I was thinking about dimethyl hydrazine (a rocket fuel) after I read about a space probe which is out of control. This then made me think about a law from the west coast of the USA which addresses carcinogens.
California has a law regarding carcinogenic chemicals, teratogenic chemicals and other chemicals which cause reproductive ills. I hold the view that society should as part of the social contract do its best to protect the citizen from harm by regulating and where possible minimizing human exposure to harmful chemicals. I think that such a matter should be under Federal law as the whole of the country should have the same high protection from both harmful chemicals and harmful silliness.
The problem is that Proposition 65 requires a bland statement demanding that all areas in which a person might encounter a carcinogen (weak or strong) at high or low concentration be labeled with the words
“WARNING: This area contains a chemical known to the State of California to cause cancer”
I think it does little if any good and I am sure that it does a lot of harm. Part of the problem is that it gives no clear suggestion as to what should be the action level. The website belonging to California where it explains the law states. (Food, drink and other products also get their own warnings)
“Under Proposition 65, there are no acceptable concentrations established for any listed chemical in any given product. An exposure that causes a significant risk of harm from a listed chemical through the use of a product would trigger the warning requirement, not merely the fact that a listed chemical is present in a product. The concentration of a listed chemical would certainly factor into the level of exposure that would result from an individual using a given product. But concentration alone is not sufficient to determine if warnings are required.”
Well after reading that I was rather confused to say the least as to what is the action level for carcinogens in the air, water or food.
I choose to look up a randomly chosen chemical in the list which Proposition 65 consider to be a threat to us all.
I selected the foul smelling organic solvent / chemical named pyridine. This is an aromatic nitrogen base which has a foul smell, tales fly around that it causes sexual health problems in men (low sperm count and importance) but I suspect that if you contaminate your body with it then nobody will want to associate with you, let alone have sex with you. Thus it might put a damper on your sex life !
It was in the list. The great problem I see is that the international body which deals with chemical carcinogens (IARC which is part of the World Health Organisation which is part of the UN) hold the view that pyridine is a chemical which falls into class three. The IARC have a total of five groups (well one class is split into two subclasses)
IARC group 1 means “Carcinogenic to humans“, this is a list of over 100 proven nasties.
IARC group 2A means “Probably carcinogenic to humans”
IARC group 2B means “Possibly carcinogenic to humans”
IARC group 3 means “Not classifiable as to its carcinogenicity to humans”, I understand this as meaning we can not make up our mind if this chemical causes cancer or not in humans.
IARC group 4 means “Probably not carcinogenic to humans”
I checked the IARC website and in a lengthy preamble it explains that for a class one carcinogen the following applies.
There is good evidence that the thing is carcinogenic in humans, or in exceptional cases where the evidence for the thing being carcinogenic in humans is weak, but strong evidence exists that this thing causes cancer in animals and it is reasonable to assume that it will cause cancer by the same mechanism in humans. (my paraphrase)
I think that based on the first part of the text it is reasonable to make 2-aminonaphthalene a group one carcinogen, and based on the reasoning in the second part it is reasonable to put plutonium dioxide powder on the group one list also. People have shown that it causes lung cancer in monkeys but I think that the evidence for it causing cancer in humans is quite weak when compared with things like 2-aminonaphthalene or beryllium.
Next I looked at class two.
This group spans a wide range, from some real nasty horrors which only just miss being in class one, through to some where no link has been seen in humans but evidence exists in animal experiments. My own view is that any chemical in class two should be regarded as a carcinogen, a great problem I see is that unless a chemical becomes widely used like benzene (used a very time ago in the dry cleaning industry and as a general industrial solvent) then it is unlikely to be seen in an epidemiology study. So I think that some class two carcinogens are likely to be more toxic than some of those on the class one list.
Now the problem is when we get onto group three. The words of the IARC on this class are
“This category is used most commonly for agents for which the evidence of carcinogenicity is inadequate in humans and inadequate or limited in experimental animals.”
they also add the comment that
“An evaluation in Group 3 is not a determination of non-carcinogenicity or overall safety. It often means that further research is needed, especially when exposures are widespread or the cancer data are consistent with differing interpretations”
I think looked at group four, for which the IARC say
“This category is used for agents for which there is evidence suggesting lack of carcinogenicity in humans and in experimental animals”
This means that rather than any evidence to suggest that the thing causes cancer, plenty of evidence exists to suggest that the substance does not cause cancer. But lets get back to pyridine, the fact that pyridine in group three suggests that no firm evidence exists either way. Now being a man of science I choose to have a look in the literature for papers about how pyridine causes cancer. I searched the web of knowledge with the search “Pyridine AND carcinogenic” and none of the first ten hits I got suggested that pyridine causes cancer. When I tried the same search with benzene instead of pyridine I was rewarded with some hits which suggest that benzene causes cancer.
Now one of my favourite tests for ability of a chemical to damage DNA and thus cause cancer is the Ames test, it is a cheap, easy and animal friendly test. I think that PETA should like it, unless they care about the welfare of salmonella. This test uses a special strain of salmonella which has a metabolic defect which is put right using a single mutation. I could not find a paper which suggests that pyridine is able to damage the DNA of the germs. While some false positives and false negatives occur when the Ames test is used to search for carcinogens, most of the time the Ames test gets it right.
So from the results tonight I have seen it appears that pyridine is not a carcinogen, the great problem I see is that the list of carcinogens which is used in California is being diluted with a series of things which are not carcinogens. Thus when all things are labeled as dangerous, nobody will be able to warn anyone else as the warning no longer means anything. It is a bit like the “boy who cried wolf”
The way I understand it if I was to rope off the whole world as an area contaminated with asbestos then those places such as old boiler rooms which harbour a real nasty threat to your health would no longer appear to be different to the clean green park (which is free of asbestos fibres). Then people would no longer be able to make reasonable choices to protect their health.
PS. If any of my readers have any strong evidence that pyridine causes cancer in humans or animals, or has even flunked the Ames test then please do write in. I will be glad to examine the evidence.