingestion of microplastics; this is true even for cases, where ingestion of microplastics contributes significantly to the total uptake of HOCs. Therefore, future studies need to focus on hydrophobic plastic additives that may exist in microplastics at a concentration higher than their equilibrium concentration with water.

Ecological and human exposure assessment to PBDEs in Adige River

The interest for environmental issues and the concern resulting from the potential exposure to contaminants were the starting point to develop methodologies in order to evaluate the consequences that those might have over both the environment and human health. Considering the feature of POPs, including PBDEs, such as bioaccumulation, biomagnification, long-range transport and adverse effects even long time after exposure, risk assessment of POPs requires specific approaches and tools. In this particular context, the MERLIN-Expo tool was used to assess the aquatic environmental exposure of Adige River to PBDEs and the accumulation of PBDEs in humans through the consumption of possible contaminated local aquatic food. The aquatic food web models provided as output of the deterministic simulation the time trend of concentrations for twenty years of BDE-47 and total PBDEs, expressed using the physico-chemical properties of BDE-47, in aquatic organisms of the food web of Adige River. For BDE-47, the highest accumulated concentrations were detected for two benthic species: Thymallus thymallus and Squalius cephalus whereas the lowest concentrations were obtained for the pelagic specie Salmo trutta marmoratus. The trend obtained for the total PBDEs, calculated using the physico-chemical properties of BDE-47, follows the one of BDE-47. For human exposure, different BDE-47 and total PBDEs concentration trends between children, adolescent, adults and elderly were observed, probably correlated with the human intake of fish products in the daily diet and the ability to metabolize these contaminants. In detail, for the adolescents, adults and elderly a continuous accumulation of the target contaminants during the simulation's years was observed, whereas for children a plateau at the end of the simulation period was perceived.

The influence of chemical degradation during dietary exposures to fish on biomagnification factors and bioaccumulation factors

The chemical dietary absorption efficiency (E_D) quantifies the amount of chemical absorbed by an organism relative to the amount of chemical an organism is exposed to following ingestion. In particular, E_D can influence the extent of bioaccumulation and biomagnification for hydrophobic chemicals. A new E_D model is developed to quantify chemical process rates in the gastrointestinal tract (GIT). The new model is calibrated with critically evaluated measured E_D values (n = 250) for 80 hydrophobic persistent chemicals. The new E_D model is subsequently used to estimate chemical reaction rate constants (k_R) assumed to occur in the lumen of the GIT from experimental dietary exposure tests (n = 255) for 165 chemicals. The new k_R estimates are corroborated with k_R estimates for the same chemicals from the same data derived previously by other methods. The roles of k_R and the biotransformation rate constant (k_B) on biomagnification factors (BMFs) determined under laboratory test conditions and on BMFs and bioaccumulation factors (BAFs) in the environment are examined with the new model. In this regard, differences in lab and field BMFs are highlighted. Recommendations to address uncertainty in E_D and k_R data are provided.

Time-varying effects of aromatic oil constituents on the survival of aquatic species: Deviations between model estimates and observations

There is a need to study the time course of toxic chemical effects on organisms because there might be a time lag between the onset of chemical exposure and the corresponding adverse effects. For aquatic organisms, crude oil and oil constituents originating from either natural seeps or human activities can be relevant case studies. In the present study the authors tested a generic toxicokinetic model to quantify the time-varying effects of various oil constituents on the survival of aquatic organisms. The model is based on key parameters applicable to an array of species and compounds with baseline toxicity reflected by a generic, internal toxicity threshold or critical body burden (CBB). They compared model estimates with experimental data on the effects of 8 aromatic oil constituents on the survival of aquatic species including crustaceans and fish. The average model uncertainty, expressed as the root mean square error, was 0.25 (minimum-maximum, 0.04-0.67) on a scale between 0 and 1. The estimated survival was generally lower than the measured survival right after the onset of oil constituent exposure. In contrast, the model underestimated the maximum mortality for crustaceans and fish observed in the laboratory. Thus, the model based on the CBB concept failed to adequately predict the lethal effects of the oil constituents on crustaceans and fish. Possible explanations for the deviations between model estimates and observations may include incorrect assumptions regarding a constant lethal body burden, the absence of biotransformation products, and the steady state of aromatic hydrocarbon concentrations in organisms. Clearly, a more complex model approach than the generic model used in the present study is needed to predict toxicity dynamics of narcotic chemicals. Environ Toxicol Chem 2017;36:128-136. © 2016 SETAC.

Modelling ecological and human exposure to POPs in Venice lagoon - Part II: Quantitative uncertainty and sensitivity analysis in coupled exposure models

The study is focused on applying uncertainty and sensitivity analysis to support the application and evaluation of large exposure models where a significant number of parameters and complex exposure scenarios might be involved. The recently developed MERLIN-Expo exposure modelling tool was applied to probabilistically assess the ecological and human exposure to PCB 126 and 2,3,7,8-TCDD in the Venice lagoon (Italy). The 'Phytoplankton', 'Aquatic Invertebrate', 'Fish', 'Human intake' and PBPK models available in MERLIN-Expo library were integrated to create a specific food web to dynamically simulate bioaccumulation in various aquatic species and in the human body over individual lifetimes from 1932 until 1998. MERLIN-Expo is a high tier exposure modelling tool allowing propagation of uncertainty on the model predictions through Monte Carlo simulation. Uncertainty in model output can be further apportioned between parameters by applying built-in sensitivity analysis tools. In this study, uncertainty has been extensively addressed in the distribution functions to describe the data input and the effect on model results by applying sensitivity analysis techniques (screening Morris method, regression analysis, and variance-based method EFAST). In the exposure scenario developed for the Lagoon of Venice, the concentrations of 2,3,7,8-TCDD and PCB 126 in human blood turned out to be mainly influenced by a combination of parameters (half-lives of the chemicals, body weight variability, lipid fraction, food assimilation efficiency), physiological processes (uptake/elimination rates), environmental exposure concentrations (sediment, water, food) and eating behaviours (amount of food eaten). In conclusion, this case study demonstrated feasibility of MERLIN-Expo to be successfully employed in integrated, high tier exposure assessment.

No measurable "cleaning" of polychlorinated biphenyls from Rainbow Trout in a 9 week depuration study with dietary exposure to 40% polyethylene microspheres

Persistent hydrophobic chemicals sorbed to plastic can be transferred to fish and other aquatic organisms upon ingestion. However, ingestion of plastic could also lead to enhanced elimination of these chemicals if the plastic is less contaminated than the fish. Here, we attempted to measure the influence of ingestion of uncontaminated polyethylene microspheres on the depuration rates of polychlorinated biphenyls (PCBs) in an in vivo fish feeding experiment. Rainbow trout were given feed contaminated with PCBs for two consecutive days, then clean feed for three days to allow for egestion of the contaminated food. A control group of fish were then fed ordinary food pellets and a treatment group were fed pellets that additionally contained 40% by weight polyethylene microspheres. Condition factors and growth rates in both groups were similar, indicating no negative effect of the plastic microspheres on the nutritional status of the fish. Fish were sampled after zero, three, six and nine weeks, homogenized, solvent-extracted and analyzed by GC/MS. PCB concentrations declined in both groups at a rate consistent with growth dilution. There was no significant difference in the elimination rate constants between the control and treatment group, indicating that ingestion of uncontaminated plastic did not cause a measurable enhancement of depuration of PCBs by the fish in this study.

Plastic as a carrier of POPs to aquatic organisms: a model analysis

It has been hypothesized that persistent organic pollutants (POPs) in microplastic may pose a risk to aquatic organisms. Here we develop and analyze a conceptual model that simulates the effects of plastic on bioaccumulation of POPs. The model accounts for dilution of exposure concentration by sorption of POPs to plastic (POP "dilution"), increased bioaccumulation by ingestion of plastic-containing POPs ("carrier"), and decreased bioaccumulation by ingestion of clean plastic ("cleaning"). The model is parametrized for the lugworm Arenicola marina and evaluated against recently published bioaccumulation data for this species from laboratory bioassays with polystyrene microplastic. Further scenarios include polyethylene microplastic, nanosized plastic, and open marine systems. Model analysis shows that plastic with low affinity for POPs such as polystyrene will have a marginal decreasing effect on bioaccumulation, governed by dilution. For stronger sorbents such as polyethylene, the dilution, carrier, and cleaning mechanism are more substantial. In closed laboratory bioassay systems, dilution and cleaning dominate, leading to decreased bioaccumulation. Also in open marine systems a decrease is predicted due to a cleaning mechanism that counteracts biomagnification. However, the differences are considered too small to be relevant from a risk assessment perspective.

Nonequilibrium of organic compounds in sediment-water systems. Consequences for risk assessment and remediation measures

In many cases, sediment risk assessment, and remediation rely on the assumption of equilibrium between chemical concentrations in sediment pore water and overlying surface water and thus rely on pore water concentrations only and do not additionally include assessment of the overlying water concentration. Traditionally, the validity of this assumption was insufficiently documented due to a lack of data. Recent studies using passive samplers, however, provided sufficient data for the first systematic evaluation of the extent of disequilibrium between sediment pore water and overlying surface water. Recent bioaccumulation studies reveal uncertainty as to which of these concentrations govern bioaccumulation by benthic organisms. Here, we provide the first review of studies measuring disequilibrium identifying general patterns and implications for the aforementioned areas of application. In most studies on water/sediment (dis)equilibrium, sediment pore water and overlying surface water are close to equilibrium. For lower molecular weight PAHs, overlying water concentrations tended to be relative low, which is tentatively ascribed to biodegradation in the water column. Substantial nonequilibrium was observed at some hot-spot locations such as in semistagnant harbors. In such cases, efficacy of sediment remediation measures to improve overlying water quality can be questioned because differences between overlying water concentrations at the hot-spots and those at reference locations typically are small. For nonequilibrium situations and some benthic taxa, exposure may be determined best by pore water concentrations. Improving our understanding in this area may further improve risk assessment of contaminated sediments.

Estimating chemical biotransformation rates from food web concentrations

Biotransformation is widely recognized as the most important and most uncertain determinant of bioaccumulation. A step-wise method for estimating organism-specific biotransformation half-lives from field observations and using established food web modeling is developed. As a proof of concept, the method is applied to the case of nine polycyclic aromatic hydrocarbons (PAHs) in a well-studied food web in Bohai Bay, China. The estimated half-lives are in good agreement with the existing literature. The proposed biotransformation estimation method, through data mining, for sufficiently defined ecosystems, may greatly reduce the necessary animal testing involved in chemical assessments by providing useful guidance to experimentalists and regulators.

Explaining differences between bioaccumulation measurements in laboratory and field data through use of a probabilistic modeling approach

In the regulatory context, bioaccumulation assessment is often hampered by substantial data uncertainty as well as by the poorly understood differences often observed between results from laboratory and field bioaccumulation studies. Bioaccumulation is a complex, multifaceted process, which calls for accurate error analysis. Yet, attempts to quantify and compare propagation of error in bioaccumulation metrics across species and chemicals are rare. Here, we quantitatively assessed the combined influence of physicochemical, physiological, ecological, and environmental parameters known to affect bioaccumulation for 4 species and 2 chemicals, to assess whether uncertainty in these factors can explain the observed differences among laboratory and field studies. The organisms evaluated in simulations including mayfly larvae, deposit-feeding polychaetes, yellow perch, and little owl represented a range of ecological conditions and biotransformation capacity. The chemicals, pyrene and the polychlorinated biphenyl congener PCB-153, represented medium and highly hydrophobic chemicals with different susceptibilities to biotransformation. An existing state of the art probabilistic bioaccumulation model was improved by accounting for bioavailability and absorption efficiency limitations, due to the presence of black carbon in sediment, and was used for probabilistic modeling of variability and propagation of error. Results showed that at lower trophic levels (mayfly and polychaete), variability in bioaccumulation was mainly driven by sediment exposure, sediment composition and chemical partitioning to sediment components, which was in turn dominated by the influence of black carbon. At higher trophic levels (yellow perch and the little owl), food web structure (i.e., diet composition and abundance) and chemical concentration in the diet became more important particularly for the most persistent compound, PCB-153. These results suggest that variation in bioaccumulation assessment is reduced most by improved identification of food sources as well as by accounting for the chemical bioavailability in food components. Improvements in the accuracy of aqueous exposure appear to be less relevant when applied to moderate to highly hydrophobic compounds, because this route contributes only marginally to total uptake. The determination of chemical bioavailability and the increase in understanding and qualifying the role of sediment components (black carbon, labile organic matter, and the like) on chemical absorption efficiencies has been identified as a key next steps.