The study, published recently in Environmental Science: Processes and Impacts, found a toxin known as Aroclor 1268 in six nesting populations of least terns (Sternula antillarum) at various locations along the Georgia coast. Aroclor 1268 is composed of polychlorinated biphenyls (PCBs), a chemical used on site at the 550-acre Linden Chemical and Plastics (LCP) facility until 1994. Since then, the plant has been closed and was designated as a Superfund site due to contamination by PCBs, mercury and other chemicals. As a Superfund site under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, the EPA began initial cleanup efforts almost 20 years ago and has the power to approve or overrule future cleanup efforts by onsite parties. The plant was the only user of the chemical in the entire southeast, co-author Gary Mills said in a University of Georgia press release.
"We wanted to look at the dispersal of Aroclor 1268… and specifically how this exposure to contaminants might be affecting the least terns nesting there," said Gabrielle Robinson, lead author of the study, and now a shorebird biologist for the south district of Cape Cod National Seashore. Although eastern populations of the least tern are not listed under the federal Endangered Species Act, they are listed in many states, and considered rare in Georgia. "We weren't expecting to find Aroclor 1268 in some of our sites that were farther away from LCP."
Over the course of two breeding seasons, the team of researchers collected abandoned eggs from sites both near and far from the LCP site. Once the eggs hatched, they took fecal and feather samples from chicks to test for contaminants, as the harmful chemicals build up in fats, or pronteinaceous tissue such as feathers. They also collected depredated chick carcasses for contaminant analysis. The team tested the samples for total mercury, total PCBs, and specifically for Aroclor 1268. They found that the birds contained high enough levels of the chemical to cause lower egg production, physical and physiological abnormalities in offspring, immune system disorders, and other adverse effects.
With sites ranging across all of coastal Georgia, this is the largest study ever done of contamination from the LCP site, and shows the greatest dispersion of Aroclor 1268. The study also indicates that the chemical is spreading farther away from the site through the food chain. Least terns in particular are being contaminated by ingesting fish that have been exposed to the toxin.
This new information is not surprising, since previous studies have documented contamination in species of reptiles, marine mammals, plants, fish and invertebrates in close proximity to LCP. However, finding the chemical in birds so far removed from the contaminated site, and many years after the plant was closed is concerning, especially because seabirds are at the top of the food chain and can indicate threats to the health of the entire coastal ecosystem. Robinson says that this new information should be considered now when doing reference studies in areas previously thought to be fairly pristine. Though there is not much that can be done to clean up the contaminants once they've entered the food web, it is an important aspect to consider when looking at quality of habitat for birds, particularly in regards to mitigation of lost habitat.
"Exposure to contaminants, as we know, can cause health and reproductive effects that are negative," Robinson said, "This species has a lot of conservation concerns, and contaminant exposure is just one more threat posed to these birds."
