Comparison of a Chemical and Enzymatic Extraction of Arsenic from Rice and an Assessment of the Arsenic Absorption from Contaminated Water by Cooked Rice

Abstract

Rice is a target food for arsenic speciation based analyses because of its relatively high arsenic concentration and per capita consumption rates. Improved speciation data for rice can be helpful in estimating inorganic arsenic exposures in the U.S. and in endemic populations. The inorganic arsenic exposure for cooked rice should include both the arsenic in raw rice plus the arsenic absorbed from the water used to prepare it. The amount of arsenic absorbed from water by rice during preparation was assessed using five different types of rice cooked in both contaminated drinking water and arsenic-free reagent water. The rice samples were extracted using trifluoroacetic acid (TFA) and speciated using IC-ICP-MS. The TFA procedure was able to extract 84-104% of the arsenic (As) from the five different cooked rice samples. Chromatographic recoveries ranged from 99% to 116%. The dimethylarsinic acid (DMA) and inorganic arsenic concentration ranged from 22 to 270 ng of As/g of rice and from 31 to 108 ng of As/g of rice, respectively, for samples cooked in reagent water. The overall recoveries, which relate the sum of the chromatographic species back to the total digested concentration, ranged from 89% to 117%. The absorption of arsenic by rice from the total volume of water [1:1 to 4:1 (water:rice)] used in cooking was between 89% and 105% for two different contaminated drinking water samples. A comparison of the TFA extraction to an enzymatic extraction was made using the five rice samples and NIST 1568a rice flour. The two extraction procedures produced good agreement for inorganic arsenic, DMA, and the overall recovery. Through the use of IC-ESI-MS/ MS with a parent ion of m/z 153 and fragment ions of m/z 138, 123, and 105, the structure dimethylthioarsinic acid was tentatively identified in two of the rice samples using the enzymatic extraction.

Inorganic arsenic levels in baby rice are of concern

“…All indications are that the bioavailability of inorganic arsenic from rice is high, is in the order of 90% (Ackerman et al, 2005;Juhasz et al, 2006). Food standards are out of step with drinking water regulations which have received recent revision.…”

Geologic structure and geochemical characteristics of sediments of fluoride and arsenic contaminated groundwater aquifer in Kalalanwala and its vicinity, Punjab, Pakistan

“…TFA accumulates for a long time due to its stability, and is eventually detected in watershed including groundwater via precipitation and evaporation (e.g., Tromp et al, 1995;Schwarzbach, 1995;Richey et al, 1997;Berg et al, 2000;Cahill et al, 2001). TFA is widely used as a reagent for organic synthesis, because of its high acidity and stability, and as a solvent for organic and inorganic As compounds (e.g., Crescenzi et al, 1997;Ackerman et al, 2005). Pesticides can be additional sources for the TFA.…”

“…6(a)), and it occupies >70% in the lower half of the first aquifer. TFA, present in that aquifer, is a strong solvent that can dissolve organic and inorganic As phases (Ackerman et al, 2005). Thus its occurrence would promote the dissolution of As into the aquifer during recharge.…”

Arsenic in the human food chain, biotransformation and toxicology – Review focusing on seafood arsenic

“…Cooking and washing foods in iAs-contaminated water have also been shown to increase the iAs concentration in the prepared food [147], especially in rice [25,148,149]. However, cooking of rice in water which has not been contaminated with iAs, rinse washing before cooking and cooking with large volume of water seem to decrease the iAs content in the prepared food [147,150,151].…”