Heavy Metals: What are they?

The mission of Safer Phosphates™ is to share knowledge and address concerns about heavy metals that are present in some phosphate-based fertilizers. We want to improve understanding of the potential risks and promote solutions that optimize fertilizer choice, in order to support food security and sustainable agriculture.

Heavy metals: Why do they matter?


According to the World Health Organization, almost 200,000 people die every year from chemical poisoning, including heavy metals. Most of these could be prevented with protective measures and effective regulation.

Human cadmium toxicity was first reported in Japan during the 1950s. It became known as Itai-Itai disease, resulting from the consumption of rice grown in a contaminated floodplain downstream of mining activities.

Dietary intake of cadmium and other heavy metals remains an area of concern, which is why regulation has been proposed in Europe to limit contamination of soils.      

How Heavy Metals enter and move around soils:  

Heavy metals contamination of soils may come from a number of different sources, including high naturally-occurring background levels, atmospheric deposition, sewage sludge or phosphate-base mineral fertilizers.


The effect Heavy Metals have on soils:

  1. Inhibit biodegradation of organic contaminants
  2. Modify soil properties, especially microbiological ones
  3. Limit number, diversity and activity of soil micro-organisms
  4. Reduce crop growth, performance & yields
  5. Could transfer into food chain, reducing food & water quality

How Heavy Metals become a health risk:

Heavy metals persist for a long time after being introduced into soils. Taking cadmium as an example, it does not decompose, but relocates to lower soil layers, or transfers into waterways. It can be taken up by plants, the extent of which is influenced by the total volume of heavy metal containing material applied, the concentration of heavy metal in the material, prevailing climate conditions, soil properties (e.g. PH levels) and plant properties.  

From here dietary intake become relevant. The higher the consumption of crops grown in cadmium, or other heavy metals, containing soils and the higher the transfer rate, the higher the risk to health via accumulation and toxicity. That said, it is not always the crops with the highest contamination that one needs to worry about. The European Food Safety Authority (EFSA) has found that while some foods can contain higher concentrations of cadmium, it is ultimately the foods that are consumed in large quantities that present the greatest risk. Some more prominent examples include potatoes, cereals (mainly wheat) and vegetables.

As is the case in soils, once ingested, cadmium is expelled slowly from the human body. So after long-term exposure, it may accumulate, particularly in the kidney, resulting in toxicity. Kidney and bone disease are the most sensitive toxicological effects of excessive cadmium intake.  

Other heavy metals such as lead, arsenic and mercury affect the skin, bones, nervous system functionality and can contribute to the development of cancer.

Extent of the exposure

The European Commission has for some time been concerned over the long-term implications of cadmium build-up across European soils. Since the 1980s it has been weighing up options to limit exposure to cadmium – including the regulation of fertilizers. In 2016, through the Circular Economy Package, the Commission has proposed introducing progressive cadmium limits to phosphate fertilizers, thereby harmonizing quality standards amongst member states and protecting the soil for future generations.