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1-Bromopropane (aka n-propyl bromide or nPB for short) is a popular solvent which came on the industrial market in 1996. Its main uses are metal cleaning, defluxing electronics assemblies, diluent for adhesives and dry cleaning garments.
When it was first marketed, there was no data on toxicity, carcinogenicity, mutagenicity etc. The makers initially proposed that the limit of the substance in the air breathed by the workers was 500 ppm, but this dropped rapidly to 200 ppm. This was the Operator Exposure Limit (OEL) and it was only a recommendation. One small French producer recommended 10 ppm. The US National Toxicity Program started work on it in the early 2000s but this is still ongoing. OSHA cannot issue a legal limit until the NTP have pronounced. In the early 2000s, anecdotal reports started coming out of neurological problems in workers exposed to the substance. The makers funded some animal tests and most of them dropped their recommendations to 100 ppm on early results in the mid 2000s after it was found that mice suffered longer nerve reactions in the CNS and lower sperm motility. Later results indicated that both the neurotoxicity and the reproductive toxicity were worse than thought and most makers reduced their recommended OEL to 25 ppm, but one recommended the old 100 ppm. This is the still valid today.
From the practical point of view, 100 ppm is fairly easy to control except in the adhesives and dry cleaning sectors. 25 ppm is at the limit of possible for metal cleaning and defluxing, using ordinary state-of-the-art machines. There are so-called "zero-emission" machines available but they cost 3-5 times more than the ordinary ones and generally they can keep average exposure down to lower single digits if used correctly.
In Europe, nPB was classed as a VOC (exempted in the USA) and regulations for this limited its use to negligible amounts. However, the REACH programme has proposed labelling it as a reproductive toxin, but this has not yet been studied. I don't know for sure the situation in Japan, but I believe it is similar to the USA. In China, where vast amounts are made and used, the limit is pending.
About two years ago, the NTP issued an interim warning that animal tests on both rats and mice indicated a strong probability of carcinogenicity and mutagenicity. The American Conference of Government and Industrial Hygienists (ACGIH) issued a Threshold Limit Value (TLV) = OEL of 10 ppm. The ACGIH is a highly respected NGO but their values have no force of law and are only recommendations based on known science. However, many companies using chemicals do try to take notice of their recommendations. The ACGIH have recently put a cat among the pigeons in that they have given an advanced notice of a change in the TLV for nPB and the proposed draft value is 0.1 ppm, an unprecedented two whole orders of magnitude lower than the current TLV. I'm not yet aware of the reason behind this, but it must be serious. Needless to say that 0.1 ppm is impossible to respect under industrial conditions so, if this value became a legal limit, nPB would be condemned to death as an industrial solvent (it is also used in small quantities as feedstock for the pharma industry in the manufacture of psychotropic drugs such as diazepam).
Why this rant?
Simply because I suggest we have it wrong, all wrong. Workers were initially exposed to what has been deemed potentially dangerous levels of nPB, up to 5,000 times higher than the proposed new "safe limit". Even today, one maker is recommending an OEL of 1,000 times the proposed OEL. This is far from the first time that workers have been told that such-and-such a chemical is safe, only to die prematurely from the effects of exposure 10, 20 or 30 years later -- I personally have known cases of people, including a close friend, who have died in their 50s and 60s from organ failures resulting from chemical exposure as young adults.
Yes, we say that chemicals are innocent until proved guilty. This is wrong and I suggest that they should be considered guilty unless proven innocent. An arbitrary tight limit should be placed on new chemicals, based on computer modelling and analogical comparison with similar known substances. This limit may be slackened if tests and experience show it is safe to do so.
Brian has spake!
When it was first marketed, there was no data on toxicity, carcinogenicity, mutagenicity etc. The makers initially proposed that the limit of the substance in the air breathed by the workers was 500 ppm, but this dropped rapidly to 200 ppm. This was the Operator Exposure Limit (OEL) and it was only a recommendation. One small French producer recommended 10 ppm. The US National Toxicity Program started work on it in the early 2000s but this is still ongoing. OSHA cannot issue a legal limit until the NTP have pronounced. In the early 2000s, anecdotal reports started coming out of neurological problems in workers exposed to the substance. The makers funded some animal tests and most of them dropped their recommendations to 100 ppm on early results in the mid 2000s after it was found that mice suffered longer nerve reactions in the CNS and lower sperm motility. Later results indicated that both the neurotoxicity and the reproductive toxicity were worse than thought and most makers reduced their recommended OEL to 25 ppm, but one recommended the old 100 ppm. This is the still valid today.
From the practical point of view, 100 ppm is fairly easy to control except in the adhesives and dry cleaning sectors. 25 ppm is at the limit of possible for metal cleaning and defluxing, using ordinary state-of-the-art machines. There are so-called "zero-emission" machines available but they cost 3-5 times more than the ordinary ones and generally they can keep average exposure down to lower single digits if used correctly.
In Europe, nPB was classed as a VOC (exempted in the USA) and regulations for this limited its use to negligible amounts. However, the REACH programme has proposed labelling it as a reproductive toxin, but this has not yet been studied. I don't know for sure the situation in Japan, but I believe it is similar to the USA. In China, where vast amounts are made and used, the limit is pending.
About two years ago, the NTP issued an interim warning that animal tests on both rats and mice indicated a strong probability of carcinogenicity and mutagenicity. The American Conference of Government and Industrial Hygienists (ACGIH) issued a Threshold Limit Value (TLV) = OEL of 10 ppm. The ACGIH is a highly respected NGO but their values have no force of law and are only recommendations based on known science. However, many companies using chemicals do try to take notice of their recommendations. The ACGIH have recently put a cat among the pigeons in that they have given an advanced notice of a change in the TLV for nPB and the proposed draft value is 0.1 ppm, an unprecedented two whole orders of magnitude lower than the current TLV. I'm not yet aware of the reason behind this, but it must be serious. Needless to say that 0.1 ppm is impossible to respect under industrial conditions so, if this value became a legal limit, nPB would be condemned to death as an industrial solvent (it is also used in small quantities as feedstock for the pharma industry in the manufacture of psychotropic drugs such as diazepam).
Why this rant?
Simply because I suggest we have it wrong, all wrong. Workers were initially exposed to what has been deemed potentially dangerous levels of nPB, up to 5,000 times higher than the proposed new "safe limit". Even today, one maker is recommending an OEL of 1,000 times the proposed OEL. This is far from the first time that workers have been told that such-and-such a chemical is safe, only to die prematurely from the effects of exposure 10, 20 or 30 years later -- I personally have known cases of people, including a close friend, who have died in their 50s and 60s from organ failures resulting from chemical exposure as young adults.
Yes, we say that chemicals are innocent until proved guilty. This is wrong and I suggest that they should be considered guilty unless proven innocent. An arbitrary tight limit should be placed on new chemicals, based on computer modelling and analogical comparison with similar known substances. This limit may be slackened if tests and experience show it is safe to do so.
Brian has spake!
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