Anamai ThetkathuekMatthew KeiferWijitr FungladdaJaranit KaewkungwalChantana PadungtodBarry WilsonSamlee MankhetkornBurapha UniversityChiang Mai UniversityUniversity of Washington, SeattleMahidol UniversityThailand Ministry of Public HealthUniversity of California, Davis2018-06-212018-06-212005-04-01Chemical and Pharmaceutical Bulletin. Vol.53, No.4 (2005), 422-424000923632-s2.0-21144434087https://repository.li.mahidol.ac.th/handle/20.500.14594/16448We sought to investigate the early biological effects of chlorpyrifos among 53 Thai fruit farm workers by measuring the plasma cholinesterase (PChE) and red blood cell cholinesterase (AChE) activities, a biomarker of organophosphate (OPs) pesticide during one fruit crop. The ChE activity (Vm/K m) was spectrophotometrically analyzed before and after exposing to chlorpyrifos. The Vm/Km values of both non-spraying and spraying seasons are found as normal distribution pattern. The median PChE and AChE activities among farm workers in the non-spraying season were 2.3×10-3s-1 and 7.26×10-5s -1, respectively. The median PChE and AChE activities of the farm workers in the spraying season were 2.02×10-3s-1 and 5.95×10-5s-1, respectively. The mean V m/Km values of PChE shifted left (t-test, p=0.013), indicating a decrease in PChE activity in the farm workers exposed to chlorpyrifos. However, the Vm/Km values of AChE in nonspraying season and in the spraying season were not different (t-test, p=0.246). We propose that PChE activity can be used as a biomarker for monitoring early toxicity induced by chlorpyrifos insecticide. © 2005 Pharmaceutical Society of Japan.Mahidol UniversityChemistryPharmacology, Toxicology and PharmaceuticsArticleSCOPUS10.1248/cpb.53.422