Soil is an important resource, especially for our agricultural economy, so protecting its quality is essential. Cadmium is one aspect of soil quality that is monitored.
Cadmium in New Zealand soils
Cadmium is a naturally-occurring heavy metal present in low concentrations in air, water and soils. It occurs naturally in phosphate rock – the main ingredient for superphosphate fertiliser.
Superphosphate benefits New Zealand's agricultural productivity by improving plant growth. But ongoing use of phosphate-based fertilisers can lead to build up of cadmium in soils.
Some evidence soil cadmium levels stabilising
Cadmium concentrations are still relatively low in New Zealand soils.
Because cadmium accumulates in soils, there was concern that levels in New Zealand soils would continue to rise. However, the latest evidence suggests that levels are stabilising. This will help reduce the risk of higher cadmium concentrations in the food chain.
In response to concerns in the late 1990s about cadmium levels in fertilisers, the fertiliser industry in New Zealand voluntarily adopted a limit for cadmium in fertilisers of 280ppm (parts per million).
Cadmium in the food chain
At high cadmium intakes, cadmium is toxic to humans. But the amount of cadmium in the diet of the average New Zealander is within World Health Organization guidelines – and well below levels that affect human health.
- Plants take up cadmium from the soil which means it can enter the human food chain, either through eating plants or food made from plants, or from eating farmed animals who have grazed on the pastures and plants.
- Cadmium accumulates in the kidneys of animals. Consequently, the sale of offal from animals older than 30 months is prohibited.
- Naturally high levels of cadmium are also found in some shellfish and crustaceans.
- Smoking cigarettes is another way you can be exposed to cadmium.
Why soil monitoring is important
To maintain the productivity of farms, phosphate fertilisers will continue to be used in New Zealand. So cadmium levels in soils must be actively monitored and managed.
If high levels are detected in some soils, it may prevent the affected land being used for certain farm activities.
How MPI monitors cadmium in soils
In 2009, MPI worked with the Cadmium Management Group to establish a Cadmium Management Strategy. Part of that strategy was to create a monitoring programme to provide information on the levels of cadmium in soils.
Further research will develop a base of New Zealand-specific information to allow us to better manage risks in the future. The Cadmium Management Strategy's objectives will be reviewed in 2017 to ensure new research and knowledge is included.
The Cadmium Management Group was formed from the Cadmium Working Group, which had run from 2006-2009, producing several reports.
- Report one: Cadmium in New Zealand agriculture [PDF, 901 KB]
- Cadmium and New Zealand agriculture and horticulture: a strategy for long term risk management [PDF, 167 KB]
- Soil maps of cadmium in New Zealand [PDF, 1.9 MB]
How MPI monitors cadmium in food
Cadmium content in food is monitored as part of the Total Diet Survey run by MPI every 5 years. The 2009 survey found dietary exposure to cadmium was well below the limit recommended by the World Health Organization.
Who to contact
If you have questions about cadmium, email firstname.lastname@example.org