Assessment of Fraction-Specific Toxicity and Derivation of Recommended Soil Quality Guidelines for Crude Oil in Agricultural/Grassland Soils

This research project was initiated in 1998 and was commissioned by PTAC (Petroleum Technology Alliance Canada). The purpose of the project is to collect, through a combination of laboratory and field studies, scientifically defensible data that can be used to derive risk-based soil quality guidelines for petroleum hydrocarbons (PHCs) in agricultural soils. The project has two phases. The purpose of Phase I is to collect ecotoxicological data for specific hydrocarbon fractions. This data will be used to develop risk-based criteria. The purpose of Phase II is to evaluate short- and long-term risks posed by hydrocarbon residuals at concentrations exceeding 1,000 mg/kg. The project is targeted for completion in 2001 but preliminary data are available and will be presented.

Phase I of the project, developing risk-based criteria, is proceeding following a staged approach. In the initial stage, the toxicity of the crude oil mixture and two hydrocarbon fractions to a battery of terrestrial plant and animal species in topsoil is being assessed. To date, toxicity assessments for unrefined Federated crude oil and two hydrocarbon fractions (C₁₀ to C₁₆ and C₁₇ to C₃₄) have been completed. Following assessment of these results, the toxicity will be further researched by testing an additional hydrocarbon fraction and investigating the toxic interactions of the fractions deemed responsible for significant portions of the ecotoxicology. Derivation of fraction-specific recommended soil quality guidelines will follow the toxicity testing. These guidelines will be compared with existing and proposed regulatory criteria. The results of both the laboratory and field studies will be integrated and the derived PHC guidelines will minimize the risk of impairment of soil physical, chemical and/or biological properties such that plant/cop productivity of agricultural soils will be protected.

Phase II of the project, evaluating risks posed by hydrocarbon residuals exceeding 1,000 mg/kg, is being accomplished using field test plots. Two sets of field plots were established in 1999. Site One is in an area of sandy loam soils being used for the production of cereal crops. Site Two is established in clay loam soils which supported pastures utilized for cattle grazing. Both sites provide appropriate uncontaminated soils for establishing impacted and control plots, in triplicate, and landowner and industry cooperation were obtained. At both sites unrefined Federated crude oil was applied in 1999 at a calculated post-incorporation concentration of 12,000 mg/kg. At Site Two, a second acute plot was established by applying crude oil at a rate of 24,000 mg/kg. At both sites, "chronic" plots were also established on areas that contained historically weathered hydrocarbon material. The combination of "chronic" and "acute" hydrocarbon contamination allows us to compare the ecotoxicological responses of fresh versus weathered PHCs in agricultural soils.