Paraquats

Paraquats are a group of herbicides based on paraquat, a non-selective contact herbicide widely used in agriculture to kill a broad range of annual and perennial weeds. The most common commercial forms are paraquat dichloride and related salts, which are highly water soluble. Paraquats are applied as foliar sprays and act mainly through contact with green plant tissue, rather than requiring systemic movement within the plant.

In plants, paraquat accepts electrons from photosystem I and undergoes redox cycling, generating reactive oxygen species that destroy cellular membranes and inhibit photosynthesis. This rapid action makes paraquat effective for immediate weed knockdown but limits crop damage when applied carefully. Paraquat typically has little residual soil activity, tending to bind to organic matter and to degrade in sunlight.

Toxicology and safety: Paraquat is highly toxic to humans, and ingestion can be fatal. Exposure by inhalation or dermal contact can cause severe irritation and systemic illness. Symptoms of poisoning include mouth ulcers, abdominal pain, kidney and liver damage, and progressive lung injury that can lead to respiratory failure. Handling formulations requires strict safety precautions, including appropriate personal protective equipment and training, to prevent accidental exposure or intentional ingestion.

Regulation and environment: Because of its toxicity, paraquat products are subject to strict regulation in many countries, with licensing, labeling, restricted use, or outright bans in some jurisdictions. Environmentally, paraquats tend to bind to soils and are degraded by light in surface waters, but spray drift and improper handling can pose risks to non-target plants, animals, and aquatic life.