Park, D, SC Hempleman, and CR Propper. 2001. Endosulfan Exposure Disrupts Pheromonal Systems in the Red-Spotted Newt: A Mechanism for Subtle Effects of Environmental Chemicals. Environmental Health Perspectives 109:669-673.

Park et al. discover that exposure to extremely low levels of a commonly-used pesticide, endosulfan, interferes with reproduction in the red-spotted newt Notophthalmus viridescens by disrupting the development of glands that synthesize a pheremone used in female-male communication. The disrupted development then leads to lower mating success.

Their experiments reveal an impact at 5 parts per billion (ppb), which was the lowest concentration they used. This concentration is well within the range of endosulfan contamination regularly encountered in the real world. Indeed, the US EPA recommends that the amount of endosulfan in lakes, rivers, and streams should not be more than 74 ppb, almost 15 times higher than the level reported by Park et al.

EPA allows 0.1 to 2 parts per million endosulfan in food. That is almost a thousand times higher.

This report is important because it shows that biologically significant effects can easily be missed by traditional toxicological testing, at levels far beneath those targeted by regulations. "Our results are the first to document that the disruption of pheromonal communication systems can be induced by exposure to low concentrations of environmental chemicals without overt signs of toxicosis. This study suggests that amphibian pheromonal systems could be one of the systems mediating subtle effects of environmental chemicals." They go on to suggest that disruption of pheremone communication may be a factor contributing to global amphibian declines.

What did they do?

Park et al. exposed female red-spotted newts to 3 different concentrations of endosulfan (0, 5 and 10 ppb) and observed the impact of exposure on a series of behavioral, morphological and endocrinological parameters, including:

• behavioral activity, including food uptake
• visual and olfactory mate selection
• mating success
• weights of ovaries and oviducts
• estradiol concentration in plasma
• measurements of glands involved in pheremone production
• electrophysiological response of males to pheremones

What did they find?

While general behavioral observations revealed no effect of exposure, pheremone-mediated mate selection and mating success were reduced in exposed females.

Higher endosulfan exposure reduces mating success in the red-spotted newt.     from Park et al. 2001

Park et al. found that exposed females were anatomically different from unexposed females in a key gland responsible for pheremone production: exposed females had smaller glands.

They also found that unexposed females were more effective at provoking a neurophysiological response in males than exposed females.

In the graph to the left, Park et al. compare the "electro-olfactogram" activity of males exposed to water containing pheremones produced by females exposed to different levels of endosulfan.   from Park et al. 2001

Taken together, the experiments conducted by Park et al. indicate the following: at low parts per billion concentrations--levels very often encountered in the real world--exposure to endosulfan disrupts glandular development in the red-spotted newt, a salamander. The affected glands normally produce a pheremone involved in female-male communication during mate selection. Affected females produce less pheremone and are less likely to attract mates than unaffected females. Their reproductive success is thus decreased.

These results identify a new mechanism by which low level contamination can cause adverse effects in animal populations, i.e., via the disruption of chemical communication.