=biology =chemistry =chemical safety
chlorine disinfection
Today, most water distributed to people for drinking is chlorinated.
Bleach is also widely used for disinfection of surfaces.
The exact
ways chlorine kills microbes aren't fully understood, but the main reasons
are believed to be:
- oxidation of thiols of enzymes
- ring chlorination of amino acids
-
direct DNA damage
Obviously, high levels of chlorine are bad for humans. Chlorine gas was used
as a chemical weapon in WW1, and drinking bleach can kill people. As for
longer exposure to lower levels, studies have found associations between
lung damage and use of indoor swimming pools, but the extent to which
harmful effects of chlorine have thresholds from saturation of enzymes is
still unclear.
Dietary studies are notoriously hard to get good
results from, and studying chlorinated water has similar issues. Studies
have concluded that, eg, over a few weeks, chlorinated water
doesn't
affect lipid metabolism much. But is that what you'd expect to see? If
there were effects, what would they be?
effects of ingested chlorine
Engineers try to minimize levels of some compounds in water that can
react with chlorine to produce toxic substances, such as chloramines and
chloroform. But...there are organic compounds in the stomach. What about
reactions of chlorine after it's consumed?
Stomachs are acidic. That
means amines are mostly protonated and unlikely to react, but other
chlorination reactions are catalyzed. My understanding is that the main
types of chlorine reaction in stomachs are:
- oxidation of thiols (this doesn't concern me much)
- phenol
chlorination (eg 3-chlorotyrosine production)
-
tryptophan oxidation
- double bond oxidation to
halohydrins
Chlorotyrosine production happening is intuitive, and it's been validated by
some rat studies.
But the topic of reactions of chlorine in stomachs hasn't been studied very
much in general.
What happens to chlorotyrosine and halohydrins
afterwards?
In cells, aliphatic chlorinated compounds tend to have
chlorine replaced with a ketone group by enzymes. For example,
dichloromethane becomes formyl chloride which decomposes to carbon monoxide
and HCl, which are less toxic than products from other chloromethanes,
making it the least toxic of them. Obviously it's also possible for
halocarbons to react spontaneously with amines before an enzyme gets to
them; that's less likely with chlorine than bromine, but any amount is still
bad.
As for chlorotyrosine...I'm not sure. Yes, people have examined
metabolism of chlorotyrosine, and found eg a
significant amount of 4-hydroxyphenylacetic acid, which indicates to me
that it might be dechlorinated during decarboxylation of
3-chlorohydroxyphenylpyruvate with some sort of quinone methide
intermediate. But that's not really the question, is it? The question is
what the effects of chlorotyrosine being present are. That
chlorine atom isn't likely to spontaneously react, but how much
chlorotyrosine is incorporated into proteins? How does that incorporation
affect protein effects? Does chlorotyrosine have some direct signalling
effects? How big are the net impacts? I don't know. At this point, I'm
probably in the top 100 worldwide for understanding of molecular toxicology,
sad as that is to say, and my knowledge here feels inadequate.
When
macrophages "eat" pathogens, they will sometimes generate hypochlorite in
the phagosome. A little bit of that hypochlorite leaks, and that leakage is
a significant fraction of harm from infection. Chlorotyrosine is
associated with
damage from immune system hypochlorite generation, but it's not clear to
what extent it's causative.
Then, there are all the other phenols
that could be chlorinated. Chlorination can cause compounds to mimic
hormones - for example, who can forget the effects of
chlorinated dioxins on the endocrine system? (Maybe people should stop
using
PBDEs, too. Sigh.) But my intuition says that chlorotyrosine is more
significant.
Bleach is also used sometimes for disinfecting food in
commercial facilities, such as vegetables and raw chicken.
Here's a study looking at chlorotyrosine levels from washing vegetables
with bleach, which concluded that:
3-chlorotyrosine exposure through the lettuce mix could be potentially a great health concern
alternatives
water treatment
UV or (UV + H2O2) can be used for
water disinfection, but it doesn't maintain disinfection while water is
piped from treatment to homes. As I've previously posted, it might be
possible to use (UV + H2O2) for initial disinfection then add a small amount
of nontoxic cationic surfactant such as choline fatty acid ester to prevent
microbe replication. This is slightly more expensive than using chlorine,
and companies that sell chlorine would be mad.
surface disinfection
As I've previously posted,
peroxyacids can be used for disinfection, but volatile ones are noxious, so
(citric acid + H2O2) is relatively suitable as a chlorine-free disinfectant.