For years wetlands have been used to remove pollutants such as nitrogen and phosphorus from wastewater. Now, researchers are reporting that the marshy habitats can also reduce hormones in runoff from livestock facilities.
Scientists and environmentalists have become increasingly concerned about reproductive hormones, such as estrogen, being released into rivers. These naturally occurring chemicals — and manmade substances, such as PCBs and some insecticides, that mimic them — can disrupt the endocrine system of fish, causing male fish to develop female reproductive organs.
Both humans and animals secrete hormones, which eventually wind up in wastewater. Traditional sewage treatment plants are unable to remove the hormones, and livestock effluent is rarely treated. Researchers in 2004 tested streams in 30 states and found estrogen in 80 percent of the waterways.
But recently, scientists led by Nancy Shappell of the federal Agricultural Research Service found that artificial wetlands at a swine facility in Greensboro, North Carolina, removed 83 percent to 93 percent of estradiol — a form of estrogen — from wastewater. They reported their findings on Dec. 6 in an online edition of the journal Environmental Science and Technology.
After wastewater left the barns at the hog farm, it was transported from manure pits into lagoons, and then piped into constructed wetlands. Researchers believe that wetlands remove estrogen through a combination of decomposition, photolysis (the breakdown of chemicals by sunlight), adsorption to soils, and absorption by plants such as cattails.
After working its way through the wetlands, the effluent was pumped into a storage pond. (An added bonus of the system is water conservation: Some of the wastewater was sent back to the barns to flush the manure pits under the pens.)
The final product was water containing less than 10 nanograms per liter (ng/L) of estrogens—the concentration recommended by the Environment Agency of England and Wales. This concentration, the agency says, causes no observable effects in fish. (To date, the EPA hasn’t established guidelines.)
“This water could then safely be released to the environment, hopefully having removed estrogenic effects that could harm the reproductive capacity and development of fish and wildlife,” says Shappell.
Daniel Schlenk, an aquatic ecotoxicologist at the University of California, Riverside, says the findings are promising.
“Removing more than 90 percent of compounds like steroid estrogens is a good thing,” says Schlenk. “It is certainly better than the alternative of not treating waterways impacted by [livestock].”
But, he adds, using wetlands to treat wastewater might not be the cure-all. Some research has shown that when Japanese killifish larvae are exposed to water with estrogen concentrations of 10 ng/L, they all turn into females. “So,” he says, “to claim that there would be no effects in fish is not accurate.”
Though the U.S. doesn’t currently regulate hormones in waterways, the EPA is looking into how hormones released from concentrated animal operations impact the environment.
Shappell is hopeful that the research will highlight issues that need further investigation, and spotlight which “management practices are effective in minimizing environmental impacts.”
“The potential impact [of estrogens] can’t be underestimated,” she says.
Story by Alisa Opar. This article originally appeared in "Plenty" in December 2006.