WASH 101: Biological Intervention – Antimicrobial Metals

May 2, 2019

Posted by Chip, Managing Director

Before we jump into today’s post about biological interventions, I just have to give you a quick reminder. You’re joining 20 Liters in an ongoing conversation. So, feel free to go back and catch up with us. We’ve already covered each part of the WASH acronym [Water, Sanitation, Hygiene], made sure we have a shared language, and looked into disparities for vulnerable populations.

Now, we’re working our way through a discussion about various solutions to make dirty water clean. We’ve divided the solutions into a few categories:

Physical Intervention: including filtration, adsorption, sedimentation, boiling & distillation
Biological Intervention: including antimicrobial metals, activated carbon & bio-sand filters
Chemical Alteration: including chlorination & flocculation
Electromagnetic Radiation: including UV Light treatment
Sourcing: including rainfall, groundwater, underground aquifers, springs, and human-intervened (bottled, wells or municipal water).

Today, we’re getting into talking about solutions to make dirty water clean that fall under the category of Biological Intervention. So, stick with us over the next few posts as we cover Antimicrobial Metals, Activated Carbon and Bio-Sand filters.

Before we get into the first solution that falls under the category of biological intervention, let’s take a moment to consider the category as a whole. Generally, biological interventions use bacterial processes to remove harmful bacteria from water. When we get to talking about Bio-Sand Filters, this description makes a lot of sense. Some of the other solutions included under this heading [including antimicrobial metals and activated carbon] don’t always work in this same way, but they are often used alongside biological interventions and therefore get grouped with them.

Antimicrobial metals

We’ve known for a while that some metals can kill off microbes. As far back as 3500 BCE, ancient Mesopotamians and Egyptians discovered that water stored in copper vessels was purer than groundwater or in other vessels. Ancient Indian texts recommend using brass utensils for “purity of water and good health”. As time progressed, we discovered that alloys of mercury, silver, copper, brass, bronze, tin, iron, lead and bismuth all have this property to varying extents.

In 1893, a Swiss botanist noted the toxic effect that metal ions have on living cells and termed this effect “oligodynamic”.  But, he was unable to explain why this effect occurred.

A 1989 paper specifically focused on copper noted that the antimicrobial mechanisms are very complex and take place in many ways, both inside cells and in the spaces between cells. They suggested that reasons that copper has an antimicrobial effect could include that: copper forms highly reactive ions which inactivate viruses; copper ions can alter the 3-dimensional structure of proteins, inhibiting normal cellular functions; and elevated copper levels cause hydrogen peroxide to form inside of cells, killing the cell.

These are some of the most compelling reasons, but the researchers cited at least 120 other investigations into the effects of copper on microbes. These findings are specific to copper, but it highlights something very important about antimicrobial metals.

We don’t know how or why antimicrobial metals work.
But we do know that they work very effectively.

Applying this knowledge to water filtration is relatively easy. You can harness the power of antimicrobial metals by mixing some silver into clay when creating ceramic filters (or ceramic tablets like the MadiDrop). 20 Liters adds brass powder to the lower layers of sand in a Slow-Sand filter. Some technologies use an electrical device called an ionizer that passes a low voltage across electrodes to release copper or silver ions into the water. Or you could just coat your filter membrane with silver nanoparticles.

Why we love Antimicrobial metals…

First, there isn’t a high resistant rate among microbes to metals like there is with other antimicrobial chemicals. These metals hardly degrade at all, providing for very long lifespans for any technologies using them. And finally, most antimicrobial metals are prevalent in nature and affordable where economies exist

But no solution is perfect.

There are several concerns with the use of antimicrobial metals. First, mining practices and the manufacture of alloys usually come with negative environmental impacts and serious labor concerns. These negative environmental impacts are compounded because the metals in these technologies are often discarded instead of being recovered, recycled or reused.

As with many antimicrobial or antibacterial products, we expect resistance to increase alongside the use of these products. And as bacterial resistance to these metals increases, the efficacy of these metals decreases.

Finally, not all metals respond the same ways to all water types or microbes. So, without testing for the specific water source, there is no way of knowing that all microbes have been killed. The end users would need training to know how long to expose their water to the metals [in the appropriate concentration for the appropriate time] to make sure the solution has time to work properly.

I hope you’re seeing the theme as we discuss the drawbacks for each of these potential solutions… it all comes back to training the end user. Keep this in mind and we’ll come back to it. Just remember, if you don’t know how to use your smartphone – a potentially life-changing technology ends up being a really expensive paperweight.


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