Estimates of heavy metals pollution in parishan wetland sediments using pollution indices

Parishan wetland is one of the most valuable and ecologically important ecosystems in the world which has completely dried up in recent years due to successive droughts (Dehghani, 2007). Considering that heavy metals are among the most important pollutants of the environment, their survival time is high in sediments (Ullah et al., 2017). Also, these metals have harmful effects on aquatic ecosystems, and sediments are both a source of and a place to store these elements. Acquiring information about these metals is important (Bhuiyana et al., 2010).

The purpose of this study was to estimate the level of contamination of Perishan wetland sediments with the heavy metals copper, iron, manganese and zinc using the enrichment index, geochemical accumulation index, degree of contamination and the comprehensive pollution factor index. In this study, 40 sediment samples with a weight of 200 g were systematically harvested. After acid digestion and filtering to read the concentration of toxic metals liberated in each sample, an AAS atomic absorption device by the Thermo Company (UK) was used. In this study, because of the lack of any specific standard for soil contamination in our country, standards from other countries were used. The average concentration of the metals studied in the region is lower than the maximum acceptable concentration (mg / kg) for the countries of Poland, Canada and Australia.

The changes in pH and electrical conductivity (Ec) were calculated in the range of 2.7-9.2 and 4.2-34, respectively, and the concentration of heavy metals based on mg/kg was found in most samples including manganese (2.18-3.71), iron (3.6-4.26), zinc (2.15-8.3) and copper (5.3-8.13), respectively. The background concentration for manganese, copper, iron and zinc was 950, 50, 41000 and 75 mg/kg, respectively. The geochemical accumulation index, the pollution factor and the comprehensive pollution factor
index were all used to determine contamination levels in the area. The geochemical accumulation index was less than zero for all metals, which shows the non-contamination class of the area. In addition, the factor of contamination index for most of the samples was in the class unpolluted, and the contamination factor for all metals was less than one, so that all data were placed in the non-contaminated class. The results also showed that the elements of manganese, copper, iron and zinc have a geological and agricultural origin, while the concentration of metals in the soil was related to their natural origin.

Finally, it can be stated that the studied area has the lowest risk of contamination with heavy metals. In fact, it can be said that the copper, iron, manganese and zinc found in this region have a geological origin and they change through the natural processes of geology and through springs in the wetland.