New and updated screening levels – January 2025
The Michigan Department of Environment, Great Lakes, and Energy (EGLE), Air Quality Division (AQD) develops health-based air toxics screening levels to provide protection to the public when breathing the ambient (outdoor) air. These screening levels are used by AQD permit engineers in their evaluation of new or modified industrial processes, which may emit air toxics.
Every month, toxicologists from the AQD determine what air toxic chemicals, if any, need to be reviewed.
Six chemicals were updated in the Air Toxics Screening Level list this past month with the following screening levels.
| CAS No. |
Chemical |
ITSL (μg/m³) |
Averaging Time |
| 124-41-4 |
Sodium methylate |
10 |
1-hour |
| 63148-62-9 |
Siloxanes and silicones, dimethyl |
2 |
Annual |
| 68037-58-1 |
Siloxanes and silicones, dimethyl [(dimethoxymethylsilyl)-oxy]-terminated |
0.1 |
Annual |
| 68037-88-7 |
Siloxanes and silicones, methyl 3,3,3-trifluoropropyl [(ethenyldimethylsilyl)-oxy]-terminated |
0.1 |
Annual |
| 68083-19-2 |
Siloxanes and silicones, dimethyl, vinyl-group terminated |
0.1 |
Annual |
| 68918-22-9 |
Siloxanes and silicones, dimethyl, chloro-terminated, reaction products with 4-(phenylamino) phenol |
0.1 |
Annual |
The screening level for sodium methylate (CAS No. 124-41-4) was updated based on a recent literature review that identified chemical-specific and more toxicologically relevant information for the screening level basis. Specifically, the screening level is now based on the parent compound’s more toxic reaction product, sodium hydroxide (CAS No. 1310-73-2). As a result, the initial threshold screening level (ITSL) is now 10 μg/m3, based on a 1-hour averaging time. Footnote #45 has been added to explain that when sodium methylate is co-emitted with sodium hydroxide, the combined impacts from both pollutants should not exceed a hazard index value of one.
The siloxanes and silicones chemicals were originally named “high molecular wt. silicon.” The “high molecular wt. silicon” label was used for multiple CAS Numbers, each of which had a different screening level. To prevent confusion, it was decided that each CAS Number would be correctly named and an updated literature review performed to find any toxicity information on which to derive a screening level.
The Air Toxics Screening Level list is now available to view in MiEnviro Portal. To view the air toxics screening levels and justification documents, follow these directions:
- Open MiEnviro portal.
- Choose “Air Toxics Screening Level.”
- This will take you to the “Air Toxic Chemical Search” page.
- In the search bar, click the “▼” on the far-right side of the search bar.
- This brings up a search box where you can enter the Chemical Name or CAS Number.
- After entering the chemical name or CAS Number, click on the blue “search” button to the right of the search bar.
- Click on the “download documents” button in the far-right column and open the file.
If you have questions on air toxic screening levels, please contact Doreen Lehner, AQD, at 517‑582‑3779. Find more information on our webpage at Michigan.gov/Air.
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