ارزیابی فلزات سنگین ناشی از ریزگردهای بیابانی در اکوسیستم‌های مرتعی استان خوزستان

ریزگردهای بیابانی که از غرب به استان خوزستان وارد می ‌شوند، به فلزات سنگین آلوده هستند و می توانند اکوسیستم منطقه را با خطر آلودگی مواجه سازند. شناسایی غلظت فلزات سنگین در ریزگردها و خاک مرتعی مناطق میزبان، می‌ تواند میزان آلودگی منطقه را نمایان سازد و راهکاری برای حفاظت از سلامت موجودات زنده نشان دهد. برای دستیابی به این رهیافت، در پژوهش حاضر هشت منطقه در استان خوزستان تعیین شد و در دو بازه ی زمانی دوره ی سرد و گرم سال، ریزگردهای جوی توسط تله های رسوب گیر جمع آوری شد. سپس طی 6 مرتبه، از خاک مرتعی این هشت منطقه نمونه ‌برداری شد. در آزمایشگاه نیز غلظت فلزات سنگین شامل سرب (pb)، روی (zn)، کادمیوم (cd) و منگنز (mn)، در ریزگردهای جوی و خاک مرتعی اندازه گیری شد. به ‌منظور ارزیابی آلودگی خاک مرتعی، از شاخص زمین ‌انباشتگی igeo استفاده شد. نتایج نشان داد که بیشینه ‌ی فلز سرب در ریزگردهای جوی آبادان (40.3)، روی و کادمیوم در اهواز (365 و 1.72 میلی گرم در کیلوگرم) و منگنز در آبادان (548 میلی گرم در کیلوگرم) بود. غلظت فلزات سنگین در ریزگردهای جوی دوره ی گرم سال نیز بیش از دوره ی سرد سال بود. نتایج غلظت این فلزات در خاک مرتعی نشان داد که در خاک‌ های مرتعی غرب استان خوزستان بیش از مناطق شرقی آن، فلزات سنگین وجود داشت = و بیشینه ی آن در مراتع آبادان و کمینه ی آن در ایذه بود. الگوی فلزات سنگین در ریزگردها و خاک مرتعی منطقه، mn>zn>pb>cd بود. بیشینه‌ ی غلظت سرب، روی، کادمیوم و منگنز به ترتیب با میانگین 140.3، 450.16، 0.81 و 561 میلی گرم در کیلوگرم، در خاک مرتعی ایستگاه آبادان مشاهده شد. ارزیابی آلودگی نیز نشان داد که مناطق غربی استان از لحاظ سرب، روی و کادمیوم، در طبقه‌ ی بسیار آلوده قرار داشتند و مناطق شرقی آن در طبقه ‌ی کمی آلوده. بنابراین ورود ریزگردهای بیابانی به منطقه، دلیل اصلی افزایش و تجمع فلزات سنگین در خاک های مرتعی غرب استان خوزستان بود.

Evaluation of heavy metals from desert dust in rangeland ecosystems of Khuzestan province

Extended abstract1 IntroductionDesert dust is formed under the influence of special weather and environmental conditions in desert areas and enters the atmosphere. Local hurricanes caused by surface air instability, passing through dry deserts, remove silt and sand particles from the surface and enter the atmosphere. Desert dust physically, in addition to its ecological effects such as lungheart disease, disruption of the physiological cycle of the plant and erosion of culturalstructural buildings, contains heavy metals that are deposited on the soil surface, water surface and canopy surfaces of plants which cause chemical changes and physiological damage to environmental ecosystems. Heavy metals are generally referred to as a group of metal elements which have a specific gravity greater than 6 g/cm3 and an atomic weight of more than 50 g. The heavy metals that are important from an environmental point of view include: cadmium, arsenic, cobalt, vanadium, zinc, mercury, iron, manganese, nickel, lead, chromium and copper, which are nondegradable in nature. Furthermore, long life expectancy of the heavy metals is also considered as a very important environmental pollutant. Due to the environmental effects of heavy metals on soils, the present study tries to identify the concentration of heavy metals in Khuzestan province. In addition to monitoring the concentration of heavy metals caused by desert dust at a height of 2 meters above the ground, the concentration of metals in surface soil rangelands were measured. 2 MethodologySeveral location on Khuzestan province were selected for carrying out the experiment which include the rangelands around the cities of Dezful, Shousha, Ahvaz, Abadan, Ramhormoz, Behbahan, Izeh and Shushtar. A sediment trap was then installed in these selected locations at a height of 2 meters above the ground to trap the fine dusts after each dust storm. The collected fine dust is then transferred to the laboratory to measure the concentration of heavy metals. The heavy metals that were measured in atmospheric particulate matter included lead, zinc, cadmium and manganese. Moreover, each time the concentration of heavy metals in the atmospheric fine dust deposited in the trap was measured; the soil of the rangeland ecosystem of the same field was also sampled and transferred to the laboratory for heavy metals measurement. Finally, in order to evaluate and determine the severity of contamination of atmospheric fine dust and rangeland soil with heavy metals, Geo accumulation Index (Igeo) was used. 3 ResultsThe results showed that the maximum Pb metal in atmospheric fine dust of Abadan is (40.3 mg / kg), Zn and cadmium in Ahvaz is (365 and 1.72 mg / kg) and manganese in Abadan is ((548 mg) in kilograms). The pattern of heavy metals in the fine dust and rangeland soils of the region was Mn> Zn> Pb> Cd. The maximum concentrations of Pb, Zn, Cd and Mn were observed in the rangeland soil of Abadan station with the mean of 140.3, 450.16, 0.81 and 561 mg / kg, respectively. The concentration of heavy metals in the atmospheric fine dust of the warm period of the year was higher than the cold period of the year. The results of heavy metal concentration in rangeland soil showed that heavy metals in rangeland soils in the west of Khuzestan province were more than its eastern regions and its maximum was in Abadan rangelands and its minimum was in Izeh.Pollution assessment also showed that the western regions of the province are in a very polluted category in terms of Pb, Zn and Cd; But the eastern regions of Khuzestan province were in a slightly polluted category. Therefore, the entry of desert dust into the region is the main reason for the increase and accumulation of heavy metals in the rangelands of western Khuzestan province. 4 Discussion ConclusionsAccording to the experiment done on different regions of Khuzestan provience, the desert dust that enters Khuzestan province contains high concentration of heavy metals which can lead to many environmental problems. Desert dust mostly enters Khuzestan from the west and settles in western parts of the country which reduce wind speed and affects its ecosystem negatively. Due to the fact that the concentration of heavy metals in atmospheric dust and soils of the western regions is higher than its eastern regions, it can be concluded that dust deposition is the main reason for the increase in heavy metals in the rangelands of western Khuzestan province.