Contents

Taking on Toxics

Mapping Contaminants

Knauss Fellows

Noteworthy

Researchers are working together on a long-term study of the harbor that is assembling data and developing predictive models to help show where contaminants come from, where they go and how they interact with living organisms.

For three days the metal jaws of a grab sampler took discrete bites out of the bottom of the Patapsco River where it forms Baltimore Harbor. Day after day, as if working a huge oyster bar, the crew on deck pulled the sampler aboard, taking on their harvest of mud. By the time they finished, they had taken more than 160 samples at 81 locations, 160 snapshots of sediments in Baltimore Harbor and the nearby waters. The purpose – to help the Maryland Department of Environment determine the extent of contaminants in harbor sediments.

Those three days, five years ago now, were part of a long and complicated detective story. The story is not only about what has been released into these waters for many decades, but also about chemical compounds that are still coming into the Patapsco River and nearby tributaries from countless diffuse sources, such as runoff from urban and industrial sites. And more – by studying the behavior of sediments, researchers have begun to piece together a detailed chronicle of how contaminants move, a story where the major actors include not only Baltimore Harbor and the Patapsco River, but also the Susquehanna River, an immense fresh water source that dominates currents throughout the upper Bay.

Helping to unravel this tale of contaminants is a team of researchers, including Joel Baker and Larry Sanford, of the University of Maryland Center for Environmental Science. Their work has been funded by the Maryland Department of the Environment for the last several years and is continuing. Baker is an expert in chemical contaminants. Sanford's expertise is in the area of physical oceanography – tracking waves and currents that move sediments through the water. With funding from the Maryland Department of the Environment (MDE), the scientists are working together, and in collaboration with others, on a long-term project. Called the Comprehensive Harbor Assessment and Regional Modeling (CHARM) Study, it is assembling data and developing predictive models to help show where contaminants come from, where they go, and how they interact with the Bay's living organisms.

A Sense of Urgency

Contaminants include not only heavy metals, PCBs and PAHs, but also substances not usually considered pollutants such as nutrients and sediments

MDE – and the researchers who are helping the state's resource agencies – find themselves facing a difficult deadline. If the state cannot show that the Bay and its tributaries have met strict federal standards by the year 2011, not only are federal funds from the U.S. Environmental Protection Agency (EPA) in jeopardy, but the EPA can actually step in and take over management of these waters. Improvements in tributaries such as the harbor could help in meeting the 2011 goals.

Driving this deadline is the Clean Water Act, a law that has been instrumental in helping reduce pollution from a number of sources, most notably so-called point sources, such as large industries. Also in the Clean Water Act, but not focused on until relatively recently, is a requirement to monitor Total Maximum Daily Loads (TMDLs), the maximum amount of various pollutants that can enter a stream, creek or river per day before causing environmental harm.

Those pollutants include heavy metals like mercury, lead and cadmium; organic compounds classed as PCBs (polychlorinated biphenyls) and PAHs (polycyclic aromatic hydrocarbons). They also include substances not necessarily considered pollutants, such as nutrients and sediments, which can impair the health of streams, rivers and estuaries.

Maryland has listed Baltimore Harbor and the Patapsco River as "impaired," because of excess contaminants, sediments or nutrients, or a concoction of all three.

The question MDE must answer for each body of water is how much of each contaminant can be released in a day without detrimental impacts – this number is the TMDL for that chemical for that system. Next, MDE must identify sources of the contaminant, then allocate percentages of that specified limit among the different sources. This includes not only industries and waste treatment plants but diffuse sources of runoff including farms, suburban and urban areas and atmospheric deposition.

Larry Sanford notes that the limits set by TMDLs don't really focus on who's responsible for local contamination – that's the state's job – but rather on the sum of all pollutants entering a water body. And that sum should not cause impairment. This means that regulatory agencies like the Maryland Department of the Environment (MDE) must understand the whole mix of contaminants and sediments and nutrients in a given tributary to determine what sources are causing damaging effects.

"We have to start out trying to understand the process," says Sanford, "and predictive models help you to do that." What Baker, Sanford and their colleagues are after in Baltimore Harbor is a view of the whole. "If the model works right, it can help a manager allocate different sources to achieve an acceptable measure of water quality," says Sanford.

Understanding River Flow

Understanding the dynamics of contaminants is the first step in trying to control their ecological impact.

Years ago, it was assumed that contaminants discharged into Baltimore Harbor and the Patapsco River were largely diluted, first in the river and then in the Bay, as currents carried contaminants down toward the Virginia capes and finally out into the Atlantic ocean. By the time those contaminants flowed that far, the reasoning went, they were presumed to be of little harm, either to fish or to human health.

In the early 1980s, however, it became clear that the Patapsco was different. Physical oceanographers Bill Boicourt of UMCES and Peter Olson of Johns Hopkins University – both were then at the Chesapeake Bay Institute – confirmed the earlier hypothesis of pioneering oceanographer Don Pritchard that water flow in the Patapsco River differs significantly from most other rivers in the Chesapeake. Most rivers in the Chesapeake can be characterized as having a two-layered circulation pattern, where buoyant freshwater from the river runs on the surface down river to the Bay, while dense saline water below pushes upriver. The Patapsco, however, more often demonstrates a three-layered circulation pattern, where fresh surface water flowing from the powerful Susquehanna River – as well as the saline water below coming up from the Bay – push up the Patapsco. The relatively weak outflow of the Patapsco is mixed into these strong inflows and emerges as a layer of intermediate salinity at mid-depth. In other words, the flow of the Patapsco River itself exerts little influence on the circulation of its estuary.

Sediment particles suspended in the Patapsco River waters (and other internal fresh water sources such as storm sewer outfalls) are similarly mixed with sediment particles that come in with fresh water from the Susquehanna and sediments that have been resuspended from the bottom. Riding on this whirl of suspended sediments are potentially toxic compounds, many of which have strong chemical affinities for particles.

These sediment-bound contaminants settle to the bottom, but are periodically lifted back up by currents, storms, dredging or passing ships. This up-and-down recycling finally ends when the old sediment particles are buried by newer sediment particles, many of them supplied by the inflow from the Bay. Burial happens sooner in the relatively calm recesses of the Inner Harbor, at Bear Creek, for example, but sedimentation rates in the Patapsco estuary are rapid in general. Rather than helping to carry contaminated sediments down the Bay, the force of the Susquehanna River actually causes more rapid burial and greater retention of contaminated sediments originating within the harbor.

"The Susquehanna River flow is a net source of sediment to Baltimore Harbor," says Baker. There is more sediment coming into the Patapsco from this source than from the surrounding landscape. "The work we've done supports that," says Baker, who adds, "the magnitude of the Susquehanna's contribution of sediment just hasn't been appreciated."

These physical patterns help to explain why Baltimore Harbor retains contaminants in its waters. "Though there is some leakage of contaminants out of the harbor into the Bay," says Baker, "much of the material that is released there just doesn't move." Even clean sediment particles coming into the Patapsco mix with waste discharges and absorb chemical contaminants. Little of what is loaded into northern Chesapeake Bay makes it south. If it did, Baker says, we would see contaminants south of Kent Island. He points to PCBs as an illustration. Samples taken from sediments in the Baltimore Harbor area showed concentrations ranging from 10 to 20 nanograms per liter of PCBs, while sediment samples taken near Kent Island showed levels at only 1 to 2 nanograms per liter. Not many PCBs made it out of Baltimore Harbor.

Measuring Contaminants

Until this study, there was no comprehensive map of the distribution and concentrations of toxic compounds.

Though MDE had been sampling sediments for contaminants for some years in Baltimore Harbor, until the CHARM Study that Baker and Sanford directed, there was no comprehensive map of the distribution and concentrations of toxic compounds. In part, the reason was cost, which accounts for the paucity of contaminant data throughout the Bay system, especially when compared with data on nutrients.

Unlike the nutrients nitrogen and phosphorus, which include only a handful of chemical forms, "contaminants" is a general term covering a complex of many compounds, among them the various forms of heavy metals, as well as PCBs and PAHs – generic names for scores of related compounds. The costs for measuring a suite of contaminants can run between $1,500-2,000 per sample, compared with $20-30 for nutrients. Analyzing the large numbers of discrete samples, necessary to construct an image of contaminant distribution, can add up to a hefty sum. In fact, the Chesapeake Bay Program's monitoring effort does not include regular measurements of metals or organic contaminants.

In supporting the work of Baker, Sanford and others on the UMCES research team, MDE made a commitment to understanding the dynamics of contaminants as the first step in trying to control their ecological impact. The scientists have taken their samples throughout the harbor and Patapsco River: in the Northwest Branch, which includes Baltimore's Inner Harbor; in highly urbanized areas along Curtis Bay, Curtis Creek and Middle Branch; along heavily industrialized Sparrow's Point; and on Bear Creek, which is largely residential upstream.

Over the following months, samples were subjected to a battery of tests in order to determine composition and concentrations. Using these data, scientists were able to create a map of the locations and concentrations of each contaminant they found. "The spatial variability is enormous," says Baker, meaning that values of any one contaminant range widely, even when sites are near each other. Still, he adds, the data reveal striking insights into the condition of sediments, as well as general water quality in the region. A substantial number of sites, for example, contained concentrations of metals and organic contaminants that were well above the "no effects" level. Though not a direct measure of biological impact, this observation suggests a strong likelihood of impaired habitat.

The mapping provides a baseline of data – it doesn't reflect how long contaminants have been in these sediments or how they move around. This is the role of predictive models. "Many people have the misconception that all toxic problems are from activities that occurred 40 to 60 years ago," Baker says. "We have been measuring concentrations of the same suite of chemicals at Gwynns Falls and Jones Falls to get an estimate of [current] loading to the Inner Harbor." While there is not enough data yet to draw conclusions, Baker believes that contaminants in such stormwater flow will emerge as a large part of the problem. Computer modeling that relates these loadings to their spatial distribution in the sediments will allow scientists to make predictions about how far a given contaminant will travel.

Inching Towards Prediction

Modeling contaminant movement depends on understanding the dynamics of suspended sediments as well as the behavior of different chemical contaminants. Organic compounds and metals have different affinities for binding to particles. "[Contaminants] with low affinities may travel around, but there is a widely varying behavior," says Sanford. The model must take into account these different binding affinities.

These samples of mud from Baltimore Harbor will be brought back to the laboratory for slow and painstaking analysis. The hope is that ongoing studies will one day provide the means by which managers can clean up some of the Bay's most polluted waters.

"The typical sediment particle that enters the harbor," says Sanford, "experiences multiple cycles of resuspension and deposition, before it's permanently removed from circulation by sedimentation." As with the sediment particles, so too with the sediment-bound chemicals. "There is, as we've seen, a huge pool of contaminants in the sediments already," says Sanford. "These are the legacy of the past – we need to know how much they impact Baltimore Harbor without any new input."

Addressing such issues are important for evaluating realistic management options. For example, if sediments in a creek feeding the Patapsco River are high in PCBs but indicate little evidence of new inputs, there may be value in considering such remediation options as removing the impaired sediments by dredging or capping them with clean sediments. On the other hand, if the model indicates that the sediment-bound PCBs are from continuing runoff sources, then land-based management efforts may need to be stepped up.

In developing a first-order model to predict sediment transport, Sanford has separated Baltimore Harbor into 24 large regions or "boxes," largely divided among the different feeder tributaries where contaminants were measured. This approach differs from traditional water quality models, which are often divided more finely into hundreds of small compartments, each of which is given a set of water quality parameters. It can take days to run a particular TMDL scenario in such a model. Sanford's box model can get results quickly by trying out different TMDL allocation scenarios. The model has required simplifying generalizations that sacrifice some accuracy for speed, Sanford says; however, it affords managers flexibility they would not have with a fine-scale model.

Looking Ahead

In its 1996 listing of impaired waters to EPA, the Maryland Department of Environment listed Baltimore Harbor as impaired for toxics – at that time, the agency could not be more specific. Based on the study by Baker and Sanford, MDE's 1998 revision listed ten chemical contaminants that would require the setting of specific TMDLs, among them, PCBs, chromium, zinc and lead.

Just what are the biological impacts of these contaminated sediments? The answers are complex – to begin with, researchers can only determine acute or lethal effects, not long-term sublethal impacts on reproduction or behavior. Even the acute effects are difficult to assess because many of these bottom areas not only have high contaminant loads, they also lack oxygen, a condition brought on by excessive nutrients.

To get a handle on the extent of toxicity in Baltimore Harbor sediments, Beth McGee, now of the U.S. Fish and Wildlife Service, collected sediments from 25 of the 81 sites in the Baker and Sanford study and tested their effects on Leptocheirus plumulosis, a small amphipod common to these waters. She found that a number of sites were clearly toxic and lethal. While the hottest were from Bear Creek, she says, other areas exhibiting toxicity included the Inner Harbor and Colgate Creek, with lower levels elsewhere in the harbor system.

Ironically, the biological impact could be greater if nutrient reduction efforts in the harbor lead to improved oxygen levels. Some benthic habitats and organisms such as Leptocheirus could flourish; feeding in these sediments, they would pass contaminants up the food chain to invertebrate and fish populations that prey on them. In other words, says Baker, improving habitat conditions could make things worse for the health of fish that feed in harbor waters – at least for a while.

Because of such scenarios, it is critical to distinguish contaminated sediments that are the result of past discharges from those that are on the receiving end of new contaminants. "We need to get a handle on loadings," says McGee, "and do some investigating on whether sediment remediation is appropriate."

For nearly two decades, curtailing nutrient flow to the Chesapeake Bay has understandably held center stage of restoration efforts. Overenrichment of nitrogen and phosphorus has set into play a network of processes that has degraded Bay waters significantly.

In contrast to nutrient overenrichment, which is a problem Baywide, chemical contamination of sediments is largely limited to Baltimore Harbor, the Anacostia River and the Elizabeth River, though there is evidence of localized problems in other parts of the Bay system. For years, it seemed little could be done in these heavily urbanized waters – not only do contaminants come in different species and forms, they behave differently under varying environmental conditions. Furthermore, pollution seemed a given in a heavily industrialized urbanized watershed, the price that had to be paid for commercial activity. That given no longer holds. Not only does the Clean Water Act require action to restore these waters, but there is clearly strong advocacy to do so.

We have come a long way in Baltimore Harbor, says Baker. "We started with knowing little and have some significant progress in the last several years." "But," he adds, "we still have a long way to go."

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