A review of the environmental impacts of lead shotshell ammunition and lead fishing weights in Canada

This report reviews the available information, from Canada and elsewhere, on the use, environmental fate, and toxicity of spent lead shot and lost lead fishing weights and discusses options for managing the negative impacts of these products. Lead shot ammunition and fishing sinkers worth an estimated $25–$35 million are purchased annually in Canada. For lead shot, more product is imported (primarily from the United States) than is manufactured in Canada; for lead sinkers, more product is produced domestically than is imported. A major proportion of Canadian lead sinker production is probably attributable to individuals and very small local companies. Between 1988 and 1993, the total deposition of lead shot and sinkers into the Canadian environment by hunters, clay target shooters, and sport anglers averaged about 2400–2700 t/yr. About 70–80% of the total deposition was lead shot from hunters. Most of the deposition of shot and sinkers occurs in Ontario and Quebec, but some deposition occurs in all provinces and territories. Local deposition rates vary from almost nil to very high in some locations (certain rivers, lakes, marshes, target shooting clubs) where shooting or angling pressure has traditionally been high. Where they have been measured, shot pellet densities at waterfowl hunting sites in Canada are comparable to those measured in the United States and elsewhere. Metallic lead pellets deposited onto soils and aquatic sediments are not chemically or environmentally inert, although tens or hundreds of years may be required for total breakdown and dissolution of pellets. The rates of erosion, oxidation, and dissolution of metallic lead pellets in the environment depend on various physical and chemical factors. Aerobic, acidic conditions enhance the rate of pellet breakdown, whereas anaerobic, alkaline conditions decrease it. Physical factors such as high water flow rates, soils or sediments dominated by the presence of coarse sand or gravel, and frequent disturbance of contaminated soils all serve to enhance the rate of lead pellet breakdown. Lead concentrations in soils and sediments of shotfall zones of clay target shooting ranges can exceed the Canadian Environmental Quality (Remediation) Criteria for lead in soils. This may also be true for sites experiencing heavy hunting pressure, but data from such sites are generally lacking. The leachable lead concentrations in soils or sediments associated with clay target shooting ranges are often sufficiently high as to exceed lead criteria for hazardous waste. Molecular lead from the breakdown of spent shot can be transferred to biota, especially soil and sediment invertebrates and terrestrial and aquatic plants, and thence to higher trophic levels. Lead shot ingestion is probably the primary source of elevated lead exposure and poisoning in Canadian waterfowl and most other bird species. For some species (e.g., Common Loons), lead sinker ingestion is a more frequent cause of lead poisoning. Based on gizzard and wing bone surveys of the species of ducks most commonly hunted and extrapolation from U.S. estimates, up to 6 million of the approximately 50–60 million game ducks migrating from Canada every fall may ingest one or more spent lead shotgun pellets while in Canada. These individuals suffer either mortality (~200 000–360 000) or sublethal lead poisoning (several million). Because the United States has banned the use of lead shot for waterfowl hunting nationwide since 1991, Canada is now responsible for an increasingly large proportion of the lead poisoning problem in North America and may be the major continental source of migrating waterfowl that carry embedded lead shot. Lead shot ingestion also occurs in a wide variety of non-waterfowl species, including upland game birds, shorebirds, raptors, and scavengers. Where it has been explicitly studied in Canada and the United States, lead poisoning mortality of Bald and Golden eagles from eating prey animals with lead shot embedded in their tissues or the gizzards of birds with ingested lead shot accounts for an estimated 10–15% of the recorded post-fledging mortality in these raptorial species. Several studies have demonstrated that the incidence of embedded shot in apparently healthy, free-flying waterfowl frequently exceeds 20%, indicating that millions of migrating ducks and geese carry embedded shot. A significant proportion of heavily hunted upland species and small game mammals, and even some nonhunted species, also carry embedded shot. Clay target shooting ranges, especially those in which the shotfall zones include ponds, marshes, lakes, rivers, beaches, or other aquatic-type environments, create