Determination of arsenic and sulfur anomalies in the soils of Dasht-e-Khash, SE Iran: long-term effects of the Taftan volcano

In this research pollution of soil samples from the southern slopes of the Taftan volcano, SE Iran, and the Khash Plain to the south of the volcano is studied. The concentrations of Arsenic and Sulfur in the soil samples are 6-14 ppm and 0.03-0.51 wt.%, respectively, both more than the quality standard values of USEPA. Pollution zoning maps indicate that samples from Khash Plain to the south are, generally, more polluted in comparison with the samples from Taftan slopes to the north of the area. This phenomenon is associated with an increase in the fine-grained portion (silt-clay), and the pH of the soil samples. It is inferred from the comparison of the AS and S contents of the Khash Plain aquifer (0.005-0.1 and 72-528 mg/L, respectively) and the groundwater pollution zoning maps that water-soil ion-exchange reactions have played important role in the soil pollution processes. Some significant arsenic anomalies in the soil sample, despite the lack of the same in the groundwater, are attributed to arsenic mineralization due to Taftan hydrothermal activities. The mineralization is related to mercury-gold generation in the area which is usually accompanied by arsenic sulfide minerals realgar, AsS and orpiment, As2S3. Therefore, hydrothermal activities of the Taftan volcano produce a particular effect on arsenic and sulfur soil pollution.