Extractability of heavy metals in saline and non-saline soils treated with municipal wastewater under two contrasting moisture regimes

Solubility and bioavailability of heavy metals are important with respect to their toxicity. The discharge of municipal wastewater in soil and surface waters can affect bioavailability and mobility of heavy metals in soils and sediments. The effect of discharge of Arak municipal wastewater on the KNO3 and DTPA extractable heavy metals in a saline soil sampled from Mighan playa (Iran) compared to a non-saline agricultural soil was studied in two moisture regimes (field capacity and flooding) in three incubation times (1, 150 and 365 day). In the saline soil, the addition of wastewater led to increase of organic carbon (OC) and decrease of Eh, pH and EC. However, in the non-saline soil, the addition of wastewater led to increase of EC and decrease of TOC and Eh simultaneously. With very few exceptions, the addition of wastewater increased the KNO3 and DTPA extractable heavy metals significantly. These changes were higher in the saline submerged soil. So, the addition of municipal wastewater in soils for irrigation of saline and non-saline croplands was safer than when it was applied in waterlogged soils. The changes of the analyzed properties were higher in the saline soil compared to those in the non-saline soil. Hence, the resilience of the saline soil compared to the non-saline soil due to its lower buffering capacity was considerably lower. We can conclude that the release of wastewater to Mighan playa soil with high level of salinity may increase the bioavailability and mobility of heavy metals towards that lake.