Degradation of Soil Fumigants as Affected by Initial Concentration and Temperature

• Published in: Journal of environmental quality Vol. 30; no. 4; pp. 1278 - 1286
• Main Authors: Ma, Q.L., Gan, J., Papiernik, S.K., Becker, J.O., Yates, S.R.
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01-07-2001; Crop Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; Allyl Compounds; Applied sciences; Biodegradation; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Correlation coefficient; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fumigants; Fumigation; Fundamental and applied biological sciences. Psychology; Herbicides - metabolism; Hydrocarbons, Chlorinated; Injection; Insecticides - metabolism; Isothiocyanates - metabolism; Kinetics; Models, Theoretical; Pollution; Pollution, environment geology; Sandy loam; Soil and sediments pollution; Soil and water pollution; Soil degradation; Soil profiles; Soil science; Soil surfaces; Soils; Temperature; Temperature gradients; California; United States; North America; America; Biodegradation; Pollutant behavior; Fumigant; Chemical degradation; Soil pollution; Kinetic model; Medium effect; Organochlorine compounds; Concentration effect; Organic isothiocyanate; Kinetics; Rate constant; Sandy loam soil; Soil temperature
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2001.3041278x

ABSTRACT
Soil fumigation using shank injection creates high fumigant concentration gradients in soil from the injection point to the soil surface. A temperature gradient also exists along the soil profile. We studied the degradation of methyl isothiocyanate (MITC) and 1,3‐dichloropropene (1,3‐D) in an Arlington sandy loam (coarse‐loamy, mixed, thermic Haplic Durixeralf) at four temperatures and four initial concentrations. We then tested the applicability of first‐order, half‐order, and second‐order kinetics, and the Michaelis–Menten model for describing fumigant degradation as affected by temperature and initial concentration. Overall, none of the models adequately described the degradation of MITC and 1,3‐D isomers over the range of the initial concentrations. First‐order and half‐order kinetics adequately described the degradation of MITC and 1,3‐D isomers at each initial concentration, with the correlation coefficients greater than 0.78 (r2 > 0.78). However, the derived rate constant was dependent on the initial concentration. The first‐order rate constants varied between 6 and 10× for MITC for the concentration range of 3 to 140 mg kg−1, and between 1.5 and 4× for 1,3‐D isomers for the concentration range of 0.6 to 60 mg kg−1, depending on temperature. For the same initial concentration range, the variation in the half‐order rate constants was between 1.4 and 1.7× for MITC and between 3.1 and 6.1× for 1,3‐D isomers, depending on temperature. Second‐order kinetics and the Michaelis–Menten model did not satisfactorily describe the degradation at all initial concentrations. The degradation of MITC and 1,3‐D was primarily biodegradation, which was affected by temperature between 20 and 40°C, following the Arrhenius equation (r2 > 0.74).