Field and laboratory assessments on dissolution and fractionation of Pb from spent and unspent shots in the rhizosphere soil

•We determined the effect of plant root growth on Pb dissolution from shot pellets.•Dissolution of Pb from shot was significantly induced more in rhizosphere than bulk soils.•Acid extractable-Pb concentration was 13-fold greater in rhizosphere than bulk soils.•Abundance of soil CaCO3 derived from shot clay-targets decreases plant Pb uptake.

The objective of this study was to determine the effect of plant root growth on Pb dissolution from shot under laboratory and field-scale conditions. For a laboratory study, a 100-d incubation experiment was conducted to assess Pb dissolution from unspent shot (new) and spent shot (>10 yr in fields) in rhizosphere and non-rhizosphere (bulk) soils using the Toxicity Characteristic Leaching Procedure (TCLP) and sequential extraction methods. This study found that increasing the soil pH value to 7.5 by liming significantly reduced Pb dissolution from unspent and spent shot (<5 mg L−1). Dissolution of Pb from shot was induced more in rhizosphere than bulk soils. Regardless of shot types, the averaged TCLP-Pb concentration in acidic and limed soils was 12.9- and 8.1-fold greater in rhizosphere than in bulk soils, respectively. For a field-scale investigation, a total of 31 individual plant samples of 6 different species and their rhizosphere soils were collected from a clay-target shooting range (<35 000 mg Pb kg−1). The Pb concentration in plant aboveground tissues depended on species with a mean value of 72 mg kg−1 (15–254 mg kg−1), which was far smaller than that reported in previous studies. Regardless of high soil Pb levels, aboveground tissue Pb concentrations of Solidago altissima (i.e., Canada goldenrod, 15 mg kg−1) and Andropogon virginicus (i.e., broomsedge, 18 mg kg−1) were below the toxicity threshold, suggesting that these indigenous species could have phytostabilization potentials. The limited Pb accumulation by vegetation was attributed to the abundance of soil calcite derived from spent clay-target fragments.