Wednesday April 30 2008
Rice is commonly grown in flooded fields
“One third of baby rice on sale in British supermarkets contains an unsafe level of arsenic”, The Daily Telegraph reported, news that could potentially cause some concern among parents.
The newspaper said that some children could be receiving six times the amount of inorganic arsenic than they should be for their height and weight through eating rice products high in arsenic, as it is also commonly found in rice milk and puffed rice cereals.
Rice fields are regularly flooded and arsenic is naturally present in the soil. Subsequently the substance is present at a relatively high level in rice. High levels of arsenic are reportedly linked to an increased risk of certain cancers. Researchers in this study tested levels in 17 samples of three unnamed brands in British supermarkets and found that 35% of them contained high levels. The Food Standards Agency is reported as saying that there is no danger to infants, but that food regulations should be updated. There are currently EU and US legislations governing inorganic arsenic content allowable in water, but not in foods.
These findings may not be representative of other baby rice brands that were not tested, or of other products containing rice. This study also does not investigate or suggest there to be, increased levels of risk of any cancer from consuming these levels of inorganic arsenic in baby rice.
This research is likely to lead to further testing of food products and reconsideration of whether legislation needs to be introduced governing inorganic arsenic content of foods.
Where did the story come from?
A commentary on the global health issue of inorganic arsenic in rice was written by Yong-Guan Zhu and Paul N. Williams at the Chinese Academy of Sciences and Andrew A. Meharg at the University of Aberdeen.
With additional researchers, they also carried out a test of inorganic arsenic levels in baby rice. The study was funded by the Natural Science Foundation of China and The Royal Societies of London and Edinburgh.
The study and the narrative commentary were both published in the peer-reviewed scientific journal: Environmental Pollution.
What kind of scientific study was this?
Inorganic arsenic is a toxic substance that occurs naturally in small amounts in the environment. It is known to be a chronic human carcinogen. Recent research has shown that, apart from people who are exposed to inorganic arsenic through drinking water, rice is the main source of it in the diet.
In the commentary, the researchers report that 50% of global cereal consumption is rice, and that half of the world’s population is reliant upon it for nourishment. The flooded fields in which rice is grown promote higher uptake of arsenic from the soil and cause levels 10 times that found in other cereals such as wheat and barley.
Although most EU countries, the US and China have legislation governing maximum allowable levels of inorganic arsenic in water, there are no such legislations for food. Consequently, people who frequently consume rice may regularly consume much higher than the permitted levels in water.
Unprocessed rice has a stiff outer layer called the husk, an inner layer called the bran that is brown in colour, and a white seed at the centre. White rice has the bran layer removed while brown rice retains some or all of the bran layer. Due to inorganic arsenic being localised in the bran layer, brown rice may have much higher levels than polished, white rice. Vegan and macrobiotic diets which include brown rice, rice milk, miso, and rice malt as a sugar substitute, may therefore be expected to contain higher levels than other diets. Although it may be easy to remove inorganic arsenic from water, removing the arsenic incorporated into the rice husk may be harder. It is suggested that cooking the rice in high volumes of water free from arsenic may be beneficial, but to the detriment of nutrients. The researchers also suggest that, if were possible, it could be beneficial to grow rice in less flooded conditions in the paddy fields for at least part of the growing season.
The researchers also suggest that if body mass is used as a measure, infants and young children may regularly be exposed to higher levels of inorganic arsenic than adults.
The separately published research on inorganic arsenic levels in baby rice was a small cross-sectional study aimed at establishing the inorganic arsenic content in a range of UK-purchased baby rice samples. To do this, 17 samples of baby rice were obtained from supermarkets in Aberdeen in 2006. The samples included both organic and non-organic brands of baby rice. If possible, a sample from each of the three main brand manufacturers was obtained at each supermarket. Only pure baby rice was looked at, i.e. not any other products containing rice.
What were the results of the study?
The researchers found that inorganic arsenic levels in the rice ranged from 0.06 to 0.16 milligrams per kilogram with an average (median) of 0.11 milligrams per kilogram. They say that these levels were high and that 35% of the products would be illegal for sale in China, which has a food limit of 0.15 milligrams per kilogram. There are no EU or US regulations on the levels of inorganic arsenic allowable in food. There are only regulations for water and WHO recommends no more than two micrograms of inorganic arsenic per kilogram of body weight.
When the researchers calculated how much inorganic arsenic could be consumed by infants (defining an infant as a one-year-old baby of average weight eating 20 grams of rice per day) they found that the levels were higher than the maximum allowed exposure for adults in water.
What interpretations did the researchers draw from these results?
The researchers say that from their results ‘it is apparent that inorganic arsenic levels in baby rice should be of concern.’ They suggest that sourcing rice grain from low arsenic-impacted areas, such as parts of the Indian subcontinent or California may help, as might switching to more wheat, barley or oat-based foods.
What does the NHS Knowledge Service make of this study?
The word ‘arsenic’ automatically conjures up ideas of poison, but arsenic actually occurs naturally in soil and very small amounts of it in food and water are common and to some extent unavoidable. The main point of this study is that, as most rice is grown in flooded fields, the quantities of inorganic arsenic that are consumed could be higher than that which is allowed by water regulations. Legislation may therefore need to be reconsidered and changed accordingly.
It should be emphasised that baby food is not being ‘poisoned’ by arsenic being added to foods during any part of the manufacturing process. These results may not be representative of other baby rice brands than those tested, or other products containing rice, including adult rice. This study also does not investigate, or suggest there to be, increased levels of risk of any cancer from consuming these levels of inorganic arsenic.
This research is likely to lead to further testing of food products and reconsideration of whether legislation needs to be introduced governing the inorganic arsenic content of foods.
Sir Muir Gray adds...
An important issue, with an urgent need for more research.