Bioavailability of heavy metals in strongly acidic soils treated with exceptional quality biosolids

New federal regulations may increase application of exceptional quality (EQ) biosolids to acidic soils, and information on the effect of this practice on bioavailability of heavy metal is limited. The objective of this study was to compare bioavailability of heavy metal in soil treated with nonalkaline or alkaline EQ biosolids with limestone-treated soils. Three acidic soils (pH 3.7-4.3) were treated with three amounts of lime-stabilized biosolids (LS), anaerobic-digested biosolids (AN), or agricultural limestone (L), and incubated at 25 degrees C. Soil solution Cd, Zn, and other chemical constituents were measured at 1, 30, 90, and 180 d incubation. Chemical fractionation of heavy metal was performed after 180 d incubation. Soil solution Cd and Zn were AN > LS greater than or equal to L, C. Soil solution Cd and Zn increased with AN applied but decreased with LS applied. The high application of LS had soil solution Zn equal to that obtained using limestone. Soil solution Cd and Zn dramatically decreased at soil pH >5.5 and >5.1, respectively, Soil solution Cd and Zn increases were AN > LS with incubation time. Biosolids treatments increased heavy metal in Ca(NO3)(2) and NaOAc fractions. Except for Cd, most metal from biosolids were in EDTA and HNO3 fractions. Heavy metal bioavailability, measured using lettuce (Lactuca sativa L.), was AN > LS greater than or equal to L, C, Although state regulations prohibiting application of nonalkaline EQ biosolids to acidic soil is a prudent practice, application of EQ alkaline biosolids that achieves soil pH >5 minimizes risk from soil solution Cd and Zn and plant uptake of heavy metal.