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Microbial Mobilization of Cadmium in Soil Under Aerobic and Anaerobic Conditions¹

ABSTRACT

The role of microorganisms in Cd mobilization from soils was investigated. Soils treated with Cd and washed to remove readily soluble Cd were suspended in a nutrient medium (at a ratio of 1:20 wt/v) and incubated (aerobically or anaerobically) for a period of 160 d. While no Cd was released from gamma-irradiated sterile soils under aerobic or anaerobic conditions, a significant amount of "strongly bound" or "fixed" Cd was mobilized from nonsterile samples of all softs tested. The rate and extent of microbial Cd mobilization was dependent on the soil type, aeration, and moisture content. Among the four soils tested, Morrison sandy loam and Morrison loam soils (Ultic Hapludalfs) showed aerobically and anaerobically a greater degree and a faster rate of microbial Cd mobilization compared to Hagerstown silt loam soils (Typic Hapludaifs). In all soils but the Morrison sandy loam soil, the amount of Cd released was considerably greater under anaerobic than aerobic conditions. Although soil moisture content did not have a distinct effect in anaerobic experiments, under aerobic conditions air-dried field soils exhibited a significantly greater rate and extent of microbial Cd mobilization than did fresh soils that had been kept moist at 5 °C. Cadmium release was much more rapid during anaerobic incubation, but upon prolonged incubation (up to 3 weeks), a continued removal of Cd from the aqueous phase occurred in anaerobic, but not the aerobic samples. In many instances, the pH of the soil suspensions decreased to an acidic level (near pH 5.5) with a concurrent release of Cd. Based on our results, mobilization of strongly bound or fixed Cd is a microbially mediated process and this is affected by soil environmental factors such as soil type, aeration, and moisture content.

Key Words: microbial activity • soil type • aeration • moisture content • heavy metals

¹ Contribution from the Laboratory of Soil Microbiology, Dep. of Agronomy, The Pennsylvania State Univ., University Park, PA 16802. This work was supported in part by the Agricultural Education Development Project (Contract no. AID/ASIA-C-1397) through the Post-graduate Institute of Agriculture, Univ. of Peradeniya, Sri Lanka. Journal Series no. 7486 of the Pennsylvania Agric. Exp. Stn.

² Graduate Student and Professor of Soil Microbiology, respectively.

Received for publication October 1, 1986.