Cadmium is a toxic element used in the manufacture of batteries and is found in cigarette smoke, some paints, soil zinc additives, some fertilisers (especially those that contain phosphorus) and some manures. Industrial activity, such as mining, can increase soil cadmium levels. The acute symptoms of cadmium ingestion include stomach irritation and cramps, nausea, vomiting and diarrhoea, headaches, flu‑like symptoms, swelling of the throat and tingling hands. Chronic ingestion of cadmium can cause kidney disease and bone weakness. Ingestion of large amounts of cadmium can damage the kidneys, liver and heart and may even cause death. Cadmium is carcinogenic when inhaled but ingestion is not thought to cause cancer.
Cadmium in Soil and Food
In Australia, the upper limit of cadmium allowed in root, tuber and leafy vegetables is 0.1 mg of cadmium per 1 kg of produce. The allowed value in your area may be different but you can use this value as a guide. The amount of cadmium in soils is generally low but once it has been added to the soil, it can take between 100 and 1000 years for the levels to drop by 50%. When cadmium is present in soil, it is more available to plants if the soil is sandy, acidic or low in organic matter. It is recommended that soil contain less than 1 mg of cadmium for every 1 kg of soil. If the concentration of cadmium in your soil is greater than 20 mg/kg it would be a good idea to have your home grown produce analysed and then seek expert guidance on whether any cadmium detected constitutes a health risk.
Preventing Contamination of Soil and Food with Cadmium
By observing the following, it is possible to prevent contamination of soil and produce with cadmium provided the heavy metal does not leach into soil from an external source (a mine for instance):
- Use low cadmium fertilisers and only use the minimum amount required for healthy plant growth
- Ensure soil pH is close to neutral (add lime if the soil is too acidic)
- Ensure the soil always contains an adequate amount of zinc
- Continuously incorporate plenty of organic matter into the soil
- If soil cadmium levels are elevated, grow plant varieties that take up less cadmium
Leafy vegetables like lettuce, cabbage and spinach take up the most cadmium. Root crops such as carrots and potatoes take up less but fruiting plants take up the least amount of cadmium. As such, this method for dealing with arsenic contamination (using raised beds for most vegetables and only growing fruit trees and bushes in the ground) can be used for cadmium if desired.
- Australia New Zealand Food Standards Code - Standard 1.4.1 - Contaminants and Natural Toxicants (F2011C00121) http://www.comlaw.gov.au/Details/F2011C00121
- [Australian] National Environment Protection (Assessment of Site Contamination) Measure 1999 Schedule B1 (F2013C00288, measures as amended, taking into account amendments up to National Environment Protection (Assessment of Site Contamination) Amendment Measure 2013 (No. 1)) http://www.comlaw.gov.au/Details/F2013C00288/Html/Volume_2