Environmental▼News Nitrate eyed as endocrine disrupter
LOUIS GUILLETTE/GUNNAR TOFT, UNIVERSITY OF FLORIDA
The nitrate in manure and fertilizer runoff is now under suspicion as a endocrine disrupter, according to new research from developmental endocrinologist Lou Guillette of the University of Florida. Although more work needs to be done to demonstrate cause and effect, scientists say the findings could have tremendous implications for water quality standards.
Studies of male alligators are pointing to nitrates as endocrine disruptors.
A retrospective study of seven Florida lakes shows that as nitratenitrogen concentrations in lake water rise above 10 parts per million (ppm), the limit for drinking water, testosterone levels in juvenile male alligators fall by 50% and the animals have smaller penises, Guillette told attendees at a water monitoring conference in Ames, Iowa, on Feb. 19. Guillette stumbled across the association between nitrate and depressed hormone expression when he found low levels of testosterone in alligators from eutrophic lakes with only traces of pesticides but high levels of nitrogen. The testosterone levels were similar to those of alligators inhabiting lakes with high levels of pesticide contamination. By analyzing the data statistically using linear regression, Guillette found a dramatic association between the low testosterone levels and high nitrogen concentrations in the water. “We know that exposure of young alligators to organochlorine pesticides can alter the
synthesis of hormones, but could nitrate in the environment continue to depress testosterone production?” Guillette warns that “these results are very preliminary, and we need to go out and measure concentrations of testosterone and nitrate in the blood and urine of individual alligators.” “Guillette’s results fit well with my studies showing that corticosterone and testosterone levels dropped by half in rats given 50 ppm sodium nitrate in their drinking water for four weeks,” says Nirmal Panesar, a steroid endocrinologist at the Chinese University of Hong Kong. He has also published research showing that exposure of testosterone-producing cells from mouse testes to nitrate shuts down their synthesis of testosterone. “These experiments show indirectly that mammalian cells can reduce nitrate to nitric oxide,” Panesar says. Nitric oxide acts as a hormone in the body, inhibiting hormone synthesis in the testis or causing vasodilation, he adds. For instance, nitric oxide action is the mechanism behind the anti-impotence drug, Viagara, but too much nitric oxide during early developmental stages appears to depress testosterone synthesis, which is necessary for normal development
of the penis, Guillette says. For a long time, scientists thought that nitric oxide in the body was only synthesized from the amino acid L-arginine. But in the mid-1990s, the cardiovascular literature began to include reports showing that mitochondria in the cell can reduce nitrate from food and water to nitric oxide, Guillette says. Nitric oxide is a potent inhibitor of cytochrome P-450, a key group of enzymes that help synthesize steroids, Panesar adds. “It appears that Guillette is seeing nitrate act as an endocrine disrupter, and if his research is published, it may intensify efforts to look at nitrate,” says Peter Weyer, associate director of the Center for Health Effects of Environmental Contamination at the University of Iowa. The nation’s waters are seriously contaminated with nitrate, and many Iowa streams report concentrations of 10–20 ppm nitratenitrogen, well above the level where Guillette is observing effects, he says. In fact, because Guillette’s preliminary work is finding an endocrine-disrupting effect of nitrate at levels around EPA’s nutrient criteria of 3.26 ppm nitrate-nitrogen, it may mean that nitrogen standards to protect wildlife and human health may have to be dropped even lower, adds Mary Skopec, research scientist with the Iowa Geological Survey. —JANET PELLEY
Common household chemicals affect algae In laboratory experiments, three common household chemicals have been found to reduce the diversity of algal communities at concentrations similar to those found for two of them in the environment. If these compounds have the same effect in freshwater streams receiving wastewater treatment plant (WWTP) effluents, they could alter the river’s food web and its ability to process potentially problematic contaminants. Moreover, because they are sensitive biotic communities, these effects on algae may be an “early warning” of future environmental problems. In this issue of ES&T (pp 1713–
162 A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / MAY 1, 2003
1719), researchers from the University of Kansas show that the antimicrobial agent triclosan, which is found in home products ranging from kitchen cleaners to toothpaste; the widely used antibiotic ciprofloxacin; and the surfactant tergitol NP10, which is found in hair dyes and most spermicidal lubricants, do not necessarily alter the total concentration of algae but rather which genera are present. There has been growing concern in both North America and Europe that pharmaceuticals and personal care products, such as these, are passing through WTTPs and enter-
