Ecological risk assessment of heavy metals in coastal sediment of Bandar abbas city

Although heavy metals are components of the earth's crust and are naturally present in all ecosystems, their concentrations are increasing significantly. In recent decades, a significant portion of marine environmental pollution has been due to the entry of heavy metals into marine environments and their harmful environmental effects have been a major topic in environmental research. Although the increasing development of industry has numerous benefits, but unfortunately it also leads to special problems such as environmental pollution and threatens all human activities in relation to nature.The main problem with heavy metals is that these inorganic pollutants are not biodegradable unlike organic pollutants, and this fact has made heavy metals one of the most dangerous groups of environmental pollutants. Heavy metals enter aquatic ecosystems through direct discharge of industrial and municipal effluents or indirectly through rainwater runoff as well as through the atmosphere, and cause serious problems, especially by accumulation in sediments. Due to their stability and lack of biological decomposition, heavy metals have a high tendency to accumulate in the body of aquatic organisms and accumulate in the tissues of mollusks, bivalves and fish.The results of Bagheri et al., (2013) in surface sediments of Bandar Abbas coasts show that more than half of all lead and cadmium in Bandar Abbas coasts are of natural origin and the increase in metal concentration in Bandar Abbas coasts due to the presence of these two amounts is more It is natural in the earth's crust in the study area.Heavy metals can enter this ecosystem due to natural factors such as erosion, floods, seawater rotation, industrial and human wastewater, oil and gas leaks, ship accidents, and unbalanced water discharge. As a result, ecosystems such as industrial coastal ports, which are chronically exposed to metals, appear to have the most contaminated sediments, leading to ecological changes on the coast and endangering human health due to their toxic effects and bioaccumulation potential.One of the most important environmental problems of Bandar Abbas city at present can be the entry of sewage and waste into the coasts and estuaries of the city, which minimizes tourism uses. Since most of the urban wastewater of Bandar Abbas and some industrial wastewater is discharged directly into the sea, the coastal waters of Bandar Abbas are heavily polluted and any aquatic abstraction from the coastal waters and swimming in these waters can be due to pollution. Preliminary studies show that the beaches of "Shilat", "Gorsuzan", "Posht-shahr", " Soro" and "Hadish" are the main swimming areas of the indigenous people and at the same time the main receiving areas of Bandar Abbas urban sewage. The purpose of this study was to assess the ecological risk of heavy metals in coastal sediments of tourism-prone areas in Bandar Abbas, Hormozgan province.

For the purpose of study, a systematic randomly classification method was used to determine the sampling points. Thus, 5 potential tourist destinations along the coast of Bandar Abbas, including the beaches of Shilat, Gorsuzan, Posht-shahr, Soro and Hadish, were randomly selected to cover the entire coastal strip of the city and were sampled as points. Sampling was performed in the spring of 2020, at full tide and almost daily between 10 and 15 o'clock. Acid digestion of the samples was performed and after purification, the concentration of each metal element was measured by atomic absorption spectrometry using calibration solutions.For the data analysis, at first, the compliance of the data with the normal distribution was examined by the Kolmogorov–Smirnov statistic quantifies test, which showed that the data have a normal distribution. After confirming the normality of the data, heavy metal concentration analysis was performed. Pearson's correlation coefficient also was used to investigate the correlation relationship between metal concentrations. Finally, the sediment quality was assessed using pollution indices and ecological risk assessment index.

According to the results, the average concentrations of elements including lead (pb), copper (Cu), nickel (Ni), cadmium (Cd), zinc (Zn) and iron (Fe) in the coastal sediments of Bandar Abbas areas were 46.75±5.75, 17.75±1.52, 62.42±4.51, 2.97±0.13, 46.09±4.56and 9944.04±1463.49, mg/kg sediment, respectively. The results show that the sequence of total concentration of heavy metals in the coastal sediments of Bandar Abbas is Fe> Ni> pb> Zn> Cu> Cd.Analysis of the correlation shows that there is only a significant correlation between iron and nickel (P <0.05) and there is no significant correlation between other elements (P> 0.05).Heavy element coefficients factor in coastal sediments of Bandar Abbas for lead, copper, nickel, cadmium, zinc and iron, were calculated 2.34, 0.39, 0.92, 9.89, 0.49 and 0.21 respectively. Furthermore, the Cd index in the five sampling stations including the beaches of Shilat, Gorsuzan, Posht-shahr, Soro and Hadish were calculated 1.42, 2.41, 1.17, 1.45 and 1.19, respectively.Based on the the Müller geochemical index, the amount of lead in Hadish is in the range of non-polluted to medium polluted and in other stations were in the range of non-polluted.In total, the measurement of potential ecological risk for the five sampling stations mentioned was calculated as 317.6, 327.2, 331.5, 331 and 270, respectively, and the total potential ecological risk of the coasts of Bandar Abbas was calculated as 315.5.

The computational results showed that the average accumulation of Cu, Ni, Zn and Fe is negative (Igeo ˂ 0), the negative of these data indicates that the coastal sediments of Bandar Abbas in terms of these elements are in the range of non-polluted sediments. The value of this measurement was calculated for lead less than one (0˂Igeo˂1) and for cadmium less than 2 (1˂Igeo˂2), which include the ranges from non-polluted to moderate pollution and moderate pollution, respectively.Comparison of heavy elements studied in this study with different standards showed that the amount of all elements except nickel is lower than global standards. The study of the ecological risk of heavy metals in the coasts of Bandar Abbas showed that the order of danger is (zinc Assessing the quality of sediments showed that the amount of modified degree of pollution index (mCd) in all cases except Gur-suzan were calculated less than 1.5 and the status of sediment pollution is estimated to be very low degree of pollution. In total, the ecological risk potential of the coasts of Bandar Abbas was calculated to be 315.5, which is within the acceptable ecological risk.Considering the location of Bandar Abbas city and considering the development of adjacent areas and various ongoing projects in the city and the pollution load caused by the entry of municipal sewage into the coast of Bandar Abbas, it is necessary to adopt appropriate strategies that can help to reduce pollutants. In this case, considering the certainty of the role of industries in polluting the coasts of Bandar Abbas and considering the conclusions obtained in this study, it is necessary to observe the rules and standards of environmental protection and apply these rules in neighboring industries.