| The subsequent accumulation of heavy metals in the soil may have serious consequences for soil ecosystem, by its damage on the components, structure and function of the soil. Hevy metals effect crop output and quality. The quality of crop, thus, affects greatly human health through food links. Therefore, the study on the contaminations in soil-crop system is important and necessary. Substantial research has been carried out to investigate the transfer of heavy metals in soil-crop system. However, most of these previous studies were carried out on the basis of pot experiments, and the conducted conclusions are different from field experiments or surveys. The present research was conducted to investigate crop uptake factor to soil heavy metals by field experiments, which were located in the suburbs of Nanjing city. In the meantime, rice grains and their corresponding soil samples were collected from paddy fields in Tonglin Mining District and region along the Yangtze River within the territory of Anhui province. This study dealt with heavy metals pollution assessment and accumulation characteristics in rice-soil system.1. Field experiment showed that the effects which exogenous added heavy metals exerted on crop yields depended on heavy metals properties and crop characteristics. Under experimental added levels, As had significant effect on reduction of rice yields,8.9%reduction for low concentration treatment,16.9%reduction for high concentration treatment. Low concentration level of Hg can significantly increase rice yields. The added levels of Cd, Pb and Cr had no significant effect on rice yields. Under experimental added levels, studied heavy metals had no significant effect on carrot yields.2. Field experiment showed that the order for rice uptake ability to soil heavy metal was Cd>Hg>As>Cr>Pb. The order for carrot uptake ability to soil heavy metal was Cd>Hg> Pb>As>Cr. Among the studied heavy metals, Cd posted the most potential risk to rice and carrot safety.3. From the relationship between heavy metal concentration in rice and total content in soil under field experiment, only Pb showed significant correlation, which As, Cd, Hg, Cr had no evident correlation. From the relationship between heavy metal concentration in carrot and total content in soil, Cd, As, Pb showed highly significant correlation, which Cd, Hg had significant correlation and no correlation respectively.4. In Tonglin Mining District and other polluted areas, The order for average contents of heavy metal in rice was Zn>Cu>Ni>Cd>As>Pb>Hg. According to Maximum Levels of Contaminants in Foods in China, the over standard rates of heavy metals in rice was in order of Cd>Pb>Hg>As=Cu>Zn.5. Field survey revealed that Cu, Pb and Cd were significantly correlated in soil-rice system with low determination coefficients (below0.1) in the region along the Yangtze River within the territory of Anhui province. No significant correlation was found for the contents of Ni, Hg and Zn between the rice and the soil samples.6. Field survey revealed that the order for rice uptake ability to soil heavy metal was Cd>Zn>Cu>Hg>Ni>As>Pb in the region along the Yangtze River within the territory of Anhui province. PUF (Plant uptake factor) ranges of heavy metals were large. The results by multivariance regression analysis showed that physiochemical properties of soil could significantly affect heavy metal concentration in rice. Parameters and fitted values of multivariance regression equation varied from kinds of heavy metals.7. The total accumulation of Cd in rice decreased with growing Zn/Cd ratio in soil. In general, there was a negative exponent between the Cd concentration in rice and Zn/Cd ratio in soil. It means that the interaction of Cd and Zn exists in rice-soil system. |
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