Human Health Risk Assessment of a pilot-plant for catalytic pyrolysis of mixed waste plastics for fuel production.

Dioxins, PCBs and VOCs are the main hazardous chemicals emitted by gaseous streams from catalytic pyrolysis of waste plastics. In this work we propose a methodology to assess toxic and cancer risk under uncertainty, due to inhalation and ingestion of these chemicals by considering complex scenarios, as repeated start-ups and short continuous operation that may occur in a pilot-plant. Different simulation tools are combined to evaluate the expected concentration of pollutants in the environmental compartments and food. Hazard Index and Cancer Risk remain under the threshold for both dioxins (HI < 0.012, CR < 5.03 10) and PCBdl (HI < 1.3 10, CR < 2.49 10) in all the simulated scenarios, also for the worst case of children ingesting vegetables and meat and uncertainty factors up to 1000. Different results are obtained for VOCs since repeated leakages during the pilot-plant operation are possible. All the risk indexes for benzene are under the threshold (HI < 0.175, CR < 1.41 10); acute toxic risk due to inhalation and cancer risk due to ingestion of grain/vegetables are over the threshold if all the uncertainties are considered. Lesson learned: HHRA is important also during scale-up; pilot-plants for pyrolysis of waste plastics must always be equipped with all the abatement systems designed for the final plant.