Propensity for the formation of dioxins during the cool-down of plumes from medical waste incinerators in South Africa

Abstract

The most toxic group of substances associated with waste incineration emission controls are the 210 dioxin compounds. Concentrations at which it is required to be measured range are 0.1 ng/m3 in the EU where large 100 000 tonne per annum plants are operated and to 0.2 ng/m3 in SA where the largest plants are less than 5000 tonne per annum. EU target daily intakes are 1 pg/kg/day and this is determined by measurements and fate and transport models of emission. Dioxin compounds are formed as by products of all combustion processes in the gas phase. With the introduction of emission controls in USA, the main source of dioxin has changed from industrial activities (12 kg/annum)1 to forest fires (1.3 kg/annum) and open burning of general waste (0.62 kg/annum)2. In SA, as in most developing countries, less than 1% of the 137 medical waste incinerators registered in SA3 are fitted with gas clean up systems, and the exhaust gases are vented at temperatures above the onset of dioxin formation (450 °C to 150 °C). It is not possible to measure in a plume, and the existing stack dispersion models do not address the conditions occurring at the exit of the stack, so it is also not possible to make estimates of the human health impacts of these emissions using international standard methodologies