Samples of sediment taken from the Kok riverbed, in Muang district of Chiang Rai and Mae Ai district of Chiang Mai, have been found to contain excessive amounts of arsenic, which is dangerous to aquatic species that feed on sediment.
The Chiang Mai Pollution Control Office reported on its website that it had collected samples of sediment from the Kok riverbed, at six locations in the two districts on March 31st and April 1st, for testing.
These tests show the amount of arsenic in the sediment ranges from 20mg/kg to 33mg/kg, which is beyond the safety level of 10mg/kg, reported the office, adding that excessive arsenic content threatens the ecological system of the river, endangering aquatic life.
Other heavy metals found to exceed safety levels in the sediment include nickel and chromium.
The Chiang Rai provincial administration has, however, offered public assurances that tap water, originating from the Kok River, is still safe for consumption.
Officials have been instructed, by the provincial governor, to collect specimens of fish caught in the Kok River for tests on a regular basis, to ensure that they are safe for consumption.
