Removal of heavy metals from agricultural runoff using constructed wetland; traces pollutants in reed bed sediments and plant biomass.

This study aimed to determine the concentrations of hazardous heavy metals in the Naseri Wetland of southern Khuzestan province and to investigate constructed wetlands for the treatment of agricultural runoffs. In this regard, the length of the constructed wetlands was divided into three equal segments (3.5 km in length, 1.2 km in width, and 0.5 m in depth) and the beginning of each segment was considered a sampling station as ST1, ST2, and ST3. The concentrations of major heavy metals such as Hg, Pb, Cr, Cd, and As were monitored at different stations over a period of 1 year (2020–2021). The results showed a direct correlation between pollutant concentrations in the wetland bottom sediments and those in the agricultural runoff. ST3 had the highest removal efficiency (RE%) of heavy metals compared to ST1 and ST2 (RE = 100% for all heavy metals examined). The meaning of 100% efficiency and zero concentration is that the pollutant concentration was so low that it was undetectable. In contrast, ST1, the closest station to the entry point, had the lowest RE with averages 29.99, 13.34, 21.24, 34.23, and 24.80% for Hg, Pb, Cr, Cd, and As, respectively. As a result, this system has been successful in bringing the quality of agricultural runoff to the desired standard for discharge into the environment and for agricultural purposes. Overall, in Khuzestan and other regions with similar climates, the development of constructed wetland as an environmentally friendly technology could represent a practical strategy for reclaiming agricultural runoff, although their design and operation need to be well-engineered. [ABSTRACT FROM AUTHOR]