The effects of weather and dispersion on lethal and sublethal toxicity of oil to Gulf killifish across a range of salinities

Aim 1: Characterize the effects of weather and dispersion on lethal and sublethal toxicity of oil across a range of salinities. Thirty mesocosms were established with ~80L of oxic water overlaying ~15L of sediment with an oxic surface layer and an anoxic subsurface similar to conditions seen along the LA coast. Ten mesocosms each were prepared at 4, 12 and 18 ppt. Additional mesocosms were prepared as extra and/or pilot systems. Shading was prepared to equalize the light exposure and temperature between top and bottom row tanks. Following advice from scientists from EPA, it was decided that oil will be pre-weathered prior to addition to mesocosms. This pre-weathering is to mimic oil during a spill event. Volatile components are removed prior to exposure as they would in a spill. During pre-weathering oil (~1:5 oil:water; ~220mL per tank), corexit (~1:50 corexit:water), and oil/corexit mixture was weathered overnight in 4, 12, or 18 ppt water. Water and oil fractions were separated and equally divided into 3 aliquots (1, 4, and 16 week tanks). Aliquots were stored refrigerated in amber glass bottles with Teflon lids until addition to mesocosms. Weathering has been completed at 4 and 12 ppt and 18 ppt.