Hendrika J. De Lange

Towards a renewed research agenda in ecotoxicology

New concerns about biodiversity, ecosystem services and human health triggered several new regulations increasing the need for sound ecotoxicological risk assessment. The PEER network aims to share its view on the research issues that this challenges. PEER scientists call for an improved biologically relevant exposure assessment. They promote comprehensive effect assessment at several biological levels. Biological traits should be used for Environmental risk assessment (ERA) as promising tools to better understand relationships between structure and functioning of ecosystems. The use of modern high throughput methods could also enhance the amount of data for a better risk assessment. Improved models coping with multiple stressors or biological levels are necessary to answer for a more scientifically based risk assessment. Those methods must be embedded within life cycle analysis or economical models for efficient regulations. Joint research programmes involving humanities with ecological sciences should be developed for a sound risk management.

Avoidance of polycyclic aromatic hydrocarbon–contaminated sediments by the freshwater invertebrates Gammarus pulex and Asellus aquaticus

Contamination of sediments is a serious problem in most industrialized areas. Sediments are often contaminated with trace metals and organic contaminants like polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Bioassays are often used to determine the effect of contaminants on biota. However, survival or growth may not be the most sensitive endpoints. Behavioral changes often occur at much lower concentrations. Our study aimed to assess the effect of PAHs on habitat choice of two common freshwater invertebrates, the amphipod Gammarus pulex and the isopod Asellus aquaticus. We spiked clean field sediment with a mixture of four PAHs, fluoranthene, pyrene, chrysene, and benzo[k]fluoranthene, to a total concentration of 30 mg PAH/kg dry weight. Both species were offered a choice between PAH-spiked sediments and clean sediments in laboratory experiments. Results show that both species avoid PAH-spiked sediment. Origin of the population, either from a clean reference site or from a polluted site, did not affect habitat choice of either species.

Ecological vulnerability in wildlife: An expert judgment and multicriteria analysis tool using ecological traits to assess relative impact of pollutants

Nature development in The Netherlands often is planned on contaminated soils and sediments of former agricultural land and in floodplain areas; however, this contamination may present a risk to wildlife species desired at those nature development sites. Specific risk assessment methods are needed, because toxicological information is lacking for most wildlife species. The vulnerability of a species is a combination of its potential exposure, sensitivity to the type of pollutant, and recovery capacity. We developed a new method to predict ecological vulnerability in wildlife using autecological information. The analysis results in an ordinal ranking of vulnerable species. The method was applied to six representative contaminants: copper and zinc (essential metals, low to medium toxicity), cadmium (nonessential metal, high toxicity), DDT (persistent organic pesticide, high toxicity), chlorpyrifos (persistent organophosphate insecticide, high toxicity), and ivermectin (persistent veterinary pharmaceutical, low to medium toxicity). High vulnerability to the essential metals copper and zinc was correlated with soil and sediment habitat preference of a species and with r-strategy (opportunistic strategy suited for unstable environments). Increased vulnerability to the bioaccumulating substances cadmium and DDT was correlated with higher position of a species in the food web and with life span and K-strategy (equilibrium strategy suited for stable environments). Vulnerability to chlorpyrifos and ivermectin was high for species with a preference for soil habitats. The ecological vulnerability analysis has potential to further our abilities in risk assessment.

Development of a feeding behavioural bioassay using the freshwater amphipod Gammarus pulex and the Multispecies Freshwater Biomonitor

The present study reports the development of a feeding behavioural bioassay using the Multispecies Freshwater Biomonitor (MFB). This device is based on the quadruple impedance conversion technique to record online different behaviours of animals. Animal movements in the water generate specific frequencies, and the MFB can estimate the percentage of time producing each frequency (from 0.5 to 8.5 Hz) by means of a stepwise discrete Fourier transformation. Two feeding behavioural bioassays were conducted in order to know the frequencies related to feeding behaviour of the freshwater amphipod Gammarus pulex. The first bioassay assessed the effects of food presence in the amphipod behaviour. The second bioassay assessed the effects of cadmium on the feeding activity (measured as leaf weight loss) and behaviour (swimming, ventilation, and feeding recorded through the MFB) of G. pulex in order to check the suitability of the developed method. The results of the first bioassay showed that the frequencies ranging from 3.0 to 4.5 Hz were highly correlated with feeding activity, especially 3.5 and 4.0 Hz. In the second bioassay, we found that cadmium reduced feeding and ventilation behaviours. Our study showed that the MFB can be used to record the feeding behaviour of G. pulex exposed to toxicants. The developed feeding behavioural bioassay allows an accurate and automatic assessment of several endpoints, including feeding, swimming and ventilation. However, the study of the complex behaviour of G. pulex using the MFB needs further research, since some behaviours seem to generate similar frequencies.

Sediment pollution and predation affect structure and production of benthic macroinvertebrate communities in the Rhine–Meuse delta, The Netherlands

Abstract Most floodplain sediments of the rivers Rhine and Meuse in The Netherlands are moderately polluted with trace metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other chemicals. The effects of these sediment-bound contaminants on the productivity of benthic macroinvertebrates are unclear. Sixteen locations along a pollution gradient were investigated in creeks in the Biesbosch floodplain area. Sediment samples were analyzed for bulk sediment characteristics and contaminants (total and bioavailable concentrations of trace metals, PAHs, and PCBs). Exclosures were used to study the effect of predation by fish and birds on macroinvertebrates. Macroinvertebrates were sampled and identified to species level, and production was estimated from biomass increases inside the exclosures during a 1-mo interval in spring. Benthic macroinvertebrate species richness was negatively affected by sediment contamination. Production of oligochaetes and chironomids was not correlated with levels of contamination, but production of gastropods was negatively correlated with contamination. Environmental variables that reflected food availability (seston and sediment organic C) were positively correlated with contamination. Predation significantly reduced invertebrate biomass, but the effects of predation and sediment contamination were not correlated with each other. Our study suggested that the moderate levels of contamination affected the structure but not the productivity of the benthic macroinvertebrate community, probably because of the counteracting effects of contamination and associated surplus of food.

Effects of UV-B irradiated algae on zooplankton grazing

We tested the effects of UV-B stressed algae on grazing rates of zooplankton. Four algal species (Chlamydomonas reinhardtii, Cryptomonas sp., Scenedesmus obliquus and Microcystis aeruginosa) were used as food and fed to three zooplankton species (Daphnia galeata, Bosmina longirostris and Brachionus calyciflorus), representing different taxonomic groups. The phytoplankton species were cultured under PAR conditions, and under PAR supplemented with UV-B radiation at two intensities (0.3 W m−2 and 0.7 W m−2, 6 hours per day). Ingestion and incorporation experiments were performed at two food levels (0.1 and 1.0 mg C l−1) using radiotracer techniques. The effect of food concentration on ingestion and incorporation rate was significant for all three zooplankton species, but the effect of UV-B radiation was more complex. The reactions of the zooplankton species to UV-B stressed algae were different. UV-B stressed algae did not affect Daphnia grazing rates. For Bosmina the rates increased when feeding on UV-B stressed Microcystis and decreased when feeding on UV-B stressed Chlamydomonas, compared with non-stressed algae. Brachionus grazing rates were increased when feeding on UV-B stressed Cryptomonas and UV-B stressed Scenedesmus, and decreased when feeding on UV-B stressed Microcystis, compared with non-stressed algae. These results suggest that on a short time scale UV-B radiation may result in increased grazing rates of zooplankton, but also in decreased grazing rates. Long term effects of UV-B radiation on phytoplankton and zooplankton communities are therefore difficult to predict.

Intraguild predation behaviour of ladybirds in semi-field experiments explains invasion success of Harmonia axyridis.

Harmonia axyridis has been introduced as a biological control agent in Europe and the USA. Since its introduction, it has established and spread, and it is now regarded as an invasive alien species. It has been suggested that intraguild predation is especially important for the invasion success of H. axyridis. The aim of this study was to compare the intraguild predation behaviour of three ladybird species (Coccinella septempunctata, Adalia bipunctata, and H. axyridis). Predation behaviour was investigated in semi-field experiments on small lime trees (Tilia platyphyllos). Two fourth-instar larvae placed on a tree rarely made contact during 3-hour observations. When placed together on a single leaf in 23%–43% of the observations at least one contact was made. Of those contacts 0%–27% resulted in an attack. Harmonia axyridis attacked mostly heterospecifics, while A. bipunctata and C. septempunctata attacked heterospecifics as often as conspecifics. In comparison with A. bipunctata and C. septempunctata, H. axyridis was the most successful intraguild predator as it won 86% and 44% of heterospecific battles against A. bipunctata and C. septempunctata respectively, whilst A. bipunctata won none of the heterospecific battles and C. septempunctata won only the heterospecific battles against A. bipunctata. Coccinella septempunctata dropped from a leaf earlier and more often than the other two species but was in some cases able to return to the tree, especially under cloudy conditions. The frequency with which a species dropped did not depend on the species the larva was paired with. The results of these semi-field experiments confirm that H. axyridis is a strong intraguild predator as a consequence of its aggressiveness and good defence against predation from heterospecific species. The fact that H. axyridis is such a strong intraguild predator helps to explain its successful establishment as invasive alien species in Europe and the USA.

Attraction of the amphipod Gammarus pulex to water-borne cues of food

We examined the ability of the amphipod Gammarus pulexto detect chemical cues released from potential food sources. Therefore, response of G. pulex to chemical cues from food was tested in paired-choice laboratory experiments. Comparisons were made between artificial and natural leaves, with and without the importance of aufwuchs, and with different components of the aufwuchs community. Our study demonstrated that G. pulex actively chose its food and that G. pulex is most strongly attracted to the aufwuchs on discs rather than to the leaf itself. Fungi and bacteria are more important in the food selection process than algae probably because fungal and bacterial cues are more specific cues for decaying leaves than algal cues, since algae also grow on mineral substrates and then do not contribute to leaf decomposition.

Wildlife vulnerability and risk maps for combined pollutants.

Ecological risk and vulnerability maps can be used to improve the analysis of pollutant risks and communication to stakeholders. Often, such maps are made for one pollutant at the time. We used the results of wildlife vulnerability analysis, a novel trait-based risk assessment approach, to map overall vulnerability of habitats in Denmark to various metals and one insecticide. These maps were combined with maps of estimated soil concentrations for the same compounds divided by their Maximum Permissible Concentrations. This combination yielded relative risk maps that can be used to assess where the highest risk conditions to wildlife from these individual pollutants in Denmark occur (hot spot identification). In order to show how cumulative risk maps can be made, the maps of the individual pollutants were combined assuming different mechanisms of joint toxicity: no addition, concentration addition, antagonism and synergism. The study demonstrated that with an accurate set of geographical and ecological data one can use the results of vulnerability analysis to make relevant ecological risk maps that show hot spot areas for risks of single or cumulative risks from soil pollutants.

Ecological vulnerability in wildlife: application of a species-ranking method to food chains and habitats.

Nature development in The Netherlands is often planned on contaminated soils or sediments. This contamination may present a risk for wildlife species desired at those nature development sites and must be assessed by specific risk assessment methods. In a previous study, we developed a method to predict ecological vulnerability in wildlife species by using autecological data and expert judgment; in the current study, this method is further extended to assess ecological vulnerability of food chains and terrestrial and aquatic habitats typical for The Netherlands. The method is applied to six chemicals: Cd, Cu, Zn, dichlorodiphenyltrichloroethane, chlorpyrifos, and ivermectin. The results indicate that species in different food chains differ in vulnerability, with earthworm-based food chains the most vulnerable. Within and between food chains, vulnerability varied with habitat, particularly at low trophic levels. The concept of habitat vulnerability was applied to a case study of four different habitat types in floodplains contaminated with cadmium and zinc along the river Dommel, The Netherlands. The alder floodplain forest habitat contained the most vulnerable species. The differences among habitats were significant for Cd. We further conclude that the method has good potential for application in mapping of habitat vulnerability.