Estimation of dioxin exposure concentrations and dioxin intakes of workers at continuously burning municipal waste incinerators

In order to examine the dioxin exposure level in incinerator workers, total dust concentration in the breathing zone and dioxin concentrations in fly ash, slag and deposited dust were determined at three municipal waste incineration plants A, B and C equipped with continuously burning incinerators of stoker type. Three incinerators were operated at plants A and B, and four at plant C. The incinerators of plants A and B were equipped with electrostatic precipitators for removing particulate matter from the flue gas stream. In plant C, three incinerators were equipped with electrostatic precipitators and one with a bag filter. Total dust exposure concentrations during daily operation of the incinerators were 0.11 to 1.50 mg/m(3), and dioxin concentrations in the deposited dust were 1.0 to 6.4 ng toxicity equivalent (TEQ)/g. Dioxin exposure concentrations were estimated to be 0.5 to 7.1 pg TEQ/ m(3). Total dust exposure concentrations during periodic cleaning of the inside of the incinerator were 30 to 780 mg/m(3), and dioxin concentrations in the slag were 0.004 to 1.1 ng TEQ/g. Dioxin exposure concentrations were estimated to be 0.5 to 48 pg TEQ/m(3). Total dust exposure concentrations during periodic cleaning of the inside of the electrostatic precipirator were 51 to 2,000 mg/m(3), and dioxin concentrations in the fly ash were 7.3 to 64 ng TEQ/g. Dioxin exposure concentrations were estimated to be 370 to 92,000 pg TEQ/m(3), which were 150 to 37,000 times as high as the dioxin administrative level (2.5 pg TEQ/m(3)). Total of occupational and environmental dioxin intakes for an incinerator worker is predicted to exceed the tolerable daily intake (TDI: 4 pg TEQ/kg/d), when dioxin concentration in fly ash is 1,000 ng TEQ/g, even if an airline mask is used during the periodic maintenance. Consequently, it is essential to decrease the dioxin concentration in fly ash. When the dioxin concentration in fly ash is no higher than 100 ng TEQ/g, if an airline mask is used during the periodic maintenance, the dioxin intake is predicted to be lower than the TDI. Thus, wearing an airline mask would be effective.