Toxicological, physiological, and behavioral responses of the Asiatic clam, Corbicula sp., to biocidal and copper perturbations
Sappington, Keith Gordon
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Experiments were conducted on the effectiveness of exposure to simultaneous temperature shock with chlorination, monochloramine, and ammonia as control agents of the Asiatic clam, Corbicula sp. Control procedures were evaluated based on lethal and sublethal responses (e.g., glycogen, tissue water, dry weight index, and siphoning activity) of clams during 30-day laboratory artificial stream studies. Studies also were conducted comparing sublethal responses (e.g., glycogen, tissue water, soluble protein, and siphoning activity) of clams to copper, a component of power plant effluents, during 30-day laboratory, site-specific, and in-situ copper exposures. This was done to evaluate the use of the Asiatic clam as a biomonitoring organism of copper contamination. Regarding temperature and chlorine interactions, it was demonstrated that an increase of l0Â° C was needed to increase significantly adult and juvenile mortality in the presence of chlorine (0.30 mg/l TRC) during winter and summer. Naturally high temperatures also increased adult mortality during in-plant chlorination procedures, with the highest mortality occurring during the spring. Significant decreases in the dry weight condition index were observed for adults chlorinated at 5Â° increases during winter and at l0Â° C increases for control (non-chlorinated) clams during both winter and summer. Similarly, glycogen content responded with a temperatureâ dependent decrease in both control and chlorinated clams during the summer. In addition, exposure to increased temperatures significantly increased the siphoning activity of control adults during summer and juveniles during winter. Chlorinated clams experienced near total inhibition of siphoning activity at all temperatures tested, except for adults exposed at 33Â° C. Increased dsiphoning activity, decreased glycogen content, and possibly ammonia accumulation in the mantle cavity were believed to be responsible for the increased mortality of clams chlorinated at higher temperatures. Total residual chlorine, with < 90% as monochloramine, was found to be equally toxic to adults and more toxic to juveniles compared to total residual chlorine containing higher amounts of free residual chlorine. Since free residual chlorine is considered to be more toxic than combined residual chlorine (e.g., monochloramine), questions were raised as to which form of chlorine was actually exposed to the tissues of adducted Asiatic clams. Ammonia was considerably less toxic to adults but more toxic to juveniles compared to chlorine. Both monochloramine and ammonia caused significant reductions in clam glycogen content and siphoning activity. The siphoning activity of clams exposed to ammonia, although significantly reduced, was considerably higher than siphoning activities observed for monochlorinated and chlorinated clams. Clam tissue water content decreased in the presence of ammonia but remained unaffected in the presence of monochloramine. Ammonia toxicity to adult clams was highly pH dependent but may be useful in controlling larval stages of Asiatic clams. More definitive research is needed to evaluate fully the potential of monochlorination as a biofouling control agent. Clams were more sensitive to copper exposures, with respect to glycogen content, in field-located (i.e. site-specific) artificial streams than in laboratory artificial streams. Specifically, the "no observable effect concentration" was between 5.5 and 8.4 Î¼g Cu/1 during the 30-day site-specific studies compared to 17.2-32.1 Î¼g Cu/1 in the laboratory. Copper significantly increased clam tissue water content during the Clinch River and June siteâ specific studies. However, clam soluble protein content demonstrated no consistent dose-dependent response during the laboratory or site-specific studies. Glycogen and tissue water content, although subject to some seasonal influences, are recommended for use in Corbicula for future site-specific and in-situ long-term toxicity experiments.
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