Study On Pollution Of Pb And Cd In Food And Controling Countermeasures

Due to the rapid development of industry and agriculture, more and more pollutants are discharged into the natural environment, especially heavy metals pollutants. Heavy metals, especially Pb and Cd, exist in many areas. It can last very long time, hardly be digested, and easy to be accumulated in the environment. Pb exists in air, soil, water as well as food;it is also hardly to be decomposed, easy to be accumulated and absorbed during digestion of human being, which is very harmful to our health. It is also very harmful for plant growth if its concentration is enough high. Cd is another harmful heavy metal, more toxic than other heavy metal not only to human being, but also to plants and animals. It can restrain growth of plant root, decrease chlorophyl productivity, disturb alimentation absorption. Through food chain, it can also be accumulated in human body, affect function of nerve, viscera, procreate and inherit system. Therefore, it is very necessary for us to study how to control total amount of heavy metal intake through food and water.Food quality and security is very much concerned by the whole world. It is also a focus point after repaid economic development and improvement of people' s life in China. Heavymetal is a kind of very harmful pollutant which may affect human health and not easy to be solved. Therefore, it is very necessary to know the real situation of heavy metals in food and environment, to find an effective measure for heavy metal pollution control in foliage rehabilitation. To investigate food heavy metal pollution in Jilin Province, from 2001 to 2004, we collect 917 samples of food products of 13 kinds from supermarkets and food markets in 6 counties in Jilin Province, and then detect Pb and Cd concentration after pre-treatment according to national standard. The results show that Pb and Cd pollution are in the same level with the ratio of superscale about 9.49%, 6.24% respectively;It is very clear that Pb and Cd all can be accumulated in food product to some extent according to the Quality Assessment Standard. Although not very serious, potential threaten to human health is very clear. Pb and Cd oncentration are very different in different kinds of food and different sample-areas as well. The results also show that the changenable tendency for concentration of Pb and Cd in food is decreasing gradually year by year. However, Pb concentration in samples of fish and animal kidney, Cd concentration in meat and kidney increase in recent years, probably because heavy metal is much easy to be accumulated in fish and kidney. It is also shown that Pb and Cd accumulation in the same kind of food is also different. Cd residual concentration inpotatoes is higher than other foods. It maybe due to pollution in some areas. Moreover, Pb residue is as follow: flour > rice > potato > bean >corn;In meat products, Cd residual concentration is chicken > mutton > pork > beef, but for Pb, mutton > chicken > pork > beef.The existing form of heavy metal will determine its bio-utilization. Normally speaking, exchangeable form of heavy metal is the feasible and the easiest form which can be utilized by plant. It is found that exchangeable Cd concentration in soil is much higher than Pb, therefore, much harmful to human health than Pb. As we know, different forms of heavy metals will determine their mobility and bioavailability, as well as their activity and toxicity. Among these, exchangeable form is the most active and toxic form, which is easy to be absorbed by plant, but the residue is the lowest. Therefore, if we can continuously monitor Pb and Cd concentration in vegetable and other foods, especially their exchangeable form, it will be very easy to predict and control Pb and Cd toxicity for affecting human health. Because most of Pb and Cd pollution is coming from air, water and soil, effective control method should be taken to remove heavy metal pollution and ensure food security.At present, biomembrane adsorption and plant rehabilitation are two good measures for Pb and Cd removal. It is known that all surface of solid phase in nature water havea layer of biomembrane which can notable adsorb and enrich heavy metal. This is because of effect of Fe, Mn oxides and organic materials, which can remove heavy metals in water effectively. Soil-foliage system is the fundamental structure of biosphere, as well as the "bridge" for communication between plant and animal. If it is polluted over its pollution load, its productivity will decrease, or even total loss. Further more, pollution in soil can diffuse to air, water and plant, hazard to human health through food chain. Therefore, study on mechanism of plant heavy metals adsorption and their affect factor can control heavy metal for entering food chain on one hand, and give basis for heavy metals foliage rehabilitation in soil on the other hand. Foliage rehabilitation is an original rehabilitation method, which can protect topsoil, reduce water & soil erosion and have less negative effect on environment. Now it is the most cleaned technique, which can be used in many areas for amelioration of soil polluted by heavy metal and recollect heavy metal for future re-use. Over-accumulation vegetable filtration is the basis of foliage rehabilitation for heavy metal polluted soil. Among these plant, weed is an ideal resource for over-accumulation due to its fast growth rate, strong survival ability, better propagation, as well as rapid biomass productivity under adapt environment. Some researchers found that nightshade, a kind of weed, is aspecial Cd over-accumulation. It is shown that under Cd concentration of 25mg/kg, Cd concentration in stemof morel is over lOOmg/kg, well known threshold standard for over-accumulation. Others found that by using mpatiens, Cd removal rate can reach 62-89% for treatment of Cd wastewater. It is also found that ramie also have very strong adsorb effect on Cd rehabilitation in field soil and cut the route for Cd entering food chain. Moreover, some researchers show that some plant can decrease Pb bio-utilization, release its toxicity. Another way for heavy metal removal is bio-extraction. For example, put mustard seed in high Pb concentration water can increase Pb concentration in its stem to about 1. 5%. Therefore, if we can mix manmade chelating agent with Pb polluted soil, it will improve Pb adsorption.In conclusion, on one hand, agriculture pollution can transfer to our food such as vegetable, food and poultry feed through soil, water;on the other hand, Industry pollution discharge and domestic sewage can affect human health through food chain. If heavy metal concentration is over the water body' s self-clean ability, enrichment may occur. In northeast China, more Pb and Cd also enrichment in vegetable through heavier flue dust. And also, during food processing, transportation, storage, Pb and Cd pollution may also occur. In a word, there are many resources for heavy metal pollution. To control its pollution, radically, cut its pollutionresource and provide a better food processing, transportation, storage environment is very necessary to ensure human health.