ENVI Committee Report
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5. POTENTIAL EFFECTS OF PESTICIDES ON HEALTH
5.1 The scientific research that describes the impact of pesticides on wildlife suggests that pesticides affect reproduction, growth, neurological development, behaviour and the functioning of the immune and endocrine systems.51 While these studies have generally been done on animals exposed to higher concentrations than those to which humans are in fact exposed, the experts use their findings to extrapolate effects on humans since it is difficult, even impossible to demonstrate what effects pesticides have on human beings. The wildlife toxicity data has shown that the young (at pre- and post-natal stages of growth) tend to exhibit greater sensitivity to pesticides, and that pesticide effects may manifest themselves later in life and may even be transmitted from generation to generation. The potential effects of the main chemical groups of pesticides are described in this Chapter using examples of toxicity data involving animals.
5.2 Exposure to pesticides can cause acute or chronic effects on health. Acute (or short-term) effects generally occur immediately after heavy exposure to pesticides, and are well-documented. Work by Dr. Pierre Mineau, a researcher with Environment Canada's Canadian Wildlife Service, has shown that an insecticide can kill instantly. Some insecticides used in granular form, such as carbofuran and terbufos, are highly toxic to birds that ingest them as dietary grit. Dr. Mineau told the Committee that a single granule of carbofuran52 can be instantly lethal to a small bird. For terbufos, the kill rate is about 50%.53
5.3 A chronic effect develops over a long period of time, and may last for several years after initial exposure. The effect may be related to long-term or repeated exposure to a pesticide at a low dosage, or to exposure to a high dosage for a short time. Chronic health effects typically include cancer, interference with the development of the fetus and child, and disruption of the reproductive, endocrine, immune and/or central nervous systems (neurotoxic effects).54 There is controversy surrounding the identification of many chronic effects of pesticide exposure, because of inconsistencies in the research, contradictions among existing studies, and because of data gaps. It is difficult, therefore, to demonstrate a conclusive link between pesticides and certain illnesses, as was pointed out to the Committee by Dr. Kelly Martin of the Canadian Association of Physicians for the Environment:
| When you review the evidence, there's a huge mishmash. There are probably 300 studies out there looking at all different outcomes in humans, but it's difficult to link with pesticides, to try to break it down into what they've been exposed to. You have to account for smoking and drinking and all the other things, which you can do in studies.55 |
Despite the confounding factors in these studies, the witness believes that the potential for serious impact on human health is cause for concern. While the evidence may be limited, the hypotheses developed by the scientific community are of sufficient concern that they warrant further investigation. Dr. Martin added:
| I would say there's concern. There's limited evidence, and there's quite a lot of concern over that. It's not like leukaemia and lymphoma, for which we have reasonably good evidence to act on. Breast cancer is the other big concern with pesticides.56 |
Dr. Merryl Hammond, founder of Action Chelsea for the Respect of the Environment also expressed her concerns to the Committee:
| Many studies published in prestigious, peer-reviewed medical and epidemiological journals and reports point to strong associations between chemical pesticides and serious health consequences, including--and I'll just read this list briefly--endocrine disruption and fertility problems, birth defects, brain tumours and brain cancer, breast cancer, prostate cancer, childhood leukaemia, cancer clusters in communities, gastric or stomach cancer, learning disabilities, non-Hodgkin's lymphoma, canine malignant lymphoma, and various acute effects. [...] 57 |
The Effects of Organochlorines
Well known organochlorines: aldrin, chlordane, DDT, dieldrin, lindane, mirex, toxaphene. |
5.4 In the course of its proceedings, the Committee learned that although pesticides in the same group will likely cause the same types of effects (appendix 3.2), each pesticide must be studied individually, because it can have effects that vary according to its inherent characteristics. Let us look first at the organochlorines which share three properties: persistence, liposolubility and volatility. These substances do not generally decompose easily in the environment and, because of their high fat-solubility, have a tendency to accumulate in the tissues of certain species of mammals. Contaminants can thus reach high concentrations in the tissues of predators, who are high on the food chain. This phenomenon is known as biomagnification. In Canada, the double-crested cormorant, a predator that eats fish, is used as a national indicator of persistent organochlorine levels because of its broad distribution across southern Canada, especially in areas of concentrated human activity.58 While most of the more persistent and bioaccumulative organochlorines were banned in North America and Europe over 20 years ago, some persistent organochlorines are still used in developing countries because they are cheap and effective against disease-bearing insects. Wind and water bring them to Canada, where they have been found in human breast milk.59
5.5 Organochlorines are also responsible for reduced fertility in birds and thinning of egg-shells. The Committee learned from witnesses that organochlorines are suspected of aggravating certain chronic health problems in humans such as cancer, weakened immune systems and the disruption of hormonal functions. The following organizations raised this concern: World Wildlife Fund, Canadian Institute of Child Health, Learning Disabilities Association of Canada, Canadian Public Health Association, Sierra Club of Canada, Canadian Environmental Defence Fund, Ontario College of Family Physicians, Canadian Environmental Law Association, Canadian Association of Physicians for the Environment, and the Inuit Circumpolar Conference.
Effects on Health of a Persistent, Bioaccumulative Pesticide* An organochlorine insecticide, dieldrin was introduced in the 1950s. In Canada, it was used in forestry and agriculture, and for both domestic and industrial purposes. Dieldrin use was restricted in the early 1970s when its effects on health were first noted, and it is not registered now. Even though it is no longer used in a number of countries, dieldrin's persistence in the environment has led scientists to study its long-term health effects. A substance with a half-life of 182 days is considered persistent: dieldrin's half-life is estimated to be between 182 days and 7 years. In addition to the insecticide's impact following acute or short-term exposure, dieldrin is suspected of causing serious chronic effects:
|
The Effects of Organophosphates and Carbamates
Well known organophosphates: chlorpyrifos,
diazinon, glyphosate, and malathion. |
5.6 Organophosphates and carbamates, unlike their predecessors the organochlorines, have a relatively short half-life in the environment. Many of these products, which include fungicides and herbicides as well as insecticides, act on a very broad spectrum. In other words, they kill non-target species as well as target species. This characteristic has a negative effect on the food chain and on wildlife habitats, and consequently there is an indirect impact on species that eat certain prey or use the affected habitats. Organophosphates and carbamates, products that are very common today, are identified by their function: they are cholinesterase inhibitors.60 This means that they kill by interfering with an enzyme that is vital for nerve transmission. In Canada, of approximately 30 approved pesticides that can poison wild birds, most are organophosphates and carbamates.61 While there are advantages to their low level of persistence in the environment, it also means that they need to be applied more than once during the growing season, and this increases the danger of wildlife exposure. Mammals are much better than birds at detoxifying organophosphates and carbamates. For example, birds are 100 times more sensitive than mammals to the common insecticide diazinon.62 In terms of impact on human health, it is believed that organophosphate compounds inhibit the enzymes that are essential for the proper functioning of the central nervous system, causing dizziness and sometimes convulsions that may lead to death.63 A number of chronic effects of carbamate exposure have also been reported, including lowered sperm counts, reduced fertility and lower haemoglobin.64
The Effects of Phenoxy Herbicides and Pyrethroids
Well known phenoxy herbicides: 2,4-D, 2,4,5-T,
dichlorprop, mecoprop |
5.7 While the effects of phenoxy herbicides on plants are well known, their effects on mammals are poorly understood. It is suspected that this group of pesticides stimulates cancer development, delays fetal development, and promotes mutations and other problems,65 but few studies have been carried out. It has also been reported that intense exposure to these herbicides can affect the peripheral nervous system, although studies using laboratory animals have not been able to demonstrate this phenomenon.66
5.8 Synthetic pyrethroids inhibit the conduction of certain minerals across the nerve cell membrane in parasites and block the transmission of nerve impulses. The effects of synthetic pyrethroids on humans are still very poorly understood,67 but some sources note, at most, that these pesticides can cause irritations.68 Pyrethroids are often combined with other active ingredients.
5.9 The Committee is aware of the confounding factors which limit scientific research on chronic effects of pesticides on human health. Research conducted on wildlife is valuable since it provides an indication of potential risks to human health. In addition, the Committee learned that there are gaps even in studies on mammals; for example, little is known about the effect of phenoxy herbicides on mammals or the long-term effects of synthetic pyrethroids. These gaps suggest that there may be other gaps in our knowledge of the effects of other chemical groups of pesticides as well. The Committee is concerned about the health of Canadians and the environment and, from this perspective, urges the government to encourage this kind of research, which is essential to a better understanding of the pesticide effects.
| The Committee recommends that the government fund research on those chemical groups of pesticides whose action and chronic effects on human health are still relatively unknown, such as synthetic pyrethroids and phenoxy herbicides. |
5.10 The subject of endocrine disruptors was raised repeatedly during the Committee's hearings. Certain artificial substances may cause changes to the hormone or endocrine system; they are referred to as endocrine disruptors. By disrupting hormone secretion, endocrine disruptors cause physiological imbalances. In humans, for example, obesity, diabetes and bone decalcification can be consequences of this kind of hormonal imbalance. Endocrine disruptors fall into the following three categories:
| 1) mimics, which set off the same chemical reactions as natural hormones and are recognized by the body as if they actually were hormones; |
| 2) blockers, which prevent naturally-produced hormones from entering cells by "locking up" the cell receptors; and |
| 3) triggers, which set off cell reactions that would not normally be produced by hormones.69 |
5.11 A number of pesticides are on the list of chemical substances suspected of having effects on the hormone system, prepared by the American Endocrine Disrupter Resource Center (EDRC), that was established by the US Institute for Agriculture and Trade Policy (IATP) (see Appendix 5.1: List of Known and Suspected Endocrine Disruptors). Half of the substances shown on that list are part of the organochlorine group. According to this organization, even minute concentrations (parts/trillion) of these products in the human body would be enough to affect the endocrine system. At this point in time, scientists are divided on the extent of this problem. Most believe that more intensive research is essential if we are to have a proper understanding of the endocrine disruptor phenomenon. Some believe that most of the substances studied seem to have at least a low impact on mammals (including humans). Others think that the effects of endocrine disrupting chemicals are seen mainly in the fetus and in developing children. Still others suggest that the scope of effects may vary depending on a host of parameters.
5.12 On this point, the World Wildlife Fund believes that the more research is done on endocrine disruptors, the more scientists realize the extent of the health problems for which these products are probably responsible:
| Approximately 60% of the poundage of contemporary-use pesticides -- these would be agricultural pesticides -- used in the United States, which compares almost identically with the list of pesticides used in Canada, are known endocrine disruptors [...]. The evidence for these statistics comes from peer-reviewed scientific literature and government reports. The list is continuing to expand as new research is published.70 |
Pesticides suspected of acting as endocrine disruptors appear to be linked to the development of breast, prostate and testicular cancers, endometriosis, abnormal sexual development, lowered male fertility, damage to the thyroid and pituitary glands, lowered immunity, and behavioural problems. A Canadian study published in the Canadian Medical Association Journal suggested pollution was one of the main causes of the average annual 2% increase in testicular cancer (60% over the past 30 years) noted in 1999.71 The results of another study indicate that growing children and fetal development are particularly vulnerable to pesticides.72 Dr. Kelly Martin stated:
| ... endocrine disruption is a big problem. In animal studies, it's well shown that you don't have the development of a penis, or you get something that's somewhere between the penis and the clitoris in animals when they're exposed to pesticides. In kids, we know we have increased rates of cryptorchidism, in which you don't have descent of the testes and you don't have normal sperm counts. We know we have that in society in general. It's a very big problem, but to link it to these things is very difficult. We haven't had the money, so the studies haven't been done. But certainly in animal studies it has been a very big concern, and there's a big push from a lot of people to get more human evidence on this.73 |
Research on Endocrine Disruptors
5.13 In Canada, under the new Canadian Environmental Protection Act, 1999, the government must do research on substances that disrupt the hormone system.74 An interdepartmental working group is focusing on endocrine disruptors; it is composed of representatives from five federal departments: Natural Resources, Environment, Fisheries and Oceans, Agriculture and Agri-Food and Health. About $2.5 million per year has been allocated for research on endocrine disruptors, both inside the government and in the academic sector.75 Dr. Theo Colborn reminded the Committee that Canada pioneered research into endocrine disrupters, thanks in particular to the Canadian Wildlife Service, whose research has demonstrated the phenomenon of endocrine system disruption in wildlife. These results blazed the trail for the international scientific community, which today is studying the question of active compounds in the environment as they affect the human population. Dr. Colborn stressed that Canada should continue investing in this type of research.76 She was critical, however, of the fact that despite this evidence, there is still no protocol for precisely detecting the effects of endocrine disruptors on fetal growth.
5.14 The Committee is very concerned by the lack of financial resources apparent from the testimony heard. Apart from the general problem of budget cuts for environmental research (including research programs on POPs, discussed in Chapter 4) wildlife research in general has also been a victim of inadequate resources. This problem was raised by Dr. Pierre Mineau:
| Finding the evidence of a bird kill involves large, intensive, systematic surveys and searches of the areas that have been treated, as well as a number of chemical and biochemical analyses. The cost of these operations is actually beyond the resources of the Canadian Wildlife Service. We're talking here of studies that may cost anywhere from $125,000 right up to possibly $1 million--and that's for every use pattern.77 |
5.15 The Committee shares the concerns expressed by witnesses about the absence of a specific protocol and about reduced financial resources, and urges the government to maintain its research programs and provide them with adequate long-term funding.
| The Committee recommends that the government strengthen its research programs on endocrine disruptors, particularly by providing adequate, permanent funding for: (1) carrying out research on wildlife and (2) developing a specific protocol for detecting the effects of endocrine disruptors on human health. |
APPENDIX 5.1: List of Known & Suspected Hormone Disruptors
Pollutants with Widespread Distribution
Reported to have |
| Dioxins and furans PCBs PBBs Octachlorostyrene |
Hexachlorobenzene Pentachlorophenol |
| 2,4,5-T 2,4-D alachlor aldicarb amitrole atrazine benomyl beta-HCH carbaryl chlordane cypermethrin |
DBCP DDT DDT metabolites dicofol dieldrin endosulfan esfenvalerate ethylparathion fenvalerate lindane heptachlor |
h-epoxide kelthane kepone malathion mancozeb maneb methomyl methoxychlor metiram metribuzin mirex |
nitrofen oxychlordane permethrin synthetic pyrethroids toxaphene transnonachlor tributyltin oxide trifluralin vinclozolin zineb ziram |
| Di-ethylhexyl phthalate (DEHP) Butyl benzyl phthalate (BBP) Di-n-butyl phthalate (DBP) Di-n-pentyl phthalate (DPP) |
Di-hexyl phthalate (DHP) Di-propyl phthalate (DprP) Dicyclohexyl phthalate (DCHP) Diethyl phthalate (DEP) |
Cadmium
Lead
Mercury
Pollutants with Widespread Distribution Reported to Bind to Hormone Receptors and therefore Suspected to have Reproductive and Endocrine-disrupting Effects |
2,4-dichlorophenol
Diethylhexyl adipate
Benzophenone
N-butyl benzene
4-nitrotoluene
NOTES
This list of substances considered to have endocrine disrupting and reproductive effects is compiled from a variety of sources including:
- Colborn, T. and C. Clement (1992) Chemically Induced Alterations in Sexual and Functional Development: The Wildlife/Human Connection. Princeton, NJ: Princeton Scientific Publishing.
- Colborn, T., F. von Saal and A.M. Soto. (1993) Developmental Effects of Endocrine-Disrupting Chemicals in Wildlife and Humans. Environmental Health Perspectives, Vol. 101, Number 5.
- Lyons, G. (1995) Phthalates in the Environment. World Wildlife Fund UK.
- Ministry of Agriculture, Fisheries and Food. (1995) Effects of Trace Organics on Fish, Phase II, Foundation for Water Research, UK.
All of the substances presently identified as hormone disruptors are now widely distributed throughout the environment, some are common constituents of consumer products, and many are now found in human tissues.
Source: The Endocrine Disrupter Resource Center, Web site, January 1999.
51 Canadian Environmental Law Association, Draft -- Regulating Pesticides to Protect Children's Health, 94 p., December 1, 1999; Environment Canada Web site, "Endocrine Disrupting Substances in the Environment," January, 2000.
52 The granular form of carbofuran is banned in Canada.
53 Evidence, Meeting No. 12, December 2, 1999.
54 M. Butterfield and D. Rosenberg, Exposure: Environmental Links to Breast Cancer, film screening, Ottawa, October 1998; M. Gilbertson, "Linking Water Quality to Wildlife and Human Health," Focus, International Joint Commission, November 1998, p.18-19; G.W. Chance and E. Harmsen, "Children Are Different: Environmental Contaminants and Child Health," Canadian Public Health Review, Volume 89, Supplement 1, May/June 1998, p. 10-14; A. Pernille, P. Grandjean, T. Jorgensen, J.W. Brock, H.B. Hartvig, "Organochlorine exposure and risk of breast cancer," Lancet, 352(9143), 1998, p. 1816-1820.
55 Evidence, Meeting No. 11, December 1, 1999.
56 Ibid.
57 Evidence, Meeting No. 10, November 30, 1999.
58 Environment Canada, Web site, "Persistent organochlorines," S and E Bulletin, January 1998.
59 S.A. Briggs, Basic Guide to Pesticides: Their Characteristics and Hazards, Rachel Carson Council, 1992, 283 p.
60 With the exception of glyphosate.
61 Environment Canada, Web site, "Pesticides and Wild Birds," Canadian Wildlife Service, Hinterland Who's Who, November 1999.
62 Ibid.
63 Canadian Institute of Child Health, Brief to the Committee; Canadian Public Health Association, Brief to the Committee.
64 S.A. Briggs, Basic Guide to Pesticides: Their Characteristics and Hazards, Rachel Carson Council, 1992, 283 p.
65 Ibid.
66 Toronto Public Health Environmental Protection Office, Pesticides: A Public Health Perspective, Technical Report, October 1998.
67 U.S. Geological Survey, Web site, November 1999.
68 University of Nebraska, Web site, Pesticide Education Resources, February 2000.
69 The Endocrine Disrupter Resource Center, Web site, January 1999.
70 Evidence, Meeting No. 5, November 17, 1999.
71 B. Evenson, "More Men Suffer Testicular Cancer: Something Strange is Going On,'' National Post, January 26, 1999, p. A1.
72 Toronto Public Health Environmental Protection Office, Pesticides: A Public Health Perspective, Technical Report, October 30, 1998.
73 Evidence, Meeting No. 11, December 1, 1999.
74 Environment Canada, Web site, ''New Funding to Implement the New Canadian Environmental Protection Act," September 14, 1999; Environment Canada, Web site, "The Canadian Environmental Protection Act : A Strengthened Act for the New Millennium,'' September 14, 1999.
75 Evidence, Meeting No. 2, November 2, 1999.
76 Evidence, Meeting No. 5, November 17, 1999.
77 Evidence, Meeting No. 12, December 2, 1999.