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Eggs from four species of aquatic birds inhabiting waterways of the Lake St. Clair region were collected in 1973 and analyzed for mercury. Species analyzed were mallard ducks (Anas platyrhynchos), common terns (Sterna hirundo), black-crowned night herons (Nycticorax nycticorax), and great egrets (Casmerodius albus). Mallard eggs contained relatively low residue levels, less than 0.05-0.26 ppm, and common tern eggs contained the highest residues, ranging up to 1.31 ppm. Mercury levels in the eggs were appreciably lower than those in the same species in 1970. The declines are attributed to the 1970 restrictions placed on industrial discharges of mercury into the St. Clair and Detroit Rivers.

Organochlorine residues and shell thicknesses were surveyed in eggs of the clapper rail (Rallus longirostris), purple gallinule (Porphyrula martinica), common gallinule (Gallinula chloropas), and limpkin (Aramus guarauna) from the eastern and southern United States. Clapper rail eggs were collected during 1972-73 in New Jersey, Virginia, and South Carolina. During 1973-74, gallinule eggs were collected in Florida, South Carolina, and Louisiana, and limpkin eggs were collected in Florida. Egg contents were analyzed for residues of organochlorine pesticides, including DDT, TDE, DDE, dieldrin, mirex, heptachlor epoxide, oxychlordane, cis-chlordane (and/or trans-nonachlor), cis-nonachlor, hexachlorobenzene (HCB), toxaphene, and endrin, and for polychlorinated biphenyls (PCBs). Shell thicknesses of recent eggs of these species were compared with archival eggs that had been collected before 1947. With the exception of the limpkin, the majority of eggs analyzed contained residues of p,p'-DDE and PCBs. Geometric means ranged from 0.10 ppm to 1.3 ppm. Small amounts (less than 1.0 ppm) of mirex, dieldrin, cis-chlordane (and/or trans-nonachlor), TDE, and DDT were detected in a few eggs. No evidence of eggshell thinning was found for any of the species studied. DDE residues in clapper rail eggs were higher in New Jersey and Virginia than in South Carolina.

More than a half million pounds of DDT were applied to control mosquitoes in salt marsh estuaries of Cape May County, New Jersey, from 1946 to 1966. The use of DDT was discontinued in the County after 1966. In 1967, mean concentrations of DDT and metabolites ranged from 0.63 to 9.05 ppm in aquatic fauna, but by 1973 mean residue levels had decreased 84 to 99 percent among nine species. DDE was still present at reduced levels in nearly all samples in 1973, but other DDT isomers had mostly disappeared. Dieldrin was detected only in clapper rails, and residue levels decreased during the period. Mean concentrations of PCB's increased in the clapper rail, remained the same in the fiddler crab and mud snail, and decreased in the sheepshead minnow, mummichog, striped killifish, and salt marsh snail. Small amounts of mirex, toxaphene, cis-chlordane (and/or trans-nonachlor), oxychlordane, and HCB were detected in a few specimens.