22 agrochemicals, including common herbicides, linked to prostate cancer
The results suggest more research is urgently needed to
further understand the role these chemicals may play in the development of this
and other cancers, the authors wrote.
“Many pesticides have not been sufficiently studied for
their potential carcinogenic effects, particularly in relation to prostate
cancer,” said study co-author Simon Soerensen, a postdoctoral researcher
at Stanford University.
The findings add to concerns about the health impacts of
chronic exposure to pesticides, and are merely the latest in years of research
to link chemicals used in farming with different cancers and other diseases.
The World Health Organization’s International Agency for
Research on Cancer classifies 2,4-D as
“possibly” carcinogenic to humans, for instance. And six other chemicals
looked at in the study are currently classified as “potential human
carcinogens” by the US Environmental Protection Agency (EPA). The EPA
classifies the herbicide diuron in particular as a known/likely carcinogen.
The study also identified four chemicals that were linked to
not just the incidence of prostate cancer, but to dying from it. These include
three herbicides, known as cloransulam‐methyl, diflufenzopyr, and
trifluralin, and an insecticide called thiamethoxam, which has been banned for outdoor use in
the European Union due its toxicity to bees.
One of the herbicides consistently linked to prostate cancer in the paper was 2,4-D. This finding stands out because of how widely it’s used, said John Leppert, a urologist and researcher, also at Stanford.
The use of 2,4-D on farms has spiked in recent years as weed
species have developed increasing resistance to other herbicides, such as
glyphosate, the active ingredient in Roundup and other brands developed by the
former Monsanto Co., prompting farmers to apply glyphosate alternatives.
The development of crops that tolerate being sprayed with
2,4-D accelerated use in recent years. There are now millions of acres of corn and
soybeans planted in the US that are genetically modified to be
resistant to 2,4-D. The chemical is also found in common backyard
herbicidal products.
One 2022 study found
that nearly-one third of the 14,395 participants had measurable levels of 2,4-D
herbicide in their urine.
In the Cancer paper, the researchers looked
at county-level use of scores of agrichemicals from 1997 to 2001, and then
looked to see, for each chemical, if there appeared to be a link with cases of
cancer in the county 14 years later, from 2011 to 2015. They did the same thing
for a second period of time, looking at using 2002 to 2006 and cancer cases and
deaths from 2016 to 2020.
All of the 22 chemicals were consistently associated with
prostate cancer across time and space. The paper attempted to quantify these
links by looking at how much a discrete increase in the use of any given
chemical in a county compared to increased prostate cancer incidence there.
It found the strongest links for the herbicides trifluralin,
cloransulam‐methyl, and tribenuronm; the fungicide propiconazole;
and the insecticide parathion. (Parathion is a highly toxic organophosphate
insecticide that has been banned in many if not most countries, including the United States.)
It found that a standard-deviation increase in the use of
the herbicide trifluralin in counties, for example, was associated with seven
additional cases of prostate cancer per 100,000 individuals.
Because prostate cancer is so common, and can be aggressive,
it’s a “tremendous health concern” whose underlying environmental risk factors
remain little understood, Leppert said.
“I think we need to be more aware of considering that what’s
in the environment could be a contributor to a man’s risk of cancer,” he
added.
Pesticides and herbicides linked to prostate cancer.
The 22 chemicals identified include herbicides (2,4-D,
glyphosate, trifluralin, cloransulam‐methyl, tribenuron, diflufenzopyr,
diuron, hexazinone, linuron, pendimethalin, sulfosate, thifensulfuron)
insecticides (parathion, thiamethoxam, acephate, bifenthrin, carbaryl,
cyhalothrin-lambda), fungicides (propiconazole, azoxystrobin, trifloxystrobin),
and soil fumigants (chloropicrin).
