Heavy metals in the soil

The soil usually contains a number of heavy metals found in nature. However, heavy metals obtained from the activity can create concentrations that lead to an increased risk of exposure. Therefore, it is necessary to use targeted cleaning methods.

Metals bind to soil organic matter and minerals, which can lead to their accumulation over time.

The three main metals in contaminated soils are lead, arsenic and cadmium. Arsenic can be naturally enriched in phosphates used for fertilizers. Cadmium is enriched in the extraction of zinc. Finally, lead can enter the soil from leaded gasoline and paint. These household items were discontinued several decades ago. However, soils can have a naturally high background due to decades of burning gasoline and peeling lead paint from old buildings. In addition, for 60 years, lead-arsenic pesticides have been used to control butterflies in orchards throughout the United States.


Heavy metals are extremely carcinogenic; Arsenic causes skin cancer because it binds to and destroys proteins in skin tissues. Lead affects brain development. Cadmium promotes kidney cancer and impairs bone development.

The EPA (US Environmental Protection Agency) limits for agricultural soils are set at 20 ppm for lead, 0.11 ppm for arsenic and 0.48 ppm for cadmium. Limit values for residential soils are much higher, as these soils are not usually used for large-scale food production.

Heavy metals in the soil are affected by the uptake and consumption of plants, the transfer and consumption of water, or the inhalation of dust-related metals. The table below lists some crops that are known to be a target for certain metals.

MetalCultures that can absorb these metals
Arsenic (As)Brown rice, lentils
Lead (Pb)Cabbage, celery, lettuce
Cadmium (Cd)Lettuce, spinach, cabbage, celery, rice

Getting metals into the body in any form is harmful, but inhalation is considered one of the worst ways of exposure, because everything that enters the lungs is considered 100% bioavailable. Bioavailable metals are parts of ingested metals that are available for intestinal absorption after digestion. Bioavailable metals are metals that enter the body, which are included in biological functions and affect this system.


If you are a new homeowner and you know about the historical activity of heavy metals in your area, determining the concentration of metals in the soil is a key point before starting any gardening activity. There are several different ways to check the metal content. The first step is to get an idea of the level of total pollution by conducting a general elemental analysis; the sample is acidified, heated and dissolved to determine the total metal content of the soil.

If you are concerned about plant uptake, the ideal approach is to extract the microelements with DTPA (diethylenetriaminepentaacetic acid), the same method used to determine the presence of microelements in the soil. Some use ammonium acetate extraction, which is commonly used to determine metabolic cations (calcium, magnesium, potassium and sodium) in soil. It can also be considered “accessible to plants”.

This article is based on information kindly provided by Ward Laboratories, Inc.

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