Development of a Nose-only Inhalation Toxicity Test Chamber That Provides Four Exposure Concentrations of Nano-sized Particles

We present a test protocol that complies with the OECD Guidelines for inhalation toxicity testing for single-and multiple-concentration exposure. The multiple-concentration inhalation chamber, which can test up to four exposure concentrations at once, will be more economical for small research institutes. To begin testing a single-concentration chamber, seal the chamber and check it for leaks at 500 and negative 500 pascals gauge for 30 minutes each.

Then, set the clean air temperature to 23 degrees Celsius and 45%relative humidity. Start flowing clean air through the aerosol inlet and the sheath at 48 and 20 liters per minute, respectively. Set the exhaust pressure differential to negative 100 pascals.

Once the flow has stabilized, measure the flow velocities at three randomly selected ports from each level to confirm that the flow is uniform. The flow rate should be about one liter per minute. Repeat the measurements twice more.

Next, stop the air flow, and load a 0.1%by weight sodium chloride solution into the aerosol generation system. Start aerosol generation at 20 liters per minute with clean air as the carrier gas. Dilute the aerosol with 28 liters per minute of clean air.

Set up a particle size measurement system, and randomly select three ports from each level of the chamber. Measure the particle size distribution at each selected port three times. To begin setting up a multi-concentration chamber, check it for leaks and set the clean air supply to 23 degrees Celsius and 45%relative humidity.

Set the exhaust to maintain a differential pressure of negative 100 pascals. Then, connect a clean air supply to a port in the top compartment, and begin flowing clean air through the compartment at 11 liters per minute. Once the flow has stabilized, measure the flow velocity at each available port of the top compartment three times.

Repeat this process for the other three compartments. Then, load a 0.1%by weight sodium chloride solution into the aerosol generator. Configure the aerosol dilution system to produce an aerosol flow at 11 liters per minute.

Connect the aerosol inlet to the top compartment, wait for the flow to stabilize, and randomly select six ports from that compartment. Measure the particle size distribution at each of those ports three times using the particle size measurement system. Repeat this process for each compartment.

Flush the compartments with clean air for 30 minutes when complete. Then, connect a clean air inlet to the top compartment, and flow clean air through it at 11 liters per minute. Configure the aerosol dilution system for low-concentration and high-concentration aerosol flows at 11 liters per minute.

Connect the low-concentration line to the second highest compartment and the high-concentration line to the bottom compartment. Wait 10 minutes for the flows to stabilize. Then, randomly select one port from each of the three compartments, and measure the aerosol concentration at the selected ports 15 times each to check for cross-contamination.

Both the single-concentration and multi-concentration exposure chambers showed good flow uniformity at each horizontal level of the chamber. The normalized flows were close to the values calculated during modeling of the system. Good flow uniformity was also observed vertically in the single-concentration chamber.

The multi-concentration chamber has only one level of ports per compartment, so direct vertical uniformity measurements were not applicable. The particle concentration was also uniform horizontally for both chambers, and was uniform vertically for the single-concentration chamber. The aerosol concentrations in different compartments of the multi-concentration chamber showed relatively little variation across 15 measurements, indicating minimal cross-contamination between compartments.

It is important to check for reproducibility throughout the procedure, especially during the experimental cross-contamination test performance evaluation test. Performance evaluation tests can be extended by comparing the experimental result to computational fluid dynamics modeling of the chamber system.