Health and sanitation
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et al., 1994). Edwards et al. (2000) attributed
the rare occurrence of blue water to corrosion
of copper plumbing. Ingesting high levels of
silver can also lead to a skin discoloration
condition called “argyria” (Drake and
Hazelwood, 2005; WHO, 2003; USEPA, 1989b).
According to WHO (2003), the lowest dose of
silver that may lead to occurrence of argyria
has not been determined, but, in general,
silver levels up to 0.1mg/L can be tolerated
without risk to health. Silver levels approaching
the SMCL of 0.1mg/L have been reported in
premise plumbing systems using CSI treatment
(Rohr et al., 1999; States et al., 1998).
Laboratory studies have been conducted on
the effectiveness of CSI in reducing levels of
other bacterial species commonly found in
built environments, including Pseudomonas,
Stenotrophomonas, Acinetobacter (all
gram-negative bacteria like legionella)
and Mycobacterium. Copper and silver
ions appear to act synergistically (the
total effect is greater than the sum of the
individual effects) toward L. pneumophila
(Lin et al., 1996), Pseudomonas and
Acinetobacter (Huang et al., 2008), while
the ions act antagonistically (the interaction
of the two metals lessens the effect of
each metal acting individually) toward
Stenotrophomonas (Huang et al., 2008).
Mycobacterium was shown to be 100-fold
less sensitive to copper and silver ions than
legionella (Lin et al., 1998b), and copper
and silver levels that controlled legionella
were unable to control the occurrence
of Mycobacterium in a hospital premise
plumbing system (Kusnetsov et al., 2001).
Shih and Lin (2010) tested CSI in a model
water system against Pseudomonas,
Stenotrophomonas and Acinetobacter with
72 hours exposure to copper and silver
concentrations of 0.2 and 0.02, 0.4 and
0.04, and 0.8 and 0.08mg/L. In biofilm,
CSI achieved 2- to 3-log reduction (99
to 99.9%) of these pathogens. In free-
floating bacteria, CSI achieved a 4-to
7-log reduction, except for Acinetobacter,
where even with 0.8 and 0.08mg/L copper
and silver concentrations, the reduction
was only 2 log (99%). The authors noted
that concentrations of copper and silver
decreased during the 72 hours, probably
because ions were attached to individual
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cells, and that this could have contributed to
regrowth during that period.
Field studies of CSI have reported some
effectiveness in reducing fungi in hospital
water systems, especially Fusarium spp.
(Chen et al., 2013). A report on health care
facilities in Spain with (n=9) and without (n=7)
ionisation treatment systems cited a fungal
isolation rate of 28% versus 77%, respectively
(Pedro-Botet et al., 2007). CSI has not been
reported to reduce levels of heterotrophic
bacteria or amoebae in either a controlled
laboratory study (Rohr et al., 2000) or a case
study (States et al., 1998).
Operational conditions
Parameter conditions indicating
operational effectiveness
Maintaining copper and silver at the levels
recommended by the manufacturer is
a best practice in achieving operation
effectiveness. Note that monitoring typically
includes measurement of the total metal
concentration, which includes copper and
silver that are bound up as complexes, as
well as copper and silver ions. The
presence of copper and silver ions is
thought to be critical for treatment
effectiveness, so maintaining proper pH
and avoiding interfering materials (e.g.,
phosphates, chlorides) is also important
(Zevenhuizen et al., 1979). Examples of
interferences include:
• In the presence of 20–40mg/L of
chloride ions, silver ion levels are
significantly (60%) decreased by
complexing with chloride (and are
presumably less microbiocidal) (Lin et
al., 2002).
• Phosphates, such as those added for
corrosion control, can bind to copper
ions as well as silver ions, reducing their
treatment effectiveness (Zevenhuizen et
al., 1979).
The presence of dissolved organic carbon at
2mg/L, calcium at 100mg/L, magnesium at
80mg/L, and bicarbonate at 150mg/L did not
appear to decrease the treatment efficacy of
copper and silver ions against L. pneumophila
in a laboratory study (Lin et al., 2002).
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June 2017 Volume 23 I Number 4