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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 Risk

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 and children.

• Basing Acceptable Levels of Pesticide Residues on the Risk of Death in an Acute Exposure Is Not Appropriate for Predicting Long-Term Human Risk

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.

Conclusions

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.

Non-Hodgkin's Lymphoma

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

Leukemia

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.

Neurological Effects

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.

Immunotoxicity

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 system.

Other Cancers

A number of studies have found associations between brain cancers and pesticides as well as soft tissue sarcomas.

Conclusions

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 no harm.

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.

Recommendations

• Risk Assessment
• Re-evaluation programs
• Post-regulation monitoring
• Understanding and Implementing the Precautionary Principle
• Pesticide Alternatives

Risk Assessment

Risk management decisions must be legislated policy and not Ministerial decisions.

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 research.

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 market.

Re-evaluation Programs

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 intervention.

Post-Regulation Monitoring

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 setting.

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 It

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 as such.

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.

Conclusions

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.

References

1. 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.
2. National Research Council. Pesticides in the Diets of Infants and Children. Washington, USA: National Academy of Science, 1993.
3. Fenner-Crisp PA. Pesticides - The NAS Report: How Can the Recommendations Be Implemented? Environmental Health Perspectives 1995; 103:159-162.
4. Hoar SK, Blair Aeal. Agricultural herbicide use and risk of lymphoma and soft-tissue sarcoma. Journal of the American Medical Association 1986; 256:1141-1147.
5. 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.
6. 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 1990; 1:349-356.
7. Persson B, Dahlander AM, Fredriksson M, Brage HN, Ohlson CG, Aselson O. Malignant lymphomas and occupational exposure. Br J Ind Med 1989; 46:515-520.
8. 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.
9. 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.
10. 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.
11. Anonymous editor. Childhood non-Hodgkin's lymphoma. 1991;
12. Leiss JK, Savitz DA. Home pesticide use and childhood cancer A case-control study. American Journal of Public Health 1995; 85:249-252.
13. 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.
14. Hoar Zahm S, Ward MH, Blair A. Pesticides and Cancer. Occupational Medicine: Sate of the Art Reviews. 1997; 12:269-289.
15. Shu SO, Gao YT, Brinton LAea. A population-based case control study of childhood leukemia in Shanghai. Cancer 1988; 62:635-644.
16. 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.
17. Lowengart RA, Peters JM, Cicioni C. Childhhood leukemia and parents' occupation and home exposures. Journal of the National Cancer Institute 1987; 79:39-46.

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