The combined and interactive effects of zinc, temperature and phosphorus on freshwater planktonic communities

The main goal of the ecological risk assessment of chemicals (ERA) is the protection of populations and communities and the correct effect assessment of chemicals on the structure and functioning of aquatic ecosystems. At present, ERA is mainly based on data obtained from standard ecotoxicity experiments. These experiments are typically conducted under standardized optimal conditions, at the species level and exposed at a single stressor at the time. However, these general ERA approaches are in sharp contrast with natural conditions. Natural populations and communities are often exposed to a mixture of multiple stressors that are biotic (e.g. food shortage, predation) and abiotic (e.g. eutrophication, non-optimal temperature or water chemistry, metals). Species interactions such as predation and competition for food are two major biotic factors that are able to significantly affect the responses of organisms to toxicants. Additionally, abiotic factors such as temperature (T) can also play an important role affecting the toxic effects of chemical pollutants (e.g. by influencing its bioavailability and toxicokinetics). Therefore, by ignoring ecological interactions and by not considering natural field conditions these single-species tests oversimplify the actual field situation and ERA may not be protective. The aim of this PhD thesis was to investigate the combined effect of Zn with natural environmental stressors (temperature and/or phosphorous) at different organization levels (population vs. community) on freshwater organisms in order to increase the realism of current ERA

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

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

Imidacloprid treatments induces cyanobacteria blooms in freshwater communities under sub-tropical conditions

Imidacloprid is one of the most used neonicotinoid insecticides all over the world and is considered as a contaminant of concern due to its high toxicity potential to aquatic organisms. However, the majority of the studies that have evaluated the effects of imidacloprid on aquatic organisms were conducted under temperate conditions. In the present study, a mesocosm experiment was conducted under sub-tropical conditions to assess the effects of imidacloprid on the structure (macroinvertebrates, zooplankton and phytoplankton) and functional endpoints of an aquatic ecosystem and to compare the results with similar temperate and (sub-)tropical mesocosm studies. Imidacloprid (0, 0.03, 0.3 and 3 µg/L) was applied to 13 mesocosms weekly over a period of 4 weeks, followed by a one month recovery period. At the community level a lowest NOECcommunity of 0.03 µg/L was calculated for the zooplankton, phytoplankton and macroinvertebrate communities. The highest sensitivity to imidacloprid (NOEC < 0.03 µg/L) were observed for Gerris sp., Diaptomus sp. and Brachionus quadridentatus. Imidacloprid induced population declines of the larger zooplankton species (Diaptomus sp. and Ostracoda) resulted in increased rotifer abundances and shifted the phytoplankton community to a graze resistant gelatinous cyanobacteria dominated ecosystem. These cyanobacteria blooms occurred at all different concentrations and could pose an important public health and environmental concern. Although there are some differences in species and community sensitivity between the present and the other (sub-)topical mesocosm studies, it can be observed that all show a similar general community response to imidacloprid. Under (sub-)tropical conditions, the toxic effects of imidacloprid occur at lower concentrations than found for temperate ecosystems