Rate constants for metam-sodium cleavage and photodecomposition in water

• Published in: Journal of agricultural and food chemistry Vol. 41; no. 7; pp. 1129 - 1133
• Main Authors: Draper, William M, Wakeham, Diane E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-07-1993
• Subjects: Agronomy. Soil science and plant productions; AGUA; Applied sciences; Biological and medical sciences; Biological and physicochemical phenomena; Brackish; DEGRADACION; DEGRADATION; EAU; Exact sciences and technology; FOTOLISIS; Freshwater; FUMIGANT; FUMIGANTES; Fundamental and applied biological sciences. Psychology; Marine; Natural water pollution; PHOTOLYSE; Pollution; REACCIONES QUIMICAS; REACTION CHIMIQUE; Soil and water pollution; Soil science; Water treatment and pollution; Light effect; Laboratory study; Pollutant behavior; Pesticides; Decomposition; Photochemical reaction; Quantum yield; Thioureas; Fungicide; Aquatic environment; Cleavage; Water pollution; Kinetics; Rate constant; Degradation product; Carbamate; Photochemical degradation
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf00031a023

Metam-sodium is a soil fumigant with many important uses in agriculture. In soil the compound is rapidly and efficiently converted to methyl isothiocyanate (MITC), a volatile biologically active product. In this laboratory study the kinetics of conversion of metam-sodium to MITC, methylthiourea (MTU), and 1,3-dimethylthiourea (DMTU) in water were investigated. In the dark metam-sodium decomposed with a rate constant of 3.3 X 10(-4) min(-1) (t1/2 = 35 h, 25 degrees C, pH 7) and was converted to MITC with a yield of 15 mol%. In spite of weak absorption of near-UV light, metam-sodium photodegraded rapidly in the photoreactor with a near-UV quantum yield of 0.36 +/- 0.093 (n = 7). Photoproducts included MITC and DMTU, and the MITC yield was 19 mol%. These findings demonstrate that metam-sodium is considerably more stable in water than in soil. When exposed to midday, midsummer sunlight in shallow water, however, the compound is predicted by modeling to photodecompose with a half-life of less than 1 h