Phytotoxicity

Phytotoxicity refers to toxic effects that substances or environmental conditions exert on plants, leading to inhibited growth, chlorosis, necrosis, reduced biomass, or impaired reproduction. It can result from herbicides and other pesticides, industrial pollutants and trace metals, salts causing osmotic stress, or natural allelopathic compounds released by certain plants. Phytotoxic responses vary with species, developmental stage, dose, exposure route, and environmental conditions.

Most phytotoxicants act by disrupting essential physiological processes. Common targets include photosynthesis (for example, inhibition of photosystem II), respiration, membrane integrity, nutrient uptake, and hormone signaling. Oxidative stress and lipid peroxidation are frequent secondary effects. Some chemicals interfere with germination or early root growth, while others affect mature tissues whether through uptake or translocation.

Symptoms range from chlorosis and necrosis to stunted growth, leaf deformation, or wilting. Assessment typically uses dose–response assays such as seed germination inhibition or root and shoot elongation tests, often reporting values like EC50—the concentration that reduces growth by 50%—or NOAEL/LOAEL for longer exposures. Physiological measurements such as chlorophyll fluorescence or gas exchange can quantify impairment.

Examples include paraquat and diquat, which generate reactive oxygen species; atrazine, which disrupts photosystem II; glyphosate, which inhibits aromatic amino acid synthesis; and heavy metals such as cadmium and lead that disrupt enzyme function and nutrient balance. In soils, phytotoxicity depends on pH, organic matter, and metal speciation, which influence chemical availability.

Phytotoxicity is a central consideration in agriculture, weed management, environmental risk assessment, and phytoremediation, guiding regulatory thresholds and monitoring of non-target impacts.