DDE, selenium, mercury, and white-faced ibis reproduction at Carson Lake, Nevada

We studied organochlorine, mercury (Hg), and selenium (Se) contamination in white-faced ibis (Plegadis chihi) nesting at Carson Lake, Nevada, in 1985 and 1986. Dichloro diphenyl dichloroethylene (DDE) was related to fewer young produced/nesting attempt (P = 0.0001), fewer young produced/successful nest (P = 0.0075), and eggshell thinning (P = 0.0001). As DDE in eggs increased to >4 ppm (wet wt), and especially > 8 ppm, productivity decreased significantly (P < 0.05) and the incidence of cracked eggs increased. Assuming that 4 ppm DDE is the critical residue level, 40% of the nesting population in 1985 and 1986 was adversely impacted by DDE, with a net loss of 20% of the population's expected production (to about 10 days old). Most eggs containing exceptionally high DDE levels (8-29 ppm) also had substantial amounts of dichloro diphenyl trichloroethane (DDT), which implies recently-used DDT as the source. No evidence of breeding ground DDE-DDT contamination was found. The white-faced ibis winter in Mexico, and mostly in the interior agricultural region. Concentrations of DDE-DDT in ibis eggs, unlike most other wading bird species from the Great Basin, did not decline during the last decade. Other organochlorine contaminants were generally low and detected in 533% of the eggs. Selenium and Hg were accumulated by ibis on the Nevada breeding grounds, but concentrations in eggs did not reach levels sufficient to impact the production of 7-10 day old young. Potential Se and especially Hg accumulation during the remainder of the summer was high, but actual effects on growing young and adults remain unknown.