Clinical toxicology of acute glyphosate self-poisoning: impact of plasma concentrations of glyphosate, its metabolite and polyethoxylated tallow amine surfactants on the toxicity.

Introduction: Common major co-formulants in glyphosate-based herbicides, polyethoxylated tallow amine surfactants, are suspected of being more toxic than glyphosate, contributing to the toxicity in humans. However, limited information exists on using polyethoxylated tallow amine concentrations to predict clinical outcomes. We investigated if plasma concentrations of glyphosate, its metabolite and polyethoxylated tallow amines can predict acute kidney injury and case fatality in glyphosate poisoning.

Methods: We enrolled 151 patients with acute glyphosate poisoning between 2010 and 2013. Plasma concentrations of glyphosate, its metabolite, aminomethylphosphonic acid, and polyethoxylated tallow amines were determined in 2020 using liquid chromatography-tandem mass spectrometry. Associations between exposure and poisoning severity were assessed.

Results: Plasma concentrations of glyphosate and aminomethylphosphonic acid demonstrated good and moderate performances in predicting acute kidney injury (≥2), with an area under the receiver operating characteristic curve of 0.83 (95% CI 0.69-0.97) and 0.76 (95% CI 0.59-0.94), respectively. Polyethoxylated tallow amines were detected in one-fifth of symptomatic patients, including one of four fatalities and those with unsaturated tallow moieties being good indicators of acute kidney injury (area under the receiver operating characteristic curve ≥0.7). As the number of repeating ethoxylate units in tallow moieties decreased, the odds of acute kidney injury increased. Glyphosate and aminomethylphosphonic acid concentrations were excellent predictors of case fatality (area under the receiver operating characteristic curve >0.9).

Discussion: The 2.7% case fatality rate with 49% acute, albeit mild, acute kidney injury following glyphosate poisoning is consistent with previously published data. A population approach using model-based metrics might better explore the relationship of exposure to severity of poisoning.

Conclusions: Plasma concentrations of glyphosate and its metabolite predicted the severity of clinical toxicity in glyphosate poisoning. The co-formulated polyethoxylated tallow amine surfactants were even more strongly predictive of acute kidney injury but were only detected in a minority of patients.