By Will Atwater
As 80-degree weather and daffodil and Bradford pear blooms purge winter from North Carolina landscapes, weekend gardeners are springing into action. Bags of grass seed, mulch and compost are hot commodities at local garden centers this time of year, and yard-sprucing plans revolve around questions like whether that shady corner gets enough sun for a flowering shrub — and what to do about weeds.
While there are several options for managing weeds, including pulling by hand and mulching, some may reach for Roundup, a popular weed killer whose active ingredient is glyphosate. Long used by farmworkers and landscape contractors — and, in smaller amounts, by homeowners — the chemical has drawn growing scrutiny from scientists who say repeated exposure may come with health risks for the people who handle it most.
Duke University researcher Nishad Jayasundara and his students conducted a study published last month that shows how, under certain conditions, persistent exposure to low levels of glyphosate, 70 times below what is currently permissible in the drinking water, could be harmful to kidneys.
During the study, adult zebrafish were exposed for weeks to low levels of glyphosate and a mixture of metals at concentrations allowed in drinking water. In earlier work, Jayasundara and colleagues found those same levels in drinking water from regions with high rates of advanced kidney disease that can’t be explained by typical risk factors. In the new study, even these low exposures led to clear signs of kidney damage, including impaired kidney function, structural injury to kidney tubules and disrupted energy metabolism in kidney cells.
Zebrafish are a commonly used animal for modeling how chemicals and pharmaceuticals affect humans.
The findings suggest that people who rely on drinking water contaminated with both glyphosate and certain metals may face an elevated risk of chronic kidney damage, and that this combined exposure may be more harmful than either contaminant alone.
“We were able to show that really low levels of glyphosate, with long-term exposure, interact with metals in ways that can compromise kidney function,” Jayasundara said. “We saw those same levels of glyphosate and metals in drinking water from farming communities around the world, where farmworkers are drinking that water and showing high rates of kidney disease without clear explanations.”
The findings are especially relevant for people who work with glyphosate regularly, such as farmworkers and landscape contractors, who may be exposed far more often than the average homeowner. Experts say the research is also a reminder that anyone using weed killers around the house should handle them carefully and consider safer alternatives when possible.
The research comes amid renewed controversy over glyphosate, after a key 2000 study backing its safety was retracted when researchers’ undisclosed ties to Monsanto came to light, amid “serious ethical concerns,” fueling questions about regulators’ reliance on the industry-backed research. At the same time, President Donald Trump has signed an executive order declaring glyphosate-based herbicides “critical” to national security, directing agencies to protect their production and extending some liability protections to manufacturers.
Minimal protection for farmworkers
In fiscal year 2023, the United States issued more than 300,000 H‑2A visas to temporary agricultural workers, according to U.S. Department of State data. In 2022, North Carolina employed more than 25,000 farmworkers through the temporary visa program.
Although farmworkers receive training on how to safely apply herbicides and pesticides, the instruction doesn’t go far enough, said Leticia Zavala, an organizer for It’s Our Future, an organization that provides support for H‑2A workers.
“There are training requirements for [chemical] applicators, and there are training requirements for workers that work in fields where [they] are being used,” Zavala said, “but they’re very minimal and not enforced.”
“We see a lot of workers who are given a video, for example — it’s like a 30‑minute video — but they don’t know who to call or what to do if they feel like that exposure puts them at risk,” she added. “Pesticide applicators also get training, but they don’t get the protective equipment, or they don’t know what they’re actually spraying.”
Safer options for landscapers and homeowners
Landscape contractors who apply herbicides and pesticides for hire are required to hold a pesticide applicator license, which means completing training, passing a state exam and periodically renewing their certification through continuing-education courses or retesting.
In North Carolina, commercial applicators must first pass a written exam on core pesticide safety and then a second exam in a specialty category such as ornamental and turf or right‑of‑way, according to information provided by North Carolina State Extension. Certification is valid for a limited period, and applicators have to earn continuing‑education credits in approved pesticide‑safety courses to keep it, or else retake the exams when it expires
For homeowners, there is a range of weed control options. The product 30 percent vinegar can be found at local garden centers as well as some big-box retailers. As the name implies, it contains a highly concentrated vinegar (acetic acid) solution, and experts recommend wearing gloves and protective eyewear when applying to avoid skin and eye injuries.
For those interested in weed barriers, newspaper or cardboard can be laid over a bed and then covered with mulch. Given the times we’re living in, old newspapers can be in short supply, so there are also landscape fabrics on the market that serve a similar purpose. In both cases, the materials eliminate or slow weed growth by blocking light and preventing many weed seeds from germinating.
Jayasundara is not calling for occasional users to stop using Roundup or other weed killers that contain glyphosate, he said. Rather, he emphasizes proceeding with caution. “If you have a garden patch and you’re using glyphosate every several months, your exposure risk and your health risks are likely low.”
However, if a person has traces of heavy metals — such as cadmium, lead or arsenic absorbed over time from food or drinking water — there’s a possibility that glyphosate exposure, even at low levels, could pose a health risk.
Cadmium exposure can occur through eating such foods as leafy greens, grains and potatoes, as well as from cigarette smoke and, in some areas, contaminated drinking water.
In their zebrafish study, Jayasundara’s team used glyphosate and metal concentrations similar to those measured in drinking water from farming communities, and found that glyphosate increased the amount of cadmium that accumulated in the kidney.
“Cadmium is a really well‑known kidney toxicant,” he said.
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