Summary of risks from cadmium in agricultural soils
Chapter 1: Setting the context – an introduction to the cadmium issue
Overview
Cadmium naturally occurs in phosphate rock, from which phosphate fertiliser is made. Phosphate fertiliser use underpins agricultural production and therefore contributes significantly to New Zealand’s economy. Cadmium tends to accumulate in soils with ongoing application of phosphate fertilisers, and there is evidence that cadmium levels in New Zealand’s soils are increasing. This raises the potential for higher cadmium concentrations in some food products grown on soils with elevated cadmium levels. Excessive levels of cadmium in food can have implications for human health, market access and trade, and the ability to change from one land use to another.
Background
Cadmium is a naturally-occurring, non-essential heavy metal which is present at low concentrations in air, water and soils. Both acute and chronic cadmium exposure can have adverse health effects on people.
In New Zealand, industrial exposure to cadmium is rare, and the main source of cadmium for New Zealanders is in tobacco products and food. Low levels of cadmium in the diet can accumulate over a person’s lifetime. The New Zealand Food Safety Authority has estimated the amount of cadmium in the diet of the average New Zealander is at a level far below that which would cause adverse health effects.
Phosphate fertilisers contain cadmium as a trace impurity, and cadmium tends to accumulate in soil with repeated application of phosphate fertiliser. Accumulation rates in soils vary between regions of New Zealand due to differences in land use history, phosphate fertiliser cadmium content, total fertiliser use, soil types, climate, and a number of other variables.
There are three key threads to the New Zealand context relating to cadmium in soils, which influence the consideration of this issue. Firstly, the dominance of agriculture in New Zealand’s economy. Secondly, agricultural production is underpinned to a large extent by phosphate fertiliser, the major source of cadmium into agricultural soils. The third issue is the importance of the international trade to New Zealand agriculture and economy, which depends in turn on factors such as consumer demand, international regulation, and the wider economic and geopolitical situation.
In order to assess and mitigate any risks associated with cadmium, the Chief Executives’ Environment Forum established a Cadmium Working Group, to investigate and assess the potential risks surrounding cadmium in New Zealand’s agriculture and food systems, and to develop responses as required.
There are two basic approaches to assessment of cadmium: a ‘risk based’ approach and a ‘mass balance’ approach. The Cadmium Working Group used and promotes a risk based approach.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
Contact this person
