Wetlands reduce estrogens from swine wastewater
Constructed wetlands can reduce natural estrogens in swine wastewater, particularly in cooler weather.
Wetlands are often referred to as nature’s kidneys, because they readily filter contaminants from water. Constructed wetlands, areas built to mimic these natural swamps, help treat wastewater, usually by decreasing levels of excess nutrients such as nitrogen and phosphorus. Research published today on ES&T’s Research ASAP website (DOI: 10.1021/es061268e) shows for the first time that constructed wetlands also decrease natural estrogens—the female sex hormones estrone (E1), estradiol (E2), and estriol (E3)—in animal wastewater.
Nancy Shappell of the U.S. Department of Agriculture and researchers at North Carolina Agricultural and Technical State University measured both estrogenic activity—as E2 equivalents—and specific E1, E2, and E3 concentrations in wastewater from the university’s swine birthing and nursery site, known as a farrowing facility.
The team used the facility’s recirculation system to follow estrogens from the barn, to a manure pit, to waste lagoons, and through the constructed wetlands. The recycled water eventually was used to flush out the barn.
Scientists are concerned about estrogens in wastewater because these hormones, both natural and synthetic, can disrupt reproductive function in fish and wildlife. In a recent review, Samir Khanal and colleagues at Iowa State University stressed the need to look at natural estrogens derived from animal operations (Environ. Sci. Technol. 2006, 40, 6537–6546). Shappell’s study is one of the first to follow estrogenic activity from swine waste—in the liquid phase—through a constructed wetland, Khanal says.
In the farrowing facility, estrogen concentrations were above 200 nanograms per liter (ng/L) in the manure pit but consistently below 3 ng/L in the wetland outflow. Because estrogen levels in the primary and secondary lagoons were higher in November than in April or July, Shappell suggests that pumping lagoon water through the wetlands may be especially effective in autumn, presumably because estrogens break down more slowly at lower temperatures. The water bypasses the wetlands in the winter, because of below-freezing temperatures, but a storage pond holds enough gray water to flush the swine house in the winter, according to coauthor Gudigopuram Reddy.
Khanal says he is concerned that the relative potencies for E1 used by Shappell differ by a factor of 10 from those used by Furuichi and colleagues, who followed estrogens in swine wastewater through a treatment process rather than a constructed wetland (Environ. Sci. Technol. 2006, 40, DOI: 10.1021/es0609598).
Shappell used the E-screen assay, which measures estrogen-dependent proliferation of a mammalian cell line. The assay used by Furuichi’s team relies on receptor-transfected cells, developed by adding estrogen receptors to the cells by genetic engineering, and has a different treatment duration, endpoint, and E2 concentration. Another commonly used assay uses receptor-transfected yeast, Shappell indicates. The various estrogens do show different potencies in different assays, and it’s important to use a physiologically relevant assay to measure estrogenic activity, she says. “When you’ve played with receptor numbers and you get a signal, what does that mean—physiologically?” she asks.
Shappell also determined actual concentrations of specific steroid hormones, including E1, E2, E3, and testosterone, with analytical methods; she found that E1 was the most persistent estrogen. Testosterone was not detected, probably because the facility had very few mature boars.
Alice Layton, an expert in analytical detection of estrogens at the University of Tennessee, Knoxville, has measured estrogen in both cattle and swine waste (Environ. Sci. Technol. 2004, 38, 3567–3573). Layton applauds Shappell’s use of both a biological assay and chemical analysis and observes that wetlands may be a low-cost solution to the problem of estrogens in animal wastewater.
Shappell’s coauthor Patrick Hunt notes that lagoon recirculation systems are the norm in facilities that, overall, handle more than 10 million swine in North Carolina, but he adds that wetland systems are uncommon in concentrated animal feeding operations (CAFOs). According to Khanal, in addition to concerns about estrogens in wastewater, the fact that many CAFOs store manure in deep pits and eventually apply it to soil is a problem because it leads to the potential for estrogens to leach into nearby waters. —BARBARA BOOTH
