THE EFFICACY OF PROTOPORPHYRIN AS A PREDICTIVE BIOMARKER FOR LEAD-EXPOSURE IN CANVASBACK DUCKS - EFFECT OF SAMPLE STORAGE TIME

We used 363 blood samples collected from wild canvasback ducks (Aythya valisineria) at Catahoula Lake, Louisiana, U.S.A. to evaluate the eff ect of sample storage time on the efficacy of erythrocytic protoporphy rin as an indicator of lead exposure. The protoporphyrin concentration of each sample was determined by hematofluorometry within 5 min of bl ood collection and after refrigeration at 4 degrees C for 24 and 48 h. All samples were analyzed for lead by atomic absorption spectrophotom etry. Based on a blood lead concentration of greater than or equal to 0.2 ppm wet weight as positive evidence for lead exposure, the protopo rphyrin technique resulted in overall error rates of 29%, 20%, and 19% and false negative error rates of 47%, 29% and 25% when hematofluorom etric determinations were made on blood at 5 min, 24 h, and 48 h, resp ectively. False positive error rates were less than 10% for all three measurement times. The accuracy of the 24-h erythrocytic protoporphyri n classification of blood samples as positive or negative for lead exp osure was significantly greater than the 5-min classification, but no improvement in accuracy was gained when samples were tested at 48 h. T he false negative errors were probably due, at least in part, to the l ag time between lead exposure and the increase of blood protoporphyrin concentrations. False negatives resulted in an underestimation of the true number of canvasbacks exposed to lead, indicating that hematoflu orometry provides a conservative estimate of lead exposure.