The government found a potentially hazardous amount of lead in some 200 tons of scrap material Thai authorities refused to accept from Japan, government sources disclosed.

The exportation of hazardous waste is banned by Japan in line with the Basel Convention, an international treaty aimed at protecting human health and the environment from the effects of harmful waste. But the latest incident signals that Japan's law lacks teeth.

The environment and industry ministries detected 10 times more lead than legally permitted, a finding apparently caused by the presence of printed circuit boards in the scrap.

The ministries issued a written warning to the Osaka-based exporter.

The scrap in question was exported to Thailand for recycling but was later found by Thai authorities in August 2014 to contain harmful electronic waste. The Thai government refused to import the scrap, citing lack of prior notification of a hazardous substance, as required by the Basel Convention.

The scrap was sent back to Japan in August this year, after which the Environment Ministry and the Ministry of Economy, Trade and Industry detected the excessive lead levels.

Although exportation of electronic waste is controlled under the convention, the number of cases in which electronic waste is intentionally exported as scrap is on the rise, the sources said Friday.