The Toxicity of Oil-Contaminated Sediments During Bioremediation of a Wetland

Abstract

ABSTRACT Inorganic nutrients were applied to oiled wetland sediments during an experiment to assess the effect of enhanced bioremediation on petroleum degradation and toxicity reduction. For a period of 6 months after the controlled application of oil to experimental plots, oiled wetland sediment samples were tested for acute toxicity. The three treatments evaluated were an oiled control, inorganic nutrient addition, and inorganic nutrient addition plus an alternate electron acceptor. Sediment toxicity was assessed using Microtox® and amphipod bioassays. The Microtox® 100% Test detected significant sediment toxicity up to 29 days after oil and treatment application while the Solid-Phase Test detected significant sediment toxicity up to Day 15. The Microtox 100%® Test showed elevated toxicity on Day 8 for nutrient plus alternate electron acceptor plots and reduced toxicity on Day 15 for nutrient plots, relative to oiled controls. The observed decrease in sediment toxicity from the Microtox® assays correlated with petroleum losses. Oiled sediments were initially highly toxic to amphipods with average mortality rates ranging from 86 to 92%. Amphipod mortality decreased significantly 71 days after treatment to between 47 and 28%. However, a significant increase in mortality was observed at Day 140 in plots receiving nutrient amendments, possibly due to elevated ammonia levels.