Pollution endangers fish reproduction

Friday, March 30, 2001 | 11:21 a.m.

Three types of male fish in Lake Mead show evidence of reproductive problems, scientists reported Thursday.

Results of recent studies indicate that effects of Las Vegas Wash pollution are more widespread than previously thought.

Scientists had already found reproductive mutations in carp in Las Vegas Bay, where the wash flows into the lake. But now the problem extends to two species of game fish: large-mouth bass and the endangered razorback sucker, experts told those in attendance during the Lake Mead Water Quality Forum meeting in Las Vegas.

The fish studied have smaller testicles, lower hormone levels and lower sperm counts than the same species of fish near Overton Bay.

The symptoms point to a condition in the fish known as endocrine disruption, and scientists said their findings confirm studies begun in 1995 that showed male fish with varying hormone levels.

No health or environmental warnings were issued as a result of the ongoing studies, but chemicals and possible toxins entering the bay from the surface of the Las Vegas Valley and the Las Vegas Wash are suspected.

The toxins include pesticides, heavy metals and chemicals, including the rocket fuel booster ammonium perchlorate, that are washed into the bay through the Las Vegas Wash. The scientists do not know yet whether there is any danger to humans, because fish, which are exposed constantly to the water, are more susceptible to the pollutants.

They're not even sure how badly the fish have been hurt.

"We don't know how significant these findings are on fish in the Las Vegas Bay," lead scientist Steve Goodbred of the U.S. Geological Survey said. "These are all pretty striking findings."

In all three types of fish, the male hormone testosterone was lower than expected. Testosterone dropped almost 50 percent in male razorback suckers taken from the bay.

While female fish of all three species fared better, razorbacks had lower estradiol, a hormone important for spawning.

"There is no smoking gun from either physical or environmental impacts," Goodbred said.

Tissue and blood samples from more than 100 fish will help researchers determine what chemicals accumulate in each species, USGS chemist Thomas Leiker said. The analysis on those samples have not been completed.

In the late 1990s federal and state researchers discovered male carp in the Las Vegas Wash and Las Vegas Bay had female egg sac protein, indicating endocrine disruption. Normal males have no female proteins. No chemical has been linked to the disruption.

The Southern Nevada Water Authority is launching a new study on fish in Lake Mead to determine whether ammonium perchlorate, a rocket fuel booster produced in Henderson, might be responsible for the reproductive problems.

The Defense Department has given $500,000 to the water authority and other researchers across the country for the study of ammonium perchlorate, its impact on fish thyroid glands and any link to reproductive problems in carp, water authority toxicologist Shane Snyder said.

"No one has ever done that before," Snyder said.

Whether fish born and bred in Lake Mead reproduce differently than those not exposed to perchlorate is the scientific question, Snyder said. "That's the link we are going after," he said.

The water authority's study will use carp because they have been studied the most, Snyder said.

Carp from the Las Vegas Wash and Lake Mead will also be compared to fish in the Overton Arm of the lake, where the water does not contain the chemical.

In addition to studying fish in the field, Snyder and other scientists will capture carp and bring them into the laboratory, where they will be exposed to various levels of perchlorate in a controlled setting.

The lab research will help scientists determine if physical changes or effects in the fish are actually caused by perchlorate or by some other substance in the water, Snyder said.