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 Sorenson & Milne 2009, Cummings et al. 2022 and Forrest et al. 2022 for technical methods, data tables, and further information
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