Responses of barley seedlings to arsenic toxicity under various pH levels in the rooting medium

The water culture experiment was conducted to observe the effect of pH on the physiology and mineralogy of arsenic (As) toxic barley plants. The pH levels were 4.5, 5.5, 6.5 and 7.5 in presence and or in absence of 13.4 µM As. The experiments were done with 3 replications. Arsenic was used as sodium meta arsenite (NaAsO2). In presence of As, the lowest growth of the plants was at pH 4.5, the 2nd lowest growth was at pH 7.5 and the highest growth was at pH 6.5, indicating that As was more toxic at pH 4.5 and 7.5 as compared to pH 6.5. Arsenic concentrations were higher in the shoots and roots of pH 4.5 and 5.5 levels as compared to pH 6.5 level, suggesting that the bioavailability of As was much higher in acidic solution. Arsenic accumulation was the highest in the pH 5.5. The result suggested that, the bioavailability of As was less in around neutral pH condition. The findings also suggested that pH in the growth media might control the bioavailability and phytotoxicity of As. Concentrations of phosphorus (P), potassium (K), Calcium (Ca), magnesium (Mg), iron (Fe) and zinc (Zn) were not affected at all in the As treated shoots, but the accumulations of those elements increased in 6.5 pH treated shoots, indicating that the As-toxicity was lower at pH 6.5. The result suggested that the pH in the growth medium should be maintained at around the neutral condition to reduce As-toxicity for sustainable graminaceous crop production