Concentration and Distribution of Toxic and Essential Elements in Traditional Rice Varieties of Sri Lanka Grown on an Anuradhapura District Farm

Abstract

Toxic heavy metals have been the focus of many investigations into chronic kidney disease of unknown aetiology (CKDu) within Sri Lanka. It has been hypothesised that exposure to nephrotoxic arsenic, cadmium and lead could play a role in the development of CKDu, and these metals have previously been found in unsafe concentrations in Sri Lankan rice. Traditional varieties of Sri Lankan rice remain popular due to their perceived health benefits, but their uptake of trace and toxic heavy metals remained unexplored. Here, we report a one-time, cross-sectional dataset on the concentrations of essential and toxic elements present in eleven samples of polished and unpolished traditional rice varieties, all regularly grown and sold in the Anuradhapura district, a CKDu hotspot. All rice was sourced from the same farm, with the exception of one store bought sample grown on another, unidentified farm. Cadmium concentrations varied significantly between varieties, and potentially unsafe concentrations of cadmium were detected in the store-bought sample (Suwadel, 113±13 μg kg^-1). Elemental imaging of the grains revealed lead to be stored mainly in the rice bran, which is removed during polishing, while cadmium was distributed in the edible portion of the grain. Essential elements were generally higher in the traditional rice varieties than those reported for non-traditional varieties and are a potential source of trace elements for nutrient-deficient communities. The concentration of selenium, an element that plays a protective role in the kidneys, was too low to provide the minimum recommended intake. The methods developed in this study could be applied to a more comprehensive study of elemental uptake of rice under controlled growing conditions.

Keywords: Essential elements; LA-ICP-MS; Sri Lankan rice varieties; Toxic heavy metals.

Fig. 1

Toxic heavy metals in Sri Lankan traditional rice. Concentration and distribution of the metals varied with variety. From top to bottom: Suwadel (a), Kalu Heenati (b), Rathal (c), polished Suwadel (d), polished Kalu Heenati (e), Madathawalu (f), polished Madathawalu (g), Siyapathal (h), Swanjatha (i), Ran Kahawanu (j) and polished Ran Kahawanu (k). Colour-scales are in normalised counts for each element

Fig. 2

Manganese (top) and zinc in polished (P) and unpolished (UP) rice grains. Polishing removes the germ where many essential elements are stored, particularly in white rice. From left to right: Suwandel, Ran Kahawanu, Kalu Heenati and Madathawalu. Colour-scales are in normalised counts