Sorption of Bioavailable Arsenic on Clay and Iron Oxides Elevates the Soil Microbial Activity

In this study, the effects of As-contaminated groundwater by various minerals in the soil were evaluated. The influence of As on microbial inhibition and activities influenced by soil minerals such as clay minerals (bentonite and kaolinite) and iron oxides (hematite, goethite, and magnetite) were investigated. The method used to evaluate the effects of soil minerals on As-contaminated groundwater was to indirectly measure microbial activity by two methods, measurement of optical density (OD) and fluorescein diacetate (FDA) hydrolysis. This study used Pseudomonas jinjuensis, a microorganism commonly found in soil and groundwater. The measurement of OD is a simple and quick method of identifying the growth of microorganisms, affecting turbidity up to dead cells after dead phase, making it difficult to identify actual living microorganisms; thus, it was inappropriate for toxicity assessment. However, the use of FDA is able to measure the bioavailability of microorganisms due to actual As contamination by the luminescence of the fluorescein caused by the enzymes of living microbes. The bentonite and hematite showed that promoting bacteria activity of 140.5% and 7.9%, respectively, and reducing the negative impact from As to bacteria, constantly, magnetite had a negative impact on bacteria activity. These results indicate that the clay minerals and iron oxides influenced the bioavailability of As in groundwater. Also, surface area and cation exchange capacity (CEC) of clay minerals and iron oxides were important parameters on the bioavailability of As.