Study On Chemical And Microbial Control Of Arsenic Bioavailability In Soils And Its Corresponding Mechanism

Arsenic contamination has become one of the environmental problems in the world. Arseniccontamination of farmland has seriously endangered the safety of agricultural products with greatinfluence on the sustainable use of land resources in China, causing a significant adverse impact onsustainable development of agricultural production in China. The safe use and control of arseniccontaminated farmland has become the current important issue of soil and environmental scienceresearch field. Through the utilization of field investigation, laboratory simulation test, pot experimentmethod, technique of hydride generation atomic fluorescence with high performance liquidchromatography (HPLC-HG-AFS) etc., the characteristics of bioavailability of arsenic contamination insoils are conducted, and the effect of the fungus with high tolerance of arsenic screened from the miningarea on the chemical behavior of arsenic in soils and its bioavailability combining with the use ofchemical conditioners. The characteristics of arsenic response in soil-plant system under microzone andthe effects of arsenic bioavailability in soils with high arsenic risk using microbial and chemicalmethods using were explored. And the preliminary model of controlling the bioavailability of arsenic insoils and safe use pattern of arsenic contaminated farmlands were established. The main results are asfollows:1. Arsenic concentration in surface soils surrounding Shimen realgar mine is7.449~932mg·kg-1, thehighest concentration appeared on the top of Shimen realgar mine, and the majority of arsenic in soils isrelatively stable and about85%of the arsenic is in residual form. The extraction efficiency of availablearsenic in soils using different chemical reagents ranked in such order: HCl extractable arsenic (9.42%)> NaHCO3extractable arsenic (1.19%)>H2O extractable arsenic (0.39%)>NH4Cl extractable arsenic(0.097%), and the soluble arsenic in soils through different reagents was significantly related with soiltotal arsenic (p<0.01). Through the correlation analysis between available arsenic of soils and arseniccontent in plants, it was found out that positive correlation between plant arsenic content and NaHCO3extractable arsenic is most remarkable, and NaHCO3extractable arsenic can be an effective reagentextracting arsenic reflecting the bioavailablity of arsenic in soils.2. Water soluble arsenic and NaHCO3extracted one were all increased steadily when resistant fungusas Trichoderma asperellum with high tolerance of arsenic was added into natural soil and sterilized soiland highest increased percentage of available arsenic appeared for natural soil added with fungustreatment, and the available arsenic was1.48times higher than original soil. The available arseniccontent in different treatments decreased in the order: Natural soil+fungus>Natural soil>Sterilized soil+fungus>Sterilization soil.The addition of arsenic resistant fungus into soil promoted arsenic releaseand dissolution, which is mainly related to the conversion process from amorphous andpoorly-crystalline hydrous oxides bound arsenic, well-crystallized hydrous oxides bound arsenic tonon-specifcally sorbed arsenic. 3. With the addition of high arsenic resistant fungi Trichoderma asperellum into artificialcontamination soil and aging time increased, the water soluble and NaHCO3extracted arsenic content insoils degraded firstly then gradually increased in the later time, and the NaHCO3extracted arsenic in thelater period was much lower than that in earlier time. Water extracted arsenic was mainly in the form ofAs (V), and the decreased percentage of available arsenic is42.8%when the incubation time reached90days compared to that in soils after2hours incubation, which is still higher than that of natural soiltreatment with the increased percentage of2.9%. The activation of arsenic in soils by resistant fungus ofarsenic was mainly connected with the transformation from amorphous and poorly-crystalline hydrousoxides bound, well-crystallized hydrous oxides bound arsenic to non-specifcally sorbed andspecifcally-sorbed one.4. Study on the microbial and chemical regulation of arsenic contaminated soil showed that watersoluable and NaHCO3extracted arsenic content in soils degraded significantly when added withamendment I (iron power) or amended with iron power and fungus. With the incubation time prolonged,available arsenic ascended totally and that for different treatments ranked in the order as following:Blank soil as control＞Sterilized soil＞Blank soil plus amendment I and fungus＞Blank soil plusamendment I＞Sterilized soil plus amendment I with fungus＞Sterilized soil plus amendment I.Relatively better effects of controlling the availability of arsenic in soils appeared in the treatments ofamendment I and amendment I combined with fungus.5. Through artificial simulation experiment using microbial and chemical regulation of arseniccontaminated soil, the available arsenic content in soils decreased with the incubation time increased.In comparison with that of control after90days’ incubation, thirty point five percent of availablearsenic was reduced for the soil treatment amended with FeSO4, and twenty six point four percent ofavailable arsenic decreased for treatment of amendment II and fungus, but that was reduced by25.1%and20%respectively for the treatments of amendment II+fungus, manure+amendment II+fungus. Theavailable arsenic increased by4.7%when the soil added with manure, and that was improved by19.5%when treated with manure and arsenic resistant fungus. Therefore, foure treatments asmanure+amendment II, manure+amendment II+fungus, amendment II+fungus, amendment II can all beselected as effective model which can control the availability of arsenic in soils effectively. However,manure should be applied correctly since it accererated the release of arsenic from soils.6. Through the study on the technique of regulating the availability of arsenic in soils and its relatedeffects, plant arsenic content was reduced by46.2%and51.4%under the treatments of amendment I(iron power) or amendment I combined with fungus. Therefore, arsenic intake by plant was significantlyreduced either for the treatment as amendment I or for that as chemical amendment I and arsenicresistant fungus, which can be used as effective methods for controlling the bioavailability of arsenicand safely utilization of contaminated soil with high risk.