An evaluation of the "GGP" personal samplers under semi-volatile aerosols: sampling losses and their implication on occupational risk assessment.

Semi-volatile (SV) aerosols still represent an important challenge to occupational hygienists due to toxicological and sampling issues. Particularly problematic is the sampling of hazardous SV that are present in both particulate and vapour phases at a workplace. In this study we investigate the potential evaporation losses of SV aerosols when using off-line filter-adsorber personal samplers. Furthermore, we provide experimental data showing the extent of the evaporation loss that can bias the workplace risk assessment. An experimental apparatus consisting of an aerosol generator, a flow tube and an aerosol monitoring and sampling system was set up inside a temperature controlled chamber. Aerosols from three n-alkanes were generated, diluted with nitrogen and sampled using on-line and off-line filter-adsorber methods. Parallel measurements using the on-line and off-line methods were conducted to quantify the bias induced by filter sampling. Additionally, two mineral oils of different volatility were spiked on filters and monitored for evaporation depending on the samplers flow rate. No significant differences between the on-line and off-line methods were detected for the sum of particles and vapour. The filter-adsorber method however tended to underestimate up to 100% of the particle mass, especially for the more volatile compounds and lower concentrations. The off-line sampling method systematically returned lower particle and higher vapour values, an indication for particle evaporation losses. We conclude that using only filter sampling for the assessment of semi-volatiles may considerably underestimate the presence of the particulate phase due to evaporation. Thus, this underestimation can have a negative impact on the occupational risk assessment if the evaporated particle mass is no longer quantified.

PCDD/F and other micropollutants in MSWI crude gas and ashes during plant start-up and shut-down processes.

Nonstationary combustion conditions at municipal solid waste incineration (MSWI) plants cause increased crude gas concentrations of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), and other products of incomplete combustion (PIC). Such transient conditions occur, e.g., during and after start-up processes in MSWI plants. The start-up and shut-down processes of a MSWI plant were investigated in detail. PCDD/F and other PIC concentrations were determined in the crude gas, in the boiler ash, and in the ash from the electrostatic precipitator (ESP ash), with the outcome that only the start-up procedure significantly affected the concentrations of the organic pollutants in the flue gas and in the ESP ash. The shut-down procedure was evaluated as less problematic for the concentration of the organic pollutants. Moreover the concentration of the PCDD/F and other PIC in the boiler ash was determined as not influenced by shut-down and start-up processes. The homologue profiles and the congener patterns as well as the PCDF/PCDD ratio in the flue gas and in the ESP ash change during MSWI start-up. The changing patterns point at a transition from dominant de novo synthesis to precursor synthesis.