Lead bioaccumulation in earthworms, Lumbricus terrestris, from exposure to lead compounds of differing solubility

This study examined the relative effects of soluble and less soluble Pb compounds on Pb accumulation by Lumbricus terrestris. The earthworms were exposed to composted cattle manure contaminated with a range of concentrations of either soluble lead acetate trihydrate (PbAc) (14.5, 72.2, 137, 257, and 603 Ag/g) or less soluble lead carbonate (Pb(CO3)2) (5.09, 171, 575, and 710 Ag/g). Relative Pb bioaccumulation rates in earthworms from the PbAc and Pb(CO3)2 lead carbonate trials were compared over time (0, 20, 40, and 60 days). The two molecular forms of Pb were heavily adsorbed onto the organic matter. Relative soluble Pb concentrations in the manure pore water were very low, at 0.049% and 0.022% of total Pb for PbAc and Pb(CO3)2, respectively. There was a significant uptake of lead by earthworms from both the readily soluble and less soluble forms of Pb. Regression surfaces relating organic matter total Pb concentration to exposure time and Pb body burden were compared. For the PbAc trial, the following equation was fitted: Body burden=2.3429+0.0014x 0.0632y+0.0008xy (R2=0.8494, pb0.0001). For the Pb(CO3)2 trial, the equation was: Body burden= 2.0760 0.0067x 0.2297y 0.0038y2+0.0003xy (R2=0.5686, pb0.0001) (for x=organic matter Pb concentration in Ag/g and y=time in days). The Pb bioaccumulation resulting from the PbAc exposure was significantly higher than that from Pb(CO3)2. Body burdens of earthworms exposed to PbAc were linearly related to exposure time and total Pb concentration. Worms exposed to Pb(CO3)2 had non-linear Pb accumulation over time that suggested a decrease in Pb bioavailability with increasing exposure time. The results indicate that L. terrestris feeding on detritus in the upper soil levels can mobilize and accumulate Pb from the principal transformation products of metallic Pb, as at shooting ranges and lead smelter sites.