Global Warming Increases Arsenic in Rice

                                                                                                                                    Dr. R. S. Sengar and Dr. Shalini Gupta

As per Paris Agreement 2015 aims at immuting the global warming to well below 2°C above the pre industrial level, preferably pursuing efforts to arrest the increase below 1.5°C through reaching zero emissions by the year 2050. The goal has to be achieved through nationally determined contributions, where each country can set its own emission resduction target.

The impact of exceeding tempratures on our environment and ecology have already become apparent in the forms of many devastative natural calamities beginning from the increased risks of extreme weather events like intense heat-waves, droughts, floods, storms, rising sea levels that threaten coastal communities and marine ecosystems, disruptions of other ecosystems leading to habitat loss, biodiversity decline and shifts in species distribution, acidification of oceans causing harm to marine life, reducing agricultural land and water resources and enhancing health problems like heat strokes and spread of many diseases.

Now, a new dimension, more dangerously linked to our day-to-day life, has been added to it by the discovery that global warming has been enhancing the levels of arsenic, a highly toxic substance, in rice.

Rice (Oryzasativa L.1 is a staple food for more than half the population of the world, especially in Asian countries like China, India, Indonesia, Japan, Vietnam, Thailand, Philippines, Bangladesh, Myanmar and Malaysia, African countries like Liberia, Guinea-Bissau. Madagascar and Senegal as well as the North and South America.

In all these countries, more than 7000 varieties of paddy with different types of grains and nutritional compositions are grown. Rice, the edible part, is obtained by dehusking it. Which is done mainly in two different ways. In one, the brain layer along with the germ is removed completely to obtain what is called white rice, and in the other, these are retained to produce brown rice.

Usually, the former has a greater consumer preference, while the latter is considered to be more nutritive (Table), because of its higher contents of dietary fibre, protein, lipid rich in HDL (High Density Lipid, known as "good cholesterol") and micronutrients like magnesium, iron, zinc, phosphorous, niacin and vitamin B6. It also has a lower glycemic indexmaking it beneficial for type 2 diabetes. Besides, it reduces the probability of heart attack and being overweight.

The bran and germ of brown rice are particularly rich in many powerful antioxidants, which are capable of neutralising harmful freeradicals, thereby preventing the possibility of chronic diseases like heart problems, cancer and type 2 diabetes. White rice also has all these benefits but to a much lesser extent.

The Structure of a Rice Grain

However, there is a saying. "The moon has a black spot too". Brown rice, particularly the bran and germ, with all these beneficial effects on health, has recently been found to be rich in arsenic. A well-known carcinogenic and mutagenic agent, it has a wide range of toxic effects on public health and also on the environment. It can be found in both inorganic form and as organic compounds in food, water, soil and as airborne particles. The former is found in the environment, mostly dissolved in water, plant-based foods like rice, wheat, ragi and vegetables grown in contaminated soil and animal products such as dairy milk and fish exposed to contaminated feed.

Among the staple food grains, rice has been found to contain more arsenic, both organic and inorganic, because rice plants have a greater ability to absorb arsenic from the contaminated soil and water used for irrigation. The latter is more harmful as it is retained for longer in the body.

A consumer Report Analysis of the US Food and Drug Administration (FDA) had reported data on 656 rice products in 2014 and confirmed worrisome levels of inorganic arsenic in both white and brown rice, particularly in the highest concentrations in the outer layers of the grain (bran and germ). Since these layers are removed during the processing of paddy to obtain white rice, it contains less of them as compared to brown (almost 80%). Then the FDA's Centre for Food Safety and Applied Nutrition began to assess the health risks of inorganic arsenic in rice and found that at present, on average, the concentrations of it in white rice and brown rice are 92 ppb (Parts per billion) and 154 ppb, respectively.

So, it concluded that cancer cases may rise by 148.6% if rice consumption is increased to two servings a day, as compared to one. Besides, it has also been linked to cardiovascular ailments, diabetes mellitus, hypertension and obesity due to increased intake of arsenic. The present findings showing the increase in the level of this toxic element in rice with the rise in global warming have added a new dimension to the problem. According to a paper published in the Lancet Planetary Health (16 April 2025) by Lewis Ziska of the Columbia University's Mailman School of Public Health and his coworkers from the US and China, rising temperature and carbon dioxide levels could lead to a substantial increase in arsenic levels in rice, potentially causing tens of millions of cancer cases by 2050.

After studying 28 rice strains over 10 years, estimating the increase in arsenic levels in those along with rise in the related health risks in some Asian countries including China, India, Bangladesh, Thailand, Nepal and Vietnam, they have come to the conclusion that by that time with an increase of 2°C temperature beyond the preindustrial level, the problem can be much more serious exposure to arsenic may see about 44% increase in bladder and lung cancer cases alone. It may also have links with rising incidents of diabetes, adverse pregnancy outcomes, cardiovascular diseases, neurodevelopmental issues, the immune system and other arsenic-related health problems.

Therefore, as mitigation measures the scientists have proposed to take immediate steps to bring down the global emission level to zero, thereby keeping the rise in global temperature below 2°C (Preferably not exceeding 1.5°C) and not to allow the level of carbon dioxide level in the atmosphere to breach 400 ppm (parts per million) which it has almost begun to do. Besides, steps can be taken to breed new varieties of rice plants (and of course, others) that can absorb less arsenic and to improve the qualities of soil and water management.

Writer: Professor R. S. Sengar, Director Training and Placement, Sardar Vallabhbhai Patel University of Agriculture and Technology, Modipuram, Meerut.