Heavy metals in soil


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A really interesting presentation from Dr Andrew Margenot. Mostly concerning Pb as it is the most concern due to leaded gasoline which has dusted more urban areas and caused higher amounts of lead levels in soil nationwide. n

Interestingly plant uptake is not as dangerous as direct exposure (83% of exposure is from small grain dust and only 3% from indirect exposure). Wear a mask when mixing amendments and soil. Root crops and low to the ground greens have more heavy metals than fruits. High levels of lead in water didn't seem to effect levels in the crops.

Compost can help decrease availability and stop plants from taking up as much lead ( 40 min mark.)

"Guanos are notoriously high in cadmium."

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"Cadmium availability is influenced by several soil properties. Plants uptake cadmium through their roots, but uptake is lowest when soil pH is higher (6.2); organic carbon (organic matter) levels are higher and levels of soil calcium (Ca), iron (Fe) and zinc (Zn) are adequate"

"Cadmium is concentrated in particular parts of plants. As a general rule, leaves contain the most Cd, followed by storage roots and tubers, and then seeds or grain and fleshy fruits. Fleshy leaf crops (lettuce, spinach) tend to have higher levels than pumpkin, cucumber etc. Storage root crops (garlic, parsnip, carrot, beetroot, onion, potato) can also all contain significant levels of cadmium, depending on levels present in the soil."

"Superphosphate (super) is manufactured by attacking a rock phosphate rock source material with sulphuric acid."

"Earlier superphosphate was made from rock phosphate from Nauru which had high levels of C0d0 contamination i.e. 600mgCd/kg P in the superphosphate."

According to this source, Guanos are generally low in cadmium however but all manures contain at least trace amounts.



" It appears that cadmium is the heavy metal of greatest concern in fertilizer. In a Washington State Department of Agriculture study that considered the plant uptake of arsenic, lead, and cadmium (coincidently, the only three metals that California regulates), cadmium was found to be of the greatest concern because cadmium builds up in the soil and plants can take it up. Some plants, such as lettuce, were found to contain more cadmium in the plant when more was available in the soil. In one study area, there was a clear linear relationship between cadmium in soil and cadmium in plants. Arsenic and lead were not taken up by plants in the same way as cadmium. "


It is readily accumulated in many organisms, notably molluscs and crustaceans. Human exposure occurs mainly from consumption of contaminated food, active and passive inhalation of tobacco smoke, and inhalation by workers in the non-ferrous metal industry.
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