Silver (and other metals) in Christchurch’s urban waterways

Abstract

The purpose of this study was to conduct a preliminary investigation of the environmental fate of silver nanoparticles in Christchurch’s freshwater environments. Sediment samples were collected from nine sites in Christchurch representing waterways that are likely to be impacted by residential and industrial activities. Two sites were sampled for the purposes of experimental control. The total concentrations of silver was measured by ICP-MS in the <2 mm and <63 μm sediment size fractions. Additionally, the silver content was measured in a primary sludge sample obtained from the Bromley wastewater treatment plant. The greatest concentrations of silver were measured in the dry wastewater sludge samples (3.1 – 3.7 mg/kg). However, these concentrations were found to be considerably lower than a previous analysis of Bromley sludge (36.3 mg/kg). The concentrations measured in freshwater sediments varied from <0.4 – 0.43 mg/kg. No samples were found to exceed relevant sediment quality guidelines for the protection of aquatic life. However, statistically significantly higher concentrations were measured in sites associated with industrial and residential activities. The proportion of silver in samples attributable to silver nanoparticles was not able to be determined using ICP-MS alone. Additional studies are recommended to characterise the silver present in Christchurch’s freshwater sediments and wastewater sludge. Regular monitoring of sites is also recommended to assess whether the increasing use of Ag-NPs may be enhancing environmental concentrations. The concentrations of other contaminant trace metals were also determined in the course of this study. This dataset is presented in Appendix 3, but results have not been interpreted as part of this study