The Pocomoke River — the scene of fish kills two years ago — has levels of dissolved metals and steroids that in some cases are “orders of magnitude” higher than those typically seen in Chesapeake tributaries, according to a new study by investigators at the U.S. Geological Survey and George Mason University.
Concentrations of some of those compounds were found at levels high enough to stress fish, without the presence of Pfiesteria piscicida in the river, according to the scientists who took the water-quality and sediment samples.
“What I think this did was open up a whole lot more questions,” said Cherie Miller of the USGS, who characterized the results as “food for thought.”
Whether the contaminants played a role in the pfiesteria outbreak is uncertain, Miller said. She and two colleagues involved in the work cautioned that their findings were based on only five water samples taken in 1997. Still, they found the results surprising enough to publish and said that they warrant further investigation.
The Maryland Department of the Environment, which is coordinating water quality monitoring in the river, is planning further sampling of the river, although officials cautioned against drawing conclusions from a handful of samples.
“We’ve got plans to look at this in more detail,” said Robert Summers, of the MDE. “Is this a one-time anomaly, is there something really going on? I’m very hesitant to make any statements on one set of samples.”
Miller and the other two scientists who examined the samples, Gregory Foster and Thomas Huff, both of George Mason University, said they took the samples because other studies in the Pocomoke were focused mostly on nutrients and a handful of other substances. “There is a lot more that needs to be learned about potential contaminants in the Pocomoke River basin,” Miller said.
The scientists reported that water column samples from four of their five Pocomoke River Basin stations had concentrations of several metals — arsenic, selenium, strontium and lithium — greater than those typically found in other Bay tributaries.
Dissolved arsenic was more than two orders of magnitude higher than those measured in studies on the Susquehanna, Potomac, James, Rappahannock, York, Choptank and Nanticoke rivers. Dissolved concentrations of selenium, strontium and lithium were higher by factors of 100, 30 and 50 respectively, than those measured last year in two nearby rivers, the Chesterville Branch and Nanticoke, the scientists reported.
Tests also found numerous kinds of steroids in the water. Steroid compounds are found in the wastes of all animals, including humans. The steroid levels measured were unusually high, the scientists reported, but the type associated with human wastes were at relatively low levels.
The greatest concentrations of cholesterol, a sterol compound and a generic chemical byproduct of animals, were found near a chicken house, and concentrations appeared to diminish as one moved downstream, the scientists said.
Not all of the steroid compounds in the river have been identified, but several are in a class of compounds called estradiols, which have the potential to be “hormone disrupters” — substances that mimic some hormones in animals, affecting growth and reproduction.
Much of the concern about estrogen-mimicking compounds has focused on PCBs and organochlorines. But the steroids in the river could be of more concern, Foster said, because they are in the water column where they are directly available to aquatic life, and because they are found at relatively high concentrations.
“These steroid concentrations are in the river at much higher levels than what you find for things like PCBs,” Foster said. “I think the potential is quite significant, but whether anything is actually happening, I don’t know. But I would say these classes of compounds need to be looked at more fully.”
The scientists who wrote the report said that the high concentrations of selenium and arsenic may also be related to the poultry industry, because both chemicals are common feed additives. Although the amounts fed to poultry are typically small, the sheer number of chickens produced on the Delmarva Peninsula suggests a potential for a large total load of these metals and chemicals to make their way into the water.
They wrote that “the data presented in this report support the hypothesis that poultry manure is a probable source of trace-metal and organic-compound contaminants found in the Pocomoke River and tributaries, but this conclusion is based on the analyses of only a few samples and should be viewed with caution.”
They said they could not rule out an undocumented source of contaminants existing in the watershed, and called for further testing both in the Pocomoke, and other Eastern Shore rivers.
Whether there is a tie-in with pfiesteria is impossible to say at this point, Miller said. “This study has documented an isolated occurrence of a number of potential contaminants in the Pocomoke River basin,” she said. “No cause-and-effect relationships between the contaminants and pfiesteria have yet been determined.”
Even without the effects of pfiesteria, though, both arsenic and selenium were found in concentrations known to stress fish.
Vicki Blazer, a USGS fish pathologist who reviewed the results, said the metals could be one of the factors that lead to the formation of deep, fungus-infested lesions on some Pocomoke fish. “Arsenic is a very potent suppressor of the immune response,” she said. In particular, she said, cells affected by arsenic are the same ones that respond to a bacterial or fungus invasion.
Work by Blazer and others has shown that all of the deep lesions that they examined during the Pocomoke fish kill were caused by a fungal infection that may have preceded the fish kills by about two weeks. It has been unclear whether the fungal infections resulted from earlier pfiesteria outbreaks or other stresses on the fish.
“I just found it real interesting that one of the places that had high arsenic levels was also one of the places where we see these lesions,” Blazer said. “So that’s definitely something we’re going to be working on this year.”
The results of the Pocomoke contaminant study can be found on the World Wide Web at: http://md.usgs.gov/publications/ofr-99-57/