Assessment of the potential environmental impacts arising from mercury-free dental restorative materials

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Binner, Hannah
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University College Cork
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The field of dentistry and with it, the application of dental filling materials, is currently undergoing changes to adopt sustainability and environmental considerations into the clinical environment. This was largely triggered by the reduction of all products in use that contain Hg (mercury), including dental amalgam, through the Minamata Convention of 2013, which has in turn caused a rise in Hg-free dental filling materials that are now becoming increasingly nano-filled. The focus of this study is on the particles released from Hg-free dental fillings. Knowledge gaps regarding the particle load and potential ecotoxicity of the particulate matter resulting from Hg-free materials exist. Moreover, the widely known environmental and human health impacts of Hg contained in dental amalgam have led to the widespread introduction of an amalgam capture device, the amalgam separator. Amalgam separators capture Hg and dental amalgam particles before wastewater discharge occurs. These amalgam separators are required to be installed in Ireland since the 1st of January 2019 in accordance with EU Directive 2017/852. The overarching objective of this thesis has been to assess whether existing amalgam separators are also effective in capturing particulate matter resulting from the use of Hg-free dental filling materials. In order to meet this objective, this study has assessed the wastewater and amalgam separator capture efficiency in three dental practices in Cork, Ireland. Three dental practices were selected based on the type of amalgam separator in use and focus of service based on private or public practice and high, medium or low utilisation. Physical and chemical parameters of dental wastewater (DWW), including pH, temperature, conductivity, Total suspended solids (TSS) and Total Dissolved Solids (TDS) have been measured. Detailed analysis of particles found in these wastewater streams has been conducted using optical and scanning electron microscopy. The potential ecotoxicity of these waste streams has also undergone preliminary assessment by conducting standardised Daphnia magna immobilisation tests. The results indicate that variation in the discharged DWWs exists, which is likely linked to the use of disinfection products, and has led to extreme observations of pH, conductivity, Total suspended solids and Total dissolved solids. Ecotoxicity results confirmed this and showed that the raw DWW caused an EC50 response at concentrations between 0.1 to 6.69 % DWW/L medium. The particulate load in the three DPs was substantial. A high abundance of microparticles was identified and trends were consistent across the three DPs. It was therefore concluded that amalgam separators may not be sufficient in capturing the particulate matter released from Hg-free dental filling materials. Further research is needed to identify the environmental fate of the particles that are released, particularly nanomaterials, as they have the potential to remain in the water after wastewater treatment has occurred.
Minamata convention , Daphnia magna , Dentistry , Waste streams , Ecotoxicity , Particle analysis , Nano-particles , Mercury-free , Resin composites , Dental filling material , Amalgam separator , Wastewater
Binner, H. 2019. Assessment of the potential environmental impacts arising from mercury-free dental restorative materials. MRes Thesis, University College Cork.