Significance of the long-chain organic cation structure in the sorption of the penconazole and metalaxyl fungicides by organo clays

• Published in: Journal of hazardous materials Vol. 160; no. 1; pp. 200 - 207
• Main Authors: Rodríguez-Cruz, M.S., Andrades, M.S., Sánchez-Martín, M.J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.12.2008; Elsevier
• Subjects: Alanine - analogs & derivatives; Alanine - chemistry; Alanine - isolation & purification; Aluminum Silicates - analysis; Aluminum Silicates - chemistry; Applied sciences; Carbon - analysis; Clay mineral; Desorption; Exact sciences and technology; Fungicide; Fungicides, Industrial - chemistry; Fungicides, Industrial - isolation & purification; Kinetics; Long-chain cationic surfactant; Organo clay; Pollution; Quaternary Ammonium Compounds - chemistry; Sorption; Surface-Active Agents; Thermodynamics; Triazoles - chemistry; Triazoles - isolation & purification; Sorption; Organo clay; Long-chain cationic surfactant; Desorption; Clay mineral; Fungicide; Ammonium; Montmorillonite; Linear regression; Pesticides; Cationic surfactant; Mobility; Hydrophobic compound; Pollution; Aqueous solution; Sorbent; Comparative study; Organic compounds; Point source
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2008.02.102

Sorption–desorption of two different hydrophobic fungicides, penconazole and metalaxyl, by a series of clay minerals layered and non-layered (montmorillonite, illite, kaolinite, muscovite, sepiolite and palygorskite) modified with the two-chain cationic surfactant, dihexadecyldimetylammonium (DHDDMA) was studied by first time in this work. DHDDMA-clays showed a good capacity to sorb both fungicides from water. Freundlich sorption constants ( K f) increased 22–268-fold for penconazole and 4–112-fold for metalaxyl in relation to natural clays. High sorption irreversibility was observed for penconazole for all modified clays, while for metalaxyl this occurred only for some of the modified clays. Additionally, a comparative study of the sorption of the fungicides by clay minerals modified with organic cations of different structure was carried out by a statistical approach. Non-layered and layered clay minerals modified with the two-chain alkylammonium organic cation DHDDMA, and with single-chain organic cations octadecyltrimethylammonium (ODTMA) and hexadecylpyridinium (HDPY) were used as sorbents. The study indicated a significant linear regression between the distribution coefficients K d of fungicides and the organic carbon (OC) content of the organo clays ( r 2 ≥ 0.80, p < 0.001). According to this sorption of fungicides by partition between the aqueous solution and the organic medium created by the alkyl chains of the exchanged ammonium cations regardless of the type and structure of these cations is suggested. However, linear relationships between K d values of each pesticide by the different organo clays and their relative OC contents revealed higher increase in sorption for HDPY-clays (penconazole) and for ODTMA-clays (metalaxyl) pointing out different effectiveness of the OC provided by each organic cation. These effects were also supported by the values of K d relative to OC, K d oc . The results evidenced the different relative weight of alkyl cations to make organo clays effective barriers to prevent the mobility of pesticides from a point source of pollution.