Some metals, when in high concentrations, can have toxic effects on aquatic life in both a dissolved state and when attached to sediment particles. Zinc and copper in particular are often used as proxies for the suite of other potential urban contaminants (e.g. polycyclic aromatic hydrocarbons, plasticisers) or legacy contaminants such as the historic pesticide DDT. These types of contaminants often end up in estuaries via stormwater runoff. Copper is approximately 5 to 10 times more toxic to aquatic life than zinc, but generally occurs in lower concentrations.
Values are rated against thresholds derived from the New Zealand Estuary Trophic Index (ETI), which in turn are scaled relative to 2018 Australia and New Zealand Guidelines (ANZG) for sediment quality. Ratings of “good” and “very good” correspond to ‘safe’ values that are less than ANZG (2018) default guidelines, while “fair” corresponds to values between the default and high-guideline values, reflecting “possible” ecological effects. “Poor” sites exceed the high-guideline value.
See Stevens & Robertson 2012, Stevens 2018a, Cummings et al. 2021 and Stevens 2022 for technical methods, data tables, and further information
Usage guide: Toggle between tabs to see different metal contaminant monitoring summaries. Click and drag the year slider on each map (if available) to see change over time, and hover over map data to see specific values. The chart below the map displays each sites' data temporally, hovering over lines will also show specific values and highlight that site on the map.