TOXICOLOGICAL MECHANISMS OF A MULTICOMPONENT AGRICULTURAL SEED PROTECTANT IN THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AND FATHEAD MINNOW (PIMEPHALES-PROMELAS)

Ethylene glycol (EG) and thiram, an aldehyde dehydrogenase inhibitor, are components of the seed protectant Vitavax-200. EG is a common solv ent, thought to be nontoxic, whereas thiram, a dithiocarbamate known t o be toxic to fish, is an active ingredient in Vitavax-200. When the t oxicities of EG and thiram were investigated individually and as a mix ture in rainbow trout (Oncorhynchus mykiss) and fathead minnow (Pimeph ales promelas), a strong synergistic toxic effect was observed. Using a constant sublethal concentration of thiram, a 5- to 19-fold increase and a 2- to 2.4-fold increase in EG toxicity was observed in fathead minnow and rainbow trout, respectively. The toxicity of EG following p retreatment of rainbow trout with pyrazole, an alcohol dehydrogenase i nhibitor, was decreased by 22% whereas pretreatment with cyanamide, an aldehyde dehydrogenase inhibitor, increased toxicity 3.4-fold. The re sults indicate that thiram inhibits the complete metabolism of EG, res ulting in the buildup of a toxic aldehyde intermediate and increasing the toxicity of EG.