Deriving sulfamethoxazole dissipation endpoints in pasture soils using first order and biphasic kinetic models.
Single first-order (SFO) kinetic model is often used to derive the dissipation endpoints of an organic chemical in soil. This model is used due to its simplicity and requirement by regulatory agencies. However, using the SFO model for all types of decay pattern could lead to under- or overestimation of dissipation endpoints when the deviation from first-order is significant. In this study the performance of three biphasic kinetic models - bi-exponential decay (BEXP), first-order double exponential decay (FODED), and first-order two-compartment (FOTC) models was evaluated using dissipation datasets of sulfamethoxazole (SMO) antibiotic in three different soils under varying concentration, depth, temperature, and sterile conditions. Corresponding 50% (DT50) and 90% (DT90) dissipation times for the antibiotics were numerically obtained and compared against those obtained using the SFO model. The fit of each model to the measured values was evaluated based on an array of statistical measures such as coefficient of determination (R(2)adj), root mean square error (RMSE), chi-square (χ(2)) test at 1% significance, Bayesian Information Criteria (BIC) and % model error. Box-whisker residual plots were also used to compare the performance of each model to the measured datasets. The antibiotic dissipation was successfully predicted by all four models. However, the nonlinear biphasic models improved the goodness-of-fit parameters for all datasets. Deviations from datasets were also often less evident with the biphasic models. The fits of FOTC and FODED models for SMO dissipation datasets were identical in most cases, and were found to be superior to the BEXP model. Among the biphasic models, the FOTC model was found to be the most suitable for obtaining the endpoints and could provide a mechanistic explanation for SMO dissipation in the soils.
Department of Civil & Environmental Engineering, Faculty of Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
Prakash
P
Srinivasan
Department of Civil & Environmental Engineering, Faculty of Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand. Electronic address: a.sarmah@auckland.ac.nz.
Ajit K
AK
Sarmah
Science & Capability, Department of Conservation, Private Bag 3072, Hamilton 3240, New Zealand.
Maheswaran
M
Rohan
D000890:Anti-Infective Agents / Q000032:analysis* / Q000737:chemistry; D001499:Bayes Theorem; D001673:Biodegradation, Environmental; D004784:Environmental Monitoring; D008956:Models, Chemical; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D013420:Sulfamethoxazole / Q000032:analysis* / Q000737:chemistry
D000890:Anti-Infective Agents; D012987:Soil; D012989:Soil Pollutants; D013420:Sulfamethoxazole
Biphasic kinetic; First-order kinetic; Modeling; Soil dissipation; Sulfonamide