Multi-stressor Effects of Ultraviolet Light, Temperature, and Salinity on Louisiana Sweet Crude Oil Toxicity in Larval Estuarine Organisms.

Abstract

When oil is spilled into the environment its toxicity is affected by abiotic conditions. The cumulative and interactive stressors of chemical contaminants and environmental factors are especially relevant in estuaries where tidal fluctuations cause wide variability in salinity, temperature, and ultraviolet (UV) light penetration, which is an important modifying factor for polycyclic aromatic hydrocarbon (PAH) toxicity. Characterizing the interactions of multiple stressors on oil toxicity will improve prediction of environmental impacts under various spill scenarios. This study examined changes in crude oil toxicity with temperature, salinity, and UV light. Oil exposures included high-energy, water-accommodated fractions (HEWAFs) and thin oil sheens. Larval (24-48h post hatch) estuarine species representing different trophic levels and habitats were evaluated. Mean 96h LC50 values for oil prepared as a HEWAF and tested under standard conditions (20 ppt, 25°C, No-UV) were 62.5µg/L tPAH50 (mud snails), 198.5µg/L (grass shrimp), and 774.5µg/L (sheepshead minnows). Thin oil sheen 96h LC50 values were 5.3µg/L tPAH50 (mud snails), 14.7µg/L (grass shrimp), and 22.0µg/L (sheepshead minnows) under standard conditions. UV light significantly increased the toxicity of oil in all species tested. Oil toxicity also was greater under elevated temperature and lower salinity. Multi-stressor (oil combined with either increased temperature, decreased salinity, or both) LC50 values were reduced to 3µg/L tPAH50 for HEWAFs and < 1.0µg/L tPAH50 for thin oil sheens. Environmental conditions at the time of an oil spill will significantly influence oil toxicity and organismal response and should be taken into consideration in toxicity testing and oil spill damage assessments.