New Publications

Tetracycline is a commonly used antibiotic in aquaculture, veterinary and agriculture. Due to its widespread use, tetracycline is commonly found in our environment where it can harm other organisms. Here we studied the effects of tetracycline on the waterflea daphnia. We particularly focused on studying the long-term effects of tetracycline, which consists of three generations of daphnia exposed to tetracycline (from grandparents to grandchildren) at the molecular level. We observed effects of tetracycline in all generations particularly targeted the molting related genes, which are in daphnia also responsible for growth. We also observed that when exposing daphnia to different concentrations of tetracycline specific genes called vitellogenin were affected and these genes could be linked to effects on reproduction. Our results show that the effects of chemicals to different generations and to different concentrations are very different and that these effects cannot be neglected in the environmental risk assessment of tetracycline.

Metal contamination of rivers and streams generally occurs as a combination of multiple metals (also called mixtures). However, it is yet unresolved how risks of mixed metal contamination to ecosystems should be evaluated. To increase the knowledge about chronic mixture effects, the authors investigated whether metal mixture effects are dependent on the biological species, mixture composition, and metal concentration ratio. The authors evaluated the effects of quaternary Ni-Zn-Cu-Cd and ternary Ni-Zn-Cu mixtures on 48-h algal growth rate (Pseudokirchneriella subcapitata) and 7-d daphnid reproduction (Ceriodaphnia dubia) using a ray design.

To obtain a better understanding of the biological responses to unpredictable environmental change, the early transcriptional response of the keystone species Daphnia magna to twelve environmental perturbations was characterised. We discovered that approximately one-third of the Daphnia genes, enriched for metabolism, cell signalling and general stress response, drives transcriptional early response to environmental stress and it is shared among genetic backgrounds. 

To assess the consequences of ongoing biodiversity changes, hundreds of biodiversity experiments have been carried out since the 1990s. However, changes in ecosystem functioning between systems can not only result from differences in the number of species, but also from differences in what species are present (i.e. species identities). Additive partitioning methods are therefore generally used in biodiversity research. These factor out species identify effects by comparing the observed level of ecosystem functioning against that predicted by the null model for the given species composition of the system. These species’ deviations from the null can be partitioned between several terms reflecting the various mechanisms through which biodiversity can affect ecosystem functioning. Current partitioning methods, however, quantify biodiversity effects based on linear relationships between species functional traits and their deviations from the null model. In this paper, we demonstrate that non-linear relationships frequently occur, and derived a non-linear extension of additive partitioning methods to quantify these more complex biodiversity effects on ecosystem functioning.

Toxicity of metals like zinc (Zn) to freshwater organisms is not only dependent on the concentration of the metals itself, but also on other properties of the water, like its hardness and its acidity (pH). This is called bioavailability. In the European Union, safe levels of Zn can be calculated as a function of these properties, using so-called bioavailability models. Previously, the existing models could not be applied to more than 25% of European waters, because hardness or pH were higher than those for which the models were originally developed. In this research, we have shown with new experimental work that the existing model for algae can also be used at a much wider range of hardness and pH than previously thought. Our work with water fleas, however, showed that the existing model needed to be considerably improved.
Metal contamination of rivers and streams generally occurs as a combination of multiple metals (so called mixtures). However, it is yet unresolved how risks of mixed metal contamination to ecosystems should be evaluated. We collated data from 30 different toxicity tests with metal mixtures and analysed them in a systematic way to derive general conclusions that can be used in risk assessment. We found  cases in which different metals, each individually causing <10% toxicity (relative to uncontaminated water), caused much larger toxicity (up to 66%) when combined. This suggests that the current metal-by-metal approach in risk assessment may not be conservative enough for the environment. We also considered the use of two common mixture toxicity models to predict metal mixture toxicity.
Copepods play a fundamental role in the food chain of our oceans as they feed on algae and get eaten by fish. Amongst others, the harpacticoid copepod species Nitocra spinipes has become a popular model species in aquatic toxicity testing over the past few decades. To understand the combined effects of chemical pollution and climate change-related stressors on copepod populations, a proper quantification of those processes is essential. In this study, GhEnToxLab researcher Josef Koch and his Swedish coauthors (Stockholm University) quantified the effects of temperature and food shortage as two climate change-related environmental stressors on Nitocra spinipes and implemented the corresponding stress functions into an individual-based population model for this species.

Darwin’s rules of “evolution” and “survival of the fittest” also apply to populations of organisms exposed to chemical substances. Our review of the scientific literature revealed that long-term exposure to two classes of persistent pollutants, PAH’s and PCB’s, can affect the evolutionary trajectory of natural populations and make them more resistant to these chemicals. In some cases, this has happened at pollutant levels below currently applicable environmental quality standards. This calls for integrating evolutionary processes into regulatory decision-making.

Over the last decade, it has become clear that epigenetic mechanisms could play a role in the toxicity of environmental toxicants. Epigenetic mechanisms are mechanisms that alter the DNA strands without changing the DNA itself.In this study, we focus on the DNA methylation patterns in the waterflea exposed to a toxic blue green algae.  We studied the methylation patterns in exposed and unexposed animals and found significant differences between the two treatments. Overall, this study suggests that DNA methylation plays an important role in the toxicity response.

Biodiversity increases the stability of ecosystem functions in fluctuating environments. Only recently, parts of the underlying processes have been uncovered. A meta-analysis of biodiversity experiments manipulating primary producer richness revealed that the increased stability in more diverse systems was driven by an increased resistance (i.e. reduced changes), rather that an increased resilience (i.e. a rapid recovery). As many ecosystem functions, comprise the joint functional contribution of the species in the system, the stability of these ecosystem functions should depend on changes in the system’s composition. Theoretical models predict that an increased number of species interactions should slow down compositional changes. By consequence, biodiversity is expected to increase both compositional and functional resistance, but these predictions have never been put to the test. In this article, Baert et al. use marine diatom microcosms to demonstrate this tight link between compositional and functional stability.