Evaluation of the ecological risk of heavy metals in the sediments of coastal wetlandsCase study: coastal wetlands of Chabahar Bay, mangrove ecosystem

Document Type : Research Paper

Authors

1 Department of Civil Engineering, Technical and Engineering Faculty, Bojnord University, Bojnord, Iran

2 Department of Water Engineering, Technical and Engineering Faculty, Islamic Azad University, Central Branch, Tehran, Iran

3 Department of Geology, Islamic Azad University, North Tehran Branch, Tehran, Iran

Abstract

In this study, the concentration of heavy metals in water and sediments in four stations of Chabahar Lagoon was investigated. Ecological risk index (RI), pollution load index (PLI), and land accumulation index (Igeo) were used to evaluate the ecological risk of heavy metals in the sediment environment. To evaluate the risk of these metals to human health, the hazard index (HI) for two age groups, adults and children  was used. The results showed that the highest value of the ecological risk index occurred in station 4 with a value of 38.73 and the lowest value occurred in station 1 with a value of 21.36. The calculated RI values for all stations were less than 150, indicating that they are in the low-risk range. The highest value of the pollution load index also occurred in station 4 with a value of 0.59, which shows that the sediments of all four stations were not polluted. However, Igeo values were less than zero, which indicates that the studied sediments are in the non-polluted range. Only station 4 had a value greater than zero and less than 1 for chromium, which is in the range of pollution, not polluted to moderate with this metal. Also, risk index values for minors and adults were calculated at each station. The highest value for minors and adults occurred at station 4 with values of 0.89 and 0.59, respectively. Although HI values are less than 1, minors are more exposed to these metals than adults. These results are very worrying for minors who are a vulnerable group in society.

Keywords

Main Subjects


Evaluation of the ecological risk of heavy metals in the sediments of coastal wetlandsCase study: coastal wetlands of Chabahar Bay, mangrove ecosystem

EXTENDED ABSTRACT

 

 Introduction

Heavy metals are a group of pollutants that can cause serious environmental problems because they are very toxic, persistent, and can accumulate and magnify in living organisms, especially in coastal and marine ecosystems. Sediments are the main sink for these pollutants, and measuring the metals in sediments is important for assessing the level and risk of heavy metal contamination that can affect human health. Different indices are used to estimate the pollution and risk of heavy metals in coastal and marine environments, such as the pollution index, concentration index, potential environmental risk index, and the Pollution Factor (CF), Pollution Load Index (PLI), Land Accumulation Index (Igeo) and Enrichment Factor (EF), which can indicate the degree of heavy metal contamination.

Material and Methodology

Chabahar mangrove habitat is near Chabahar industrial city in Azad Zone, where steel and petrochemical factories discharge their wastewater into this habitat, exposing it to high levels of pollutants like heavy metals. Chabahar Bay is in the northeast of the Oman Sea and is part of a special coastal area that is influenced by changes in sea level. It covers an area of about 320 square kilometers. The samples were collected in December 1401 from the sediment (10 cm from the surface) and water according to Iranian and international standards from the selected stations. Stations S1 and S3 were chosen because they are upstream and downstream of the sewage channel, respectively, so that the impact of sewage on heavy metal concentration can be evaluated. Station S4 is where the mangrove vegetation starts and station S6 is where it ends, with a distance of about 2285 between them.

Discussion and results

The cadmium concentration along the route is almost stable and ranges from 0.25 to 0.3. The other heavy metals show different patterns, so Zn, Pb, and Ni decrease from upstream to downstream (S1 to S3), but As and Cr increase and reach their peak at station S4, and then drop to their lowest value at station S6, which is also lower than the starting station (S1). Compared to the Canadian EQG standard, Cu and Pb concentrations are lower than the standard for all four stations, indicating that the sediments are not polluted by these metals. According to this standard, stations S1, S3, and S4 are polluted by Cr, and only station S6 has a lower concentration of this metal. Stations S1 and S4 are polluted by Ni, but they are not polluted by Cd, As, and Zn. Compared to the NOAA standard, station S4 is polluted by Cu, stations S1, S3, and S4 are polluted by Cr and Ni, and in other cases where the metal concentrations are lower than the NOAA standard, the sediments are not polluted.

Conclusion

In the sediment environment, only cadmium showed a nearly constant pattern, while the other metals decreased from the first to the third station, then increased downstream, and reached their maximum value at the fourth station. The pollution load index was less than one for all four stations, indicating that they are not polluted. The highest value of the risk index was at the fourth station, with a value of 78.38, and the lowest value was at the first station, with a value of 36.21. The risk index values for four.

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