What are Safe Levels of Arsenic in Food and Soils?

A perspective on arsenic “safety” in food and soils in Bangladesh is provided by using current limits or standards for arsenic (As) that have been established by various countries and organizations. Approaches to setting standards for Bangladesh using some of these values are discussed. One approach to determining safe levels of As in food is by comparison to safety standards for drinking water. This comparison is made on the basis of inorganic As species as these are considerably more toxic than organic As species. Rice is considered by itself because of the large intake of rice in the Bangladesh diet (~ 450g/adult/day or 80% of caloric intake). With an adult daily intake of 450 g rice and 4L of water, equivalent intakes of inorganic As from these two sources occur at As levels of 550 and 110 ppb As in rice for water standards of 50 ppb (Bangladesh) and 10 ppb (WHO and many western countries), respectively. This calculation assumes that 80% of the As in rice is inorganic (Williams et al., this symposium) and that the bioavailability of As in rice is similar to that in water (demonstrated in a pig feeding study; Naidu [personal communication]). Several countries, including the UK and Australia, currently use a 1 ppm limit for arsenic in food and this is often cited as a “safe”level for rice. This value is clearly too high for the Bangladesh level of rice consumption. An alternative strategy in establishing As standards for both drinking water and rice is to consider the combined dietary intake of inorganic arsenic from these sources, rather than evaluating each individually. In 1989, the FAO and WHO jointly established a provisional tolerable dietary intake of 0.015 mg inorganic As/kg body weight/week, or 130 μg/day for a 60 kg adult. This level is already exceeded by the intake of 200 μg/day from drinking 4 L of water containing 50 ppb As. A tolerable limit for intake of inorganic As has not been established for Bangladesh, but how this could be used to evaluate dietary As intake from rice and water at daily intakes of 450 g and 4 L, respectively, is illustrated in the table for a 200 μg/day inorganic As intake limit. Scenario Max. Acceptable As (ppb) Rice Water Sources equal 277 25 Water 10 ppb 444 10