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 Occupational exposure to these chemicals, known as biocides, was
associated with a 65 percent higher risk of thyroid cancer, the
study found. For people whose jobs might have led to the most
cumulative exposure to biocides over time, the odds of thyroid
cancer was more than doubled.
The study also looked at pesticides, and didn’t find an increased
risk of thyroid cancer linked to these agricultural chemicals.
“Limited studies have investigated occupational exposure to
pesticides in relation to thyroid cancer and have reached
inconsistent results,” said lead study author Dr. Yawei Zhang, an
environmental health researcher at Yale University in New Haven,
Connecticut.
“Our study did not support an association between occupational
exposure to pesticides and risk of thyroid cancer, but suggested
that occupational exposure to other biocides might be associated
with an increased risk of thyroid cancer,” Zhang said by email.
Scientists aren’t certain what causes thyroid cancer, though the
odds of these malignancies are higher with certain genetic disorders
and with exposure to high amounts of radiation, especially during
childhood.
Women are much more likely to get thyroid tumors than men, and this
type of cancer is more common in white people than in other racial
or ethnic groups.
For the current study, researchers compared data on 462 adults with
thyroid cancer in 2010 and 2011 to 498 people who didn’t get these
tumors but who were otherwise similar and around the same age.
Researchers asked study participants to report all jobs held for at
least one year during their lifetimes and to provide detailed
information on their job title, duties, company name, type of
industry and dates of employment.
Then, researchers calculated potential exposure to biocides and
pesticides based on a state database of occupational contact with
specific chemicals and pollutants.
Pesticides included primarily agricultural chemicals like
insecticides, herbicides and rodenticides. The jobs most often
linked to these chemicals were farmer, rancher and other
agricultural managers; postal worker; and supervisor of landscaping,
lawn services and grounds keeping workers.
Biocides in the study were typically used in medicine or cleaning.
Jobs most often tied to these chemicals included healthcare
providers involved in diagnosing or treating patients; psychiatric
and home health aides; and building cleaning workers.
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Women with any occupational exposure to biocides were 48 percent
more likely to develop thyroid cancer, while men had more than
tripled odds, the study found.
Although the underlying mechanisms linking biocides to thyroid
cancer are unclear, it’s possible that these chemicals alter thyroid
hormones, researchers note. Triclosan, for example, a chemical
widely used in cleaning products, has been shown to decrease levels
of two thyroid hormones involved in growth and metabolism.
Another chemical, the wood preservative pentachlorophenol, has been
show to lower thyroid hormone levels in rats, the authors also point
out.
The study wasn’t a controlled experiment designed to prove biocides
or pesticides directly cause thyroid cancer.
Other limitations include the five-year age bands researchers used
to compare people with thyroid tumors to similar healthy
individuals. It’s also possible the state data on occupational
chemical exposure might not always reflect the level of exposure to
certain biocides or pesticides by individual people in the study.
But the findings suggest it makes sense for people to be cautious
about biocide and pesticide exposure, researchers conclude.
“People should take caution when they apply pesticides or other
biocides in work place or at home by wearing protective clothes or
mask and washing hands afterwards,” Zhang said.
SOURCE: http://bit.ly/2lmoJQV Occupational and Environmental
Medicine, online February 15, 2017.
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