Monod kinetics rather than a first-order degradation model explains atrazine fate in soil mini-columns: Implications for pesticide fate modelling

• Published in: Environmental pollution (1987) 2010-05, Vol.158 (5), p.1405-1411
• Main Authors: Cheyns, K., Mertens, J., Diels, J., Smolders, E., Springael, D.
• Format: Article
• Language: English
• Subjects: Atrazine; Atrazine - chemistry; Biodegradation; biomass; HYDRUS-1D; Inverse modelling; Kinetics; leaching; Models, Chemical; Monod kinetics; Pesticides - chemistry; rain; risk; soil; Soil Pollutants - chemistry
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2009.12.041

Pesticide transport models commonly assume first-order pesticide degradation kinetics for describing reactive transport in soil. This assumption was assessed in mini-column studies with associated batch degradation tests. Soil mini-columns were irrigated with atrazine in two intermittent steps of about 30 days separated by 161 days application of artificial rain water. Atrazine concentration in the effluent peaked to that of the influent concentration after initial break-through but sharply decreased while influx was sustained, suggesting a degradation lag phase. The same pattern was displayed in the second step but peak height and percentage of atrazine recovered in the effluent were lower. A Monod model with biomass decay was successfully calibrated to this data. The model was successfully evaluated against batch degradation data and mini-column experiments at lower flow rate. The study suggested that first-order degradation models may underestimate risk of pesticide leaching if the pesticide degradation potential needs amplification during degradation. Population dynamics of pesticide degrading population should be taken into account when predictions of pesticide fate are made to avoid underestimation of pesticide break-through towards groundwater.