G
Guest
Interesting, informative article on the ban of the dry cleaning chemical perchloroethylene (PCE).
CA Ban on Perchloroethylene
I think CA is once again leading the pack in terms of environmental reform. The sale of PCE in drycleaning operations should have been banned A LONG TIME AGO. EPA has picked up this issue at the national level and will probably put through similar rulemaking at the Federal level.
It humors me a tad to read the evils of PCE in the news article, when the real problems arise from the degradation breakdown products, such as:
Trichloroethylene (TCE) - much more persistent, toxic, and mobile. Lower solubility, so get more of it in dissolved phase. The OSHA criteria was vacated for TCE because it is known to have relatively high toxicity. The standard will most likely be dropped significantly.
Vinyl Chloride (VC) - more persistent, toxic, and mobile. VC has yet even a lower solubility so you get even more of it in dissolved phase. Toxicity criteria in water is 1 ppb (as opposed to 3 ppb for TCE and PCE in FL). Harder to get 'clean' to 1 ppb. Degradation usually of contaminant typically gets 'stalled' at the VC phase - last chlorine atom difficult to strip off to complete mineralization to Ethene, Ethane.
1,4-Dioxane (1,4-D) - this is the truly evil component. It was used as a stabilizer in PCE, TCE mixtures to some degree but more prevalent in 1,1,1-Trichloroethane (1,1,1-TCA) formulations. 1,4-D is completely miscible in water - its' solubility limit is infinite. It is completely unretarded in groundwater flow, so it 'goes' where the groundwater goes. Toxicity has been dropped from 10 ppb to 5 ppb to 3.2 ppb recently in FL. Analytical methods are difficult for this compound - reliable detection limits are around 50 ppb. This compound has specific gravity of 0.998 and practically no volatility so it loves to stay in the dissolved water phase. Treatment is difficult (expensive) for the same reasons.
Many of the projects I work on are contaminated with chlorinated solvents, so I thought I would share a few ideas/impressions.
JR
CA Ban on Perchloroethylene
I think CA is once again leading the pack in terms of environmental reform. The sale of PCE in drycleaning operations should have been banned A LONG TIME AGO. EPA has picked up this issue at the national level and will probably put through similar rulemaking at the Federal level.
It humors me a tad to read the evils of PCE in the news article, when the real problems arise from the degradation breakdown products, such as:
Trichloroethylene (TCE) - much more persistent, toxic, and mobile. Lower solubility, so get more of it in dissolved phase. The OSHA criteria was vacated for TCE because it is known to have relatively high toxicity. The standard will most likely be dropped significantly.
Vinyl Chloride (VC) - more persistent, toxic, and mobile. VC has yet even a lower solubility so you get even more of it in dissolved phase. Toxicity criteria in water is 1 ppb (as opposed to 3 ppb for TCE and PCE in FL). Harder to get 'clean' to 1 ppb. Degradation usually of contaminant typically gets 'stalled' at the VC phase - last chlorine atom difficult to strip off to complete mineralization to Ethene, Ethane.
1,4-Dioxane (1,4-D) - this is the truly evil component. It was used as a stabilizer in PCE, TCE mixtures to some degree but more prevalent in 1,1,1-Trichloroethane (1,1,1-TCA) formulations. 1,4-D is completely miscible in water - its' solubility limit is infinite. It is completely unretarded in groundwater flow, so it 'goes' where the groundwater goes. Toxicity has been dropped from 10 ppb to 5 ppb to 3.2 ppb recently in FL. Analytical methods are difficult for this compound - reliable detection limits are around 50 ppb. This compound has specific gravity of 0.998 and practically no volatility so it loves to stay in the dissolved water phase. Treatment is difficult (expensive) for the same reasons.
Many of the projects I work on are contaminated with chlorinated solvents, so I thought I would share a few ideas/impressions.
JR