VOA标准英语2009年-Fish Kills Linked to Water Pollutants（在线收听）

By Zulima Palacio
Washington
19 October 2009

 
Scientists dissect fish from a river near Washington, DC
Since 2002 thousands of fish in the United States have died and continue to die in many rivers, most in the rivers of the southern east coast.   Researchers have found what they call "the feminization of fish" or the presence of immature eggs in male fish. They have also found different levels of water contamination all related to human activity. The government says twenty percent of male black bass in river basins across the country have immature egg cells in their sexual organs.

This is a different way of fishing. With electric shocks delivered in the water, all fish nearby rise to the surface, belly up. 

Rick Router is with the Virginia Department of Environmental Quality. "We are applaying about 300 volts to the water at 6 amps. It doesn't kill the fish, it just stuns them momentarily," he says.

The fish recover in a minute or two. But they don't live much longer, because the scientists test their blood and then dissect them. 

Here on the Potomac River, south of the U.S. capital, fish are being caught for complex analyses. It's part of a joint study between the states and federal government.

It began seven years ago when thousands of fish were found dead in rivers of the Shenandoah region on the US east coast.

The frequent fish kills are triggering questions - but there are few answers.

Fish pathologist Vicki Blazer, of the U.S. Geological Survey, has been studying both the fishkills and the live fish. She says, so far, there are two major findings: deadly external lesions and another condition called intersex, also known as feminization. Scientists say both findings are related to contaminants in the water. "Intersex as we see it in the smallmouth bass is the presence of immature oocytes (immature eggs) in the testes of the male bass. So far the females look fairly normal although it is not just the males that are dying in the fish kills. The females also die in the fish kills," she says.

Blazer and the scientists on her team are studying smallmouth bass in this region of the Potomac. "This is a blood sample which when we get back to the lab we'll centrifuge and get the plasma," she says.

The plasma is analyzed to determine what is killing the fish. Blazer also checks for lesions and other abnormalities that could kill them. On this fish, one eye is abnormal, while this one has defects on its fin. "These are pale discolor areas on the gills that is not normal," she says.

Research biologist Luke Iwanowicz removes some of the vital organs for further study. "This is a male. That's the testy. Many of the changes we can't see with the naked eye just looking at the testy itself. We need to fix the tissue and look at the cells under a microscope," he says.

Blazer says a national study also found intersex characteristics and lesions. 

She and other scientists agree the cause is related to water quality. 

Scientists have found contaminants such as herbicides, pesticides, estrogen and birth control chemicals in the river. Higher concentrations were found where farming is intense and human population dense. In general, water treatment plants do not remove all chemicals before dumping water back into rivers.
 
So called endocrine disruptors are especially worrisome because they can change sexual behavior. "One of the concerns is if you have a less aggressive male, they may be less able to protect their nest and do what they are supposed to do. We have done some studies to look at the quantity and quality of the sperm, and intersex bass did have somewhat lower sperm count as well as less motor sperm," she says.

Environmental biologist Fred Pinkney is with the U.S. Fish and Wildlife Service. He is studying another area -- the Chesapeake Bay. "I think these fish are sort of swimming in a mixture of low level concentrations of pesticides, of hormones that are released either from waste water plants or from failing septic systems," he says.

He believes the problems are related to hormones, whether from human medical treatments or from farms with large numbers of animals. "People excrete hormones, including things like birth control pills, that largely go untreated through the waste water plants and into the rivers," he says.

Pinkney is also concerned about drinking water. He says fish all over the planet could be developing similar problems because of pollution.