Gas-particulate mixtures at workplace: Development of novel wearable sample collectors and Investigation of the different toxicity of gases and particles

Status:

completed 08/2022

Aims:

Semi-volatile organic compounds (SVOCs) frequently pollute our breathing air indoors and especially at workplace (Cao, 2022). Aim of this project was to investigate their behaviour and toxicological effects. SVOCs can exist in both gas and particulate phase simultaneously. The workplace environment (e.g., temperature and pressure) along with other factors (e.g., chemical composition, particle size and vapour pressure of the compounds) determine the gas-particle partitioning (GPP) behaviour of SVOCs. This complex behaviour also causes sampling problems at the workplace. The coexistence of gas and particle phase must be considered for a comprehensive toxicological evaluation as well.

In this project, we tried to improve the personal sampling tools commonly used at workplace. Another objective was to study the health effects of SVOCs in gas and particle phase separately using an appropriate in vitro Air-Liquid Interface (ALI) cell exposure system.

Activities/Methods:

The charcoal denuder used in the personal samplers ("Gesamtstaub-Gas-Probenahme-System" GGP) during the previous projects is not available in the market anymore. Therefore, a new charcoal denuder was characterized and tested for its gas adsorption capacity and particle transmission efficiency.

Dibutyl phthalate (DBP) was selected as a representative SVOC compound for cell exposures. Different types of particles (e.g. alkane and DBP) were produced using a condensation particle generator (SLG 270, Topas GmbH).

To investigate the toxicological effect of SVOCs, a new cell exposure system was built and tested in our laboratory. The new system was set up inside a refrigerator, modified to work as a climate chamber at 37 °C by adding a water bath and a ventilation system. The original exposure module provided by VITROCELL® Company along with a new humidification system were installed inside to serve now as fully integrated exposure system. The humidification system consists of a water-filled glass tube with dialysis membrane inside to let the aerosol flow passes through. In this way, relative humidity can reach >90% in the aerosol flow. The Vitrocell module is attached to an extra water bath to stabilize the cells in the required temperature range of 37±0.5 °C. For safety purposes, all the exits are attached to filters and carbon denuders and are guided to a fume hood. This new system is less complex and safer than the original VITROCELL® ALI system, especially for toxic aerosols. The aerosol guidance system is simplified with short tubes, resulting in less particle loss during the exposure. This also helps to estimate the deposited dose more accurately. A computer model was developed to estimate the deposited dose in a Vitrocell module. The results from the model were compared to measurements by a Liquid Chromatography-Mass Spectrometer (LC-MS) system.

To separate the gas from the particle phase in the exposure aerosol flow, denuders and filters were used. The new charcoal denuder was crafted by hand in size and shape to fit into the exposure module’s aerosol inlet, as close as possible to the cell layer (i.e. inside the "trumpet" flow-shaper). The gas phase of the aerosol was adsorbed by the denuder and only the particle phase could pass through. In another system configuration, a glass-fibre filter was installed in place to collect the particle phase and pass the gas phase. We set up five different exposure configurations (clean air / filter / denuder / filter+denuder / no installation) which correspond to five experimental protocols (clean air / gas phase / particle phase / no aerosol / total aerosol), respectively.

Results:

The results show that the new charcoal denuder has a high gas adsorption capacity even for more-volatile compounds like Toluene. The breakthrough of Toluene was very low (less than 2 % even after 24 hours). The particle transmission efficiency of the new denuder was tested for small particles with soot and for larger particles with Hexadecane. Due to diffusion, the greatest loss occurred for small particles at low flow rates. For larger particles, the transmission efficiency of particles decreased with increasing particle size and increasing flow rate. Impaction of large particles at the denuder-face at high flow rates might be the main reason.

The cell viability experiments with clean air in the new exposure system show that the system is suitable to host cells longer than the convenient 2-4 hours, and even up to 24 hours. This is technically not possible with previous cell exposure systems. The results of the first study showed that DBP infers DNA and chromosome damage in human lung A549 cells in occupationally relevant exposure concentrations, while the newly designed ALI exposure system was able to distinguish effects in gas and particle genotoxicity, in which oxidative DNA damage seemed to be related to a DBP particle-induced effect, while gas phase exposure led to genotoxic effect through a distinct mode of action. The calculated deposited dose for DBP particles was in a good agreement with the measured deposited dose using the Liquid Chromatography Mass Spectrometry (LC-MS) system.

Model calculations for DBP droplets of 1-10 µm diameter show a "life span" between 70 s and 1000 s. This span is long enough to perform experiments reliably with and without ambient vapor pressure. Model calculations of the deposited dose in the human respiratory tract show, that the dose in ALI experiments can be adjusted to yield comparable results for the micrometer particles used. Consequently, our ALI experiments can be classified as "health relevant".

Conclusions: In the personal samplers the new charcoal denuder can be considered as a replacement for the old one (which is not on the market anymore). Further research is needed to test the new charcoal denuder with different chemical compounds and at the workplace. The charcoal denuder is also suitable for gas phase adsorption in cell exposure experiments, due to the very low aerosol flow in the exposure system (≤ 100 ml/min).

The newly developed cell exposure-/chamber-system is safe, even for experiments with toxic substances, and is tested to host cells longer than the conventional 2-4 hours, and up to 24 hours. The simplified tubing system results in a reduced particle loss and in a more accurate dose estimation, which is one of the main issues in cell exposure systems. In this study, the system was used for DBP. Further investigation on toxicological cell response with compounds of higher volatility than DBP is recommended.

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