Wet weather, more pests (and more pesticides)

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by Louise Kosta
Chief writer, The Human Ecologist

"Generally, whenever you have mild winters and large amounts of rainfall, you are going to have an incidence of...[more] fungal diseases, weeds and insects, especially," a spokesman for the American Crop Protection Association told Chemical & Engineering News in March 1998. Weather conditions during the 1997-1998 winter caused the ACPA to anticipate increased use of insecticides, fungicides and in some areas, herbicides. If you're in the pesticide industry, that's good news: sales and profits go up with increased demand.

The Centers for Disease Control and Prevention, and researchers at Johns Hopkins University, also predicted that insecticide use to prevent the spread of disease by ticks, mosquitoes and other biting insects would also increase in response to weather-related effects on insect proliferation. If you're concerned about health, this is a double dose of bad news: With increased insect populations the risk of insect-borne disease increases-- but with the increased use of pesticides to control those insects, the risk of pesticide poisoning increases too. (For more information about ticks and health, see CDC's Morbidity and Mortality Weekly Report for June 19, 1998; see also “Tickborne illness: It's not just Lyme Disease anymore.")


Pesticides in foods -- and elsewhere

"Crop protection" sounds as if it should be of concern only to farmers and agribusiness. But pesticide residues in food are of concern to both the public and to regulators. The public has a proven track record of responding with alarm and outrage at the idea of pesticide residues in foods: witness the "Alar in apples" incident of nearly a decade ago. It is less often noted that the public also expects the food supply to be abundant and inexpensive. These expectations run contrary to public fears about pesticide residues, according to some commercial food producers: Their view is that you can't have it both ways, and that pesticide use has made America's abundant and inexpensive food supply possible. Moreover, they claim, federal regulations have set such stringent limits on pesticide residues in food that residues--when they're present at all--pose no threat to health.

Others disagree, not just about pesticide residues in food, but about pesticides in the environment generally. Pesticides in food represent only part of the pesticide exposure picture, they say. Pesticides are also present in water, in the air, and in indoor and outdoor environments where people can come into contact with them. People can become exposed to similar pesticides, or the same pesticides, through the food and water they ingest, the air they breathe, the surfaces they touch. And it is the combined effect of all these exposures that must be considered when the impact of pesticides on health is discussed.

This second viewpoint has long been held by environmentalists and by those who have concerns about overall environmental exposures and human health. It has become more "mainstream" in recent years to take this approach to pesticide-related health risks. The Environmental Protection Agency has long been engaged in a "re-registration" process for pesticides. Under the terms of the Food Quality Protection Act of 1996, the agency is required to reassess the tolerances for all pesticides currently in use, and to consider as a group all pesticides that have a "common mechanism of action or mode of action." (Thus organophosphate pesticides that act similarly will be considered together.) This assessment involves looking at the total effect of combined exposures from food, air, water, and contact. Based on the total exposure for each group of pesticides with similar action, tolerances for the pesticides may be revised, and some uses of some pesticides may be restricted or banned altogether.

Such changes lie in the future, however--the new reassessment process is just beginning. In the meantime, circumstances that favor the proliferation of pests-- such as the mild wet weather experienced in the past year in the US-- also increase the likelihood of more frequent exposure, and perhaps larger individual exposures, to pesticides. One of the pesticides likely to be called into use to control disease-bearing insects and insects that threaten crops and property is chlorpyrifos.



Chlorpyrifos is an organophosphate pesticide in wide use in the US. Like other organophosphate pesticides (over 40 were approved by EPA for various pest control uses as of 1997) chlorpyrifos is toxic to the human nervous system. It inhibits a crucial enzyme in the nervous system, which allows a harmful buildup of another nervous system chemical. Depending on where the buildup occurs, muscle twitching or cramping, glandular secretion, or sensory and behavioral disturbances can result. In severe cases, effects may be lasting and debilitating. In extreme cases, death can result.

Chlorpyrifos is used against some of the same pests that will be burgeoning this year because of the mild wet weather: termites, mosquitoes, ticks, and fleas-- as well as many agricultural pests. But chlorpyrifos, like other pesticides, is not without its own downside: It's a poison. Nevertheless, it is widely used, and many people are exposed to it.

"As a result of [its] widespread use, there have been numerous exposures and poisonings [associated with chlorpyrifos]," according to a 1997 EPA memorandum. EPA estimated that about 3000 such cases are reported to Poison Control Centers each year, though the agency also noted that chlorpyrifos poisoning "can be easily misdiagnosed, which suggests that some individual cases of poisoning are missed."
In June 1997, EPA and the pesticide industry agreed to reduce consumer exposures to chlorpyrifos. The reductions were to be accomplished by eliminating the pesticide from pet products and from foggers. In addition, the manufacturers were to "take steps to ensure" that chlorpyrifos was not applied to toys, drapes, and furniture; a new warning label to this effect was due to appear on chlorpyrifos products in 1998.

But a recent study suggests that these measures may not protect consumers from chlorpyrifos.


Recent research on chlorpyrifos and health

"By far, principal pathways that cause children and adults in the United States to be exposed to pesticides are in the home," begins a recent study of chlorpyrifos residues in the home. The scientists observed that, while this is a truism, few actual measurements of such exposures had been done. They performed an experiment in order to measure pesticide exposure from nondietary ingestion and skin contact arising from an indoor application of chlorpyrifos. In the study, two identically furnished apartments were treated with Dursban (chlorpyrifos) broadcast sprays applied by a licensed pest control operator using approved application methods. This ensured that the pesticide would not be present in amounts greater than would result from standard application methods. Windows in the apartments were kept closed during treatment and for two hours afterwards; then they were opened for four hours and a fan was run near a window. Afterwards the windows were kept closed for the remaining two weeks of the study. This partial ventilation was intended to approximate homeowner behavior during and after pest control applications.

At intervals during the study, air, surface and toy samples were taken for analysis. The pesticide underwent two phases after application. First it was deposited on treated surfaces as particles. Then over time, it gradually vaporized into the air. Once in this 'gas phase,' the pesticide could diffuse and attach itself to various surfaces in the rooms. Plush polyurethane foam toys, mattresses and pillows proved to be especially likely to be contaminated by these pesticide residues.

The scientists drew several conclusions from this study. The first was that indoor surfaces such as furniture and toys, can act as reservoirs for pesticides. That is, they can accumulate on certain surfaces after the initial application. Such pesticide residues from indoor treatments can be a significant source of ongoing exposure, particularly for small children who play with plush toys that were present during the pesticide application. Small children are most at risk from this type of pesticide residue because they put things (including their toys and their hands) into their mouths.

The scientists also concluded that the interval of time between pesticide application and occupant re-entry of the treated space as currently described in "proper application" instructions is inadequate to protect small children from pesticide residues. The scientists also pointed out that application instructions that use drying of the pesticide as a means to determine when the space can be safely re-occupied do not protect human health.

The scientists estimated that the contribution of pesticide residues from routine indoor treatments, plus dietary intake of pesticide residues in food, can amount to cumulative body burdens of pesticides that exceed current reference dose levels as well as current allowable daily intake levels. (A reference dose is the amount of a substance to which a person can be exposed without harm over a lifetime.) In fact, exposure levels estimated on the basis of samples taken in this study by themselves exceeded both reference dose and allowable daily intake levels.

The scientists stated: "[C]hildren's toys and other plush objects ...must not be stored in open rooms for at least a week after a single [pesticide] application.... [A] long-term consequence of leaving toys out in rooms routinely treated with pesticides such as those used in our study, could be an accumulation of high levels of pesticides in toys and other plus objects made with polyurethane foam."

Environmental Health Perspectives, in which this study appeared, noted that this study" ... signals that regulators can no longer simply measure air concentrations to determine if dangerous levels of certain pesticides exist in a room."

This study has other implications as well. The scientists' emphasis on pesticide contamination of toys, while very important, obscures the importance of another finding in this study: Pesticide residues also accumulate in other household items with which occupants have long and intimate contact. These include pillows and mattresses, and other foam-upholstered furniture.

Lack of emphasis on these items may encourage some people to think that indoor pesticide residues only pose a problem for families with small children, and that it can be solved simply by removing toys from the premises before pesticide applications and not re-introducing them into the premises for a week after treatment. This may solve the toy problem, but leaves the less portable bed and other foam furnishing problem unaddressed. This may be of particular importance to people with chronic illness who spend long periods of time in bed or resting on upholstered furniture, either at home or in long-term care facilities.

This study did not investigate the potential of pesticide particles to adhere to carpet, or the potential of pesticide vapors to accumulate in foam carpet padding. This may be of importance not only for homes, but for schools, health care facilities, office buildings and other carpeted public places. Chlorpyrifos residues on indoor surfaces may migrate into the air where it can be breathed, and from which it can be deposited onto other surfaces which can in turn become exposure pathways for people who come into contact with them.

Another recent study looked at prenatal exposures to pesticides. Researchers identified mothers of children who had participated in an earlier study of childhood brain tumors. In that study, more than half the mothers had a child with such a tumor. The researchers interviewed mothers who had participated in the earlier study, both those who had children with brain tumors, and those whose children did not have brain tumors. The researchers asked the mothers about home pest control while they had been pregnant with the child who had been in the earlier study.

Although the researchers asked about a variety of pesticides, only flea and tick foggers and sprays (some popular types of which have contained chlorpyrifos in the past) were associated with increased risk of brain tumor in the children-- and the risk increased with the number of treatments. The children most likely to have brain tumors were those of women who had prepared, applied, or cleaned up these products while pregnant- especially if they ignored product instructions. Overall, prenatal exposures to these products were twice as likely in children with brain tumors, and five times as likely in that whose tumor was diagnosed before age 5.


Accidents will happen -- even when you hire pros

Warm damp weather conditions favor termites, which threaten property. One of the major non-agricultural uses for chlorpyrifos is for termite control. Most property owners and managers rely on professional structural pest control services to do termite pest control. However, this has not always proved to be protective of the health of either the building residents or of the pest control personnel themselves.

EPA quotes a 1994 statement from DowElanco (manufacturer of Dursban) in which the industry claimed that they had "never observed significant depression in red blood cell cholinesterase or symptoms of cholinesterase inhibition [both symptoms of organophosphate poisoning]" in the twenty years they had manufactured the pesticide with "regular monitoring of workers' health status." Moreover, the company said, "In 15 years of use in the marketplace, there have been no incidences that we are aware of where signs of symptoms of organophosphate poisoning have occurred with the use of chlorpyrifos." EPA pointedly comments that documents supplied to EPA by DowElanco in 1994 belie the company's claims: the documents contain over 200 reports of alleged human health effects that the company had collected over ten years but failed to report to EPA.

"Clearly, "EPA says in a 1997 memorandum, "PCO [pest control operator] applications of Dursban in the home or at work environment are overwhelmingly responsible for the majority of reported cases [of health effects including peripheral neuropathy (a chronic nerve condition), chronic neurobehavioral effects, and 'symptoms consistent with multiple chemical sensitivity']." "Termiticide applications of Dursban TC appear to be a particular hazard which is not surprising given the large volume of material used per application and the relatively poor education and training reported among many PCOs."

In the 1997 memorandum, EPA lists ten incidents in which pest control operators were reported to have been directly responsible for building occupant exposure to chlorpyrifos: In one instance, a pest control operator who had treated a home once per year began to treat it weekly; after three months, the entire family residing in the home became ill. In another instance, a family vacated their home during chlorpyrifos treatment and on their return, found pesticide dripping down the interior walls of their basement. In another instance, a family incurred a reported $150,000 in medical and clean-up bills after a pest control operator drilled 98 holes and injected chlorpyrifos into them-- resulting in 96 injections of the pesticide going into open space

On the competence of PCOs to handle pesticides safely, EPA cites a "biased, self-selected" sample derived from a newsletter for PCO companies. The newsletter published an exam intended to assess whether PCOs have sufficient mathematical skills to perform their work (such as mixing dilutions of pesticides prior to applications). Those who took the test on average got only 52% of the answers right. While this survey was hardly scientific, it suggested to EPA that requirements for PCO certification may need to be upgraded "for pesticides like chlorpyrifos that can result in damage to property and significant adverse health effects that may cost thousands of dollars per case."


In the future, fewer pesticides?

In late May 1998, the Wall Street Journal and the Washington Times reported that some organophosphate pesticides may be canceled under the 1996 Food Quality Protection Act, according to officials at the White House, the EPA, and the US Department of Agriculture. However, these sources also reportedly said that, as a result of industry pressure, a 50-member advisory panel has been formed to find ways to limit negative impacts on agriculture from pesticide cancellations. The advisory panel includes members from both the EPA and the Agriculture Department, and is to base its decisions on "sound science" to enable farmers to transition to alternatives to banned pesticides, and to obtain "input from affected constituencies." The EPA plans to decide on the organophosphates by August 1999.


  • Environmental Health Perspectives [Forum], January 1998.
  • Gurunathan, S et al., Accumulation of chlorpyrifos on residential surfaces and toys accessible to children. Environmental Health Perspectives 106(1): 9-16. January 1998.
  • OPPT Newsbreak, May 29, 1998
  • J.M.Pogoda and S. Preston-Martin, Household pesticides and risk of pediatric brain tumors. Environmental Health Perspectives 105(11),1214-1220, November 1997.
  • J. Raloff, Science News , December 13, 1997.
  • Ann Thayer, Chemical & Engineering News, March 23, 1998.
  • Wall Street Journal, "Panel Will Ease Farmers' Transition to a Probable Ban on More Pesticides." 29 May 98, B7B. In OPPT Newbreak May 29, 1998
  • Washington Times, "Panel Tries to Soften Pesticide Ban Impact. Farmers Likely to Lose Favorite Chemicals." , 29 May 98, A6. In OPPT Newbreak May 29, 1998


At a Glance: Pesticide close-up -- chlorpyrifos c. 1997

  • First registered: 1965
  • Increase since 1975 in number of chlorpyrifos products produced: twenty-six fold
  • Number of products containing chlorpyrifos: 972
  • Pounds of chlorpyrifos used per year in the US: 19-27 million (estimated)
  • Pounds of chlorpyrifos used in agriculture: 9.0 - 13 million
  • Principle crop use: field corn (4.0 - 7.0 million pounds)
  • Pounds of chlorpyrifos used in households and other non-agricultural settings: 10-14 million
  • Principle non-agricultural use: termite control (5.0 - 7.5 million pounds)
  • Remaining non-agricultural outdoor use: 4.0 - 4.5 million pounds
  • Remaining non-agricultural indoor use: 1.0 - 2.0 million pounds
  • Percentage of US households having chlorpyrifos products on the premises: 18%
  • Other locations where chlorpyrifos is used indoors: commercial buildings (offices, motels), industrial buildings (warehouses, food handling establishments) and institutional buildings (schools, nursing homes, hospitals)
  • Total annual number of unintentional pesticide exposures reported to US Poison Control Centers (1994, the most recent year): 109,761
  • Percentage of unintentional chlorpyrifos exposures affecting children under 6 years old: 49%

Sources: US EPA OPPT 7506C, Chlorpyrifos Q & A . February 1997. US EPA OPPT, Review of chlorpyrifos poisoning data [memorandum]. January 14, 1997.


Chlorpyrifos in the environment

Millions of pounds of chlorpyrifos are used outdoors each year, in agricultural and non-agricultural applications. It does not simply vanish once it accomplishes its pest control mission, however. Like chlorpyrifos indoors, it persists in several phases, and can move through the environment, sometimes traveling long distances in rivers and streams. Contamination of the Chesapeake Bay has been studied for some time, because many streams in the northeast US drain into it, carrying pollutants along with the water. In 1993 a year-round survey of the Chesapeake Bay mainstream detected chlorpyrifos in 100% of air and water samples taken. Water concentrations were highest in March and April, lowest in September. Air concentrations were highest in June, lowest in March. Scientists conclude that during mid to late summer, chlorpyrifos in the atmosphere makes a significant contribution to Bay contamination. For more see LL McConnell et al., Environmental Science and Technology 31(5) 1390-1398, 1997.

Environmental Science & Technology News & Research Notes, May 1997



HEAL Board comments on USDA's Organic Food Standard proposed rule

Organic food -- food as free as possible from contamination with harmful environmental, agricultural and pharmaceutical chemicals--is of vital concern to many HEAL members. Unlike other groups, whose concerns about organic food stem from broad environment and health concerns, HEAL's membership represents a group for whom organic food is not a strong preference, but a survival issue

In December 1997, the Department of Agriculture posted its proposed rule for setting a federal standard for organic foods. In April 1998 the public comment period on the rule closed. HEAL's Governing Board made the following comment to the USDA regarding their proposed organic food standard:

"The Human Ecology Action League (HEAL) has a deep concern regarding the USDA's proposed standards for organic foods. In essence, the USDA rules would change the standards of purity for organic foods as we now know them. Many HEAL members are very sensitive to the low-level effects of pharmaceuticals, pesticides and other chemicals which would enter the food chain under the rules now proposed by the USDA.

"By allowing the use of genetic engineering, sewage sludge, the intensive confinement of animals, and irradiation in processing, truly organic foods would no longer be available, which would place the health of HEAL members in jeopardy.

"It is commendable to try to set nationwide standards but not at the expense of the present organic farming industry and the ultimate consumers. If the proposed USDA rules go into effect, HEAL members will not have available a commercial source for 100% organic food products.

"It is regrettable that the USDA plans to label processed foods "organic" even though they may contain up to 5% of non-organic products. The term "organic" should not be used unless the product is 100% organic. The present organic food industry has not operated in that manner for over 20 years. This change would mean that HEAL members could never reply upon using processed foods because of low-level chemical effects from non-organic products."

In early May 1998, Chemical & Engineering News reported that USDA had received an estimated 200,000 comments about the proposed standard. The overwhelming majority of the comments objected to permitting foods raised on sewage sludge, or irradiated or bioengineered foods, to be considered organic. C&E News reported that "All observers expect the [final] rule to reflect the preponderance of comments" on these issues.

However, this may not be enough to satisfy the organic food industry. Although Congress established a National Organic Standards Board in the 1990 Organic Food Production Act, USDA largely ignored the Board's recommendations in its proposed rule. Secretary Dan Glickman has stated that USDA's goal is "to develop a final rule that the organic community and all the public can embrace." As of late May, the Organic Trade Association had not specified acceptable changes in the proposed rule, but had already begun to discuss setting up an independent accreditation board for organic producers.

Stay tuned: USDA's final organic food rule is expected to be out by the end of 1998. –
[] HEAL Public Information Committee


  • HEAL Governing Board, Comment to USDA regarding proposed organic food standard. April 1998.
  • B. Hileman, Chemical & Engineering News, May 11, 1998.