| There are all kinds of aquatic vegetables in our life. They not only have rich nutrition, but also have healthy care function, which are characteristics vegetables in our country. In recent years, because of the rapid development of small and medium-sized enterprises of middle areas in Zhejiang province, regional environment pollution was caused by "three wastes" emissions. Heavy metals were one of the aquatic vegetables priority control pollutants. In our country, Pb, Cd and As were monitored projects for aquatic vegetables. Firstly, investigation and study the Pb, Cd, Cr, Cu, Zn and As of aquatic vegetables and it’s growth environment in the middle areas of Zhejiang, to understand the pollution of heavy metals, secondly, the effects of Hg and As on Zizania latifolia and Trapa bispinosa’s growth and migration characteristics were studied to furtherly understand the harm of heavy metals in aquatic vegetables quality and provide important reference basis for food security. The results obtained as the following:1. The average content of heavy metals in soil of surveyed areas were all exceeded background value. The single factor pollution index was less than 0.7, except of Cd (5.37), which showed that investigated soil was heavy polluted by Cd. Comprehensive pollution index was 3.87, belonging to heavy pollution level. The size coefficient varia-tion of the six heavy metals was:Cd> Cu> Cr> Pb> Zn. The coefficient of variation of Cr, Cu, Pb and Zn were all around 0.2, which showed they were not influenced by the hum-an factors in outside.2. The content of Cd, Cr, Cu and As in the water of background areas were not detected. As and Cd in the water of surveyed areas were not detected. It showed that the aquatic environment of surveyed areas were not significantly affected by As and Cd. Average content of Pb and Zn were similar to that of the background. Single factor pollution index of heavy metals in water were less than 1, belonging to the non-pollution. Integrated pollution index was 0.36, belonging to the safety level. In the middle area of zhejiang, the effects of Pb, Cr, Cd, Cu, Zn and As on the aquatic environment of aquatic vegetables were not obvious.3. In the surveyed areas, the average content of Pb, Cr and Zn of aquatic vegetables all exceeded the value of evaluation standard, and Cd, Cu and As did not exceeded. The rank of single factor pollution index was:Pb(2.95)> Cr(2.24)>Zn(1.54)>Cd(0.53)> Cu(0.4)> As (0.27). It showed that the investigated aquatic vegetables were heavy polluted by Pb and Cr, polluted by Zn. The integrated pollution index was 2.29, which indicated compound pollution of these heavy metals belonged to secondary pollution level.4. THQ values comparison of Single heavy metals in aquatic vegetables was:Cr> Pb> Zn> Cu> Cd>As. In adult, the THQ of Cr was greater than 1, which showed the adult would suffer Cr risks when they ate the investigated aquatic vegetables. For children, the THQ values of Pb and Cr were more than 1. It reflected the children would suffer Pb and Cr’s exposure risks when they ate the investigated aquatic vegetables. For adults and children, the contribution rate of composite health risks was essentially equality. But the children were more sensitive to heavy metal pollution.5. Vegetables’s growing environment was disposed by As and Hg. with the extended of cultivation time, the content of As and Hg in water showed the trend of migrating to soil and aquatic vegetables. After a period of time, it achieved a dynamic balance. In soil, the content of As and Hg showed a trend of decline after rising first. The absorbed As would dissolve from soil, then absorbed by vegetables, whereas a large amount of Hg still stay in soil. When the As and Hg in the same aquatic environment, the addition of Hg could suppress As’s migration to soil and aquatic vegetables. Study of As and Hg’s migration characteristics in the organs of Zizania latifolia and Trapa bispinosa, found that As enriched in vegetables was more easily than Hg. The organs of As’s enrichment coefficient was larger than Zizania latifolia (greater than 6). The organs of Zizania latifolia and Trapa bispinosa of enrichment coefficients to As and Hg were:stems (roots)> leaves. Stems and roots were the main organs, which enriched large of As and Hg.6. Effective prevention and control of heavy metals:vegetables cultivation field should be far away from the pollution areas. And pollution source should be stricted to control. Choosing appropriate planted varieties and scientific layout method. The corresponding physical, chemical, biological and other measures should be combined to effectively reduce the toxic of heavy metals. Strengthening the research of prevention and control of agricultural science. reducing the process of vegetables cultivation, which depend on pesticides and other harmful substances, and perfecting standards of fertilizer and other products. Government should enhance to supervision, and establish long-term effective mechanism of food safety protection. Universal participation and common maintenance are all important. |
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