The combined and interactive effects of zinc, temperature, and phosphorus on the structure and functioning of a freshwater community

Ecotoxicological studies mainly consist of single-species experiments evaluating the effects of a single stressor. However, under natural conditions aquatic communities are exposed to a mixture of stressors. The present study aimed to identify how the toxicity of zinc (Zn) is affected by increased temperature and increased phosphorus (P) supply and how these interactions vary among species, functional groups, and community structure and function. Aquatic microcosms were subjected to 3 Zn concentrations (background, no Zn added, and 75 and 300 μg Zn/L), 2 temperatures (16–19 and 21–24 °C), and 2 different P additions (low, 0.02, and high, 0.4 mg P L−1 wk−1) for 5 wk using a full factorial design. During the study, consistent interactions between Zn and temperature were only rarely found at the species level (4%), but were frequently found at the functional group level (36%), for community structure (100%) and for community function (100%; such as dissolved organic carbon concentrations and total chlorophyll). The majority of the Zn × temperature interactions were observed at 300 μg Zn/L and generally indicated a smaller effect of Zn at higher temperature. Furthermore, no clear indication was found that high P addition by itself significantly affected the overall effects of Zn on the community at any level of organization. Interestingly, though, 90% of all the Zn × temperature interactions observed at the species, group, and community composition level were found under high P addition. Collectively, the results of our study with the model chemical Zn suggest that temperature and phosphorus loading to freshwater systems should be accounted for in risk assessment, because these factors may modify the effects of chemicals on the structure and functioning of aquatic communities, especially at higher levels of biological organization. Environ Toxicol Chem 2018;37:2413–2427.</p

Aquatic exposures of chemical mixtures in urban environments: approaches to impact assessment

Urban regions of the world are expanding rapidly, placing additional stress on water resources. Urban water bodies serve many purposes from washing and sources of drinking water to transport and conduits for storm drainage and effluent discharge. These water bodies receive chemical emissions arising from either single or multiple point sources, diffuse sources which can be continuous, intermittent or seasonal. Thus, aquatic organisms in these water bodies are exposed to temporally and compositionally variable mixtures. We have delineated source-specific signatures of these mixtures for diffuse urban runoff and urban point source exposure scenarios to support risk assessment and management of these mixtures. The first step in a tiered approach to assessing chemical exposure has been developed based on the Event Mean Concentration concept with chemical concentrations in runoff defined by volumes of water leaving each surface and the chemical exposure mixture profiles for different urban scenarios. Although generalizations can be made about the chemical composition of urban sources and event mean exposure predictions for initial prioritization, such modelling needs to be complemented with biological monitoring data. It is highly unlikely that the current paradigm of routine regulatory chemical monitoring alone will provide a realistic appraisal of urban aquatic chemical mixture exposures. Future consideration is also needed on the role of non-chemical stressors in such highly modified urban water bodies

Dataset for: Zinc toxicity to <i>Daphnia magna</i> in a two-species microcosm can be predicted from single-species test data: the effects of phosphorus supply and pH

Ecological interactions and abiotic stress factors may significantly affect species sensitivities to toxicants and these are not incorporated in standard single species tests. This study tests the hypothesis if a model, calibrated solely on single species data, can explain abiotic stress factors in a two-species microcosm, a test applied to the effects of nutritional stress (phosphorus (P)-limitation) on zinc (Zn) toxicity to <i>Daphnia magna</i>. A population model was developed based on P- and Zn-dependent algal and daphnid growth. Two separate two-species (phytoplankton <i>Pseudokirchneriella subcapitata</i> and consumer <i>D. magna</i>) microcosm experiments with P×Zn factorial combinations and a different pH (7.3 and 7.8) were set up to validate the model. The 21-day daphnid population size was considerably reduced by increased Zn and by decreased P supply with a significant (p<0.001) interaction among both factors. The observed median effective concentration (EC50) of Zn on <i>D. magna</i> population size varied 12-fold (25 to 310 µg Zn L-1), with the lowest EC50’s found at the highest pH and high P treatments. For both experiments, Zn toxicity to <i>D. magna</i> was correctly predicted within a factor of two for EC50-values and are explained by the model through: (1) a higher phytoplankton Zn sensitivity at higher pH, affecting food supply to <i>D. magna</i> and (2) an increased algal P-content at higher Zn, offering a nutritional benefit to daphnids that counteracts direct Zn toxicity under P-limitation. This study illustrated that indirect effects of Zn via producer-consumer relationships can outweigh the direct toxic effects, and that models calibrated solely on single species test data can help with interpreting these results in two-species systems

Mixture Toxicity of Herbicides with Dissimilar Modes of Action to Myriophyllum spicatum

Considering the vital role of rooted macrophytes in the aquatic ecosystem, validating assumptions on the interactive effects of herbicides with different modes of action at an environmentally relevant mixture ratio is necessary. We investigated the effects of diflufenican (a carotenoid biosynthesis inhibitor) and iodosulfuron-methyl-sodium (IMS; an acetolactate synthase inhibitor) in a 14-day growth inhibition experiment with Myriophyllum spicatum, wherein single compounds and their combination were tested in parallel (n = 84). The assessment was done using three different methods: significance testing, model deviation ratio (MDR), and mixture interaction factor (MIF). Interactions relative to both concentration addition and independent action were assessed via significance testing. This revealed that diflufenican and IMS acted antagonistically relative to both models for fresh weight and total shoot length (p < 0.05) and that there was slight synergism for the number of side shoots (p < 0.001) relative to concentration addition. The MDR and MIF can only assess interactions relative to the concentration addition model. According to MDR, the mixture appeared to show no interaction (neither antagonistic nor synergistic), whereas the MIF method revealed that the compounds acted antagonistically for fresh weight and that there was a slight synergism for total shoot length and number of side shoots. We conclude that inferences about mixture toxicity interactions are method- and endpoint-dependent, which can have implications for regulatory mixtures assessment. Environ Toxicol Chem 2022;00:1–12

The fatty acid profile of rainbow trout liver cells modulates their tolerance to methylmercury and cadmium

The polyunsaturated fatty acid (PUFA) composition of fish tissues, which generally reflects that of thediet, affects various cellular properties such as membrane structure and fluidity, energy metabolism andsusceptibility to oxidative stress. Since these cellular parameters can play an important role in the cellularresponse to organic and inorganic pollutants, a variation of the PUFA supply might modify the toxicityinduced by such xenobiotics. In this work, we investigated whether the cellular fatty acid profile has animpact on the in vitro cell sensitivity to two environmental pollutants: methylmercury and cadmium.Firstly, the fatty acid composition of the rainbow trout liver cell line RTL-W1 was modified by enrichingthe growth medium with either alpha-linolenic acid (ALA, 18:3n-3), eicosapentaenoic acid (EPA, 20:5n-3),docosahexaenoic acid (DHA, 22:6n-3), linoleic acid (LA, 18:2n-6), arachidonic acid (AA, 20:4n-6) or docos-apentaenoic acid (DPA, 22:5n-6). These modified cells and their control (no PUFA enrichment) were thenchallenged for 24 h with increasing concentrations of methylmercury or cadmium. We observed that (i)the phospholipid composition of the RTL-W1 cells was profoundly modulated by changing the PUFA con-tent of the growth medium: major modifications were a high incorporation of the supplemented PUFA inthe cellular phospholipids, the appearance of direct elongation and desaturation metabolites in the cellu-lar phospholipids as well as a change in the gross phospholipid composition (PUFA and monounsaturatedfatty acid (MUFA) levels and n-3/n-6 ratio); (ii) ALA, EPA and DPA enrichment significantly protected theRTL-W1 cells against both methylmercury and cadmium; (iv) DHA enrichment significantly protectedthe cells against cadmium but not methylmercury; (v) AA and LA enrichment had no impact on the celltolerance to both methylmercury and cadmium; (vi) the abundance of 20:3n-6, a metabolite of the n-6 biotransformation pathway, in phospholipids was negatively correlated to the cell tolerance to bothmethylmercury and cadmium. Overall, our results highlighted the importance of the fatty acid supply onthe tolerance of fish liver cells to methylmercury and cadmium

Sea Spray Aerosols Contain the Major Component of Human Lung Surfactant

Marine phytoplankton influence the composition of sea spray aerosols (SSAs) by releasing various compounds. The biogenic surfactant dipalmitoylphosphatidylcholine (DPPC) is known to accumulate in the sea surface microlayer, but its aerosolization has never been confirmed. We conducted a 1 year SSA sampling campaign at the Belgian coast and analyzed the SSA composition. We quantified DPPC at a median and maximum air concentration of 7.1 and 33 pg m(-3), respectively. This discovery may be of great importance for the field linking ocean processes to human health as DPPC is the major component of human lung surfactant and is used as excipient in medical aerosol therapy. The natural airborne exposure to DPPC seems too low to induce direct human health effects but may facilitate the effects of other marine bioactive compounds. By analyzing various environmental variables in relation to the DPPC air concentration, using a generalized linear model, we established that wave height is a key environmental predictor and that it has an inverse relationship. We also demonstrated that DPPC content in SSAs is positively correlated with enriched aerosolization of Mg2+ and Ca2+. In conclusion, our findings are not only important from a human health perspective but they also advance our understanding of the production and composition of SSAs

Dataset for: Multigenerational effects of nickel on <i>Daphnia magna</i> depend on temperature and the magnitude of the effect in the first generation

Ecological risk assessment (ERA) is commonly based on single generation ecotoxicological tests that are usually performed at one standard temperature. We investigate the effects of nickel (Ni) on <i>Daphnia magna</i> reproduction at 15, 20 and 25°C along four generations. Multigenerational Ni effects on <i>D. magna</i> reproduction depended on the magnitude of the effect in the first generation (F0) and showed very different patterns at different temperatures. At low effect level concentrations ( D. magna were necessary to induce the same Ni toxicity than at higher temperature. Overall, our results indicate that low single-generation chronic effect concentrations of Ni to <i>D. magna</i> (here EC10) are also protective in a long-term, multigenerational context and that temperature should be taken into account in ERA of Ni

Dataset for: The effects of a mixture of copper, nickel and zinc on the structure and function of a freshwater planktonic community

It is generally assumed that as long as the majority of species experiences no direct adverse effects due to a single substance (i.e. Potentially Affected Fraction, PAF < 5%), no significant structural or functional effects at community-level are expected to occur. Whether this assumption holds for mixed metal contamination is not known. Here, we tested this by performing a microcosm experiment in which a naturally occurring freshwater planktonic community was exposed to a Cu-Ni-Zn mixture for 8 weeks, and in which various structural and functional community-level traits were assessed. In the low mixture concentration treatments (i.e., Ni-Zn mixtures, because there was no difference of Cu concentrations in these treatments with the control), community-level effects were relatively simple, only involving phytoplankton species groups. In the high mixture concentration treatments (Cu-Ni-Zn mixtures), community-level effects were more complex, involving several phytoplankton and zooplankton species groups. Multi-substance PAF (msPAF) values for all mixture treatments were calculated by applying the concentration addition model to bioavailability-normalised single-metal species sensitivity distributions (SSD). Consistent effects on the structural traits community composition, abundance of zooplankton species groups, species diversity, and species richness and on the functional trait dissolved organic carbon (DOC) concentration (as a proxy for the microbial loop and pelagic food web interactions) were only observed at msPAF values above 0.05, i.e. in the Cu-Ni-Zn mixture. However, consistent effects on the abundance of various phytoplankton species groups (structural traits) and on two measures of community respiration, i.e. overnight ∆DO and ∆pH (functional traits) were already observed at msPAF values of 0.05 or lower, i.e. in th

Dataset for: A framework for ecological risk assessment of metal mixtures in aquatic systems

Although metal mixture toxicity has been studied relatively intensely, there is no general consensus yet on how to incorporate metal mixture toxicity into aquatic risk assessment. Here, we combined existing data on chronic metal mixture toxicity at the species level with species-sensitivity-distribution (SSD)-based in-silico metal mixture risk predictions at the community-level for mixtures of Ni, Zn, Cu, Cd and Pb, in order to develop a tiered risk assessment scheme for metal mixtures in freshwater. Generally, independent action (IA) predicts chronic metal mixture toxicity at the species level most accurately, while concentration addition (CA) is the most conservative model. Mixture effects are non-interactive in 69% (IA) and 44% (CA) and antagonistic in 15% (IA) and 51% (CA) of the experiments, while synergisms are only observed in 15% (IA) and 5% (CA) of the experiments. At low effect sizes (around 10% mixture effect), CA overestimates metal mixture toxicity at the species-level by 1.2-fold (i.e. the Mixture interaction Factor [MiF]; median). Species, metal presence or number of metals does not significantly affect the MiF. To predict metal mixture risk at the community-level, bioavailability-normalization procedures were combined with CA or IA using SSD-techniques in 4 different methods, which were compared using environmental monitoring data of a European river basin (Dommel, the Netherlands). We found that the most simple method, in which CA is directly applied to the SSD (i.e. CASSD), is also the most conservative method. CASSD has a median Margin of Safety (MoS) of 1.1 and 1.2 for binary mixtures relative to the theoretically more consistent methods of applying CA or IA directly to the dose response curve (i.e. CADRC or IADRC, respectively)[...