The North Carolina Science Advisory Board (NC-SAB) for Toxic Air Pollutants (TAP) has published a draft risk assessment recommending a 9x increase in the Acceptable Ambient Level (AAL) for arsenic and arsenic-containing inorganic compounds. The recommended increase comes as a result of the NC-SAB reassessing the AAL in response to a request made by the North Carolina Division of Air Quality (DAQ).
An AAL is an airborne concentration at or below which no appreciable risks of adverse health effects are expected to occur in the general population.
The current AAL for arsenic and inorganic arsenic-containing compounds, established in 1990, is 2.3 x 10-7 mg/m3, averaged annually. Upon review of the updated toxicological and epidemiological literature, the NC-SAB recommends revising the AAL to 2.1 x 10-6 mg/m3, the central estimate within an exposure range from a lower bound of 1.6 x 10-6 mg/m3 to an upper bound of 3.0 x 10-6 mg/m3. This updated AAL is based on an estimated lifetime exposure risk of 1 additional lung cancer death per 1,000,000 population over a 78-year lifespan.
The draft for public comment can be found online at the DAQ website by clicking here:
For a variety of emission source, particularly combustion sources, the arsenic AAL has often been problematic in TAP air dispersion modeling. In some cases, affected facilities have had to improve pollution control systems, increase stack heights or place operational limits to demonstrate compliance with the arsenic AA.