Bioavailablity and toxicity of lead shot to small mammals and soil invertebrates from Canadian prairie shooting ranges

Abstract

Environmental contamination by lead (Pb) from shot pellets is a common cause of poisoning in waterfowl, raptors, passerines, and other wildlife. In Canada and the United States, Pb shot has been banned for waterfowl hunting, but its continued use on shooting ranges contributes tonnes of Pb shot each year into the environment. This study assessed the uptake and toxicity of Pb shot in soil invertebrates, and native small mammals from three Canadian prairie trap and skeet shooting ranges. Information about recreational shooting in the Canadian prairie provinces was obtained by distributing a questionnaire during the fall of 2000 to all identified gun clubs in Alberta, Saskatchewan and Manitoba. The survey return rate was 22%. Three trap and skeet shooting ranges located in Eastend Saskatchewan, Provost Alberta, and Vegreville Alberta were selected as study sites, based on results of the questionnaire. Field research was conducted at the chosen study sites during the summer of 2001. The sublethal effects of Pb on 𝐸𝑖𝑠𝑒𝑛𝑖𝑎 𝑓𝑒𝑡𝑖𝑑𝑎 were evaluated in the laboratory using freshly spiked soil and soil collected from the trap and skeet shooting ranges in the fall of 2002. Earthworm lysosomal neutral red retention time (NRRT) was reduced in soil spiked with Pb acetate in a concentration-dependent manner (𝑝 < 0.001), and was negatively correlated with earthworm body burdens (𝑟 = -0.80,𝑝<0.001). After exposure to soil from the three trap and skeet shooting ranges, earthworm growth and fecundity measurements did not differ significantly between any of the skeet ranges and their reference sites. However, NRRT was significantly reduced in all three ranges compared with their reference sites (𝑝 < 0.05). Lysosomal NRRT was negatively correlated with Ca((N0₃)₂-extractable Pb (𝑟 = -0.80,p < 0.001) and soil total Pb (𝑟 = -0.73,𝑝 < 0.001), and with earthworm Pb tissue levels (𝑟 = -0.67,𝑝 < 0.002). Lead shot density was high in surface soil at all three sites, however soil total Pb (after removal of Pb pellets) and Ca(N0₃)₂-extractable Pb levels were remarkably low and ultimately determined the results for all biological endpoints measured. Small mammal (ground squirrels and deer mice) tissue Pb concentrations measured at all shooting ranges and reference sites fell within the range reflective of background exposure for both species and all tissue types (blood, liver, kidney, femur) measured. Blood Pb concentrations fell below the threshold associated with inhibition of the enzyme 8-aminolevulinic acid dehydratase (ALAD), and no correlation between blood Pb and ALAD activity was found.