The Role of Pesticides and Pollution in Autism

The Role of Pesticides and Pollution in Autism

September 14, 2019 72 By Ewald Bahringer


“The Role of Pesticides
and Pollution in Autism” The prevalence of autism has
increased dramatically in the U.S. We’re not exactly sure how
prevalent it used to be, but these days
about 1 in 68 kids born in the United States
will have it. Despite a massive influx
of research funding, we still don’t know:
what’s the cause. This sharp increase in
prevalence remains unresolved. Yes, changes in
awareness and diagnosis can account for
some of the increase, but it also might be something
we’re exposed to in the environment. For example, all the new
chemicals we’re now exposed to. Out of 80,000 agents the
chemical industries now put out, we have evidence that
at least a thousand may have neurotoxic properties, yet only a small fraction
have been studied in humans during critical windows
of development. The current chemical risk
assessment approach is typically based on the toxicity
caused by a single chemical without acknowledging the effects
of different chemical mixtures. There are hundreds of chemicals
currently allowed in food that may have potential
harmful effects on the developing brain. “Each individual chemical
may or may not have a harmful effect on its own, but we know next to nothing
about their cumulative biological effects on the brain.” “If we really want to protect
children’s brains from chemicals…, we first need to recognize and deal with the massive dearth of basic hazard and exposure information ”
about any risks posed by environmental chemicals. A lot of the data we do have
is from preclinical studies, meaning like test tubes
and lab animals. Well yeah, it’s not like you
can expose people on purpose. That’s where epidemiological
research can step in, studying exposures within populations. That’s how we found about
other well-known hazards, like benzene and asbestos. You can’t ethically force
people to smoke for a study, but you can note how many people
exposed to cigarette smoke day in and day out get lung
cancer compared to nonsmokers. Industries spewing poison
like to patronize the public that we shouldn’t worry
our pretty little heads, but what does the science show? What does the epidemiological
evidence have to say about exposures to environmental
chemicals and autism? For example, there’s
a bunch of studies on the effects of smoking during
pregnancy on autism rates. I’ve talked about these
so-called forest plots before, where values greater than 1 suggest at least a tendency
towards an increased risk, whereas the values less than 1 suggest more of a
protective association, and should the whiskers
here cross the line, then that means that
particular finding did not reach
statistical significance. This allows you with
a quick glance to interpret a huge amount of
data from multiple studies. So, regarding this figure here, does it look like smoking
during pregnancy has any effect on autism rates? No, about half skewed to
one side, half to the other, and hardly any of the results
reached statistical significance, meaning they may have just
been largely chance finding. Same thing with
thimerasol exposure, the mercury-containing
preservative used in vaccines. Yeah, one study found significantly
increased risk of autism, but three other studies
found that those with more vaccine
mercury exposure had lower the risk of autism. But mostly, they just showed
no relationship either way; not that it matters
much at this point, since thimerosal has been
removed from most vaccines. But check out the
air pollution data. This is exposure to car
exhaust and diesel fumes during pregnancy and infancy. See how all the data is
skewed to the right, with half the findings reaching
statistical significance, meaning a significant correlation between air pollution and autism. But correlation doesn’t
necessarily mean causation. This could be a true
cause-and-effect relationship, or maybe it’s just
that poor people live in the inner cities next
to polluted highways, or the traffic noise
is causing stress, or some other confounding factor. The other suspicious link they
found was pesticide exposure. Again, just a few-second
blink at this chart, and you can see where most
of the evidence trends. Lots of environmental toxicants
have been implicated in autism: plastics, chemicals,
PCBs, solvents, toxic waste sites,
and heavy metals, but the strongest evidence
has been found for air pollutants and pesticides. Yeah, clinicians can advise
pregnant women and parents to try to avoid exposures to harmful
substances in their environment. But, instead of just advising
patients one-by-one, a more powerful strategy
would be for us clinicians to band together and
take a leadership role in advocating for a
healthy environment and society-wide actions
to help everyone.