Submitted to: Marine Environmental Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/11/2000
Publication Date: 11/1/2000
Citation: EVANS, J.J., SHOEMAKER, C.A., KLESIUS, P.H. IN VIVO AND IN VITRO EFFECTS OF BENZOTHIAZOLE ON SHEEPSHEAD MINNOW (CYPRINODON VARIEGATUS). MARINE ENVIRONMENTAL RESEARCH. 50 (2000) 257-261. Interpretive Summary: Benzothiazole, a common chemical associated with tire manufacturing and industrial wastewater, was determined to be a principal component of both freshwater and estuarine tire leachate. Tire leachate is a complex chemical mixture and has been shown to be a neurotoxicant to larval sheepshead minnows. This study was initiated to determine if benzothiasole eis the chemical in tire leachate responsible for previously observed cellular damage to the central nervous system, brain and eye. Larval sheepshead minnows were exposed to benzothiazole in a toxicity bioassay and evaluated for survival, growth and microscopic cellular alterations in all organs. Mortality of sheepshead minnows occurred after 5 days of exposure to 60 mg/L (Lethal Concentration 50 = 41.9). Significant decreases in larval growth was noted. Microscopically, the central nervous system lacked the severe cellular damage. Gills were severly damaged suggesting that gill tissue is a target organ of benzothiazole. Tissue culture results indicate primary cultures of sheepshead brain cells are less sensitive to benzothiazole than epithelial cell lines. Significant cytotoxicity (suppression of cellular respiration and cell proliferation) to the epithelial cell lines was observed. Taken together, the present study indicates that benzothiasole is not a neurotoxicant affecting brain cells. However, given the lethal and growth and respiratory inhibiting effects of benzothiasole to fish as well as the limited biodegradability, stability and persistence of this compound in the aquatic environment, benzothiasole concern for aquatic animal health in coastal watersheds suggest it is.
Technical Abstract: Benzothiasole, a common chemical associated with tire manufacturing and industrial wastewater, is a principal component of both freshwater and estuarine tire leachate, a neurotoxicant to larval sheepshead minnows (Cyprinodon variegatus) in in vivo estuarine studies. The neurotoxic potential of benzothiasole was investigated following in vivo and in vitro exposure of sheepshead minnows to 3.75, 7.5, 15, 30 and 60 mg/L benzothiasole. Following benzothiasole exposure, fish were evaluated for survival, growth and histological alterations. Fish mortality occurred after 5 days of exposure to 60 mg/L (LC50 = 41.9). Significant decreases in larval growth were noted at all concentrations. Histologically, the central nervous system lacked the severe cellular damage seen in previous tire leachate exposure studies but gills had cellular alterations. Benzothiasole cytotoxicity to primary cultures of brain cells from sheepshead minnow and tilapia (Oreochromis niloticus) and two epithelial cell lines were evaluated using a tetrazolium salt assay, (MTT) at 1 and 4 days. In vitro results indicate primary cultures of brain cells are less sensitive to benzothiasole than epithelial cell lines. Significant cytotoxicity to the epithelial cell lines was noted at 30 and 60 mg/L concentrations. Histologically and cytotoxicologically, the present study indicates that benzothiazole is a gill toxicant and not a neurotoxicant.