The Trouble with Toxics in the Bay

By Jack Greer

Does the Chesapeake Bay have a toxics problem?

Are the chemicals that run off the land or the particles that descend from the sky measurably affecting the Bay's food web? Are the effects of heavy contaminant loading in harbors and industrial areas confined to these regions, or do physical and biological processes carry them farther into the Bay? Is oyster disease a signal that toxic chemicals are compromising the oyster immune system? These are the kinds of questions that citizens and scientists throughout the Bay watershed are asking. The answers, however, are far from simple.

According to ongoing research, there are indicators suggesting contaminants could have important, if sometimes subtle, effects on the Bay's ecology. While these indicators are often ambiguous, a team of researchers, with the support of the Chesapeake Bay Environmental Effects Committee (CBEEC), have begun to map the relationship between sources of contaminants and their biological effects.

A Smoking Gun

At least as long ago as 1962, when Rachel Carson in her book Silent Spring fingered DDT among other compounds as a random chemical killer, environmentalists and resource managers alike have often searched for a "smoking gun" - a chemical contaminant guilty of causing a significant ecological problem. In the case of the Chesapeake Bay, there have been clear cases of what writer William Styron has called "a murder most foul."

Public opinion surveys show that public perception is out of whack. Most people still believe that industry - big industry - is the problem. But most contaminants do not come out of a pipe.

Styron was referring, in a newspaper article, to the "killing" of the James River by the pesticide Kepone, spilled into the river by Allied Chemical Company and its contractor until authorities closed the Hopewell, Virginia plant in 1975. Because of the spill, authorities worried about contaminated shellfish and other seafood, and scientists were indeed able to track the entry of that poison into the food web. In other cases as well - oil spills, high chemical contaminant loads in the sediments of commercial harbors - the causes and effects of toxic pollution in the Bay are relatively clear.

But beyond these specific cases, what is the overall impact on the Bay of a steady rain of contaminants on the ecosystem? In order to address this question, the Sea Grant College Programs of Maryland and Virginia, with the support of the National Oceanic and Atmospheric Administration's Chesapeake Bay Office, and the cooperation of the U.S. Environmental Protection Agency and the Chesapeake Bay Program, brought together scientists from across the Bay region to meet at the Belmont Center near Baltimore to distill from recent research what we know - and what we don't - about contaminants in the Chesapeake.

A Contentious Debate

The issue of toxic contaminants in the Chesapeake Bay is not new. A six-year study of the Bay, supported by the Environmental Protection Agency, culminated in a series of reports in the early 1980s that documented the presence of metals and other contaminants in the Bay and called for a more thorough understanding of how these contaminants move through the Bay and its food web.

But, how to begin this discovery process is a problem in itself. There are numerous "camps" of scientific thought that argue for differing approaches. Some researchers call for a greater focus on bioassays that can track chemical contaminants in the tissues of living organisms. Other researchers call for a more ecosystem-oriented approach that studies how contaminants move from one level of the food web to another. Still others argue for close investigation of responses at the cellular level, for example, to see how contaminants might affect an organism's ability to fend off disease.

Scientists and resource managers meeting at the Belmont Center represented some of these approaches - though by no means all. "Our goal," says Chris D'Elia, director of the Maryland Sea Grant Program, who helped convene the meeting, "was to have researchers in the CBEEC Program assess the status of our knowledge about contaminants in the Bay and to identify information and research needs."

The scientists' answers to the fundamental questions about contaminants are summarized in a new report, Chemical Contaminants in the Chesapeake Bay, highlighted in a sidebar accompanying this article.

Repeatedly, the scientists at this meeting emphasized that while we know a fair amount about inputs of toxic materials into the Bay, we are still just learning how to measure the effects of those contaminants on Bay organisms, and on the Bay ecosystem itself.

Not Just the End of a Pipe

Contaminants enter the Chesapeake Bay from a number of sources, according to Joel Baker and other scientists at the Belmont meeting. Says Baker, "Public opinion surveys by the Chesapeake Bay Foundation and the Chesapeake Bay Program show that public perception is out of whack. Most people still believe that industry - big industry - is the problem. But most contaminants do not come out of a pipe." Even in the case of urban runoff, he says, where pollutants may come out of a pipe, the pipe is owned not by industry but by the city.

"Over the past thirty years," continues Baker, "we have seen an evolution from end-of-pipe sources to more diffuse sources. Maybe we need to use the same approach with toxics that we've used with nutrients." Nutrients also often come from diffuse sources, such as runoff from farms in rural areas or stormwater in developed areas. Baker points out that getting people to understand the real sources of contaminants will take a good deal of public education. He also notes that dealing with diffuse sources requires different management strategies.

Generally, he says, the upper Bay is more dominated by the input of rivers, so it receives more of its relative contaminant load from riverine sources. The lower Bay, where the rivers have less direct influence, sees a greater impact from diffuse sources, including from the atmosphere.

The Chesapeake Bay Program's Chesapeake Bay Basinwide Toxics Reduction Strategy Reevaluation Report lists much of what we know about sources of contaminants found in the Bay. For example, the report holds that metal loading to the Bay is highest in the Potomac River, followed by the Susquehanna, the west Chesapeake, the James, the mainstem Bay, the Patuxent, Eastern Shore, York and Rappahannock basins.

In general, the scientists at the Belmont Center felt confident, from extensive monitoring data, that environmental legislation - such as the Clean Water Act and the Clean Air Act - has led to vastly reduced inputs of chemical contaminants into the Bay from business and industry and other "point" sources. Because of these point-source reductions, and because of a growing population in the Bay's 64,000-square-mile watershed, diffuse or "nonpoint" sources of contaminants are becoming more important all over the Bay, and these sources remain more difficult to track and more difficult to control.

Over the past thirty years, we have seen an evolution from end-of-pipe sources to more diffuse sources. Maybe we need to use the same approach with toxics that we've used with nutrients.

What are these diffuse sources? For one thing, whenever we burn something, we potentially put contaminants in the air. Even before the colonists arrived in the sixteenth and seventeenth centuries, Native Americans set fire to the forests to hold down the undergrowth and to improve their hunting grounds. Now we seldom burn off our forests, but we do burn ancient forests constantly - in the form of heating fuel, coal, diesel and gasoline. This constant conflagration, whether from expansive suburbs burning heating oil all winter or from the endless parade of cars and trucks up and down the region's many highways, sends a cloud of hydrocarbons and other compounds into the air. Wind, rain and other precipitation bring it down again - into the watershed of the Bay and its tributaries.

As University of Maryland professor Alan Taylor has said, 90% of the watershed is land, not water, and once contaminants fall on the land, following their path to the Bay "becomes difficult." Clearly contaminants from both burned and unburned (as from oil spills) fuels find their way into the Bay, as PAHs (polycyclic aromatic hydrocarbons) and other compounds that are listed on the Bay Program's Toxics of Concern list.

In addition to fossil fuel products, the incineration of garbage, which may contain toxic products such as batteries, can lead to the emission of mercury and other contaminants. Though not as widespread as the fossil fuel problem, such diffuse sources are one of many delivery mechanisms to the Bay. Another poorly understood mechanism throughout the watershed is seepage into groundwater from septic tanks, which may contain traces of solvents and wastes poured down the drains of countless households. From both suburbs and cities, stormwater runoff also delivers an onslaught of motor oil, cleaning fluids, and assorted contaminants from driveways, roadways and parking lots. And from agricultural areas and even forests, the Bay receives pulses of herbicides and pesticides, such as the gypsy moth treatment Dimilin.

What Happens to Contaminants in the Bay?

The toxics story becomes more complex once contaminants enter the Bay. Researchers such as scientist Larry Sanford have been tracking their movement. Sanford, of the University of Maryland Center for Environmental Science' (UMCES) Horn Point Laboratory, has worked with his colleagues to calculate how contaminants move along the surface of the sediment, how they interact with other particles and how they are finally buried.

According to Sanford, tidal action in the mid-Bay erodes a thin layer of sediment - about 0.1 to 1 mm thick. This thin layer migrates with tidal currents, lengthening the time it takes for contaminants to become buried.

The key question, and one still under investigation by researchers, is whether contaminants - in or on the sediments, for example - find their way into the food web, and begin to move through Bay's living organisms. Significant evidence has emerged to date that this does indeed occur.

In the Baltimore Harbor, for example, researcher Jim Sanders and his colleagues at the Benedict Estuarine Research Center (BERC) found that a small fish (the mummichog) took up more contaminants at low tide than at high tide. They concluded that this occurred because fish feeding in the shallows would come into direct contact with contaminated sediments more often at low tide, when very little water covered the tidal flats.

Beyond these direct contacts with contaminants, scientists are tracking more puzzling possibilities. In the Patuxent River, for example - an area clearly less polluted than Baltimore or Norfolk harbors or the Anacostia River - phytoplankton in the river can concentrate contaminants. Sanders and his colleagues have determined that once concentrated, the contaminants can be tracked to the Bay floor, as the phytoplankton sink to the bottom. There, the contaminants have the potential to enter the food web that thrives on the riverbed.

Most importantly, Sanders has determined that contaminants may also cause an unwanted shift in the populations of phytoplankton. Arsenic, for example, appears to cause one type of algae to die down while another type takes off. This means that algae blooms can differ widely, especially in their effect on such organisms as copepods and other zooplankton that graze on them.

"Our findings suggest that the biomass [the overall amount of phytoplankton] doesn't really change," Sanders says, "but the composition of that biomass does."

For animals that feed on phytoplankton, this change may be crucial. Dan Terlizzi, a Sea Grant Extension Specialist trained in the study of phytoplankton, compares it to a cow eating normal grass versus grass blades the size of a tree trunk. Clearly, he says, in the latter case the cow would go hungry. This is the case with zooplankton that graze on algae. Oysters also feed on algae, and there has been much speculation that they too are finding fewer desirable and nutritious species to eat.

Since phytoplankton form the very base of the Bay's food chain, any change there affects not only the zooplankton that graze on them, but the small fish that graze on the zooplankton, and the larger fish that eat them. According to UMCES researcher Ed Houde, zooplankton (like copepods) make up a major source of food for juvenile species of fish, such as striped bass. Other fish, menhaden, for example, feed directly on phytoplankton, and in turn become a major food source for larger fish, like blue fish. By unintentionally causing shifts at the base of the food pyramid, we may have caused shifts at the top - shifts we still do not fully understand.

Is the Gun Smoking?

For many years, Robert Anderson of the UMCES Chesapeake Biological Lab has been looking as closely as anyone for a direct connection between chemical contaminants in the Chesapeake Bay and the poor health of species such as the oyster and the striped bass.

He has been experimenting with low doses of tributyltin and other compounds, to determine whether or not such doses interfere with the immune system. According to his research, the effects are clear. He can document that the immune response slows and becomes less effective once an oyster has been dosed with TBT.

But when asked whether he thinks chemical contaminants are responsible for the decline of oysters in the Chesapeake Bay, Anderson refuses to make that leap. To nail down that connection in a truly scientific manner, researchers will have to continue to study the effects of contaminants in the open environment under a range of natural conditions, such as changes in salinity, oxygen and temperature, which alone can affect an oyster's resistance to disease. (See for example, "Building Better Predictors of Stress," Marine Notes, September-October 1996.)

For now, the researchers who attended the Belmont Center meeting conclude that we have made great strides in understanding where contaminants come from and how they move - physically and chemically - throughout the Bay. Where we have only begun to make progress, they say, is in understanding the biological effects those contaminants can have - not only on large organisms like fish, but also on the microscopic plants and animals that make up the foundation of the Bay's food web.

For a copy of Chemical Contamination in the Chesapeake Bay: A Synthesis of Research to Date and Future Research Directions, the report compiled from the workshop on toxics held at the Belmont Center, contact the Maryland Sea Grant College by phone, (301) 405-7500; fax (301) 314-5780; or e-mail, connors@mdsg.umd.edu.

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