Abstract
The effect of arsenic contaminated water and soil on rice. Ph.D. Dissertation. Dept. of Soil Science, Bangladesh Agricultural University, Mymensingh.
The study was undertaken with the three main objectives: (i) to assess the quality of different sources of irrigation water and their effect on soils and rice crop, (ii) to understand the adsorption and fractionation of arsenic in soils, and (iii) to evaluate the effect of arsenic addition on the arsenic accumulation and yield of rice. The first objective was achieved through a survey, the second objective by a laboratory experiment at a constant temperature, and the third objective by pot culture experiments. Fifty five each of irrigation water, soil and rice samples from Nabipur Union of Muradnagar Upazila under Comilla district was analyzed for As and many plant nutrients. It appeared that most of the STW waters contained As above 100 μg L1 while the DTW had As less than 100 μg L'(maximum permissible limit for irrigation water). All the irrigated soils (except 7 STW irrigated soils) had As content less than 20 mg kg (the maximum acceptable limit for agricultural soils). There was a significant positive correlation between irrigation water As and soil As, grain As or straw As. The adsorption of As by soil increased with the increase of As additions, however the relationship was non-linear (quadratic). The As adsorption fits well to the Langmuir and Freundlich adsorption isotherms. Both adsorption maxima and binding strength of As were in the order of terrace soil of Gazipur > non-calcareous soil of Muradnagar > calcareous soil of Chapai Nawabganj indicating the clay coupled with Fe content as the principal factor for As adsorption. The proportion of different As fractions of soils followed the order of exchangeable Fe-bound As (50.61%) > residual reducible As (16.16%) > exchangeable Al-bound As (12.99%) > residual As (11.75%) > Ca-bound As (7.75%) > easily exchangeable As (0.74%). The pot culture experiments indicate that the addition of As resulted in a yield loss with an accumulation of rice grain. The grain yield was reduced drastically due to addition of As at 15 mg kg soil or 2 mg L irrigation water. The reduced grain yield and accumulation of grain As were related to the reduced root biomass of the crop, as induced by As addition.