Assessing the potential toxicity of trace elements in agricultural soils with focusing on lead (Pb) and remediation options for cleanup of a contaminated site | |
| Author | Wanida Nobuntou |
| Call Number | AIT Diss. no.EV-12-02 |
| Subject(s) | Soil remediation--Toxicology--Thailand Soil pollution--Thailand |
| Note | A dissertationsubmitted in partial fulfillment of the requirements for thedegree of Doctor of Philosophy in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-12-02 |
| Abstract | There are many abandonedand operationalmines in the mountainous areas of Thailand. Toxic elements including heavy metals such as lead (Pb), cadmium (Cd) and arsenic (As) have been released and transported from the mining sites to the adjacent landscape. In Thong Pha Phum District, KanchanaburiProvince, Thailand Pb contamination in the vicinity ofa operational minehas occurred which could lead to potential health problems indownstream communities. Therefore, the overall goal of this study is to assess trace element distribution in environmental media and develop approachesfor remediation of Pbcontaminated soil using soil washing and phytoremediation techniques. To better understand the current status of Pb contamination and accumulation in the surrounding environment and potential health impacts, surface sediment, soil and including cropssamples were collected. Environmental monitoring showed that Pb concentrations in the surface sediment were as high as 869mg kg-1and varied significantly betweenstations sampled. Lead content in agricultural soil ranged from 138 to 614mg kg-1and was inversely proportion to the distance from the point source. At the highly polluted monitoring stations, concentrations of Pb in soil exceeded the maximum allowable concentration for Pb in agricultural soils (55 mg kg-1)by 1.7-2 times.The predominantform of Pb in the soilswas that associated with Fe/Mn oxides(49-56%) followed by organic boundPb(25-30%). Lead uptake by plantsvaried significantly and was speciesdependent. However,root and tuber crops like cassava (19.92 mg Pb kg-1dry wt.) and curcumin (3.25 mg Pb kg-1drywt.) could have removed Pb from the soil which suggests that growing root crops in Pb contaminated soils should be avoided. Lead concentrations in rice grain, an important staple food for local inhabitants in this area ranged from 0.14 to 0.29 mg kg-1which is up to1.5 times higher than the maximum permissible levelestablished by WHO/JECFA. Based on the status of Pb in rice grain, a hazard quotient (HQ) showed values of Pb was less than 1, indicating that local inhabitants who consume rice would not be exposed to a potential health risk from dietary Pb.Remediation of Pbpolluted soil is problematic. One potentially viable cleanup technologyis soil washing using a chelating agent. EDTA (Ethylenediamine tetraacetic acid) is a very effective chelating agent in soil washing, but has the drawback that ithaslow biodegradability in the environment. Consequently, there is the potential risk of Pbbeing leached to groundwater. The goal of this work was to investigate the effectiveness of EDDS (S-S, ethylenediaminedisuccinic acid) a biodegradable chelating agent as a potential alternatives to EDTA. Therefore various batch extraction and column leaching experiments were conducted. Results of thebatch soil washing experiments demonstratedthat Pb extraction efficiency slightly increased with increasing soil:solution ration (S/L). Further, at pH 9.28 EDDS at a S/L ration of 1:10 appeared to be effective in mobilizing Pb from contaminated soil while at a S/L ration of 1:25, EDTA demonstrated optimum Pb removal from the soil. The results of extraction time experiments indicated for both EDDS and EDTA, 6 hours was the optimum extraction time for Pb.Thus at the optimum extraction time at pH 9.28 and a S/L ratio of 1:10, biodegradable EDDScan be removeup to 70-80%of total Pb from contaminated soil. In contrast, at pH 4.5 and a S/L ratio of 1:25 EDTA greater efficacy for Pb removal (85-95%). A series of column leaching experiments, using EDDS and EDTA as leaching solutions were undertaken. For the Pb contaminated soil tested, both EDDS and EDTA showed a high efficacy for Pb removal at 6-7 pore water volume removing 75-80% and 90-95% of total Pb from soil, respectively. Therefore, the results indicate that EDDS is an effective biodegradable alternative chelating agent in soil washing. |
| Year | 2012 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-12-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian |
| Examination Committee(s) | Nguyen Thi Kim Oanh ;Athapol Noomhorm |
| Scholarship Donor(s) | Royal Thai Government Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2012 |