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Contaminated Land

A contaminated site is defined by the Ministry for the Environment as:

A site at which hazardous substances occur at concentrations above background levels and where assessment indicates it poses, or is likely to pose, an immediate or long-term risk to human health or the environment.

“Background levels” is generally defined as the “ambient levels of a contaminant in the local area of the site under consideration”. This basically refers to the concentrations of an element in soils attributed only to lithological processing (i.e. weathering of parental rock material etc.) and not linked to any identifiable event or activity.

Land can become contaminated through the manufacture, use, storage and disposal of hazardous substances. While contamination is usually associated with industrial activities, the use of hazardous substances in agriculture and residential settings can also cause contamination.

People can become exposed to contaminants in soil through contact with the soil, soil ingestion, eating produce grown on contaminated land and drinking contaminated ground or surface water. If a contaminant is volatile, people may also be exposed by inhalation. The health risk associated with contaminated soil will depend on the type of hazardous substance, the exposure route and the length of time a person is exposed.

Download the Ministry of Health's Soil Contaminants and Health leaflet (PDF, 270KB)
Download the Ministry of Health's Arsenic and Health leaflet (PDF, 310KB)

Contaminants Toxicity Score Predominant Sources
Arsenic 5 Timber treatment
Asbestos 5 Building, insulation
Benzene 5 Fuel combustion, fuel-service stations, ports and airports
Cyanide gas / hydrocyanic acids 5 Electroplating, gold mining, pest destruction, gas works
Lead (inorganic or organic) 5 Paint, batteries, plastics, leaded petrol additives
Mercury 5 Pulp and paper, dentistry, batteries, electronics, seed treatment
Phenols 5 Resin manufacturing
Poly-aromatic hydrocarbons (PAHs) 5 Fuel combustion
Polychlorinated biphenyls (PCBs) 5 Electrical
Polychlorinated dibenzodioxins and furans 5 chlorination/incineration, timber treatment
Cyanides (excluding gas or hydrocyanic acid) 4 Electroplating, gold mining, pest destruction, gas works
Volatile halogenated organics 4 Industrial solvents and cleaning
Bacterial/viral material 3 Hospital waste, animal waste, sewerage, organic / domestic waste
Cadmium 3 PVC, Ni-Cd batteries
Chromium (IV) 3 Timber, tanning
Formaldehyde 3 Glues, resins wood products
Landfill gases 3 Landfill
Nickel 3 Metal applications, batteries
Pesticides 3 Manufacture, storage, inappropriate disposal or use
Volatile non-halogenated organics (excluding phenols and PAHs) 2 Fuels and fuel combustion
Acids and alkalis 1 Cleaning, waste treatment, metal finishing
Chromium (VI) 1 Timber and tanning
Copper 1 Fungicides, timber, metal applications
Organic corrosives 1 Metal finishing, photographic
Semi-volatile non-halogenated organics (excluding phenols and PAHs) 1 Oil refining, gas production
Tar, oils and fats (that contain no high or medium ranking substances) 1 Oil refining, road construction, food by-products
Putrescible waste 1  
Zinc 1 Fungicide, animal remedies, PVC, metal

Table 3: Major group of contaminants, their toxicity scores and predominant sources*

*Source: modified from the Ministry of Health (1996).

The Healthy Environments Team has been working closely with the territorial and local authorities (TLAs) in the assessment and management of contaminated sites in the Auckland region.

Further information on contaminated sites is available from the Auckland Council or Contaminated Land in the UK website.

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