Pesticide Exposure implicated in Autism, Developmental Delay

This article by Jerry Cates was first published on 25 June 2014, and last revised on 20 July 2014. © Bugsinthenews Vol. 15:06(01)


My professional work in the field of entomological research began in the early 1960’s. Between 1963 and 1967 I studied the biology of anopheline and culicine mosquitoes in southeast Asia, focusing on the means by which malaria and yellow fever are transmitted by those mosquitoes to humans. Much of that research was conducted on-site, in Vietnam, during nearly two and a half years of residence in that country. Using the published studies of Sir Ronald Ross and Giovanni Battista Grassi to guide me, I delved into the various control methods used, historically, to reduce populations of mosquitoes around human dwellings. Of course, much had changed since the time when Ross and Grassi carried out their studies, with new and highly effective mosquito control products in use worldwide.

In those days a singular pesticide was the leading choice for mosquito control. That “miracle” chemical had, less than 15 years earlier, been praised by Sir Winston Churchill as “The excellent DDT powder which has been fully experimented with and found to yield astonishing results…” Churchill added that DDT “will henceforth be used on a great scale.” And it was so used, during WWII and afterward, until evidence of bioaccumulation throughout the world, and reports of injurious consequences — of various kinds to a wide assortment of wildlife — surfaced.

Even in the early 1960’s, when such evidence was scarce, the concomitant risks associated with indiscriminant pesticide applications were a concern.

Rachel Carson’s seminal book, Silent Spring, published in 1962, sounded an early warning about such dangers. She was, at that time, a respected 55-year-old veteran marine biologist whose writings about the sea and marine ecosystems had generated critical acclaim worldwide. It can be said with some confidence that, in Silent Spring, Ms. Carson was not engaged in a childish rant about something she knew little or nothing about, and I found her concerns about the real and potentially harmful effects of chemical pesticides compelling. Following her lead, my attention was directed toward finding natural, non-pesticidal approaches to mosquito control, despite the near-total reliance, at the time, on DDT in the developed world and wherever western military forces were deployed.

Natural, non-pesticidal approaches to mosquito control were then, and remain today, an important part of the native way of life in Vietnam and much of the rest of Asia, primarily because access to pesticides in such places is limited.  My studies added to earlier evidence that the native implementation of primitive habitat modification techniques significantly reduced the incidence of malaria infection, entirely without the use of pesticides. When combined with additional measures, like burning incense and lining sleeping mats with strong-smelling fresh leaves from native pine, cinnamon, and eucalyptus trees, effectively obliterating body odors that attract mosquitoes to human dwellings, the reduction of malaria infections can be dramatic. Of course, such measures did not eradicate malaria in the places where they were practiced. It is undeniable, however, that they helped reduce malaria incidence, and their successes, meager as they were, suggested that natural methods of mosquito control deserved to be investigated further.

My personal entomological investigations were temporarily shelved in 1969, when I left New York and moved to Texas, accepting employment at Texas Instruments to take up computer programming. The challenge and fascination of writing computer code — in a long list of programming languages, and on a host of different computers — diverted my attention for the next decade. Though not directly working in pest management at the time, I watched with interest as the Environmental Protection Agency came into being, largely as a result of Carson’s influence a decade before. And I followed the news of the chemical pollution of Love Canal, in New York state (less than 200 miles from where I’d worked stateside in the 1960’s, at Rome Air Development Center), as it unfolded during 1976-1978.

In 1980, I returned to my former entomological pursuits, this time as a pest management specialist with my own pest control company. As before, the dangers pesticides posed to humans were of great concern, a concern that — for me — was heightened by my work as a volunteer Emergency Medical Technician with a local fire department. I was also aware that a number of my fellow pest managers in Texas had fallen victim to unusual diseases, likely as a result of their exposure to the chemical pesticides they’d applied in their daily work. I realized I’d have to work hard to avoid a similar fate.

Over the 34 years since, I’ve continued my studies in emergency medicine, and have served as a firefighter and EMT in five different Texas fire departments. My pest management work focuses on nursing and medical facilities, where the imperative of keeping pesticide use to a minimum is, for the most part, deeply ingrained. And, for the most part, I’ve managed to limit my exposure to toxic pesticides.

That hasn’t been easy. In fact, several times during those years I’ve been blindsided by discoveries, after the fact, that pesticides previously touted as “safe as table salt” actually harbored important, though largely hidden, risks.

Which brings me to the point of this short introduction:

During the past 51 years I’ve witnessed important advances in human awareness of the genuine risks  attending pesticide exposure. During the 34 years I’ve worked in the pest management field a number of pesticides have been ordered removed from the market, and more are scheduled to be sidelined in the not-too-distant future, as our understanding of the dangers they pose to us and other mammals has increased.

In many ways, as a result of those actions, the safety of pesticide appliers and their customers has markedly improved. In other ways, however, a sense of security has emerged that is likely unwarranted.

Many Americans recognize the importance of avoiding unnecessary exposure to the “bad” pesticides of the past. That’s good, as far as it goes. But many of us labor under the almost-certainly-mistaken presumption that all the “bad” pesticides have already been identified, and are now off the shelves.

Strong evidence — from a number of respected, authoritative sources — suggests that isn’t the case.

Reputable scientists are, at this very moment, studying and reporting on potential links between pesticide exposure and important human diseases. Some are serious, debilitating, childhood diseases, like autism spectrum disorder and developmental delay. Others affect humans later in life, like Alzheimer’s, Parkinson’s disease, and various forms of dementia. The pesticides these studies point to as potential causes of these diseases are, ironically, some of the ones we’ve come to believe to be the safest bug-killers on planet earth.

This article will examine some of the most recent scientific studies that implicate a link between many of the presumably “safe” pesticides on today’s shelves and some of mankind’s most devastating diseases. It will take time to flesh the story out, so bear with me, but at the outset I feel moved to make one thing very clear: if the links these studies describe are legitimate, limiting our exposure to pesticides is just as important today as it was in the 1960’s, before the EPA was even thought of.

Practically every pesticide in use today is potentially harmful to the human body in one way or another. Some, as the studies that this article will review point out, have the potential to produce permanent, severely disabling conditions in susceptible humans exposed to them.

Though it can be argued that some pest insects and spiders are also harmful to man, it is crucial to recognize that most bugs are not. In fact, the vast majority of the insects and spiders in our midst are beneficial, which calls into question the wisdom of seeking, as one major pest management chain puts it, to “destroy every … pest that dares to invade your home(, a)nd keep them out.” True, some insects and spiders should be attacked with a vengeance, but most are not only harmless but play an important role in keeping our environments safe. It is incumbent on us, as wise stewards of our own lives and the lives of those around us, to learn the difference.



  • Roberts, E. M., et al. 2007. Maternal residence near agricultural pesticide applications and autism spectrum disorders among children in the California Central Valley. Environ Health Perspect 115(10): 1482-1489.
  • Shelton, J. F., et al. 2012. Tipping the balance of autism risk: potential mechanisms linking pesticides and autism. Environ Health Perspect 120(7):944-951.
  • Shelton, J. F., et al. 2014. Neurodevelopental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study. Environ. Health Perspect; DOI:10.1289/ehp.1307044.


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