When survey crews tossed their nets into Maryland’s South River looking for fish last year, what they pulled up was a bit of an ecological mystery.

The crew from the U.S. Fish and Wildlife Service, who were conducting a survey for yellow perch, noticed strange pink bumps on the lips of catfish found on their nets.

Follow-up sampling revealed the river had the highest rate of skin tumors, and the second highest rate of liver tumors, that biologists had seen in any catfish outside the Anacostia River.

“There is really no local industry, and there is nothing that jumps out at you that indicates the prevalence would be that high,” said Fred Pinkney, an environmental contaminants biologist with the USF&WS Chesapeake Bay Field Office in Annapolis.

The South River watershed covers about 66 square miles south and west of Annapolis. About half of the watershed is still forested, although other areas have been rapidly developing in recent years. The samples were taken in the river near the Route 50 bridge, which is roughly in the middle of the watershed.

“In a way, it was really surprising,” said Drew Koslow, the riverkeeper for the South River Federation. “The headwaters of the river are really beautiful. There are wood ducks and marshes. You wouldn’t expect this issue to be hidden under the surface.”

Yet out of a random sample of 30 brown bullheads pulled out of the river, 16 had raised, pinkish red lesions around the mouth. John Harshbarger, a tumor pathologist with George Washington University Medical Center, confirmed the lesions were tumors. He found that 13 of the 16 fish had invasive cancers, and the remaining three had noninvasive skin tumors—an overall tumor rate of 53 percent. In addition to the skin cancers, six of the 30 fish—or 20 percent—had liver tumors.

According to the USF&WS, scientists consider an area to be highly contaminated when skin tumor rates are higher than 12 percent and liver tumor rates are more than about 5 percent. A USF&WS fact sheet called the South River rate “alarming.”

In comparison, the long-term tumor rate for bullheads on the Tuckahoe River on Maryland’s Eastern Shore, which scientists consider a relatively clean reference site, is 4 percent for liver tumors and 1 percent for skin tumors.

In studies in the Great Lakes and in the Anacostia River in the District of Columbia, elevated tumor rates were associated with high concentrations of polycyclic aromatic hydrocarbons (PAHs) in the sediment. PAHs are a byproduct of fossil fuel combustion, and are also a major component of asphalt and tar.

The surprise, Pinkney said, is that past sediment samples from the South River did not not have particularly high concentrations of PAHs, although most of those samples were taken nearly a decade ago.

No new sediments were sampled as part of last year’s work. “It was sort of a bare-bones study,” Pinkney said. In fact, he had to turn to the South River Federation, the local watershed group, to fund the tumor analysis work.

Nonetheless, Pinkney said, PAHs cannot be ruled out.

“It’s possible that there may be certain locations within the watershed which are higher and just haven’t been sampled yet, and it could also be that those locations are where bullheads congregate at an early age,” Pinkney said. “We just don’t know.

“We can make a strong case for PAHs as being one of the major drivers for bullheads in general, but in the South River we can’t make any connection yet,” Pinkney said.

The brown bullhead is a species of catfish that lives in fresh and tidal waters. They are bottom-feeding fish and therefore are susceptible to liver and skin tumors after being exposed to contaminants that accumulate in sediment. Because they have a limited range, they are considered to be a good indicator of local habitat quality.

Pinkney suggested more study is needed on the movements of the fish. In addition, he suggested studies on other nearby rivers to determine whether the South is a “hot spot” for tumors, or whether they represent a more widespread problem. The Bay Program is considering whether to help support such studies.

Koslow said the South River Federation was planning to collect and pay for the analysis of several sediment and stormwater runoff samples.

“We’re determined to figure out what is going on,” he said. Koslow said PAHs remain the “obvious suspect” because of past work linking the chemical to tumors in bullhead catfish. Also, PAH contamination in water tends to be closely related to stormwater runoff, and parts of the watershed have had rapid growth—and therefore increased runoff—in recent years, he said.

Koslow said the information could back his organization’s support for better stormwater control.

Stormwater is considered a major source of PAHs entering waterways, because roadways and parking lots collect vehicle exhaust, oil dripping from cars, and even tiny particles rubbing off tires—all of which may contain PAHs, which can be flushed into streams during rainstorms. Once in the water, they can accumulate in the sediment.

Further, PAHs are found in high concentrations in coal-tar based asphalt sealants that are used on parking lots. A recent study by the U.S. Geological Survey found that particles in runoff from parking lots coated with coal-tar based sealants have PAH concentrations nearly 65 times higher than those from parking lots that have not been seal-coated.

According to studies by the USGS, PAH concentrations have increased in urban and suburban waterways across the nation in the last three decades.

While most of the emphasis in the Chesapeake Bay cleanup is focused on nutrients, the South River finding is a reminder that chemical contaminants remain a concern for many places of the watershed.

The extent to which Bay cleanup efforts should focus on stormwater control has been a subject of debate because it is typically far more costly than controlling nutrients from other sources. But Koslow said the South River findings may show that stormwater controls are also important for other pollutants.

“I think this really highlights that in addition to the sediment and nutrients, we have this other 800-pound gorilla out there that we don’t know anything about, really,” Koslow said.

In fact, recent research at the Smithsonian Environmental Research Center shows that PCB levels in fish tissue tend to rise as land in a watershed is developed and runoff increases. (See As soon as we build roads, wildlife hits the highway,” December 2004.)

The South River was not considered clean. The river was listed on Maryland’s 303(d) list—also known as the impaired waters list—because of the presence of PCBs in fish. And a recent study of chemicals in osprey eggs found surprisingly high levels of PCBs from nests in the river. (See “Ospreys doing better in the Bay area, although concerns linger,” April 2004.) PCBs, though, have not been linked to tumors in fish.

Nonetheless, the river is not considered to have severe chemical contamination problems like those seen in the parts of the Anacostia and Elizabeth rivers and in Baltimore Harbor, which are considered “regions of concern” by the Bay Program.

“Our surprise is that a river that we thought was kind of in a moderate contaminant zone is showing that high a rate of a biomarker,” said Greg Allen, toxics coordinator with the EPA’s Bay Program Office. “What that might say is that the tipping point is lower than we might have thought.”

The Maryland Department of the Environment has a fish advisory for the river that urges the public not to consume more than 50, 8-ounce meals of spot or 37, 8-ounce meals of white perch annually because of PCB contamination.

Neither Pinkney nor Koslow said the new findings necessarily suggest an increased risk for fish consumption. At high levels, PAHs impact animal health, but any impact on human health is uncertain although the Department of Health and Human Services has determined that some PAHs—there are nearly 100 types—may be carcinogenic.

But Koslow said it does raise questions.

“People are really up in arms about this,” he said. “They may not understand stream dynamics and what happens when watersheds get developed with impervious cover, but they understand cancer. Now people are calling to ask if it’s safe for their kids to swim in the river, is it safe to eat crabs?

“I probably will still eat crabs,” Koslow added, “but I’m certainly going to think about it.”

Toxics & the Chesapeake Bay

While most of the emphasis in the Chesapeake Bay cleanup effort is focused on nutrients, chemical contaminants remain a concern for many places.

That is reinforced by a map recently completed by the Bay Program’s Toxics Subcommittee which shows that half of the Chesapeake’s tidal tributaries have water quality impairments stemming from a chemical contaminant.

Out of 60 tidal rivers and segments (a subsection of a river), 30 were listed on state 303(d) lists in 2004 for some type of toxic pollutant, which means they did not meet their water quality standards.

This color-coded map shows the impaired segments, and the cause of the impairments. PCBs were the leading cause of impairments, accounting for 53 percent of the segments on the list.

That was followed by listings involving both PCBs and metals, which accounted for 23.5 percent of the segments. Metals causing impairments may include cadmium, chromium, copper, lead, nickel, selenium or zinc.

Even though their manufacture was banned more than 25 years ago, PCBs are a persistent chemical that remains in the sediments of many Bay tributaries. It is a concern because it can bioaccumulate in fish and birds and pose a threat to humans who consume large numbers of contaminated fish over a period of time.

Many of the metals, while occurring naturally, can be toxic to water dwellers when present in high levels, usually as the result of industrial discharges or stormwater runoff.

Two other chemicals causing impairments, chlorpyrifos and tributyltin, are both pesticides.

What the map does not indicate is the relative severity of contamination at each location. The three most contaminated areas, or “regions of concern” that have been identified by the Bay Program are Baltimore Harbor, and parts of the Elizabeth and Anacostia rivers.

The number of segments affected by toxics may increase in the future as more monitoring information becomes available. All of the states with Bay tidal waters are in the process of updating their impaired waters list, which is required by the EPA every two years.

The ultimate Bay Program toxics goal is to “Reduce chemical contaminants to levels that result in no toxic or bioaccumulative impact on living resources that inhabit the Bay or on human health.”