Research Product

Discharge of chlorine into estuarine and coastal waters may result in undesirable toxic effects to many of the organisms residing in these habitats. There is a substantial volume of information on short-term chlorination toxicity in marine invertebrates and fishes; however, little is known about the long-term effects of chlorination on the American oyster, Crassostrea virginica (G). Galtsoff reports that adult C. virginica showed reduced pumping rates at concentrations of chlorine of less than 0.05 mg/l. At concentrations of 1.00 mg/l or greater, oysters closed their valves and ceased to pump; the longest period of exposure, however, was only 48 hr. Recent work of Bongers et al reports little mortality in adult C. virginica exposed to chlorine (0.35-0.85 mg/l) and bromine chloride (BrCl) (0.17-0.86 mg/l) for 15 days. Sublethal responses revealed that new shell growth was greater in controls than in chlorine and BrCl-exposed oysters, with the amount of shell deposition decreasing with increased toxicant concentrations. No significant difference in the reduction of new shell deposition occurred in tests with chlorinated and BrCl-treated effluents. A study of the acute toxicity of chlorination to molluscan larvae revealed that chlorination is very toxic to both oyster (C. virginica) and clam (Mercenaria mercenaria) larvae. The 48-hr median effective concentration (EC50) was estimated to be less than 0.005 mg/l for larval oysters and 0.006 mg/l for larval clams. The estimated 96-hr EC50 (by shell deposition) for juvenile oysters was 0.023 mg/l. Oyster larvae survival under intermittent chlorination was much higher than for continuous chlorination. Products formed from chlorination of natural waters are a function of physical and chemical parameters of the water, including but not limited to temperature, pH, ammonia, sunlight (UV) and salinity (or the amount of bromine available as a reaction component). Since sea water typically contains 60 mg/kg bromide, bromination rather than chlorination may predominate as salinity increases. Thus, the chlorine-produced oxidant (CPO)12 levels measured during this study may include varying proportions of hypochlororus acid and hypochlorite ion, as well as hypobromous acid and hypobromite ion, depending upon the ambient salinity. In addition, photolysis may influence the level of bromate produced during chlorination of saline waters. The objective of this study was to examine the effects (lethal and sublethal) of chlorination to adult oysters, Crassostrea virginica, during chronic exposures on a seasonal basis.