Arsenic is a naturally occurring metalloid found widely in the earth’s crust. This element becomes a concern when it enters the food supply, particularly in its toxic form. Rice, a staple crop for a large portion of the world’s population, is uniquely efficient at drawing arsenic from its environment. The plant’s specific growth conditions and biological makeup allow it to accumulate significantly more arsenic than most other common cereal grains, establishing rice as a notable dietary source of this contaminant.
The Unique Way Rice Absorbs Arsenic
The high arsenic content in rice is largely due to a combination of agricultural practices and the plant’s own biology. Rice is typically grown in flooded paddy fields. This low-oxygen state chemically transforms arsenic normally bound to soil particles into arsenite, a highly mobile and absorbable form. Arsenite is significantly easier for the rice plant to take up through its roots compared to the form found in dry-soil conditions.
Rice is a silicon accumulator, meaning it has specialized root transporters to efficiently bring silicon into its system for structure. However, the arsenite form of arsenic is chemically similar enough to silicon that it is mistakenly recognized and taken up by these same high-efficiency silicon transporters.
This unintentional uptake creates a highly efficient pathway for arsenic to move from the flooded soil into the rice plant’s tissues, eventually concentrating in the grain. Crops like wheat or corn are generally grown in dry, aerobic conditions where the arsenic remains less mobile, and they do not rely on the same silicon uptake system, which results in much lower arsenic levels.
Understanding Inorganic vs. Organic Arsenic
Arsenic exists in both inorganic and organic forms. The term “organic” in this context refers to the element bonded with carbon, not to farming practices. Organic arsenic compounds, such as arsenobetaine found predominantly in seafood, are generally considered less harmful to human health because they pass through the body relatively quickly without significant metabolism.
In contrast, inorganic arsenic is the form found in rocks, soil, and water, and it is far more toxic to humans. This form is classified as a known human carcinogen and is the type predominantly accumulated by rice. The risk associated with consuming rice stems almost entirely from its content of this inorganic form.
The chemical structure of inorganic arsenic allows it to interfere with cellular processes in the body, which leads to its toxicity. When rice absorbs arsenic from the soil, the element is primarily taken up as inorganic arsenite.
Health Risks of Long-Term Exposure
The health risks associated with rice consumption are not due to acute poisoning but rather from chronic, low-level ingestion of inorganic arsenic over an extended period. Long-term exposure has been strongly linked to an increased risk of several types of cancer, including skin, bladder, and lung cancer. The World Health Organization classifies inorganic arsenic as a human carcinogen based on this evidence.
Beyond cancer, chronic exposure is also associated with cardiovascular and metabolic disorders. Studies have shown links to increased risk of heart disease, high blood pressure, and Type 2 diabetes.
Infants and children are considered a particularly vulnerable group because they consume more food relative to their body weight than adults, which can lead to a higher proportional intake of arsenic from rice-based products. Early life exposure has been connected to negative neurodevelopmental outcomes, including cognitive impairment and lower IQ scores.
Practical Steps to Reduce Arsenic in Cooked Rice
Consumers can take several steps at home to reduce the inorganic arsenic content in their cooked rice. Rinsing the raw rice thoroughly before cooking can remove some surface arsenic, though this is not the most effective method.
The most impactful reduction comes from altering the cooking method by using a high water-to-rice ratio. Cooking rice in a ratio of about six parts water to one part rice, and then draining the excess water afterward, has been shown to reduce inorganic arsenic levels by 40% to 60%. This process allows the arsenic to leach out of the grain and into the discarded cooking water.
Selecting certain varieties and sources of rice can also help lower total exposure. Basmati rice from India or Pakistan and Jasmine rice from Thailand often contain lower levels of arsenic than other types. Rice grown in California also tends to have lower concentrations compared to rice grown in the south-central United States. Furthermore, brown rice generally contains more arsenic than white rice because the element concentrates in the outer bran layer, which is removed during milling.