Study on the influence of acid rain on the intake of trace elements into rice plant from soils

Rice plant samples were grown in 14 cultivative pots by irrigation using the six conditions of artificial acid rain waters (pH : 6.5, 6.0, 4.5, 3.5, 3.0 and 2.5) and tap water (pH : 7.5). The artificial acid rain waters were prepared by adding a mix solution of 1N H2SO4 and 1N HNO3 (1:1) to tap water. The rice grain yielded were separated into three parts, i.e., polished rice, bran and chaff, and they were reduced to powder one by one. Twenty six element contents in the three parts of grain (each 14 samples) were determined by a neutron activation analysis. It was clarified that the contents of Cr, Fe, Ni, Zn, Cu, Rb, Mo in the polished rice increased with decreasing of pH of the irrigation waters. The contents of Se and Br, on the contrary, decreased with decreasing of pH of the irrigation waters. Significant changes of the contents were not observed for the elements Na, Al, Cl, Sc, Mn, Co, V. The relationships between the trace element contents in the bran or chaff and pH of the irrigation waters were not so clear as the case of polished rice. The enrichment factor of trace elements to soils were calculated for the polished rice, bran and chaff. The high enrichments of Cl, Mo, Zn, Se, Cu and Ni were observed in the polished rice. The elements K, Rb, Mn, Mg and Cr were highly concentrated in the bran. (author)