Evaluation of the suitability of responses on various organisational levels in terrestrial Oligochaeta to determine species sensitivity relationships

[摘要] ENGLISH ABSTRACT: Species differ in their sensitivities to toxicants and these differences are exploited in ecological risk assessment methods such as species sensitivity distributions (SSDs). The most commonly used endpoints for ecotoxicity testing and thus to generate data for use in SSDs are on the whole-organismal level, and usually include the evaluation of survival and reproduction. However, suborganismal biomarker responses are in many instances more sensitive than these whole-organismal responses. Therefore, this study investigated and compared responses on various biological organisational levels to determine their suitability for use in SSDs.Five terrestrial oligochaete species (earthworms) were selected as model test organisms, and were exposed to a range of concentrations of a well-studied pesticide, copper oxychloride. The investigated responses included survival, biomass change and reproduction on the whole-organismal level. In order to investigate responses on the suborganismal level, cells (coelomocytes) were extracted non-invasively. The spectrophotometric neutral red retention (NRR) assay was used to determine cell survival and the MTT assay to determine mitochondrial metabolic activity of the coelomocytes. The alkaline single cell gel electrophoresis (comet) assay was used to assess DNA integrity in these cells. The amount of Cu taken up by earthworms was also determined and compared to their responses.Species differences were observed in all responses, and EC50 and EC10 values were calculated for the whole-organismal endpoints and used to generate SSDs. From these SSDs, the hazardous concentrations where 5% of all species would be detrimentally affected (HC5) were calculated, which indicated that the most sensitive whole-organismal endpoint was mass change, followed by reproduction and survival.It was found that earthworms avoided feeding on the contaminated substrate in high copper oxychloride concentration exposures. The concentration where this behaviour occurred could be estimated for each species, and an SSD was constructed with these data. The HC5 value indicated that this response is more sensitive than earthworm survival, but less sensitive than the other responses.It was shown that the earthworms regulated their body Cu concentrations in a species-specific manner. This regulation of Cu was reflected in the suborganismal responses, and the species that had taken up the highest amount of Cu was the most sensitive species for all three suborganismal assays. Due to this regulation of Cu, the resulting dose-responses for the suborganismal endpoints did not allow for the calculation of EC50 values in most of the species and such data could thus notbe used to generate SSDs. Sufficient EC10 values were however generated to construct SSDs from the results of the NRR and comet assays.The HC5 values obtained from SSDs constructed with EC10 values for both suborganismal and whole-organismal endpoints indicated that the NRR assay was the most sensitive endpoint, followed by both the comet assay and earthworm mass change, and subsequently the other whole-organismal endpoints.In conclusion, the majority of the responses on the various levels of biological organisation investigated during the present study were shown to be suitable to determine species sensitivity relationships in the terrestrial oligochaete species studied.

[发布机构] Stellenbosch University