The Unsettled—and Unsettling—Science of Lawn Chemicals

For people with yards, keeping grass lush can often feel like a full-time job: planting, treating, mowing, bug-killing, watering—and repeating. Because of the many products and services this entails, the lawn and garden care industry raked in $16.8 billion globally in 2020, according to analytics firm Allied Market Research.

But the roots of lawn care are more sinister than a bright lawn might suggest. Fertilizer grew in popularity after World War II, when the factories that made vast quantities of nitrogen for bombs diverted that production capacity toward agriculture. Around the same time, the insecticide DDT—which writer and conservationist Rachel Carson famously called out for its detrimental environmental and health impacts in her book Silent Spring—also made its way into everyday use.
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Since then, pesticides and other lawn treatments have evolved, with newer, safer products. Yet much of what people apply in backyards today still contains potentially harmful chemicals. These toxicants have been linked to cancer and other maladies in people and pets. Nutrient runoff from yards can also have adverse impacts on the environment.

Here’s what experts say people should do to keep their grass, and themselves, healthy—including some chemicals to consider using with caution, or avoiding altogether.

What are the different types of lawn treatments?

People can apply a number of different products to their lawns, such as fertilizers, herbicides, pesticides, and insecticides. Each has a specific function. Fertilizers are meant to add nutrients to the soil, while herbicides, pesticides, and insecticides contain substances that target weeds, plant and animal pests, and bugs, respectively.

To figure out what—if anything—you want to do to your lawn, people should start by asking themselves, “What is the problem and how can I treat that problem?” says Jennifer Sass, senior scientist at the environmental organization National Resources Defense Council (NRDC). That way they can address the specific issue at hand.

A soil test, which measures pH, nutrient levels, and more, can be a good place to start, suggests Chrissie Segars, a turfgrass specialist at Texas A&M University. She says that most states have universities or extension programs that offer affordable testing for the public. At Texas A&M, a soil test starts at just $12, and while Segars says getting one every year is ideal, she acknowledges that every few years is probably more realistic for most people.

Can lawn fertilizer and other treatments make you or your pets sick?

A number of chemicals in lawn-care products have come under scrutiny in recent years over their potential health impacts—particularly the herbicides glyphosate and 2,4-Dichlorophenoxyacetic acid (more commonly known as 2,4-D). Exposure can occur via ingestion, inhalation, or skin contact. And according to the U.S. Centers for Disease Control and Prevention (CDC), exposure to large amounts of one or both of the chemicals can result in adverse effects ranging from nausea and vomiting to respiratory issues.

Glyphosate is the main active ingredient in Roundup, which is one of the most widely used weed killers in the world. While the U.S. Environmental Protection Agency (EPA) found “no evidence that glyphosate causes cancer in humans” when it reviewed the available data in a 2020 report, the World Health Organization’s (WHO) International Agency for Research on Cancer (IARC) classifies the compound as “probably carcinogenic to humans.” One 2019 meta-analysis of studies on the topic found that exposure to glyphosate was associated with an increased risk of ​​Non-Hodgkin lymphoma, a type of blood cancer, in humans.

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Communities in several states have started restricting or banning the use of glyphosate. So have some countries, including several in Europe such as Austria, France, and Portugal. The emerging concern has been accompanied by mounting lawsuits—including a class-action consumer suit against Bayer, the manufacturer of Roundup, alleging that Roundup did not have adequate cancer warnings. Bayer recently settled the lawsuit for at least $23 million. Last year, Bayer announced that it will stop selling glyphosate-based products for residential use in the U.S. in 2023.

Some experts are also concerned about 2,4-D, another common chemical found in many weed killers. The EPA says that 2,4-D “generally has low toxicity for humans,” while WHO lists it as a “possible” carcinogen, though the evidence in humans remains “inadequate.” Some research has linked occupational exposure to 2,4-D—in farmers and professionals who apply herbicides—to a higher risk of lymphatic cancers, particularly Non-Hodgkin lymphoma. A number of studies have explored the link between 2,4-D exposure in pets and increased cancer risks; one published in 1991 found that the risk of malignant lymphoma in dogs doubled with four or more yearly applications of 2,4-D. While research is ongoing, Sass recommends erring on the side of caution and avoiding it.

Sass adds that there is also concern over organophosphate insecticides, such as chlorpyrifos and malathion, which can damage nerves and cause headaches, sweating, nausea, and muscle tremors. “Kind of like having a panic attack,” she says. “For a pet, they can be lethal.”

“Many of the health impacts are under the intended conditions of use, and according to the label,” says Sass. The IARC, however, says that the evidence of cancer in humans from real-world exposure to glyphosate is “limited” and the CDC says “the levels of 2,4-D found in the environment are lower than levels known to cause health problems.”

Segars argues that fully reading and following lawn-care product instructions should help keep users safe. “Doing your best to follow the label will reduce your risk of being sick,” she says. She urges people to pay attention to the recommended quantity of each application, as well as some of the more overlooked parts of the label, such as the environmental conditions under which a product should be used and how long to wait until using your lawn again. Windspeed, rain, and other factors can all be part of the calculus. As for when to return, she says most products are safe once they’ve dried, and that waiting 24-48 hours after an application is a good rule of thumb if a time isn’t given.

“Wear the long sleeves, wear the long pants, wear the gloves [during application]”, Segars advises. “Always read the bags.”

Are lawn fertilizers and other treatments bad for the environment?

Fertilizer is a major environmental concern for scientists because rain can wash it from farmers’ fields or neighborhood lawns into waterways, which can eventually carry the pollution into oceans. Although the agricultural sector is the main culprit on this front due the sheer volume of fertilizer used, the mechanics are more or less the same for treatments applied at home.

Two primary components of fertilizer are nitrogen and phosphate, which are designed to promote plant growth. But when they get into waterways they can cause algae—including toxic algae—to proliferate and oxygen levels in the water to plummet, making it difficult for much aquatic life to survive. Pollution from crop fertilizers, for example, has contributed to a massive “dead zone” in the Gulf of Mexico.

“You want to minimize the amount of nitrogen,” says Jim Galloway, a biogeochemist at the University of Virginia, though he notes that agricultural rather than residential use is the primary area of concern. “Lawns are a really, really tiny part of the question.”

Nitrogen is also a primary component of ammonia, which is a key ingredient in many fertilizers and is produced using fossil fuels that contribute to climate change. (It is sometimes explosive as well.) Additionally, unabsorbed nitrogen can lead to the release of nitrous oxide, a greenhouse gas roughly 300 times more potent than carbon dioxide.

Other lawn-care treatments can have an impact on wildlife as well. Insecticides containing neonicotinoids (often referred to just as “neonics”) are popular because they’re water soluble—meaning they soak into the soil and get into the moisture absorbed by plants, thereby increasing plants’ resistance to pests. In recent years, however, research has shown neonics to be harmful to bees, which provide valuable pollination services. The chemical has been shown to impact bees’ ability to forage and contributes to colony collapse.

Even chemical-free lawn care can be bad for the environment, thanks to the emissions from gas-powered lawn mowers.

What can I do to make my lawn care healthier?

One guaranteed way to reduce the risk and impact of lawn care is to have less lawn in the first place. That may mean replacing swaths of grass with native plants, or designing landscapes that limit the need for irrigation (also known as “xeriscaping”). Even leaving your grass a bit longer can help, Sass says, “If you do less work, the longer lawn will choke out the weeds.”

But if you are set on buying lawn-care products to maintain your yard, Ryan Anderson, the community integrated pest management manager with the non-profit Integrated Pest Management (IPM) Institute of North America, recommends avoiding products with glyphosate, 2,4-D, organophosphates, and neonics. He also says that people buying fertilizer sometimes don’t realize that there may be herbicides already mixed in, such as with so-called “weed and feed” blends—so double check before leaving the store. There are also some lower risk products, such as Fiesta, that he points people to if they insist on applying weed or pest control—though he warns that they can be expensive.

Sass also suggests that unless someone is a particularly experienced gardener, they can avoid unnecessary complications or accidents by staying away from products that they have to mix themselves from a concentrate. “I hope they are buying those products that are ready-mixed,” she says. She also adds that, instead of putting mosquito treatments on lawns, people could consider using bug repellent. (“Try not to apply directly on the skin,” she says, and aim for clothing instead.)

On the fertilizer front, Anderson recommends natural compost as an alternative, which can be sprinkled onto areas in need of nutrients. Aeration is another way to promote a healthy lawn, he says. Local hardware stores rent aeration machines, which put small cores in the lawn; you can also do it manually using specialized tools or even just a pitchfork to poke holes in the soil. The process helps revive compacted soil, he says, and doing it once a year should be sufficient.

“All those steps are best in the fall,” says Anderson, though he adds that the process may take time to show results, especially if a lawn has become accustomed to chemical treatments. “​​If you used it a lot in the past, there’s a risk of your grass feeling stressed out,” by a sudden lack of treatments, he says. “It’s not going to happen overnight”—but a healthier approach to lawn care is worth it.

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Contributor: Tik Root