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 found in low concentrations in air, water, and soils. It occurs naturally in phosphate rock – the main ingredient for superphosphate fertiliser.
Superphosphate helps New Zealand agriculture by improving plant growth. But ongoing use of phosphate-based fertilisers can lead to a build-up of cadmium in soils. Cadmium concentrations are still relatively low in New Zealand soils, though.
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 280mg Cd/kg. Testing shows current average fertiliser content of just 180mg Cd/kg.
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. This means it can enter the human food chain through eating plants or food made from plants, or from eating animals which have eaten plants.
- Cadmium builds up in the kidneys of animals. To prevent this entering the human food chain, offal from animals older than 30 months cannot be sold.
- 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 2019, MPI worked with the Cadmium Management Group to refresh the Cadmium Management Strategy. The strategy provides an agreed ongoing approach to managing cadmium in New Zealand. It also provides a basis for government agencies, regional councils, and the farming and fertiliser sectors to work together. It is important to base management of cadmium on accurate information, so the strategy includes monitoring and research.
The Cadmium Management Group was formed from the Cadmium Working Group, which ran from 2006 to 2009. Members include representatives from the fertiliser industry, grower sector groups, industry organisations, research organisations, regional councils, and central government. The Cadmium Management Group has produced several reports and other resources:
- Tiered Fertiliser Management System for Soil Cadmium (2019) [PDF, 2.5 MB]
- Cadmium in New Zealand agriculture [PDF, 901 KB]
- Status of cadmium in New Zealand soils: 2014
How MPI monitors cadmium in food
Cadmium levels in food are monitored as part of the New Zealand Total Diet Study run by MPI every 5 years. Results from the latest Total Diet Study continue to confirm that the amount of cadmium in the diet of the average New Zealander is within World Health Organization guidelines. This is well below levels which affect human health.
Find out more
Who to contact
If you have questions about cadmium, email firstname.lastname@example.org