Expert Consensus Panel – Domestic Use of Pesticides and Cancer

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

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).

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
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

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 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.
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 1993. This is a
28.3% decline.

Before taking a step such as banning or severely restricting the use of pesticides, a large body of
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
non-organically 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




• 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?