RISEN, Amy J.; SURMACZ*, Cynthia A.; Bloomsburg University; Bloomsburg University: Sublethal and Lethal Responses to Acute Exposures of Methyl Tertiary-Butyl Ether (MTBE) in Lumbriculus variegatus

The widespread presence of methyl tertiary-butyl ether (MTBE), a gasoline additive, in groundwater and surface water has raised concerns about its potential ecological impact. Recent toxicity studies concluded that current MTBE levels in US surface water (<0.1 mg/L) do not pose a risk to aquatic ecosystems. However, further work is needed to characterize the full spectrum of sublethal responses to MTBE, to understand its specific organismal effects, and to better assess its ecological impact. The sublethal effects of acute, 15 min MTBE exposure were investigated in the freshwater worm Lumbriculus variegatus. Sublethal responses to MTBE occurred at concentrations that were 10 � 20 times lower than those causing lethality. Pulse rate was elevated at >792 mg/L MTBE. The EC15 and EC50 for pulse were 7 and 560 mg/L, respectively. Pulse rate increased 200%, peaked in 3110 mg/L MTBE and declined at higher concentrations. Tactile responses were decreased at >970 mg/L MTBE. Tactile response was less sensitive to MTBE than changes in pulse, but had a steeper concentration-response curve. The EC15 and EC50 for tactile response were 1009 and 1377 mg/L. After MTBE exposure, autotonomous fragmentation did not differ from controls, was highly variable, and displayed no predicable pattern. These studies show that MTBE alters the physiology and responsiveness of this aquatic worm at levels lower than lethal concentrations and illustrates its utility for assessing MTBE toxicity in aquatic ecosystems. Further investigations of sublethal endpoints are needed that examine specific mechanisms of action and the effects of chronic MTBE exposure. Supported by a Bloomsburg University Faculty Professional Development Grant.