The Law Of Bioavailability And Action Mechanism Of Trace Heavy Metals In Soils

Following the deep research in the problem of the law of removing and transforming of heavy metal in the soil-plant system and form fractionation of heavy metal in soil, the evaluation on soil pollution with total heavy metal appears obviously inadequate in actual application. The transportation and conversion of heavy metal from soil to plant is decided by the form distribution and the law of bioavailability of heavy metal in soil-plant systems. The bioavailability of heavy metal usually means the level of absorption and accumulation or toxicity of heavy metal within a living organism. The study of bioavailability can offer theoretical basis for environmental monitoring and ecological remediation. Two kinds of typical soils which were Haikou vegetables plantations soils and Shilu iron mines area soils were the objects of study. Vegetables and wild plants and their habit soils were collected and the physics and chemistry character of soils were determined. The content distribution and enrichment characteristics and form distribution and the law of bioavailability of heavy metals (Pb, Cd, Cu, Fe, Mn, Zn), the plants action mechanisms of heavy metal were studied. The main results were as following:The contents of Fe, Mn, Cu, Zn, Pb, Cd in samples were determined by high pressure sealed digestion-Flame/Graphite Furnace Atomic Absorption Spectrometry. The method was with good correlation coefficient, R2>0.99, the detection limits of the method were satisfied for analysis, the RSD was low(the method of FAAS and GFAAS were5%and8%respectively), the recovery was95%-107%, the method had good precision and high accuracy. The difference of the physics and chemistry character between Yeli Cun soils and Shilu iron mines area soils were remarkable, but their soil-plant systems of had a similar contents distribution, all their soil contents distribution were Fe>Mn>Zn>Cu>Pb>Cd, and all their plant contents distribution were Fe>Mn,Zn>Cu>Pb,Cd, it reflected the inherent characteristic of Hainan soils and the characteristics of bioavailability of heavy metals in soils. The order of enrichment coefficients of vegetables and dominant plants to heavy metals in Yeli Cun and Shilu iron mines area soils were Cd>Zn>Mn>Pb>Cu>Fe and Cd>Zn>Cu>Fe> Mn>Pb relatively, all the enrichment coefficients of Cd and Zn were high, this showed the bioavailability of Cd and Zn were high. The concentration level of Mustard to six heavy metals was relatively high and Bone greens was relatively low, Hemp fimble leaf showed enrichment selectivity to different heavy metals. The enrichment coefficients of dominant plants of iron mines area to Cd (except White tephrosia) were rather large, the enrichment coefficients of Bothriochloa root to six heavy metals were rather high, White tephrosia and Cyperus alternifolius had the higher metastasis potential to Mn, Zn, Cd. The relevance of pH and the enrichment coefficients of plants to Cd, Pb, Fe, Mn, the relevance of Eh and the enrichment coefficients of plants to Zn, Fe, Mn, and the relevance of moisture content and the enrichment coeffidents of plants to Cd, Cu, Fe, Mn were the same in the Yeli Cun soils and Shilu iron mines area soils, this meaned that the effects of changing the physics and chemistry character of soils to the enrichment of heavy metals were in accordance in two places.Extracting effect of five extractants EDTA-2Na, DTPA, hydrochloric acid, acetic acidand and ammonium acetate to two typical soils were different, extracting effect of EDTA-2Na to Fe,Cu and DTPA to td in two soils were fairly good, there were the same extracting effect of five extractants to Pb, it indicated that the occurrence ways of Fe, Cu, Cd, Pb in two soils had certain similarity. BCR sequential extraction procedures indicated that heavy metals in iron mines area soils were in inert forms and the bioavailabilities of heavy metals in iron mines area soils were inferior to Yeli Cun soils. In the Yeli Cun soils, the contents of Zn activated fractions(acidextractants fraction and reducible fraction) were the highest, Mn and Cd were mainly based on residual fraction and the proportions of acidextractants fraction and reducible fraction were relatively high, Pb was mainly based on oxidizable fraction, Cu was mainly based on residual fraction and the contents of acidextractants fraction were not much, Fe was mainly based on residual fraction, the order of bioavailabilities were Zn>Cd>Mn>Pb>Cu>Fe, which was very near with the order of enrichment coefficients of vegetables. In the iron mines area soils, as far as acidextractants fraction which had activity, Cd was the highest, the next were Mn, Zn, Cu, the lowest were Fe and Pb, which was very near with the order of enrichment coefficients of dominant plants. The forms which were separated by five extractants and BCR sequential extraction procedures were used to indicate bioavailabilities of heavy metals, the results indicated that there was any coincidence and a discrepancy in the effects of the physics and chemistry character of soils to the bioavailabilities of heavy metals in the two typical soils. The influence of pH to the bioavailabilities of Fe, Pb, Mn, Eh to the bioavailability of Fe and moisture content to the bioavailabilities of Fe, Cd, Mn were consistent.From rhizosphere soils to non-rhizosphere soils of Edible rape and Rassica capestris, acidity and moisture content increased and oxidability atmosphere decreased. The order of biological absorption coefficients of Edible rape and Rassica capestris to heavy metals in soils were Cd>Zn>Mn>Cu>Pb>Fe and Cd>Zn>Cu>Mn>Pb>Fe respectively, the biological absorption coefficients of two vegetables to Cd were all high. The forms of heavy metals which were separated by sole extraction and BCR indicated that: when the activity forms contents of heavy metals increased and amplitudes of the relative change rates were greater, biological absorption coefficient tended to be bigger, when the activity forms contents of heavy metals decreased and amplitudes of the relative change rates were greater, biological absorption coefficient tended to be smaller. The changes of heavy metals contents and forms were caused by rhizosphere effect in rhizosphere soils and non-rhizosphcre soils, it affected the absorptions of plants to heavy metals to a large extend. But the biological absorptions of plants to heavy metals were not only relevant to the forms of heavy metals in soils but also relevant to the absorptions of plants, transportation efficiency of heavy metals and rhizosphere active efficiency. The comprehensive actions of these factors decided the level of transportation and transformation and efficiency of heavy metals to plants.