Many people question the safety of chemicals used in agriculture and on home lawns, specifically asking if fertilizer products can cause cancer. To address this public health inquiry, it is necessary to differentiate between the core nutrients in fertilizer and other chemical substances that may be applied alongside them. Understanding a product’s specific composition is the first step toward clarifying potential health risks.
What Are We Talking About? Fertilizer Components vs. Associated Chemicals
Fertilizer is primarily defined by the three macronutrients plants require: Nitrogen (N), Phosphorus (P), and Potassium (K), often referred to collectively as NPK. These compounds are fundamental chemical building blocks designed to support plant growth. The risks associated with fertilizer often do not originate from these primary nutrients themselves but from two entirely separate categories of substances.
The first category includes contaminants, which are unintended impurities present in the raw materials used to manufacture the fertilizer. The second category involves co-applied products, such as herbicides or pesticides, that are intentionally mixed with or applied at the same time as the fertilizer. Products like “weed & feed” mixtures exemplify this confusion. The cancer risk, where it exists, is generally linked to the contaminants or the co-applied products, not the core NPK nutrients.
Reviewing the Direct Evidence: NPK and Heavy Metals
The core NPK compounds are not generally classified as carcinogens, but risks arise from impurities and chemical breakdown products. Nitrogen fertilizers can lead to the formation of nitrate in soil and water. When ingested, nitrate can be reduced to nitrite, which may then react in the stomach to form N-nitroso compounds (NOCs). NOCs are known animal carcinogens and are considered probably carcinogenic to humans, with studies linking high nitrate exposure in drinking water to potential increases in the risk of gastric, colon, and kidney cancers.
Heavy metals represent a second, distinct risk category, particularly those found as contaminants in the phosphate rock used to produce phosphorus fertilizer. Elements such as cadmium, arsenic, and lead are naturally present in these raw materials and can remain in the final product. Long-term use of fertilizers containing these impurities can lead to the accumulation of heavy metals in agricultural soils, where they may be taken up by crops or contaminate water sources. Chronic exposure through the food chain or drinking water can lead to long-term health concerns.
Cadmium is a heavy metal of particular concern, with concentrations varying depending on the geographical origin of the phosphate rock used. Regulatory bodies monitor these levels to limit soil accumulation and transfer to the food supply. While some studies have suggested that high dietary nitrate intake, especially from vegetables, may not increase the risk of digestive system cancers, the risk from environmental exposure, particularly contaminated drinking water, remains a focus for regulatory oversight. The evidence overall suggests that the primary cancer concerns related to fertilizer are linked to the long-term impact of heavy metal contaminants and the environmental breakdown of excess nitrogen into N-nitroso compounds.
The Glyphosate Confusion: Clarifying Herbicide vs. Fertilizer Risk
Much of the public concern attributed to “fertilizer” is rooted in the controversy surrounding the herbicide glyphosate, a chemical frequently used in conjunction with fertilizers. Glyphosate is a broad-spectrum systemic herbicide, chemically distinct from NPK nutrients. It is often sold in blended products like “weed and feed” or applied simultaneously on agricultural fields, leading to the public conflation of the two different chemical products and their associated risks.
The classification of glyphosate remains a subject of international debate among scientific and regulatory agencies. The World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate in 2015 as “probably carcinogenic to humans” (Group 2A). This classification was based on “limited” evidence in humans, primarily linking it to non-Hodgkin lymphoma in occupational exposure settings, and “sufficient” evidence from animal studies.
In contrast, other major regulatory bodies, such as the European Food Safety Authority (EFSA) and the United States Environmental Protection Agency (EPA), have concluded that glyphosate is unlikely to pose a carcinogenic hazard when used according to instructions. This difference in classification often comes down to whether the agency evaluates the hazard (the intrinsic capacity to cause cancer) or the risk (the probability of exposure causing harm under real-world conditions). Regardless of the regulatory classification, it is important to remember that glyphosate is an herbicide designed to kill plants, not a plant nutrient like NPK.
Minimizing Exposure: Safety Practices for Home Use
Home users can significantly reduce potential exposure risks by adopting simple safety practices when handling garden chemicals.
Key Safety Practices
- Always read and strictly follow all application and safety instructions provided on the product label.
- Observe the recommended re-entry time, which dictates how long people and pets must stay off the treated area until the product has settled or dried.
- Wear appropriate personal protective equipment (PPE), such as impermeable gloves, long-sleeved clothing, and protective eyewear, to prevent skin and eye contact.
- After application is complete, sweep up any excess granular product from hard surfaces like sidewalks or driveways to prevent runoff into water systems and to protect children and pets.
- Store all products in their original, tightly closed containers in a cool, dry, and secure location, such as a locked cabinet or high shelf, away from children and pets.