Cadmium Contaminated Soil Hyperaccumulators And Research

Soil is the main place where people performed agriculture production,and soil contamination is confidentiality,accumulation,long-term characteristic,irreversibility and directly concerning the safety of food chain and human health.Undoubtedly,research and treatment of heavy metal contamination of soil have great theoretical and practical significance to us.Phytoremediation is a kind of green remediation technology in removing environment pollutants and has developed quickly in recent years.And it has been studied by many environmental researchers for its safe and cheap characters.Screening the hyperaccumulator becomes key point which the domestic and foreign scholars study.In order to seek the plants which can grow well in the contaminated soil and have the strong capacity to absorb,enrich,transfer the cadmium in contaminated soil,the author selected 10 species of plants which is Yellow heart cabbage,Datura stramonium,Brassica oleracea Linnaeus var.acephala,Kochia scoparia Linn.Schrad,Capsicum annuum,Lolium perenne,Apium graveolens,Allium fistulosum,Poa annua and Oenothera biennis,performed model pot-culture under various density of cadmium.Through determination the biomass,the Cd content of plant's different spot and calculating BCF and TF,analyses the ability of absorption,accumulation and transference cadmium from soil to the body of plants.Compare the indicators of the same species of plants harvested at different stages to study the effects of cultivation time on the ability of plants to absorb the cadmium.The main results are the following:(1)The effect on the plants caused by the density of soil is different for the kind of plants.The tested 10 kinds of plants present four rulers.①Fluctuation increasing plants:Yellow heart cabbage,Datura stramonium's biomass increases along with the Cd density in the soil,slightly has the fluctuation;②Decreasing plants:Biomass of Kochia scoparia Linn.Schrad,Oenothera biennis, Lolium perenne and Poa annua decreases along with the density of Cd incease;③Raised plants: Biomass of Brassica oleracea Linnaeus var.acephala,Allium fistulosum,Apium graveolens increases while the density of Cd in the soil under low level(Cd＜50 mg·kg^-1),and decreases with the rising of density of Cd in high level(Cd＞75mg·kg^-1);④Concave plants:Biomass of Capsicum annuum's change is quite special,which reduces after first increases.(2) Characters of absorption of the tested plants are the following①A lot of Cd is accumulated in down-ground tissue but the Cd content of above-ground tissue is low.When the Cd content of above-ground tissue of Oenothera biennis is in 0.012～4.3mg·kg^-1, BCF is from 0.003 to 0.029,and the Cd content of down-ground tissue is in 0.37～68.63mg·kg^-1, BCF is in 0.06～0.46.Explained that Oenothera biennis's root may absorb the ration cadmium in soil and detained it in the under-ground portion,so causes above-ground portion' cadmium content is low. Also has Apium graveolens,Lolium perenne and Poa annua with Oenothera biennis characteristic similar plant.Based on these,this kind of plant has bad ability of Cd transference.②A lot of Cd is accumulated in above-ground tissue but the Cd content of down-ground tissue is low.When the density of Cd in soil is lower than 75mg·kg^-1,Kochia scoparia Linn Schrad's the Cd contents of above-ground tissue is 0.26～74.00mg·kg^-1,and the Cd contents of down-ground tissue is 0.07～0.63mg·kg^-1.Indicate that it has the very strong Cd transference ability.③The Cd contents of above-ground tissue and down-ground tissue are both high,and the Cd content of the plant is rising with the rising Cd density in soil.The plants grow normally and don't show any toxic symptoms.Just like the Cd content of above-ground tissue of yellow heart cabbage is 82.37mg·kg^-1 when the density of Cd in soil is 25mg·kg^-1,but its BCF is more than 1;while the density of Cd in soil is from 50mg·kg^-1 to 150mg·kg^-1 the Cd content of above-ground tissue of yellow heart cabbage surpass the standard of hyperaccumulator(the Cd content of above-ground tissue is 100 mg·kg^-1),meanwhile within these densities of Cd the BCF of the plant are all more than 1.But TF are all lower than 1.Based on these,conclusion is that yellow heart cabbage has good ability of Cd accumulation and enrichment but poor ability of transference.Datura stramonium has the similar condition.(3) There is a density of Cd in soil under which the Cd content of above-ground tissue is higher than others.When the density of Cd reached this value the plant capable of Cd,enrichment is strongest and repairing ability is best.Yellow heart cabbage,Datura stramonium and Kochia scoparia Linn.Schrad are selected from the test have strong capacity of accumulating Cd. The Cd content of above-ground tissue of them reach up to high When the density of Cd in soil is 75mg·kg^-1,these show that the ability of a plant absorb Cd would be best under some certain density, if the density is lower or higher than the amount,the restoration effect would decline.(4) Planter time to plant absorption cadmium influenceKochia scoparia Linn Schrad and Oenothera biennis' biomass is low,therefore completely harvests it in 70d time,and not performe the comparative trial according to the planter time's length. Through carry on the contrastive analysis to different time harvest's same plant's each target, discover that along with time increase,the other 8 plants' biomass,cadmium content,BCF and TF have the respective change rule①Biomass change rule:Along with time increase,the biomass increases,the most plants display this kind of situation,like Datura stramonium,Brassica oleracea Linnaeus var.acephala, Capsicum annuum,Lolium perenne,Apium graveolens,Allium fistulosum;Yellow heart cabbage and Poa annua's biomass to increase along with the time reduces.②The Cd contents and BCF change rule:Change rule of the Cd contents and BCF is corresponds along with the time change.Along with time increase,the Cd contents of above-ground and down-ground of Capsicum annuum,Brassica oleracea Linnaeus var.acephala,Apium graveolens reduce,and BCF reduce too;the Cd contents and BCF of above-ground of Allium fistulosum increase,and the Cd content and BCF of down-ground reduce;the Cd contents and BCF of above-ground of Yellow heart cabbage and Datura stramonium reduce and the Cd contents and BCF of down-ground of them increase.③TF change rule:Along with time increase,TF of Yellow heart cabbage,Datura stramonium, Poa annua reduce;TF of Allium fistulosum,Apium graveolens increase;TF of Capsicum annuum in the low concentration sector increase;when the density of Cd in soil is from 50mg·kg^-1 to 75mg·kg^-1, TF of Brassica oleracea Linnaeus var.acephala increases obviously;when the density of Cd in soil is from 50mg·kg^-1 to 125mg·kg^-1,TF of Lolium perenne increases.(5) Analyzed by synthesis all the factors including the Cd content of above-ground tissue,BCF and TF of the 10 tested plants,and taken them as the indexes to measure the plant capable of cadmium enrichment,from these conclusions is that the ability of yellow heart cabbage,Datura stramonium and Brassica oleracea Linnaeus var.acephala absorbing Cd are the strongest.Secondly, Kochia scoparia Linn.Schrad,Capsicum annuum and Allium fistulosum are stronger.Lastly,the plant capable of cadmium enrichment of Lolium perenne,Apium graveolens,Poa annua,Oenothera biennis are the worst.This experiment has not been able to screen one kind ideally plant to absorb Cd, but has also provided the precious material for the future screening.