Combined Effects from γ Radiation and Fluoranthene Exposure on Carbon Transfer from Phytoplankton to Zooplankton

Modelling the combined effects of ionising radiation and chemical pollutants on wildlife populations

A population model is presented to study the combined effects of ionising radiation and chemical pollutants on wildlife. The model is based on first order, non-linear and logistic differential equations combining mortality, morbidity and reproduction phenomena with life history data and ecological interactions. Acclimation is considered as a possible mechanism to study theoretically this effect at low levels of radiation or chemical concentration. Radiation and chemical-induced damages are represented by a 'repairing pool' mediating between healthy, damaged, acclimated, and irrecoverable individuals. Damages to population, fecundity and the repairing pool are represented by a linear-quadratic function combining radiation dose and chemical concentration terms. The endpoints of the model are repairable damages (morbidity), impairment of reproductive ability and mortality. The model is evaluated with a mixed ionising radiation/arsenate demonstration scenario to illustrate the combined effect of radiation and chemical pollutants upon the sustainability of a hypothetical vole population, including the influence of acclimation, given the assumption that the repair of both radiation and toxicity damages share the same mechanism. A sensitivity analysis of the model illustrates the effects of combining radiation dose and chemical concentration on self-repairing and reproductive ability for the population, exploring cases of antagonism and synergism by varying the relevant model parameters. This model provides a conceptual framework to address mixed radiological and chemical effects to wildlife populations. It can be used to assess the robustness of the benchmarks used in wildlife radiological assessment, informing ongoing regulatory debates on their applicability to mixed stressor situations. Future research will enable to draw conclusions about the most restrictive mixed exposure situations in terms of effects to the population.

Spatial-temporal variations of metals and arsenic in sediments from the Doce River after the Fundão Dam rupture and their bioaccumulation in Corbicula fluminea

The rupture of the Fundão dam in Brazil released tons of mining tailings into the Doce River Basin (DRB). This investigation aimed to determine the bioaccumulation of metals in soft tissues of the bivalve Corbicula fluminea exposed to sediments collected in the DRB in four periods (just after, 1, 3, and 3.5 years after the dam rupture). In the exposure bioassays, the concentrations of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in sediments and bivalve soft tissues were quantified. The concentration of some elements (As, Cd, Mn, and Al) in sediments exceeded the federal limits or regional backgrounds at some sampling sites, but their concentrations tended to decrease over time. However, higher concentrations of many elements were detected in the winter of 2019. Several elements were detected in C. fluminea soft tissues, but the bioaccumulation factors were generally low or not related to those elements associated with the ore tailings, evidencing that the bioavailability of metals to bivalves, in laboratory conditions, was limited. Integr Environ Assess Manag 2024;20:87-98. © 2023 SETAC.

Daphnia magna Gut-Specific Transcriptomic Responses to Feeding Inhibiting Chemicals and Food Limitation

Transcriptomic responses combined with apical adverse ecologically relevant outcomes have proven to be useful to unravel and anchor molecular mechanisms of action to adverse outcomes. This is the case for feeding inhibition responses in the model ecotoxicological species Daphnia magna. The aim of the present study was to assess the transcriptomic responses in guts dissected from D. magna individuals exposed to concentrations of selected compounds that inhibit feeding and compare them with the responses associated to 2 levels of food restriction (low food and starvation). Chemical treatments included cadmium, copper, fluoranthene, λ-cyhalothrin, and the cyanotoxin anatoxin-a. Although the initial hypothesis was that exposure to chemical feeding inhibitors should elicit similar molecular responses as food limitation, the corresponding gut transcriptomic responses differed significantly. In moderate food limitation conditions, D. magna individuals increased protein and carbohydrate catabolism, likely to be used as energetic sources, whereas under severe starving conditions most metabolism-related pathways appeared down-regulated. Treatment with chemical feeding inhibitors promoted cell turnover-related signaling pathways in the gut, probably to renew tissue damage caused by the reported oxidative stress effects of these compounds, and inhibited the transcription of gut digestive gene enzymes and energetic metabolic pathways. We conclude that chemical feeding inhibitors, rather than mimicking the physiological response to low- or no-food conditions, cause specific toxic effects, preventing Daphnia both from feeding and from adjusting its metabolism to the resulting low energy intake. Environ Toxicol Chem 2021;40:2510-2520. © 2021 SETAC.

Contribution of Dietary Uptake to PAH Bioaccumulation in a Simplified Pelagic Food Chain: Modeling the Influences of Continuous vs Intermittent Feeding in Zooplankton and Fish

Dietary uptake is important for trophic transfer of polycyclic aromatic hydrocarbons (PAHs) in the freshwater pelagic ecosystem. In this study, we hypothesized that both the dietary uptake rate and interval significantly influenced its relative contribution to bioaccumulation. We developed a toxicokinetic model framework for the bioaccumulation of deuterated PAHs (PAHs-d₁₀) in aquatic organisms considering different feeding intervals ranging from none for phytoplankton to approximately continuous for zooplankton to discrete for fish and built a simple artificial freshwater pelagic food chain composed of algae Chlorella vulgaris, zooplankton Daphnia magna, and zebrafish. We conducted bioaccumulation experiments and simulations for Daphnia magna and zebrafish under different algal densities based on our model. The results showed that intermittent feeding led to a large fluctuation in the PAH-d₁₀ concentrations in zebrafish compared to a leveled-off pattern in Daphnia magna because of approximately continuous feeding. Trophic dilution of PAHs-d₁₀ occurred in the food chain when there was waterborne-only uptake, but dietary uptake largely mitigated its extent that depended on dietary uptake rates. The assimilation efficiency, dietary uptake rate, and its relative contribution to bioaccumulation of PAHs-d₁₀ in zebrafish were all higher than those in Daphnia magna, suggesting that dietary uptake played a more important role in bioaccumulation of PAHs at higher trophic-level organisms.

Joint effects of gamma radiation and cadmium on subcellular-, individual- and population-level endpoints of the green microalga Raphidocelis subcapitata

Interpreting and predicting the combined effects of toxicants in the environment is an important challenge in ecotoxicology. How such effects are connected across different levels of biological organisation is an additional matter of uncertainty. Such knowledge gaps are particularly prominent with regards to how ionising radiation interacts with contaminants. We assessed the response of twelve endpoints at the subcellular, individual and population level in a green microalga when exposed singly and jointly to gamma radiation and cadmium (Cd). We used a fully factorial experimental design where observed effects were compared to those predicted by the Independent Action (IA) model for mixture toxicity to determine whether they deviated from additivity. Subcellular endpoints (e.g., catalase, thiamine diphosphate, xanthophyll cycle pigments) showed an increased antioxidant and/or photoprotective response. However, our results indicate that this protection was not sufficient to prevent lipid peroxidation, which also increased with dose. At ecologically relevant doses, most interactions between gamma radiation and Cd regarding subcellular-, individual- and population-level endpoints were additive as predicted by the IA model. However, exposure to binary mixtures displayed antagonistic interactions between gamma radiation and Cd at the higher end of the tested dose spectrum. No correlations were observed between subcellular endpoints and higher-level endpoints, but there were linkages between individual and population endpoints. Our results suggest that antagonistic interactions between gamma radiation and Cd can occur at higher doses and that these interactions seem to disseminate from subcellular and individual to population level. Possible consequences for aquatic primary production and food-web interactions are discussed.

Gamma radiation induces dose-dependent oxidative stress and transcriptional alterations in the freshwater crustacean Daphnia magna

Among aquatic organisms, invertebrate species such as the freshwater crustacean Daphnia magna are believed to be sensitive to gamma radiation, although information on responses at the individual, biochemical and molecular level is scarce. Following gamma radiation exposure, biological effects are attributed to the formation of free radicals, formation of reactive oxygen species (ROS) and subsequently oxidative damage to lipids, proteins and DNA in exposed organisms. Thus, in the present study, effects and modes of action (MoA) have been investigated in D. magna exposed to gamma radiation (dose rates: 0.41, 1.1, 4.3, 10.7, 42.9 and 106 mGy/h) after short-term exposure (24 and 48 h). Several individual, cellular and molecular endpoints were addressed, such as ROS formation, lipid peroxidation, DNA damage and global transcriptional changes. The results showed that oxidative stress is one of the main toxic effects in gamma radiation exposed D. magna, mediated by the dose-dependent increase in ROS formation and consequently oxidative damage to lipids and DNA over time. Global transcriptional analysis verified oxidative stress as one of the main MoA of gamma radiation at high dose rates, and identified a number of additional MoAs that may be of toxicological relevance. The present study confirmed that acute exposure to gamma radiation caused a range of cellular and molecular effects in D. magna exposed to intermediate dose rates, and highlights the need for assessing effects at longer and more environmentally relevant exposure durations in future studies.

Direct and indirect effects of ionizing radiation on grazer-phytoplankton interactions

Risk assessment of exposure to radionuclides and radiation does not usually take into account the role of species interactions. We investigated how the transfer of carbon between a primary producer, Raphidocelis subcapitata, and a consumer, Daphnia magna, was affected by acute exposure to gamma radiation. In addition to unexposed controls, different treatments were used where: a) only D. magna (Z treatment); b) only R. subcapitata (P treatment) and c) both D. magna and R. subcapitata (ZP treatment) were exposed to one of three acute doses of gamma radiation (5, 50 and 100 Gy). We then compared differences among treatments for three endpoints: incorporation of carbon by D. magna, D. magna growth and R. subcapitata densities. Carbon incorporation was affected by which combination of species was irradiated and by the radiation dose. Densities of R. subcapitata at the end of the experiment were also affected by which species had been exposed to radiation. Carbon incorporation by D. magna was significantly lower in the Z treatment, indicating reduced grazing, an effect stronger with higher radiation doses, possibly due to direct effects of gamma radiation. Top-down indirect effects of this reduced grazing were also seen as R. subcapitata densities increased in the Z treatment due to decreased herbivory. The opposite pattern was observed in the P treatment where only R. subcapitata was exposed to gamma radiation, while the ZP treatment showed intermediate results for both endpoints. In the P treatments, carbon incorporation by D. magna was significantly higher than in the other treatments, suggesting a higher grazing pressure. This, together with direct effects of gamma radiation on R. subcapitata, probably significantly decreased phytoplankton densities in the P treatment. Our results highlight the importance of taking into account the role of species interactions when assessing the effects of exposure to gamma radiation in aquatic ecosystems.

Joint Toxicity of Cadmium and Ionizing Radiation on Zooplankton Carbon Incorporation, Growth and Mobility

The risk of exposure to radioactive elements is seldom assessed considering mixture toxicity, potentially over- or underestimating biological and ecological effects on ecosystems. This study investigated how three end points, carbon transfer between phytoplankton and Daphnia magna, D. magna mobility and growth, responded to exposure to γ-radiation in combination with the heavy metal cadmium (Cd), using the MIXTOX approach. Observed effects were compared with mixture effects predicted by concentration addition (CA) and independent action (IA) models and with deviations for synergistic/antagonistic (S/A), dose-level (DL), and dose-ratio (DR) dependency interactions. Several patterns of response were observed depending on the end point tested. DL-dependent deviation from the IA model was observed for carbon incorporation with antagonism switching to synergism at higher doses, while the CA model indicated synergism, mainly driven by effects at high doses of γ-radiation. CA detected antagonism regarding acute immobilization, while IA predicted DR-dependency. Both CA and IA also identified antagonism for daphnid growth. In general, effects of combinations of γ-radiation and Cd seem to be antagonistic at lower doses, but synergistic at the higher range of the doses tested. Our results highlight the importance of investigating the effects of exposure to γ-radiation in a multistressor context.