Cadmium

History

Cadmium (Cd) is a heavy metal that is a rare contaminant in urban soils. All soils contain background levels of Cd at relatively low concentrations due to naturally occurring soil cadmium minerals. Everyone is exposed to very small amounts of cadmium every day with no apparent harm [3]. Cadmium exposure occurs mainly through food because crops absorb naturally-occuring cadmium in the soil. This differs from soil lead and arsenic exposure, where incidental soil ingestion of dust particles transferred from hands or cleared from the airway is the main exposure pathway. Cadmium is easily taken up by plants, while lead and arsenic are not.

Average U.S. background soil Cd 0.1-1.0 mg kg-1 Cd [1]. In central Ohio the maximum background Cd concentration is around 0.8 mg kg-1[2], and soils with Cd concentrations above this are contaminated. Even though Cd content is elevated, a contaminated soil may or may not pose a risk to human health. When soil Cd concentrations and exposure are sufficient to pose a health risk, the soil is polluted. Cadmium-polluted soils may be found where industrial activities such as mining and smelting zinc or cadmium and electronics recycling or incineration have taken place [3].  

Potential health risks of soil Cd exposure 

The primary impact from cadmium exposure is kidney damage. Cadmium has been identified as a cancer-causing agent (carcinogen) [4]. Higher exposures to Cd can lead to bone and nervous system problems. Though the main cadmium source for the average person is food, poisoning from cadmium-contaminated crops is extremely uncommon [1,5]. Instead, cadmium poisoning occurs primarily through occupational exposure and tobacco smoke [3].

Gardening in Cd-contaminated soils

Exposure to cadmium through urban gardening is unlikely. If electronics recycling, mining, smelting, or waste incineration occured on your site, test the soil for cadmium. Compare soil test results with the Interpretation Table to determine if the soil is appropriate for gardening. 

References

[1] Page, A.L., A.C. Chang, and E.A. Mohamed. 1987. Cadmium levels in soils and crops. The United States scope 31: 120–122.

[2] Ohio Environmental Protection Agency. 2013. Evaluation of Background Metal Soil Concentrations in Franklin County - Columbus Area,.

[3] World Health Organization. 2019. Preventing disease through healthy environments: exposure to cadmium: a major public health concern. https://apps.who.int/iris/handle/10665/329480 (accessed 20 March 2020).

[4] European Commission. Anonymous. 2016. Cadmium. Food Safety - European Commission. https://ec.europa.eu/food/safety/chemical_safety/contaminants/catalogue/cadmium_en (accessed 20 March 2020).

[5] Huang, Y., C. He, C. Shen, J. Guo, S. Mubeen, et al. 2017. Toxicity of cadmium and its health risks from leafy vegetable consumption. Food Funct. 8(4): 1373–1401. doi: 10.1039/C6FO01580H.