Toxaphene Degrades!

Former Toxaphene dip-vat

Former Toxaphene dip-vat

My team and I will begin remediating soils at the South Fork Te-Moak Indian Reservation near Elko, NV this Spring.  Based on experience with similar Toxaphene-contaminated sites, we’ve selected ex-situ bioremediation as the treatment technology best suited to achieving Site cleanup goals.At previous sites of this type, we’ve constructed lined and covered cells (referred to as “burritos”) filled with a mixture of contaminated soil, water, and nutrients to promote the anaerobic biodegradation of Toxaphene. The winning nutrient “recipe” thus far includes 0.50 percent (by weight) blood meal, 0.50 percent (by weight) phosphates (9 parts disodium phosphate to 1 part monosodium phosphate), and 0.40 percent (by weight) starch, so that 1.4 percent of the total solid mixture (by weight) consists of amendments.

To test applicability at South Fork, I recently conducted a bench-scale test.  For this I mixed approximately 80g of contaminated soils with 0.50% commercial blood meal nutrient and some Royal brand rice for starch.  The mixtures were prepared in 1-liter nalgene-brand sample bottles.  The test bottle was then flooded while the control was left dry – both were sealed and submerged.  The test flasks were left for 9 weeks and were sampled on December 28, 2012.  Two-samples were sent to the EPA Region 9 laboratory for Pesticide analysis after a 1:1 Acetone/Hexane extraction.

Metlar balance containing sample container.

Results demonstrated a 54% reduction in Toxaphene concentration from 61,000 ppb to 28,000 ppb as well as a reduction in Chlordane concentration, thought to be a recalcitrant “biomarker”.  This crude test demonstrated that indigenous bacteria in the South Fork Site soil can degrade Toxaphene and therefore supports this treatment approach for the Site.The treatment cells we construct are designed to maximize the potential for anaerobic bacteria to degrade toxaphene. The cells are lined with visqueen in order to prevent water loss and promote anaerobic conditions. Cell contents are homogenized during several phases of the cell construction process to distribute Toxaphene contamination and nutrients as evenly as possible.Excavated soil will be run through a sieve to remove rocks and debris. Nutrients will be added to the soil and mixed in a bin, slightly moistened, and moved to the treatment cells. Water will be added to the treatment cells as they were filled with the amended soil mixture.  Finally the cells will be sealed with visqueen and sampling ports with gas release valves will be installed around the perimeter of each cell.  We should be able to collect samples periodically to demonstrate reductions in Toxaphene concentrations.

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