Image: eutrophication&hypoxia;'s photostream, Flickr
Natural human optimism leads one to hope that hazardous chemicals wastes discarded by humans are broken down in the natural environment, until they are once again harmless. When scientists concern themselves with this process, it is usually to study the extent to which toxic chemicals harm the environment before they are finally degraded, or to measure the impacts of the degradation process, such as oxygen-starved dead zones. So it comes as a shock that North Carolina State University toxicologists have discovered that nitrates and nitrites (NOx) carried off of farms, golf courses, and gardens may be more hazardous than previously thought because water fleas convert the NOx to significantly more toxic nitric oxide.In an article published in Plos ONE, the scientists report that water fleas, known by their latin name daphnia magna among toxicologists, can convert nitrites and nitrates to nitric oxide (NO). The nitric oxide can cause developmental and reproductive toxicity in the tiny water fleas. For example, water flea babies are born without the appendages needed for swimming.
"Nitrite concentrations in water vary across the United States, but commonly fall within 1 to 2 milligrams per liter of water," says Dr. Gerald LeBlanc, professor of environmental and molecular toxicology at NC State and corresponding author of the paper. "We saw negative effects to water fleas at approximately 0.3 milligrams per liter of water."
These results were surprising. Although plants can convert the NOx to NO, the pathways for this conversion by animals are not well known. The team of scientists plans to identify the cellular machinery used by water fleas for the conversion of nitrites and nitrates to nitric oxide, as well as to further evaluate the mechanisms of toxicity of the nitric oxide, including potential risks to humans.
Nitrite and nitrate run-off remains largely tolerated, managed mostly in the interest of reducing dead zone effects. This evidence of toxicity at lower concentrations than the current control levels will pose challenges in using fertilizer more effectively, and controlling run-off.
More on Fertilizer Run-off:
Above Average Gulf of Mexico Dead Zone Forecast by NOAA Scientists
Crop Biodiversity A Cure for Ocean Dead Zones?
Excessive Fertilizer Use Decreasing Grassland Biodiversity: Scientists Discover Why
Grist Sheds Light on the Dark Side of Nitrogen