Thread by @petermbenglish

1/ (Second attempt to publish this thread: for some reason a glitch meant that only the first few tweets were published on my last attempt.)

Thanks for putting this list together, Edwin @uk_domain_names - very interesting.

https://twitter.com/uk_domain_names/status/1452711087498014724

2/ I am a little uncertain what to make about this huge twitter storm about sewage.

tl;dr - it is a hazard; but it's a very low level of risk to health or to the environment.

There are more important things to worry about.

3/ Until I retired in January, I have been a consultant in communicable disease control since Feb 1998. Part of this job has always involved liaising with water companies over incidents etc., and with emergency planning bodies including local authorities.

4/ I have been involved with the management of many flooding incidents.

It might be worth clarifying some meanings.

"Surface water" is "run-off" from roads, roofs and gutters, and elsewhere.

5/ It picks up dirt from the surfaces - tyre-rubber and other particles from the roads; whatever's in the fields (including sometimes fertiliser and pesticides), but these things are usually very dilute.

6/ "Foul water" includes water from drains in households and elsewhere - including from toilets.

7/ It can be a valuable source of surveillance: SARS-CoV-2 RNA (mostly non-viable rather than infectious) can be passed in faeces and detected in foul water, giving an indication of the level and location of infections.

"Sewage" is the fluid in the sewers.

8/ If you don't separate surface and foul water (as, commonly, we don't in the UK) it obviously contains a mixture of both.

9/ "Sewerage" - which I note has widely been used as a longer, more-impressive-sounding synonym for "sewage" on twitter - actually refers to the system of drains and sewers.

"Treatment" (of sewage or runoff) can mean a lot of different things.

10/ Some water treatment plants are designed to make sewage clean enough to discharge into rivers; others are designed to bring it to drinking water standards.

So it's not at all clear what "untreated" means.

11/ Even if the processes of sedimentation, micro-filtration, chemical treatment and so on haven't been done, filtration to remove larger contaminants - leaves, boots, sanitary products, condoms etc. - may well have been done.

12/ I am not sure if the "untreated" water discharges that the legislation refers to means completely untreated, not even filtered to remove macroscopic objects. So I am not sure if the more disgusting claims made on twitter (about nappies, condoms, tampons, etc) are correct.

13/ Sewage will contain both "dead" or non-viable bacteria and viruses.

In order to be infected, you need an "infectious dose". The amount of virus/bacteria which amounts to an infectious dose varies between organisms.

14/ A very small quantity of E coli O157 bacteria, for example, can infect you.

15/ But sewage is usually very dilute, so it's generally unlikely that anybody will consume an infectious dose: it is (perhaps surprisingly) unusual for people to become infected from contact with sewage.

16/ Bacteria and viruses in sewage will be killed by heating - boiled water, or contaminated food that has subsequently been cooked - will not be infectious.

17/ (If flood water was chemically contaminated people are likely to be advised not to consume vegetables grown in contaminated soil.)

18/ Even when there have been floods in which flood-water containing sewage has poured onto people's gardens, there have been practically no cases of people with infections caught from the sewage.

19/ And rates of such infections (which are monitored constantly in various ways) have not increased in the areas following floods.

20/ Indeed, the only significant infection or poisoning cases I can recall have occurred when diesel generators were used indoors (usually to work pumps to get water out of downstairs rooms or cellars), causing carbon monoxide poisoning.

21/ When there is flooding (usually due to heavy rainfall) the sewers don't always cope, and sewage can be released.

But when there is flooding the foul water will be diluted by the flood water - it will be much more dilute than usual.

22/ And natural water courses are incredibly good at cleaning up water - microbiologically, at least. (Some pesticides - metaldehyde slug killers were, I think, a particular problem - may be more persistent, albeit at extremely low levels.)

23/ So discharge of some sewage into rivers and watercourses during periods of flooding (which is, I think, what the legislation was permitting) is a hazard. But it is an extremely low-level hazard, very unlikely to do harm to human health.

24/ I don't know, but strongly suspect that environmental experts would probably say that it is also minimally harmful to the environment.

25/ The government's has failed egregiously to protect the population against Covid-19, tolerating rates that are ten times as high as in comparable Western European countries, and telling us we "have to live with the virus".

26/ Which also means: to die from or suffer long term sequelae as a result of Covid-19 infection.

27/ Ministers keep repeating, through words and deeds, that neither we, nor politicians are expected to follow non-mandatory guidelines, no matter how strongly distancing and mask-wearing are recommended.

28/ They have failed to introduce controls on air quality, that would dramatically reduce infection rates in schools and workplaces.

Given the far more serious public health threat from Covid-19, I worry that we may be getting the sewage release issues rather out of proportion.

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