Limes on sale at a Vietnamese market

If you grab a beer in Mexico your camarero will wedge a lime in the top. The same simple action, with a dash of sunlight, can be used to treat contaminated water in developing countries. Researchers at the John Hopkins Bloomberg School of Public Health have found that adding lime juice to a solar disinfection method speeds up the removal of harmful bacteria, such as E. coli, significantly faster than by sunlight alone.

For low-income families solar disinfection is a vital way to decontaminate water. One form of solar disinfection, known as SODIS is widely used as a simple method to treat water in developing countries. By filling a clear plastic bottle (preferably PET) and exposing it to sunlight for at least six hours, the pathogens within the contaminated water are killed by heat and exposure to UV.

A sip in the sun

The new method, published in the American Journal of Tropical Medicine and Hygiene, takes advantage of the high UV absorption of an active component of limes – psoralen. Instead of the minimum six hours it takes to treat water by SODIS, the extra lime notably reduced E. coli levels in water in as little as half an hour.

In South-East Asia and Africa, diarrhoea is responsible for as much as 8.5% of all deaths, most of whom are under five years old. Diarrhoeal diseases are spread by bacterial, viral and parasitic organisms within water so preventative measures, such as SODIS, are vital.

“For many countries, access to clean drinking water is still a major concern. Previous studies estimate that globally, half of all hospital beds are occupied by people suffering from a water-related illness,” says Professor Kellogg Schwab, senior author of the study.

Diagram of the SODIS method

Bottled water

The researchers filled PET bottles with unchlorinated water and added lime juice, lime slurry or synthetic psoralen. Then they added disease causing microbes for E. coli, MS2 bacteriophage or murine norovirus and measured the levels of residual microbes after treatment under simulated and natural sunlight. The results showed that the lime juice and slurry proved statistically more effective at disinfecting the water than by SODIS alone for all microbes except the norovirus.

“Many cultures already practice treatment with citrus juice, perhaps indicating that this treatment method will be more appealing to potential SODIS users than other additives such as TiO2 (titanium dioxide) or H2O2 (hydrogen peroxide),” says Schwab.

At present, boiling water is the most effective way of disinfecting water, and still is for noroviruses at least. More research is needed to put the lime SODIS method on par with boiling and to see whether other citrus fruits have the same effect. The study holds hope for a cheap method to save many from infectious disease – and as only half a Persian lime per bottle is needed, the extra squeeze won’t pinch.

DOI: 10.4269/ajtmh.2012.11-0370

Photo credits: nist6dh on Flickr, S1m0nB3rry on Flickr