Effect of fuel zinc content on toxicological responses of particulate matter from pellet combustion in vitro.

Significant amounts of transition metals such as zinc, cadmium and copper can become enriched in the fine particle fraction during biomass combustion with Zn being one of the most abundant transition metals in wood combustion. These metals may have an important role in the toxicological properties of particulate matter (PM). Indeed, many epidemiological studies have found associations between mortality and PM Zn content. The role of Zn toxicity on combustion PM was investigated. Pellets enriched with 170, 480 and 2300 mg Zn/kg of fuel were manufactured. Emission samples were generated using a pellet boiler and the four types of PM samples; native, Zn-low, Zn-medium and Zn-high were collected with an impactor from diluted flue gas. The RAW 264.7 macrophage cell line was exposed for 24h to different doses (15, 50,150 and 300 µg ml(-1)) of the emission samples to investigate their ability to cause cytotoxicity, to generate reactive oxygen species (ROS), to altering the cell cycle and to trigger genotoxicity as well as to promote inflammation. Zn enriched pellets combusted in a pellet boiler produced emission PM containing ZnO. Even the Zn-low sample caused extensive cell cycle arrest and there was massive cell death of RAW 264.7 macrophages at the two highest PM doses. Moreover, only the Zn-enriched emission samples induced a dose dependent ROS response in the exposed cells. Inflammatory responses were at a low level but macrophage inflammatory protein 2 reached a statistically significant level after exposure of RAW 264.7 macrophages to ZnO containing emission particles. ZnO content of the samples was associated with significant toxicity in almost all measured endpoints. Thus, ZnO may be a key component producing toxicological responses in the PM emissions from efficient wood combustion. Zn as well as the other transition metals, may contribute a significant amount to the ROS responses evoked by ambient PM.

Industrial worker exposure to airborne particles during the packing of pigment and nanoscale titanium dioxide.

CONTEXT: Titanium dioxide (TiO2) factory workers' source specific exposure and dose to airborne particles was studied extensively for particles between 5 nm and 10 µm in size. OBJECTIVE: We defined TiO2 industry workers' quantitative inhalation exposure levels during the packing of pigment TiO2 (pTiO2) and nanoscale TiO2 (nTiO2) material from concentrations measured at work area. METHODS: Particle emissions from different work events were identified by linking work activity with the measured number size distributions and mass concentrations of particles. A lung deposit model was used to calculate regional inhalation dose rates in units of particles min⁻¹ and µg min⁻¹ without use of respirators. RESULTS: Workers' average exposure varied from 225 to 700 µg m⁻³ and from 1.15 × 104 to 20.1 × 104 cm⁻4. Over 90% of the particles were smaller than 100 nm. These were mainly soot and particles formed from process chemicals. Mass concentration originated primarily from the packing of pTiO2 and nTiO2 agglomerates. The nTiO2 exposure resulted in a calculated dose rate of 3.6 × 106 min⁻¹ and 32 µg min⁻¹ where 70% of the particles and 85% of the mass was deposited in head airways. CONCLUSIONS: The recommended TiO2 exposure limits in mass by NIOSH and in particle number by IFA were not exceeded. We recommend source-specific exposure assessment in order to evaluate the workers' risks. In nTiO2 packing, mass concentration best describes the workers' exposure to nTiO2 agglomerates. Minute dose rates enable the simulation of workers' risks in different exposure scenarios.

Effects of a catalytic converter on PCDD/F, chlorophenol and PAH emissions in residential wood combustion.

Catalytic converters can be used to decrease carbon monoxide, organic compounds and soot from small-scale wood-fired appliances. The reduction is based on the oxidation of gaseous and particulate pollutants promoted by catalytic transition metal surfaces. However, many transition metals have also strong catalytic effect on PCDD/F formation. In this study birch logs were burned in a wood-fired stove (18 kW) with and without a catalytic converter with palladium and platinum as catalysts. PCDD/F, chlorophenol and PAH concentrations were analyzed from three phases of combustion (ignition, pyrolysis and burnout) and from the whole combustion cycle. PCDD/F emissions without the catalytic converter were at a level previously measured for wood combustion (0.15-0.74 ng N m(-3)). PAH emissions without the catalytic converter were high (47-85 mg N m(-3)) which is typical for batch combustion of wood logs. Total PAH concentrations were lower (on average 0.8-fold), and chlorophenol and PCDD/F levels were substantially higher (4.3-fold and 8.7-fold, respectively) when the catalytic converter was used. Increase in the chlorophenol and PCDD/F concentrations was most likely due to the catalytic effect of the platinum and palladium. Platinum and palladium may catalyze chlorination of PCDD/Fs via the Deacon reaction or an oxidation process. The influence of emissions from wood combustion to human health and the environment is a sum of effects caused by different compounds formed in the combustion. Therefore, the usage of platinum and palladium based catalytic converters to reduce emissions from residential wood combustion should be critically evaluated before wide-range utilization of the technology.

Development of a highly controlled gas-phase nanoparticle generator for inhalation exposure studies.

We have developed a gas-phase nanoparticle generator that produces stable and well-defined size distributions for TiO(2). The online analyses of the gas-phase compounds and total number concentration of the generated particles as well as the off-line analysis of the filter samples confirmed the stability of the production. The major advantage of this reactor is that the test substance is directly in the aerosol phase, and thus no preprocessing is needed. This eliminates the physicochemical changes between bulk and administrated material during storing or processing. This system is easy to adjust to different experimental setups and precursors. As a result, well-characterized nanomaterials for inhalation exposure studies can be produced. At mass concentration of 30 mg/Nm(3), the count mean diameter was 126 nm (geometric SD 1.6), mass mean diameter was 161 nm (2.0), mass median aerodynamic diameter was 125 nm, and the concentrations of harmful gas-phase by-products remained low. The produced powder consisted of crystals of anatase (77 vol%) and brookite (23 vol%), and its specific surface area was 69 m(2)/g.