Sunlight Plus Lime Juice Makes Drinking Water Safer

[Ceph Lotus]

Johns Hopkins Bloomberg School of Public Health
Office of Communications and Public Affairs
Media Contacts: Natalie Wood-Wright
410-614-6029
[email protected]
April 18, 2012

FOR IMMEDIATE RELEASE

SUNLIGHT PLUS LIME JUICE MAKES DRINKING WATER SAFER

Looking for an inexpensive and effective way to quickly improve the
quality of your drinking water? According to a team of researchers
from the Johns Hopkins Bloomberg School of Public Health and the
Johns Hopkins School of Medicine, sunlight and a twist of lime might
do the trick.

Researchers found that adding lime juice to water that is treated
with a solar disinfection method removed detectable levels of harmful
bacteria such as Escherichia coli (E. coli) significantly faster than
solar disinfection alone. The results are featured in the April 2012
issue of American Journal of Tropical Medicine and Hygiene.

"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," said Kellogg Schwab, PhD, MS, senior author of the study,
director of the Johns Hopkins University Global Water Program and a
professor with the Bloomberg School's Department of Environmental
Health Sciences. "The preliminary results of this study show solar
disinfection of water combined with citrus could be effective at
greatly reducing E. coli levels in just 30 minutes, a treatment time
on par with boiling and other household water treatment methods. In
addition, the 30 milliliters of juice per 2 liters of water amounts
to about one-half Persian lime per bottle, a quantity that will
likely not be prohibitively expensive or create an unpleasant flavor."

In low-income regions, solar disinfection of water is one of several
household water treatment methods to effectively reduce the incidence
of diarrheal illness. One method of using sunlight to disinfect water
that is recommended by the United Nations Children's Fund (UNICEF) is
known as SODIS (Solar water Disinfection). The SODIS method requires
filling 1 or 2 L polyethylene terephthalate (PET plastic) bottles
with water and then exposing them to sunlight for at least 6 hours.
In cloudy weather, longer exposure times of up to 48 hours may be
necessary to achieve adequate disinfection. To determine if one of
the active constituents in limes known as psoralenes could enhance
solar disinfection of water, Schwab and Alexander Harding, lead
author of the study and a medical student at the Johns Hopkins School
of Medicine, looked at microbial reductions after exposure to both
sunlight and simulated sunlight. The researchers filled PET plastic
bottles with dechlorinated tap water and then added lime juice, lime
slurry, or synthetic psoralen and either E. coli, MS2 bacteriophage
or murine norovirus. Researchers found that lower levels of both E.
coli and MS2 bacteriophage were statistically significant following
solar disinfection when either lime juice or lime slurry was added to
the water compared to solar disinfection alone. They did find
however, that noroviruses were not dramatically reduced using this
technique, indicating it is not a perfect solution.

"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]," suggest the authors of the
study. However, they caution, "additional research should be done to
evaluate the use of lemon or other acidic fruits, as Persian limes
may be difficult to obtain in certain regions."

"Using Limes and Synthetic Psoralens to Enhance Solar Disinfection of
Water (SODIS): A Laboratory Evaluation with Norovirus, Escherichia
coli and MS2," was written by Alexander S. Harding and Kellogg J. Schwab.

The research was supported in part by the Osprey Foundation of
Maryland, The Johns Hopkins University Global Water Program, the
Johns Hopkins University School of Medicine Dean's Funding for Summer
Research and the Johns Hopkins University School of Medicine
Scholarly Concentrations.

###

[David Thomas]

Ceph,

Thanks for the link. That's an interesting approach, especially for a base-camp setting in the third world. I assume that they used limes because they are cheap and available throughout the semi-tropics and can be locally produced instead of a drain on an area's / family's hard currency.

For BPing uses, I'd wonder if the citric acid is the active ingredient, because powdered citric acid would be very cheap and light.

Anyone know what the UV transmission through PET plastic is? It's great that you could just hike with the bottle in an outside pocket. But for camp use, what about leaving it in a shallow plastic pan (bottom third of a gallon milk jug?) to maximize UV exposure?

[Stephen Barber]

….adding lime juice to the water when using a Steripen would make it more effective????

[Joe Clement]

How about adding lime…….and gin?

[Stephen Barber]

@ Joe: Yes indeed! The gin would kill even more bacteria! In fact, the more gin, the fewer bacteria! Excellent idea!!! ;)

[Tim Zen]

Don't forget the quinine for malaria.

[Mary D]

I notice there was no testing of the effect on protozoan cysts (giardia, cryptosporidium). Those critters are a lot harder to kill!

[Steven Paris]

Mary, that's what the blender is for.

[Author]

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