Day: March 6, 2006

Leftovers may explain perfluorinated compound puzzle:

See my earlier post about this. Looks like the EPA did want the companies to phaseout not just the PFOA, but the precursor compouds as well, and according to this article, quite a bit of progress has been made.

Eight companies have pledged to slash releases of several perfluorochemicals at their operations around the world, EPA announced on March 2.

Arkema, Asahi, Ciba, Clariant, Daikin, DuPont, 3M/Dyneon, and Solvay Solexis have agreed to reduce emissions of perfluorooctanoic acid (PFOA), its longer chain homologs, and compounds that can degrade into PFOA, EPA said. The companies will also reduce levels of these compounds in their products. Responding to a challenge EPA made in January, the eight firms volunteered to cut industrial releases of PFOA as well as amounts of the chemical in products 95% from 2000 levels by 2010 or earlier. The companies also pledged to work on eliminating releases and content of PFOA in products by 2015.

Here are the individual companies’ commitment letters. They all loudly proclaim their commitment to reduce PFOA levels in their products, not quite so universally unequivocal on the precursors… I need a lawyer to parse some of the language. 3M, for instance, says that they do not “manufacture” the telomers’, which is not the same as saying they do not use them. Solvay Solexis, is extremely straigtforward and agrees to the EPA conditions in a letter actually written in plain English! Dupont, good letter too. Let’s see how this situation plays out, outright elimination in 10 years seems nice, which leads me to believe that the companies are already moving in this direction. The journal article suggests that the residuals are mainly due to inefficiencies in the manufacturing process. The reaction yield is 70%, meaning the 30% left behind from the monomer formation reaction will need to be removed from the product.

ES&T Online News: Can drugs found in water harm humans?

Researchers agree that aquatic species face the greatest risk from exposure to low levels of pharmaceuticals, such as synthetic hormones, which can act as endocrine disrupters at environmental levels. However, little is known about the potential human health effects arising from complex drug mixtures.

Well, it is often more difficult to analyze complex mixtures because Experimental Design 101 makes you want to isolate the effects. And when you do compounds one by one in series, the tendency is to always add them up from the individual experiments. Unfortunately, body chemistry is not like that. I’ve always wanted to design a study that started complex and then tried to isolate later.

To his surprise, Pomati observed that this mixture of drugs at environmental levels inhibited the growth of human embryonic kidney cells. After 48 hours of exposure, cell proliferation was reduced by 10–30% compared with controls. However, no inhibition was observed when cells were exposed to only the toxic cancer drug at environmental levels.

Well, that seems conclusive enough, but here comes the “Experimental Design 101” Scold:

The results show that the growth inhibition is not due to the single most cytotoxic compound alone. But that does not conclusively prove that synergistic or additive effects exist between drugs in the mixture, cautions Thomas Heberer of the Institute of Food Chemistry at the Technical University of Berlin. To show that the individual drugs behave additively, Heberer suggests that researchers should analyze the effects of compounds with a common mode of action, such as antibiotics, alone and in various mixtures.

No, No, and No. Doing this presupposes that you know that mechanism of action, meaning you’ve half answered your question. The question Heberer is trying to answer is “do individual drugs with the same mode of action behave additively”. The question Pomati is trying to answer is “Can we demonstrate cytotoxic effects of a cocktail of drugs at ambient levels in a laboratory setting”? These are two completely different questions and Pomati’s question is more valuable at this point in time. Heberer’s strategy, on the other hand, will keep a lab well funded for years to come! But, it is very much the final step.

It is more important at this point in time to demonstrate other effects such as endocrine disruption, mutagenicity, etc in the lab at environmentally relevant levels of mixtures. Then we can get a better handle on which  effects are relevant and which ones to ignore.