A STUDY OF ABSORPTION OF TOXIC ELEMENTS: Cd. As. Cr. Pb & IIg I SELECTED RICE VARIETIES (ORIZA SATIVA L.) IN RELATION TO THEIR STATUS IN TWO DIFFERE T MANAGEMENT SYSTEMS.

Abstract

Five traditional rice varieties (TRV) and five newly improved hybrid rice varieties (NIHRV) were cultivated according to split-plot design at Yala and Maha seasons in two regions: Anuradhapura: which is a hot-spot for CKDu patients and Kurunegala (where no CKDu patients were recorded) where contents of these metals in water and soil together with agrochemicals used were previously estimated under conventional and organic farming conditions. Samples were processed and microwave acid digested according to US EPA 3052 method and analyzed for the selected toxic elements: Cd, Pb. As. IIg and Cr using atomic absorption spectrometry.' Cadmium contents in rice varieties analyzed (Bg 300, 366, 352. 358. 360 , Suwandel, Madathawalu, Kurulu Thuda. Pachcha Pcrumal and Kalu I {eeneti) were in the range of below limit of detection to 158.9 fig kg'l in both cultivation seasons and thcy did not exceed the maximum allowed limit of 200 fig kg,l sct by Codex Alimentarious commission. Chromium contents were one tcnth of the maximum allowed limit of 2000 fig kg'l set by Codex Alimentarious commission.2,3 As. Ilg and Pb werc bclow the detection limits. Among these varieties: Pachcha Pcrumal repeatedly showcd a high tolerance to Cd absorption in both scasons in both regions. Varieties Kuruluthuda and Madathawalu showed a moderate resistance compared to other varieties. However there were no significant difference (p > 0.05) between the mean Cd contents with respect to farming condition, location or season of cultivation. Metalloid As was below the detection limits in agrochemicals, soils and irrigation waters indicating that there is, no source for Arsenic to accumulate in the rice plant. Cd. Pb and Cr was present in agrochemicals below the SLSI limits of 10 mg kg" and 250 mg kg'l respectively. Cd was detectcd in rice straws. Use of the rice straws as organic manure has to be minimized as it can be ultimately transferred and accumulated on the rice plant. Further, no distinct correlations were obtained with the physiochemical parameters determined in soil and irrigation water with the accumulated Cd content in rice grain.The correlations were tested using linear regression to fit data on to Freundlich model