Greatly Accelerated Microbial Degradation of Aldicarb in Re-treated Field Soil, in Flooded Soil, and in Water

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Abstract
Two successive annual applications of aldicarb, as subsurface band-in-row soil treatments at 4 kg (AI)/ha in the same field plots, resulted in development of strains of microorganisms that rapidly broke down aldicarb in acid mineral soils of pH above ca. 6.0. Concentration and time required for breakdown for laboratory applications of 10–750 μg (AI)/g (ppm) of soil were positively correlated. Breakdown of these concentrations ranged from 1 to ca. 14 days. Concentrations higher than ca. 800 ppm appeared to retard bacterial action and inhibited fungal growth in the soil. A 5,000-ppm application inhibited fungal growth for > 6 months and retarded growth during the following 6–8 months. Toxic residues from 2,000- to 5,000-ppm applications persisted for 6 months to 1 year or more in the moist soil but degraded faster in flooded soil. Breakdown of repeated 50- or 100-ppm applications was most rapid in alkaline and near-neutral acidic soil or water media, much slower at pH levels near 6.0, and negligible at pH levels below ca. 5.6. Rate of accelerated microbial degradation depended on pH and moisture content of the soil, amount applied per treatment, numbers of treatments, and time period between treatments of aldicarb.