Environmental toxins making biological 'clock' tick the wrong way?

Environmental toxins may be disrupting the circadian rhythms, according to a recent study.

"This research shows that exposure to environmental toxins may be depressing the function of our circadian clock, the disruption of which is linked to increased rates of cancer, diabetes, obesity, heart disease, and depression," said senior author Jennifer Hurley from Rensselaer Polytechnic Institute.

The research builds on recent findings from the Jefferson Project at Lake George, showing that a common species of zooplankton, Daphnia pulex, can evolve tolerance to moderate levels of road salt in as little as two and a half months.

That research produced five populations of Daphnia adapted to salt concentrations ranging from the current concentration of 15 milligrams per liter of chloride in Lake George, to concentrations of 1,000 milligrams per liter as found in highly contaminated lakes in North America.

"Plankton, which are key consumers of algae and a food source for many fish, may be making a monumental tradeoff to tolerate increased road salt," said co-author Rick Relyea. "The circadian rhythm guides these animals through a daily migration, to deep waters during the day to hide from predators and shallow waters at night to feed. Disrupting that rhythm could affect the entire lake ecosystem."

Hurley said adaptation to salt is likely affecting Daphnia at the epigenetic level, a heritable change in gene levels rather than genetic code. The research has wide applicability in multiple fields beyond human health and is a demonstration of cutting-edge, interdisciplinary research resulting from cross-collaboration between CBIS and the Jefferson Project.

"The implications are substantial," Hurley said. "You've exposed Daphnia to an environmental toxin, and its clock was suppressed, probably through epigenetic mechanisms. The clock and biology of Daphnia is very similar to the clock and the biology both in our brains and most organisms. Is it possible that we can see epigenetic changes in the human brain because of exposure to environmental toxins?

The study appears in Ecology and Evolution.