| The organochlorine pesticide (OCP) Lindane is the gamma isomer of hexachlorocyclohexane (HCH). Technical grade HCH contains a mixture of additional isomers, predominantly alpha-, beta and deltaHCH. The physical properties, persistence and toxicity of the isomers differ because of different chlorine atom orientations (axial or equatorial). Bioremediation of HCH-contaminated soil was demonstrated using DaramendRTM organic amendments (D6386 and D6390), in long-term (>300 days) bench-scale soil microcosms and at full-scale in a two-year field experiment. Daramend RTM bioremediation technology, developed by Adventus Remediation Technologies, promotes and enhances natural Bioremediation rates by adjusting soil conditions to stimulate biodegradation of contaminants by indigenous microorganisms. The amended soil was treated using either a strictly oxic, or cycled anoxic/oxic treatment protocol. The effects of variables such as addition of a commercial emulsifier (INIPOL(TM), supplemental organic amendments, inorganic nitrogenous amendments and soil moisture content, were investigated in microcosm experiments. Mineralization of HCH in soils subjected to both treatment protocols was monitored in the microcosms using 14C-gamma-HCH. Biodegradation of indigenous, aged HCH in the contaminated soil was equally enhanced by both the anoxic/oxic cycled and strictly oxic Daramend RTM protocols, in soil microcosms and at field-scale. However, mineralization of the 14C-gamma-HCH spike was completely inhibited (<10% recovery of 14CO2) in microcosms where the cycled treatment was applied, compared to over 40% recovery of 14CO 2 in microcosms where the oxic treatment was applied. Use of Daramend RTM product D6386 in the strictly oxic protocol enhanced both bioremediation of indigenous HCH and mineralization of the 14C-gamma-HCH spike. INIPOL(TM), when used in moderation (0.27% w/w, applied once or twice) enhanced removal of the recalcitrant beta isomer in cycled treatments, but, if used excessively, inhibited degradation of alpha-HCH in all treatments and dramatically inhibited 14C-gamma-HCH mineralization in oxic treatments. Initial rates of 14C-gamma-HCH mineralization were reduced in soil amended with ammonium nitrate. Accumulation of ammonium (NH4+-N) was observed in soils where mineralization was inhibited, suggesting a relationship between nitrogen concentrations and HCH degradation. In summary, HCHs were biodegraded and mineralized most effectively in microcosms subjected to the oxic DaramendRTM treatment protocol, with no requirement for supplemental amendments or nutrients. |
