EH Update.

Algae and Bacteria Influence Breakdown of Herbicides

Some species of green algae that help break down soil-applied herbicides could help improve soil and water quality, according to scientists from the U.S. Department of Agriculture's (USDA's) Agricultural Research Service (ARS). Microbiologist Robert M. Zablotowicz, of the ARS Southern Weed Science Research Unit in Stoneville, Mississippi, discovered the one-celled organisms in three Mississippi watershed lakes - Beasley, Deep Hollow, and Thighman.

The study is part of the USDA-ARS Mississippi Delta Management Systems Evaluation Area (MSEA) project, which is evaluating farming practices in the 7,320-acre area surrounding the three lakes. The goal of the project is to improve farming techniques and ultimately to enhance soil and water quality.

Studies conducted by Zablotowicz and his colleagues indicate that management practices influence microbial populations and their impact on water quality. The Deep Hollow watershed, where intensive conservation practices such as winter cover crops and reduced tillage are employed, had the lowest levels of sediment and the highest populations of Selenastrum and Ankistrodesmus. These algae can absorb and break down herbicides such as atrazine and fluometuron, which are commonly used in corn and cotton production.

Another major finding, according to Zablotowicz, is that a specific group of bacteria, called fluorescent pseudomonads, can degrade metolachlor, propanil, and trifluralin - three herbicides commonly used in the MSEA area.

Zablotowicz and other ARS scientists will continue to study how microbes like algae and bacteria help improve soil and water quality. Knowledge gained from the MSEA study will ultimately be used to develop techniques for maintaining diverse aquatic microbial populations that can degrade agrochemical pollutants.

More Stringent Standard Needed for Arsenic in Drinking Water 

The U.S. Environmental Protection Agency (U.S. EPA) should develop a stricter standard for arsenic in drinking-water supplies as soon as possible, according to a new report by a committee of the National Research Council (NRC). Arsenic has long been identified as a poison, and its presence in drinking water has been associated with skin cancer and other disorders. Now, more recent studies suggest that high levels of arsenic in drinking water also can lead to bladder cancer and lung cancer, which are more likely to be fatal.

"New information on arsenic exposure and cancer indicate that the current standard does not sufficiently protect public health," said committee chair Robert Goyer, professor emeritus of pathology at the University of Western Ontario. "Although additional research on arsenic is needed, available data indicate that U.S. EPA should set a new standard."

Inorganic arsenic, the form most likely to cause cancer, occurs naturally in the Earth's crust. The arsenic is released into groundwater that travels through underground rocks and soil. As a result, well water often has higher concentrations of arsenic than does surface water in lakes and streams. Arsenic also can be found in plants, fish, and shellfish.

U.S. EPA's standard for arsenic in drinking water was developed decades ago and remained in place after an assessment of skin cancer risks in 1988. That assessment did not consider the risks of lung cancer and bladder cancer, however.

New data and more precise models for estimating risk suggest that the likelihood of cancer risk from drinking water that contains U.S. EPA's maximum allowable amount of arsenic greatly increases when lung and bladder cancers are considered. For example, men who daily consume water that contains 50 micrograms of arsenic per liter have been shown to have a risk of about 1 in 1,000 for bladder cancer - that risk far exceeds U.S. EPA's goal of limiting cancer risks to 1 in 10,000.

Congress has required U.S. EPA to propose a new maximum allowable amount for arsenic in drinking water by January 2000. The new standard must be finalized by 2001. To help inform the agency's decision, NRC was asked to evaluate the latest information on the health effects of arsenic in drinking water, as well as U.S. EPA's methods for assessing cancer risks.

Effects of Arsenic

The committee examined clinical studies reported in medical literature and epidemiological data from several international studies, including research from Taiwan, Argentina, and Chile. These studies show that in addition to causing skin cancer, bladder cancer, and lung cancer, arsenic in drinking water can cause skin lesions, anemia, nerve damage, and circulatory problems.

Arsenic is readily absorbed from the gastrointestinal tract into the blood. The mechanisms through which arsenic causes cancer are not well understood, but data suggest that arsenic probably causes chromosomal abnormalities that lead to cancer. Sensitivity to the toxic effects of arsenic - including the carcinogenic effects - varies with each individual and appears to be influenced by factors such as nutrition and genetic susceptibility.

For many years, scientists have debated whether small amounts of arsenic could actually be beneficial in the human diet. Arsenic has not been tested as an essential nutrient for humans, and, according to the NRC committee, no evidence suggests that arsenic is required for any human biochemical processes. Animal studies show that adding very high concentrations of arsenic to the diets of chicks, goats, and rats appears to affect growth, fertility, and litter size. More research is needed, however, to determine whether arsenic has any nutritional effects in humans and animals.

Uncertainties in Estimates

No human studies of sufficient scope have directly examined whether regular consumption of drinking water that meets U.S. EPA's current arsenic standard increases the risk of cancer or other adverse health effects. Rather, the NRC committee's characterization of risk is based on findings from the international studies, experimental data on the mechanisms through which arsenic causes cancer, and available information about human susceptibility.

The committee underscored the problems inherent in applying the data from the international studies. The studies measured regional exposure to arsenic in drinking water, not the amount of arsenic to which each individual was exposed. Moreover, most people in the studies were exposed to arsenic concentrations of more than 100 micrograms per liter of water. These uncertainties do not, however, change the committee's finding that exposure to arsenic in drinking water increases the risk of developing bladder and lung cancer.

The committee recommended further research in several areas:

* more epidemiological evaluations to improve the understanding of how arsenic exposure triggers cancer and other disorders, especially at very low levels;

* research on how metabolism and environmental, genetic, and dietary factors interact with arsenic and affect susceptibility to cancer;

* studies of peoples with high incidences of arsenic-related cancer to determine the role of nutrition and genetics; and

* development of data on the relationship between level of exposure and the concentration of arsenic retained in the body

To purchase a copy of NRC's Arsenic in Drinking Water report, call [phone] or [phone].

U.S. Cancer Incidence and Death Rates - Decline Continues, but Not Irreversibly

Between 1990 and 1996, three important cancer statistics declined in the United States, according to a new report released by the American Cancer Society (ACS), the National Cancer Institute (NCI), and the Centers for Disease Control and Prevention (CDC):

* There was a decline in the rate at which new cancer cases of all types occurred.

* There was a decline in the rate at which people died from all types of cancer combined.

* There was a decline in the rate at which new cases occurred for most of the top 10 types of cancer taken individually.

Nevertheless, lung cancer rates are likely to start increasing again unless an increase in adolescent smoking can be reversed.

The "Annual Report to the Nation on the Status of Cancer, 19731996, with a Special Section on Lung Cancer and Tobacco Smoking" was published in the April 21, 1999, issue of the Journal of the National Cancer Institute. For all cancers combined, the incidence rate (the number of new cancer cases per 100,000 persons) declined an average of 0.9 percent per year between 1990 and 1996. This trend reversed a pattern of increasing incidence rates that occurred from 1973 to 1990. Also, cancer death rates have been falling an average of 0.6 percent per year.

By far, the greatest decline in cancer incidence rates has been among men, who overall have higher rates of cancer than do women. The largest decreases occurred among men 35 to 44 years of age and those 75 and older. The largest incidence trends for women were a decrease among those 35 to 44 years of age and those 85 and older. The report analyzed data for white, black, Asian/Pacific Islander, American Indian/Alaska natives, and Hispanic populations and noted large differences in incidence by race and ethnicity, with incidence rates highest for African-Americans for all major cancers except breast cancer. Death rates also were highest for the black population - for cancer overall and for the major types of cancer.

From 1990 to 1996, four types of cancer - lung, prostate, breast, and colorectal - accounted for more than half of all new cancer cases and were also the leading causes of cancer deaths. Tracking trends for those primary sites shows that

* incidence and mortality rates for prostate cancer are going down;

* for breast cancer, incidence rates have shown little change in the 1990s, but death rates have been declining about two percent per year; and

* incidence and death rates for colorectal cancer have continued to decline for both men and women.

The pattern is different for the two top types of cancer:

* Incidence and death rates for non-Hodgkin's lymphoma are continuing to increase, although more slowly in the 1990s than in the past decade.

* Incidence rates of melanoma are on the rise, up about three percent annually, but death rates have remained constant.

The report has a special section on lung cancer and tobacco, with state data on lung cancer deaths and the prevalence of smoking among adults and youth. Lung cancer causes more deaths than any other cancer, accounting for 28 percent of all cancer deaths each year. Lung cancer also represents 145 percent of new cancer cases and continues to be a key factor driving overall cancer trends.

The prevalence of cigarette-smoking among adults has declined over the past 25 years, but this trend has stalled during the last four to five years. At the same time, the number of high school students smoking cigarettes has continued to increase, and unless this trend can be reversed, the lung cancer rates that are currently declining may rise again.

Environmental Health-'Net

Indoor Air Quality Resources

<http://www.dehs.umn.edu/resources.html>

The University of Minnesota environmental health and safety web page addresses a number of on-campus environmental health issues, including indoor air quality. Information is available on airborne fungi; the air quality effects of flooding; and the decontamination of heating, ventilation, and air-conditioning (HVAC) systems. The site also links to the Minnesota Indoor Air Quality Consortium Homepage, which addresses indoor air quality in homes, providing information on indoor air pollutants, health effects, repairs, and building design. Further links take the user to other state and national organizations involved with indoor air quality.

Drinking-Water Safety Information

<http://www.epa.gov/enviro/html/sdwis/sdwis_ov.html>

From the U.S. Environmental Protection Agency's Safe Drinking Water Information System (SDWIS), users can locate their drinking-water suppliers and view violations and enforcement history for the past 10 years. SDWIS also provides information on maximum contaminant levels, treatment techniques, and monitoring and reporting requirements.