Low Levels Of Arsenic In Drinking Water May Suppress Human Immune Response To Influenza
Chronic drinking water Arsenic exposure increases capillary leakage at day 7 post infection. Image credit:EH Perspectives, excerpted from Figure 3.,in "Low Dose Arsenic Compromises the Immune Response to Influenza A Infection in vivo."
Arsenic can occur at very dangerous levels in raw, potable water supplies that depend in part, or completely, on water wells. A serious arsenic problem seldom arises from surface waters, however. When USEPA last proposed lowering maximum contaminant levels (MCL's) for arsenic in finished potable water, in 2001, there was much howling and screaming from US municipalities about cost. (See EPA website for details.) Many felt they could not afford to treat water to meet the more stringent standards being proposed. That was before it was shown that low-level arsenic ingestion, via drinking water, may potentially compromise the human immune response, decreasing the ability of people to fight off influenza. Read on for details. When EPA was proposing finally revised arsenic standards in 2001, as you may recall, Congress was overheated with the spirit of the so-called "property rights" movement ('big gummint' should not be telling cities to spend more money). The resulting standard can therefore be viewed as something of a compromise, even without potential immune response issues in play.
SciDevNet reported this with the story: Arsenic exposure may decrease immunity to flu.
In a US-based study, mice were given drinking water containing 100 parts per billion of arsenic for five weeks before being exposed to the influenza A (H1N1) virus — the influenza subtype that includes swine flu. When researchers then measured the animals' immune response to infection, it was found to be significantly weakened when compared with that of mice in a control group.Full report from Environmental Health Perspectives may be downloaded as a pdf file here.
Comments on what this means.
Some of the high arsenic exposures we read about in India and Bangladesh, for example, are an indirect result of excess water withdrawals brought about by the so-called "Green Revolution." Developing nations generally lack centrally managed potable water treatment plants; and, if they do have them such facilities, rural villages and small cities are probably in not a position to afford arsenic removal capabilities.
Now would be a good time to point out also that fly ash containing arsenic can be a potential source of contamination to both surface water and ground water.
And, yes, I do realize that the cited experimental evidence is based on work with lab mice. That's how the science works. If you've a better idea how to dimension chemical ingestion risk, tell the toxicologists about it, please.
How "low" was the low dose studied?
From the published paper:-
Briefly, bone marrow cells were collected from the femurs of C57BL/6J mice exposed to control of 100 ppb As in the drinking water for five weeks (in the absence of infection).The same drinking water arsenic dose was used for the infected mice.
USEPA's 2001 arsenic standard for drinking water is 10 parts per billion (ppb), an order of magnitude lower concentration than the control and experimental doses cited.
The World Health Organization has a provisional guideline that is almost identical to USEPA's; but it is "provisional," remember.
If suppression of human immune response were indicated for much lower concentrations than the chronic dose tested in this work (100ppb drinking water arsenic), USEPA may need to revisit the 10ppb "MCL" level, as set in 2001. At that point - I'm here supposing the potential for human immune suppression at 10pb exists (we simply don't know yet) - the issue could be transformative of the roles EPA and CDC play in protecting public health.
As the WHO guidance for drinking water arsenic levels is provisional, they are likely to take this work into account before a final guidance is issued.
Next step for public health agencies: support research that tests progressively-lowered dose testing, until "no effect" is seen.
Additional posts on arsenic and drinking water.
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