In recent decades, numerous studies have indicated that the level of cadmium contamination in mineral fertilisers has a considerable negative impact on agricultural soils and, consequently, on plants, animals and human beings.
Cadmium is a toxic heavy metal, naturally present in varying concentrations in mineral phosphorous, which is extracted for the manufacturing of fertilisers. These fertilisers are often used on food crops, which reintroduces cadmium into the food chain. In the long term, low-level exposure to the heavy metal can affect human health, causing diseases and illnesses such as kidney dysfunction, loss of respiratory capacity, hypertension, bone problems (osteoporosis), and can also have carcinogenic effects, for example on the lungs and prostate.
The recent review study conducted by Current Opinion in Environmental Science & Health demonstrated that various factors could affect the impact of cadmium on living beings.
For example, soil contamination may result from agricultural practices or due to proximity to contaminating sites such as industrial plants, landfills or areas of mining activity. However, phosphate rocks (apatite and phosphorite) are a source of cadmium in mineral phosphate fertilisers. Phosphate fertilisers are gradually reduced and retained in the soil when they interact with it through a variety of biochemical, microbiological, and physical processes. Once in the soil, cadmium from the fertiliser accumulates in crops.
Cadmium is not usually found in seeds, but tends to be rapidly absorbed by root tissues, where it accumulates even when absorbed by the leaf apparatus. There is particular concern regarding the transfer of cadmium from crops into the human diet. When cadmium enters the body, it gets into the bloodstream and then accumulates in the kidneys, liver, and gut. Cadmium excretion from the body is slow and has long term toxic effects.
To avoid crop production losses, methods other than deceasing the use of phosphate fertilisers would need to be employed in order to lower cadmium concentration in soil. Solutions include the utilisation of plants for cadmium bioremediation, lowering soil pH, and using fertilisers with low cadmium concentrations. A combination of methods is optimal, in particular one that considers the local crop production system, climate, and soil type.
More information on the findings of this review study is available at https://doi.org/10.1016/j.coesh.2022.100392