Study finds Atrazine exposure impairs fish reproduction at levels below federal water quality guidelines

We’ve known for a long time that atrazine, one of the most commonly detected pesticide our rivers, lakes, and streams is bad for fish.  Even at low doses, studies have shown that atrazine can effect endocrine-related functions in bluegill, Atlantic salmon, and zebrafish.  Now researches with the United States Geological Survey have shown that atrazine exposure can also lower fish reproduction and cause abnormalities in fish reproductive organs.

In a study in Aquatic Toxicology, USGS scientists raised flathead minnows in tanks with atrazine-laced water.  Some fish were in tanks with no atrazine, while others were raised in tanks with .5, 5, and 50 parts per billion (ppb) of atrazine.

The results?  First, “cumulative mean egg production (cumulative mean number of eggs/tank) was reduced at all three exposure concentrations of atrazine.”  The reductions were significant (between 19 – 39%), with the lowest dose (.5 ppb) showing a 25% reduction in egg production.  Second, the scientists found abnormalities in the reproductive organs of both the exposed male and female fish.  Female fish exposed to atrazine were found to have increased ovarian lipid accumulation and atretic follicles; three female fish were also found to have “multiple ovarian cysts that occupied a large portion of the ovary.”  As for the males, researchers reported testicular abnormalities (lesions) in the exposed fish and at least one “intersex” male fish (a very unusual occurrence for the flathead minnow), which was found in the tank with 5 ppb of atrazine.

There’s two big take-aways from this study.  First, these fish were exposed to levels of atrazine well below those established by the Environmental Protection Agency’s water quality guidelines, which sets an “Aquatic Life Benchmark” of 65 ppb for chronic exposure of fish. Second, the exposure levels were similar to atrazine levels regularly recorded throughout Midwest watersheds.  Spikes in atrazine concentration far higher than 50 ppb are not unusual and many watersheds have annual average concentrations of that exceed the lowest doses used in this study.

As the study itself concluded:

The effects on egg production and spawning in fathead minnow suggest the reproductive risks of atrazine exposure to feral fish populations in high use, agricultural areas may be under estimated by current evaluations.

It’s time to phase out the use of atrazine in the United States--something Europe did years ago.