(21g) Environmental Contaminant Glyphosate: Occurrence, Persistence, and Health Effects

Among the most widely used agricultural chemicals globally, glyphosate-based herbicides have applications in agriculture, forestry, industrial weed control, lawn care, gardening, and aquatic environments. Agricultural sites with the largest glyphosate use include soybean, corn, cotton, pasture, and hay fields. Active ingredients in glyphosate-based herbicides include glyphosate acid, glyphosate isopropylamine salt, and glyphosate ammonium salt. Sorption of glyphosates onto soils is strongly pH-dependent. Glyphosate can accumulate in natural environments and can be toxic not only to plants, but also to humans, animals and bacteria. Glyphosates exhibit a high leaching potential, thereby contaminating water sources including groundwater; however, glyphosate herbicides can be microbially degraded. In addition to discussing its relative agricultural and horticultural utility, public policy must weigh the economic and social impacts of glyphosate use.

The best-known glyphosate-containing herbicide is Roundup. The amount of glyphosate in Roundup varies depending on the specific product, ranging from ~1% in ready-to-use formulations to >50% in concentrated versions. Concentrations of glyphosate in Roundup are summarized below:

• Roundup Ultra, Glyphomax Plus, Glyphos, Roundup, etc.: contain 3 lbs/gal of glyphosate.
• Roundup UltraDry: contains 64.9% glyphosate.
• Concentrated Roundup: Products like Roundup Pro Weed Killer contain 50.2% glyphosate;
• Generic Glyphosate: Generic glyphosate herbicides, like Weed Pro Glyphosate 41% (Roundup) Herbicide, contain 41% glyphosate;
• Other Roundup Products: Some Roundup formulations, like Roundup Concentrate Plus, contain 18% glyphosate;
• Roundup UltraMax: contains 3.7 lbs/gal of glyphosate;
• Ready-to-Use Roundup: Products like Roundup Ready-To-Use Extended Control Weed & Grass Killer Plus Weed Preventer II contain around 1% glyphosate:

Many foods have shown elevated concentrations of glyphosates, including honey, fruits and nuts (pears, blackberries, limes, raisins, and walnuts), vegetables (yams, potatoes, peas, and dried lentils), and meat and fish.

Human exposure to glyphosate can result in eye and skin irritation, gastrointestinal effects, nasal discomfort, tingling and throat irritation. The lethal dose 50 (LD₅₀) for glyphosate in humans is not well-established due to limited data and the complex nature of glyphosate formulations. Animals exposed to glyphosate-derived herbicides have displayed anorexia, lethargy, hypersalivation, vomiting, and diarrhea. Studies in animals have shown that the acute dermal toxicity LD₅₀ for glyphosate is generally high, ranging from 4,900 to 10,537 mg/kg body weight. Roundup has an acute dermal toxicity LD₅₀ exceeding 5,000 mg/kg and an acute oral toxicity for rats exceeding 4,320 mg/kg. The acute oral LD₅₀ in mice and goats was greater than 10,000 and 3,530 mg/kg, respectively. Glyphosate is not carcinogenic in lifetime feeding studies in rats and mice, indicating lower toxicity in acute exposures. Chronic exposure to glyphosate, even at low levels, has been linked to adverse health effects concerns in some studies. The U.S. EPA has classified glyphosate as “not likely to be carcinogenic to humans”; however, the IARC, of the World Health Organization, reclassified glyphosate in 2015 as “probably carcinogenic to humans”. Therefore, while the acute carcinogenicity of glyphosate to humans appears low, health agencies must urge the public to avoid exposure; and, where unavoidable, to follow safety guidelines.

Although known to degrade relatively quickly in soil following application, glyphosates and their metabolites can persist in soil, water, and plant tissues. The median half-life of glyphosate in soil has been reported to be between 2 and 197 days, with a typical half-life of 47 days as a recommended value. The median half-life of glyphosate in water ranges from a few days to 91 days. If chelating cations are present, the half-life can be greatly increased. Surface water contamination and soil erosion are likely from aquatic uses of glyphosate.

Beyond human health effects, this presentation also addresses effects of glyphosate on aquatic species and microorganisms. As an example, the long-term exposure of glyphosate to Nile Tilapia had adverse effects on the histopathological and biochemical alterations of the fish. Glyphosate also affects cell development in the early stages of life in humans and animals, and has a significant toxic effect on neurotransmission. It can induce oxidative stress, neuroinflammation and mitochondrial dysfunction. Thus, it requires significant regulatory oversight.