Monday, June 11, 2012

Arsenic and Rice

Deborah Blum:
The researchers of that study, based at Dartmouth College, identified rice as the primary source of inorganic arsenic. They found it (again, in very tiny amounts) in rice syrup used to sweeten baby formula, rice cereal,  rice flour used in making crackers and cookies. This does not mean that rice is by by nature  a poisonous plant. It isn’t.
But both soil and groundwater can contain arsenic -  as a naturally occurring element and as a residue from the use of arsenic-based pesticides. And , as the Dartmouth scientists noted,  “Although As (arsenic) is not readily taken up by crops or transported to the edible parts, a notable exception is rice…The magnitude of this uptake varies widely between cultivars but the ability to take up elevated concentrations of As (in comparison with other cereal crops) appears to be a trait found in the entire rice germplasm.”
In other words, rice turns out to be outstandingly good at absorbing arsenic from the environment and storing it.  One reason is that the plant is designed to easily absorb the mineral silicon which helps give rice grains their elegantly smooth structure. The crystalline structure of arsenic is just close enough that rice plants readily uptake arsenic as well. In fact, a toxic metal study, also from Dartmouth, describes rice as “a natural arsenic accumulator.”
The efficiency of this system also means that the arsenic tends to be absorbed directly in its more toxic inorganic from rather than being converted to an organic form of arsenic. And rice, experts say, seems to be a primary source of arsenic in the human diet..  Or as a newly published book  by Andrew Meharg,  at the University of Aberdeen in Scotland, Rice and Arsenic, puts it, “Rice is the major exposure route globally to the non-threshold carcinogen inorganic arsenic.”
She also brings up arsenic in chicken feed and apple juice.  Could Chinese pollution be adding more arsenic to rice-growing soils in Asia and eventually increasing arsenic uptake in rice?

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