Paraquat adsorption and distribution in soils of Yom River Basin | |
| Author | Wapakorn Amondham |
| Call Number | AIT Diss. no.EV-05-1 |
| Subject(s) | Paraquat--Thailand--Yom River Basin Soils--Environmental aspects--Thailand--Yom River Basin |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science |
| Publisher | Asian Institute of Technology |
| Abstract | Environmental behavior of paraquat in representative tropical soils of Yom River basin, Thailand was investigated. The behaviors in each type of soils include adsorption, dissipation, speciation and remobilization were evaluated using both laboratory and field experiment techniques. Adsorption of paraquat was investigated in the representative eight soil samples from the study area using batch equilibration techniques. The results indicated that adsorption depended on soil chemical characteristics, such as exchangeable basic cations and iron content. Multiple regression analysis indicated significant contribution of exchangeable calcium percentage (ECP), total iron content (TFe) and exchangeable sodium percentage (ESP) to paraquat sorption (Q) at low paraquat concentration level (400 mg paraquat kg^-1 ). The ESP and TFe were significant at all concentration levels studied, while ESP was significant only at low level of paraquat adsorption. Adsorption characteristics of paraquat were thoroughly examined in two soils (Soil#1 and Soil#6) which represent clay and sandy loam texture of soil. It was found that adsorption of paraquat was followed Freundlich model and exhibited nonlinear sorption curve with 1/n value less than 1. Paraquat adsorption was higher as expected in clay soil (Soil#1) than sandy loam (Soil#6) soil with the adsorption coefficient (Kf) value of 787 and 18, respectively. Paraquat desorption using 0.01 M CaCl2 was found at very small amount which were 1.92 - 2.36% and 11.72 - 17.95% in Soil#1 and Soil#6, respectively, this indicated hysteresis effect or desorption resistance even in sandy loam soil. Paraquat sorption on soils was characterized by a rapid initial step followed by much slower step. The time dependence of paraquat adsorption was fit to Elovich kinetic model indicated a rate:.. limiting of diffusion process. Rate of sorption in Soil#6 was exceedingly slower than Soil#1. Speciation of paraquat in 300 mg kg-1 spiked sample of Soil#l was identified by sequential extraction technique. Paraquat in a mobile fraction as water soluble and exchangeable fraction were not found in the studied sample. Major fraction of Paraquat was accumulated in the lattice of clay mineral (84.3%) which was the non-mobilized fraction. The minor fraction was organic bound which mobilizable in long-term (15.6%). The readily mobilizable which was oxide and carbonated bound was unimportant in the experiment with the amount less than 0.1 % of total fractions. Paraquat mobility and dissipation studies were conducted using both field and laboratory soil column experiments. Clay soil showed low mobility of paraquat with accumulation occurred mostly in the surface (0-5 cm) layer under field conditions and in the 0-1 cm layer in a laboratory soil column experiment. Dissipation of paraquat in soil was faster under field condition than at ambient laboratory conditions. The dissipation rate followed a first-order kinetic model with the DT5o value at 36-46 days and DT90 around 119-152 days. It is interesting to note that paraquat dissipation in the tropical soil conditions as found from this study was faster than in the temperate region with half-life than 100 days. Potential risk of paraquat to environment and ecosystems interpreted from its behaviors indicated that the potential of paraquat exposure could be expected in surface water by the movement of strong adsorbed paraquat with eroded soil. The potential exposure in groundwater, soil organisms and human are nil because of the low mobility and less desorption capacity. |
| Year | 2005 |
| 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) | Chongrak Polprasert;Yuwaree In-na;Samorn Muttamara;Khan, Shahamat U. |
| Scholarship Donor(s) | Naresuan University;Asian Institute of Technology Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2005 |