غلظت فلزات سنگين در خاك‌هاي اراضي فضاي سبز شركت فولاد مبارك

آب و خاک  

دوره 30 - شماره 5

نوع مقاله: Original Article
چكيده: با توجه به كمبود آب در نواحي خشك و نيمه خشك كشور، استفاده از آب هاي نامتعارف نظير فاضلاب هاي تصفيه شده جهت آبياري گياهان ضروري است. شركت فولاد مباركه جهت آبياري قطره اي حدود ۱۳۵۰ هكتار از اراضي فضاي سبز خود از فاضلاب صنعتي تصفيه شده اين مجتمع استفاده مي كند. لذا اين مطالعه به منظور بررسي تأثير آبياري با پساب تصفيه شده اين شركت به مدت ۲، ۶ و ۱۸ سال بر غلظت فلزات سنگين خاك در مقايسه با آب چاه و خاك بدون آبياري انجام گرفت. بدين منظور از ناحيه پياز رطوبتي درختان از سه عمق ۲۰-۰، ۴۰ -۲۰ و ۶۰-۴۰ سانتي متر نمونه‌هاي خاك تهيه و غلظت قابل دسترس و كل فلزات سنگين در آن‌ها اندازه گيري گرديد. نتايج اين مطالعه افزايش معني داري را در غلظت آهن، مس، روي، سرب، كادميم و نيكل قابل دسترس در خاك هاي آبياري شده با پساب به مدت ۶ و ۱۸ سال نسبت به خاك بكر (نمونه شاهد) نشان داد. مقادير كل فلزات سنگين نيز نسبت به نمونه شاهد افزايش يافت ولي غلظت اين فلزات بطور قابل توجهي كمتر از استانداردهاي سازمان محيط زيست كشور بود. بنابراين، استفاده از پساب حاصل از تصفيه فاضلاب صنعتي، حتي در درازمدت، سبب آلوده شدن خاك هاي اراضي فضاي سبز شركت فولاد مباركه نشده است. بنابراين، آبياري اراضي جنگلي با پساب تصفيه شده مي تواند به عنوان روشي مناسب در مديريت بحران آب در مراكز صنعتي كشور مورد استفاده قرار گيرد.
Soil Heavy Metal Concentrations in Green Space of Mobarake Steel Complex
Article Type: Original Article
Abstract: Introduction: Water shortage in arid and semiarid regions of the world is a cause of serious concerns. The severe water scarcity urges the reuse of treated wastewater effluent and marginal water as a resource for irrigation. Mobarake Steel Complex has been using treated industrial wastewater for drip-irrigation of trees in about 1350 ha of its green space. However, wastewater may contain some amounts of toxic heavy metals, which create problems. Excessive accumulation of heavy metals in agricultural soils through wastewater irrigation may not only result in soil contamination, but also affect food quality and safety. Improper irrigation management, however, can lead to the loss of soil quality through such processes as contamination and salination. Soil quality implies its capacity to sustain biological productivity, maintain environmental quality, and enhance plants, human and animal health. Soil quality assessment is a tool that helps managers to evaluate short-term soil problems and appropriate management strategies for maintaining soil quality in the long time. Mobarakeh Steel Complex has been using treated wastewater for irrigation of green space to combat water shortage and prevent environmental pollution. This study was performed to assess the impact of short- middle, and long-term wastewater irrigation on soil heavy metal concentration in green space of Mobarake Steel complex.
Materials and Methods: The impacts of wastewater irrigation on bioavailable and total heavy metal concentrations in the soils irrigated with treated wastewater for 2, 6 and 18 years as compared to those in soils irrigated with groundwater and un-irrigated soils. Soils were sampled from the wet bulb produced by under-tree sprinklers in three depths (0-20, 20-40 and 40-60 cm). Soil samples were air-dried, and crushed to pass through a 2-mm sieve. Plant-available metal concentrations were extracted from the soil with diethylenetriaminepentaacetic acid-CaCl2-triethanolamine (DTPA-TEA). To determine the total concentration of heavy metals, the soil samples were digested in 6 M HNO3. Concentrations of heavy metals in the extracts were determined by Atomic Absorption Spectroscopy. Finally, available metal micronutrient levels in the soil were compared with the critical deficiency ranges suggested for calcareous soils. Also, total concentrations of the metals in the soils were compared with the standards of the Iranian Environmental Protection Agency to assess possible contamination of soils with heavy metals in the studied area.
Results and Discussion: The results of this study showed significant increases of plant-available Fe in the soils irrigated with wastewater for 6 and 18 years as compared to the unplanted control. Regardless of the type of irrigation water used, available Mn and Ni were significantly increased in all forested areas as compared to the unplanted soils. Available Zn fraction was significantly higher in the soils with history of 6 and 18 years of wastewater irrigation. Increase in available Cu concentration was statistically significant only in the soils irrigated with wastewater for 18 years. As the metal concentration in the wastewater used for irrigation was very low, it seems that the major source of metal accumulation in the soils is particulate fallout or emissions directly from the dump sites and metal plating operation. Furthermore, irrigation and forestation practices might have improved bioavailability of micronutrient metals in the soils of green space of Mobarakeh Steel complex through increasing organic matter content of the soils which enhances metal chelation reactions. Total concentrations of the metals in the forested soils also increased as compared to those of the control. Total Fe, Mn, and Zn concentrations were notably higher in all soils of the green space area as compared to those in the unplanted control sites. Wind-driven particle transport from dumping site to nearby soils may be the main reason for metal build-up in the green space soils. Total concentration of Cu showed no significant difference among the soils of the treatments and the control. Although metal accumulation has been occurring in the soils of the Mobarakeh Steel complex green space, total concentrations in the soils were still considerably lower than the allowable levels recommended by the Iranian Environmental Protection Agency.
Conclusions: The results of this study revealed that metal accumulation has been occurring in the green space soils of the Mobarakeh Steel complex. Considering the short distance of the dumping and metal smelting sites with the green space and very low concentrations of metals in wastewater, in may be concluded that fall out of metallic particles on the soil surfaces from the dumping and smelting sites is the main route for metals accumulation in the soils of the green space areas.
قیمت : 20,000 ريال