Search

Direct and indirect effects of the fungicide carbendazim on ecosystem structure and functioning were studied < or =8 weeks after application (nominal concentrations: 0, 3.3, 33, 100, and 1000 microg/L) to outdoor microcosms in Thailand. Direct effects on macroinvertebrates are discussed in detail in a separate article. The present article presents the effects on other end points and discusses the hypothesized ecologic effect chain. Negative treatment effects on the zooplankton community were only recorded for the highest carbendazim treatment (NOEC(community) = 100 microg/L). The rotifer Keratella tropica, cladocerans (Moina micrura, Ceriodaphnia cornuta, and Diaphanosoma sp.), and cyclopoid copepods were decreased or even eliminated at this treatment level. The decrease in zooplankton and macroinvertebrate abundances was accompanied by an increase in numbers of several tolerant invertebrates, presumably caused by a release from competition and predation. The death of sensitive invertebrates probably also led to an overall decreased grazing pressure because increased levels of chlorophyll-a and bloom of the floating macrophyte Wolffia sp. were noted. The increase in primary producers is discussed to be the probable cause of changes in physicochemical water conditions, eventually resulting in an anoxic water layer during the last 3 weeks of the experiment. This is likely to have resulted in decreased invertebrate abundances noted in that period. Furthermore, the decreased decomposition of Musa (banana) leaves observed 8 weeks after application is considered to be the indirect effect of a decreased microbial activity resulting from these anoxic water conditions, rather than a direct toxic effect of carbendazim.

Contaminants in soils can enter food chains through primary producers. Bioavailable contaminants can induce growth, and reproductive or biochemical changes in plants. To evaluate the bioavailability of heavy metals in two soils from Jales mine surroundings, bioassays with the plants Brassica rapa (RCBr) and Avena sativa were performed. Biochemical parameters (protein and malondialdehyde [MDA] content, and catalase and peroxidase activities) were also measured. The soils had different heavy metal contents: JNC soil contained low heavy metal concentrations, whereas JC soil had high heavy metal contents. Results stressed the difference between species sensitivity, with A. sativa showing no toxicity effects when exposed to both soils. On the other hand, B. rapa presented a decrease in growth parameters when exposed to JNC soil and no changes when exposed to JC soil. A Life Cycle Bioassay confirmed this trend for B. rapa exposed to JNC soil, but also evidenced that JC soil was affecting B. rapa in terms of flower and seed pod production. Biochemical assays showed that plants affected by heavy metals also displayed oxidative stress, with an increase in MDA production, reduction of protein content, and reduction of catalase and peroxidase activities. All bioassays revealed that JNC soil, although with a lower heavy metal content, had a higher bioavailable fraction when compared to JC soil, which consequently increased its toxicity to plants.

Soil ecotoxicology studies are usually performed in standard soils such as Organization for Economic Cooperation and Development artificial soil or LUFA ST. 2.2, a natural soil. When assessing the toxic effects in the environment, soil properties are often different from those in standard soils, which might lead to different exposure situation for the test species and therefore to misleading conclusions. Selected to cover a broad range of properties and based on the Euro-Soils concept, 17 different soils were studied regarding their suitability to two tes species: Folsomia candida and Hypogastrura assimilis (Collembola). In reproduction tests, the test species reacted differently to the soils. F. candida was less affected by soil properties: 500 to 1200 juveniles/vessel were found in untreated soils (i.e. controls). These differences can be attributed to normal interindividual variability. H. assimilis showed a significant correlation with maximum water-holding capacity and also a tendency to lower the reproductive output in soils with a low pH (<4). Therefore, some soils were revealed to be inappropriate for tests with H. assimilis. In the main tests, the effect of the reference test substance Phenmedipham (formulation Betosyp) was studied in those soils where sufficient reproduction was determined beforehand. Clearly, the chronic end point was more sensitive than survival when testing Phenmedipham. In H. assimilis, because of high variability and low effects of tested dosages, no conclusions could be drawn. In F. candida, different soils caused different toxic effects: Juveniles preferred soils with high C-to-N ratios. Higher microbial activity might support a quicker metabolization of the test substance. In general, the toxic response is caused by a synergistic action of several soil properties with each of them exerting an effect too small to be clarified with the available set of data.

Enchytraeids are important members of the soil fauna living in the true soil layer instead of the humus like most earthworms, resulting in a different interaction with chemicals in soil. It is well known that the detectable concentration of contaminants in the soil cannot fully predict a biological effect; therefore bioaccumulation studies are of great importance. In this study the bioaccumulation pattern of the pesticide lindane ([(14)C]gamma-HCH) in Enchytraeus albidus was analyzed in two different soil types, an artificial Organisation for Economic Co-operation and Development (OECD) soil and a natural agricultural soil. The effect of aging on bioaccumulation and bioavailability was also analyzed. Aging experiments consisted of having the same procedures at different times after soil contamination: Immediately after contamination and 1, 2, 4, 6, and 10 months after that. Major differences occurred within the first month. Considering the overall data (10 months), it is possible to observe that in OECD soil there is a correlation between concentration in soil and in the organisms, but that was not observed for the natural soil. The decrease patterns for concentration in soil and in watery soil extracts were different: monophasic behavior occurred in OECD soil, and a biphasic pattern was measured in natural soil. It was observed that the bioavailable ( i.e., water-extractable) fraction of lindane in the natural soil decreased faster than the total soil concentration. In natural soil the decrease of concentration appeared faster than in OECD soil; this may be related to the lower amount of organic matter content.