Heavy metal load in sediment

  • Image, Heavy metal load in sediment.

    Heavy metals occur naturally in estuaries, but high concentrations suggest contamination from another source. The metals can be transported along waterways from urban environments (and, for cadmium, from farmland) and accumulate in estuarine and coastal sediments. They are toxic and accumulate in fish and shellfish. We focus on four heavy metals: lead, copper, zinc, and cadmium.

    We classified Heavy metal load in sediment as a case study.

    Key findings

    In the five years from 2010 to 2014, most monitored sites in 10 regions had concentrations of lead, cadmium, copper, and zinc below the threshold effects level (TEL) for adverse biological effects to occur.

    • 94 percent of sites (350 of 374) were below the TEL for lead (30.2 micrograms per gram – µg/g), with 24 sites exceeding it. No site exceeded the probable effects level (PEL, 112 µg/g).
    • 95 percent of sites (286 of 300) were below the TEL for cadmium (0.68 µg/g), 3 percent (10) exceeded it, and 1 percent (4) exceeded the PEL (4.21 µg/g), above which adverse effects on seabed species are frequent.
    • 89 percent of sites (334 of 374) were below the TEL for copper (18.7 µg/g), with 40 sites (11 percent) exceeding it. No site exceeded the PEL (108 µg/g).
    • 92 percent of sites (343 of 374) were below the TEL for zinc (124 µg/g), 7 percent (27) exceeded it, and 1 percent (4) exceeded the PEL (271 µg/g).

     

    Note: The graph shows the number of monitored sites in 10 regions with heavy-metal (lead, cadmium, copper, and zinc) concentrations in estuarine and coastal sediment below or above biological-effects levels (Macdonald et al, 1996). The concentrations are based on the most recent sample in 2010–14. TEL – threshold effects level below which adverse effects on benthic species are rare. PEL – probable effects level above which adverse effects on benthic species frequently occur. Data from Auckland Council; regional councils of Bay of Plenty, Canterbury, Hawke's Bay, Northland, Otago, Waikato, and Wellington; and Gisborne and Marlborough district councils.

    Definition and methodology

    Heavy metals are toxic, even at low concentrations. They accumulate in sediment, where they can be taken up by organisms, and are harmful to species and habitats. They also bio-accumulate (are found in higher concentrations in species further up the food chain).

    We report concentrations of four heavy metals in sediment (lead, cadmium, copper, and zinc) in coastal and estuarine environments as a measure of ecosystem health. The concentration for each site in 10 regions is based on the most recent sample over the five years 2010–14.

    These concentrations are reported against the levels above which adverse biological effects may occur. These levels are:

    • exceeding the probable effects level (PEL), meaning adverse effects occur frequently on benthic species above this level
    • exceeding the threshold effects level (TEL), meaning adverse effects can occur on benthic species above this level
    • below the TEL, meaning adverse effects are unlikely to occur on benthic species (Macdonald et al, 1996).

    The PEL for each heavy metal is: lead (112 µg/g), cadmium (4.21 µg/g), copper (108 µg/g), and zinc (271 µg/g).

    The TEL for each heavy metal is: lead (30.2 µg/g), cadmium (0.68 µg/g), copper (18.7 µg/g), and zinc (124 µg/g).

    A contributing factor to the low heavy metal concentrations reported for this period may be the low concentrations found at Canterbury sites. Heavy-metal concentrations decreased in many estuary sites in the region as a result of liquefaction and other effects from the 2010/11 Canterbury earthquakes. Heavy metal concentrations were below the TEL for all 18 Canterbury sites.

    Data quality

     Topic Classification   Relevance Accuracy 
    Marine water and sediment quality and ocean acidity Case study

    relevance-partial 
    Partial

     accuracy-medium
    Medium

    See Data quality information for more detail.

    References

    MacDonald, DD, Carr, RS, Calder, FD, Long, ER, & Ingersoll, CG (1996). Development and evaluation of sediment quality guidelines for Florida coastal waters. Ecotoxicology, 5(4), 253–278. Accessed 18 August 2015 from www.dep.state.fl.

    Archived pages

    See Heavy metal load in sediment (archived October 2016).

    Updated 27 October 2016

marine-domain

Related content

Access data files

Water quality data

 

Related indicators

Coastal and estuarine water quality

 

Related links

Our marine environment 2016

Environment Aotearoa 2015

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