Abstract
Chronic toxicity of an antifouling biocide 4,5-dichloro-2-n-octyl-3（2H）-isothiazolone （Sea-Nine 211） for a marine teleostean fish, red sea bream （Pagrus major） was estimated from the acute to chronic ratio （ACR） obtained from the mummichog （Fundulus heteroclitus）. The mean 96-h median lethal concentration values of Sea-Nine 211 （based on the actual toxicant concentrations） for red sea bream and mummichog were 5.1 and 4.7 μg/L, respectively. Early life-stage toxicity （ELS） testing using mummichog embryos revealed that growth was the most susceptible endpoint, and the lowest and no-observed effect concentrations based on the actual toxicant concentrations were 2.8 and 1.1 μg/Lg/L, respectively. Thus, the maximum acceptable toxicant concentration was
determined to be 1.8 μg/Lg/L. Using the calculated ACR value （4.7:1.8） for the mummichog, the chronic toxicity for red sea bream was predicted to be 2.0 μg/Lg/L. Considering the concentrations of Sea-Nine 211 currently detected in the coastal waters of Japan, we consider risk from using this biocide to the fish population to be low. In addition, Sea-Nine 211 exhibited acetylcholinesterase-inhibiting activity, but did not induce morphological abnormality in the ELS test. Accumulation of the toxicant in the body of mummichog may not be enough to cause morphological abnormality because of its rapid degradation.
