High mineral adsorption of glyphosate versus diethyl phthalate and tetracycline, during visible light photodegradation with goethite and oxalate

The increasing presence of pesticides, pharmaceuticals and plasticizers in environmental media is threatening public health and ecosystems. Remediation of contaminated waters by Fenton-like photoreactions to degrade pollutants is considered as sustainable because this method mimics natural attenuation and involves safe iron oxides and oxalate. However, knowledge about the degradation efficiency of organic pollutants is scarce, notably in the presence of minerals. Here, we tested the degradation of the tetracycline antibiotic, the diethyl phthalate plasticizer, and the glyphosate herbicide using combinations of visible light, goethite (FeO(OH)), and oxalate. Pollutant residues were also extracted from the precipitate at the end of a reaction. Results show that pollutant removal, including adsorption and degradation, reached 99.7% for tetracycline, 87.1% for diethyl phthalate, and 83.3% for glyphosate using a goethite/oxalate/visible light system. The corresponding degradability was 99.5% for tetracycline, 87.1% for diethyl phthalate, and only 39.7% for glyphosate. These findings show that, whereas tetracycline and diethyl phthalate are well degraded, a major proportion of glyphosate remains adsorbed on goethite. As a consequence, glyphosate levels and toxicity may have been underestimated in previous investigations since glyphosate and glyphosate residues may be further desorbed from minerals and reenter aquatic and biological media.