Mitigation of Inorganic Arsenic in Rice

Abstract

Arsenic and its inorganic compounds are classified as class one non-threshold carcinogen. Arsenic’s main route in to the human body is by ingestion of rice, as rice is the staple diet of over half the world population. Here I present results from global survey of market available polished white rice, circa 1200 samples were analysed from 29 distinct sampling zones, across 6 continents. The global average for inorganic arsenic was 66 µg/kg, ranging from trace levels to 399 g/kg. South America rice was universally high for inorganic arsenic, with the peak values coming from Europe. Only southern hemisphere, eastern latitudes had truly low inorganic arsenic rice, namely East Africa and the Southern Indonesian islands. Existing agronomic, growth management and breeding methods of arsenic mitigation are not only expensive and scale limited but also suffer from the diversity of soil and growing conditions around the globe preclude any clear answer. Two chapters in this thesis show that effective treatments allow significant reductions for inorganic arsenic grain content. Novel parboiling is shown to decrease the final polished grain inorganic arsenic by 25%, while enriching the calcium content by 213%. Cooking rice with percolating hot water is shown to reduce inorganic arsenic content by up to 85%, in conjunction with standard pre-soaking and washing. These relatively low technology solutions can be applied from rural settings through to urban kitchens. The last section of this thesis shows that the western market is reacting to the setting of guidelines and limits for inorganic arsenic content in certain foods, particularly foods aimed and children and babies. Although fewer pure rice products seemed available those tested showed lower inorganic arsenic levels, presumably by selective sourcing on behalf of the producers. Another approach was the dilution of inorganic arsenic by mixing with other gluten free grains.

Date of Award	Jul 2020
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Andy Meharg (Supervisor) & Christopher Elliott (Supervisor)