June 2006, Vol. 18, No.6

Waterborne Anthrax Resistant to Chlorine

anthrax

A recent study has revealed that the spore-forming bacterium Bacillus anthracis, or anthrax, may be resistant to the traditional form of chlorine disinfection used in water treatment. 

 Waterborne Anthrax Resistant to Chlorine

A recent study has revealed that the spore-forming bacterium Bacillus anthracis, or anthrax, may be resistant to the traditional form of chlorine disinfection used in water treatment.

Anthrax, according to the U.S. Centers for Disease Control and Prevention, is an acute infectious disease which can lead to organ failure and death in humans. Its three forms are categorized by how the spores enter the body, through inhalation or ingestion, or cutaneously — when spores enter through a lesion in the skin. Gastrointestinal anthrax, when the spores are consumed through eating or drinking, has the second highest mortality rate of the three forms, making the spores’ ability to survive in treated water a point of concern.

“The purpose of this study was to determine the fate of anthrax spores in a drinking water system that uses chlorine as a disinfectant,” said Jon Calomiris, a microbiologist at the Air Force Research Laboratory at Aberdeen Proving Ground (Edgewood, Md.). “Though researchers have some knowledge of how other waterborne pathogens may survive or die in drinking water systems, little is understood about the fate of anthrax spores in chlorinated water systems.”

The study examined the survival rate of anthrax spores in water containing 1.0 mg/L of chlorine, which is a typical concentration for tap water, according to a news release issued by the American Society for Microbiology (Washington, D.C.). After 60 minutes in the chlorinated water, the number of viable spores had not decreased significantly, the study revealed.

Calomiris also tested the anthrax spores’ ability to attach to the inside of pipes by running contaminated water continuously through pipes made of copper, chlorinated polyvinyl chloride (CPVC), or galvanized iron. According to the news release, 20% to 40% of spores had attached themselves to the copper and CPVC pipes after 6 hours. In that same time, 95% of the spores attached to the iron pipes. In copper pipes where biofilms were present, 80% of the spores attached in 6 hours.

“The data seem to suggest that anthrax spores can tolerate water treatment, can attach to pipes of biofilms within the pipes, and could pass through the pipe system to reach the consumer tap,” Calomiris said.

The study showed that higher concentrations of chlorine are more effective at killing the anthrax spores. At 5.0 mg/L, 97% of spores were killed after 1 hour, and at 10.0 mg/L, 99.99% were killed. However, chlorine levels this high make water undrinkable, so an alternative treatment method would be required if anthrax were released into the water supply.

According to “Gastrointestinal Anthrax: Review of the Literature,” by Mark E. Beatty, David A. Ashford, Patricia M. Griffin, Robert V. Tauxe, and Jeremy Sobel, published in the Nov. 10, 2003, issue of Archives of Internal Medicine, ingested anthrax takes one of two forms — oropharyngeal or intestinal. The symptoms of oropharyngeal anthrax, which affects the oropharynx, the part of the pharynx between the soft palate and the epiglottis, include a fever of more than 39°C (102°F), neck swelling, a severe sore throat, and ulcers in the posterior oropharynx. Intestinal anthrax, which involves infection of the stomach or bowel wall, is indicated mainly by ulceration of the bowel and includes many symptoms, such as nausea, anorexia, vomiting, and a fever higher than 39°C (102°F), severe abdominal pain, and bloody diarrhea. Like all forms of the disease, it can be fatal, but it may be treated with penicillin.

The amount of Bacillus anthracis needed to cause gastrointestinal anthrax in humans is “not known,” the article notes. However, it states that the dose may be similar to what causes the disease in pigs. According to the article, 10 spores were not enough to cause anthrax in pigs, nor was that enough to cause infection in guinea pigs, rabbits, and rhesus monkeys — three species considered “more susceptible to anthrax than humans,” the article states.

According to an anthrax fact sheet from the Centers for Disease Control, “anthrax is not known to spread from one person to another person.”

— Meghan Oliver, WE&T

Pesticides Detected Frequently in Streams, Groundwater

Pesticides and their degradation byproducts are present most of the time in streams draining watersheds with substantial agricultural or urban areas, according to a decade-long assessment by the U.S. Geological Survey (USGS). The measured concentrations were seldom at levels likely to affect humans, but they often occurred in streams at levels that may have effects on aquatic life or fish-eating wildlife.

“While the use of pesticides has resulted in a wide range of benefits to control weeds, insects, and other pests, including increased food production and reduction of insect-borne disease, their use also raises questions about possible effects on the environment, including water quality,” said Robert Hirsch, USGS associate director for water, on the report’s release in March.

Pesticides in the Nation’s Streams and Groundwater describes the occurrence of pesticides in 51 major river basins and aquifer systems from 1992 to 2001. Water samples were analyzed for 75 pesticides and eight degradates, including many of the most heavily used herbicides and insecticides. Additionally, bed sediment and fish tissue samples were analyzed for organochlorine pesticide compounds, most of which are no longer used in the United States but still persist in the environment. The study was undertaken as part of the first cycle of the National Water Quality Assessment (NAWQA), a USGS program.

“Findings show where, when, and why specific pesticides occur and yield science-based implications for assessing and managing pesticides in our water resources,” Hirsch said.

Eileen O’Neill, chief technical officer of the Water Environment Federation (Alexandria, Va.), agreed. “This particular study provides important baseline information on the status of the nation’s streams and groundwater with regard to pesticide contamination,” she said. “It suggests that streams are more vulnerable, but that the potential for groundwater contamination is also of concern, especially in agricultural and urban locations.”

Mixtures Common
Pesticides seldom occurred alone, but rather as mixtures of multiple compounds, including degradates resulting from the transformation of pesticides in the environment, according to the report. More than 90% of the time, water samples from streams with agricultural, urban, or mixed land-use watersheds contained two or more pesticides or degradates, and about 20% of the time, they had 10 or more.

“Most of the time, you’re dealing with five or more compounds present, and that’s just of the ones we measured,” said Robert Gilliom, chief of the national pesticide synthesis under the NAWQA program. Indeed, the pesticides studied included only a fraction of all those currently in use and few of their degradates, according to the report. So, “the aquatic ecosystem is seeing exposure to a very wide range of contaminants at any particular time,” Gilliom added.

More than 80% of urban streams and more than 50% of agricultural streams had concentrations in water of at least one pesticide that exceeded a water-quality benchmark for aquatic life, the study found. (Benchmarks are estimates of concentrations above which pesticides may have adverse effects on human health, aquatic life, or fish-eating wildlife.)

Insecticides — particularly diazinon, chlorpyrifos, and malathion — frequently exceeded aquatic-life benchmarks in urban streams. The report also notes that most urban uses of diazinon and chlorpyrifos have been phased out since 2001 because of use restrictions imposed by the U.S. Environmental Protection Agency (EPA). Consequently, concentrations are declining. In agricultural streams, chlorpyrifos, azinphos-methyl, and alachlor were among those pesticides most often found at concentrations that may affect aquatic life. In 2001, agriculture accounted for about 75% of total national pesticide use, according to the report.

Regulatory Implications
Most of the toxicity information, as well as the water-quality benchmarks, used in the report was developed for individual chemicals, Gilliom pointed out. Levels measured were typically below human health benchmarks, yet “the common occurrence of pesticide mixtures, particularly in streams, means that the total combined toxicity of pesticides in water, sediment, and fish may be greater than that of any single pesticide compound that’s present,” he said.

Risk assessments on the effects of contaminant mixtures are still in the early stages, but Gilliom noted that “our results indicate that such studies should be a high priority.”

EPA’s Office of Prevention, Pesticides, and Toxic Substances (OPPTS) uses USGS data extensively in its exposure and risk assessments for regulating the use of pesticides, said Steven Bradbury, director of the OPPTS Environmental Fate and Effects Division. For example, EPA used USGS data in its risk assessments for the re-evaluation of diazinon, chlorpyrifos, cyanazine, and alachlor. Uses of the first three have now been significantly limited, and usage of alachlor was voluntarily reduced and largely replaced by a registered alternative.

Bradbury cautioned, however, that USGS measured “with very sophisticated techniques, so they’re getting down to very low concentrations and consequently finding a number of combinations of materials.” Part of solving the mixture problem is first asking which ones may have similar modes of action, he noted, adding that a “lot of theory and research has been done on the additive toxicity of [such] chemicals.”

As part of the Food Quality Protection Act, EPA is moving forward in the reregistration process to look at the cumulative and additive effects of various chemicals, Bradbury said. But “what remains a challenge for the scientific community and EPA is how to deal with mixtures of chemicals that don’t have the same mechanism of action,” he noted. The agency and others are pursuing approaches to this end, he said.

Long-Term Trends
Meanwhile, the NAWQA findings show strong associations between the occurrence of pesticides and their use, and point out that some of the frequently detected pesticides, including the insecticide diazinon and the herbicides alachlor and cyanazine, are declining, showing responses to regulatory actions and reduced use.

This type of information “gives us a chance to track the performance of our regulatory decision-making, which, in turn, is based on our risk assessments,” Bradbury noted.

One of the most notable trends is that concentrations of DDT, dieldrin, and chlordane — organochlorine pesticide compounds that were no longer in use when the study began — continue to slowly decline. Nevertheless, they still occur at levels greater than benchmarks for aquatic life and fish-eating wildlife in many urban and agricultural streams nationwide.

In contrast, the NAWQA findings also show that concentrations of relatively mobile and short-lived pesticides in stream water respond more rapidly to changes in use than the less mobile and more persistent organochlorine insecticides, Gilliom said. “The half-lives of organochlorines are all much longer than the half-lives of most of the chemicals in use today or recently,” he noted. “In most cases, the half-life of modern compounds is less than a year,” he said, so if a change in use is made, “it’s usually reflected quite rapidly in stream concentrations.”

Overall, “what they found, they found in very low quantities, and I think it’s a representation of how farmers use [the chemicals] judiciously,” said Don Parrish, senior director of regulatory relations for the American Farm Bureau Federation (Washington, D.C.). “The only ones they found that are problematic are the ‘oldies,’ which, unfortunately, stay in the environment for a long time, even after we banned them.”

Jay Vroom, president and chief executive officer of CropLife America (Washington, D.C.), a pesticide trade association, agreed. He pointed out that “simply detecting a pesticide does not automatically translate to a need for concern,” adding that “these detections are indicative of recent advances in technology that allow detection of trace levels.”

But Jay Feldman, executive director of the environmental group Beyond Pesticides (Washington, D.C.), said that “the big issue for us is the finding of pesticide mixtures.” What that means is that “the real-world exposures that people are experiencing aren’t being fully assessed by the agency responsible for protecting public health and safety, and that’s a problem,” he said.

From Monitoring to Prediction
For the second NAWQA cycle, USGS scientists are adding more pesticides to their analysis and continuing their study of long-term trends, according to Gilliom.

Additionally, USGS, together with EPA, is developing statistical models to predict concentrations of pesticides, particularly in streams, nationwide. For example, a NAWQA model for atrazine was developed from measured pesticide concentrations in streams, information on pesticide use and land use, climate and soil characteristics, and other natural features, according to the report. Estimates gleaned from it have been used to identify locations that have the greatest likelihood of elevated atrazine concentrations and, therefore, are the highest priority for additional monitoring in reregistration decisions, Bradbury noted.

“The models are evolving to a point where we’re very confident in using them to design monitoring studies that allow us to focus in on specific places, or timing, or help to get monitoring data that’s more focused,” Bradbury explained.

Current modeling efforts involve an expansion to other pesticides, according to Gilliom. USGS also is conducting studies on urban streams examining the correlations between different types of urbanization and pesticide use to try to determine what effects these chemicals may be having on urban stream ecology.

For more information, access the report at water.usgs.gov/pubs/circ./circ1291.

— Kris Christen, WE&T

U.S. EPA Advisers Raise Concerns About Perchlorate Cleanup Goal

Small children are not sufficiently protected from exposures to perchlorate under the preliminary remediation goal set in late January by the U.S. Environmental Protection Agency (EPA) for Superfund sites, according to the agency’s Children’s Health Protection Advisory Committee (CHPAC). The new cleanup target of 24.5 ppb “is not supported by the underlying science and can result in exposures that pose neurodevelopmental risks in early life,” wrote Melanie Marty of California’s Office of Environmental Health Hazard Assessment, who chairs the CHPAC panel, in a March 8 letter to the EPA administrator.

Perchlorate is the primary ingredient used in the manufacture of solid propellant for rockets, missiles, and fireworks. It also is a high-priority substance on EPA’s list of unregulated contaminants of concern, known as the Contaminant Candidate List. Wastes from the manufacture and improper disposal of perchlorate-containing chemicals are increasingly being discovered in soils, groundwater, and surface waters, according to EPA. To date, the agency has confirmed perchlorate releases in more than 25 states nationwide.

EPA has yet to set a drinking water standard for perchlorate. In the interim, under the remediation guidance issued in January by the agency’s Office of Solid Waste and Emergency Response, concentrations of the chemical at contaminated sites must be reduced to 24.5 ppb. This limit, EPA officials said, is based on a reference dose for perchlorate of 0.0007 mg per kilogram of body weight per day, which was recommended by the U.S. National Academy of Sciences (NAS) in 2005. This reference dose translates into a drinking water equivalent level of 24.5 ppb, according to EPA, and assumes an uncertainty factor of 10 to protect the most sensitive populations, including fetuses and infants.

The U.S. Department of Defense (DOD), which faces liability at several contaminated sites nationwide, immediately responded, establishing 24 ppb “as the current level of concern for managing perchlorate” at all active and closed DOD sites.

Not Protective Enough
EPA’s CHPAC panel, which includes 26 scientists, maintained, however, that the tenfold uncertainty factor is not protective enough and puts babies at unnecessary risk of neurological damage. Panel members recommended that EPA lower the preliminary remediation goal, taking infant exposures and susceptibility into account, although they did not specify a particular level. Additionally, CHPAC called on EPA to develop a drinking water standard for perchlorate and, in the interim, to issue a health advisory for potable water.

Perchlorate can interfere with iodide uptake into the thyroid gland, disrupting its functions, according to EPA. The thyroid helps regulate metabolism in adults and also plays a major role in proper child development. Impairment of the thyroid function in expectant mothers may affect the fetus and newborn, as well as result in behavioral effects, delayed development, and decreased learning, according to EPA. Chronic lowering of thyroid hormones due to high perchlorate exposure through drinking water or food may result in thyroid gland tumors, the agency said.

Consequently, EPA in 2002 recommended a preliminary drinking water standard of 1 ppb for perchlorate, but DOD officials objected, saying that existing data supported a standard as high as 200 ppb. Because of the uncertainty surrounding the severity of health effects at various concentrations in drinking water, NAS was called on to review the risk assessment EPA used to develop the draft limit. NAS concluded that perchlorate does not pose as much health risk as EPA scientists had estimated, but that it is more harmful than the defense industry had suggested.

For now, the Superfund cleanup guidance of 24.5 ppb is in effect. EPA’s previous screening level ranged from 4 to 18 ppb, and CHPAC voiced concerns that in the absence of a federal drinking water regulation, the 24.5 ppb cleanup target could become the de facto standard.

EPA officials declined to comment on the specific concerns raised by the CHPAC advisory panel. However, Dale Kemery, an EPA spokesman, said “it’s too early to tell how the NAS’s recommended reference dose will translate to public health conclusions about drinking water consumption.” In developing a maximum contaminant level goal (MCLG), EPA still must

  • determine how much perchlorate exposure comes from water, as opposed to food and other sources;
  • establish the appropriate body weight on which to base the standard;
  • estimate the amount of water consumed by a person of appropriate weight; and
  • conduct the necessary research on treatment and residuals disposal.

“If the decision is made to develop a drinking water regulation, EPA would set a maximum contaminant level as close to the MCLG as feasible, with feasibility defined as the level that may be achieved with the use of best available technology, treatment techniques, and other means which are available, taking cost into consideration,” Kemery said.

Removal Costs
Regardless of what federal drinking water standard EPA finally sets, if it sets one, the cost implications of the new cleanup standard are significant.

“When cleanup goals are decreased by an order of magnitude, it significantly increases remediation costs, especially for in situ remediation,” noted Kent Sorenson, a vice president and hazardous waste remediation manager in the Denver office of CDM (Cambridge, Mass.), a consulting engineering firm. “Some of the major stakeholders, a big one being DOD, had been advocating a preliminary goal more along the lines of 100 ppb, so this is obviously going to have a big impact on DOD cleanup costs,” he said.

Several treatment technologies currently are in use, and the main ones include biological treatment and ion exchange, which can reduce perchlorate concentrations to nondetectable levels, said Greg Pulliam, director of environmental services for Black & Veatch (Overland Park, Kan.), a consulting engineering firm. At this point, biological systems cost less to operate but more to build. “The capital facilities are typically much more extensive,” Pulliam explained, “but when you get into the operational mode, the ‘bugs’ regenerate themselves after destroying the perchlorate, so you’ve got nothing left at the end that has to be disposed of.” With ion exchange, on the other hand, the resins used to trap the perchlorate must be disposed of and replaced when their exchange capacity is reached. Additional treatment technologies are under development, according to EPA.

States Going Own Way
In the absence of a federal drinking water standard, several states are moving forward with their own. To date, at least eight states — Arizona, California, Maryland, Massachusetts, Nevada, New Mexico, New York, and Texas — have nonenforceable advisory levels for perchlorate in drinking water ranging from 1 to 18 ppb.

Massachusetts is the farthest along, proposing in March a drinking water and cleanup standard of 2 ppb. Perchlorate was first detected in that state in 2002 in the aquifer underlying the Massachusetts Military Reservation on Cape Cod, when officials found it to be moving toward drinking water wells in the town of Bourne. Since then, the contaminant has been found in drinking water sources at 10 locations across the state.

In justifying a level lower than EPA’s cleanup standard, Robert Golledge, commissioner of the Massachusetts Department of Environmental Protection, said the agency believes “a larger uncertainty factor than NAS applied is appropriate to protect sensitive subpopulations,” which include pregnant women, nursing mothers, infants, and individuals with low levels of thyroid hormones.

— Kris Christen, WE&T