Robert said the IRIS reference concentration is 003 mgm3 which is approximately

Robert said the iris reference concentration is 003

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Robert said the IRIS reference concentration is 0.03 mg/m3, which is approximately equal to 0.01 ppm. Bruce said that was a couple of orders of magnitude below what the committee is contemplating. Robert said that the IRIS value is based on public health risk. Dagmar said it is based on 24 hour exposure. Allan asked how the number is derived. Robert said that they identified a NOAEL and divided by 100. Will said that IRIS has different reference values based on routes and endpoints. There is a cancer potency endpoint. IRIS has difference reference concentrations corresponding to difference acceptable risks. A 10E-6 cancer risk corresponds to 0.1 ug/L (oral in drinking water), which is probably lower than the reference concentration. There are different approaches to cancer and non-cancer endpoints. Bruce asked if the 10E-6 is a lifetime risk at 1 L/day. Robert said that if you ingested 0.1 ug/L, with the assumption that you consume 2 L/day, there is a 1/1 million incremental risk of cancer. Bruce asked if nasal mucosa weren't the target organ. Will said there are various numbers. For chronic inhalation, the number is 0.03 ug/m3. Robert said there were a series of numbers for inhalation. Richard asked if the NIOSH was 0.1. Mike said that was for ETO. Tim said there is no safe level in NIOSH, no threshold. Robert said that for cancer risk IRIS uses the multi-stage linear model, which has no threshold. But information in the ACGIH documentation indicates there may be a threshold. There may be enough of a detoxification mechanism to handle low levels of PO. Allan asked what the breakdown product is. He said that sometimes what appears to be a "threshold" is only inadequate data at lower doses. He asked if there is more than one paper. Robert said that several studies talk about it from a mechanistic standpoint. The documentation doesn't talk much about the mechanism, or what product binds to the DNA. It's not a novel mechanism, it's fairly well recognized. He thought maybe the NIOSH reference which talks about the DNA repair might be useful. Will said this brings the committee back to the question regarding how to handle carcinogens. There are risk assessments. The committee needs to decide on acceptable risk. What is an acceptable risk in the workplace? Robert said that the documentation states that OSHA policy is 10 E-3. Richard said, that's not what they've done, onasbestos it's lower. Bruce said that the asbestos PEL had been set in a lengthy appeals court process. They couldn't hit the 10E-3 target. The benzene decision says that a risk that is greater than 10E-3 is not acceptable. OSHA couldn't sample that low, to achieve a limit corresponding to 10E-3, so they added the automatic controls for certain classes of work. Tim said that workers have to be provided with higher levels of protection in different kinds of work. Allan said that the average cancer risk is 1 to 2 in 100 in current workplace standards. If you wanted to lower the risk, you might be able to target a 1/1000 risk. 1/10000 may be too abrupt. You need a systematic approach and a policy decision.
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