River surface size fractioned sediments pollution with heavy metals Case study: Sefidroud river

In recent years, restrictions of fresh water resources in the world and protection of the quality of these resources cause attention of many scientists about pollution of aquatic fresh waters like rivers. One of the most river pollutants is heavy metals. Unlike the organic compounds, these elements do not disintegrate by natural processes and have toxic potential risks for living organisms and environment. Metals are the natural components of water ecosystems and most of them are necessary for organisms. Only when the contents exceed from the limitation, they can water pollutants. It is general phenomenon that metal contaminants in aquatics accumulated mostly in fine sediments. Accordingly, few studies have been done about heavy metals pollution in size fractioned sediments. This study aims to examine the changes of heavy metals concentration
in Sefidroud size fractionated sediments as one of the most important and largest river in the country using some common pollution indices. Finally, It also assessed the sources of heavy metals by using multivariate statistical analysis.
The study area was Sefidroud river in south west of Caspian Sea ,that have been located within Gilan Province .Its catchment area is about 14041km2 and is located between 50° 36' 00"and 48° 34' 00"E longitude and 38° 27' 00"and 36° 34' 00"N latitude. According to Iran Meteorological Organization reports, Gilan Province is the most rainy province with an average of 580 mm rain per year in Iran.
The Talesh Mountains and the western Alborz belt as gigantic barrier is located between this territory and Iran inland. This is the only natural connection of the Gilan territory with Iran inside plateau, and is through the Sefidrood valley. Gilan Province is composed by two following regions: The lowlands, adjacent to Caspian Sea and the mountainous region.
Moreover, important and interesting particularities of Gilan Rivers include a massive hydrographic network with a large number of rivers as well as high range of water flow in the rivers. The inundating rivers, is created by transporting circular stone pieces and blocks through under-washing the ridges overlooking the farms and orchards, threaten the cultivated areas and gardens.
According to the Iran Ministry of Industries and Mines data 60 active and 19 abounded mines are located in study area that may release heavy metals into the environment. Coal mining activities are of the examples of mine type in the catchment area.
Sampling sites were located on different geological formations in the catchment areas of the Sefidroud river. Five surface sediment samples were taken from this river from upstream to estuaries during June to July 2013.Surface sediment samples were collected by mini Ekman type grab sampler. All samples were transferred to the laboratory in sealed plastic bags under 1 to 4 °C. Grain-size analysis was carried out using wet standard sieving methods for particles larger than 38µm using sieve shaker (Analysette 3 Pro, Fritsch) and laser grain size analyzer for particles less than 38 µm (Analysette 22, Fritsch) at the Research center for applied geology, Geological Survey of Iran, Sediment logy Laboratory.The 5 collected river samples were separated into six particle size ranges; Discussion of - Size fractioned river sediment Generally, size fractioned river sediments is used for a preliminary physical characterization of sediment samples. This phenomenon is emphasized by more researchers that because of higher specific surface area in fine particles, larger pollutants such as heavy metals can present them. It was found that more than 29.1% of the river sediment particles at all of the sampling sites are between 250-500 µm.
- Size fractioned sediments and metal pollution
Total metal concentrations (Cu, Zn, Cr, Fe, Mn, Pb, Ni and Cd) and statistical parameters of 5 samples across the six particle size ranges, The aim of this research is recognizing the contamination of Sefidroud river sediments and the effects of particle size.
To reach the purpose of these research, heavy metals concentration in six sediment sizes were measured.
Generally, the results of analysis showed that by reducing the particle size, the heavy metals concentration were more than average amount of sediments and Earth’s crust.
Degree of sediment toxicity index showed that with decreasing of sizes, the indexes increasing. Finally, multivariate analysis showed that concentration of some metals like Cr and Ni were high because of anthropogenic sources. Other metals like Fe and Mn have natural sources.