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Perth Children's Hospital: how dezincifcation can elevate lead levels in water

Perth Children's Hospital: how dezincifcation can elevate lead levels in water

Date Published: 04-May-17

ChemCentre, the state’s leading provider of specialist chemical and forensic science services, has played an integral role in assisting the state government with its investigation into the source of lead in water at the Perth Children’s Hospital construction site. 

At its heart, this issue is all about chemistry, and that’s why our expertise has been so important.
 
Since September 2016 we have been engaged to analyse water samples and other material from across the hospital site. Below is a summary of our work, and you can also find the link to our internal report which was also provided in the media release of 3 May by Health Minister Roger Cook and Treasurer Ben Wyatt.
 
What we did
ChemCentre undertook independent research to determine if brass fittings could leach lead into solution at levels above the Australian Drinking Water Guideline (ADWG) standard of 0.01mg/L. Further, if lead did leach, would treatment with phosphate alleviate this problem? The tests showed that Perth tap water could leach lead from the fittings tested, but that subsequent phosphate treatment could quickly reduce the lead levels to below ADWG levels. On the basis of this research, in-situ phosphate treatment of brass fittings at PCH offers a potential means of solving the lead issue at the Perth Children’s Hospital.

What is dezincification
Brass is an alloy primarily of zinc and copper and commonly used in plumbing fittings. Dezincification, also known as selective leaching, can occur in brass where the zinc preferentially leaches out of the alloy. Lead is commonly added to make the brass more easily machined. Other elements can be added to give ‘dezincification resistant (DR) brasses’. It should be recognised, however, that even DR brasses can undergo dezincification under certain conditions. 
 
Brass that has undergone dezincification can have a large surface area that is enriched in copper and lead. The lead is often present as oxides or carbonate that are more soluble than lead as metal, and they can also become particles in water flowing past fittings.
 
Solution to dezincification: orthophosphate treatment
Orthophosphate treatment of brass converts the surface lead compounds to lead phosphates which are much less soluble than the oxides or carbonates. This type of treatment has been used successfully in North America and Europe to lower the lead content to acceptable levels in potable waters that have been delivered via lead pipes. It has offered people in these locations an in-situ means of achieving lower lead content potable water without the need to replace pipes and fittings. 
 
ChemCentre has reconfirmed its commitment to work with government to provide advice where necessary. 

Image: brass fittings submerged in water
 
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