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Microbial Degradation of 1,2-Dibromoethane in Shallow Aquifer Materials¹

ABSTRACT

The use of 1,2-dibromoethane (ethylene dibromide, EDB) as a soil fumigant in agriculture has resulted in groundwater contamination. The objective of this study was to determine the importance of microbial degradation to natural decontamination of EDB in aquifer materials. Shallow aquifer materials were obtained from two sites in Connecticut that are contaminated with EDB. Experiments were conducted in batch microcosms of core soil material and groundwater (no additional nutrients) at temperatures and initial EDB concentrations representative of the sites (9°C, 0.5–5 µg kg^–1). Ethylene dibromide was degraded aerobically in all samples except autoclaved controls; products of [¹⁴C]-EDB degradation included varying amounts of ¹⁴CO₂, solid-bound ¹⁴C (microbial biomass), and a nonvolatile water soluble fraction. At one of the sites, rates were faster in samples obtained from within the contaminant plume, suggesting adaptation of the microbial community to the presence of the chemical. Degradation was slowed at low-oxygen (ca. 0.1 mg O₂ L^–1) compared to air-saturated (ca. 11 mg O₂ L^–1) conditions. The compound was also degraded in the absence of oxygen but the products were not investigated. First-order half-lives under all conditions tested ranged from 35 to 350 d. The implications of these results to natural loss of EDB at one of the sites are discussed.

Key Words: Ethylene dibromide • Groundwater contamination • Microbial adaptation • Halogenated hydrocarbons • Pesticide • Soil fumigant

¹ Contribution from the Dep. of Soil and Water, The Connecticut Agric. Exp. Stn., 123 Huntington Street, P.O. Box 1106, New Haven, CT 06504.

² Assistant scientist, Dep. of Soil and Water, The Connecticut Agric. Exp. Stn., New Haven, CT.

Received for publication February 25, 1987.