Why Canadian Physicians Are Concerned
about the Policies Regulating Pesticide Use
Presentation by Kelly Martin, M.D.,
to the Standing Committee on the Environment
Review of the Evidence
In 1997 the Ontario College of Family Physicians requested a review of
the evidence on pesticides and human health effects, which I authored.
The increasing concern by the public created the demand for physician
knowledge in this area. The Cochrane approach, which uses a pre-stated
methodology to search the literature and assess the quality of studies,
was used to assess the evidence on the effects of pesticides on the pediatric
and adult population in Canada.
Serious Problems with Pesticide Regulation
This review led us to conclude that there is a serious problem with the
amounts of pesticide that the population is exposed to, particularly the
pediatric population. As well, there are great deficiencies in the way
in which risk is being assessed in Canada, underestimating the amounts
and the effects of pesticides on the human population. In the research
that has evaluated this risk, it is fair to conclude that the number and
quality of studies done on each specific health outcome varies, particularly
in the ability to quantify exposure to pesticides. However, the combined
evidence from animal and human studies is sufficient to create concern
regarding the health effects of pesticides at the levels that Canadians
are presently exposed. We will never have the opportunity to randomly
and blindly assign human subjects to pesticides and compare their health
to those that are unexposed. Thus, as in most areas of medicine, we must
rely on observational studies that can provide very sound evidence in
conjunction with animal studies.
Producers must demonstrate that pesticides are safe. In similar situations
in the past, we have waited decades to take action in situations while
epidemiological evidence mounts and those with financial interests argue
for evidence of cause and effect. This has led to the 20+ year delay in
taking action on cigarettes, lead and numerous other toxins. The public
pays high costs for these delays: in their health, in the financing of
cleanups, further research and health care costs. More recently, the HPB
has officially adopted the "Precautionary Principle" and is now in the
position to apply it, to avoid the mistakes made in the past. If the Health
Protection Branch is truly in existence to protect the health of Canadians,
and is to live by its agreement to implement the precautionary principle,
then it must now take some concrete action on the testing and use of pesticides.
It is no longer acceptable to expect the scientific community to prove
beyond a doubt that there are serious health implications while the public
pays for the health care costs, clean ups and years of research. With
reasonable evidence of harm, producers of pesticides must now be responsible
to prove beyond a doubt that these chemicals are safe.
The Effects of Pesticides on Human Health
The following findings are of particular interest in the review of the
importance of policy on pesticide regulation.
National Research Council (US) Report
Some of the most thorough review of the evidence comes from the National
Research Council (US) report on Pesticides in the Diets of Infants and
Children. This is an impressive committee of researchers, physicians and
risk assessors who conclude that:
Infants and Children Are at Greater Risk from the Effects of Pesticides
Studies of fungicides, herbicides and insecticides demonstrate that each
of these compounds is more toxic to the newborn than the adult. This has
very practical implications. For example, the presently acceptable levels
of aldicarb on watermelons is such that a 10 kg child could easily consume
enough of the pesticide to experience acute toxicity, including vomiting,
seizures and respiratory failure.1
Pesticides are effective in killing pests through their neurotoxic effects.
Infants appear to be particularly susceptible to the effects of these
pesticides because they have incompletely developed acetylcholinesterase
systems and their immature livers cannot detoxify these compounds.2
We Cannot Predict the Risk of Infants and Children on the Basis
of Adult Evidence
A number of researchers have demonstrated that age-related differences,
particularly in the effects of pesticides on neurologically mediated motor
activity, could not have been predicted on the basis of the studies that
are presently being used in risk assessment.2
The research demonstrates that more sensitive indices need to be used
to monitor potentially vulnerable systems in infants and children, including
the hormonal and reproductive systems, the immune system, and the neurological
and behavioural systems.
The Use of Animal Evidence Is Not Sufficient for Predicting Human
The evidence suggests that human infants and children are much more susceptible
to the effects of pesticides, particularly organophosphates and carbamates,
than animal species.2 The present assessment
of the risk of pesticides is almost exclusively based on animal studies
and this may greatly underestimate the risk to humans, particularly infants
Basing Acceptable Levels of Pesticide Residues on the Risk of Death
in an Acute Exposure Is Not Appropriate for Predicting Long-Term Human
Present risk assessment uses lethality (death) and cancer outcomes in
animals as the primary end points. The use of these endpoints does nothing
to predict the risk of damage to organ systems that would occur from low
levels over longer periods of time such as; reproductive effects on fertility,
genitalia abnormalities and other fetal effects, neurological effects,
behavioural and psychological effects and immunological effects.
Quantification of Infant and Child Exposure Is Inadequate
The committee concluded that there is no good information on the quantity
of pesticides that infants and children are exposed to. They consume much
greater amounts of certain foods that contain numerous pesticide residues,
and this becomes very pertinent when the pesticide exposure is calculated
on a residue per kilogram of body weight. For these reasons, it is not
acceptable to use the estimations of pesticide exposure based on adult
exposure.2 In Canada, we have even less information.
There has not been a market basket assessment of food consumption since
that done prior to 1992 (verbal report from Agriculture Canada). We have
never done any collection of information on the dietary patterns of infants
and children and thus have no information from which to quantify their
pesticide exposure through water and food consumption. This, in conjunction
with their exposure from many play surfaces, lawn and garden spraying,
and exposure from indoor application of pesticides, needs to be quantified
to set reasonable maximum allowable limits of pesticides in foods, water
and post-lawn and garden application.2 This is stated as a priority of the US EPA3 but is not being considered in Canada.
A group of acclaimed scientists from the National Research Council have
thoroughly reviewed the evidence and conclude that the pediatric population
is at considerable risk given the current methods of setting allowable
limits of pesticides. The American government has taken steps to attend
to these issues (FQPA 1996). Seven years later the Canadian government
has done nothing, and talks of taking some actions by 2005. This is well
substantiated evidence with clearly stated actions that need to be taken.
The solutions are being held up by Canadian policy makers' inability to
make the health of our infants and children a priority.
Scientific Evidence - Pesticides and Human Health Effects
This is a brief summary of a selected number of the health effects.
The most convincing evidence that herbicides (pesticides used most commonly
in agriculture) are human carcinogens come from epidemiologic studies.
A number of studies have revealed elevated risks of non-Hodgkins's lymphoma
with chronic exposure to herbicides, with the relative risk of developing
non-Hodgkin's lymphoma being 5-6 times the normal risk.4-9
In those studies that have examined dose-response relationships, they
have found statistically significant increases in the risk of developing
non-Hodgkin's lymphoma with increasing amounts of herbicides used.4,6,8
These are the findings reported by the National Cancer Institute of Canada's
Advisory Committee on Cancer Control10 and are
well accepted relationships between pesticides in populations with common
exposures, like farmers and golf course caretakers.
Childhood non-Hodgkin's lymphoma has been shown to be associated with
household or garden insecticide use11 as well
as home extermination using pesticides12 and
parental occupational exposure to pesticides.13
Beginning in the late 1970s, there have been reports linking pesticides
to leukemia in children. Case-control studies have linked pesticide exposure
to childhood cancer, in some instances with greater magnitude of risk
than in studies of occupationally exposed adults.14 A number of studies have demonstrated that maternal
employment in agriculture has been shown to be associated with leukemia.14-16
Use of pesticides on the lawn or garden during pregnancy was associated
with a 5.6 fold increase in childhood leukemia in a Los Angeles study.17
Pest strips, typically made with organophospates, were associated with
childhood leukemia in another US study.12 The
organochlorines have been associated with an increased risk of leukemia.14
Although the majority of these are no longer used in Canada, there is
continued use of organochlorines in the medical sector as well as in agriculture.
Their continued use and the persistent presence of these chemicals in
water, meat, poultry and vegetable food sources make the organochlorines
a continued risk.
The acute neurological effects of pesticides are well known as the mechanism
of action of most pesticides is neurological toxicity, which acts in the
same way on humans. There are numerous reports of pediatric cases of neurotoxic
effects (seizures, confusion) after skin exposure to insect repellents
and medical treatment of head lice with pediculocides. The evidence on
the long term effect of pesticides on the neurological system is less
well established but the existing studies strongly suggest that there
are chronic effects, especially with organophosphates and carbamates,
presently some of the most widely used pesticides.2 Studies of the long term effects strongly suggest developmental
effects from low level exposures similar to the effects found for lead.
Neuropsychological and developmental data collected on children exposed
to certain pesticides in utero and infancy, particularly polybrominated
biphenyls (PBBs), shows that significant differences exist in neuropsychological
and development outcomes related to the dose of exposure. There is a clear
mechanism for neurological toxicity with some human evidence to support
long term effects. These studies are more costly and extensive because
of the duration of follow-up required but is an area that has been targeted
by the American NRC as needing immediate regulatory body support for action
and further study.
Numerous animal studies show a variety of effects of pesticides on the
immune system, including decreased antibody formation by 70% after exposure
to common pesticides such as captan, lindane,malathion as well as decreased
cell mediated immunity.2 In human exposures to
pesticides, decreased functioning of the immune system has been documented
(T-cells react abnormally, decreased T4 and T8 counts, increased energy)
that is associated with an increased report in clinical illness.2
The amount of research in this area has been limited, particularly in
human studies and in the long term effects of pesticides on the immune
A number of studies have found associations between brain cancers and
pesticides as well as soft tissue sarcomas.
There is considerable debate between regulatory bodies and industry regarding
the quality of the evidence associating pesticides with cancer outcomes.
It is clear that obtaining good exposure data in observational studies
is difficult. However, we have to accept that we will never have the opportunity
to conduct drug like trials with pesticides where we expose children or
adults to placebo vs pesticides. Our knowledge of the toxicity of pesticides
makes this ethically unthinkable. We can work towards better studies with
greater numbers of subjects but our regulatory system does not encourage
this. Industry is presently responsible for providing the "evidence" that
the pesticide is safe and this consists of acute exposures to rats or
laboratory animals where we look at lethality and some cancer endpoints
only. As has been outlined, this does not reflect the real risk to humans.
Using the evidence that we have, animal and human, we can conclude that
a number of pesticides that we readily use pose significant risks to human
health. It is appropriate that we take policy and public health measures
to ensure that the population is aware of the risks and that those with
reasonable evidence of harm be withdrawn until further evidence demonstrates
Pesticide Policy and Recommendations for Improvements
Involvement with the regulation of pesticides in Canada as a physician
and epidemiologist is a disturbing experience. It is hard to imagine that
the disarray that appears to exist from the outside in fact exists at
a greater level when one is actually involved in the process. Canadians
increasingly question the will and the ability of this federal government
to protect them from the risks of pesticides. As a member of the Pesticide
Management Advisory Council (PMAC) and as a researcher evaluating the
existing evidence on the effects of pesticides on human health, I think
their concern is well founded. In fact, I think that it would be much
greater if they were fully aware of the inadequate assessment of health
risks that the Canadian government requires prior to release of pesticides,
the inability to re-assess pesticides, some of which have not been evaluated
for risk for over 20 years and the close relationship that the regulatory
body, the PMRA, has developed with industry, often putting economic concerns
of the private sector ahead of the need for public health protection.
We now have a thorough and damning report of the process from the Commissioner
of the Environment and Sustainable Development. We are being pressured
by the American policy makers to at least meet some of their minimal standards
on risk assessment and re-evaluation. And, the scientific and public community
has lost all confidence that the federal regulatory system is adequate.
We have talked about changes for over 20 years. More discussion is not
what is required. We need to set down clear objectives, with time lines
and accountability and force the regulatory bodies to move on these issues.
- Risk Assessment
- Re-evaluation programs
- Post-regulation monitoring
- Understanding and Implementing the Precautionary Principle
- Pesticide Alternatives
Risk management decisions must be legislated policy and not Ministerial
Presently, and in the revised risk assessment that the PMRA is proposing,
the risk and value decisions are made by the Minister. They argue that
our legislative system does not allow the inclusion of this in policy
as is done, for example, in the US. Clearly, the Minister is not in the
position to make risk assessment decisions and it is not appropriate to
have a moving target in terms of what risk is acceptable in each pesticide
that is evaluated or re-evaluated. This leaves scientific decisions open
to political influences and risks inappropriate or very delayed decisions
being made. The level of risk that we, as Canadians, are willing to accept
needs to be clearly defined and included in detailed policy, as it is
done in other countries.
The risk assessment process has to be clearly defined and available so
that discussion of the adequacy of this process can occur. One can easily
obtain very complete information on the risk assessment process in other
countries - but it is unobtainable in Canada. For example, the PMAC has
been requesting this information for the last 18 months from the PMRA.
One assumes that if risk assessment is ongoing and that, when the PMRA
is projecting 2005/6 as the earliest possible date for revision of this
process, that we do in fact have a process. The PMRA continues to assure
the advisory committees, as well as yourselves, that issues of pediatric
risk, multiple exposures etc are presently being attended to in risk assessment.
Many of those involved in the process argue is not the case and from the
material presented to the PMAC by the HPB, it is simply not true that
we are incorporating the elements that result in increased risk to infants
and children nor are we assessing the effect of real life (multiple simultaneous)
exposure. Clearly, if this regulatory body cannot come up with any outline
of what is being done we cannot pretend that we have a standardized risk
assessment process. This is an issue of the regulatory body being in disarray,
with no mandate or will to make the basis of the assessment of pesticides
transparent. We need a clearly defined risk assessment process that is
available for critique and discussion now - not in 2005 as presently proposed.
The PMRA has outlined the two elements of risk assessment as they see
them - Risk and Value (see letter from the PMRA of 09/03/99). Human risk
assessment, under the auspices of the HPB, can be concerned only with
the acceptable human risk. If a product does not meet this, regardless
of it's cost effectiveness, it is not acceptable for use. The HPB needs
to clearly define cutoffs for acceptable risk - in a way that it is clear
when it is exceeded. Further to this, we need to have specific actions
to be taken when a pesticide, either alone or in the combinations in which
Canadians are exposed, exceeds this risk.
Risk Assessment Must Be Based on Human Risk
The present practice of using animal (mice and rat) data for estimating
human risk is not adequate. Numerous studies, outlined by the NRC, have
demonstrated that the organ systems affected varies amongst species. They
also clearly identify that the 16+ years of ongoing organ development
in the human child makes the chronic impact of pesticides very different
than that seen in the rat or mouse that reaches maturity in weeks.2 Because of these differences human epidemiological
studies must be used in conjunction with animal studies. Both approaches
have limitations however the PMRA must require human epidemiological studies
and be prepared to collaborate with other departments to support the required
Maximum Residue Limits (MRLs)
The risk of pesticides must be based on the true experience of exposure.
Canadians are exposed to pesticides through food, water, contact with
sprayed surfaces (both lawns and in their homes), inhalation and through
occupational exposure. As well, many pesticides of the same family will
be found on any food product or water source. When safety of a pesticide
is assessed, we must consider the average and maximum dose that Canadians
of all ages are consuming. For example, in our present system one organophosphate
is decided to be safe at level x. Agriculture Canada reports that the
average Canadian grown peach contains the residues of, on average, 40
of these organophosphates. They all work at the level of the neurotransmitter,
thus their effect is at least additive if not multiplicative. It is unacceptable
to regulate in a manner that we ensure that each organophosphate on that
peach should be less than the maximum allowable level. Instead, the combined
effect of the 40 residues plus the exposure from other food, water, etc.,
sources must be less than the maximum allowable level for all populations.
The PMRA has to ensure that the risk assessment process reflects Canadian
risk. They must mandate that risk assessment includes human studies and
multiple exposures. This must be implemented now, not in 2005 or some
moving time target.
Thorough Evaluation of Developmental Neurotoxicity and Endocrine Disruption
should be a mandatory requirement. This information should be provided
before a product is considered for evaluation or re-evaluation. The evidence
of the effect of pesticides on these endpoints if substantial enough to
warrant their evaluation on all pesticides that are used in the Canadian
The present intent of the PMRA is to re-evaluate all products registered
up to 1994 by 2005-6. Of 500 active ingredients in registered pesticides,
over 300 were approved before 1981 and over 150 before 1960. Priorities
for re-evaluation were outlined in 1986 by Agriculture Canada. In 1988
the Auditor-General again identified the shortcomings of the re-evaluations
that still had not taken place. In 1995 the PMRA was directed to develop
and implement a re-evaluation program. No funds have been allocated specifically
to the re-evaluation and the PMRA now proposes to attempt completion sometime
in the new millennium. The present plan for financing the re-evaluation
is to use money "shifted from submission backlog review that should increase
as improvements to the efficiency of submission review allow more resources."
Industry is strongly opposing this method of financing and such an approach
will almost definitely ensure that the re-evaluation will not take place.
Absence of an effective re-evaluation means that we are living with the
risks that we thought were acceptable 20 or 30 years ago. Twenty years
of accumulated scientific evidence will clearly make great differences
in our assessment of the risk of these pesticides. The PMRA needs to have
an imposed list of priority substances for re-evaluation with firm dates
for completion of the re-evaluation. The source of funding needs to be
clear and not the continuing obstacle to carrying out this process. Twenty
years of delay, now continued by the PMRA, necessitates this forceful
There is presently no systematic monitoring of either human or ecosystem
health effects of pesticides. The Commissioner of the Environment and
Sustainable Development concludes that the federal government's approach
to monitoring is disorganized and lacks focus. The Commissioner reports
that even for the most toxic pesticides, that have been identified as
"priority toxic residues," there is no monitoring even in areas of heavy
use. This results in the government's inability to detect the presence
of toxic substances in our environment and inability to determine what
risks they pose.
As physicians, we are acutely aware of this lack of monitoring. In situations
where we have apparent pesticide toxicities, particularly in infants and
children following dermal or inhalation exposure, our Poison Control Centres
can offer us no information on the incidence of these occurrences, on
the appropriate diagnostic or treatment interventions and have no mechanism
in place to record these toxic exposures that we are seeing in the clinical
We require a system where quantities and types of pesticides being used
in Canada are routinely documented. As well, we are in need of an easily
accessible system where apparent human pesticide toxicities can be recorded.
Precautionary Principle and the PMRA - Understanding and Implementing
The PMRA states that "the required pre-market review of pesticides is
in itself implementation of the precautionary principle." This clearly
outlines the PMRA's lack of understanding of one of the key principles
that they are obliged to implement. Reviewing a drug or food or pesticide
before allowing public exposure is a necessary part of controlling public
exposure to toxins. It has nothing to do with the precautionary principle
which states that "[w]here there are reasonable grounds to believe that
exposure to an agent may cause serious or irreversible damage to human
health, the appropriate body will take cost-effective precautionary measures,
even if some cause and effect relationships are not fully established
scientifically. Where possible, the body will strive to anticipate and
prevent health risks rather than merely to control those that already
exist." The PMRA needs to understand and implement the precautionary principle.
This applies to the risk assessment process, to decisions regarding the
amount of acceptable risk and finally the decision to register or re-register
a pesticide. This is an obligation of the PMRA and needs to be treated
Alternatives to Pesticides
This needs to be a serious undertaking of the PMRA. It is the mechanism
by which we can rid ourselves of the serious health effects of pesticides
in the future. There is no evidence that the PMRA is seriously committed
to this aspect of pesticide management. We need to see adequate resources
allocated with clear plans and time lines from this division of the PMRA.
The PMRA must recognize that it is a part of the Health Protection Branch
and as such its primary responsibility is to protect the health of Canadians.
Other aspects of pesticide regulation, including economic considerations
are secondary to this objective. As such, the PMRA and associated departments
must recognize that their primary role is in the assessment of evidence
on the effects of pesticides and the implementation of policy that ensures
that there are clear guidelines to removing pesticides that pose an unacceptable
risk to human health. The Environmental Commissioner's Report outlines
troubling criticisms of the current federal regulation of pesticides,
concluding that these deficits make the federal government's ability to
assess and prevent harmful effects of toxic substances uncertain. These
include lack of cooperation or collaboration between government agencies,
lack of public access to pesticide related information, lack of effective
monitoring of the environmental fate and the health effects of pesticides,
inconsistent procedures for applying risk assessment and risk management.
These problems must be responded to with solutions that incorporate clear
timelines. The Environmental Commissioner also notes that the Toxic Substance
Management Policy is an over arching tool which provides the federal government's
most important basis for implementing a preventative and precautionary
approach. They conclude that neither the PMRA nor the Federal Government
Departments have adequately implemented this policy. This should be an
immediate priority imposed upon the PMRA and the departments involved
in the regulation of pesticides.
- Goldman LR, Beller M, and Jackson RJ. Aldicarb food poisonings in
California, 1985-1988: Toxicity estimates for humans. Archives of Environmental
Health 1990; 45:141-147.
- National Research Council. Pesticides in the Diets of Infants and
Children. Washington, USA: National Academy of Science, 1993.
- Fenner-Crisp PA. Pesticides - The NAS Report: How Can the Recommendations
Be Implemented? Environmental Health Perspectives 1995; 103:159-162.
- Hoar SK, Blair Aeal. Agricultural herbicide use and risk of lymphoma
and soft-tissue sarcoma. Journal of the American Medical Association
- Hoar ZS, Blair A, Holmes FF, Boysen CD, Robel RJ. A case referent
study of soft-tissue sarcoma and Hodgkin's disease: farming and insecticide
use. Scand J Work Environ Health 1988; 14:224-230.
- Hoar ZS, Weisenburger DD, Babbitt PA, Saal RC, Vaught JB, Cantor KPea.
A case-control study of non-Hodgkin's lymphoma and the herbicide 2,4
- dichlorophenoxyacetic acid (2,4-D) in eastern Nebraska. Epidemiology
- Persson B, Dahlander AM, Fredriksson M, Brage HN, Ohlson CG, Aselson
O. Malignant lymphomas and occupational exposure. Br J Ind Med 1989;
- Wigle DT, Semenciw RM, et al.. Mortality study of Canadian male farm
operators: non-Hodgkins's lymphoma and mortality and agricultural practices
in Saskatchewan. Journal of the National Cancer Institute 1990; 82:575-582.
- Woods JS, Polissar L, Severson RK, Heuser LS, Kulander BG. Soft tissue
sarcoma and non-hodgkin's lymphoma in relation to phenoxyherbicide and
chlorinated phenol exposure in western Washington. Journal of the National
Cancer Institute 1987; 78:899-910.
- Ritter L, For the Ad Hoc Panel on Pesticides and Cancer. Report of
a Panel on the Relationship between Public Exposure to Pesticides and
Cancer. Cancer 1997; 80:2019-2033.
- Anonymous editor. Childhood non-Hodgkin's lymphoma. 1991;
- Leiss JK, Savitz DA. Home pesticide use and childhood cancer A case-control
study. American Journal of Public Health 1995; 85:249-252.
- Kristensen P, Andersen A, Irgens LMea. Cancer in offspring of parents
engaged in agricultural activities in Norway: Incidence and risk factors
in the farm environment. Int J Cancer 1996; 65:39-50.
- Hoar Zahm S, Ward MH, Blair A. Pesticides and Cancer. Occupational
Medicine: Sate of the Art Reviews. 1997; 12:269-289.
- Shu SO, Gao YT, Brinton LAea. A population-based case control study
of childhood leukemia in Shanghai. Cancer 1988; 62:635-644.
- Buckley JD. Occupational exposures of parents of children with acute
nonlymphocytic leukemia: A report from the Children's Cancer Study Group.
Cancer Res 1989; 49:4030-4037.
- Lowengart RA, Peters JM, Cicioni C. Childhhood leukemia and parents'
occupation and home exposures. Journal of the National Cancer Institute