E X T O X N E T
Extension Toxicology Network, Toxicology Information Briefs
Revised 9/93; http://ace.orst.edu/info/extoxnet/tibs/partperm.htm

INTRODUCTION

The health effects of any toxic substance are related to the amount of exposure, also known as the dose. The greater the dose the more severe the effects. Some chemicals can cause toxicity at very low doses and so it is important to be able to understand how these very small amounts are described. It is especially important to understand how low doses compare to one another and what they represent when compared to amounts of more familiar substances.
Parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt), are the most commonly used terms to describe very small amounts of contaminants in our environment. But what do these terms represent? They are measures of concentration, the amount of one material in a larger amount of another material; for example, the weight of a toxic chemical in a certain weight of food. They are expressed as concentrations rather than total amounts so we can easily compare a variety of different environmental situations. For example, scientists can measure the concentration of a chemical in the Great Lakes by looking at small samples. They do not have to measure the total amount of chemicals or water in all of the lakes.

An example might help illustrate the part per ... idea. If you divide a pie equally into 10 pieces, then each piece would be a part per ten; for example, one-tenth of the total pie. If, instead, you cut this pie into a million pieces, then each piece would be very small and would represent a millionth of the total pie or one part per million of the original pie. If you cut each of these million minute pieces into a thousand little pieces, then each of these new pieces would be one part per billion of the original pie. To give you an idea of how little this would be, a pinch of salt in ten tons of potato chips is also one part (salt) per billion parts (chips).

In this example, the pieces of the pie were made up of the same material as the whole. However, if there was a contaminant in the pie at a level of one part per billion, one of these invisible pieces of pie would be made up of the contaminant and the other 999,999,999 pieces would be pure pie. Similarly, one part per billion of an impurity in water represents a tiny fraction of the total amount of water. One part per billion is the equivalent of one drop of impurity in 500 barrels of water.

COMPARISONS AND CONVERSIONS

Sometimes, instead of using the part per ... terminology, concentrations are reported in weight units; such as the weight of the impurity compared to the weight of the total. The metric system is the most convenient way to express this since metric units go by steps of ten, hundred and thousand. For example, a milligram is a thousandth of a gram and a gram is a thousandth of a kilogram. Thus, a milligram is a thousandth of a thousandth, or a millionth of a kilogram. A milligram is one part per million of a kilogram thus, one part per million (ppm) is the same as one milligram per kilogram. Just as part per million is abbreviated as ppm, a milligram per kilogram has its own abbreviation -- mg/kg. Using our abbreviations, one ppm equals one mg/kg.

Kilograms and milligrams are units of weight so they don't apply to volumes of liquids or gases. Instead of a kilogram, the unit of liquid volume most commonly used is the liter. A liter of water weighs one kilogram. If the contaminant is a solid, it is measured in milligrams. Thus, one part per million of a solid in a liquid can be written as a milligram per liter and abbreviated mg/l.

These are the most common units that are encountered. However, with the ability to detect even smaller amounts of contaminants, the terms part per billion and part per trillion are becoming more common. In the metric weight system, a microgram is a thousandth of a milligram. Since a milligram is a millionth of a kilogram, and the microgram is a thousand times smaller, it is equivalent to a billionth of a kilogram. Microgram is abbreviated ug. Thus, a part per billion of solid measure is equal to a ug/kg. Similarly, a part per billion of a solid in a liquid is equal to a ug/l.

Before going on to discuss a real example of how these measurements are used, we can compare metric weight quantities to the quantities we are most accustomed to using. A kilogram is equal to about two pounds. Thus, a milligram is less than a millionth of a pound. Looked at another way, it would take about five thousand milligrams (5000 mg) to make up one teaspoonful of a solid (such as salt). The unit of liquid volume, the liter, is very close to a quart. Thus, a milligram per liter is about the same as a milligram per quart.

THE CASE OF PCBs:

An Example

In order to appreciate how these quantities can be used in a real situation, an example is in order. In this example, we use the part per ... terminology to compare the relative importance of PCBs in Great Lakes fish versus PCBs in Great Lakes drinking water; that is, which source might contribute most to PCB exposure of humans living in the Great Lakes states. The maximum level of PCBs legally allowed in fish sold in interstate commerce is 2 ppm (parts per million).

Although there are no legally established levels for PCBs in drinking water, measurements have shown that the average PCB content of the Great Lakes drinking water is about 4 ppt (parts per trillion).

Since a part per trillion is a million times less than one part per million, the maximum allowable concentration of PCBs in fish is about a million times higher than the level of PCBs in drinking water. However, we generally consume a lot more water than fish. At the extreme, people might eat as much as a pound of fish a day or as little as one pound every 100 days (1/100 lb/day). On the other hand, people generally drink about 2 liters (equivalent to about 5 pounds) of water a day.

Thus, the consumption of water might range from about 5 to 500 times the consumption of fish.However, since there are a million times more PCBs in a pound of fish compared to a pound of water, fish can be a much greater source of PCBs than drinking water. The total amount of PCBs consumed depends most on the amount of fish eaten, how contaminated it is, and how it is prepared. Thus, the best way to reduce human exposure to PCBs is to reduce the levels in fish, reduce human consumption of fish with the highest contaminant levels and prepare the consumed fish in the most appropriate manner.

CONCLUSION

The ability to measure concentrations of chemicals in a uniform manner provides a powerful tool for the comparison of water quality from area to area, for the establishment of water quality guidelines or a comparison of doses of chemicals as are commonly found throughout the Pesticide Information Profiles. The use of the metric system provides an easy way to utilize both liquid and solid measurements.

METRIC SYSTEM QUANTITIES
For Solids

1 kilogram (kg) = 1 million milligrams (mg)
so: 1 mg/kg = 1 part per million

1 kilogram (kg) = 1 billion micrograms (ug)
so: 1 ug/kg = 1 part per billion

For Liquids

1 liter (1) of water weighs exactly 1 kg
so: 1 mg/l = 1 part per million and
1 ug/l = 1 part per billion
1 kg = about 2.2 pounds
1 l = about 1 quart

Bill Would Require School Pesticide Plans

Source: The Tennessean
Publication date: 2001-02-08

All school systems in Tennessee would be required to adopt a pestmanagement program `when economically feasible` under legislation planned by Rep. Carol Chumney, D-Memphis.
The program would require that parents be notified of planned use of toxic pesticides in schools. The legislation also `strongly encourages` the use of alternative pesticides that are classified by the Environmental Protection Agency as reduced-risk. Several school systems in Tennessee, including Davidson and Shelby counties, already have such programs, Chumney said.
Chumney said a 1999 General Accounting Office report on school pesticides revealed 2,300 instances from 1993 to 1996 in which children had been affected by pesticides at school, including more than 300 cases in which medical care was necessary. "Poisonous pesticides pose significant health risks to the children, teachers and staff," Chumney said. "Exposure to these pesticides poses a similar health risk to those of lead paint and asbestos, and now we would never think of using these in our schools. Symptoms of exposure to some pesticides include headaches, rashes, allergic reactions, asthma attacks, nausea, fever and other flu-like conditions" Chumney said. She said she had no specific knowledge of the extent of the problem in Tennessee.

Source: U.S. Newswire
9 Feb 2001
INDIANAPOLIS, Ind., Feb. 9 /U.S. Newswire/

A new report shows a shift to organic farming methods could increase pesticide use by hundreds of millions of pounds per year.
Representing less than 1 percent of total agriculture, this research reveals that even a marginal increase of land placed under organic farming methods could result in significant increases in use of persistent and toxic "organic" pesticides such as sulfur, copper and other natural chemicals allowed in organic production.
The "natural" pesticides used by organic farmers are among the most heavily used, toxic, and persistent in American agriculture today, according to a report from Hudson Institute's Center for Global Food Issues. A mandate for organic-only farming would lead to massive increases in pesticide use, soil contamination, and topsoil loss. The result would be a major decrease in the sustainability of American agriculture, the report concludes.
"The myth that organic farming is toxics-free should be buried forever. The American public has been misled through poor reporting and aggressive marketing schemes to believe organic is 'pesticide-free' and safer for human and ecological health," said Alex Avery, the report's author.

The report, "Nature's Toxic Tools: The Organic Myth of Pesticide-Free Farming," concludes that:
-- Organic pesticides are the most heavily used pesticides in the United States
-- One organic insecticide accounts for more than half of all U.S. insecticide use
-- One organic fungicide accounts for more than half of all U.S. fungicide use
-- Switching to all organic production would result in up to a 700 percent increase in U.S. fungicide use
-- An all-organic mandate would lead to a massive increase in soil erosion and reduced sustainability
-- U.S. regulators have no information at all on the use of most organic pesticides, despite the fact that millions of pounds of these toxic pesticides are used in the United States every year

"At this moment of critical debate about the health and environmental benefits of conventional farming and genetically improved crops, organic farming is being promoted as the ideal alternative. The reality is organic is less understood, untested and potentially riskier for both people and the environment," said Avery.

The report is available at the Center for Global Food Issues' Web site at: http://www.cgfi.org/pubs2.cfm

By THE ASSOCIATED PRESS
February 9, 2001

MONTPELLIER, France (AP) -- A prosecutor on Friday asked a court to hand down a three-month prison sentence for activist Jose Bove, on trial in France raiding a laboratory and destroying more than 1,000 genetically altered plants.
Calling the June 1999 burning of the rice plants ``intolerable,'' prosecutor Olivier Decout also sought a three-month sentence for a second defendant, Rene Riesel who, like Bove, has been previously convicted in a separate case. The prosecutor asked for a three-month suspended sentence for the third defendant, Dominique Soullier, because he has no prior record. A verdict was expected later Friday.
Decout denounced the ``premeditated, deliberate'' operation, saying the use of hammers and crowbars and the destruction of doors and computers were ``unacceptable methods in a state of law.'' Bove, 47, a militant sheep farmer, gained fame after attacking a McDonald's restaurant as part of his battle against globalization. He is being tried on charges he raided a greenhouse belonging to CIRAD, an international center for agronomy research in Montpellier. CIRAD, a civil party in the case, is seeking $1.7 million in damages.
In the past, Bove received an eight-month suspended sentence for plowing up a field planted with genetically modified corn. In September, he was sentenced to three months in prison for vandalizing the McDonald's in Millau in southern France. An appeal of that verdict is to be heard next week. Bove is under investigation for allegedly destroying genetically altered corn in two other regions in France. Bove is a leader of the Farmers Confederation, a militant group of farmers fighting against what they see as the encroachment of multinationals producing standardized, unhealthy food.

Syngenta AG, the makers of atrazine, are awaiting testing designs that are being developed by an expert panel of academic researchers. The studies are designed to examine non-cancer effects of atrazine - with special emphasis on the endocrine system.
A draft EPA hazard assessment submitted by the Scientific Advisory Panel on December 4, 2000 indicated that atrazine is not likely to cause cancer in humans. The SAP was charged with examination of atrazine due to earlier research that indicated early onset of tumors in one strain of rat that is naturally prone to tumor formation. The panel indicated that the mode of action in the rat is understood, and that tumor formation was only observed at high exposure levels. They stated that the mode of action was not relevant to humans.
Endocrine disruption, one of the key topics of FQPA, is becoming the endpoint of concern for the pesticide manufacturing industry. If effects on the endocrine system are detected, regulatory actions can be delayed. Pesticides in this category (endocrine disruptors) are unlikely to be registered by the EPA because they fall into "a bottomless pit of study."

Source: Chem. Speak. January, 2001 (Chemical Regulation Reporter Vol. 25, No. 1).

Four companies, linked to a massive pile of DDT on the ocean floor off the coast of Los Angeles, either owned or operated a manufacturing plant in Torrance, CA, that produced DDT. The plant is currently abandoned. The settlement is the largest sum ever paid for environmental damage from pollution other than oil.
Thirty million dollars will be spent to restore natural resources, such as bird and fish habitat, while the remainder will be spent to clean up or cap the 110 tons of DDT that is spread over a 17-square-mile area of the Palos Verdes shelf.
Government scientists contend that the DDT in the sediments is slowly released into algae and bottom feeding fish, and then travels up the food chain. DDT has been detected in white croaker tissue, and it is believed to be the cause of reproductive effects plaguing eagles, pelicans, and peregrine falcons that consume fish from the waters.
Capping trials (covering the contaminated soil with clean sediment) began in September, and results will be available by spring 2001.

Source: Chem. Speak. January, 2001
(Chemical Regulation Reporter Vol. 25, No. 1).

In addition to the individual risk assessments required by FQPA, this law also mandates that a cumulative risk assessment be conducted for pesticide groups which have a common toxicological effect. The idea behind the cumulative assessment is that lifetime exposure (and consequent effects) may be greater for a group of compounds with similar mode of toxicity than for a single compound. In addition to having the same toxic effect, the criteria outlined by the EPA requires that the toxic effect be expressed in the same organ or tissue and that the pesticides cause an effect by a common mechanism. The organophosphates, carbamates, and pyrethroids are believed to be three groups that fulfill the definition. However, it may be difficult to find common groups other than these three.
Beyond the common mechanism grouping, scientists performing the assessments will be tasked with trying to normalize the potencies of compounds. For instance, one OP insecticide may be twice as effective as another, and thus have twice the potency units than the less active insecticide.

Source: Chem. Speak. January, 2001 (Chemical Regulation Reporter Vol. 25, No. 1).

Although popular polls have demonstrated lukewarm concern by Americans regarding biologically-modified foods, organizations in other parts of the world have been propagandizing, protesting, and pulling up plants. Since many people have been swamped with information from these "sources", it may be advantageous to obtain some information "from the horse's mouth."

Stanley Abramson is an environmental lawyer with the Washington D.C. firm of Arent Fox Kintner Plotkin & Kahn. He also worked for the EPA in the 1980s. He recently completed an assignment for the national Academy of Sciences which was tasked with investigating the risks and benefits of biotech crops as well as their regulation. He served on the committee with 10 scientists and one economist and together they issued a unanimous consensus report. The conclusion of the report was that no evidence exists to conclude that products on the market today pose any harm.

Mr. Abramson also categorized biotech misconceptions into six myths. The first myth is that genetically modified plants are not regulated. Mr. Abramson helped craft the coordinated framework which requires EPA, USDA, and FDA input into the regulatory process. In thecae of a B.t.-toxin-producing plant, EPA regulates the protein, USDA reviews the plant itself, and FDA's jurisdiction includes the safety of the entire product. No comparable oversight exists for conventional varieties.

Another myth is that no data exists to support genetically modified products. Again, information is required by all three agencies and there is a great deal of it, all open to public review. For a modified potato cultivar, it took seven years of review by the agencies to review all the submitted data. If an issue is raised that cannot be addressed by required information, then additional data are requested by the agencies.

The third myth is that the public is excluded from the process. Mr. Abramson recounted how in the 70s and 80sthat many public hearings were held and comment periods provided. Very few members of the public or media attended the meetings. The public continues to have avenues to participate through web sites and public comment periods listed in the Federal Register.

The fourth myth is that benefits of biotechnology do not exist, or that the only benefit is to the developer of the crop. Although not readily apparent to consumers, crops like B.t. cotton reduce pesticide input into the environment and reduce exposure of applicators and consumers to insecticides. Mr. Abramson emphasized that the same groups that came to the EPA in the 80s demanding that certain pesticides be canceled are now demanding a ban on the crops which reduce use of those pesticides.

The fifth myth is that the modified plants harm the environment. Mr. Abramson reports that in the past 14 years of intensive governmental, academic, and commercial scrutiny, not a single incidence of actual harm to health, safety or the environment has ever been documented concerning the crops on the market today.

The final myth is that none of the biotech crops are labeled. This is erroneous. For example, if an orange was developed that has less vitamin C than expected in the market today, that information must be provided.Mr. Abramson stated that the labeling line is crossed when certain groups desire food labeled for societal purposes.

(Farm Industry News Reference No. 4915, April 5, 2001).

Seed producers meeting with government officials (USDA, EPA, and FDA) on March 1 stated that traces of StarLink® genetic material was present in some conventional corn varieties. The seed industry representatives were unaware of the magnitude of the contamination at that time.

On November 21, 2000, Garst Seed Co. Of Slater, Iowa, announced that it had detected the StarLink® genetic trait in an entirely unrelated corn variety. This discovery prompted the USDA's Grain Inspection, Packers, and Stockyards Administration to send a letter to seed companies on December 28, 2000, urging them to test all 2001 planting season seed corn for the presence of StarLink® genetic material.

The letter urged producers to test all seed lots, and divert any contaminated corn seed to animal feed or ethanol production plantings. The letter stated "collective efforts of all market participants is necessary to ensure that corn currently containing Cry9C protein is directed to approved uses, and that future corn production does not contain Cry9C protein" and that "cooperation and additional efforts to ensure 2001 seed corn does not contain Cry9C protein is essential."

To assure that no contaminated seed is planted, the National Corn Growers Association has instituted a "verify before you buy" program, in which corn growers would request assurances that their seed be StarLink_free before purchasing it. Due to the negative impact that the StarLink contamination had on corn exports in 2000, it is imperative that the scenario is not repeated.

In a related announcement, the EPA released a draft report on Cry9C protein in the milling process. Reportedly, the protein is completely degraded in the wet milling process, which is used to produce corn oil, corn syrup, alcohol, and corn starch, which comprise 80 percent of corn food products. Additionally, the EPA stated that no more split registrations (i.e., animal feed only) would be issued for biotechnology products. The draft report is available at www.epa.gov/pesticides/biopesticides/ . On March 7, the USDA stated that it would buy StarLink_contaminated corn seed but that growers would be required to "verify before you buy" and control volunteer StarLink® corn.
Source: Chem. Speak. March, 2001 (Chemical Regulation Reporter, Vol. 25, No. 10 and Agnet).

Los Angeles Times
Thursday February 8, 2001

In the botanical equivalent of turning iron into gold, two scientific teams have discovered how to convert a plant's leaves into petals. The finding contributes to understanding the complex genetic workings that lead to the creation of flowers and raises the possibility of interesting new plant forms, including roses that might bloom all along their stems.
 

Scientists have known for a decade how to convert petals and other flower parts back into leaves but have not been able to turn leaves into petals until now. The findings are reported by UC San Diego's Martin Yanofsky in this month's issue of the journal Current Biology and by Takashi Honma of Kyoto University in Japan in a recent issue of the journal Nature.
 

The new finding shows that two genes in a class of genes recently discovered by Yanofsky are needed to convert the leaves into petals. In both cases, the findings were made in the weed Arabidopsis, a plant widely used by biologists because its genetics are so well described.

Atrazine Risk Assessment to Examine Drinking Water Exposure for Multiple Sites

Atrazine has been detected above the level of health concern for 9,000 infants served by 24 community water systems, all of which utilize surficial water. Total population served by the systems is approximately 130,000 people. States affected include Iowa, Illinois, Indiana, Louisiana, and Missouri. Atrazine is the most commonly detected pesticide in surface and ground water in the United States and annual use is estimated at 64 to 75 million pounds of active ingredient. Of greatest concern is the "pulse" of atrazine that is present in drinking water during May and June.

The preliminary risk assessment was conducted using monitoring data rather than modeling data since substantial atrazine monitoring data exists. However, the dietary risks associated with atrazine were within acceptable levels, based on probabilistic modeling. This type modeling will also be used to further refine the risk to children from drinking water processed by the 24 systems under examination. The Office of Pesticide Programs also stated that atrazine poses residential risk concerns to adults and toddlers for short_term post_application lawn exposures and for toddlers through incidental oral exposure.
Source: Chem. Speak. March, 2001 (Chemical Regulation Reporter, Vol. 25, No. 8).

Antibiotic Resistant Genes Traced from Farms to Groundwater

CHAMPAIGN, Illinois, May 1, 2001 (ENS) - Genes resistant to tetracycline, a common antibiotic, have been found in groundwater as far as a sixth of a mile downstream from two swine facilities that use antibiotics as growth promoters. The finding shows the potential for spreading antibiotic resistance back into the food chain of animals and people, researchers say.

For more than 50 years, U.S. farmers have used tetracycline and other antibiotics to enhance the growth of livestock. In humans, an overuse of antibiotics is blamed for a growing resistance to many antibiotics, and agricultural use has been suspected in the spread of resistance genes. The European Union is phasing out such agricultural use, while Sweden banned it in the 1980s.

Researchers from the University of Illinois (UI) and Illinois State Geological Survey used a DNA amplification technique to analyze samples from lagoons, wells and groundwater on and near two Illinois facilities, said Rustam Aminov, a visiting professor of animal sciences at the UI. Their research appeared in the April issue of "Applied and Environmental Microbiology."

"The use of tetracycline on farms is pushing the evolution of these genes," said Aminov. "We found tetracycline resistance genes in soil and groundwater bacteria. The genes are transferred to this type of bacteria, where they can survive and travel long distances in the environment." "It has been suggested that there is horizontal transfer of antibiotic resistance genes, but we had only seen it in laboratory experiments, not in in-situ studies," added Aminov. "Here, we see such a transfer is occurring in the environment."

The researchers were able to identify the trail taken by the resistance genes. The DNA fingerprints in the samples matched resistance genes previously identified in livestock and feed. "These genes were found to be predominant in the gastrointestinal tracts of pigs and steers," the authors wrote. "The elevated frequencies of these genes in the environment surrounding the farms were consistent with the hypothesis that this occurrence was the result of gene flow from the animals."

Once resistance genes make their way into drinking water, they will find their way into the guts of the people, animals and wildlife that drink it, Aminov said. "We are potentially passing on resistance in a continuous gene cycle in the environment," said Aminov.
Source: Ameriscan: May1, 2001

Seattle Study Reveals Toddler Organophosphate Exposure

A bio-monitoring study, reportedly the first of its kind, was conducted by the University of Washington's Department of Environmental Health in 1998 and published in the March issue of Environmental Health Perspectives. Urine specimens from 110 children (ages 2 to 5) residing in the Seattle metropolitan area were analyzed for five dialkylphosphate (DAP) metabolites. These metabolites are biomarkers for organophosphate exposure.

At least one of the metabolites was detected in 89 percent of the children in the spring and 92 percent in the fall. The most noteworthy trend was the association between reported residential pesticide use and elevated urinary DAP concentrations. Children whose families reported pesticide use in their gardens had significantly higher diethyl DAP concentrations than those whose families had gardens but did not use pesticides. Interestingly, only one child tested negative in both the spring and fall. This child's parents reported only organic food consumption and did not employ household pesticides. The methyl and dimethyl DAP metabolites were also significantly greater in samples from children of households that reported using garden pesticides.

The levels of dimethyl DAP ranged up to 0.45 mol/L in the samples from homes where pesticides were applied to gardens and up to 0.15 mol/L in samples from homes where garden pesticide use was not reported. For diethyl DAP metabolites, these values were 0.06mol/L and 0.04 mol/L, respectively. No such associations were noted for pet or household treatments.
Chem. Speak. May, 2001 (Pesticide & Toxic Chemical News, Vol. 29,

Nevada Town Wonders About a Cancer Cluster

By Angie Wagner
Associated Press
Washington Post
Saturday, February 10, 2001

FALLON, Nev. -- A blur of sagebrush, along what's called the loneliest road in America, leads to this small farming and military town that boasts of its simpler way of life. A barber is giving $9 haircuts and there's talk of the annual Hearts O' Gold Cantaloupe Festival.

But soon, the talk turns to the children. To 11 kids, all stricken with leukemia that some fear might have something to do with living in the self-proclaimed "Oasis of Nevada."

For 5-year-old Dustin Gross, it started like the flu. Then came the bruises, and his lips turned translucent. "You can see it in his eyes," Dustin's father said. "When they really start turning dark."

Acute lymphocytic leukemia is the most common childhood cancer, but still rare. Just 2,000 new cases are diagnosed annually in the entire United States. What puzzles people is that 11 of those cases since 1997 have been in and around Fallon, a town of 8,300. Eight cases were diagnosed last year.

This is a cluster, the state health department says. A chance occurrence, perhaps? Or something else that may never be known. The uncertainty has forced the state to ask for help from national experts. While they look for answers, the residents worry.

Mayor Ken Tedford Jr. has lived in Fallon, 60 miles east of Reno, his whole life. His granddaddy was mayor, and his uncle too. "We're just kind of a small town," the mayor said. "People worry about each other a lot."

At the downtown Ideal Barber Shop, which doubles as a motorcycle parts shop, former police officer Lyndell Smiley mentions the water as he talks of the kids. "Nothing wrong with the water, Smiley," barber Joe Rando responded. Water is a common topic in Fallon: It has arsenic levels 10 times the federal standard, and the city has been ordered to clean it up. Arsenic is a naturally occurring chemical that in high concentrations is poisonous. It's sometimes used as an insecticide or to kill weeds, but has never been linked to leukemia. A byproduct of the area's soil, the arsenic has been around so long that many doubt it would be making people sick now. Besides, the children drank from different sources -- city water, well water and bottled water.

The arsenic is so accepted that residents don't seem to mind. "Some more arsenic water?" a waiter at Angelica's Steakhouse asks a customer. A square dance club calls itself the Arsenic Swingers.

Tammi Beardsley has gone over it repeatedly in her mind. "You relive those days. What did I feed him? Where did we go? That's what you do when you're a mom and you're desperate." Her 5-year-old son, Zac, was No. 9, diagnosed in November. He is too sick this day to have visitors or go outside. Too much risk for infection. Zac was born in Canada, but spends summers and part of each winter in Fallon. He never drank tap water, only bottled.

Of course, Zac's cancer might have nothing to do with what he drank or how he lived. Cancer results from mutant genes. But what causes the mutations? The seeds of Zac's disease could have been there since birth, written into his genetic blueprint. The survival rate of this type of childhood leukemia is 80 percent. None of the children here has died.

From 1961 to 1982, the federal Centers for Disease Control and Prevention investigated 108 cancer clusters in 29 states and five foreign countries. No clear cause was found. Since the mid-1980s, no CDC staff have been dedicated full time to investigating cancer clusters. "At this point, we're not finding things that are strikingly in common," state epidemiologist Randall Todd said. "We're beginning to look for other sources of information. What has changed in this community?"

Health officials are looking for a link among the children, who ranged in age from toddlers to 19-year-olds when diagnosed. Each family was asked about their habits and medical history. The only common characteristic: All the children live or have lived in this area. Is something spreading though the community? Or is it a statistical anomaly -- just a coincidence, like flipping a coin 11 times and having it come up heads each time?

Often the cause of clusters cannot be found because science cannot yet identify what triggers them, said Michael Thun, head of epidemiology at the American Cancer Society. "It is extremely

rare in a community to pin down a cause or to exclude chance with confidence," he said. The state has asked for help from the CDC, the National Cancer Institute and outside epidemiologists. Legislative hearings and town meetings are planned. Sen. Harry M. Reid (D-Nev.) is sending top staffers from the Senate Environment and Public Works Committee to investigate.

There's concern about nuclear weapons testing near Fallon in the 1950s. Epidemiologists say ionizing radiation is a risk factor to leukemia, but tests for radioactive substances in the water proved negative.

Some residents blame jet fuel dumped by military aircraft at the nearby Naval Air Station. Or agricultural chemicals. Or something from industrial plants. Or, of course, the water.

Thun said there have been studies of this cancer and its relation to pesticides and chemical exposures to parents, but nothing is conclusive.

The Navy said it has no reason to believe the base is doing anything to lead to the illnesses.

Some residents don't want to hear any more about it. "I think it's a bunch of bull," said Madeline Rando, co-owner of the Ideal Barber Shop. "I think it's just a freak thing." But restaurant workers say they've noticed more customers asking for bottled water. Some parents have brought in water jugs for their children's school classrooms so they can avoid city water.

Dustin showed a picture of himself with no hair. "Leukemia," he said. A softball tournament to raise money for Dustin's medical bills has become the annual "Dustin Gross Fun Day." For now, a community waits. Waits to see if epidemiologists can find a link among the children. Waits to see if any more children will become sick. And waits for its young victims to heal.

Floyd Sands and his daughter moved away from Fallon, but were drawn into this mystery when she was diagnosed with the leukemia in 1999. She was 19 then, and learned of her condition on her son's first birthday. "It's worse than looking for a needle in a haystack," the father said from his home in Mehoopany, Pa. "First you have to find the haystack." 

Dioxin Makes the List of Known Carcinogens

By REUTERS, January 19, 2001

NEW YORK (Reuters Health) - The government has placed a type of dioxin called TCDD on the list of substances that are known carcinogens.

The announcement was made by the National Toxicology program on Friday and is based on ``sufficient evidence of carcinogenicity from studies in humans,'' according to statement released by the National Institute of environmental Health Sciences, a branch of the National institutes of Health (NIH). It is now clear that there is ``acaudal relationship between exposure to TCDD and human cancer,'' the group said.

The term ``dioxins'' refers to a group of compounds that share a certain chemical structure and biological characteristic. Sometimes the term dioxin is also used to refer to the most well-studied and one of the most toxic dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD),according to the Environmental Protection Agency (EPA).

``TCDD is not deliberately produced today but has been found as a contaminant in some herbicides and pesticides, and is formed as an inadvertent by-product of incineration of waste,'' according to the NIH.

The chemical was scheduled to appear in the Ninth Report on Carcinogens, released earlier this year, however the addition of TCDD was held up due to litigation.

Dioxin can cause ``skin rashes, skin discoloration, excessive body hair and possibly mild liver damage,''according to the EPA.

``Because dioxins exist throughout the environment, almost every living creature including humans has been exposed to dioxins,'' according to the EPA. ``The health effects associated with dioxins depend on a variety of factors including: the level of exposure, when someone was exposed, and how long and how often. Because dioxins are so widespread, we all have some dioxins in our bodies.''

Dioxin came to public attention as the contaminant in agent Orange, a controversial herbicide used by US forces in Vietnam. In 1983, the EPA forced the evacuation and demolition of the entire town of Times Beach, Missouri, after the discovery of dioxin contamination on city streets.

Over the past 5 years, the EPA has imposed regulations on major dioxin emitters, including municipal waste combustors, medical waste incinerators, hazardous waste incinerators, cement kilns that burn hazardous waste, pulp and paper operations, and sources of PCBs.

One source likely to be targeted in the future is uncontrolled residential waste burning, such as burning trash in backyards, particularly in rural areas. The agency also is discussing the possible regulation of other sources such as sludge disposal from privately owned waste-treatment facilities and the regulation of other air sources of pollution.

ENTRY AND FATE OF CHEMICALS IN HUMANS

E X T O X N E T
Extension Toxicology Network
Toxicology Information Briefs
Revised 9/93.

ROUTES OF ENTRY

Chemicals, including pesticides, are widely distributed in the environment. Therefore there are many possible sources of exposure to these chemicals for humans. Substances which are in ambient and indoor air may be inhaled into the lungs while those in water or food may be ingested or inhaled through mist or steam (such as in the shower). Direct contact with the chemical is the most prevalent way environmental chemicals can penetrate the skin, but exposure through the skin may also occur as a result of contact with chemical contaminants in air and water (for example bathing or swimming).

A single chemical can enter the body through all three routes of exposure -- inhalation, ingestion and skin penetration (dermal exposure). A compound, such as chloroform, which evaporates readily and which may be found in drinking water illustrates this point. When this water is used for drinking, ingestion is the route of exposure. When it is used for showering, exposure may occur due to inhalation of the steam or mist and from direct contact through the skin. Similarly, pesticide use can involve more than one route of exposure if precautions are not taken. A pesticide which is sprayed can be inhaled during use; penetrate through the skin during mixing and application; and be ingested through food if not washed off hands or food before eating.

ABSORPTION, DISTRIBUTION AND FATE

Once a chemical enters the body, it is often absorbed into the bloodstream and can move throughout the body. The amount absorbed and the rate of absorption depend on the chemical and the route of exposure. This movement of the substance through the bloodstream is called distribution. Through distribution a chemical can come into contact with all parts of the body, not only the original site of entry. In some cases, such contact, distant from the site of entry, can lead to adverse health effects. For example, ingestion of the pesticide paraquat into the stomach can lead to damage to the lungs.

Once a chemical is absorbed into the bloodstream, it can have several different fates. In many cases, it is rapidly removed from the body through the urine or feces. In other situations, it may be stored in various parts of the body, such as fat or bone, and remain in the individual for many years. A compound may also lead to a toxic effect through interaction with certain organs or tissues in the individual or with other compounds in the body.

Often, a substance which is absorbed into the body interacts with particular body chemicals and is changed into one or more other chemicals. This process is called metabolism and the products are called metabolites. Metabolism may lead to products which are easier for the body to excrete and so can protect the body from possible adverse effects. In other cases, however, the metabolites may be more toxic than the original chemical which was absorbed. The variety of products resulting from metabolism may have the same possible fates as the original chemical -- storage, excretion or toxicity.

CHEMICAL PROPERTIES

The particular properties of the absorbed chemical are quite critical to its fate in the body. Certain chemicals are very resistant to metabolism and readily dissolve in fat so that they tend to be stored. Dieldrin is a good example of this type of compound. Other chemicals are more rapidly metabolized and excreted and are gone before they can cause adverse effects. The organophosphate pesticides tend to behave this way at low doses.

AN INDIVIDUAL'S CHARACTERISTICS

The characteristics of the individual who is exposed are also very important in the fate of the chemical. The age, sex, genetic background, previous exposures, diet and other factors play important roles in the way that the body interacts with a chemical and in turn the potential for adverse effects. Thus, the characteristics of both the chemical and the exposed individual are important factors determining the fate of the chemical in the body.

THE TIME COURSE FOR EXPOSURE

In the case of a single event exposure, it is the total amount of chemical to which a person is exposed that determines the severity of the toxic effect, if any. The greater the amount of exposure, the greater the potential for adverse health effects. In some cases, this is due solely to the inherent toxicity of the chemical and, in others, also to the overwhelming of the body's ability to respond. In the latter case, the body may not be able to metabolize the chemical rapidly enough to prevent an increase in concentration to toxic levels. In such a situation, there is a clear threshold above which toxic signs and symptoms appear.

In the case of (repeated) multiple exposures to a chemical, it is not only the total amount of exposure, but also the rate or timing of exposure that is quite important. All processes in the body normally proceed at specific rates so that metabolism, excretion and storage occur during a particular period of time after a chemical is absorbed. For a one occurrence exposure, the time needed for the various processes that breakdown the compound to be completed will determine the length of time that a toxic response, if any, persists.

However, if there are repeated exposures to the same chemical, the situation is more complicated. If there is enough time between exposures so that all of the chemical from the initial exposure is excreted, and no effects persist, then each exposure is essentially independent of the previous one and can be treated as a single exposure. However, if the time between exposures is so short that some of the chemical remains from the first exposure, then a buildup of the chemical can occur. Over time this buildup can lead to levels which are toxic.

The total amount of exposure can have different results depending on whether the exposure occurred all at once or repeatedly over time (the time course of exposure). A high dose given once may have a toxic effect while the same total dose given in small amounts over time will not. For example, drinking several ounces of alcohol at once may cause inebriation while drinking one ounce every few hours may not. Also, a particular dose given a few hours apart may have an adverse effect while the same total dose given a few days apart will not.

SUMMARY

The possible toxic effects of exposure to a particular chemical depends on many factors. These include the characteristics of the chemical and the individual exposed; the route of exposure; the total dose and the time course of exposure. Unfortunately, scientists have not been able to determine exactly how each of these factors will affect any specific individual so that present understanding of chemical exposures provides only general guidance. Minimizing exposure will minimize the potential for adverse effects. In addition, a general knowledge of all the contributing factors will help reveal the situations which have the most potential for adverse health effects and can aid in determining the best ways to manage chemicals.

A new website has been developed by Michigan State University to address the issue of pesticide resistance. The information can be accessed at: http://www.cips.msu.edu/resistance. (MSU Pesticide Notes, March-April 2001).

A new biological fungicide (Contans® WG) has been granted EPA approval. Produced by Encore Technologies, the material is billed as the only biological control product available in the U.S. for controlling Sclerotinia diseases in the soil (caused by S. sclerotiorum and S. minor).