The environmental fate of agro-chemicals: A case study in the mae sa noi watershed

Abstract

© 2007, Springer-Verlag Berlin Heidelberg. “Pesticides spread their toxic reach,” and “the source of life is poisoned”. These were headlines of the daily Bangkok Post in 1997 and 2001. When the agriculture of Thailand shifted from subsistence farming to the production of cash crops about three decades ago, the farmers in the mountainous area of northern Thailand also rapidly increased their use of pesticides. Farmers, whose livelihoods depend on the downstream flow of water claim that there is too much poison in the rivers. Considerable concentrations of pesticide residues have also been detected in soils, food and breast milk (Baun et al., 1998; Thapinta and Hudak, 2000; Stuetzet al., 2001). Moreover, it was reported that local lychee farmers are poisoned by organochlorine pesticides, indicating careless handling of these substances (Stuetz et al., 2001). Careless use of pesticides may also cause a direct input of pesticides into surface waters. Atmospheric deposition of volatilized pesticides, soil surface runoff and leaching through the soil are further potential pathways through which surface water may be contaminated. However, we are not aware of any studies of the flow pathways of water and contaminants in Thai soils. Thus, the overall aim of our study was to quantify the leaching of pesticides through a soil in a lychee orchard in order to evaluate the contribution of this pathway to the total river water contamination.