Environmental t News Bacteria contribute to freshwater PCB contamination Water Resources Center, Universit y of Minnesota
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cientists who model the paths that contaminants take through aquatic food chains traditionally focus on transfers from algae to microscopic animals to fish, but this approach ignores the role played by bacteria. Research published in this issue of ES&T (pp 9500–9508) reports the first measurements of PCB concentrations in bacteria from a freshwater lake. By showing that PCB concentrations in bacteria are about 10 times higher than those in algae, the research demonstrates that classic bioaccumulation models must account for microbial food-web interactions, say experts. Resource managers use foodweb bioaccumulation models for contaminants to produce fish consumption advisories, says Matt Hudson with the Great Lakes Indian Fish and Wildlife Commission, lead author of the study. “This study is an important advance in understanding the biomagnification process in aquatic food webs, because the concentrations of PCBs and other hydrophobic contaminants have not often been measured in bacterial fractions and not previously in freshwater systems,” says Derek Muir from Canada’s National Water Research Institute. “We now know that bacteria are an important reservoir of PCBs in Lake Superior and could be a significant entry point for PCBs into the food web,” says Jim Cotner of the University of Minnesota, a coauthor of the paper. Bacteria are consumed by singlecelled microbes, which are in turn consumed by zooplankton. In lownutrient waters, such as Lake Superior, where these studies took place, the zooplankton eat more bacteria than they would in a nutrient-rich
Matt Hudson samples Lake Superior water for bacterial analysis from the deck of the R/V Blue Heron, a University of Minnesota research vessel.
lake with lots of algae, he explains. This increases the importance of bacteria to contaminant behavior in such ecosystems, he says. Cotner and a team of University of Minnesota scientists took samples from the open waters of Lake Superior and analyzed them for PCB concentrations, bacteria, and suspended particulate matter. Log bioaccumulation factors—the ratio of a substance’s concentration in an organism to its concentration in water—ranged from 6.7 to 7.3 in bacteria; this was higher than the 5.8–7.0 values for the particulate fraction and roughly an order of magnitude more than the 6.1 previously measured for Lake Michigan algae. Surprisingly, the bacteria contained 25% of the PCBs in the total particulate pool, a much greater level than predicted by their contribution by weight relative to the particulates, Hudson says. The researchers found that the
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octanol–water partition coefficient (Kow) consistently underpredicted the bioaccumulation factor for PCBs in bacteria. The magnitude of the underprediction was within the range of error associated with food-web models of contaminants; this hints that the error may arise because scientists have left bacterial pathways out of the models, says Jake Vander Zanden from the University of Wisconsin–Madison. He adds, “It also raises an intriguing question—are the bacteria actively taking up PCBs?” “We think it’s a function of their structure. [Bacteria have] got more cell membrane per unit volume than, for instance, phytoplankton, and that may enhance bioaccumulation,” says Deborah Swackhamer, a coauthor of the paper. PCBs have a higher affinity for the polar phospholipids in cell membranes than for the neutral lipids inside the cell; this perhaps explains why bacteria have greater PCB concentrations than algae, she says. This might also explain why Kow, which predicts neutral lipid partitioning very well but underestimates partitioning to polar lipids, fails to predict PCB partitioning to bacteria, she says. Research in Canada found that lakes with a higher proportion of protozoa, which feed on aquatic bacteria, had higher levels of PCBs, Muir says. “The results [of the Minnesota study] help explain the relatively high concentrations of PCBs and [the pesticide] toxaphene in Lake Superior compared to nearby lakes,” he says. Lake Superior appears to have higher proportions of protozoa than the nearby lakes, and thus the bacterial bioaccumulation pathways for contaminants may not be as important in those other lakes, he adds. —JANET PELLEY © 2005 American Chemical Society
Erin Amweg
When Don Weston, an adjunct professor of ecotoxicology at the University of California, Berkeley, checked streams in a suburban neighborhood outside Sacramento, Calif., he found sections devoid of Hyalella azteca, a small bottom- dwelling crustacean that the U.S. EPA happens to use to test for toxicity in sediments. In a study published in this issue of ES&T (pp 9778–9784), Weston and his co-workers report that the sediment from these streams contains toxic levels of pyrethroids, a class of insecticides found in household sprays and lawn care products. These findings have caught the attention of EPA, which is now in the process of reregistering these insecticides. Although they have been on the market for decades, pyrethroids have only dominated the popular garden insecticide market in recent years. This began after 2000, when EPA reached agreements with pesticide manufacturers to start phasing out many residential uses of organophosphates, a class of insecticides that has troubling health risks for humans. Although substantially safer for humans than organophosphates, pyrethroids were never properly tested to see whether they pose an envi-
Pyrethroid use has increased in U.S. gardens in recent years as more dangerous insecticides have been banned for residential application.
ronmental risk, say experts. Although these products are commonly found on the shelves of hardware stores and garden centers, says Weston, the data on their environmental toxicity are sparse. Weston says that other than the U.S. Geological Survey, which checks for permethrin as part of its extensive monitoring program for pesticides, his group is the only one that has monitored these compounds in the environment. Westin adds that his group’s other studies have found that permeth rin is the least toxic compound of the pyrethroid group. In earlier research, Weston’s group discovered high concentrations of pyrethroids in creeks that pass through agricultural land (Environ. Sci. Technol. 2004, 38, 2752–2759). In the new study, they descended on Roseville, a classic suburban California community that is completely surrounded by houses and receives no water runoff from industry or agriculture. “We found [pyrethroids] in every one of our samples, not always at toxic levels, and in about half of our samples they caused total or near-total mortality [to H. azteca],” Weston says. To calculate toxicity, Weston exposed the crustaceans to sediments collected from 21 sites around Roseville. After 10 days, samples from 9 sites had killed more than 90% of the test animals. Analysis of these sediments for 28 pesticides, including 7 pyrethroids, found a correlation between H. azteca mortality and high levels of pyrethroids. In fact, one of the pyrethroids, bifenthrin, was found at levels about 15 times higher than those reported in areas of California with intensive agriculture. Reported toxicity data are lacking because companies were nev-
News Briefs China powers up
The world’s largest hydroelectricity project, the Three Gorges Dam in China, is ahead of schedule. The last of the 14 power generators on the dam’s left bank, each with a capacity of 700 megawatts (MW), began commercial operation in the middle of September, a year earlier than planned. Work on 12 generators on the right bank is expected to begin soon. Since starting up in 2003, the dam has generated more than 80 billion kilowatt-hours of electricity. By 2009, China Three Gorges Project Corp., the company responsible for the dam’s construction, hopes to produce 22,400 MW, about 20% more than originally thought. It claims that the dam has already eased energy problems in eastern and central China.
Polar satellite crashes
A European Space Agency (ESA) environmental satellite crashed into the Arctic Ocean after its launch in northern Russia went wrong on October 8. Part of the booster system on the launcher is believed to have failed. CryoSat was carrying equipment designed to take measurements of the polar ice caps with an accuracy that ESA claims has never been achieved before. Using two radar antennae, the satellite was to determine the extent of the polar ice masses as well as their precise thickness. ESA scientists had hoped that the data would help explain the connection between polar ice melting and the rise in sea levels. The $165 million satellite was to have stayed in orbit gathering data for 3 years. ESA is reluctant to speculate about launching another similar satellite.
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Household pesticides are poisoning city creeks
Environmentalt News er required to submit all possible environmental impacts of pyrethroids to EPA, says Kelly Moran, president of TDC Environmental, a consulting company for many California water-quality agencies. Industry did test these insecticides for toxicity to fish, but the results are probably not very useful because pyrethroids do not readily dissolve in water, she adds. Instead, they quickly bind to dirt and other surfaces. EPA is conducting a reregistration for pyrethroid insecticides, as
required by the 1996 Food Quality Protection Act, says Bill Jordan with EPA’s Office of Pesticide Programs. However, Jordan was steered away from commenting on Wes ton’s paper by EPA press officer Eryn Witcher. Another EPA official refused to be identified because EPA had sent out an email in early October that instructed agency staff not to discuss pyrethroids with the press. The official explained that EPA did not have sediment toxicity data on this class of
Tackling a short list of endocrine disrupters It’s no surprise that trace concentrations of pharmaceuticals and endocrine-disrupting compounds are showing up everywhere researchers look. But what is the relevance of these trace levels for human health, particularly in areas like the arid western U.S., where wastewater—a primary source of these contaminants—is increasingly being recycled and used to augment drinking-water supplies? “We can’t remove everything to zero, because the analytical methods are too good,” says Shane Snyder, an environmental toxicologist at the Southern Nevada Water Authority. “So we have to put a line in the sand, so to speak, and say, ‘This is a safe level, and this is an unsafe level.’ There’s going to be some level of contamination that I think we’re all just going to have to accept.” To give state regulators some answers as soon as possible, as well as help them establish meaningful treatment and detection goals, Snyder and his colleagues have narrowed the universe of emerging contaminants to a list of roughly 30 compounds, a draft of which was presented at the WateReuse Association’s annual meeting in September. These include chemicals that the researchers expect have the highest toxicity levels or that are most likely to occur in drinking water. Snyder said
that he and his colleagues plan to conduct occurrence monitoring for these chemicals at as many as 20 drinking-water utilities nationwide and develop provisional reference doses for those with sufficient toxicological data; this would follow the U.S. EPA’s standard human health risk assessment process. They also plan to screen for these chemicals in some foods and bottled beverages, particularly milks and fruit juices that contain natural phytoestrogens, such as soy. Previously, Snyder and other researchers have argued that the human health threat of these trace contaminants in drinking water has been overblown (Environ. Sci. Technol. 2005, 39, 397A). Now, Snyder hopes to back up this assertion with real data. Snyder and his colleagues predict that the concentrations and bioactivity from contaminants could be higher in many of the foods and bottled beverages than in wastewater effluents. “I fully understand that we’ll open up a can of worms and probably create more questions than answers,” Snyder notes. However, “I truly believe we need to get started, because there are so many monitoring programs and so many people just going after treatment [of microcontaminants in wastewater].” The fallacy, says Snyder, is that such efforts may not change overall exposure levels, because these con-
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compounds until industry submitted the data just last month. “You’ve got a compound that is now taking over the market,” says the official. Given these new data, limits will probably be placed on pyrethroid applications, says the EPA source. “Legally, the city of Roseville is responsible to ensure that the water in its creek is not polluted,” says Moran. “But they don’t have control over what is sold in stores, and they can’t prevent the use of pesticides.” —PAUL D. THACKER
taminants are probably in things we consume other than drinking water. EPA is also working toward developing regulations for such contaminants in drinking water through its Endocrine Disruptor Screening Program. However, with an estimated 86,000 chemicals in line to be tested, the agency “is very far behind, because the assays have to be validated, reproducible, and transferable,” Snyder told conference attendees. In devising their list, Snyder and his colleagues began with the top 200 most prescribed pharmaceuticals and selected those that carried potential health risk at low concentrations, were most likely to be present in drinking water in an active form, and represented different drug classes. Those chosen included substances that have effects on each of the major classes of endocrine function—estrogenic, androgenic, and thyroidal—and meet the criteria of “most likely to occur”, “most powerful at each of the endpoints”, and “availability of toxicity data”. Their efforts will focus on parent drug compounds only, not metabolites. “It’s quite an ambitious project,” much larger in scale and more systematic than other studies to date, says Charles Staples, president of Assessment Technologies, Inc., and a member of the project’s advisory committee. “The program’s overall strength is [in] putting these low detection levels in perspective.” —KRIS CHRISTEN
