After researchers, water quality managers, and policy makers came together for a day to review information about toxics in the Bay’s water column, they had a question put to them: What level of concern should they have about the issue?
Their reply: There wasn’t enough information to answer the question. Some data presented showed evidence of toxic impacts related to water column contaminants in areas thought to be relatively “clean;” but it was unclear how serious — or widespread — such problems are. Most clear problems were focused around known “hot spots” such as Baltimore Harbor and the Elizabeth River.
“To be frank, there’s very little evidence of a problem,” said Fritz Riedel, of the Benedict Estuarine Research Laboratory, who participated in the forum — one of a series held in conjunction with the reevaluation of the Bay Program’s toxics reduction strategy. “In some cases, that may be because we haven’t looked hard enough. In other cases, it’s because the biological variability of the system is going to completely mask any effects.”
Riedel pulled together the available water quality data regarding metal concentrations in the Bay and its tidal tributaries as part of the critical issue forum held by the Toxics Subcommittee last year.
For more than two years, the subcommittee has reviewed what is known — and unknown — about toxics in the Bay, including issues such as contaminated sediments; fish and shellfish tissue; atmospheric deposition; impacts on wildlife; pesticides; and other sources. Their findings will help mold a new toxics strategy, to be completed this year, that will spell out toxics reduction goals and outline future research priorities.
Regarding water column information, Riedel found that little monitoring is done in the Bay and its tributaries to target toxics. Information that is available was “scattered around” and “not systematic in any real sense,” he said. What data that is available, he said, generally shows that contaminants — metals, organics, and pesticides — in the water column are at levels that are usually below the EPA’s water quality criteria, and often below detection limits.
Toxics in the water column are important because it is the way many species — as well as their eggs and larvae — may directly be exposed to contaminants. Also, regulatory standards — and discharge limits in water permits — are based on state water quality standards.
Yet much remains unknown about how toxics act in the water, and even how to measure their impact on aquatic life. Routine water column testing for toxics is expensive, and concentration levels in the water can be highly variable — a sample taken at the wrong time can miss a sudden surge in contaminant levels altogether. As a result, monitoring efforts aimed at identifying trends and problem “hot spots” have focused on studying sediments [See the July 1993 Bay Journal for more on toxics in the sediments].
“I feel there’s a fairly large gap between what we know, and what we need to know,” said Lenwood Hall, of the University of Maryland’s Wye Research and Education Center.
Indeed, forum participants raised a number of concerns about toxics in the water column. Some believe the EPA’s water quality criteria for some contaminants may be too high. For other substances, the EPA’s criteria — the concentration level generally linked to impacts — is not related to the “bioavailable” form of the contaminant. For example, some metals, such as cadmium, break down into different forms in the water. Certain components, or species, are toxic while others are not. EPA’s criteria may not indicate the amount of the toxic form that is actually in the water.
Compounding those issues are questions about the cumulative impacts of several different contaminants on organisms in the water, and the effects from long-term exposure to low levels of contaminants.
But Riedel said it was almost impossible to sort out impacts caused by metals at low levels from those caused by other pollution-related problems, such as low dissolved oxygen. Figuring out whether changes in the population of a species — or even an entire community — are caused by contaminants or by natural population cycles makes the task even more difficult.
“Given the biological variability,” Riedel said, “it would be very difficult to show any toxic effect of anything in the Bay.”
That doesn’t mean there is no reason for concern, he added. Research in large experimental aquariums at the Benedict Lab, for example, has shown that low-level concentrations of arsenate in the water can shift the phytoplankton population concentrations from larger diatoms — which are the favored food of many fish species — toward dinaflagellates, a less desirable form of algae. But whether that impact could be detected in the real world is difficult to say, Riedel added.
Therein lies something of a Catch-22. A comprehensive study of metals in the Bay’s water column would be hugely expensive, and it may only reveal that there are no problems — or provide results that are inconclusive.
“A systematic program to look at maybe one or two metals in the Bay would probably cost hundreds of thousands of dollars,” Riedel said. “A wide suite [of metals and other contaminants] would run into the millions.”
Riedel suggested that such efforts might best be targeted at specific “hot spots.”
As difficult and expensive as it may be to study metals, organic contaminants — manmade chemicals — are even tougher to grasp. “A lot of these compounds are at concentrations that are below detection limits in the water column by our analytical methods,” said Mike Unger, of the Virginia Institute of Marine Science. As a result, people looking for evidence of impacts from exposure to organics have focused on the sediment where materials may accumulate to measurable amounts. That is particularly useful for organics, Unger said, because they tend to be more “hydrophobic” than metals, meaning they more rapidly separate into the sediments where they accumulate in larger concentrations than found in the water.
On the other hand, he noted, some compounds may be extremely toxic in the water at levels below detection limits. Unger and others were involved during the 1980s in an intensive study of tributyltin (TBT), an anti-fouling agent used on ship hulls which leaches into the water. Because of its extreme toxicity — effects were seen in laboratory experiments with shellfish at levels of exposure below detection limits — new methods were developed so TBT could be detected at concentrations of less than 1 part per trillion in the water.
That research, funded largely by the Navy, cost millions of dollars. That kind of cost, Unger said, poses a major obstacle to any systematic check for organics in the water.
Another problem with routine monitoring for toxics in the water is that concentrations can fluctuate dramatically. For example, if a sudden storm flushes a large amount of contaminant materials into the water, samples taken shortly thereafter will show higher levels than those taken at another time. “There’s a lot of noise in the system in terms of measuring water column concentrations,” Unger said.
Those issues have led researchers to rely on the use of sediment or biota as indicators of problems. “That doesn’t mean there is not concern,” Unger said, “I think it’s more a reflection of the amount of work that is necessary to get meaningful numbers.”
Hall, though, cautioned against putting too much emphasis on sediment alone. While accumulated toxics in the sediments provide important information about past problems, Hall said that water-column testing provides information about “transient-type conditions.”
“In other words,” he said, “if you had a rainfall event at a farm that had just applied a pesticide, you might be able to detect the concentrations in the water column and you might not see anything in the sediment.”
Indeed, a recent review of water-quality data related to pesticides in Bay tributaries by the U.S. Department of Agriculture found that while there were relatively few instances where the pesticides exceeded water quality standards, the greatest frequency of detection — and the highest levels — came after storm events.
During the 1980s, Hall conducted research on striped bass larvae at several locations in the Bay and in the tributaries. In the study, he found the survival of striped bass larvae was low in the Potomac River. Larvae mortality appeared to coincide with periodic spikes in concentrations of certain metals in the water, during which the detection levels rose above EPA’s criteria. Hall said it was also possible that mortality was caused by several metals mixing together at levels below the EPA’s water criteria.
The findings, he said, raise some concerns about the ability to protect the fragile life stages of some species. “The larval yoke-sac stage of the striped bass that we test is a very sensitive life stage,” he said. “We have to make sure the most fragile stage is protected” or they will never mature.
“In the environment, you’re going to get very high natural mortality,” he said. “But even if the contaminants only contributed a very small faction of a percent to the overall mortality, that could be the difference between having a good or poor year class in the river.”
Because of that concern, Hall cautioned against trying to make conclusions about the whole Bay with too little data. Nonpoint source pollution, he said, could be causing problems in areas that are relatively unstudied. While much of the emphasis in the new toxics strategy development has been focused on identifying “regions of concern,” where much of the toxics research and cleanup will be focused, Hall said it is important to evaluate the ecological status of “clean” areas as well.
“We want to monitor areas that are clean and have high resource value because we want early warning signals that will give us the ability to do something before resources are impacted,” he said.
In those marginally contaminated areas, toxics could provide an added stress that could put populations of some species at risk. “Basically, what you’re trying to do is alleviate all the stresses that you can,” Hall said. “You can certainly argue how important contaminants may or may not be in a system, but you can’t argue that they aren’t a stress. The only thing you can argue is how much of a stress they are.”