RETROSPECTIVE STUDY OF THE DIAGNOSTIC-CRITERIA IN A LEAD-POISONING SURVEY OF WATERFOWL

Between 1983 and 1986 the National Wildlife Health Center (NWHC) condu cted a nationwide study of lead poisoning of waterfowl from federal an d state refuges. This survey was done to assist in identifying zones w ith lead-poisoning problems. One thousand forty one moribund or dead w aterfowl were collected and examined, The presence or absence of 13 gr oss lesions selected as indicators of lead poisoning and three lesions indicating body condition was recorded. Lead-poisoning diagnoses were based on the finding of at least 6-8 ppm (wet weight) lead in the liv er and either lead shot in the gizzard content or at least one convinc ing gross lesion indicative of lead poisoning. Four hundred twenty-one of these waterfowl were diagnosed as lead poisoned. The NWHC survey p rovided a comprehensive basis for estimating the sensitivities, specif icities, and likelihood ratios of the gross lesions of lead poisoning and the associated hepatic lead concentrations for several species of waterfowl. Some of the 13 defined gross lesions were more common than others; frequencies ranged from 3% to 80% in the 421 lead-poisoned wat erfowl. The most reliable indicators of lead poisoning were impactions of the upper alimentary tract, submandibular edema, myocardial necros is, and biliary discoloration of the liver. Each of the 13 lesions occ urred more frequently in the lead-poisoned birds, but each of the lesi ons also occurred in waterfowl that died of other causes. The number o f lead shot present in a bird's gizzard was only weakly correlated wit h its hepatic lead concentration; however, this weak correlation may h ave been adequate to account for differences in hepatic lead concentra tions among species, once the weights of the species were taken into a ccount. Although lead-poisoned ducks tended to have higher hepatic mea n lead concentrations than did lead-poisoned geese or swans, the diffe rences were probably a result of a greater dose of shot per body weigh t than to kinetic differences between species. Hepatic lead concentrat ions were independent of age and sex. Ninety-five percent of waterfowl diagnosed as lead poisoned had hepatic lead concentrations of at leas t 38 ppm dry weight (10 ppm wet weight). Fewer than 1% of the waterfow l that died of other causes had a concentration that high. This fifth percentile, of 38 ppm dry weight (10 ppm wet weight), is a defensible criterion for identifying lead-poisoned waterfowl when interpreting he patic lead concentrations in the absence of pathological observations.