Quebec Woodcock

Canadian Wildlife Service (CSW) Québec region

In 1995, a team of biologists from the Canadian Wildlife Service undertook a study of lead contamination in the American Woodcock (Scolopax minor). Since this species is not known to ingest lead shot, we all assumed that lead concentrations would be low or barely above the limit of detection. We were stunned, however, when the results of the chemical analyses proved the opposite. In fact, some concentrations were higher than those found in ducks. To set this study in its proper context, we need to go back in time a little. As early as 1995, the federal government had announced its intention to ban the use of lead shot for hunting migratory birds as of 1997. This measure was a response to studies showing that there was a risk of poisoning in waterfowl ingesting lead shot. However, most of the studies were done in aquatic environments, and there is very little information on land species. In order to fill this gap, the Canadian Wildlife Service decided in 1995, to set up a study, to determine lead exposure levels in the American Woodcock. Lead in the wing I have to say that after seeing the results of the chemical analyses (Table 1), most of my colleagues, including myself, were very surprised. On average, woodcocks are two to three times more heavily contaminated than ducks. The Québec and Atlantic regions are the most heavily polluted, and adult birds are more contaminated than the young, because they probably have been exposed longer. Lead concentrations were measured in the bones, where the metal accumulates over the bird’s life span. Thanks to the cooperation of hunters, we were able to gather enough wings. Only the ones in good condition, some 1 600, were kept for chemical analysis. The sex and age of each bird was determined with the use of identifiers. Where does this lead come from? Such high lead concentrations raised many questions. First of all, where does this heavy pollution come from, and what is the source of the lead? It is easy to conclude that the lead may come from food or lead shot. Food, in the case of the American Woodcock, means earthworms, which make up 80% of the woodcock’s diet, or soil ingested with prey. The second part of the question, however, — the source of the lead — is harder to answer. Very often, a series of plausible hypotheses can be put forward, but proving any of them can sometimes turn into a police investigation. First of all, what are these hypotheses? Lead may be ingested directly as shot, or it may spread slowly through the food chain as shot breaks down in the soil over the years, or it may come from residues of the leaded gasoline used in Canada for so many years, airborne pollution from foundries and other industries that use lead, or from the pesticides once commonly applied. We must now try to identify the hypothesis explaining the lead’s origins. Acting as detectives, we decided to investigate the victims, namely the woodcocks. We therefore asked hunters to send us the wings and stomachs of the birds they had shot. We were able to verify that there was no shot in their gizzards. We then visited the scene of the crime, so to speak, and gathered evidence, taking soil samples and worm specimens at a number of stations in Québec, the Maritimes and Ontario in woodcock habitat. These samples were analyzed for lead and arsenic content. Average lead concentrations in the earthworms and soil samples were 26 g/g and 24 g/g (dry weight) respectively. Soil lead concentrations were highest in the area south of Montréal, with values varying from 60 to 200 g/g. Soil arsenic concentrations were very low, thus dismissing the hypothesis that the lead might come from the pesticides containing both arsenic and lead widely used in local orchards until the seventies. Analyzing the atomic structure of lead Continuing with our inquiries, we resorted to a more sophisticated technique: isotope analysis of the lead in wings, soil and earthworms. Just as the police uses DNA to identify a suspect, we used isotopes to try to identify the sources. Lead isotopes have already been used to determine the origin of arctic air pollution (Europe was its main source). In some cases of lead poisoning in children, paint was determined to be the source, on the basis of comparisons of isotope ratios in soil and paint samples. However, we may never really be able to correctly identify the origin of the lead because it may come from a variety of sources. The results of comparisons of lead isotope ratios in soil, worms and woodcock wings allow us to conclude that in Ontario and the Maritimes the lead doesn’t come from the leaded gasoline that was in use for a long time. What sets Québec apart from other regions is that no trend or pattern has emerged so far, but other chemical and statistical analyses are under way. An answer is needed In short, much to our surprise, high concentrations of lead were found in the bones of the American Woodcock. Two potential sources have been eliminated: leaded gasoline in the Ontario and Maritime regions and pesticide in all three regions. No clear pattern is apparent so far in Québec, but a lot of work remains to be done in order to obtain a more complete answer.