No silver lining
SOUTH AFRICA
Critical warning to Cape Town:
water restrictions remain in place
After two years of drought, Cape Town’s dams are critically depleted.
Colloidal silver and silver nanoparticles are increasingly
being promoted for treating potentially contaminated
drinking water in low-income countries. This is despite
a lack of evidence of their effectiveness as a water
disinfectant. Scientists are warning that this water
treatment, widely used in developing countries, could
be damaging the DNA of those drinking it. It could in
fact cause genotoxicity, which is damage to DNA, and
affects reproduction and future generations, according
to a study led by the University of East Anglia (UEA).
Prof. Paul Hunter from UEA’s Norwich Medical
School said the study highlights the potential risks.
“Colloidal silver as a water treatment is sold across
Africa and in countries like Haiti, despite the fact
that it doesn’t treat water very effectively. The World
Health Organization (WHO) advises against its use as
a primary water treatment. If it isn’t doing any good,
we wanted to investigate if in fact it could be causing
harm.”
The effects of silver, silver nitrate, and silver
nanoparticles have been measured in vivo on living
animals, in previous studies. While the results varied,
more studies than they expected showed some
indication of genotoxicity, reporting effects including
chromosomal abnormalities, DNA fragmentation, and
damage to sperm.
WHO guidelines for drinking water quality do
not currently include a value for silver in water, but
indicate that a concentration of 0.1 milligrams per litre
could be tolerated without risk to health. However, this
was determined as a level unlikely to cause argyria and
did not consider potential damage to DNA.
Prof. Hunter said, “There is an urgent need for
more research in this area to determine if people
drinking water treated with silver have evidence of
DNA damage.” u
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Water Sewage & Effluent July/August 2017
Due to the severity of the drought, above-target consumption,
as well as the unpredictability of climatic conditions, Level 4
water restrictions remain in place indefinitely and could be
intensified if warranted.
All water users in Cape Town are warned not to increase
consumption as dam levels remain critically low and rainfall
uncertainty high. Dam storage levels are at 23.1%. With the
last 10% of a dam’s water mostly not useable, dam levels
are effectively at 13.1%. Worryingly, consumption has again
shot up and is 40 million litres per day above the target of 600
million litres per day.
Dam levels have only increased by about 3.7%, despite
the recent big storm, and including subsequent spells of rain.
The drought crisis continues as dam levels are critically lower
than usual at the start of the winter.
“All consumers must continue to use less than 100 litres
per person per day in total, whether at work, home, school or
elsewhere,” says the City’s Mayoral Committee Member for
Informal Settlements, Water and Waste Services, and Energy,
Councillor Xanthea Limberg.
For further information on how to adhere to the less than
100-litre usage requirement, residents should please visit the
water restrictions page on the City’s website at
www.capetown.gov.za/thinkwater. u
“All consumers must continue to use
less than 100 litres per person per day
in total, whether at work, home, school
or elsewhere,” says Xanthea Limberg.