Why doesn’t the tube make handpoles out of self-sterilising metals? And what is grippage?

Why don't these kill germs? The interior of an ageing Circle line train in 2010. Image: Maurits90/Wikimedia Commons.

In February 2015, bacteriologists from Cornell University published their results after spending more than a year swabbing New York City’s Subway trains and stations for bacteria. The results sounded icky: not only are there hundreds of different microbial species living throughout NYC’s transit system, on the poles and seats and turnstiles that humans touch every day, but half of them were completely unfamiliar to science. Anthrax and the bubonic plague were among those bacteria which were recognised.

Of course, the fact that New Yorkers aren’t dying off like 14th century Europeans implies that the dirtiness (or, rather, perceived dirtiness) of the subway isn’t a pressing public health issue. The study authors were keen to point out that commuters shouldn’t overreact to the news.

The same will apply to London, both in terms of the microbes living throughout the Underground and in the near-non-existent risk they pose to travellers. Yet as I was sat on one of Transport for London’s new S Stock trains on the Hammersmith & City line last week, fully aware of the first signs of a cold in my nose and my throat, my thoughts drifted to that study.

TfL likes to colour-code its lines so that the interior decor of the trains matches the lines they run on (so orange on the Overground, blue on the Piccadilly, etc.). These new trains are running on the Metropolitan (purple), District (green), Hammersmith & City (pink) and Circle (yellow) lines – yet all are decked out in bright, garish yellow. God knows what’s living on those neon poles and handstraps that keep passengers from falling down.

We know that public transport is a vector for disease transmission, especially when it comes to seasonally-influenced illnesses like the flu. We also know that there are materials which self-sterilise – that is, they’re highly toxic for any single-cell organisms that are unfortunate enough to land on them. This “oligodynamic effect” was first discovered in 1893, and lots of different metals – from silver to aluminium, lead to copper – possess it.

So the question is: why aren’t the hand poles in Underground cars and on buses made of antimicrobial metal?

 

A Santiago metro station, complete with bacteria-killing handrails. Image: AntiMicrobialCopper.com.

In some parts of the world, the answer is actually “they are”. The subway system in the Chilean capital Santiago, for example, uses antimicrobial brass handrails, which were installed in 2011 as part of a wider healthcare campaign. But this is an exception, not a rule.

Jean-Yves Maillard is a pharmaceutical microbiologist from the Cardiff University who researches the use of antimicrobial materials in hospitals, and specifically the two most promising metals: silver and copper (or alloys of copper, rather). It turns out that these things kill germs best when “humidity is 100 per cent, so they are underwater – and that’s not how these surfaces exist on the metro, or Tube, or buses.”

Instead, to get a better idea of how well they work, he’s tested them when they’re dry (which means between 30 and 40 per cent humidity, which is typical for the UK), and when they have “droplets” (i.e. someone’s sneezed) on them.

The results are still impressive: within 30 minutes of contact with the most effective copper alloys, 99.99 per cent of Staphylococcus aureus bacteria – a bug responsible for everything from skin infections to respiratory diseases, and including the infamous antibiotic-resistant MRSA strain – were exterminated in the droplet test, while the dry test still saw around a 90 per cent reduction.

“When it's very dry – the worst case scenario, a very dry summer and so on, above 20 degrees – you'd get something like 99.99 per cent reductions within 30 minutes,” he said. “If someone sneezes, then after 30 minutes on that surface the bacteria is likely to be killed. I imagine for some viruses it would be the same as well. [But] if you haven't got droplets, then that activity really drops sharply. You'll get at most 90 per cent reductions, but probably less than 90 per cent, within 30 minutes. You'll kill some, but not all.” Silver was less effective in the droplet test, and not effective at all in the dry one.

This might make switching to copper-based antimicrobial subway and bus poles seem like an easy win that TfL missed when ordering its newest trains. But Maillard is keen to stress that there are some important downsides.


It rhymes with "fromage"

Firstly, if a surface is cleaned relatively frequently, then the extra cost from using more expensive materials might be more than those of simply paying for someone to wipe everything down a bit more frequently each day, for the same result. And these surfaces are no substitute for cleaning – Maillard emphasises that antimicrobial surfaces work “in addition” to cleaning, not as a replacement. And, when I contacted TfL, health & safety director Jill Collis made it clear that they clean the network “throughout the day and night” already.

The second reason is appearance. According to Collis, “the handrails in carriages are designed to be easy to see, meet safety standards and be suitable for daily use by millions of customers”. (I also discovered that the internal TfL term for the things that passengers hold onto isn’t “handrails”, but “grippage” – pronounced to rhyme with “fromage”.)

This is an important point – and TfL also said that, in accordance with the Vehicle Accessibility Regulations Act 2010, “any passenger handrail fitted in or to a rail vehicle must … contrast with the parts of the rail vehicle adjacent to that handrail”.

In other words, the bright colours on the Tube are primarily so that the visually-impaired are better able to see them. While the brass handrails of the Santiago subway may look somewhat classy, they also blend into the background in dark, underground spaces.

A third important issue is value for money. The handrails on the Tube are made of aluminium, which has a good ratio of weight to cost to strength; copper and silver, less so. “In hospitals, the debate is all about costs,” Maillard said. “[Surfaces] maybe get cleaned once a day, and with copper surfaces there are indications that at the end of the day the [the microbial burden] will be less than normal metal surfaces. That's the interest in it. But the big question is, is it cost effective?”

Then there’s even a fourth issue, most relevant to silver, which is that it perversely seems to make drug-resistant superbugs more likely. Making subway poles out of solid silver is, clearly, ridiculous, but it’s common for nano-particles of silver to be placed within other material to give it some antimicrobial properties – not as good as copper alloys, of course, but still something.

Maillard points to a January 2015 report from the EU Commission’s Scientific Committee on Emerging and Newly Identified Health Risks (Scenihr) into the possible dangers posed by the use of nano-silver in medical and consumer devices. It found that research is “urgently needed” into the possible toxic effects of long-term exposure to silver in consumer products, and also that the genetic adaptation of bacteria to silver could increase resistance.

“What you will find is that now you have a huge amount of surfaces that contain antimicrobials,” Maillard explained. “Lots of plastics, washing machines, photocopiers, in pens, televisions, television remote controls – most of them contain silver or nano-silver, because they don't affect the colour. The concentration that they use is very low, there are question marks over its efficacy, and questions about whether it's going to promote resistance of those organisms with those products.”

So, put it all together and it doesn’t look good for Tube poles that clean themselves. Copper alloys work best, but would have to be painted to comply with health & safety legislation, defeating the purpose. And, while it’s possible to stick silver particles into the paint as an alternative, it’s not very good, especially when the extra cost is factored in – and that’s without considering make it more likely that truly nasty bacteria can thrive and evolve on public transport.

Best stick to hand sanitising gel. Much easier.

Want more of this stuff? Follow CityMetric on Twitter or Facebook

 
 
 
 

What can other cities learn about water shortages from Cape Town’s narrow escape from ‘Day Zero’?

Cape town. Image: Pixabay/creative commons.

Cape Town was set to run dry on 12 April, leaving its 3.7m residents without tap water.

“Day Zero” was narrowly averted through drastic cuts in municipal water consumption and last-minute transfers from the agricultural sector. But the process was painful and inequitable, spurring much controversy.

The city managed to stave off “Day Zero,” but does that mean Cape Town’s water system is resilient?

We think not.

This may well foreshadow trouble beyond Cape Town. Cities across the Northern Hemisphere, including in Canada, are well into another summer season that has already brought record-setting heat, drought and flooding from increased run-off.

Water crises are not just about scarcity

Water scarcity crises are most often a result of mismanagement rather than of absolute declines in physical water supplies.

In Cape Town, lower than average rainfall tipped the scales towards a “crisis,” but the situation was worsened by slow and inadequate governance responses. Setting aside debates around whose responsibility it was to act and when, the bigger issue, in our view, was the persistence of outdated ways of thinking about “uncertainty” in the water system.

As the drought worsened in 2016, the City of Cape Town’s water managers remained confident in the system’s ability to withstand the drought. High-level engineers and managers viewed Cape Town’s water system as uniquely positioned to handle severe drought in part because of the vaunted success of their ongoing Water Demand Management strategies.

They weren’t entirely mistaken — demand management has cut overall daily consumption by 50 per cent since 2016. So what went wrong?


Limits to demand management

First, Cape Town’s approach to water management was not well-equipped to deal with growing uncertainty in rainfall patterns — a key challenge facing cities worldwide. Researchers at the University of Cape Town argued recently that the conventional models long used to forecast supply and demand underestimated the probability of failure in the water system.

Second, Cape Town’s water system neared disaster in part because demand management seemed to have reached its limits. Starting late last year, the city imposed a limit on water consumption of 87 litres per person per day. That ceiling thereafter shrunk to 50 litres per person per day.

Despite these efforts, Cape Town consistently failed to cut demand below the 500m-litre-per-day citywide target needed to ensure that the system would function into the next rainy season.

The mayor accused the city’s residents of wasting water, but her reprimanding rhetoric should not be seen as a sign that the citizens were non-compliant. The continuously shrinking water targets were an untenable long-term management strategy.

Buffers are key to water resilience

In the end, “Day Zero” was avoided primarily by relying on unexpected buffers, including temporary agricultural transfers and the private installation of small-scale, residential grey-water systems and boreholes in the city’s wealthier neighbourhoods. The former increased water supply and the latter lowered demand from the municipal system. These buffers are unlikely to be available next year, however, as the water allocations for the agricultural sector will not be renewed and there is uncertainty in the long-term sustainability of groundwater withdrawals.

For more than a decade, Cape Town has levelled demand, reduced leaks and implemented pressure management and water restrictions. This made Cape Town’s water system highly efficient and therefore less resilient because there were fewer reserves to draw from in times of unusual scarcity.

The UN Water 2015 report found that most cities are not very resilient to water risks. As water managers continue to wait for climate change models to become more certain or more specific, they defer action, paralysing decision-makers.

If we really want our cities to be water-resilient, we must collectively change long-held ideas about water supply and demand. This will require technological and institutional innovation, as well as behavioural change, to create new and more flexible buffers — for example, through water recycling, green infrastructure and other novel measures.

Although Cape Town avoided disaster this year, that does not make it water-resilient. Despite the arrival of the rainy season, Cape Town is still likely to face Day Zero at some point in the future.

The ConversationThere’s a good chance that the city is not alone.

Lucy Rodina, PhD Candidate, University of British Columbia and Kieran M. FindlaterUniversity of British Columbia.

This article was originally published on The Conversation. Read the original article.