Protecting Children from Pesticides - the Neglected Legacy of Rachel Carson
by Bruce Lanphear
At the turn of the 20th century, the greatest threat to the health of children was infectious diseases, like cholera, tuberculosis and typhoid.
The development of vaccines and antibiotics played an important role in reducing deaths from infections, but the single greatest factor in reducing death rates and improving life expectancy was altering the environment to make it inhospitable to infectious agents: providingaccess to clean water, better housing and sanitation.
Over the past 50 years, the burden of childhood illness and disability has shifted from infectious disease to chronic conditions like asthma, diabetes and obesity, and behavioural problems, such as autism and ADHD.
Several environmental contaminants and pollutants contribute to these disabilities that collectively afflict about one in five children. These contaminants include (but are by no means limited to) lead, mercury, tobacco, air pollutants, DDT, organophosphate pesticides and PCBs.
The good news is that we have the opportunity to prevent many of these childhood disabilities. The sanitarians of the early 20th century understood that uncovering a pattern of disease was often sufficient to act, sometimes decades before the bacterial or viral agents were discovered. One way to apply that lesson today is by revising the way we regulate environmental chemicals and pollutants.
Currently, environmental chemicals are “innocent until proven guilty.” They can be introduced without being fully tested for toxicity: indeed, of more than 200 industrial chemicals known to have neurotoxic effects in adults, only a handful have been tested for neurotoxicity at lower (subclinical) doses.
Moreover, a chemical is only taken off the market or a pollutant regulated when harmful effects are proven definitively; by convention, this means that a chemical or pollutant has to be proven toxic in laboratory experiments and in a series of epidemiologic (human) studies, which usually take decades to complete. In the interim, millions of people, including children and pregnant women, will have been exposed and possibly harmed.
Thousands of chemicals are currently in the environment, making it difficult to attribute disability or disease to any one particular chemical.
For persistent chemicals, even when harmful effects are identified, stemming the tide of exposure may be the most that can be accomplished.
Rachel Carson’s work led to the insecticide DDT being banned in the 1970s, but one recent study found that its metabolite, DDE, can be detected in 95% of Americans. DDE has been linked with diabetes, preterm birth and diminished IQ scores in children. PCBs, which have been linked to lower IQ scores and thyroid dysfunction, have been banned for decades; however, they are routinely detected in newborns and children around the world; exposure is nearly universal.
Our experience with lead, tobacco, PCBs, mercury, and other toxicants indicates that Canada and the US should adopt the precautionary principle and identify toxicants before they are marketed and widely disseminated in the environment.
“One part in a million sounds like a very small amount – and so it is. But such substances are so potent that a minute quantity can bring about vast changes in the body.”
Fifty years ago, Rachel Carson warned us about the toxicity of even small amounts of chemicals, like pesticides. We now know that, depending on when an exposure occurs in a child’s development, an environmental chemical can result in irreversible effects at concentrations in the parts per billion. In fact, for a given exposure, the effects of some chemicals are greater at lower levels of exposure.
“For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death.”
Researchers have found strong links between exposures to environmental toxicants and behavioural problems. ADHD, which affects about one in 10 children, is on the rise among US children. We found, in a study of over 3000 children, that those who had higher blood lead concentrations were two and a half times more likely to have ADHD than children with the lowest exposure. We also found that tobacco exposure magnified the effects of lead; children who were in the highest lead category and were prenatally exposed to tobacco smoke were eight times more likely to have ADHD than children who had neither exposure.
Other chemicals which are routinely found in pregnant women and children, such as organophosphate pesticides and PCBs, have also been linked to the development of ADHD. The long latency between exposure and the onset of ADHD makes it difficult to establish these links with absolute certainty, but these studies raise troubling questions about a regulatory system which essentially allows children to be exposed to environmental contaminants until there is definitive proof that they are toxic.
The incidence of autism has increased dramatically. Autism has a genetic component, but the rapid increase in the condition points to an increase in one or more environmental risk factors. A few early studies have found that the risk of autism increases in children if their mother lived near a highway during the third trimester of pregnancy. Autism may be a “test case” for the ubiquity and variety of man-made chemicals and pollutants. It would not be surprising if a chemical (or combination of chemicals acting together) were contributing to the increase in autism.
Another group of chemicals, endocrine-disrupting chemicals (EDCs), are raising new questions about how chemicals may cause harm. Several researchers have found that prenatal exposure to phthalates and Bisphenol A was associated with a decreased anogenital distance (a condition linked to later problems with infertility), decreased “masculine” play behaviours in boys, and hyperactivity in three-year-old girls. Bisphenol A has been banned by Health Canada for use in baby bottles, but many other routes of exposure for pregnant women still exist.
While most of the evidence on the effects of EDCs concerns sex hormones or the thyroid, some EDCs (known as “obesogens”) can mimic hormones involved in the development of obesity. The chemical tributyltin is one possible obesogen. A study in adolescent girls also found an association between obesity and phthalates.
More than a quarter of Canadian children are considered either overweight (17%) or obese (9%). In the United States, childhood obesity has more than trebled in 40 years. Obese children are more likely to become obese adults, who are at heightened risk for type II diabetes, cardiovascular disease, and some cancers. Diabetes is also on the rise in young people, where it can have especially serious health consequences (compared with a later onset). While many factors contribute to the rise in obesity, there is mounting evidence that some chemicals may also play a role.
“Thalidomide and pesticides represent our willingness to rush ahead and use something new without knowing what the results are going to be.”
Thalidomide was an early and dramatic warning of our failure to regulate drugs. Widely prescribed in the 1950s to treat morning sickness at doses established to be non-toxic for adults, the drug turned out to have devastating effects on fetuses.
Many environmental exposures, which are often beyond our control, including environmental chemicals and contaminants, can have substantial and lifelong implications for children. Unfortunately, these subtle effects are unlikely to be recognized.
Tragically, as David Rall, former director of the National Institute of Environmental Health Sciences, once remarked, “If thalidomide had caused a ten-point loss of IQ instead of obvious birth defects of the limbs, it would probably still be on the market.”
“The choice, after all, is ours to make. If, having endured much, we have at last asserted our ‘right to know’, and if, knowing, we have concluded that we are being asked to take senseless and frightening risks, then we should no longer accept the counsel of those who tell us that we must fill our world with poisonous chemicals; we should look about and see what other course is open to us.”
It’s not impossible to change the way we regulate chemicals. Other governments have already adopted the precautionary principle. In 2007 the European Union instituted the REACH Program, which requires manufacturers to prove that chemicals are safe before they are marketed.
Surely the children of Canada and the United States deserve as much?
Bruce P. Lanphear, MD, MPH, is a Professor of Children’s Environ-mental Health at BC Children’s Hospital, Vancouver.