Effect of pH, Oxidation States of Arsenic and, Inorganic and Organic Fertilizers on Accumulation of Arsenic in Vegetables

Abstract

Background/Objectives: The groundwater of 60 districts out of 64 in Bangladesh was contaminated with arsenic, whose irrigation usage is increasing over last two decades to raise food production. In this context, we studied the effects of pH and different oxidation states of arsenic (As3+ and As5+) in irrigation water and of both inorganic and organic fertilizers on arsenic-accumulation in vegetables. Method/Statistical Analysis: Five vegetable plants were grown with sandy clay loamy soil in pots under open field conditions and irrigated with model water of 10 mg As L-1. The pot experiments were well justified by field trails (n=80) that roughly showed 1:1 correlation. The samples were acid-digested and analyzed by GF-AAS for total concentration of arsenic. The regression equations of the fitted models were cross-checked by analyzing ANOVA, P value, r value and Durbin-Watson statistics. Findings: Prolonged use of irrigation water of pH range 5.00-11.00 for 90 days changed pH of surface soil of 0-3 cm depth from 6.22 to 8.93. The concentration of As in vegetables, [As]veg, although varied irregularly, was comparatively higher at both lower pH (5.00) and higher pH (10.00) of irrigation water corresponding to soil pH of 6.22 and 8.34 respectively. Arsenic in +3 oxidation state accumulated more in vegetables than that in +5 oxidation state. Comparison showed that urea and TSP increased arsenic content in vegetables by 72.37% and 18.83% respectively, whereas potash and cattle manure decreased that by 14.76% and 51.16% respectively. The reduction of [As]veg by the cattle manure is probably due to adsorption of As by cellulosic materials and microorganism induced methylation of As in soil, as we found 50.72% organic matter, 30.32% Organic C in cattle manure and about 106 Fecal Coliform bacteria per 100g of cattle manure amended soil. Novelty/Improvements: To our knowledge, this is the first paper that reports the effect of different oxidation states of arsenic (As3+ and As5+) of irrigation water towards arsenicaccumulation in vegetables. Our findings reveal that for As phytoremediation, soil pH should be around 6.80 and application of cattle manure should be highly encouraged, whereas uses of urea and TSP should be controlled. This study highlights the appropriate practices in cultivation process towards safety of human health. Keywords: Arsenic, Effect, Fertilizer, Oxidation State, Vegetables, pH