Concentrations of PLABs in water samples collected in Tokyo, Malaysia, and the Mekong Delta ranged from o0.005–0.638 mg/L, from 0.007 to 0.913 mg/L, and from o0.005–0.867 mg/L, respectively (Fig. 4). Significant concentrations of PLABs were detected at all stations except for four out of nine groundwater samples in the Mekong Delta and six headwater samples in the Minamiasakawa River and Yajigawa River in Tokyo. Higher concentrations of LABs were more often found in Southeast Asian waters than in the urban rivers of Tokyo. The highest concentrations in Southeast Asia were observed at urban sites such as Kuala Lumpur,Malacca, and George Town in Malaysia, and Can The
City in the Mekong Delta. On the other hand at rural sites in Malaysia and in the Mekong Delta, PLABs concentrations were generally lower than 0.1 mg/L which suggest less input of sewage and/or dilution by large mass of river water.