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Environmental fate & pathways

Biodegradation in soil

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Biodegradation in soil and identification of degradation products are not required according to Annex IX because of a combination of three aspects: no adsorption to soil is expected + degradation is unlikely and highly dependent on media, bacterial and nitrate contents, so that as a worst-case it seems more relevant to consider an absence of degradation; + investigation of degradation is not useful for PBT/vPvB assessment as there is no relevant bioaccumulation in fish.

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The presented study examined the effect of biodegradation on perchlorate fate and transport in soils. Solute transport experiments were conducted on two surface soils. Pulses of solution containing perchlorate and Br- were applied to saturated soil columns at steady state water flow. Perchlorate behaved like a non reactive tracer in Columbia loam (coarse-loamy, mixed, superactive, nonacid, thermic Oxyaquic Xerofluvent) but was degraded in Yolo loam (fine-silty, mixed, super-active, nonacid, thermie Mollic Xerofluvent). Batch experiments demonstrated that perchlorate removal from solution in Yolo loam was caused by biodegradation. Other batch experiments with Yolo loam surface and subsurface soils, Columbia loam surface soil, and dredge tailings demonstrated that perchlorate biodegradation required anaerobic conditions, an adequate carbon source, and an active perchlorate­degrading microbial population. The sequential reduction of perchlorate and NO3- by an indigenous soil microbial community in Yolo loam batch systems was also studied. Nitrate reduction occurred much sooner thon perchlorate reduction in soils that had not been previously exposed to perchlorate, but nitrates, and perchlorate were simultaneously reduced in soils previously exposed to perchlorate.