Arsenic and lead levels exceeding surface-water standards were detected at three monitoring locations in Saraburi's canal network, the Pollution Control Department (PCD) said.
The findings were based on water samples collected on May 27 from Klong Nong Nam Khiao, Klong Ket and Huai Takhe as authorities investigate the source of pollution that recently turned parts of the waterway black.
However, tests showed that raw water met Type 3 surface-water standards, and treated tap water complied with drinking-water safety limits.
At the upstream section of Klong Nong Nam Khiao, arsenic was measured at 0.013 mg/litre and lead at 0.072 mg/litre, above the respective limits of 0.010 mg/litre and 0.050 mg/litre.
Elevated arsenic levels were also detected downstream of an industrial estate, where arsenic reached 0.019 mg/litre.
At Kut Nok Phlao weir, arsenic and lead were recorded at 0.020 mg/litre and 0.076 mg/litre, respectively, both above surface-water standards.
The PCD said no heavy metals exceeding standards were detected downstream from Huai Takhe near Suankularb Witthayalai School to the end of Klong Phriao, although some metals were found at certain points.
The PCD said analysis is under way to determine possible links between the heavy metals and pollution sources, based on findings from joint inspections carried out with the Department of Industrial Works (DIW) on May 28 and Thursday.
Additional sediment samples will also need to be examined for examine heavy-metals, said the department.
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