PARENT SESSION
3B General and multipurpose analysis
9:00 AM to 7:00 PM, Tuesday, 08 May 2001

(T/EH121) Determination of organo-phosphorus pesticides in water samples from some typical agricultural areas of Vietnam by solid phase microextraction.

Nguyen, Hung Minh¹, Pham, Hung Viet¹, Pham, Ngoc Ha¹, Phan, Thu Thuy¹, Giger, Walter², Berg, Michael², ^{1 2}

ABSTRACT- Solid phase microextraction (SPME) combined with GC/MS quantification was optimized for the analysis of polar and non-polar pesticides in water samples from agricultural areas in Northern Vietnam. The target compounds were organo-phosphorus and triazine pesticides. Using polyacrylate (PA) coated fibers, the SPME method was optimized for both, adsorption and desorption processes. Water samples of only 1.3 mL or 4.0 mL were necessary for automated or manual SPME, respectively. With regard to the broad polarity range of the target pesticides, optimum adsorption conditions were reached by addition of 6 mol/L NaCl to the water sample (salting out) and with a fiber exposure for 50 min. at 60 °C. Desorption from the SPME fiber was best at 250 °C. The method detection limits (MDLs) were 3-40 ng/L, depending on the pesticide's polarity. By applying deuterated compounds (e.g. d10-diazinon, d5-atrazine) and similar-structured compounds (e.g. chlorthion, prothoate) as internal standards, high recoveries of 75-116% (SD 1-9%) were reached for pesticide concentrations of 50-100 ng/L. Water samples from irrigation channels, rice fields, lakes, and rivers were collected in agricultural areas in Northern Vietnam (Thaibinh, Hanoi). In the irrigation channels, the two most abundant pesticides fenitrothion and diazinon had maximum concentrations of 980 ng/L and 196 ng/L, respectively. In the lakes, highest concentrations were 175 ng/L for fenitrothion and 117 ng/L for diazinon. Very high fenitrothion concentrations of 510'000 ng/L were measured in water of flooded rice fields after pesticide application. However, fenitrothion in the flooded fields decreased rapidly (i.e. within 3-5 days) to levels 220 ng/L, mainly due to flushing with unpolluted water. Triazine herbicides were not abundent in the rice growing area.

Key words: organo-phosphorus pesticides, water, solid phase microextraction, Vietnam