New Publications

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.

Microplastic pollution in deep-sea sediments

env pollutWe have all heard the phrase: "We know more about the surface of the moon than the deep sea". Unfortunately, this is not exaggeration: the deep sea is the largest ecosystem on Earth, but also one of the least studied despite it harbouring a high biodiversity and a wealth of resources. Sadly, the deep seafloor is still, for most people, out of sight and therefore out of mind. This has encouraged the dumping of waste of all sorts into deep waters. For centuries, this was organic, degradable matter. Now, our solid wastes often contain synthetic elements, plastics in particular. In recent years, more and more reports have been published that demonstrate the large presence of plastic litter in the deep sea: the seafloor of the Mediterranean, Atlantic canyons and even Arctic waters are covered with plastic litter. Recently, our lab added another pollutant to the list: for the first time ever, microplastics were recorded in deep-sea sediments originating from several location worldwide. These results show that microplastics have penetrated the marine environment to a larger extent than previously assumed.

Epigenetics in an ecotoxiological context

mutation researchChildren of obese fathers are more likely to have chronic diseases in their later life. That was the conclusion of a remarkable study by Dr. Adelheid Soubry in BMC Medicine (De Standaard, 08/02/2013). She identified one of the mechanisms responsible to be DNA-methylation. DNA-methylation, among other mechanisms, are so-called epigenetic mechanisms. They can alter the DNA without actually altering the DNA code itself. These epigenetic mechanisms are also shown to be important in an ecotoxicological context. This was recently summarized by our post-doc Michiel Vandegehuchte in a review in Mutation Research/Genetic Toxicology and Environmental Mutagenesis.

Combined exposure to cyanobacteria and carbaryl results in antagonistic effects on the reproduction of Daphnia pulex
etcIn aquatic ecosystems, Daphnia are exposed to a wide variety of natural and chemical stressors that can cause interactive effects resulting in an increased impact on aquatic ecosystems. The authors therefore investigated the interactive effects of harmful cyanobacteria (cyanoHABs) with carbaryl in Daphnia pulex, because cyanobacteria have become an important concern for aquatic ecosystems. Daphnia were exposed for 21 d to 4 selected cyanobacteria (Aphanizomenon sp., Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Oscillatoria sp), carbaryl, and all binary combinations of carbaryl and each individual cyanobacterium. Results were analyzed with both the independent action and the concentration addition model.

Assessment of marine debris on the Belgian Continental Shelf

marinepollutionbulletinA two-year comprehensive assessment of marine litter in Belgian coastal waters was performed. Abundance, weight and composition of marine debris, including microplastics, was assessed by performing beach, sea surface and seafloor monitoring campaigns. Plastic items were the dominant type of macrodebris recorded: over 95% of debris present in the three sampled marine compartments were plastic. In general, concentrations of macrodebris were quite high. Especially the number of beached debris reached very high levels: on average 6,429 ± 6,767 items per 100m were recorded. Microplastic concentrations were determined to assess overall abundance in the different marine compartments of the Belgian Continental Shelf. In terms of weight, macrodebris still dominates the pollution of beaches, but in the water column and in the seafloor microplastics appear to be of higher importance: microplastic weight is approximately 100 times and 400 times higher, respectively, than macrodebris weight.


Ecotoxicity and uptake of polymer coated gold nanoparticles

nanotoxicologyBioconjugated gold nanoparticles (Au NPs) are a promising tool for pharmaceutical applications. However, the ecotoxicity of these types of NPs has hardly been studied. We investigated the ecotoxicity and uptake of 4-5 nm Au NPs to which two types of polymer coatings were attached. One coating was an amphiphilic polymer only and the other an amphiphilic coating to which 10 kDa polyethylene glycol chains were attached. In both 72 h algal growth inhibition tests with the alga Pseudokirchneriella subcapitata and in 24 h resazurin cytotoxicity tests with the rainbow trout gill cell line RTGill-W1, the pegylated Au NPs were found less toxic compared to the amphiphilic coated particles. No uptake or direct interaction between particles and algal cells was observed. However, uptake/adsorption in fish gill cells reached up to >10(6) particles/cell after 1 h and particles were eliminated for ≥96% after 24 h depuration. Both particle types were found within membrane enclosed vesicles in the cytoplasm of RTgill-W1 cells.

Emerging contaminants in Belgian marine waters: Single toxicant and mixture risks of pharmaceuticals

marinepollutionbulletinKnowledge on the effects of pharmaceuticals on aquatic marine ecosystems is limited. The aim of this study was therefore to establish the effect thresholds of pharmaceutical compounds occurring in the Belgian marine environment for the marine diatom Phaeodactylum tricornutum, and subsequently perform an environmental risk assessment for these substances. Additionally, a screening-level risk assessment was performed for the pharmaceutical mixtures.

No immediate risk for acute toxic effects of these compounds on P. tricornutum were apparent at the concentrations observed in the Belgian marine environment. In two Belgian coastal harbours however, a potential chronic risk was observed for the ?-blocker propranolol. No additional risks arising from the exposure to mixtures of pharmaceuticals present in the sampling area could be detected. However, as risk characterization ratios for mixtures of up to 0.5 were observed, mixture effects could emerge should more compounds be taken into account.

Full reference (link)

Claessens M, Vanhaecke L, Wille K, Janssen CR. 2013. Emerging contaminants in Belgian marine waters: Single toxicant and mixture risks of pharmaceuticals. Marine Pollution Bulletin. In press. 

Cloning and functional analysis of the ecdysteroid receptor complex in the opossum shrimp Neomysis integer (Leach, 1814)

aquatic toxicologyIn this paper, the non-target effects of tebufenozide were evaluated on the estuarine crustacean, the opposum shrimp Neomysis integer (Leach, 1814). Tebufenozide is a synthetic non-steroidal ecdysone agonist insecticide and regarded as potential endocrine-disrupting chemical (EDC). N. integer is the most used crustacean in ecotoxicological research in parallel to Daphnia sp. and has been proposed for the regulatory testing of potential EDCs in the US, Europe and Japan.

Major results were: (i) cDNAs encoding the ecdysteroid receptor (EcR) and the retinoid-X-receptor (RXR), were cloned and sequenced, and subsequent molecular phylogenetic analysis (maximum likelihood and neighbor-joining) revealed that the amino acid sequence of the ligand binding domain (LBD) of N. integer EcR (NiEcR) clusters as an outgroup of the Crustacea, while NiRXR-LBD clusters in the Malacostracan clade (bootstrap percentage = 75%). (ii) 3D-modeling of ligand binding to NiEcR-LBD demonstrated an incompatibility of the insecticide tebufenozide to fit into the NiEcR-ligand binding pocket. This was in great contrast to ponasterone A (PonA) that is the natural molting hormone in Crustacea and for which efficient docking was demonstrated. In addition, the heterodimerization of NiEcR-LBD with the common shrimp Crangon crangon (Linnaeus, 1758) RXR-LBD (CrcRXR-LBD) was also modeled in silico. (iii) With use of insect Hi5 cells, chimeric constructs of NiEcR-LBD and CrcRXR-LBD fused to either the yeast Gal4-DNA binding domain (DBD) or Gal4-activation domain (AD) were cloned into expression plasmids and co-transfected with a Gal4 reporter to quantify the protein–protein interactions of NiEcR-LBD with CrcRXR-LBD. Investigation of the ligand effect of PonA and tebufenozide revealed that only the presence of PonA could induce dimerization of this heterologous receptor complex. (iv) Finally, in an in vivo toxicity assay, N. integer juveniles were exposed to tebufenozide at a concentration of 100 μg/L, and no effects against the molting process and nymphal development were scored.

In conclusion, the in vitro cell reporter assay, based on NiEcR-LBD/CrcRXR-LBD heterodimerization in Hi5 cells and validated with the natural ecdysteroid hormone PonA, represents a useful tool for the screening of putative EDCs. As a test example for non-steroidal ecdysone agonist insecticides, tebufenozide had no negative effects on NiEcR/RXR receptor dimerization in vitro, nor on the molting process and nymphal development of N. integer at the tested concentration (100 μg/L) in vivo.

Full reference (link)

De Wilde R, Swevers L, Soina T, Christiaens O, Rougé P, Cooreman K, Janssen CR, Smagghe G. 2013. Cloning and functional analysis of the ecdysteroid receptor complex in the opossum shrimp Neomysis integer (Leach, 1814). Aquatic Toxicology 130–131:31–40.

Modelling the effects of copper on soil organisms and processes using the free ion approach: Towards a multi-species toxicity model

env_pollutOur lab has a long history of metal bioavailability research. Here, the results of previous terrestrial studies performed by our lab was used and integrated with other datasets to develop a general biovailability model for copper. The free ion approach has been previously used to calculate critical limit concentrations for soil metals based on point estimates of toxicity. In this study, the approach was applied to dose–response data for copper effects on seven biological endpoints in each of 19 European soils. The approach was applied using the concept of an effective dose, comprising a function of the concentrations of free copper and 'protective' major cations, including H+. A significant influence of H+ on the toxicity of Cu2+ was found, while the effects of other cations were inconsistent. The model could be generalised by forcing the effect of H+ and the slope of the dose–response relationship to be equal for all endpoints. This suggests the possibility of a general bioavailability model for copper effects on organisms. Furthermore, the possibility of such a model could be explored for other cationic metals such as nickel, zinc, cadmium and lead.

Full reference (link)

Lofts S, Criel P, Janssen CR, Lock K, McGrath SP, Oorts K, Rooney CP, Smolders E, Spurgeon DJ, Svendsen C, Van Eeckhout H, Zhao F-Z. 2013. Modelling the effects of copper on soil organisms and processes using the free ion approach: Towards a multi-species toxicity model. Environmental Pollution 178:244–253.