New Publications

Hard X-ray nanoprobe investigations of the subtissue metal distributions within Daphnia magna

AnalBioChemTo improve our capacity to evaluate the impact of metals on aquatic organisms, the fundamental processes of uptake, elimination and detoxification need to be fully understood. To this end, the freshwater crustacean Daphnia magna has long served as a model organism for studying whole body bio-accumulation. In order to fully comprehend the active regulation of internal concentrations within aquatic biota, the toxicological research needs to move from the microscopic tissue scale towards a (sub)cellular field of view. We developped a novel sample preparation technique which, when coupled to advanced elemental imaging, reveals the distributions of Ca, Fe and Zn within D. magna at the subtissue level. The presented technique was found to be well suited for trace-level bio-imaging which may ultimately aid in the discovery of new insights in the detoxification processes within aquatic model organisms.

Additive modelling reveals spatiotemporal PCBs trends in marine sediments 

marinepollutionbulletinThe environmental fate and toxicity of persistent organic pollutants (POPs) are of global concern. Spatiotemporal trend analyses of such hazardous substances are identified as a key priority by the OSPAR commission. In this paper we analyse one of the largest, longest and most complete data sets of PCBs using a regression-based technique in order to compare the levels and time trends of marine and estuarine PCB sediment concentrations between and within the Belgian Coastal Zone (BCZ) and the Western Scheldt estuary. The time trends unraveled a two to three-fold decrease in PCB concentrations in the BCZ during the past 20 years (1991-2010). However, in the Western Scheldt estuary, time trends were spatially heterogeneous and did not exhibit a significant decrease. These results demonstrate that international efforts to reduce PCB emissions have effectively reduced concentrations in open water ecosystems like the BCZ but have not affected urbanized and industrialized areas of the Scheldt estuary. The ten PCB congeners we considered followed the same trend, suggesting that no point sources are present in our study area for these congeners.

The Combined Effect of Dissolved Organic Carbon and Salinity on the Bioaccumulation of Copper in Marine Mussel Larvae 

ESnTDue to natural and anthropogenic influences, copper concentrations can be elevated in the aquatic environment. However, the total dissolved Cu concentration is, by itself, an inefficient predictor of copper toxicity. Considerable efforts have been made to improve the prediction of toxic effects by taking into account the aquatic concentration of other elements and dissolved organic carbon (DOC). These models are based on Cu accumulation at a so-called biotic ligand somewhere in the exposed organism. Mussels, and especially the larvae, are very sensitive to copper. Because of their ecological and economical importance, more specific knowledge about the influence of salinity and DOC on Cu accumulation and distribution in mussel larvae was needed. By collaborating with the X-ray microscopy and imaging group of the UGent (XMI), we could use synchrotron X-ray fluorescence spectroscopy and measure the Cu body burden of individual larvae with a spatial resolution up to 100*100nm. The results indicate that accumulated Cu is homogenously distributed in mussel larvae and decreases with increasing DOC concentrations. Salinity also altered Cu accumulation in a nonlinear way which indicates that alterations in salinity change the physiology of the larvae. The latter is important because this means that Cu accumulation in mussel larvae cannot be predicted solely based on water chemistry.

An approach to assess the regulatory relevance of micro-evolutionary effects in ecological risk assessment of chemicals: A case-study with Cd

etc thumb medium121 159Through ecological risk assessment (ERA) policy makers try to set protective norms for harmful chemicals in the environment. Typically, such ERAs are based on ecotoxicological research performed in the lab. However, these laboratory conditions tend to lack some measure of realism compared to the actual situation in the environment. For instance, usually only one particular individual of a species is considered in ecotoxicological tests, while in the environment multiple, different individuals are present. As with us, humans, some of these individuals can cope better with a certain chemical in the environment than others. Under continuous presence of such a chemical these, more tolerant, individuals will survive and reproduce, while the other individuals will perish. Overall, the group of individuals will become more tolerant to the chemical, a process which is called micro-evolution. In this most recent paper an approach is suggested to take this micro-evolutionary processes into account in ERA to, ultimately, make our risk assessment of chemicals in the environment more realistic.

The initial tolerance to sub-lethal Cd exposure is the same among ten naïve pond populations of Daphnia magna, but their micro-evolutionary potential to develop resistance is very different

aquatic toxicologyDifferences between the ecological reality in the field and the controlled test conditions in the lab make ecotoxicological results sometimes difficult to extrapolate from the lab to the situation in the field. One of the conditions that are different in the field compared to the lab is the presence of different individuals of an organism. First, each of these individuals differ in their tolerance to toxic stress. Second, the presence of different individuals allow for evolution which results in a group of individuals having a higher tolerance to toxic stress compared to an unevolved group. To characterize these two problems and to investigate possible solutions to them, we compared in our latest paper the tolerance and the potential to evolve in ten groups of individuals orginating from ten natural 'field' populations in Belgium. Although the tolerance of the individuals in these ten groups is quite similar, their potential to evolve an enhanced tolerance is very different.

Toxicity – biodiversity relationships unravelled

ecol lettersThe production and use of chemicals is regulated by environmental legislation so as to protect the diversity of our surface waters. Until recently, however, it was impossible to predict the relationship between chemical toxicity and the diversity of aquatic communities, which hampered effective environmental conservation. Together with an international consortium, the laboratory of environmental toxicology (, UGent) developed the first theory to predict biodiversity along gradients of toxic stress. Combining this theory to data from polluted algal communities, the scientists reveal that the variability of toxicity tolerance in these communities is five to ten times higher between individuals from the same species than between individuals from different species. The results of this research also demonstrate that this 'within-species variability' is a buffer against species loss in ecosystems polluted with chemicals. These findings, which have been published in the nr 1-ranked ecology journal 'Ecology Letters', raise important concerns regarding the use of species-based tolerance data for environmental protection and explain ecosystem resistance during chemical spills.

Migration and opportunistic feeding increase PCB accumulation in arctic seabirds

ESTPolychlorinated biphenyls (POPs) are resistant towards common degradation pathways and accumulate, because of their lipophilicity, in organisms' fatty tissues. In addition, the transfer of POPs in a foodweb typically results in elevated POP concentrations at the highest trophic levels (i.e. biomagnification). Previous modeling efforts hence focused on the importance of an organism's trophic level and the lipophilicity of the chemical as predictors for the organism's POP body concentration. However, field studies have not only demonstrated that Arctic seabirds, as top predators, have elevated POP body concentrations compared to their environment, but also that POP body concentrations can differ substantially between species that occupy similar trophic levels.

An investigation of the inter-clonal variation of the interactive effects of cadmium and Microcystis aeruginosa on the reproductive performance of Daphnia magna

aquatic toxicologyStressors seldomly occur isolated in the environment. In a mixture, stressors can interact with each other. That might have profound adverse effects on the animals that live in the environment. Indeed, in mixture toxicity, one plus one does not always equals two. Imagine for instance the effect of throwing a mentos candy in coke (Youtube: MythBusters - Diet Coke and mentos). The effect of both combined is much larger than what you would expect. Such (synergistic) interactions between the metal cadmium and the cyanobacterium Microcystis are what De Coninck et al. (2013) studied in their most recent paper. Cyanobacteria are toxic blue-green algae that tend to increase in occurence due to climate change (for instance, Global Water Forum).

Transcription patterns of genes encoding four metallothionein homologs in Daphnia pulex exposed to copper and cadmium are time- and homolog-dependent

aquatic toxicologyIn a recent publication, Asselman et al. (2013) studied the role of metallothioneins, or metal binding proteins, in metal detoxification upon exposure to copper and cadmium. In their study, Asselman et al. (2013) used the freshwater crustacean Daphnia as a model organism but their results will help to elucidate the function of this important protein in other (higher) organisms as well. Indeed, metal pollution has significant impacts on fish (Scientific American).

Development and validation of a quantitative structure–activity relationship for chronic narcosis to fish

etcQuantitative structure–activity relationship models (QSAR models) typically relate a set of predictor variables to the response variable. These models are useful tools in predictive ecotoxicology as the can be used to predict the (adverse) biological activity of a chemical (the response variable) based on the physico-chemical properties of the chemical (the predictor variables). As animal testing, and especially vertebrate testing, are generally strongly discouraged, the use of QSAR models offers an alternative. However, in ecotoxicology, QSAR models that describe the relationship between the physico-chemical properties of chemicals and their chronic toxicity to vertebrates are scarce. This lagoon in our knowledge is filled by the research described in our latest paper.