Jeremy Hopwood, former senior lecturer and now Affiliate at the School of Applied Science at the University of Huddersfield, has been investigating the growth of unusual crystals of lead phosphate called spherulites that were discovered whilst he was running a project on lead in tap water for Yorkshire Water. The crystals are rounded with two lobes joining each other, resembling stems of broccoli.
Lead water pipes are present in a third of all UK properties, where they typically run under the front garden or path and connect the house to the mains pipe in the street. The legal limit is currently 10ppb.
Water utilities add small amounts of phosphate to tap water to prevent lead coming off lead pipes. One explanation is that the phosphate reacts with the lead to form a protective layer of insoluble lead phosphate crystals. Usually, crystals grow with flat faces like those seen in a crystal shop. However, Jeremy noticed that the lead phosphate crystals on customer lead water pipes are sometimes spherical or rounded in shape, indicating that something unusual was taking place.
A literature review revealed that similar shaped crystals are found in other systems and that these crystals are called spherulites.
Jeremy ran BSc and MSc projects to identify the conditions needed for lead phosphate spherulites to grow. The aim being to investigate more fully mechanisms of lead phosphate formation in lead water pipes and use this information to understand how phosphate controls the level of lead in tap waters.
Jeremy benefitted from access to technology available at the 3M BIC. He used the Zeiss Scanning Electron Microscopy (SEM) equipped with an elemental analyser to image the spherulites and determine their composition.
Jeremy and his students found that lead carbonate minerals, which are present in the mineral layer on lead water pipes, dissolve and reprecipitate as lead phosphate minerals when phosphate is added to the tap water and that these minerals are spherulitic when dissolved organic molecules are present. Citric acid and a small organic molecule were used to test the idea.
The initial findings were included in a paper entitled ‘Spherulitic Lead Calcium Apatite Minerals in Lead Water Pipes Exposed to Phosphate-Dosed Tap Water’, which was published in 2023 in the ACS Journal of Environmental Science and Technology. Che Singh, who is doing a Masters by Research, is currently looking at the kinetics of lead phosphate spherulite formation. Citric acid, a small organic molecule, is being used to test the idea.
Jeremy will be using the results from the 3M BIC Fellowship to write a new paper on spherulite formation and is hoping to carry on working in this field. The work is important as the public health issues surrounding lead in tap water will continue to be a concern in UK and worldwide water utilities for the foreseeable future.
“I have really enjoyed working with the team at the 3M BIC and tapping into their technical expertise and hope to continue to work with them in the future as they are an excellent interface between the University of Huddersfield and industry.”
Dr Jeremy Hopwood, Independent Researcher and Affiliate at the School of Applied Science, University of Huddersfield.