Photoenhanced toxicity of weathered oil to Mysidopsis bahia

The toxicity of a water-accommodated fraction (WAF) prepared from weathered oil was assessed in a 7-day static renewal test with Mysidopsis bahia. Wea thered oil was collected from the 5 x monitoring well at the Guadalupe oil held. Solar ultraviolet and visible light intensities were measured in vari ous habitats in the vicinity of the weathered oil sample collection site, a nd the resultant measurements were used to produce laboratory light treatme nts that were representative of the on-site quality and intensity of natura l solar radiation. Each of five WAF dilutions and a control without WAF was tested under three different simulated solar radiation intensities. During the test, survival and growth of the mysids, irradiance, and total petrole um hydrocarbon (TPH) concentrations in the test treatments were measured. S ignificant increases (P less than or equal to 0.05) in mortality occurred a mong mysids exposed to 0.57 and 1.30 mg TPH/l and the effects were potentia ted as irradiance increased. Seven-day LC50 (0.92-0.42 mg TPH/l) and LC20 ( 0.58-0.15 mg TPH/l) values decreased as the simulated solar irradiance incr eased. Calculated EC20 and EC50 values for mysid growth indicate that survi ving mysids exposed to 0.1-1.0 mg TPH/l would incur significant reductions (P less than or equal to 0.05) in productivity (biomass). Results of the pr esent study indicate that effects elicited through the interaction of WAF o f weathered oil and solar radiation will substantially increase the toxicit y of weathered oil. Further, the photomediated effects of petroleum compoun ds measured as TPH on mysid survival and growth demonstrate a need to consi der the interactions of ultraviolet light and contaminant to avoid under es timating toxicity that might occur in the environment. (C) 2000 Elsevier Sc ience B.V. All rights reserved.