| In order to study the mechanism of arsenic (As) accumulation and detoxification in hydrophytes exposed to different As speciation, a hydroponic culture method was used to determine plant biomass, total As adsorption and absorption of three aquatic plants (Hydrilla verticillata, Pistia stratiotes and Eichhornia crassipes). The three plants were exposed to various concentrations of As(Ⅲ)(0-0.5mg·L-1), As(Ⅴ)(0-5mg·L-1), and DMA (0-5mg·L-1). A liquid chromatography hyphenated atomic fluorescence spectrophotometry was used to determine As speciation in the culture solution and plant body. The arsenate reductase (AR) activities of roots and shoots were also determined. In addition, aiming to the increase of plant As uptake and the improvement of the remediation efficiency of As-contaminated water, we also investigated the plant biomass, total As adsorption and absorption as affected by Fe3+(0-2.0mg·L-1) and NH4+-N (0-10mg·L-1) in the three aquatic plants, which were exposed to a middle concentration of three As species [As(Ⅲ):0.3mg·L-1, As(Ⅴ) and DMA:3mg·L-1], with an emphasis on the changes of As contents and its speciation in the culture solution and plant body, respectively. The results showed as follows:1. Arsenic accumulation mainly occurred via biological uptake rather than physicochemical adsorption. The lower accumulation of DMA than As(Ⅴ) was noticed. P. stratiotes showed highest accumulation of inorganic As but E. crassipes showed lowest even P. stratiotes and E. crassipes had the same life forms. We found that E. crassipes showed the highest accumulation of DMA dissimilarly. As speciation analysis results in culture solution showed that after10days of incubation, As(Ⅲ) was transformed to As(Ⅴ) in all As(Ⅲ) treatments. The oxidation rate was H. verticillata> P. stratiotes> E. crassipes> no plant. However, the As species was not changed in the culture solution at As(V) or DMA treatment.2. Results from plant As species analysis showed that As(Ⅲ) was the predominant species in both roots (39.4-88.3%) and shoots (39-86%) in As(Ⅲ)-exposed plants. As(Ⅴ) was the predominant species in roots (37-94%) and As(Ⅲ) was the predominant species in shoots (31.1-85.6%) in As(Ⅴ)-exposed plants. DMA was the predominant species in both roots (23.46-100%) and shoots (72.6-100%) in DMA-exposed plants. The As(Ⅲ) contents and AR activities in P. stratiotes roots and H. verticillata shoots significantly increased when exposed to1.0mg·L-1and3.0mg·L-1As(Ⅴ). As the key mechanism of As detoxification, arsenate reduction occurred in aquatic plants. In case of As(Ⅴ)-exposed plants, tolerance was attributed to the increase of AR activities.3. Total As contents in P. stratiotes and E. crassipes exposed to As(Ⅲ) and in three plants exposed to As(Ⅴ) increased with the addition of Fe3+. However, the total As contents in the three plants were not affected by Fe3+addition at DMA treatment. Results from As speciation analysis in culture solution showed that after10days of incubation, As(Ⅲ) was transformed to As(Ⅴ) at As(Ⅲ) treatment. As(Ⅴ) concentrations in culture solution of H. verticillata or E. crassipes exposed to As(Ⅴ) were decreased when high concentration of Fe3+was added. DMA concentrations in the culture solution of E. crassipes exposed to DMA were also decreased with the addition of Fe3+.4. Results from As speciation analysis in plant parts (root and shoot) showed that root As(V) and As(Ⅲ) contents in P. stratiotes, and root As(Ⅴ) contents in E. crassipes increased with the addition of Fe3+at As(Ⅲ) or As(V) treatment. At As(Ⅲ) treatment, the shoot As(Ⅲ) contents in P. stratiotes, and the shoot As(Ⅴ) contents in E. crassipes increased with the addition of Fe3+. At As(V) treatment, the shoot As(Ⅴ) and As(Ⅲ) contents in H. verticillata, and the shoot As(Ⅲ) contents in P. stratiotes and E. crassipes increased with the addition of Fe3+. At DMA treatment, the DMA contents in the roots of E. crassipes increased with the addition of Fe3+. The DMA contents in the shoots of E. crassipes increased with the addition of high concentration of Fe3+(2mg-L"1). This work indicated that a suitable concentration of Fe3+could increase As uptake of aquatic plants and improve the remediation efficiency of As-contaminated water.5. Total As absorption was greatly affected by NH4+-N addition in three plants. Total As contents in P. stratiotes exposed to As(Ⅲ) and in three tested plants exposed to As(Ⅴ) increased with the addition of NH4+-N. However, total As contents in the three plants were not affected by NH4+-N addition at DMA treatment. After10days of incubation, As(Ⅲ) in culture solution was transformed to As(V) at As(Ⅲ) treatment. At As(Ⅴ) treatment, As(Ⅴ) concentrations in culture solution of H, verticillata were decreased when low concentration of NH4+-N was added and As(Ⅴ) concentrations in culture solution of E. crassipes were also decreased when middle or high concentration of NH4+-N was added.6. The root As(Ⅲ) contents in P. stratiotes and E. crassipes at As(Ⅲ) treatment increased with the addition of NH4+-N. The root As(Ⅴ) contents in P. stratiotes and E. crassipes and root As(Ⅲ) contents in P. stratiotes at As(Ⅴ) treatment increased with the addition of NH4+-N. At As(Ⅲ) treatment, the shoot As(Ⅲ) contents in P. stratiotes increased with the addition of NH4+-N. At As(Ⅴ) treatment, the shoot As(Ⅲ) contents in three plants increased with the addition of NH4+-N. At DMA treatment, the DMA contents in the roots of E. crassipes increased with the addition of high concentration NH4+-N (10mg·L-1). Therefore, the addition of NH4+-N significantly improved As accumulation by aquatic plants and it was helpful to remove As from As-containing eutrophic water body. |
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