Arsenic occurs naturally in the environment in minerals and from there enters the soil, water, and air. The use of arsenic pesticides, before regulations were put in place, is another source of arsenic in our environment. Arsenic stays in the soil for long periods of time, which can then be taken up by plants or washed down into groundwater, thus presenting a threat to humans. The most important factor in determining whether arsenic gets taken up by plants is the genetic makeup of the plant itself (1).
Arsenic can be either organic or inorganic. Both forms are toxic to humans but inorganic arsenic is more detrimental to human health. Almost half of the arsenic in U.S. rice is inorganic arsenic, but almost 80% of all arsenic rice from Bangladesh is inorganic. The key to understanding arsenic accumulation lies in the genes that control uptake from the soil and storage within the plant itself (1).
Rice is a natural arsenic accumulator. Normally, rice plants take up large amounts of silicon from the soil, unlike other cereal plants. They use the silicon to strengthen their stems and husks to protect the grain from a pest attack. Arsenic and silicon are chemically similar under the soil conditions found in rice paddies. Consequently, arsenic fits into the silicon transporters and finds its way into the plant and the grain which we consume (1).
The soil is China’s rice producing regions show high levels of heavy metal contamination due to its close proximity to the mining, smelting, and industry sectors. In the Hunan Province, China’s top rice producer, researchers have found soil containing cadmium levels 200 times the national health standard. A study done by Greenpeace has added: “arsenic rice,” “mercury rice,” “zinc rice,” and “lead rice” to the list. Of these five toxic substances, only the mercury levels seem relativity safe (2).
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