ADAPTATION TO FLUORANTHENE EXPOSURE IN A LABORATORY POPULATION OF FATHEAD MINNOWS

Tolerance of toxicant exposure is common in polluted sites in nature. However, in most cases, the processes underlying tolerance acquisition are not well understood. In the case of exposure to polycyclic aromatic hydrocarbons (PAHs) in particular, reports are lacking on the capacity for tolerance acquisition. To evaluate the potential for adaptation to this class of contaminants we exposed a large laboratory population of fathead minnows to fluoranthene, commonly a major constituent of PAH contamination. The exposure concentration chosen did not cause mortality but was sufficient to diminish reproductive capacity in exposed breeding fish relative to a control population. This level of exposure also significantly diminished hatching success and larval survivorship in the exposed population. The estimated value of selection against susceptibility (the product of all assessments of effect) was 0.67. Tests for tolerance acquisition included comparative larval 96-h LC50 determinations, and comparative juvenile median time to death (LT50) determinations. Enhanced tolerance was not apparent in the LC50 determinations, although an examination of the concentration-response distribution suggested an adverse effect due to egg and larval exposure to fluoranthene prior to the test. In contrast, results of the comparative LT50 determination indicated that the exposed population was approximately 30% more tolerant, relative to the control population, when exposed to an acutely toxic concentration of fluoranthene. These results suggest that tolerance to PAH exposure can occur in nature and that this population-level response needs to be examined relative to other recognized effects in PAH-contaminated areas.