Roberts, J. R., Dawley, E. H., & Reigart, J. R., “Children’s low-level pesticide exposure and associations with autism and ADHD: a review,” Pediatric Research, 2019, 85(2), 234-241. DOI: 10.1038/s41390-018-0200-z.
Pesticides are chemicals that are designed specifically for the purpose of killing or suppressing another living organism. Human toxicity is possible with any pesticide, and a growing body of literature has investigated possible associations with neurodevelopmental disorders. Attention deficit disorder with or without hyperactivity (ADHD) and autism spectrum disorder (ASD) are two of these specific disorders that have garnered particular interest. Exposure to toxic chemicals during critical windows of brain development is a biologically plausible mechanism. This review describes the basic laboratory science including controlled pesticide dosing experiments in animals that supports a mechanistic relationship in the development of ADHD and/or ASD. Epidemiological relationships are also described for low-level pesticide exposure and ADHD and/or ASD. The available evidence supports the hypothesis that pesticide exposure at levels that do not cause acute toxicity may be among the multifactorial causes of ADHD and ASD, though further study is needed, especially for some of the newer pesticides. FULL TEXT
Reigart, Routt, Roberts, James, “Recognition and Management of Pesticide Poisoning,” US EPA Office of Pesticide Programs, 2013, Sixth Edition.
Reigart, Routt, Roberts, James, “Pesticides in Children,” Pediatric Clinics of North America, 2001, 48:5, DOI: 10.1016/S0031-3955(05)70368-0.
The term pesticide includes various agents devised to control a wide range of pests. Although the public perception of pesticides is often that pesticide is synonymous with insecticide, most pesticide usage and much acute and chronic toxicity from pesticides are not related to insecticidal agents. Other important classes of pesticide agents are herbicides (for plants), fungicides (for fungi), nematocides (for nematodes), and rodenticides (for rodents). An additional important class is the fumigants, highly toxic volatile agents or gases that are used as broad-spectrum killing agents for many forms of plant and animal life. Although most pesticide agents are synthetic chemical toxicants, a significant and increasing proportion are biologic agents, such as Bacillus thuringiensis, a microbial insecticide. In addition, sulfur and other elemental chemicals have been used as pest-control agents but usually are not considered as “conventional” pesticides.
The most recent (1997) US Environmental Protection Agency (EPA) estimate of pesticide usage in the United States was 443 million kg (975 million lb) of active ingredient.3 Of this enormous total, approximately 66% were herbicides and fungicides, which tend to have low acute toxicity in humans but may be persistent in the environment and in the human body. Some of these agents, including, for instance, vinclozolin, a fungicide, and atrazine, an herbicide, also are thought to be endocrine disruptor agents.
Children in the United States and elsewhere are exposed to enormous quantities of pesticides of various types, by multiple routes. Although some of this exposure is by ingestion of food and water—routes that are considered by the public to be primary—much exposure occurs in homes, gardens, and schools. A total of 34.5 million kg (76 million lb) of active pesticide ingredients were used in home and garden settings in this survey. Approximately 75% of home and garden pesticides are herbicides and fungicides, and approximately 22% are insecticides. The insecticides most used in homes and gardens are diazinon and chlorpyrifos, both organophosphates, and carbaryl, an anticholinesterase carbamate. Recent decisions by the EPA to remove the approval for usage of diazinon and chlorpyrifos in homes and gardens is likely to cause a significant shift in patterns of insecticide usage. It is likely that there will be significant increases in the use of pyrethroid compounds, requiring more intense evaluation of the risks of these compounds to infants and children.
Although there is considerable public concern over pesticide usage and exposure, the quantity of pesticides used each year has remained relatively constant over the past 20 years. The concerns shared by the public, environmental activists, and many scientists have not resulted in appreciable decreases in usage of pesticides or in children’s exposure to pesticides.
In considering pediatric pesticide effects, it is essential to attend to issues of exposure and effect. Because children differ from adults in behavior, physiology, and physical configuration, their patterns of exposure are dramatically different. Likewise, differences in the biology of children, particularly as related to developmental effects, result in quantitatively and qualitatively different responses to pesticide exposure. In the case of children, a further important complication is the need to assess the risks for subclinical effects that may lead to lifetime morbidity. This morbidity may occur in the absence of the acute poisoning symptoms that often have dominated the consideration of pesticide effects on children.