The effects of organophosphate exposure on non target terrestrial and aquatic organisms following different exposure regimes : linking biomarker responses and life-cycle effects

[摘要] ENGLISH ABSTRACT: The use of organophosphate pesticides is still an integral part of commercial farmingactivities and these substances have been implicated as a major source of environmentalcontamination in South Africa. Evidence exists that many non target animals in and aroundagricultural areas are at risk of being affected due to the mobile nature of pesticides and theintermittent nature of pesticide application. The extent to which non-target animals areaffected by exposure to two organophosphates (azinphos-methyl and chlorpyrifos) wasinvestigated through monitoring selected biomarker responses and life cycle effects underlaboratory conditions in two selected test species. A representative species from both theaquatic and terrestrial environment was used as these two compartments of the environmentare inevitably linked due to the mobility of pesticides from the area of application tosurrounding areas. The earthworm Eisenia fetida was used as test organism in the terrestrialenvironment while the fish Oreochromis mossambicus served as representative of the aquaticenvironment. Juvenile life stages of both species were subjected to standard acute toxicitytests which showed that for both species, juvenile life stages were more sensitive to bothpesticides than adults. It was also illustrated that azinphos-methyl is more toxic thanchlorpyrifos to both species.Both test species were also subjected to an intermittent exposure regime in order to assess theeffects of repeated pesticide application on biomarker, life-cycle and behaviour responses.The results indicated that for similar exposure regimes, azinphos-methyl was more toxic toE. fetida than chlorpyrifos and detrimentally affected all endpoints investigated. The presentstudy suggests that exposure concentration may have a more pronounced effect in inducing atoxic response than exposure interval, irrespective of the pesticide used. In addition to this,E. fetida was unable to avoid the presence of these pesticides in soil, even at concentrationsas high as 50% of the LC50 value, indicating that the presence of pesticides in the soil pose arealistic threat to earthworms and other soil dwelling organisms. Biomarker responses,morphological effects and feeding behaviour was assessed for O. mossambicus and similar tothe terrestrial toxicity experiments, there was evidence to suggest that in the case of anintermittent exposure scenario, azinphos-methyl was more hazardous than chlorpyrifos to thisspecies. For the majority of endpoints that were investigated, it appeared that exposureinterval played a more important role in inducing an effect than exposure concentration. At a shorter exposure interval, the majority of endpoints showed no difference between higher andlower exposure concentrations, while at a longer exposure interval the effects of exposureconcentration became evident. In addition, feeding behaviour was affected by pesticideexposure in a dose-dependent manner.The present study yielded important results that improve the understanding of biologicalimpacts of pesticide pollution on the environment. This can aid in optimising farmingpractices such as pesticide application not only in terms of eradicating the pest organisms, butalso in terms of mitigating the environmental effects associated with large-scale pesticide use,thereby ensuring sustained biodiversity in these areas.

[发布机构] Stellenbosch University