New study says some rice varieties have excess arsenic, Some paddy plants absorb ten times the toxin in the soil
Arsenic poisoning may not just be caused by drinking water in areas affected by the problem. Research now shows that eating certain rice varieties may also lead to arsenic poisoning.
Indian scientists under a project of the Council of Scientific and Industrial Research ( CSIR) have found that some rice varieties accumulate much more arsenic from the soil.
Scientists from the National Botanical Research Institute ( NBRI), Lucknow, screened about 90 varieties from the Bardhaman district and Purbasthali in Birbhum district of West Bengal.
“ We found that most of these varieties had high arsenic — about ten- fold higher than the permissible limit,” Dr Rakesh Tuli from the NBRI said while speaking at the Indian Science Congress session here. Only 10 per cent of these varieties had low arsenic. The names of rice varieties used in the study have not been revealed.
The NBRI team found that some of the plants had accumulated ten- fold more arsenic than was present in the soil. The levels of arsenic in the soil were about 10- 12 microgram of arsenic per kilogram of soil.
Arsenic was found in both grain and bran. Despite being grown in the same areas, some of these rice varieties accumulated up to 1,250 micrograms of arsenic per kilogram of grain while others accumulated only 150 micrograms of arsenic per kilogram of grain.
Arsenic poisoning has been reported widely in West Bengal. In addition, some areas in Orissa, Bihar and eastern Uttar Pradesh have also reported the problem.
So far, arsenic- contaminated water from tube wells was thought to be the main cause of arsenic poisoning in humans. The safe limit of arsenic in water is 0.05 micrograms per litre of water.
Long- term exposure to arsenic via drinking- water causes cancer of the skin, lungs, urinary bladder, and kidney, and can also result in skin changes such as pigmentation changes and thickening. Immediate symptoms on an acute poisoning include vomiting, abdominal pain, and bloody ‘ rice water’ diarrhoea. “ There are techniques available to remove arsenic from water, but once it gets into the food chain through grain and cereals, it is impossible to remove it,” said Thuppil Venkatesh, arsenic poisoning expert based in Bangalore.
The NBRI study was carried out using rice varieties provided by the Indian Council of Agricultural Research ( ICAR) near Kolkata.
“ We will inform the state government about this. We need more studies to see the quantum of consumption of these varieties in these areas,” said Dr Samir K. Brahmachari, director- general of CSIR. Scientists indicated that stopping consumption of these varieties may help in controlling arsenic poisoning.
However, scientists pointed out that these are preliminary findings and more studies need to be carried out to ascertain the full extent of arsenic contamination of rice varieties.
The present experiment was carried out in the two areas which have considerably high levels of arsenic in soil. “ There are areas which have even higher levels of arsenic in soil and arsenic- contaminated water may have been used for irrigation as well,” Tuli said.
So more studies will have to be carried out to know how much arsenic is accumulated when these same varieties are grown in low arsenic soils. The aim is to ultimately find out which varieties are good for growing in arsenic rich soils, scientists explained. So far this concept has not been used in selecting rice varieties for largescale cultivation.
The team is now screening more varieties in West Bengal.
The NBRI also plans to carry out studies with agricultural research institutes in Orissa and UP to analyse the levels of arsenic accumulation in rice varieties grown there.
Scientists said that there was no information on how many of these varieties were being consumed and to what extent. But certainly, some of these are being consumed widely in local areas. There is also a possibility that these varieties may also be in market places in the country including in Delhi. So far, India does not even have standards on arsenic levels in food.
“ The problem has been found in the US and China. Market samples lifted over the last two years in the US and China had high levels of arsenic,” Tuli said.
The problem is being witnessed largely since the past two- to- five years. A third of the baby rice tested by the US Food Standards Agency was found to contain high levels of arsenic.
However, this was attributed to planting of rice in soil rich in arsenic and use of arsenic- contaminated water.
A World Health Organisation report in 2005 had assessed that some seven million people living in West Bengal had problems related to arsenic poisoning. The report attributed about 10,000 deaths to arsenic poisoning.
Studies have shown that high concentration of arsenic in soil and irrigation water often leads to high levels of arsenic in crops.
At present, twelve countries in Asia have reported high arsenic levels in their groundwater resources, according to the Food and Agricultural Organisation.
A study by the Bangladesh University of Engineering and Technology in arsenic- affected areas in Bangladesh had shown that rice plants accumulate arsenic from soil and water, but the accumulation of arsenic varies for the different parts of plants. The quantity of accumulated arsenic decreases gradually from the root to the shoot.
While arsenic accumulation was seen in different parts of the rice plant, no arsenic accumulation was found in the rice grain in some cases. In some cases, arsenic was found in rice husk but not in rice grain and vice versa. Such variations could depend on many factors such as rice variety, composition of irrigation water, soil quality and the fertiliser used. Bangladesh researchers say that arsenic from contaminated irrigation water accumulates in the root, stem and leaf of the rice plant that may cause risks for cattle and human health. Similar results have been reported by Chinese scientists as well.
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