The combined effects of metal mixtures and natural stressors on aquatic invertebrates: Relating changes in metal accumulation to altered behavior and ecological effects

Date: 5 March 2019

Venue: Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim)

Time: 4:00 PM

Organization / co-organization: Department of Biology

Principal investigator: Lieven Bervoets, Ronny Blust

Short description: PhD defence Marjolein Van Ginneken - Faculty of Science, Department of Biology


Metals are posing a worldwide threat to aquatic ecosystems. In these contaminated environments, trace metals most often occur in different mixtures, in which metals can interfere with each other, producing antagonistic, synergistic or additive toxic effects. Besides pollutants, natural stressors, such as fluctuating temperature, food shortages and predators, are present as well, which could alter metal toxicity. Yet, current environmental quality standards (EQS) are mainly based on laboratory tests in which test organisms are exposed to single metals under constant, favorable conditions. Moreover, in the setting of environmental standards, behavioral endpoints, which are more sensitive than mortality, have never been used. As a result, the current EQS for metals might result in under- or overprotection of the environment.

By combining metal mixtures with natural stressors and assessing the effects on different levels of biological organization, the present thesis aimed to contribute to the development of environmentally-relevant risk assessment. Firstly, we investigated the effects of metal mixtures and the natural stressors, temperature and predation pressure, on (sublethal) endpoints of the aquatic invertebrate Asellus aquaticus. This isopod is an important decomposer in freshwater ecosystems in the northern hemisphere. We linked the effects on metal accumulation, mortality, respiration, growth and, as behavioral endpoints, feeding rate and activity to metal water and body concentrations. Secondly, metal mixture effects on a whole aquatic community were assessed in small artificial ecosystems.

We determined that natural stressors, both biotic and abiotic factors, can change the toxicity of metals. Additionally, other metals can interact as well. These interaction patterns are complex and it is difficult to predict their combined effects. Depending on the exposure concentrations, the metals in the mixture and the endpoint, stressor interactions and effects can change. The Water Framework Directive does not take these additional stressors into account and, thus, does not accurately assess the toxicity of metals in freshwater ecosystems. Therefore, we advise complementing chemical-based monitoring with effect-based tools in situ to better identify ecological risks.