Is There Such a Thing as ‘Safe’ Herbicide?

Avoiding chemicals and herbicides seems more than prudent advice, given recent headlines about potentially devastating health effects of such substances, even if in some cases humans aren’t directly exposed to them. The presence of toxins in the food chain and atmosphere make it virtually impossible to avoid all of them. But what about those once believed safe enough to be present in, say, our drinking water?

The herbicide in question here is known as atrazine, or ATZ. It has been banned in the European Union since 2004 “because of ubiquitous and unpreventable water contamination”. However, it is still commonly in use in the USA – due to reportedly “flawed scientific data as evidence of no harm”, according to a study published in the International Journal of Occupational and Environmental Health -- as well as in Australia, where researchers at the University of Melbourne have been studying the chemical’s effects on male fertility in mice.

Published in January 2019 in the journal Reproduction, Fertility and Development, the Melbourne researchers’ study title virtually says it all, as far as effects on male fertility: “Exposure to atrazine during puberty reduces sperm viability, increases weight gain and alters the expression of key metabolic genes in the liver of male mice.”

ATZ’s long-known effects on fertility

Concerns about the effects of ATZ on male fertility are nothing new. A March 2010 study published in the Proceedings of the National Academy of Sciences of the USA (PNAS) warned that exposure to ATZ in male frogs could wind up turning them into females.  As many as 75 per cent could become chemically castrated with 10 per cent showing the full change.

Mincing no words regarding the team’s findings, study leader Tyrone B. Hayes, professor of integrative biology at the University of California, Berkeley, told Science Daily, "What people have to realize is that, just as with taking pharmaceuticals, they have to decide whether the benefits outweigh the costs”.

A study published approximately 18 months later in the Journal of Steroid Biochemistry and Molecular Biology confirmed the effects of ATZ across a range of species, including homo sapiens, concluding that the once-believed-safe herbicide “demasculinizes male gonads producing testicular lesions associated with reduced germ cell numbers” in various forms of fish, reptiles, amphibians, and mammals.

The authors also pointed out that "low fertility, low sperm count, and poor semen quality were also associated with atrazine humans living in agricultural areas”.

The effects of ATZ on male reproductive performance were once again examined, this time on a species commonly known as the fruit fly, in a January 2015 study published in the Journal of Insect Physiology. Scientists concluded that their results “strongly suggest that ecologically-relevant doses” of ATZ exposure to larvae impacted male reproductive performance. Males that were exposed took more time to mate with females with which they’d previously mated. And females mating with one male produced fewer eggs.

Testing the reliability of government standards

Back to the University of Melbourne School of BioSciences study: As previously noted, researchers looked into the effects of ATZ on the reproductive abilities of male mice. They zeroed in on ATZ precisely because it is a widely used contaminant found in waterways Down Under. In fact, 3,000 tons of the poisonous material are said to be applied to soils in Australia every year.

The research team, led by Professor Andrew Pask and Dr. Mark Green, used two different doses of ATZ – the so-called ‘safe’ level for drinking water as determined by Australian government officials, and a dose 10 times higher. Both dosages were delivered to the mice in their drinking water from weaning until they were 12 weeks old.

In a press release, Professor Park said, “We found a change in gene expression in the liver following ATZ exposure. Two genes implicated in fat uptake were found to be over-expressed, an early stage of ‘fatty liver disease’.” This suggests that ATZ can impact liver gene expression and affect weight. And, Dr. Green added, “We know that the combined effects of weight gain and decreased sperm quality have major effects on male reproductive success and the health of offspring.”

The researchers are continuing to study the effects of ATZ exposure on embryos, while also attempting to learn of potential ATZ effects on successive generations of exposed mice, with an emphasis on determining whether the effects can be inherited.

ATZ continues to be used in the USA (at an estimated yearly rate 10 times that of Australia’s, according to Park and Green), and concerns about its possibly devastating impacts remain. All the more reason to protect your assets as early as practicable – before a so-called “safe” herbicide’s effects prove too late to reverse or mitigate.