(Beyond Pesticides, July 9, 2007) New field and laboratory research reveals that organochlorine pesticides reduce the hatching rate of alligator eggs. This finding adds to previous studies demonstrating that pesticides cause endocrine disruption in alligators, resulting in poorly developed reproductive organs.
American alligators, which were delisted from the endangered species list in the late 1980s, are still experiencing low hatching rates around contaminated wetlands. In Florida, many wetlands were converted or are adjacent to farmlands and some farmlands have been restored back into wetlands in efforts to improve ecosystem health. Agricultural runoff has altered the surrounding aquatic environments by depositing pesticide residuals and skewing nutrient levels. Organochlorine pesticides, such as chlordane, toxaphene and dieldrin, have been especially problematic due to their persistent nature.
The link between pesticides and reproductive problems in alligators has been firmly established since the 1990s. University of Florida zoologist Louis Guillette, Ph.D., found pesticides are linked to smaller penises and abnormal egg development in exposed alligators.
Florida Fish and Wildlife Conservation Commission official Allan Woodward has also observed fewer hatches around lakes with high pesticide levels. He reports the hatching rate has improved around Lake Apopka, a large lake in central Florida, during the last two decades from 10% to 50%, noting, “we still don’t see the hatching rate that we’d like to see.”
Building on this knowledge, the current study, Parental Exposure to Pesticides and Poor Clutch Viability in American Alligators, compares organochlorine levels in alligator eggs from four highly contaminated lakes to two less contaminated ones. This fieldwork has confirmed a strong correlation between pesticide levels and reduced hatching rates.
For the second step of the study, the researchers fed captive alligators environmentally relevant levels of organochlorine pesticides. The eggs from the exposed alligators show similar pesticide levels and hatching rates to those found in proximity to the contaminated lakes. These results suggest wild alligators have been consuming pesticides through their diet, which implies the entire food chain is ingesting these toxic chemicals as well.
“[I]t indicates that if this is happening to alligators, it’s happening to turtles. If it’s happening to turtles, it’s happening to frogs and birds,” says coauthor Timothy Gross, Ph.D., who is finding similar effects in other species.
Several pesticides and other common contaminants can cause endocrine disruption (i.e. interfere with the natural signals controlling development, daily maintenance of the body and other hormonal functions). Research links the presence of endocrine disruptors to reproductive disorders, alterations in neurodevelopment, cancer, immune suppression and other adverse health endpoints. Many scientists believe that wildlife provides early warnings of effects produced by endocrine disruptors, which may as yet be unobserved in humans.