Cd, Zn and Se content of the polished rice samples from some Chinese open markets and their relevance to food safety

This paper is aimed at reporting its investigation over the content of heavy metals in different sorts of rice so far available on the Chinese markets by sampling 91 sorts of rice including 47 of Japonica and 44 of Indica. The motive of our research is closely related to the health hazards due to food exposure for Chinese people. It is well known that rice has been a predominant diet source in our country. The samples of ours have just been randomly chosen from some open markets over China in 2005. Their respective content rates of Cd, Zn and Se are then determined by using atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS) individually with the mutual relationship among these elements analyzed. The results of our investigation show that about 10% of the samples had a Cd content beyond the State Food Security Standards (0.2 mg·kg-1), while 70% of the above samples is likely to exert potential health hazards due to the exposure of Cd if the RfD ( USEPA, 2000) value is taken as a reference. In addition, the content levels of Zn and Se in the rice samples prove generally rather low, failing to meet the health need regulation through the regular dietary intake. On the other hand, it is found from our research that there indeed exists positive correlation between the content of Cd and that of Zn, as well as between Se content and that of Zn ratio, which indicates a slight accumulation of Zn in relation to Cd and Se. However, on the whole, 90% of the rice samples has a lower Cd/Zn ratio than the critical value of 0.015 proposed by the American standard. In addition, samples with high Cd content may not be necessarily beyond the regular high Cd/Zn ratio. The fact is that the rice samples of Indica may imply much higher Cd and Se content level than that of Japonica, with the former suggesting a far higher Cd exposure hazard than the latter. Therefore, the present research can be used as a valuable reference to further studies for the potential effects of the toxic heavy metal content in rice on the human health as well as their relation to the soil-crop-food security.