Toxicity of diesel contaminated soils to the subantarctic earthworm Microscolex macquariensis

Several fuel spills have occurred on subantarctic Macquarie Island (54°30' S 158°57' E) associated with storing fuel and generating power for the island's research station. The Australian Antarctic Division began full-scale, on-site remediation of these sites in 2009. To develop appropriate target concentrations for remediation, acute and chronic tests were developed with the endemic earthworm, Microscolex macquariensis, using avoidance, survival, and reproduction as endpoints. Uncontaminated low (3%), medium (11%), and high (38-48%) carbon content soils from Macquarie Island were used to examine the influence of soil carbon on toxicity. Soils were spiked with Special Antarctic Blend (SAB) diesel and used either immediately to simulate a fresh spill or after four weeks to simulate an aged spill. Earthworms were sensitive to fresh SAB, with significant avoidance at 181 mg/kg; acute 14-d survival median lethal concentration (LC50) of 103 mg/kg for low carbon soil; and juvenile production median effective concentration (EC50) of 317 mg/kg for high carbon soil. Earthworms were less sensitive to aged SAB than to fresh SAB in high carbon soil for juvenile production (EC50 of 1,753 and 317 mg/kg, respectively), but were more sensitive for adult survival (LC50 of 2,322 and 1,364 mg/kg, respectively). Using M. macquariensis as a surrogate for soil quality, approximately 50 to 200 mg SAB/kg soil would be a sufficiently protective remediation target.