Abstract
Municipal composts from two Connecticut towns, Fairfield and Greenwich, were analyzed for heavy metals (cadmium, chromium, copper, nickel, lead, and zinc) using nitric acid : hydrogen peroxide (HNO3 : H2O2) digestion as outlined in Environmental Protection Agency Method 3050 for digestion of solid wastes, sludges, and soils. Potential leachability of heavy metals was determined by leaching compost with water in laboratory columns, and by irrigation-leaching of compost used as growth medium for container plants in the field. Acid digests and aqueous leachates were analyzed for heavy metals by inductively coupled plasma (ICP) emission spectrometry and graphite furnace atomic adsorption (GFAA) spectrometry. Concentrations of cadmium, chromium, copper, nickel, lead, and zinc in the composts varied from 3 to 5, 43 to 118, 323 to 649, 38 to 81, 110 to 213, and 331 to 1143 mg/kg, respectively. Following the initial rapid leaching of heavy metals for 2 to 3 days in laboratory columns and 2 to 4 weeks in field containers, metals continued to leach at low concentrations, generally below the drinking water standards. The initial rapid leaching of metals is attributed to their soluble or readily exchangeable forms and the subsequent release at low concentrations is likely controlled by the solubility of the solid phases.
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