Cornelis A.M. van Gestel

Protein differential expression induced by endocrine disrupting compounds in a terrestrial isopod.

Endocrine disrupting compounds (EDCs) have been studied due to their impact on human health and increasing awareness of their impact on wildlife species. Studies concerning the organ-specific molecular effects of EDC in invertebrates are important to understand the mechanisms of action of this class of toxicants but are scarce in the literature. We have used a dose/response approach to unravel the protein expression in different organs of isopods exposed to bisphenol A (BPA) and vinclozolin (Vz) and assess their potential use as surrogate species. Male isopods were exposed to a range of Vz or of BPA concentrations. After animal dissection, proteins were extracted from gut, hepatopancreas and testes. Protein profiles were analysed by electrophoresis and differentially expressed proteins were identified by MALDI mass spectrometry. EDCs affected proteins involved in the energy metabolism (arginine kinase), proteins of the heat shock protein family (Hsp70 and GRP78) and most likely microtubule dynamics (tubulin). Different proteins expressed at different concentrations in different organs are indicative of the organ-specific effects of BPA and Vz. Additionally, several proteins were up-regulated at lower but not higher BPA or Vz concentrations, bringing new data to the non-monotonic response curve controversy. Furthermore, our findings suggest that some common responses to EDCs in both vertebrates and invertebrates may exist.

METAL-BASED NANOPARTICLES IN SOIL: FATE, BEHAVIOR, AND EFFECTS ON SOIL INVERTEBRATES

Metal-based nanoparticles (NPs) (e.g., silver, zinc oxide, titanium dioxide, iron oxide) are being widely used in the nanotechnology industry. Because of the release of particles from NP-containing products, it is likely that NPs will enter the soil compartment, especially through land application of sewage sludge derived from wastewater treatment. This review presents an overview of the literature dealing with the fate and effects of metal-based NPs in soil. In the environment, the characteristics of NPs (e.g., size, shape, surface charge) and soil (e.g., pH, ionic strength, organic matter, and clay content) will affect physical and chemical processes, resulting in NP dissolution, agglomeration, and aggregation. The behavior of NPs in soil will control their mobility and their bioavailability to soil organisms. Consequently, exposure characterization in ecotoxicological studies should obtain as much information as possible about dissolution, agglomeration, and aggregation processes. Comparing existing studies is a challenging task, because no standards exist for toxicity tests with NPs. In many cases, the reporting of associated characterization data is sparse, or missing, making it impossible to interpret and explain observed differences in results among studies.

Physico-chemical and biological parameters determine metal bioavailability in soils

The Netherlands Stimulation program on System-oriented Ecotoxicological Research focused on three study areas, including two floodplains and a peaty grassland. All three areas were polluted with metals, with total soil concentrations often exceeding Dutch Intervention Values. The floodplain areas showed a homogeneous distribution of metal pollution, while pollution in the peaty area was more heterogeneous. This study aimed at establishing possible general trends in metal bioavailability by combining results obtained at the three different study sites. Available metal concentrations, measured as pore water or 0.01 M CaCl2 extractable concentrations in soil, were lowest in the floodplain soils, probably due to the high pH (> 7.0) and high organic matter (8-30%) and clay contents (13-42%). In the peaty soil, having a lower soil pH (4.5-6.5) but higher organic matter contents (38-60%), in some but not all samples Cu concentrations in pore water and Cu and Pb concentrations in 0.01 CaCl2 extracts were higher than in non-polluted reference areas. Plants in the floodplain areas had only low metal concentrations in their leaves, but soil invertebrates and small mammals did contain elevated concentrations in their body. Cd showed high levels in earthworms, snails and small mammals, while also Cu levels were sometimes increased in earthworms, millipedes and small mammals from the floodplain areas. Earthworms from the peaty area contained increased levels of Cu and Pb. These results suggest that metal bioavailability cannot be predicted from available concentrations in pore water or 0.01 M CaCl2 soil extracts, but requires measurement of biota and more insight into the biodynamics of metal uptake.

Acetylcholinesterase inhibition and increased food consumption rate in the zebrafish, Danio rerio, after chronic exposure to parathion.

Acetylcholinesterase (AChE) inhibition is widely regarded as a good biomarker of exposure to organophosphorus pesticides (OP). However, less is known about the relationship between AChE inhibition and consequences for growth, reproduction and survival on organisms. Acute toxicity tests with fish have shown that high percentages of AChE inhibition are needed to cause detrimental effects, but not much is known about the consequences of chronic exposure to this group of chemicals for both AChE activity and higher levels of biological organisation. In this study, zebrafish (Danio rerio) were exposed to sublethal concentrations of the OP parathion for 250 days in a flow-through system. Besides AChE activity, a variety of other parameters were measured: whole-body protein and lactate content, consumption rate, survival, growth and reproduction. AChE inhibition was correlated with exposure concentration, but not with exposure time, and was significant above 0.9 microg/l after 144 days and above 4.3 microg/l after 250 days of exposure. Both parathion and the cosolvent dimethylsulfoxide (DMSO) significantly increased food consumption rate of the fish. Survival, growth, reproduction and lactate content were not affected, while protein concentrations showed only minor effects. These findings support the hypothesis that AChE is a very sensitive biomarker for exposure, but not accurately predict higher level adverse effects following long-term exposure to OPs.

Chronic toxicity of ZnO nanoparticles, non-nano ZnO and ZnCl2 to Folsomia candida (Collembola) in relation to bioavailability in soil

The chronic toxicity of zinc oxide nanoparticles (ZnO-NP) to Folsomia candida was determined in natural soil. To unravel the contribution of particle size and free zinc to NP toxicity, non-nano ZnO and ZnCl(2) were also tested. Zinc concentrations in pore water increased with increasing soil concentrations, with Freundlich sorption constants K(f) of 61.7, 106 and 96.4 l/kg (n = 1.50, 1.34 and 0.42) for ZnO-NP, non-nano ZnO and ZnCl(2) respectively. Survival of F. candida was not affected by ZnO-NP and non-nano ZnO at concentrations up to 6400 mg Zn/kg d.w. Reproduction was dose-dependently reduced with 28-d EC50s of 1964, 1591 and 298 mg Zn/kg d.w. for ZnO-NP, non-nano ZnO and ZnCl(2), respectively. The difference in EC50s based on measured pore water concentrations was small (7.94-16.8 mg Zn/l). We conclude that zinc ions released from NP determine the observed toxic effects rather than ZnO particle size.

Ring-testing and field-validation of a terrestrial model ecosystem (TME)--an instrument for testing potentially harmful substances: conceptual approach and study design.

During spring and summer 1999 a ring-test and field-validation study with an open, intact Terrestrial Model Ecosystem (TME) was conducted at four different European sites (Amsterdam, The Netherlands; Bangor, U.K.; Coimbra, Portugal; Flörsheim, Germany). The objective of the study was to establish a standardised method which allows the impact of chemical stressors on terrestrial compartments at ecosystem level to be investigated and possible uses of such data in existing Environmental Risk Assessments (ERAs) for chemicals to be evaluated. This issue of Ecotoxicology presents in a series of papers the results of the TME ring-test and field-validation study. Additionally, results derived from an open-homogeneous terrestrial microcosm (Integrated Soil Microcosm, ISM) are included in this series as a separate paper. In this first paper of the series background information on the planning and organisation of the study are given. The conceptual approach and the design of the study with TMEs are briefly outlined, based on the scientific discussion on the use of terrestrial microcosms in ecology and applied environmental sciences during the last 25 years. Further, some suggestions are presented on the selection of measurement endpoints to quantify structural and functional aspects of terrestrial ecosystems. Finally, the main results of the TME-study are summarised and conclusions are drawn on the technical feasibility of TMEs, their comparability with field studies and the potential use of TMEs in ERA.

Soil invertebrates as bioindicators of urban soil quality

This study aimed at relating the abundance and diversity of invertebrate communities of urban soils to chemical and physical soil characteristics and to identify the taxa most sensitive or tolerant to soil stressors. The invertebrate community of five urban soils in Naples, Italy, was sampled. To assess soil quality invertebrate community indices (Shannon, Simpson, Menhinick and Pielou indices), Acarina/Collembola ratios, and the soil biological quality index (QBS) were calculated. The chemical and physical characteristics of the soils strongly differed. Abundance rather than taxa richness of invertebrates were more affected by soil characteristics. The community was more abundant and diverse in the soils with high organic matter and water content and low metal (Cu, Pb, Zn) concentrations. The taxa more resistant to the urban environment included Acarina, Enchytraeids, Collembola and Nematoda. Collembolans appeared particularly sensitive to changing soil properties. Among the investigated indices, QBS seems most appropriate for soil quality assessment.

Soil ecotoxicology: state of the art and future directions.

Abstract Developments in soil ecotoxicology started with observations on pesticide effects on soil invertebrates in the 1960s. To support the risk assessment of chemicals, in the 1980s and 1990s development of toxicity tests was the main issue, including single species tests and also more realistic test systems like model ecosystems and field tests focusing on structural and functional endpoints. In the mean time, awareness grew about issues like bioavailability and routes of exposure, while biochemical endpoints (biomarkers) were proposed as sensitive and potential early-warning tools. In recent years, interactions between different chemicals (mixture toxicity) and between chemical and other stressors attracted scientific interest. With the development of molecular biology, omics tools are gaining increasing interest, while the ecological relevance of exposure and effects is translating into concepts like (chemical) stress ecology, ecological vulnerability and trait-based approaches. This contribution addresses historical developments and focuses on current issues in soil ecotoxicology. It is concluded that soil ecotoxicological risk assessment would benefit from extending the available battery of toxicity tests by including e.g. isopods, by paying more attention to exposure, bioavailability and toxicokinetics, and by developing more insight into the ecology of soil organisms to support better understanding of exposure and long-term consequences of chemical exposure at the individual, population and community level. Ecotoxicogenomics tools may also be helpful in this, but will require considerable further research before they can be applied in the practice of soil ecotoxicological risk assessment.

Toxicity of zinc oxide nanoparticles in the earthworm, Eisenia fetida and subcellular fractionation of Zn

The extensive use of nanoparticles (NPs) in a variety of applications has raised great concerns about their environmental fate and biological effects. This study examined the impact of dissolved organic matter (DOM) and salts on ZnO NP dispersion/solubility and toxicity to the earthworm Eisenia fetida. To be able to better evaluate the toxicity of NPs, exposure in agar and on filter paper was proposed for enabling a comparison of the importance of different uptake routes. A dose-related increase in mortality was observed in earthworms exposed in agar with almost 100% mortality after 96 h exposure to the highest concentration (1000 mg ZnO/kg agar). Scanning electron microscopy (SEM) showed that the addition of salts enhanced the aggregation of ZnO NPs in agar and consequently affected the dissolution behavior and biological availability of the particles. On filter paper, mortality was the highest at the lowest exposure concentration (50 mg ZnO/L) and seemed to decrease with increasing exposure levels. TEM images of ZnO showed that the solubility and morphology of NPs were changed dramatically upon the addition of humic acids (HA). The subcellular distribution pattern of Zn in earthworms after 96 h exposure in agar and on filter paper showed that the Zn taken up via dietary ZnO particles (from agar) was mainly found in organelles and the cytosol while the Zn accumulated as soluble Zn from filter paper was mainly distributed in cell membranes and tissues. Antioxidant enzymatic activities (SOD, CAT, and GSH-px) were investigated in the worms surviving the toxicity tests. A slight increase of SOD activities was observed at the lowest exposure dose of ZnO (50mg/kg), followed by a decrease at 100mg/kg in the agar cubes. Activities of both CAT and GSH-Px enzymes were not significantly influenced in the worms exposed to agar, although a slight decrease at 500 and 1000 mg ZnO/kg agar was observed. A similar change trend of SOD activities was observed for the earthworms on filter paper, but a significant decrease began at a higher ZnO NP concentration of 500 mg ZnO/L. The use of soil extracts instead of deionized water (DW) to simulate a realistic exposure system significantly reduced the toxicity of the ZnO NPs on filter paper, which increases the predictive power of filter paper toxicity tests for the environmental risk assessment of NPs.

Water-extractability, free ion activity, and pH explain cadmium sorption and toxicity to Folsomia candida (Collembola) in seven soil-pH combinations

Toxicity of cadmium to Folsomia candida was determined in soils at different pHs (3.5, 5.0, and 6.5). The Langmuir sorption constant (K(L)), based on pore-water or water-extractable concentrations, showed a pH-related increase of cadmium sorption that was most pronounced when using free Cd2+ ion activities ([Cd2+]s). Two-species Langmuir isotherms that used total cadmium concentration ([Cd]) or [Cd2+] and pH in the water-extractable fractions gave the best description of cadmium sorption on all soils together. Cadmium concentrations causing 50% reduction of growth and reproduction (median effective concentrations [EC50s]) differed by a factor of 4.5 to 20 when based on total soil concentrations and increased with increasing pH. However, when based on water-extractable or pore-water [Cd] or [Cd2+], EC50s decreased with increasing pH, but differences between soils were still a factor of 4.5 to 32. The EC50s differed by less than a factor of 2.2 when based on body [Cd] in the surviving animals. Two-species Langmuir isotherms were used to relate body [Cd] in survivors to [Cd2+], corrected for pH in water-extractable or pore-water fractions. An excellent description of effects on growth and reproduction was found when related to the body concentrations predicted in this way; the difference in EC50s between soils was reduced to a factor <2. This demonstrates that F. candida is mainly exposed to cadmium through the soil solution, and suggests that principles of a biotic ligand model approach may be applicable for this soil organism.