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Oregon Air Toxics Benchmarks

Oregon's air toxics benchmarks (referred to in Oregon Administrative Rule 340-246 as air benchmark concentrations) help DEQ identify, evaluate and address air toxics problems. Oregon air toxics benchmarks, or ABC's, are protective of human health, including the health of our most sensitive individuals, and are based on cancer effects, non-cancer effects, or both. For benchmarks based on cancer effects, they are set at concentrations that are not to exceed a cancer risk of one-in-a-million additional incidents of cancer based on a lifetime of exposure.

Air toxics benchmarks are numerically equivalent to Toxicity Reference Values, or TRVs.

TRVs are regulatory standards used by the Cleaner Air Oregon program to regulate emissions of air toxics from operating facilities. In contrast, the benchmarks used by the Air Toxics program provide consistent health-based concentration goals, which DEQ uses to develop strategies to reduce air toxics in Oregon. Air benchmark concentrations and TRVs are the same values, but they are named differently and used differently in the two programs – air benchmark concentrations are still used as goals in the Air Toxics program, and TRVs are used as regulatory standards in the Cleaner Air Oregon program.  


In 2004, the first Air Toxics Science Advisory Committee was convened by DEQ to assist with identifying health-based protective concentrations for the air toxics of most concern in Oregon. The ATSAC was made up of a panel of external experts experienced in toxicology; environmental science and engineering; epidemiology or biostatistics; public health medicine; and air pollution modeling, monitoring, engineering, and meteorology. As a result, ABCs were adopted for 54 air toxics in 2006. Only one ABC was assigned to each air toxic, even if the chemical was known to have both cancer and noncancer effects. Most ABCs ended up being based on cancer effects, as cancer effects usually resulted in the more-stringent protective level. ABCs were used as goals, rather than standards, to focus staff time and funding on the air toxics that significantly exceeded their related ABCs. Oregon rule required that DEQ, in consultation with the ASTAC, would review all ABCs at least every five years. 

The ATSAC met again in 2009 and 2010. Because of new scientific information available, the committee adopted by rule revised and/or new ABCs for four air toxics emitted in Oregon: lead; ethyl benzene; manganese; and mercury.

The ATSAC was convened a third time beginning in December 2014 and assisted DEQ in reviewing the 52 existing ABCs to determine if new toxicity data had become available since 2010.

In 2018, 55 ABCs were adopted into the Air Toxics rules. 23 of the original 52 were assigned revised ABCs. 29 of the 52 ABCs remained the same. ABCs were also developed for three new chemicals: n-propyl bromide, phosgene, and styrene. 

That same year, the new Cleaner Air Oregon program was launched, and required that operating facilities emitting air toxics could not release them at levels that exceeded protective health-based concentrations stipulated by the program. These health-based concentrations include the Toxicity Reference Values mentioned above and Risk-Based Concentrations based on the TRVs. 

By the end of 2018, there was recognized overlap between the work performed by the two programs, including ABCs used by the Air Toxics program and the TRVs and RBCs used by the Cleaner Air Oregon program. To address this situation, a Rule Alignment Rulemaking took place in 2021 that aligned the two sets of rules and their protective levels. This made the rules easier to understand and use. As part of this alignment process, the existing 55 ABCs adopted by rule in 2018 were rolled into the larger list of TRVs used by Cleaner Air Oregon. Numerically, then, the ABCs became numerically equivalent to the TRVs.

Another wrinkle in the equivalent numerical relationship between ABCs and TRVs is that a TRV triennial review is currently underway as of October 2022 as a requirement under Cleaner Air Oregon rules. The rules stipulate that TRVs should be reviewed every three years to ensure that they are based on the most current toxicity information available. This means that many of the current TRVs are likely to change and more chemicals with TRVs may be added. When the TRVs are updated by rule (likely by the end of 2023), the list of ABCs will automatically change as well, since the two sets of protective levels are numerically equivalent. ​


Email Morgan Schafer