Parental Pesticide Exposure Linked to Childhood Cancer
By Jennifer Runkle, PhD, MSPH
Research linking pesticide exposure and cancer in children is now substantiating public concern over pesticide exposure in children. The American Academy of Pediatrics recently released a report suggesting pesticides may induce chronic health complications in children, including cancer.1 Though cancer in children is a rare event, incidence rates are on the rise.2 With the exception of a few known risk factors, the etiology of this complex disease is largely unknown. Numerous studies now provide evidence that parental exposure to pesticides is an important environmental risk factor in the development of cancer in children.
Pesticides are a heterogeneous class of chemicals conveniently classified as herbicides, insecticides, fungicides, and rodenticides based on the target pests. In children, cancer cases have been indiscriminately associated with all pesticide classes. Recent meta-analytic findings demonstrate a more than two-fold excess risk of child leukemia among mothers occupationally exposed to insecticides and herbicides during pregnancy.3,4 Even more surprising are studies indicating a 50% increase in childhood leukemia risk following routine maternal pesticide use in the home or garden.5 Paternal occupational exposure to herbicides, fungicides and insecticides has also been positively associated with risk of child brain tumors.5,6 The evidence now extends beyond workplace exposures and highlights the importance of reducing household pesticide exposure as an important risk factor.
Vulnerable Farmworkers and their Children as Sentinel Indicators
An estimated 2 billion men and women working in agriculture are regularly exposed to the toxic agrochemicals used on the global food supply.7 It is now well-established that vulnerable, low-income farmworker populations are disproportionately affected by acute- and chronic-pesticide related illnesses. Annual surveillance has documented as many as 25 million cases of unintentional pesticide poisoning occurring in farmworkers worldwide.8 Despite U.S. federally required pre-market testing in animals, evidence from prospective studies has consistently demonstrated excess risks for breast cancer, leukemia, multiple myeloma, non-Hodgkin lymphoma and prostate cancer in licensed pesticide applicators and their family members.9 While research shows pesticide-associated cancers are higher in farmworkers, data are suggestive that cancer is higher in farmworker children. A number of predisposing events occurring prior to conception, in utero, and/or after birth likely result in greater susceptibility to pesticide-related cancer in farmworker children.
Pesticide exposure levels in reproductive-age farmworkers consistently exceed levels in the general population. Prior studies have suggested that preconception levels of exposure may lead to maternal or paternal germ-cell mutations.9 Recent evidence indicates prenatal exposure to toxic pesticides is a potential initiator of cancer-promoting events in utero. In addition to important behavioral, dietary, and physiological differences, young farmworker children encounter higher levels of pesticides through parent take-home exposure as well as from household contamination. Higher levels of organophosphates (OP), a probable human carcinogen, have been detected in the urine of farmworkers’ children.10 Perhaps equally alarming are documented cases of hospital-acquired OP poisoning in medical personnel not wearing appropriate protective equipment while caring for patients contaminated with OP.11 Though extreme, these incidences further emphasize the vulnerability of farmworker children, who encounter secondhand pesticide exposure repeatedly.
Overburdened farmworkers and their families provide sentinel notification of the devastating human health effects of highly exposed persons. However, research now shows that all exposures, even low-level exposures, are associated with some level of health risks. A recent NAS report underlined “background” low-level exposure to environmental chemicals may exact as much or more harm than higher levels of these toxic, cancer-causing chemicals.12
Background exposure linked to Chronic Health Effects
All persons worldwide are exposed to ubiquitous and sometimes biologically persistent toxins in the air, soil, and water. A classic example of the persistence of these chemicals is DDT, one of the first widely used agricultural insecticides in the 1950s. Although DDT was banned by the USEPA in 1972, detectable levels are still present in the blood, placenta, and breast milk of the contemporary US population.13,14 According to the President’s Cancer Panel, pre-adolescent girls exposed to DDT were five times more likely to develop breast cancer later in life.15 Mouse models and cell studies have also shown that low levels of exposure not only promote chronic disease development among those directly exposed, but may also be involved in the promotion of adult onset disease transgenerationally.16
As many as 70 widely used pesticides are currently classified as probable or possible human carcinogens, with countless other high-volume chemicals waiting further testing.17 Even more importantly, pesticides with known carcinogenic activity are being replaced with alternative pesticides having cancer-causing potential. For example, residential and agricultural use of organophosphates, a large subclass of pesticides with known carcinogenicity, has largely been replaced by cypermethrin. Consequently, based on limited evidence from animal studies, cypermethrin is also considered a possible human carcinogen by the USEPA.18
Critical Role of Health Providers
Compelling scientific evidence revealing that preconception and prenatal exposure to toxic environmental chemicals can have a profound and lasting effect on health across the life-span is rapidly gaining momentum in the consumer, legislative and even the health care arenas. In 2013, the American College of Obstetricians and Gynecologists released a Committee Opinion calling the attention of all reproductive and health specialists to the reduction of exposure to toxic environmental agents as a critical area of intervention.19 Protecting farmworker children from childhood cancers and other pesticide-related health effects, as well as protecting the general public, requires dedicated action to reduce parental exposure to pesticides.
Medical providers are uniquely poised to have a significant impact in diminishing these exposures through anticipatory guidance at multiple stages, including the ever-critical preconception, prenatal and postnatal periods. For health providers, steps toward action require: 1) becoming more knowledgeable about how environmental exposures can influence adverse reproductive and developmental health outcomes;20,21 2) obtaining a detailed environmental and occupational exposure history;18, 22 3) encouraging farmworkers and other patient populations (men and women of reproductive age and pregnant women) to discuss possible sources of contact with pesticides;23 4) understanding potential exposures for vulnerable patient populations in the geographic service area; 5) connecting with a local Pediatric Environmental Health Specialty Unit;24 and 6) reporting pesticide-related illness to the appropriate agency.18,25
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