LEAD-POISONING IN WATERFOWL FROM THE EBRO DELTA, SPAIN - CALCULATION OF LEAD-EXPOSURE THRESHOLDS FOR MALLARDS

Lead poisoning in waterfowl was investigated during 1991/92 at the Ebr o Delta Natural Park. Sediment examination showed a lead shot concentr ation available to waterfowl ranging from 60,149 to 544,748 shot pelle ts/ha in some zones. Examination of gizzards from 108 bird carcasses c onfirmed that four different species had ingested lead shot. To establ ish prevalence values for waterfowl, 50 ducks, mainly mallards (Anas p latyrhynchos) (n = 40), were captured. Examination of the gizzard cont ents revealed that 25% of the mallards had ingested lead pellets. Lead concentration in liver and kidneys was determined by atomic absorptio n spectrometry, and the diagnostic concentration values for both of th e organs were studied. The mallard population was divided into two gro ups, based on the presence or absence of lead shots in their gizzards. After a probit transformation of data, threshold values were 1.5 mu g /g WW in liver and 3.0 mu g/g WW in kidneys. The results derived from lead concentrations and gizzard examination showed that 27% of the mal lards in the winter period were poisoned, which represents about 10,00 0 individuals of a population of 36,500 mallards in the Ebro Delta.