John Ashworth (ALS Laboratory Group, Edmonton), Elisabeth Henson (HydroQual Laboratories, Calgary) and Bryon Shore (HydroQual Laboratories, Calgary)
2012
Abstract
The rapid (2-h) bioassay developed during this project is intended for soils that are contaminated with petroleum hydrocarbons (PHC) above Tier 1 remediation criteria, but which may be sufficiently weathered to make them candidates for Tier 2 site-specific assessment. The aim is not to replace any of Environment Canada’s battery of Tier 2 tests, but to screen out soils with toxic levels of bio-available PHC, thus avoiding the fruitless expense of subjecting such soils to those time-consuming tests.
A representative soil sample is shaken with aqueous cyclodextrin (CD) to recover bio-available PHC; the centrifuged extract is treated with amylase before being subjected to a standard Microtox test, employing luminescent bacteria. Extracts with > 100 mg/L of PHC exhibit marked toxicity (bacterial light reduction), believed to be due to enzyme-catalyzed hydrolysis of the CD-PHC inclusion complex. An uncontaminated sandy loam, and an artificial soil, each freshly spiked in the lab with a range of levels of diesel oil (F2 and F3 PHC), yielded toxic CD extracts at spike levels above 1,000 mg/kg PHC. Six real-world soils from PHC-contaminated sites in Alberta were donated to the project by CAPP/PTAC member companies or their contractors. CD extracts of these soils were non-toxic (toxicity index < (1) except in one case (soil 11-2094, with an index of 2.5).
Results of 35-day earthworm survival bioassays reflected the CD-Microtox bioassay results. Earthworm survival was similar to that in controls with no PHC, except for soil 11-2094 and the lab-spiked soils with > 1,000 mg/kg PHC. The rapid bioassay seems therefore to be a reliable indicator of earthworm survival. However, in 63-day reproduction bioassays, juvenile production and juvenile weights were lower in all six real-world soils, as well as in the two lab-spiked soils, than in controls. Improved reproduction observed in three of the real world soils, after they were amended with peat, suggests that low soil porosity may exacerbate the effects of PHC on earthworm reproduction.
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