Evaluation of Risk Potentials and Determination of Zn, Pb and Cd Source in Soil around Angouran Mineral Processing Complex

Soil is a bed to the accumulation of nutrients and pollutants and plays an important role in environmental sustainability. Among all types of soil pollutants, heavy metals are considered as a major threat to environmental health due to their non-degradability in the environment and their long life span. Heavy metals are naturally present in the earth's crust. Rocks and minerals have a high impact on the concentration of elements in the soil and sometimes increase the concentration of the elements in the soil beyond the permitted level. Besides, human activities such as mining and related processing cause heavy metals propagation in the environment. Angouran Mineral Processing Complex includes Zinc and Lead Concentration Complexes and Zinc Factory is located in Dandi, Mahneshan city, northwest of Zanjan, Iran. Because of industrial activities development, some heavy metal processing has led to increasing their concentration in soil and other environmental media. hence, the purposes of this study were to determine the spatial pattern of Zn, Pb and Cd spreading around Angouran Mineral Processing Complex, to investigate their potential risk using different environmental indices, to identify ecological risk and carcinogenic risk, and to determine the contribution of anthropogenic and geogenic origin.
Angouran Mineral Processing Complex, with the geographical coordinate of 36°34′20 ˝N and 47°37′40 ˝E. The area is located in a metamorphic complex of the Sanandaj-Sirjan microplate in the Zagros orogenic belt affected by the Tertiary to Quaternary volcanic activities as well as the geothermal activities of the Urumieh-Dokhtar zone. It is composed of the present age river banks and alluvial deposits in the center along with conglomerate and red tuffs in the northern part.
Soil sampling was done from 0-20 cm depth in June 2016 (n=74). After the preparation of the samples, they were sent to the Zarazma laboratory for analysis of Zn, Pb, and Cd by ICP-OES. Statistical analysis of the data and index calculations were performed using Excel and SPSS software. Also, PMF 5.0 EPA (Positive Matrix Factorization) software was used to determine the source contribution to metal dispersion. Applied indices include enrichment factor (Ef), Geoaccumulation index (Igeo), pollution load indices (PLI) and modified pollution degree (mCd), ecological risk potential (PERI) and cancer risks (CR).
The soil in the study area is in a poor and serious condition that threats agriculture and animal husbandry, the main activities besides the industrials. Zn had the highest concentration with an average of 1648.1 ppm in the region and fallowed by Pb and Cd with a mean of 467.9 and 9.8 ppm, respectively.
The Igeo mean for Pb, Zn, and Cd were 1.7, 2.0, and 0.4, respectively, which indicated average contamination of Pb and Zn and non-contaminated to intermediate contamination of Cd. Igeo's result showed that the metals accumulation order was Zn> Pb> Cd. The extent of metal contamination was -2.4 to 8.9 for Pb, -0.4 to 8.3 for Zn, and -2.4 to 7.1 in terms of Cd, suggesting negative values for these metals which are in the range of non-polluted soils. High Cd contamination was observed only in 4.9% of the samples while EF showed high Cd enrichment (72/1). The mean Ef calculated for Zn, Pb and Cd were 37.1, 45.7 and 72.1, respectively, suggesting strong enrichment for Zn and Pb, but extremely strong for Cd. Cd is the most mobile metal in the soil and is likely to be absorbed through the plant's roots. The enrichment degree for all three metals in the region is wide. Contamination severity (Ff>10) in total observed for Zn, Pb, and Cd in 29.6%, 25.6% and 59.4% of samples, respectively, which indicates the very high impact of anthropogenic contamination sources. In general, it can be concluded from the Igeo and Ef index that samples collected from this area have enriched and contaminated by the examined heavy metals.
Given the various toxic effects of metals on the human body, the PERI index of metals in the soil varies from 42.8 to 35500.5 and showed a high environmental risk for Cd than for Zn and Pb. Based on the classification, 35% of sampling points showed high ecological risk.
The metal contamination degree in the soil was higher than expected. In the study area, mCd ranged from 0.8 to 723.4 and 60% of the samples showed high contamination. PLI calculation showed that the contamination range is between 0.7 and 627.8. The contamination range calculated by mCd and PLI revealed that 60% and 40% of the area is in very poor and inappropriate conditions, which shows a significant risk in agricultural land use.
CR for adults ranges from 0.2×10-2 to 0.5×10-5 while the mean is 0.1×10-3. Unexpectedly, Zn with an impact of 96.9% had the highest share in the carcinogenic risk of ingested contaminated soil. CR for children varies from 0.4×10-2 to 0.9×10-5 with a mean of 0.2×10-3. Similar to the results obtained from adult CR, Zn with 99.1% had the greatest effect on the carcinogenesis probability due to ingestion. Based on the CR classification, the risk was a middle and upper class for children.
The CR calculation for children and adults showed that the ingestion risk of contaminated soils contain Zn had the greatest effect on the risk of carcinogenicity and health problems. Absorption via skin and respiration of Zn, Pb and Cd were the next highest risk factors. Soil and dust ingestion was a potential source of exposure to environmental chemicals for both adults and children. Children may, in particular, consume large amounts of soil because of their tendency to play on the ground and carry the soil coated objects to their mouths. Due to the wide range of industrial activities in the region, agriculture in the study area poses a greater risk of carcinogenicity for the adult population.
PMF model was used to quantify the contribution of the different sources in Cd, Zn and Pb pollution. Comparing the metals prevalence in each factor and the information obtained from the regional field for the probable source of heavy metals, two factors were considered to the probable source of the heavy metals. Geogenic origin was the first-factor and anthropogenic origin was the second one. According to the results, the concentration of Zn in the second factor was 99% while the first factor was 1%. Therefore, the greatest impact on Zn concentration in the region is due to anthropogenic activities. Pb and Cd the second factor were estimated to be 90.2 and 95.7%.
Therefore, there is a need to reduce the risk of exposure to soil metals in order to maintain the health of the residents 'health and sustainability of the environment and animals in the area, including soil refining.