Investigation On Mechanism Of High Arsenic Groundwater Formation In Chinese Loess Area

Many groundwater in Chinese Loess Plateau area is characterized by high concentrationarsenic. Anaerobic bacteria have been considered to act key roles in promoting arsenicreleasing from loess to groundwaters. However, this hypothesis remains unconfirmed. Basedon modeling experiments, this study investigates the speciation of arsenic in loess firstly, andthen explores the release rates and quantities of arsenic with the mediation of anaerobicbacteria. What，s more, this study simulates the actual groundwater leaching in Loess Plateauarea under oxidizing conditions and simulates different minerals in the groundwater whicheffect arsenic release during the leaching process. Select several typical ions(HPO42-, CO32-,SO42-, Ca2+, Mg2+and Na+) of groundwater and set to different concentration, explores theseions how to effect arsenic releasing from loess separately existence and co-existence.The results showed that arsenic contents in loess are between23to30mg·kg-1. There isnot obvious arsenic content difference among loess samples was observed. The ratios forspecific adsorbed, iron oxides coprecipitaed and silicate coprecipited arsenic are37.76%,36.15%and25.69%, respectively.Indigenous microorganisms, dissimilatory iron reducing bacteria (DIRB) and sulfatereducing bacteia (SRB) can all promote the release of arsenic from loess. Organic mattershighly affect the release rates. More than100mg·L-1sodium lactate is needed for all bacterialexperiments supposing obvious arsenic release is observed. On considering the redoxcondition in loess, the contribution of SRB on arsenic release in loess area is less feasible thanthat of DIRB and indigenous microorganisms.However, the concentration of arsenic in the groundwater caused by the anaerobicmicrobial reduction is far less than high concentration arsenic, loess with high porosity causethat it stays in aerobic state in most cases, so arsenic releasing caused by anaerobicmicroorganisms and mineral effects may not be the main mechanism. Therefore, it is neededto further explore other factors which cause groundwater with high concentration arsenic.Thus, we carry out the experiment under aerobic conditions, investigating the arsenic releasingdegree caused by typical ion of groundwater. Studies have shown that the arsenic release situation is different, cationic play no role in promoting arsenic release, anion play obviouspromoting role in arsenic release, especially phosphate, followed by carbonate. Then there islittle change in the release of arsenic in different parts of the Loess Plateau area.