The international scientific community has grown increasingly concerned that exposure to low levels of anthropogenic chemicals may disturb hormone function and/or sub lethal toxicity to other cells or organ systems in vertebrate and invertebrate species. This research programme was designed to develop, evaluate, and apply a range of biological and chemical indicators in the laboratory and/or field to assess the impact of sublethal toxicants including potential endocrine disaipting chemicals in the aquatic invertebrates, Asellus aquaticus (isopod) and Pacifasiacus leniiisciiius (decapod). Laboratory exposures of A. aquaticiis to environmentally realistic concentrations of known contaminants present within the river systems have demonstrated a link between health status and chemical exposure. Exposure to the organoiins, tributyltin and triphenyltin, and the pesticides, dichlorvos and endosulphan, demonstrated that adults were adversely affected at the biochemical (esterase activities) and physiological level (ventilation rates), as well as disrupting embryo development during in vitro investigations. Field studies demonstrated that cholinesierase and carboxyleslerase activities, ventilatory rates, growth, sex ratios, number of copulatory pairs and ovigerous females, fecundity, and embryonic growth, development and survival were all adversely affected to some extent in the isopod at sites downstream of industrial and domestic effluent discharges in comparison to control populations. Some links were established between the biological parameters measured and sediment faecal sterol content and/or water physico-chemical parameters and comparisons of multiple biomarkers did demonstrate differences between organisms collected at reference and contaminated sites which may be an indicator of environmental stress. A preliminary field investigation of P. lenittscultis collected from sites of mild sewage pollution indicated statistically significant changes in some responses at the cellular (cell viability), molecular (micronucleus formation), and physiological (heart rate) level. The significance of these changes at the population level was not determined, however, there is evidently a need to conduct laboratory exposures of P. leniusculits to sewage effiuent and its individual components to determine whether the responses observed in the field are indicative of sewage contamination. In the present study, the sublethal responses of A. aquaticits and P. len len leniusculus to a range of endocrine disrupting chemicals has been investigated in laboratory and field settings and although cause and effect could not be demonstrated conclusively, this study has gone some way in identifying possible causative agents of these adverse effects in invertebrate populations.

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