Health and sanitation
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Copper – silver ionisation( Continued)
There is an understanding of how bacterial gene systems can confer resistance to copper and silver( Nies, 1999). Some of these gene systems are found in legionella( Bondarczuk and Piotrowska-Seget, 2013).
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Environmental Protection Agency, document EPA 810-R-16-001
One common resistance mechanism in gramnegative bacteria( such as legionella) requires an energy-dependent protein that protects the cell by acting as a pump to export copper ions out of the cell( Bondarczuk and Piotrowska-Seget, 2013). The occurrence of legionella strains potentially tolerant of silver in CSI treatment was noted by Rohr et al.( 1999); however, Lin( 2000) commented that Rohr et al.’ s( 1999) conclusion is not supported by any data in their report and noted the silver ion levels used were below the recommended levels for control of legionella. Rohr( 2000) responded to Lin( 2000) that the multiple regression analysis reported in the 1999 paper shows a decreasing influence of silver ions on legionella counts during the 4-year study period.
Hypochlorous acid, the active disinfecting chlorine species, is in part toxic to bacterial cells by virtue of interfering with the production of energy( in the form of adenosine triphosphate( ATP)) needed for many cellular processes including heavy metal resistance enzymes( Barrette et al., 1989). The synergy between free chlorine and heavy metal ions on legionella copper resistance mechanisms and legionella susceptibility is generally unstudied. However, Landeen et al.( 1989) showed increased( although not statistically significant) inactivation rates of L. pneumophila with copper and silver ions in the presence of 0.4mg / L free chlorine.
Potential water quality issues Use of CSI may result in corrosion. Materials compatibility and water quality will dictate the severity of corrosion. Awareness of the types of materials and water chemistry in a premise plumbing system is critical to maintaining system integrity. Loret et al.( 2005) observed corrosion marks on mild and galvanised steel coupons installed in pipe loops for CSI treatment that were similar to corrosion effects for other disinfectants( chlorine, chloramine, chlorine dioxide and ozone), except that the coupons exposed to CSI also had copper deposits. Although pitting corrosion was not observed during the study, intense corrosion occurred within the pipe loop after the study was completed, suggesting that CSI treatment may lead to pipe corrosion under some conditions. Type III pitting usually occurs in soft water with alkaline pH > 8.0( Edwards et al., 1994), at distal or stagnant locations and at moderately warm temperatures( Edwards et al., 1994). Lytle and Schock( 2008) found that waters with high pH( pH 9 and possibly as low as 8), low dissolved inorganic carbon(< 10mg / L and possibly as high as 25mg / L) and chloride levels of 14 – 38mg / L promoted pitting corrosion.
High concentrations of both copper and silver have been reported in systems employing CSI, to levels approaching the maximum contaminant level goal and action level for copper( 1.3mg / L) and the secondary maximum contaminant level( SMCL) for silver( 0.1mg / L)( States at al., 1998; Rohr et al., 1999). As copper levels in copper piping can rise during periods of stagnation, high levels of copper can occur in early morning first-draw water samples( Araya et al., 2004; Araya et al., 2003a; Araya et al., 2003b; Araya et al., 2003c; Araya et al., 2001; Knobeloch et al., 1994). Copper, but not silver, was found to concentrate on biofilm material in premise plumbing systems employing CSI treatment( Liu et al., 1998; Zevenhuizen et al., 1979).
Copper toxicity from ingestion of drinking water has been reported even without the contribution of copper from CSI systems( Araya et al., 2004; Araya et al., 2003a; Araya et al., 2003b; Araya et al., 2001; Knobeloch et al., 1998; Knobeloch et al., 1994). Symptoms of copper toxicity include nausea, abdominal cramps, vomiting and diarrhea.
Both copper and silver can have negative aesthetic effects on water: colour, taste, and odour and staining issues( Hong et al., 2010; Dietrich, 2009; Stout and Yu, 2003; Edwards et al., 2000; Knobeloch et al., 1998; Knobeloch
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www. plumbingafrica. co. za June 2017 Volume 23 I Number 4