A weedkiller widely used in the Willamette Valley poses serious danger to frogs and other amphibians — even at very low concentrations — according to research by Reed College senior Taylor Stinchcomb. by: PHOTO COURTESY OF  AUSTEN WEYMUELLER - Reed College student Taylor Stinchcomb found a common weedkiller harms frogs, in research conducted at the college's biology lab.

In experiments conducted for her senior thesis, Stinchcomb demonstrated that diuron, a broad-spectrum herbicide in use since 1967, killed tadpoles at high concentrations and led to birth defects, developmental delays, and circulatory abnormalities at lower concentrations. Even at very low levels of exposure, female frogs produced weaker tadpoles that were less likely to survive, she found.

“Continued unabated and indiscriminate application of diuron poses a risk to amphibian life and may threaten human health,” concluded Stinchcomb, an environmental studies-biology major who graduated on Monday.

Her advisor, Reed biology professor Bob Kaplan, described the research as “outstanding.”

Diuron is the third most heavily applied weedkiller in the Willamette Valley, where it is commonly used to control weeds on grass-seed fields, along roads, railways, and utility lines, according to the Oregon Department of Agriculture.

Scientists have long suspected that diuron might be an endocrine disruptor, but little research has been conducted on its effects.

Stinchcomb found that when pregnant frogs were exposed to water containing extremely low levels of diuron—approximately 125 parts per billion—their tadpoles suffered significant abnormalities, including delayed development of their hind limbs, which renders them more vulnerable to predators.

Last week, she won Reed’s prestigious Class of ’21 Award for her senior thesis.

“I am humbled and honored, as you can imagine,” she wrote after learning she won the award.

Steve Law can reached at 503-546-5139 or This email address is being protected from spambots. You need JavaScript enabled to view it..

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