A METAL ISOTOPE TOOLKIT FOR TRACING HEAVY METALS IN THE ENVIRONMENT

J. Gadd (NIWA), C. Stirling, M. Druce & M. Devakumar (Department of Geology, University of Otago), M. Ellwood (Australian National University)

ABSTRACT 

INTRODUCTION

Declining water quality is of serious concern for most New Zealanders. Aotearoa New Zealand’s freshwater streams, estuaries and harbours are pressured by increasing levels of metal contaminants from nearby transport, construction, agricultural and horticultural activity. At some sites, metal concentrations already exceed guidelines for ecological health. Mounting land-use pressures are only expected to intensify these adverse effects, through population, primary-industries, construction-sector and tourism growth.

Heavy metal contamination is traditionally monitored using metal concentrations and future predictions are based on our knowledge of existing sources. Although some sources of metals are well known (like zinc from vehicle tyres, copper from brake pads), there are major gaps in our knowledge of where anthropogenic heavy metals come from. For instance, we only know where about half of the copper in urban stormwater comes from (Kennedy & Sutherland 2008). The ubiquity of many metals limits our ability to identify specific pollution sources. Without knowing the sources of metals, our predictive models have high uncertainty, limiting the ability of New Zealand’s regulatory authorities to anticipate contamination before it occurs.

To overcome this shortfall, our project will develop metal-isotope ‘fingerprinting’, to offer improved discriminatory power over concentrations alone for quantifying the sources, transport-pathways, and sinks of heavy-metal contaminants as they move through the environment.

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