Glyphosate, the active ingredient of more than 750 herbicides, is the most widely used herbicide in Australia (15,000 tons/y) and worldwide (826,000 tons/y).
Glyphosate is considered environmentally safe due to its physico-chemical properties, presenting: (i) strong binding to soil; (ii) relatively rapid degradation; and (iii) potentially negligible risk to non-target organisms (mode of action specific to plants, fungi and some bacteria). However, studies reveal higher mobility of glyphosate in soils than expected and longer half-lives in soils (days-months) and water (<4-315 days).
Generally, acute effects are not expected at glyphosate levels found in the environment. However, several sublethal effects have been observed in different organisms (rats, fish, amphibians, invertebrates) at glyphosate concentrations below regulatory guidelines: hepatorenal damage, endocrine disruption, reproductive impairment, genotoxicity, morphological alterations, oxidative stress. Toxicity is species- and development-specific, with higher toxicity expected in amphibians and the early-life stages of organisms. In addition, the outbreak of glyphosate-resistant weeds (12 Australia; 32 worldwide) has led to increased use (multiple sprayings per season) of glyphosate, alone or combined with other herbicides. After the controversy arose in 2015, several regulatory authorities, in Australia and worldwide, concluded that glyphosate does not pose a carcinogenic risk to humans at realistic exposure levels.
Recent studies suggest that glyphosate-based herbicides are not as innocuous as expected. Some surfactants used in commercial formulations are more toxic than glyphosate itself. Thus, whole mixtures need to be evaluated to establish their potential risk. Comprehensive studies on the persistence of glyphosate in the environment and the associated chronic long-term effects, at population- and ecosystem-level, are still needed.