Evaluation of the effects of arsenic contamination on soil enzyme activity and bacterial diversity
Arsenic in soil results from human activities including pesticide use, mining, ore processing operations, waste disposal, and smelting. The contamination of soils by arsenic and heavy metals is an important issue, because of the adverse effects that it may have on food quality, soil health, and the environment. Arsenic is toxic to most of the known bacteria, which are critical to the maintenance of the soil’s ecosystem functions. Oxidized forms of arsenic have been reported to cause enzyme inhibition and competitive substitution of phosphate due to the resemblance between arsenic and phosphorous compounds, especially in aerated systems. A wide range of microorganisms has been reported to develop immunity to arsenic toxicity due to development of resistance to the presence of arsenic. The importance of assessing the impact of arsenic contamination on microbial properties is predicated on the premise that microbes are instrumental in nutrient cycling and are strong soil quality indicators. Understanding the effect of arsenic on the composition and function of microbial communities that can tolerate arsenic toxicity can be useful in developing technologies for soil remediation. The objective of this study is to determine the effects of arsenic concentration and type on soil microbial composition through: an assessment of soil microbial function by utilizing Phosphatase and β-glucosiadase enzyme assays; and understand the effects of arsenic on microbial communities pertaining to soil quality and nutrient cycling. Treatments included Arsenic (III) treated soil and Arsenic (V) treated soil with three different dosage amounts (1 ppm, 5 ppm, and 10 ppm) along with a control in a soil microcosms setting. Samples were assayed for Phosphatase and β-Glucosidase enzyme activity, and microbial composition and diversity was examined using the PowerSoil Extraction Kit (MOBIO). DNA extractions quantified the presence of DNA in significant concentrations in soils treated with arsenic, signifying the survival of microbial populations.
Phosphatase and β-Glucosidase assays showed that significant enzymatic activity was present at individual levels within the treatments. β-Glucosidase even showed increased activity in the presence of 5 parts per million of Arsenic (III). Microbial communities expressed significant changes in proteobacteria classes and specific species such as Massilia timonea, which were found to be associated with carbon cycling. Further results shows that not only are bacteria able to withstand arsenic, but in some cases can possibly reach comparable levels of function to uncontaminated soils in the presence of arsenic.