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 ).
By
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