چكيده لاتين :
Just as the world we inherited today, is what our past generation left on us, the future generations would inherit the legacy we leave for them. Water is essential for life on earth. Water is a unique liquid, without it, life as we know is impossible. Water the "Elixir of Life" is facing a severe threat due to pollution. Water, due to its great solvent power, is constantly threatened to get polluted easily.
The requirement of water in all forms of lives, from micro-organisms to man, is a serious problem today because all water resources have been reached to a point of crisis due to unplanned urbanization and industrialization. The topic of our concern here is pollution of wetland. Heavy metals constitute an important group of environmentally hazardous substances. During this century, many wetlands in Iran have received elevated inputs of heavy metals as a result of an increase in various activities. Municipal and industrial discharges, urban storm-water runoff, and agricultural drainage can result in trace metals, nutrients, pesticides, and organic wastes being transported into aquatic ecosystems. In aquatic ecosystems, contaminants are often rapidly removed from the water column via sorption processes. Given that trace metals are not subjected to degradation processes, they tend to accumulate in benthic sediments. However, trace metals are not necessarily fixed permanently to sediments; rather they may be remobilized via chemical, physical, and biological processes.
The pollution of aquatic ecosystems by trace metals is a significant problem as trace metals constitute some of the most hazardous substances that can bio-accumulate. Metals that are deposited in the aquatic environment may accumulate in the food chain and cause ecological damage while also posing a risk to human health. Human activities have lead to accumulation of toxic metals in the aquatic sediments. Sediments and suspended particulate matters (SPM) of aquatic environment have an important role in adsorption of dissolved heavy metals, although they can be a potential source of metal pollution by releasing adsorbed metals during changing physical-chemical characteristics of the aquatic environment. Since concentrations of most heavy metals in river waters are very low and subject to highly variations during a year, sediments and SPM are good indicators of metal pollution in the river environment. In the recent year more attention has been paid to the aquatic environment. These environments are being polluted by various sources including sewages from residential, agricultural and industrial sectors.
Sediments of aquatic environment act as a major reservoir of metals and also as a source of contaminants. Enrichment of heavy metals due to industrialization and urbanization was recorded in sediments of coastal seas all over the world. The monitoring of metal contents from anthropogenic activities is particularly important for the assessment of environmental quality and protection. Metal distributions in lagoon and intertidal sediments have frequently been used to investigate chronological inputs and spatial distribution of contaminants. Enrichment of heavy metals, radio nuclides and radioactive pollutants is recorded in sediments of coastal areas like Bombay, Goa and Cochin because of industrialization. In view of this, the present study is taken up to estimate the metal concentrations in the Bamdedj wetland. The present study deals with the spatial and temporal variations of trace metal contents, their controlling factors and an assessment of the pollution levels in the surficial sediments. The study focuses to test the hypothesis that concentrations of metals subject to anthropogenic inputs would increase in recent sediments as urbanization of the watershed continued to increase.
As is well known, elements can be divided into two categories based on their biological roles, i.e. essential (or biophilous), and non-essential. The first type of elements includes a large group of metals (such as Co, Cr, Cu, Zn, etc.) which are functionally necessary for living organisms in small concentrations; however, at high levels they become toxic by interfering with necessary biochemical functions. The non-essential category of elements includes chalcophile elements such as Pb, Cd, Hg and As, which are extremely toxic and represent a serious danger to living organisms.
Subsequently amongst organic and inorganic pollutants, most of the research prefers to study the inorganic pollutants due to the ease of measurements. In the present study we have tried to measure heavy metals such as Ni, Cd, Pb, Zn, As and Hg along with Ca and Fe. For these purpose the six sediment samples were collected from Bamdedj marsh in the province of Khuzestan. Most trace metals tend to enrich in the modern organic sediments rather than inorganic sediments. Chemical bonds of metals in sediments and^PM is an important factor in detecting pollution in the particulate phase of the river. Many sequential extraction and chemical partitioning methods have been developed and applied for determination of metal bonding and pollution detection in particulate phase. It is believed that metals in adsorbed, carbonate, sulfide and organic bonds are more related to pollution and have higher risk of bioavailability and contamination of the environment. The marsh sediments, which were brown to black in color, were air-dried and passed through a 63-jim mesh (equivalent to a No. 230 sieve, ASTM E-l 1).
The sieved sediment was powdered using an agate mortar and pestle. About 0.5 g of the powdered sample was placed in a Teflon beaker containing 10 mL aqua regia. The mixture was heated until most of the liquid had evaporated, and allowed to cool before 5 mL of hydrogen fluoride (HF) were added. The samples were further cooled to room temperature before being filtered. The filtrates were transferred to 50 mL volumetric flasks and brought to volume with 1 N HC1. Chemical partition studies were conducted in four sequential steps: (1) acetic acid 25%v/v, (2) acetic acid 25% v/v-0.1 M hydroxylamine hydrochloride, (3) 30% H202 "extraction with 1 M ammonium acetate" and (4) hot 50% HC1. Trace metals (Cu, Zn, Cd, Pb, Ca, Fe and Al) were measured using a UNICAM flame atomic absorption spectrometer. Calibration curves were established using known standards. Procedural blanks and duplicates were run alongside the samples as part of the quality assurance program. The analytical accuracy was approximately ±3% for all elements. A standard sample (MESS-1) was analyzed using the same methods as an accuracy check. The Weighted Pair Group method (GWP) was used to identify clustering tendencies among the samples.
To assess the intensity of metal contamination in Shur River sediments, the geochemical accumulation index
was calculated using:
Igeo=Log2[Cn/Bn*1.5]
Where Igeo is the geochemical accumulation index, Cn is the sediment metal concentration and Bn is the metal concentration in the shale
The results of cluster analysis (Fig. 1) show that Hg and as are originated from organic sources as they form cluster "D" with LOI at a meaningful similarity coefficient. On the other hand one may conclude that Ni is mainly originated from lithogenic source since it forms cluster "B" with Fe at a significant similarity coefficient. It seems that Pb is mainly originated from biogenic source since it has developed a highly significant similarity coefficient with Ca in cluster "A".
The source of Zn and Cd (cluster C) cannot be furnished through cluster analysis. The results of geochemical studies show various concentrations for studies metals. While using Igeo index, we noticed that Hg fall within the category of "high pollution" in sediments of Bamdedj marsh. This is clearly evident through bulk chemical analysis as well as chemical partitioning studies. The elements such as Fe and Zn fall within "no pollution" class. Therefore, we can suggest a lithogenous source for Zn. Through cluster analysis we could not bring out a proper source for Zn but combination of chemical analysis and cluster analysis can show a better means of interpretation of data. It should be pointed out cadmium falls within "medium pollutionʹ class according to geochemical index.
Ca Fe Ni In Cd Hg As LOI
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Fig. 1: Cluster analysis for studied metals in Bamdedj marsh sediment
It seems that a great portion of metals have been incorporated into the sediments through usage of agricultural fertilizers that are being widely used by farmers. It can be concluded that agricultural activities are the major source for distribution of metals in Bamdedj sediments since there are not any industrial activities in the vicinity of marsh. It should be pointed out that sewages from residential sector can also contribute to the metal pollution in marsh. The presence of Ca in loosely bonded ions can be attributed to the nature of Ca to dissociate from contaminant sources at lower pHs. A higher pollution. Herewith, we suggest that Environmental Planning Management (EMP) should be prepared to monitor the pollution in marsh from time to time. The EMP should be simple with minimum parameters (such as Hg as an indicator) and the period of measurement should be feasible and economical. Also the future studies should focus on sediment and water interaction to know about the risk assessment of metals in dissolved form. On the other hand, the bio-availability of the metals should be examined in the sediments to possible know about the risk of transfer of metals into the aquatic life of marsh.
