A Rapid Bioassay for Predicting Toxicity of PHC-Contaminated Soil

John Ashworth, ALS Environmental

The project goal is to fully develop an existing rapid, accurate bioassay for soil at PHC-contaminated sites; especially soils that are likely non-toxic to biota, but which exceed CCME criteria for solvent-extractable F2-F4 hydrocarbons.

Costly Tier-2 testing of soils that failed this rapid bioassay could thus be reconsidered. Vice versa, Tier 2 testing would likely be more cost-effective for PHC-contaminated soils that passed the bioassay.

The bioassay will be based on a combination of cyclodextrin (CD) extraction, followed by a Microtox test on the soil extract. It has been established for a range of soils (Axiom 2005) that CD extraction recovers only bio-available PHC, and that amounts of CD-extractable PHC are well correlated with earthworm reproduction data. (However, in this project quantification of extracted PHC is not the goal.)

CD-extracts of soil are usually non-toxic in the Microtox bioassay, but recent ALS work has shown that CD-extracts can be activated, releasing PHC. Extracts of soils with sufficient bio-available PHC then fail the Microtox test.

A wide range of real-world soils will be obtained, some courtesy of Stantec who are doing current work comparing CD extraction against other analytical methods for PHC. Other suitable soils will be obtained from PTAC / CAPP members. A range of PHC-spiked soils will also be tested.
Earthworm survival data (already available for Stantec’s soils) will be obtained by HydroQual Ltd. (S. Goudey).
CD-extraction of all projects soils, and subsequent extract activation followed by Microtox testing will be done at ALS Edmonton (J. Ashworth) who will also correlate data and provide interim and final reports.