Increased Organochlorine Use and Hermaphroditic Cricket Frogs

Newswise — Examining frogs collected by museums in Illinois from 1852 to 2001, researchers found a dramatic increase in hermaphrodism, or intersexuality, correlating with the rise in popularity of organochlorines such as DDT and polychlorinated biphenyls (PCBs), according to a study published today in the March issue of Environmental Health Perspectives. The study team worked from the theory that exposure to these industrial compounds and their by-products, known endocrine disruptors, impairs reproductive development of frogs and led to their marked decline in the state.

Researchers examined 814 cricket frog museum specimens for evidence of intersex gonads, defined as testes that produce egg cells or the presence of both a testicle and an ovary. Even at low environmental concentrations, industrial chemicals can interfere with sensitive endocrine-driven processes such as gonad development. Frogs are especially susceptible to developmental abnormalities because embryonic development occurs in the water, in open contact with contaminants.

The research time span of 1852 to 2001 comprised five periods: a preorganochlorine period prior to the use and release of organochlorines (1852"1929); a period of industrial growth and initial uses of PCBs (1930"1945); a period of rapidly increasingly DDT use and further industrialization (1946"1959); a period of declining use and the eventual ban of DDT as well as the beginning of industrial pollution controls (1960"1979); and a period of substantial reduction of organochlorines in the environment (1980"2001).

The team's findings suggest that endocrine-disrupting organochlorine contaminants initially released in Illinois in the 1930s likely contributed to the decline of cricket frogs, especially in the industrial northern region. From 1946 to 1959, the percentage of intersex frogs increased notably, and there was a corresponding reduction in the proportion of females to males. This can be attributed to the fact that heavy industrialization from the 1930s to 1950s, especially in the Chicago region, yielded emissions of combustion products and organochlorine contaminants. Cricket frogs virtually disappeared from the northeast during this time.

An increase of hermaphrodism occurred during the industrial period corresponding with the decline in cricket frog population, but the intersex prevalence in recent years is low and may be a result of contaminants persisting in soils and waters of the Midwest at reduced levels. One organochlorine herbicide in use today, atrazine, may also contribute to intersexuality. The study did not draw specific conclusions relative to any potential impact of atrazine.

Although the low levels of intersex frogs today may represent a near-baseline condition, the study authors write that they "cannot conclude that the era of endocrine disruption in cricket frogs has come to an end, because in areas with the most severe decline in populations and most severe endocrine disruption historically, numbers of remaining cricket frogs are now insufficient to permit sampling."

Dr. Jim Burkhart, science editor for EHP, says, "Frogs are important in part because they may show the effects of ecological change more quickly or more obviously than other species. The historical approach this study takes helps us align the various periods of increased intersexuality and population reduction in cricket frogs with distinct stages of time."

The lead author of the study was Amy L. Reeder of the University of Illinois at Urbana"Champaign. Other authors included Marilyn O. Ruiz, Allan Pessier, Lauren E. Brown, Jeffrey M. Levengood, Christopher A. Phillips, Matthew B. Wheeler, Richard E. Warner, and Val R. Beasley. The article is available free of charge at http://ehp.niehs.nih.gov/members/2004/7276/7276.html. Funding sources for the research as reported by the authors included the John G. Shedd Aquarium through support from the Dr. Scholl Foundation.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/.