Urine samples (24 h) were collected from the rice farmers before and post insecticide application. Samples were analysed for 3,5,6-trichloropyridinol (TCP), the major urinary metabolite of chlorpyrifos, using an enzymatic pre-treatment before extraction followed by HPLC-MS/MS. Absorbed Daily Dose (ADD) of chlorpyrifos for farmers were then estimated from urinary TCP levels, expressed as 渭g g鈭? creatinine. The analytical method for urinary TCP had a low detection limit (0.6 渭g L鈭?), acceptable recovery values (80-114%), and low relative percentage differences in duplicate and repeated samples.
Post-application chlorpyrifos ADD of farmers varied from 0.4 to 94.2 渭g kg鈭? (body weight) d鈭? with a mean of 19.4 渭g kg鈭? d鈭? which was approximately 80-fold higher than the mean baseline exposure level (0.24 渭g kg鈭? d鈭?). Hazard Quotients (ratio of the mean ADD for rice farmers to acute oral reference dose) calculated using acute oral reference doses recommended by United States and Australian agencies varied from 2.1 (Australian NRA), 4.2 (US EPA) to 6.9 (ATSDR).
Biological monitoring using HPLC-MS/MS analysis of urinary TCP (24 h) was found to be an effective method for measuring chlorpyrifos exposure among farmers. This case study found that Vietnamese rice farmers had relatively high exposures to chlorpyrifos after application, which were likely to have adverse health effects.