نوع مقاله : مقاله پژوهشی

نویسندگان

گروه محیط زیست، دانشکده منابع طبیعی و علوم دریایی، دانشگاه تربیت مدرس، نور، مازندران، ایران

چکیده

سابقه و هدف:
ذرات معلق از مهم ترین آلاینده­ های هوا در شهر تهران بوده که براساس مطالعات اپیدمیولوژیک، برای سلامتی انسان بسیار مخاطره ­آمیز می­ باشند. این ذرات حاوی مقادیری از فلزهای سنگین هستند که برخی از آن­ها جزء عنصرهای سمی سرطان­زا محسوب می­ شوند. با توجه به اینکه ذرات معلق با قطر کوچکتر از 4 میکرومتر می ­توانند به نای، نایژه ­ها و کیسه­ های هوایی نفوذ کنند، بنابراین در این مطالعه، به بررسی میزان فلزهای سنگین همراه باPM4 در هوای تهران و ارزیابی ریسک سلامت ناشی از آن­ها پرداخته شد.
مواد و روش ­ها:
نمونه ­برداری از ذرات معلق PM4 در دو منطقه مسکونی: تهرانپارس در شرق و اکباتان در غرب تهران توسط دستگاه نمونه ­بردار ذرات معلق هوای Chrono با دبی مکش 10 لیتر در دقیقه، بطور همزمان در دو ایستگاه و هر 6 روز یک بار انجام شد و غلظت ذرات معلق PM4 به روش وزن سنجی محاسبه شد. برای اندازه ­گیری غلظت فلزهای سنگین، نمونه­ ها با استفاده از محلول استخراج (شامل اسید HCl و HNO3) هضم شده و آماده­ سازی انجام گرفت. سپس غلظت فلزهای سنگین در نمونه ­ها به­وسیله دستگاه ICP-MS اندازه­گیری شد. جهت بررسی غنای فلزی فاکتور غنی ­شدگی و برای ارزیابی ریسک سلامت فلزهای سنگین، ریسک سرطان­ زایی محاسبه شد.
نتایج و بحث:
در هر دو ایستگاه نمونه ­برداری بالاترین غلظت در تمام نمونه ­هایPM4 مربوط به آلومینیوم و آهن بود که دلیل آن فراوانی زیاد این عنصرها در پوسته زمین می­ تواند باشد. نتایج سنجه غنی ­شدگی نشان دادAl، Fe، Tiو Mn همراه با ذرات معلق دارای غنی­ شدگی کم بوده (1EF≤) و منشاء این فلزها بطور عمده پوسته زمین است. Ni و Cr دارای غنی­ شدگی بالا (10>EF>1) و Zn، Pb، Cu، Sn، As و Cd دارای درجه غنی­ شدگی بسیار بالا(45<EF) بوده و بیشتر منشاء انسانی دارند. غلظت ذرات معلق PM4 بین دو ایستگاه شرق و غرب تفاوت معنی ­داری نداشت ولی مقایسه میانگین غلظت فلزهای اندازه­ گیری شده در نمونه ­های PM4 بین دو ایستگاه نشان داد که غلظت Mn، Cu، Sn، Ni و As در ایستگاه شرق بطور معنی­ دار بالاتر از ایستگاه غرب بود. مقایسه فاکتور غنی­ شدگی بین دو ایستگاه نمونه­ برداری نیز نشان داد مقادیر EF عنصرهای مورد مطالعه در ایستگاه شرق بالاتر از مقادیر آن در ایستگاه غرب بود که می­تواند نشان از سهم بالاتر منبع­ های انسانی در شرق نسبت به غرب باشد. در میان عنصرهای مورد مطالعه بالاترین ریسک سرطان­ زایی مربوط به Cr(VI) بود (در شرق 6-10×61.2 و در غرب 6-10×54) که این امر به ­دلیل سمیت بالای آن می ­باشد. ریسک سرطان ­زایی کل براساس میانگین مقادیر فلزهای سمی همراه با PM4 در ایستگاه شرق 6-10×120.1 و در ایستگاه غرب 6-10×83.1 بود.
نتیجه ­گیری:
بسیاری از فلزهای سنگین همراه باPM4 شرق و غرب تهران بطور عمده منشاء انسانی داشته و ناشی از فعالیت­ هایی چون حمل و نقل و وسایل نقلیه هستند. میانگین غلظت برخی فلزهای سنگین همراه با PM4 شرق تهران بالاتر از غرب بود که درنتیجه آن، ریسک سرطا ن­زایی ناشی از فلزهای سمی همراه با این ذرات نیز در شرق بالاتر از غرب است. مخاطره­ آمیزترین عنصر همراه با ذرات معلق هوای شهر تهران از نظر سرطان­ زاییCr(VI) بود که بیشتر باید مورد توجه قرار گیرد و منبع­ های انتشار انسانی آن کنترل گردد.

کلیدواژه‌ها

عنوان مقاله [English]

Assessment of heavy metals in Tehran's airborne particulate matters (PM4) and their associated health risk

نویسندگان [English]

  • Sohrab Mazloomi
  • Abbas Esmaeili Sari
  • Nader Bahramifar

Department of Environment, Faculty of Natural Resources and Marine Sciences, University of Tarbiat Modares, Nour, Mazandaran, Iran

چکیده [English]

Introduction:
Particulate matters are one of the most important air pollutants in Tehran and very dangerous for human health according to the epidemiological studies. The ambient particles contain heavy metals, some of which are toxic and carcinogenic components. Therefore, in this study, the content of heavy metals in airborne particulate matters (PM4) of Tehran was measured and the related health risk was assessed.
Material and methods:
Sampling of PM4 was conducted every six days using Chrono PM Sampler with a 10 L/min flow rate at two residential areas including Tehranpars in the east and Ekbatan in the west of Tehran. The concentration of PM4 was calculated with Gravimetric analysis. After the preparation of the samples using the extraction solution (HCl and HNO3), the concentration of heavy metals was measured by ICP-MS. The metal richness was assessed using the enrichment factor. For health risk assessment of heavy metals in PM4, excess cancer risk was calculated.
Results and discussion:
At both sampling stations, the highest concentrations in all PM4 samples were related to Al and Fe due to the high abundance of these elements in the earth's crust. The results of the enrichment factor indicated that Al, Fe, Ti and Mn in PM4 had low enrichment degree and the source of these metals might mainly be the earth's crust. Ni and Cr had a high enrichment degree. In addition, Zn, Pb, Cu, Sn, As, and Cd had a very high enrichment degree and were mainly anthropogenic. The concentration of PM4 was not significantly different between the two stations in the east and west, but the comparison of the mean concentration of metals in PM4 samples between the two stations showed that the concentrations of Mn, Cu, Sn, Ni, and As at the eastern station were significantly higher than the western station. The comparison of the enrichment factor between the two sampling stations also showed that the EF values of the studied elements at the eastern station were higher than those at the western station, which could indicate a higher contribution of anthropogenic sources in the east. Among the studied elements, the highest excess cancer risk was related to Cr(VI) due to its high toxicity. The total excess cancer risk based on the average concentrations of toxic metals in PM4 was 120.1×10-6 at the eastern station and 83.1×10-6 at the western station.
Conclusion:
Most of heavy metals in PM4in the east and west of Tehran had mainly anthropogenic sources and were generated by human activities, especially transportation. The average concentration of heavy metals in PM4 at the east of Tehran was higher than the west, and as a result, the excess cancer risk of toxic metals in PM4 was also higher in the east. The most dangerous carcinogenic element in particulate matters of Tehran was Cr(VI), which should be taken more under consideration and its anthropogenic emission sources must be controlled.

کلیدواژه‌ها [English]

  • Heavy Metals
  • Particulate matter
  • Enrichment factor
  • Health risk assessment
  • Excess cancer risk

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