Only 39 out of 160 waste incineration plants in China answered inquiries about how they deal with their fly ash, and the air pollutant discharge of most plants exceeded national standards, two environmental protection organizations reported recently.

The organizations also queried environmental protection authorities, which are legally obliged to respond, but authorities frequently gave late, incomplete or no answers, said a report sent to the Global Times by Friends of Nature and the Wuhu Ecology Center.

Fly ash is made of fine particles that rise with the gases that result from incineration. There is little public information about how waste incineration plants dispose of their toxic fly ash, which contains the carcinogenic agent dioxin.

The two organizations requested 103 environmental protection bureaus disclose their monitoring data for 10 major air pollutants in 2014. They also asked 160 incineration plants to explain how they dispose of fly ash.

According to the report, 51 bureaus responded with data about air pollutants discharged by 65 waste incineration plants. Of those, 45 exceeded national standards.

Out of the 39 plants that explained how they dispose of fly ash, 26 sent it to a landfill, five used it as construction material and only eight sent it to qualified hazardous waste disposal sites, according to the report.

"Fly ash is categorized as hazardous waste but the disposal situation in China is bad," Yue Caixuan, head of the solid waste project of Wuhu Ecology Center, told the Global Times.

Pollutants contained in the fly ash, like dioxin, might be exposed in the air if it is made into construction materials, Yue said.

The organizations aimed to urge authorities to strengthen supervision over waste incineration plants by applying for information disclosure, but most environmental protection agencies gave inadequate replies, especially in Beijing, Shanghai and Guangzhou.

Some local governments issue subsidies to waste incineration plants to help them deal with household waste.

Yue said the amount of pollutants from incineration would be reduced if people sorted their garbage into different categories while disposing of it.

"We hope more citizens learn about waste incineration," said Yue, adding that the waste could become a valuable resource with the right approaches.