The Food and Drug Administration has revoked the licences for two brands of mosquito coil after finding unregistered chemicals in the products.
In an announcement posted on the FDA website, deputy secretary-general Somchai Preechataweekit said on Wednesday the decision was made at a meeting on Sept 21.
Tests found dangerous substances were imported from China for use in Ranger Scout coils and Ars Plus mosquito coil 1 products.
The FDA had not found the chemical d-Allethrin in the products, as registered by the manufacturers. Instead, there were three unregistered chemicals -- Bioallethrin, Meperfuthrin and Heptafluthrin -- in the coils.
The FDA had never registered two of the three chemicals, Meperfluthrin and Heptafluthrin, for use in mosquito repellents, nor had the World Health Organisation.
There had been no studies to decide the suitable amounts of those chemicals to use in mosquito coil products.
The three chemicals were considered dangerous substances as they had not yet passed evaluation tests for efficiency, safety and suitable amounts to use for humans, animals and the environment, he said. They must be registered before they can be imported.
To protect consumers, the FDA decided to revoke the licences for Ranger Scout and Ars Plus mosquito coil 1.
Mr Somchai said he has asked the importers of the unregistered chemicals to recall the two products from sale.
The manufacturer of Ranger Scout, Thanatkorn International Co, insists that its products do meet safety and quality standards.
The firm posted a letter explaining its position on its website www.thanakorn.com on Sept 19.
The company said competitors had made false accusations its products would negatively affect customers.
Also posted was a copy of a letter purporting to be from the office of public prosecution, dated July 16 this year, saying it had decided not to prosecute the company for importing three dangerous chemicals.