Document Type : Research Paper
Environmental sciences Department, Islamic Azad University, Isfahan (Khorasgan) Branch, Isfahan, Iran
Waste and Wastewater Research Center, Islamic Azad University, Isfahan (Khorasgan) Branch, Isfahan, Iran
Department of Biology and Aquaculture, Artemia and Aquaculture Research Institute, Urmia University, Urmia, Iran
Unfortunately, in the past decade, the growing trend of various human activities, despite the benefits, has brought major environmental challenges to humans, among which, aquatic ecosystems are exposed to serious risks due to their higher developmental capabilities. The physical and chemical parameters of water are constantly changing, and therefore are not suitable indicators for water quality monitoring. Sediments are the most important part of lithosphere, since they are final accumulation site for potentially toxic elements in aqueous ecosystems and in maybe could be a source of water pollution. Therefore, sediments are suitable indicators for environmental pollution. One of the most important international wetlands in Iran is Urmia lake. However, human and natural factors have caused problems in the lake in 2 past decades. Urmia lake is one of the largest saline lakes in the world, comparable to the Great Salt Lake in the United States. The Urmia Lake bridge, is the largest and longest bridge in Iran, and crosses Lake Urmia, connecting the provinces of East Azerbaijan and West Azerbaijan. This project was completed in November 2008. The construction of the causeway for the bridge, along with other ecological factors, will contribute to the drying up of Lake Urmia, turning it into an inland salt marsh, and adversely affecting the climate of the region. The 1,276 meters’ gap in the causeway is not wide enough to permit and adequate flow between the two portions of the lake. Therefore, this study aimed to evaluate the arsenic contamination in Urmia Lake sediments and the possible reasons for the arsenic pollution in this valuable ecosystem.
Materials and Method:
Based on distances and covering the study area, 12 stations on both sides of the highway, has been selected. Sediment samples were collected in autumn and winter at a depth of 30 cm and arsenic concentration of each sediment sample was measured. The sediment samples were collected by plastic shovel and placed in thick polyethylene plastic bags. Finally, all samples were placed in ice and transferred to the laboratory in less than 24 hours and stored in the freezer. For acidic digestion of the samples, the samples were kept at ambient temperature to freeze and dry. After the samples lost their initial moisture at laboratory temperature,
The Geo-Accumulation Index:
The Igeo index was calculated based on equation 1:
Igeo = Log2 [Cn/(Bn*1.5)] (1)
Cn: The measured concentration of examined metal in the sediment.
Bn: The geochemical background value in the Earth’s crust: 6.8 for As, 14.8 for Pb and 0.1 for Cd
The value “1.5” is introduced to minimize the effect of the possible variations in the background values which might be attributed to lithological variations in sediment.
This method is based on the contamination degree(Cd) of each pollutant.
Cd = Mx/Mb (2)
Mx is metal concentration in the sample and Mb is background value in the Earth’s crust.
The total average concentration of arsenic in the lake is 7.48 mg /kg. The average concentration of arsenic at stations 4 and 11 is significantly higher than the ISQGs standards (7.24 mg/kg).
Table 1. Muller and contamination degree results
Station Igeo(autumn) Igeo(winter) Cd(autumn) Cd(winter)
-0.12 1.99 1.38
2 -1.35 -2.12 2.24 0.34
3 0.14 -1.31 6.28 0.60
4 0.14 0.94 6.25 2.87
5 -0.58 -0.44 3.79 1.10
6 -5.68 -4.25 0.11 0.08
7 -0.98 -0.36 2.88 1.17
8 -1.19 -0.41 2.49 1.13
9 -0.07 -0.11 5.43 1.39
10 -0.21 -0.37 4.91 1.16
11 0.07 0.22 5.96 1.75
12 -0.1 -0.99 5.31 0.75
The average concentration of arsenic at station 4 in the central area of the lake and station 11 in the east of the lake is significantly higher than the global standard, which is about station 11, due to the estuaries of the rivers that put a significant load of pollutants to the lake. Station 4 is also located near the estuary of the western riverside. The results of the chemical indices also put stations 4 and 11 in the remarkable to very high contaminated category. Among all the stations, station 6 has the least contamination of arsenic, which can be due to being located in the central area of the lake and away from pollution sources.
More than 20 permanent and seasonal rivers and 49 river streams cross into Lake Urmia, and each year it adds a considerable amount of suspended matter with high absorption capacity. Which can be the main source of heavy metals concentration, including arsenic. Agricultural activities and especially fertilizers, herbicides, fungicides and insecticides containing arsenic. Also, the discharge of urban and rural sewage into the lake and the rivers can be a major factor in increasing of arsenic in sediments. In a study by the Remote Sensing Research center of Sharif University of Technology, some areas of the Urmiah lake, have been identified as potential dust centers. the center of the 2 in the east of Lake Urmia has overlap with east stations in the present study, especially Station 11. According to studies, the wind direction dominates from Lake Urmia towards the city of Tabriz in winter. Therefore, in the case of drought in Urmia Lake, high-concentration arsenic and other heavy metals can have unfortunate consequences for the health of the population in affected areas.
Due to the closure of the Urmia Lake, all the pollutants are accumulated in the lake. For this reason, the continuous monitoring of river water entering the Urmia Lake can be very helpful in understanding the changes in ecological status of Lake. Urmia Lake is located in Azerbaijan as the industrial-agricultural heart of Iran. Lack of standard system for wastewater treatment, use of fertilizers, herbicides, fungicides and insecticides containing arsenic in the agriculture and finally discharge of urban and rural wastewater drainage caused by leaching of land. Lake farming as well as the effluent of nearby factories into the lake and rivers leading to it can be a major contributor to the increase in arsenic in the sediments.
Urmia Lake is one of the most international wetlands also 105 important bird areas(IBA) of Iran. One of the most important values of Urmia Lake National Park is its habitat suitable for wildlife, migratory birds and aquatic life. Urmia Lake is habitat to many aquatic birds as wintering, summering and inbreeding habitat. Heavy metals can accumulate in kidney, liver, muscle, bone, feather, blood and eggs of birds. Various studies have shown that weight loss also reproductive, behavioral and nutritional disorders in birds are due to heavy metals. Inorganic arsenic can cause muscular dysfunction, slowness, falls and other symptoms in birds. Arsenic transfer in the form of arsenobetaine and dimethylarsinic from the female to the eggs. In addition, the negative impact of sediment heavy metals on the abundance and density of organisms as well as on the morphological characteristics of organisms have been proved. Thus, increasing the heavy metals contamination such as arsenic in sediments, can be an alarm signal for the continued generation of birds and other aquatic organisms in the lake. Then, monitoring of the rivers, prevention of overuse of fertilizers and pesticides, preventing industrial and agricultural effluents and municipal wastewater from discharging to the lake, can be used to reduce the pollution load of this valuable ecosystem.
Keywords: Arsenic, Sediment, Urmia Lake, Particulate matters (PMs)