Adsorption and biodegradation of carbaryl on montmorillonite, kaolinite and goethite

Bioavailability of pesticides adsorbed on mineral surfaces is an important determinant of their environmental fate. Carbaryl (1-naphthyl-N-methylcarbamate) was used as a model compound to illustrate the impact of adsorption characteristics and microbial activity on the bioavailability of organic compound adsorbed on clay minerals and goethite. Batch experiments were applied to determine the sorption isotherms and biodegradation kinetics. Metabolic activity of Pseudomonas putida in the absence and presence of montmorillonite, kaolinite or goethite was monitored by microcalorimetry. Adsorption mechanisms of carbaryl were studied by Fourier Transform Infrared Spectroscopy (FTIR). Montmorillonite presented a higher adsorption capacity for carbaryl than goethite and kaolinite. Degradation of adsorbed carbaryl by P. putida followed the sequence montmorillonite > kaolinite > goethite, which is in accordance with the binding strength of carbaryl on the minerals. The presence of montmorillonite enhanced the activity of P. putida and ultimately stimulated the bioavailability of carbaryl. Goethite displayed an inhibitory effect on bacterial activity and reduced carbaryl degradation. The biodegradation of mineral-adsorbed carbaryl was mainly controlled by the activity of the degrading microorganisms.