A population genetic analysis of the potential for a crude oil spill to induce heritable mutations and impact natural populations

The primary environmental impact following an oil spill typically is acute toxicity to fish and wildlife. However, multigenerational effects through t oxicant-induced heritable mutations might also occur. Some polycyclic aroma tic hydrocarbon (PAH) components of crude oil are potentially mutagenic, al though specific components and doses that induce mutations are poorly known . We applied population genetics concepts to assess the extent of mortality and the persistence of deleterious heritable mutations resulting from expo sure to potential mutagens, such as crude oil. If lethal mutations are indu ced, the population will experience some mortality, but the mutations are q uickly removed or reduced to low frequency by natural selection. This occur s within one or a few generations when mutations are dominant or partially recessive. Totally recessive alleles persist in low frequency for many gene rations, but result in relatively little impact on the population, dependin g on the number of mutated loci. We also applied population genetics concep ts to assess the potential for heritable mutations induced by the Exxon Val dez oil spill in Prince William Sound, Alaska, to affect pink salmon popula tions. We stress that breeding units (e.g., streams with distinct spawning populations of salmon) must be considered individually to assess heritable genetic effects. For several streams impacted by the oil spill, there is in consistency between observed egg mortality and that expected if lethal heri table mutations had been induced by exposure to crude oil. Observed mortali ty was either higher or lower than expected depending on the spawning popul ation, year, and cohort considered. Any potential subtle effect of lethal m utations induced by the Exxon Valdez oil spill is overridden by natural env ironmental variation among spawning areas. We discuss the need to focus on population-level effects in toxicological assessments because fish and wild life management focuses on populations, not individuals.