Scientists explore connection between pollution, intersex fish.

A biological role reversal of fish in the Monocacy River and other local Maryland waterways has scientists wondering what problems might lie ahead for aquatic life — and humans. Frederick News-Post, Maryland. [related stories]

Scientists explore connection between pollution, inter-sex fish
Originally published February 11, 2007
By Nancy Hernandez

News-Post Staff 
Frederick News Post, Maryland

FREDERICK — A biological role reversal of fish in the Monocacy River and other local waterways has scientists wondering what problems might lie ahead for aquatic life — and humans.

Immature eggs have been found in male small-mouth bass while female fish of the same species were lacking an egg yolk precursor, according to Vicki Blazer of the U.S. Geological Survey.

She spoke at Hood College this week about the findings of a recent fish study she led involving about 15 governmental agencies and universities across several states.

Beginning in 2005, fish were collected at sites downstream and upstream of several treatment plants on the Monocacy River and Conococheague Creek in Pennsylvania. Scientists wanted to see what, if any, role wastewater treatment plants have played in the problem, Blazer said.

The gonads of male fish were not as developed downstream of wastewater treatment plants, with the biggest discrepancies found along Conococheague Creek, she said.

As much as 100 percent of the male small-mouth bass in some locations exhibited male and female characteristics, she said. The male fish had sperm and immature eggs. Some also had produced vitellogenin, while their female counterparts had not. Vitellogenin is an egg yolk producer typically found only in female fish.

Male largemouth bass also possessed inter-sex characteristics, but not as frequently, she said.

The sex abnormalities are not limited to the local region, she said. In the south branch of the Potomac River, about 58 percent of roughly 230 male fish exhibited inter-sex characteristics.

Inter-sex fish have been discovered in recent years around the world, Blazer said. The severity of the problem ranges from location to location, even within watersheds, and from season to season, she said.

What causes the sex abnormalities has not been determined, but chemical pollution is a suspect.

Roughly 15 chemicals have been identified in the Monocacy River and scientists estimate many more are present. Under current regulations, water quality limits are set for individual chemicals and not for the myriad of compound possibilities, said Robert Ballinger, a spokesman for the Maryland Department of the Environment. The Monocacy River meets water quality standards for the individual chemicals, he said.

But chemicals do not necessarily pose health hazards individually, rather creating toxic compounds when combined, Blazer said. In local fish, compounds commonly called endocrine disrupters appear to be the problem behind the gender confusion, Blazer said.

Endocrine disrupters that mimic estrogen are intercepting and distorting the normal hormonal signals of the small-mouth and largemouth bass. Both wild fish and those exposed to chemical compounds in the laboratory developed the sex abnormalities, Blazer said.

She hopes to collect more fish this spring, before and after spawning season, to study what influence the sex abnormalities might have on reproduction and future fish populations.

Further south, researchers in Virginia are trying to determine if the sex abnormalities played a role in the deaths of thousands of small-mouth bass since 2000. One 2005 episode in the south fork of the Shenandoah River wiped out about 80 percent of the small-mouth bass and redbreast sunfish population, Blazer said.

While no data has definitely linked sex abnormalities with large numbers of fish being killed, the two problems are likely related, said Drew Ferrier, a biology professor at Hood College.

Endocrine disrupters also can intercept and distort other body functions, such as the thyroid and immune system, he said. Humans are susceptible to endocrine disrupters as well.

More study is needed to determine what chemical compounds lead to inter-sex fish and to pinpoint where the chemicals are entering the waterways, he said. “There are many more questions on this topic than answers,” he said.

Contamination is likely coming from multiple sources, such as human wastewater, runoff from farms and industrial sites and atmospheric pollution, Blazer said.

“Many times, we want to blame agriculture and industry but when we use fertilizer to kill dandelions, use antibacterial soap, flush our prescriptions down the toilet, we need to think about that,” she said.

Blazer’s team will continue to analyze the collected data and hope to perform additional studies, such as chemical analysis of the soil where small-mouth bass lay their eggs.

Figuring out what is harming the fish will benefit people as well, Blazer said. Humans breathe the same air, drink the same water and eat food grown in the same ground that animals do. Aquatic species that are battling health problems offer clues that something is amiss in the environment. “Fish are an indicator of our ecosystem’s health,” she said.