After a natural disaster like last week’s earthquake in New Zealand, the obvious physical signs of damage are just the thin end of the wedge of a range of survival problems. Modern living is built on a complex infrastructure to supply the essentials we need, such as clean water. The lack of drinking water is a problem that most of us don’t ever have to think about, but without it we are at risk of a whole host of diseases from contaminated water.

Think about it: if the taps run dry where are you going to get enough water to survive? At the time of writing I have a carton of orange juice to keep me going. After that I could get water from the pond in the garden. I saw it yesterday though and it was full of frogs writhing around. I think they were having sex, so I’m going to need to be pretty thirsty before I start drinking that I can assure you.

When disaster strikes water can be transported in of course. But it’s awkward to move around; it takes up a lot of space and it’s heavy. And often there isn’t a shortage of water, there’s just a shortage of water that isn’t heaving with bacteria.

Scientists at McGill University in Canada may have come up with a very slick answer: silver. Silver has been used as a biocide for centuries. The Greeks and Romans used silver jugs to keep their water and wine sweet. In the USA in the nineteenth century silver dollars were dropped in to milk to keep it fresh. Nowadays we have nano-particles of silver in bandages, socks, chopping boards, children’s toys – the list goes on.

At McGill researchers have impregnated thick, porous paper with silver nano-particles to make a silver enhanced filter paper. The paper itself will filter out bits of twig,  frog goo and other particulates, and the nano-silver will kill the bacteria. Contaminated water passing through the paper has been found to have virtually all the bacteria killed and the filtrate is clean enough to meet the standards set by the American Environmental Protection Agency.

So how is the silver working? Well, as with all nano-particles, the surface area per unit mass of the silver is colossal. This provides a lot of contact between the silver and the bacteria. In addition, the small size of the particles mean that they can reach deep into the cells of an organism. Nano-silver has particles ranging from 1 to 100 nanometres. Now anything under 300 nanometres can penetrate the cell membrane and get inside the cell. Particles under 70 nm can even get into the nucleus of the cell.

Once in place the silver causes utter mayhem. Elemental silver will produce toxic silver ions.  The silver can be thought of as a reservoir of silver ions.

Silver is thought to inhibit a respiratory enzyme which results in the build-up of reactive oxygen species (ROS). These are substances that are strongly oxidising and also contain an unpaired electron. This means that they are radicals and very reactive.

The upshot of all this is a disruption of the cell metabolism, damage to proteins and DNA, and inflammation and distortion of the cell leading to lysis (the cell membrane ruptures).

With nano-silver impregnated filter papers the idea is that the filters would be transported to disaster zones to clean up water in the field.  It is much easier to transport and store filter papers than water, so this would be a major aid to helping people avoid water-borne diseases.

It’s still in the early days of development so it may be a while before you see this idea in action. Even if this work makes it to full scale production I’m still going to be very reluctant to drink my pond water after what the frogs have been doing in it!

See the original article at Producing clean water in an emergency