Department of Agriculture has annually conducted a pesticide and herbicide monitoring program in major rivers, including Chao Phraya river, Pa Sak river, Tha Chin river and Bang Pakong river, in the fiscal years
of 2009-2012 [3].The concentration of the pesticides and herbicides was found at the maximum values in the rainy season because the pesticides and herbicides were directly rinsed off-and-drain out to the rivers before they had been adsorbed on the soil.