Organochlorine and metal residues in royal terns nesting on the central Texas coast

Royal Tern (Sterna maxima) eggs collected from two study areas on the central Texas coast in 1978 contained organochlorine residues at levels below those known to have adverse effects on avian reproduction and survival. Residues of zinc, copper, selenium, and arsenic were present at what appeared to be background levels. Mercury residues were elevated. Average organochlorine and metals residues did not differ significantly between an agricultural-industrial study area and a less developed control area. The thickness of eggshells collected in 1978 was statistically similar to the thickness of shells collected before 1943. There was a significant improvement in mean eggshell thickness from 1970 to 1978 with a corresponding decline in DDE and PCB residues.