This study has two objectives, namely: 1) to design and develop a micro-watershed protocol for pesticide monitoring; and 2) to pretest the developed protocol in the monitoring of certain target pesticides in their immediate points of discharge.

The identification of the target pesticides was based on a survey done among the rice farmers on June 14, 2002. The pesticides identified, as targets were the commonly used pesticides such as Decis, Karate, Basudine, Cymbush, Machete, Bayluside, Lorsban and Sumithion. Correspondingly, their active ingredients are deltamethrin, L-cyhalothrin, diazinon, cypermethrin, butachlor, niclosamide, chlorpyrifos and fenitrothion.

A multi-residue extraction procedure was developed in order to analyze a mixture of pesticide residues from the water samples taken from sources. Using Gas Chromatograph equipped with either Nitrogen Phosphorus Detector (GC-NPD) or Electron Capture Detector (GC-ECD), individual retention times of the pesticides were determined to ensure that the pesticides would not overlap during the reading. The results showed that six pesticides can be detected using GC-NPD and GC-ECD without their chromatograms overlapping and these are chlorpyrifos and diazinon for GC-NPD and chlorpyrifos, butachlor, L-cyhalothrin, cypermethrin, deltamethrin for GC-ECD. A method was also developed to determine the run time for the pesticides. For GC-NPD, run time was about 10 minutes. For GC-ECD run time was 17.29 minutes except for deltamethrin. During the validation, two analytical protocols were compared- SPE Mini Column (C 18) and Liquid/liquid extraction (US-EPA Method). The latter was seen to be more appropriate on the basis that it could detect the active ingredients of the five target pesticides.

In order to test the protocol developed, two sampling stations were selected according to a set of criteria- these are Wangan 1 and Wangan 2. Wangan 1 is about 120 hectares and was chiefly planted with rice. Wangan 2 is more than 1,000 hectares and is located outside a pineapple plantation.

In Wangan 1, chlorpyrifos, an organophosphate, was the most frequently detected. The other pesticides traced were: diazinon, another organophosphate, butachlor, an organochlorine and L-cyhalothrin, a pyrethoid. The presence of detectable levels of pesticides in the water samples were noted to coincide with certain farming activities such as planting in August and harvest from late October to November. On these occasions, soil tillage/movement led to soil erosion as evidenced by the heavy presence of silts in the sampling sites.

In Wangan 2, three organophosphates were detected and these were diazinon, chlorpyrifos and fenitrothion with diazinon and chlorpyrifos being more frequently detected than fenitrothion. Elevated levels were noted in the monitoring done on October 30. The water in the sampling sites during this date was visibly laden with silts per observation of its color.

Whenever pesticide concentrations exist in detectable levels, the pesticides were commonly traced in more than two stations suggesting transport or movement. It was further noted that the concentrations of the pesticide residues tend to be higher in Wangan 2 than in Wangan 1. This may be related to the sizes of the cultivated lands that are the immediate sources of pesticides.