Vega-Pérez, Jacqueline

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    Adsorción y degradación de Metolachlor y Chlorpyrifos en suelos carbonatados y no carbonatado Puerto Rico.
    (2011) Vega-Pérez, Jacqueline; Arocha, Marco A; College of Agricultural Sciences; O’Hallorans, Julia M.; Dumas, José A.; Department of Crops and Agro-Environmental Sciences; Arocha, Marco A.
    Sorption and degradation are major processes that influence the fate of pesticides in the environment. Both processes affect the persistence and impact that these compounds may have on the environment. Leaching and runoff of pesticides into ground or surface waters increases with their persistence. The persistence of pesticides depends on chemical, physical and biological processes, occurring in the soil, and organic matter (OM) plays a major role. Our main objectives in this study were 1) to characterize the adsorption and degradation of the pesticides chlorpyrifos and metolachlor, in carbonate and non-carbonate soils, 2) to quantify and characterize organic matter in carbonate and non-carbonated soils, and 3) to characterize the processes of chemical degradation of chlorpyrifos and metolachlor in carbonate and noncarbonated soils in Puerto Rico. The carbonate soil series used in this study were: Aguilita, Colinas and Yauco, and the non-carbonated soils were, Bayamón, San Antón, and Tiburones. The results showed that both, chlorpyrifos and metolachlor, are less adsorbed in carbonate soils. The partition coefficient values (Kd) for chlorpyrifos were higher (132.58 to 406.11 L kg -1 ) than those obtained for metolachlor (4.36 to 11.63 L kg -1 ). The chlorpyrifos adsorption coefficient of organic carbon (Koc) for both, carbonate and non-carbonate soils is: San Antón ≥ Bayamón > Colinas ≥ Yauco > Aguilita ≥ Tiburones, and for metolachlor is: San Antón > Bayamón > Colinas > Tiburones ≥ Yauco > Aguilita. The values of the apparent degradation rate constant (K, d-1 ) for chlorpyrifos were -0.0397, -0.0359, -0.0250, -0.0224, -0.220 and -0.0155 d-1 for the series Yauco, San Antón, Colinas, Aguilita, Tiburones and Bayamón, with a t ½ of 18, 19, 28, 31, 32 and 45 days, respectively. Metolachlor obtained a K of -0.0203, -0.0182, -0.0179, -0.0175, -0.0136 and -0.0131 d-1 for the series Yauco, Aguilita, Colinas, San Antón, Tiburones, and Bayamón with a t ½ 34, 38, 39, 40 and 51 days, respectively. The results show that carbonate soils adsorbed fewer amounts of both pesticides than non-carbonated soils. There were differences in chemical and physical properties of OM between types soil. These results indicate that differences in adsorption and persistence of pesticides are related to the type of OM. The OM is the soil component that best correlated with the adsorption parameters in this study and the adsorption of pesticides in both soil types was less effective in carbonate soils. The retention and persistence of pesticides in carbonate soils is lower than in non-carbonated soils. This study represents a significant contribution in understanding the chemistry of pesticides in the environment bringing a special attention for pesticides best management application practices.