DDE, Selenium, Mercury, and White-Faced Ibis Reproduction at Carson Lake, Nevada

Abstract

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, fewer young produced/successful nest and eggshell thinning. As DDE in eggs increase to >4ppm (wet wt), and especially >8ppm, productivity decreased significantly 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 poplation'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. Concentration 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 {le}33% of the eggs. Selenium and Hg were accumulated by ibis on the Nevada breeding grounds, but concentrationsmore » 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.« less