the effect of leather processing industries' waste water on chromium and its fractions in soil

abstract chromium is among the metals that has numerous applications in various industries due to its specifications. widespread use of this metal in different industries has unfortunately been accompanied by its increased release into environment and this entails numerous environmental hazards. in the first phase of the research that was conducted to evaluate the effect of the leather processing companies' sewage on chromium behavior on soil, samples of soil affected by the sewage of leather processing companies were studied hexavalent chromium and chromium distribution ratio in exchangeable organic, carbonated and residual fractions of these soils were examined. the second phase of this research was conducted to assess the effect of time, chromium, soil texture and soil organic mater on chromium distribution in soil fractions. in this phase of the research also the reduction process of hexavalent chromium with time was evaluated. in the evaluation of the soils affected with chromium in charmshahr area of mashhad the contamination was observed in 45-centimeter depth of the soil. in sequential extractions of these soils it was shown that 90% of the chromium was in the residual fraction. the chromium distribution order in various fractions of these soils was as follows: exchange fraction> organic fraction> carbonated fraction> residual fraction the results showed that time had an important effect on the chromium distribution in various soil fractions especially in short term. treatments of this section had not a significant effect on the chromium distribution in various fractions statistically except in limited cases. among the most important results of this phase, we can cite the increased contribution (percentage) of chromium to exchangeable fraction with increased level of chromium in soil and this is so important from the environmental point of view. key word: chromium, organic matter, fraction