The purpose of this study was to assess health risk and cholinesterase levels due
to chlorpyrifos exposure among rice farmers in Phatthalung Province. The 31 study subjects
used chlorpyrifos insecticides. Air samples were collected in the breathing zone of the rice
farmers using OSHA (Occupational Safety and Health Administration) versatile sampler (OVS-
2) tubes, containing a glass fiber filter and two sections of XAD-2 adsorbent, following NIOSH
method no. 5600. The accuracy, precision and detection limit of this method were also tested.
Blood samples were collected and questionnaires were also administered by interviewers.
Results revealed that the limit of detection of the method was 0.1 µg/tube. The percent
recoveries of the method ranged from 99.20% to 102.83% with coefficients of variation of less
than 7.00% for chlopyrifos concentrations of 1-3 μg/tube. The average occupational chlorpyifos
exposure among rice farmers was 0.062 ± 0.092 mg/m3. Thirty subjects (96.8%) had been
exposed to chlorpyrifos concentrations less than the TLV-TWA of 0.1 mg/m3 recommended by
the American Conference of Governmental Industrial Hygienists (ACGIH). Many farmers had
developed signs and symptoms, sweating (80.7%), chest tightness (32.3%), vomiting (25.8%)
and blurred vision (35.5%). A high correlation coefficient was found between chlorpyrifos
exposure and levels of cholinesterase in blood (r=0.872; p=0.01). The estimated daily intake of
chlorpyrifos exposure through inhalation was 0.004 mg/ kg-day. The risk of exposure to
chlorpyrifos was not acceptible (HQ ≥ 1).