Offsetting Risks of Mitigation Strategies
It is however beyond the scope of this document to do a complete life cycle (from production, through use and release) risk assessment for these chemicals. First, the list of possible substitutes is growing, second the production and use information for many of these compounds is constantly changing and not generally available and finally with the exception of the more or less well-known substitutes such as the hydrochlorofluorocarbons and other chlorofluorocarbons, the toxicology database for is inadequate. Thus in this section, we present only a qualitative assessment of the toxicity information on some of the better characterized substitutes and indicate where readers can find more information.
All three HFAs, -132b, -133a, and -142b, demonstrate a low acute inhalation toxicity. HFA-132b showed a moderate level of toxicity upon repeated exposure in standard toxicity tests, but demonstrated maternal and fetal toxicity at all concentrations in a reproductive toxicity study. For technical and toxicological reasons it is thus not being actively pursued as an ODS substitute. HFA-133a demonstrated moderately high toxicity to most systems upon repeated exposures with a No Observed Adverse Effect Level (NOAEL) of 24,000 mg/m3. However, adverse reproductive effects were observed in several studies with a NOAEL recommended as 485 mg/m3. Company occupational exposure limits have been established between 5 and 24 mg/m3. HFA-142b demonstrates a moderate level of toxicity upon repeated exposure with a NOAEL for chronic exposure of 82,000 mg/m3. There is some evidence of cardiovascular sensitization potential but only at very high levels (205,000 mg/m3) and no evidence of carcinogenic, reproductive or developmental effects. An 8-h occupational exposure levels of 1000 ppm has been proposed.
All three HFCs, -32, -125, and -134a, demonstrated low toxicity upon acute and repeated inhalation exposure in standard toxicologic testing protocols. None demonstrated any reproductive toxicity and only one, -134a demonstrated any fetotoxicity (NOAEL 10,000 ppm in one study and 100,000 ppm in a second which was also the dose at which maternal toxicity was observed.)
All three HCFCs, HCFC-21, HCFC-124, and HCFC-141b demonstrate low acute inhalation toxicity, and HCFC-124 and -141 demonstrate generally low toxicity overall. The recommended occupational standard for these two HCFCs is 1000 ppm. HCFC-21 demonstrates greater toxicity than the other two HCFCs, with liver toxicity and cardiac sensitization at relatively low concentrations (15 ppm and 1000 ppm, respectively.) The recommended occupational standard for HCFC-21 is 10 ppm.
Table 2.1. CFC Substitutes
|Common name||Chemical name||CAS No||Reference|
|Methylene chloride||75-09-2||ECETOC 1984|