DISTRIBUTION OF ORGANOCHLORINE PESTICIDES IN THE CHAO-PHRAYA RIVER, THAILAND

Water samples from the Chao Phraya River, the main river in Thailand w ere collected and analyzed during 1988-1994. Organochlorine pesticides such as HCHs, DDTs, aldrin, dieldrin and chlordanes were determined. Aldrin and dieldrin had high frequencies of occurrence in water sample s. The concentration median of the pesticides was approximately one or der of magnitude higher than those of total HCHs and DDTs. Levels of a ldrin were relatively high in the upstream while levels of DDTs were h igh in the urban area of Bangkok during 1989-1990. p,p'-DDE levels wer e relatively higher in 1992. No clear trends in the levels of pesticid es were observed.