Reduction in lead exposure of mallards (Anas platyrhynchos) in New Zealand: concentrations of lead in blood and liver, and frequency of shot ingestion by ventricular retention

Context Lead (Pb) poisoning from ingestion of spent Pb ammunition has caused widespread avian mortality globally, particularly in waterfowl through direct neurotoxicity and indirectly reducing fitness through sublethal effects. In New Zealand, Pb shot has been restricted for waterfowl hunting around waterways since 2001; however, Pb ammunition remains widely available, and no restrictions apply to its use in wetlands for non-game species, which likely means environmental Pb contamination will have persisted. Aims To determine if Pb poisoning is still a threat to waterfowl in New Zealand, and whether the consumption of wild ducks can expose humans to Pb. Methods We assessed Pb ingestion through gizzard analysis, and analysis of Pb concentrations in blood, livers and eggshells of mallards (Anas platyrhynchos) during 2014–17. Key results Elevated blood Pb concentrations (>0.2 mg L−1) were found in 9.4% of pre-breeding females and in 7.1% of post-breeding season females, with some individuals reaching thresholds for clinical poisoning (>0.5 mg L−1). Eggshells from 8 of 59 successfully hatched clutches had detectable concentrations of Pb. In mallards killed by hunters, all 336 livers analysed showed measurable concentrations of Pb with higher hepatic Pb concentrations in males than females. There was weak evidence that adults had higher hepatic Pb concentrations than juveniles. Of 343 gizzards, 55 (16%) contained ingested shot; primarily steel (n = 47) though Pb shot was also detected (n = 8). Conclusions Although regulatory restrictions appear to have reduced Pb exposure, they have not eliminated it. Implications The concentrations and frequency of Pb found in multiple tissues indicate that Pb is still a persistent contaminant, with ongoing exposure risk to waterfowl and potential implications for human consumers.