Scienceline, NY
08-01-07
Wading in Hormones
Feminized fish: Susceptible victims of a changing aquatic environment or
harbingers of worse to come?
By Andrea Anderson
Male fish taking on female characteristics. A community plagued by high breast
cancer rates. Waterways polluted by manure from animal feedlots. These
phenomena may seem unrelated, but some researchers suspect they share a
common link: hormone pollution.
Natural hormones and synthetic compounds that mimic them are increasingly
being detected throughout the environment, especially in waterways. Of
particular concern are estrogenic compounds—natural and manmade forms of
the group of hormones that includes estrogen—which can have dramatic effects
on aquatic animals. Although links to human health problems are much more
tenuous, concerns are growing.
“We should probably be concerned about what’s in our drinking water as well as
what we’re dumping into rivers and lakes,” says University of Colorado
endocrinologist Dave Norris. Late last year, his team made headlines when they
showed that even low concentrations of estrogenic compounds released into
rivers through treated water from sewage plants are giving male fish female
characteristics in rivers near Boulder, Colorado.
The team studied white sucker, a fish species that lives both upstream and
downstream of the sewage discharge sites. Certain fish species naturally
undergo a process called intersex, where they switch from male to female, but
it’s rare in white suckers—under normal conditions.
But in Boulder Creek and the South Platte River, researchers found more
feminized fish downstream of sewage effluent sites than upstream. According to
Norris, sewage treatment systems “weren’t designed to remove this stuff” from
wastewater. His team found that at least two estrogen compounds—a natural
estrogen and a type of synthetic estrogen found in birth control pills—contributed
to the feminization. Each compound is potent enough to cause changes in fish on
its own, but together they have an even greater impact.
“Many of these compounds work through the same [biological] mechanism, so
they can add up,” Norris explains.
The feminized Colorado fish are not an isolated incident. In 2002, following large
fish kills in tributaries of the Potomac River in West Virginia, researchers found
fish with numerous abnormalities, including male smallmouth bass whose testes
contained egg cell precursors. At some test sites nearly all smallmouth bass
showed intersex, says U.S. Geological Survey biologist Doug Chambers. When
Chambers led a subsequent study (completed this year), his team found many
chemicals, including estrogen mimics, even in rivers crossing sparsely populated
areas of West Virginia.
On some level, the hormone problem is unavoidable. People and animals
naturally produce and excrete estrogens. Drugs like birth control pills also contain
estrogens. But the problem is exacerbated when people carelessly flush unused
drugs and estrogen mimics down the drains.
Estrogen mimics, or “endocrine disruptors” are chemicals that influence the
body’s endocrine system which is normally controlled by the body’s own
hormones. These estrogenic compounds can come from unexpected products
like personal care items, perfumes and detergents, and some plastics. When
these products are disposed of, the compounds may combine with natural and
pharmaceutical hormones from human and animal waste to create a potent
hormone cocktail.
“If it’s causing these problems in fish, we have to assume that there could be
human health effects.” says Retha Newbold, a biologist with the National
Institutes of Health, who has been studying estrogenic compounds for more than
30 years.
In humans, an excess of natural estrogen has been implicated as a risk factor for
many conditions, including some reproductive cancers and breast cancer. Tests
on lab animals suggest that other organ systems and pre-natal development may
also be affected, says Newbold. There’s less research on the effects of manmade estrogenic compounds, but they may pose similar risks.
Nevertheless, not all researchers are willing to make the leap from sewage
effluent and fish feminization to drinking water and human health. “There are no
smoking guns in terms of the human health effects from drinking water,” says
Bruce Brownawell, a Stony Brook University marine biologist. “The evidence to
date is that it’s much more of an ecological issue.” Like Norris, Brownawell
focuses his research on how estrogenic compounds affect aquatic life.
Brownawell believes that the levels of estrogenic compounds detected in drinking
water are largely due to false positive measurements and over-analysis. He and
his team are working to develop advanced mass spectrometry techniques to
better detect detergents, natural estrogens and pharmaceuticals in waterways.
He argues that the estrogenic dose an adult would get from drinking three liters
of the “worst drinking water” every day is about one millionth the minimum dose
of estrogen given therapeutically. “It doesn’t give me much reason for concern,”
he says.
Colorado’s Norris agrees that the concentration of any one estrogenic pollutant in
drinking water is not high enough to affect an adult human. “The people who are
saying drinking water is safe are correct – by itself,” he says. But all together, he
speculates, the compounds may have unrecognized effects, particularly for
developing fetuses.
Basic wastewater treatment removes about 90 percent of estrogenic compounds,
on average, while secondary treatments can increase this to more than 99
percent, according to Samir Khanal, an engineering professor at Iowa State
University, who studies estrogenic compounds as they move through the
wastewater treatment system. He says the greatest risk of groundwater
contamination may not be from sewage effluent but from biosolids–the sewage
sludge that is removed during sewage treatment and applied to land as fertilizer.
“[Estrogenic compounds] physically attach to the biomass,” Khanal explains,
which is problematic because biosolid treatment removes hormones less
efficiently. In the United States, about 50 percent of biosolids removed during
sewage treatment end up being applied to the land as fertilizer, according to
Khanal. Other studies have raised additional concerns about hormones in
manure-based fertilizers and feedlot run-off.
Regardless of the source of the contaminated biomass, when the land sits above
a shallow drinking water sources, estrogenic compounds can enter into
groundwater, adds Khanal.
In rural areas with less comprehensive sewage treatment, the risk of
groundwater contamination may also increase. For example, researchers from
Silent Spring, a Massachusetts-based research and advocacy organization
focused on women’s environmental health risks, are studying a Cape Cod
community where most residents rely on septic systems in which solids settle in
septic tanks and liquids filter through the soil.
Women in this community have an elevated breast cancer risk – as much as 20
percent higher than the average risk for women elsewhere in Massachusetts.
When preliminary studies ruled out “the usual suspects,” such as an older
population, higher mammography levels, or family history, researchers started
looking at possible contamination in the shallow aquifer that provides drinking
water for the area.
The group did detect estrogens and other wastewater chemicals in groundwater
samples, but they cannot directly link them to the community’s breast cancer
problem. “We are very limited in what we know about people’s lifetime exposure
[to estrogenic compounds],” explains Silent Spring Institute executive director
Julia Brody.
Norris insists that until we better understand the effects, any excess hormone
exposure is too much. “It’s best not to get this stuff in there in the first place,” he
says.
While estrogens from human and animal waste will be difficult, if not impossible,
to cut, many argue that estrogenic compounds in laundry detergents, optical
brighteners, and plastics can and should be replaced or reduced. “There’s no
simple solution. It’s a very complicated problem and it involves a multi-billion
dollar industry,” Norris says. “The bottom line is that we can’t stand around and
point fingers at anyone other than ourselves.”