Expert Consensus Panel Re: Domestic Use of Pesticides and Cancer

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John Preston
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1 Expert Consensus Panel Re: Domestic Use of Pesticides and Cancer PREFACE Over the years the Advisory Committee on Cancer Control (ACOCC) of the National Cancer Institute of Canada (NCIC) has reviewed controversial topics. Generally this process takes place over several months and, because of embargoes being in effect while papers are awaiting publication, the conclusions are not available on a timely basis for the Canadian Cancer Society (CCS). Thus, ACOCC has committed to a process that will provide the CCS with more rapid answers to controversial issues based on review of the scientific literature. This document constitutes the product of the second of these rapid response projects. During the past few years the CCS has received enquiries on the subject of the impact of the domestic use of pesticides on cancer risk. A list of commonly asked questions has been compiled and responses have been prepared by a small panel of experts who have reviewed the current published scientific literature. Relevant papers published in English were identified through a computer search. These were augmented with additional studies cited in review articles. These responses represent the conclusions of the panel based on the scientific literature currently available. As the findings of new well-conducted studies are published it may become necessary to update these responses. The panel members included: Tye Arbuckle, PhD Aaron Blair, PhD Helen McDuffie, PhD Howard Morrison, PhD Eleanor Nielsen, RN, BscN, MHSc Len Ritter, PhD Richard Stanwick, MD Barbara Whylie, MB, Bch, BAO Don Wigle, MD, MPH, PhD, Chair September 18, 1998 FREQUENTLY ASKED QUESTIONS What are pesticides? The term "pesticide" is used to describe a broad range of chemicals and biological agents with diverse activity that are designed to control or eliminate un-wanted plants (herbicides), fungi (fungicides) or animals including insects (insecticides, pesticides).

2 1. Do pesticides cause cancer? Most pesticides in use now and in the past are chemicals; biologic pesticides are of recent origin and are unlikely to cause cancer. Chemical pesticides are a broad group of chemicals which have different health effects on humans. Based on expert assessment of human and animal studies by the International Agency for Research on Cancer (IARC), only one class of pesticides, arsenicals, is known to cause cancer in humans. IARC has classified two specific pesticides (captafol and ethylene dibromide) and occupational use of non-arsenical insecticides as probable causes of cancer in humans. IARC classified several pesticides as possible causes of cancer in humans; these include amitrole, aramite, chordane, chlordecone, chlorophenoxy herbicides (weedkillers), DDT, dichlorvos, heptachlor, mirex and toxaphene. The human evidence underlying the IARC ratings comes mainly from epidemiologic studies of persons occupationally exposed to pesticides i.e. at levels substantially higher than those of the general population. The risk to an individual is related to the degree of exposure. There are many different types of exposure ranging from those experienced by workers engaged full-time in pesticide application throughout their working year, down to those experienced by the general population in the course of daily life. Cancers linked to occupational exposure to pesticides include: non-hodgkins lymphoma: the herbicide 2,4-D, the insecticide DDT, diazinon and arsenical insecticides ovarian cancer: triazine herbicides lung cancer: arsenicals non-melanoma skin cancer: arsenicals 2A. What do studies say about a possible relationship between the domestic use of pesticides and cancer? Very few studies have been done on this topic. There are two main reasons for this: (i) it is very difficult to measure exposures in the home; most people are not aware of the sources of exposure in their homes (e.g. well contamination, flea treatments for pets, house dust); (ii) even when sources of exposure are identified, it is difficult to measure the "exposure dose". Studies need to be done about how to measure and confirm exposure. In addition, because both the exposure levels and the likely cancer risk are probably small, effective research needs large populations to study. Nevertheless some studies have suggested that there is a link between exposure to some pesticides in the home setting and brain cancer, Wilm's tumour and leukaemia in children. These associations need to be clarified through further research. 2B. What is the usual and/or most dangerous means of exposure to domestic pesticides (e.g. inhalation, ingestion, skin)? All routes of exposure are important but different routes are important for different substances and different conditions. In general skin contact leads to the highest exposure. For example, a child sitting or playing on a lawn after spraying will experience a higher exposure level than he/she will by inhalation (breathing into the lungs). Ingestion (swallowing and entering the stomach and intestines), especially by children is very

3 dangerous and should be avoided at all costs. Care must be taken that all pesticides are stored and handled safely. 2C. What is the best way to dispose of pesticides? It is advisable to contact one's municipal authorities about disposing of unused quantities of pesticides. 3A. Do pesticides cause specific types of cancer? The Harvard Report on Cancer Prevention (1996) states "the designation of a substance as a human carcinogen (cause of cancer in humans) is a matter of collective judgement". In animals studies the evidence suggesting an association between some pesticides and some cancers is quite compelling. Evidence from studies of humans is based on only a relatively small number of good studies. In 1991 the International Association for Research on Cancer reviewed over 50 pesticides with respect to their carcinogenicity in humans. Of these, one (arsenic), was classified as a known cause of cancer in humans, and 2 were categorized as probable human carcinogens (occupational exposures in spraying and application of non-arsenical insecticides and the fungicide captafal). A further 14 were categorized as possible human carcinogens and there was sufficient evidence to assess the remaining compounds. Besides those noted in question 1. associations have been observed in a small number of studies between exposure to some pesticides and some types of cancer but there have also been studies showing no association; more research is required before these relationships can be determined. Examples of these associations include: * breast cancer and organochlorines; * prostate cancer and organochlorines; and * brain cancer in children and pesticides used to treat fleas on pets. Many pesticides, both old and new, have not been studied with respect to their potential carcinogenicity. 3B. How does the cancer risk of pesticide exposure in the home setting compare with other cancer risks? The Harvard Report on Cancer Prevention 1996 summarised what we know from epidemiological research on what does and does not contribute to the risk of developing cancer. As shown in the list below, this report suggests that all environmental pollution is responsible for 2% of cancer deaths. Percentage (%) of Cancer Deaths Attributable to Established Causes of Cancer tobacco 30% adult diet/obesity 30 sedentary lifestyle 5 occupational factors 5 family history of cancer 5

4 viruses/other biologic agents 5 perinatal factors/growth 5 reproductive factors 3 alcohol 3 socioeconomic status 3 environmental pollution 2 ionizing/ultraviolet radiation 2 prescription drugs/medical procedures 1 salt-other food additives/contaminants 1 Overall, domestic exposure to pesticides probably causes less than 1% of cancer deaths and is therefore a small but potentially important concern. In making decisions to use pesticides in the home individuals should consider what level of risk they are willing to assume and consider all of the available alternatives. 4. If the evidence is inconclusive, why? Why do studies show different answers to these questions? Humans are complex and the science of studying the risks of low level exposures in humans is difficult. Effects shown in animals cannot be assumed to necessarily apply to humans. In addition, the risks that have been observed in humans are relatively small and difficult to measure accurately. Larger and better studies are required to determine cause and effect relationships. 5. Do fruits and vegetables (especially garden grown) need special cleaning before consumption? All fruits and vegetables should be thoroughly washed before eating. This is particularly important for reducing health risks associated with germs. Commercially available fruit and vegetables are subject to regulations and are monitored by the Canadian Food Inspection Agency for contamination. (Market basket surveys are done on produce). Studies have shown that in more than 80% of retail produce no pesticide residues are detectable using current analytic methods. Targeted inspection is also carried out on imported produce. With home grown fruit and vegetables there is no control on use of pesticides and residue levels have not been assessed. Residues could be high if persons apply excessive amounts of pesticides. Individuals who grow their own fruit and vegetables should be sure to apply pesticides safely according to manufacturer's instructions, avoid application of pesticides within 2 weeks of harvesting and wash produce thoroughly before eating. 6. We use weedkillers on our lawn. Is there a cancer risk for our family? The risk associated with exposure to weed-killers through lawn spraying has not been clearly shown. However, the possibility exists. Individuals considering lawn-spraying must therefore make their own decisions about accepting some level of risk. Because the possibility of risk exists it is advisable to minimise one's exposure by wearing protective clothing, washing up immediately after spraying, following manufacturer's instructions and keeping children and pets off the lawn following

5 spraying according to instructions (at least 24 hours and often longer depending on climatic conditions and type of herbicide used). In the case of granular applications residues can remain longer than 24 hours. 7. Our neighbours have their lawn sprayed with weedkillers. Is there a cancer risk for our family? There is little direct information about this situation; however, such as there is suggests that exposure is either absent or exceedingly low. 8. We use insecticides on our garden/trees. Is there a cancer risk? Fewer human studies have been done on insecticides than on herbicides. The risk associated with exposure to tree-spraying has not been clearly shown. However the possibility exists. Individuals considering lawn-, shrub- or tree-spraying must therefore make their own decisions about accepting some level of risk. Because the possibility of risk exists it is advisable to minimise one's exposure by wearing protective clothing, following manufacturer's instructions with regard to safety practices for application and delaying harvesting at least 2 weeks after spraying. With home grown fruit and vegetables there are no regulations on use of pesticides and residue levels have not been assessed. Individuals who grow their own fruits and vegetables should be sure to apply pesticides according to manufacturer's safety instructions, avoid application of pesticides within 2 weeks of harvesting and wash produce thoroughly before eating. 9. We have used pesticides in our house to control insects. Is there any risk? Only pesticides intended for indoor use should be used. Indoor use of pesticides poses increased exposure which can increase risk. Pesticides used in the home remain longer than those used outdoors. The decision to use pesticides indoors should be made only after careful consideration of alternatives. As with other applications exposure should be minimised through application of safety practices: wear protective clothing; follow manufacturer's instructions; keep children and pets away from areas of application according to manufacturer's instructions; if possible open windows; leave the premises for the recommended period following application; wash up immediately. If fumigation for termites or other pests is necessary it should be done professionally; a reputable firm should be used; the recommended period of time out of the home should be strictly observed. 10. What are the most important sources of pesticide exposure in the home setting? Sources of pesticide exposure within the home may result from pesticide use within the home and from tracking of pesticides into the home from an outside source. Common sources of pesticide exposure from use within the home result from use of flea collars and other flea treatments on pets; wood preservatives and burning of preserved wood in fireplace; inappropriate indoor use of pesticides; pest strips; pesticide-contaminated house dust. Exposure also results from tracking residues in from outside use. This is particularly of concern in farming communities. Individuals who work with pesticides should be aware of this and always take appropriate precautions including removing footwear and clothing before entering the home.

6 Pesticides can accumulate in carpets and persons living on farms, in particular, may wish to consider alternatives to carpets. 11A. Is there a greater risk of developing cancer if I live in a farming community? Very few scientific studies have addressed this question. The indications are that in exceptional circumstances there may be increased exposure related to well-water contamination and to living next to intensively sprayed farmland. However it is likely that risk is very low among those who are not directly involved in spraying. 11B. If an individual has other risk factors for cancer do pesticides compound the risk? Very few studies have addressed this question. However scientists believe that there is interaction between risk factors for many diseases. This has been shown for exposures other than pesticides. For example, exposure to asbestos has been shown to compound the risk that cigarette smokers will develop lung cancer. It is speculated that children may be more susceptible than adults to increased cancer risk through exposure to pesticides. 12. Does pesticide use contaminate our water supply? There is evidence to indicate that the use of pesticides, particularly in agricultural settings, produces very low levels of pesticide residue in water supplies. 13. Why are we waiting for evidence before "doing something" about pesticides -- too much damage could be done while waiting for studies to be completed and to evaluate long-term effects? In fact many actions have already been taken by governments and policy makers. These include: * regulations requiring the use of protective equipment by applicators * regulations limiting the amount of pesticide used per acre in farm spraying * monitoring residue levels through market basket surveys * progress in the development of pesticide alternatives including biological and organic products and integrated pest management programs * elimination of dioxin contamination in manufacturing processes * funding of research into the health effects of pesticide exposure. In addition, a 1994 federal survey of over 20,000 samples of fruits and vegetables in Canada was done using sensitive methods to detect pesticide residues. 85% of samples contained no detectable pesticides. Less than 3% of all samples contained pesticides above Canada's maximum limits. These actions have resulted in measurable progress. For example, reported pesticide use in Ontario declined from 8,700 to 6,200 tonnes of active ingredient per year between 1983 and This is a 28.3% decline. Before taking a step such as banning or severely restricting the use of pesticides, a large body of

7 evidence supporting the contemplated action is required. In some cases there is not enough evidence to justify taking large-scale societal action. A decision to eliminate the use of pesticides would be such a large scale societal action since there are known health and economic benefits from the use of these products. These benefits include the increased production of fruits and vegetables which makes produce affordable and readily available. Fruits and vegetables are known to reduce cancer risk. However it is always prudent to take action to minimise exposure. 14A. Do pesticides on fruits & vegetables cause cancer? Food is popularly perceived as an important source of exposure to pesticides. However, it is generally agreed that the use of pesticides in food production has improved crop yields and has increased the quantity of fresh fruits and vegetables in the diet, thereby contributing to significant improvements in public health. Indeed, the Committee on Diet and Health of the U.S. National Research Council noted that there is no evidence that pesticides or natural toxins in food contribute significantly to cancer risk in the U.S. In its report, the Committee also noted that increased consumption of diets high in plant foods such as fruits, vegetables, legumes, and whole grain cereals (invariably related to an increase in availability and a decline in cost) are associated with a lower occurrence of coronary heart disease and several malignancies involving the lung, cólon, esophagus, and stomach. Although the pathophysiology underlying these effects is not completely understood, the decreased cancer risk may reflect the fact that diets rich in plant foods also tend to be low in total fats. A high fat diet has been associated directly with the risk of certain cancers. Indeed, of all dietary factors, fat has attracted the most interest. Similarly; diets rich in fruits and vegetables that contain complex carbohydrates such as starches and fibre, vitamins, minerals, and trace elements also confer protection against certain cancers and coronary heart disease. Epidemiologic studies have suggested that consumption of carotenoid-rich foods are associated inversely with the risk of lung carcinoma whereas animal laboratory studies consistently provide strong evidence that certain retinoids prevent, suppress, or retard the growth of chemically induced cancers at a number of anatomic sites, including the esophagus, pancreas, colon, skin, breast, and bladder. The Panel concluded that despite consideration of worst- case hypothetic scenarios, the benefits of dietary modification to include more fruits and vegetables far outweigh the potential for adverse effects "which is minimal, if any." The benefits of a diet rich in fruit and vegetables are also emphasized in Canada's Guidelines to Healthy Eating. However complacency must be avoided. Continued vigilance is necessary to maintain and improve upon low levels of contamination and to limit imports from sources with less stringent safety practices. 14B. Is organically grown produce safer? Approximately 90% of commercially grown Canadian produce contains no measurable pesticide residue. It is important to ensure that families receive an adequate supply of fresh fruit and vegetables. There is no evidence that organically grown produce conveys more benefit than nonorganically grown produce. 14C. Has there been enough research in this area? All of the evidence available has been collected on a broad base There is a need for specific studies of exposure on subsets of the population including children, vegetarians, pregnant women, people who grow their own fruit and vegetables etc. 15. What concrete things can people do to limit their exposure to pesticides? carefully reflect on the necessity of any application of a pesticide become informed about alternatives familiarise yourself with and follow label/manufacturer's instructions conscientiously

8 use recommended safety and protective equipment have a professional undertake the application investigate the professional applicator's reputation before entering into the contract avoid skin contact. If skin is exposed, wash the material off immediately always ensure that pesticide are stored safely always wash fruits and vegetables before eating be particularly careful about protecting children from exposure to pesticides both through application and through careless storage. (Children may be more susceptible, may put contaminated material in their mouths, play in contaminated areas such as lawns and carpets, hug pets with flea collars or following flea treatments etc) 16. What information is available regarding golfing and harmful exposure to pesticides? Very few scientific studies have addressed this question. The indications are that in exceptional circumstances there may be increased exposure related to well-water contamination and to adjacency to intensively sprayed golf courses. However it is unlikely that exposure is significant among those who are not directly involved in spraying. 17. What do we know about the safety of exposure to mixtures of pesticides? Laboratory studies have assessed the effects of individual chemicals. Human studies study the effects of mixed exposures i.e. "real life" exposures. Hence studies referred to in previous answers refer to exposure to multiple agents. Evidence currently available does not suggest a strong multiplicative effect re risk through exposure to more than one agent. Comments and suggestions about this website may be sent to: webadmin@cancer.ca

Organic Vegetables: High Levels of Heavy Metals!

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