Lead poisoning in waterfowl from the Ebro Delta, Spain: Calculation of lead exposure thresholds for mallards

Abstract

Lead poisoning in waterfowl was investigated during 1991/92 at the Ebro Delta Natural Park. Sediment examination showed a lead shot concentration available to waterfowl ranging from 60,149 to 544,748 shot pellets/ha in some zones. Examination of gizzards from 108 bird carcasses confirmed that four different species had ingested lead shot. To establish prevalence values for waterfowl, 50 ducks, mainly mallards (Anas platyrhynchos) (n=40), were captured. Examination of the gizzard contents revealed that 25% of the mallards had ingested lead pellets. Lead concentration in liver and kidneys was determined by atomic absorption spectrometry, and the diagnostic concentration values for both of the organs were studied. The mallard population was divided into two groups, based on the presence or absence of lead shots in their gizzards. After a probit transformation of data, threshold values were 1.5 μg/g WW in liver and 3.0 μg/g WW in kidneys. The results derived from lead concentrations and gizzard examination showed that 27% of the mallards in the winter period were poisoned, which represents about 10,000 individuals of a population of 36,500 mallards in the Ebro Delta.