LAKE MEAD NATIONAL RECREATIONAL AREA
OVERTON, CLARK COUNTY, NEVADA
In general, the concentrations of DDE reported by the EPA-10 and APPL laboratories were comparable to or less than those reported by the EPA-9 laboratory. Therefore, the health risk posed by the DDE contamination, if calculated with the new data, would be comparable to or less than ATSDR's previous estimates.
The EPA-10 and APPL laboratories reported a lower analytical detection level for DDE than the EPA-9 laboratory. Therefore, EPA-10 and APPL detected low levels of DDE in some samples that were reported as not-detected by the EPA-9 laboratory. This would not affect ATSDR's previous evaluation, since ATSDR assumed, for risk assessment purposes, that fish with no detectable DDE residues contained DDE at half the detection level.
The APPL laboratory did not detect endrin in any of the 8 fish samples they analyzed. The EPA-10 laboratory reported detecting endrin in 2 of 10 fish; however, the concentrations were lower than those reported by the EPA-9 laboratory.
As ATSDR stated in our previous consultation, endrin is an uncommon fish contaminant, and there is no known source for it in Las Vegas Bay . Therefore, the EPA-9 laboratory data may contain some false positives or overestimates of actual endrin concentrations. The health hazard posed by endrin contamination, if calculated with the new data, would be less than ATSDR's earlier estimates.
The APPL laboratory detected PCBs in one of eight fish samples at a concentration comparable to that detected by the EPA-9 laboratory. The EPA-10 laboratory detected PCBs in ten of ten fish samples at concentrations that were comparable to those reported by EPA-9. The health risk posed by PCB contamination, if calculated with the new data, would not differ significantly from those calculated in ATSDR's previous health consultation.