تاثیر برخی مواد اصلاحی آلی و معدنی برکاهش زیست فراهمی و توزیع شکل های شیمیایی سرب و کادمیوم در یک خاک آهکی آلوده به عناصر سنگین

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری علوم خاک، گروه علوم خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران

2 دانشیار گروه علوم خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران

3 استاد گروه علوم خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران

چکیده

آلودگی منابع آب و خاک به فلزات سنگین، از چالش­های مهم عصر کنونی است؛ به­همین دلیل، آلودگی­زدایی چنین خاک­هایی، پیش­نیاز هرگونه بهره­برداری بهینه از این منابع است. یکی از روش­های مقرون به­صرفه برای پیش­گیری از انتشار فلزات سنگین در منابع آب و خاک، تثبیت و جامدسازی آن­هاست. طی این فرایند، فلزات سنگین در خاک­های آلوده با اصلاح­کننده­هایی همچون مواد آلی و  معدنی واکنش داده و با تشکیل موادی کم­محلول یا نامحلول در محیط، به صورتی پایدار باقی­ می­مانند. در این پژوهش، به‌منظور بررسی اثر مواد اصلاحی آلی (بیوچار تهیه شده در دمای 640 و زمان 30 دقیقه از کاه و کلش برنج و بیوچار تهیه شده در دمای 420 و زمان 2 ساعت از کاه و کلش برنج) و معدنی (پومیس، لیکا، زئولیت و بنتونیت) در سه سطح صفر، 1 و 5 درصد وزنی بر عدم تحرک و تثبیت دو فلز کادمیوم و سرب در خاک­های آلوده، آزمایشی در قالب طرح کاملا تصادفی با سه تکرار  انجام گرفت. نتایج حاصل از این پژوهش نشان داد که افزودن مواد اصلاحی به خاک، موجب کاهش غلظت کادمیوم و سرب عصاره­گیری شده با DTPA و EDTA شد. بیشترین کاهش غلظت سرب عصاره­گیری شده با DTPA و EDTA (بخش محلول یا زیست فراهمی) در تیمار سطح 5٪ بیوچار 640 مشاهده شدکه در مقایسه با شاهد، به­ترتیب کاهشی معادل 68 و 2/41 درصد داشتند؛ همچنین بیشترین کاهش غلظت کادمیوم عصاره­گیری شده با DTPA و EDTA به­ترتیب مربوط به تیمارهای سطح 5٪ پومیس و زئولیت  بود که به ترتیب 39 و 8/28 درصد نسبت به شاهد کمتر بودند. بیشترین کاهش غلظت سرب و کادمیوم در بخش تبادلی  در سطح 5٪ بیوچار 640 مشاهده شد که در مقایسه با شاهد، به ترتیب کاهشی معادل 96/54 و 41 درصد  داشتند. کاربرد اصلاح­کننده­ها، اثری معنی­دار بر مقدار کل سرب و کادمیوم خاک نداشتند. بنابراین، تکنیک حاضر، می­تواند به طور مؤثری، زیست فراهمی سرب و کادمیوم را در خاک کاهش دهد که این مساله می­تواند در اصلاح خاک استفاده شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Effects of some organic and inorganic amendments on the bioavailability and distribution of different Fractions of lead and cadmium in a calcareous contaminated soil

نویسندگان [English]

  • Somayeh Sefidgar shahkolaie 1
  • Mojtaba Baranimotlagh 2
  • Farhad Khormali 3
  • Esmael Dordipour 2
1 PhD Student, Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
2 Associate Prof., Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.
3 Professor., Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
چکیده [English]

Introduction At present, contamination of water and soil resources is an important environmental challenge. Therefore, decontamination of such is a prerequirement for using these resources. Cadmium (Cd) and lead (Pb) often coexist in contaminated soils and there is currently no effective means for their concurrent removal. Concerns about their mobility and bioavailability have increased because of food safety, potential health risks and its detrimental effects on the ecosystems. The stabilization/solidification is a cost effective remediation method that prevents spreading of heavy metals in soil and water resources. In this process, contaminated soil reacts with amendments such as organic and liming materials to form low soluble or non-soluble stable materials. The objective of this study was to evaluate the effect of several low cost amendments on Cd and Pb stabilization by a sequential extraction method.
Materials and Methods In this research, in order to investigate the effect of organic amendments (biochar 640°C, and biochar 420°C) and inorganic amendments (Pumice, Leca, Zeolite, and Bentonite) on Pb and Cd stabilization in a contaminated soil, an incubation experiment was carried out. One kilogram of each amended soil and the control soil were packed into respective pots. Soils were amended in the laboratory using biochar 640 (BI1), biochar 420 (BI2) bentonite (BE), pumice (P), leca (LE), and zeolite (Z). A control treatment (C) without adding amendment was also prepared. The amendment materials were applied at 1 and 5 percent wt. Each treatment was performed in three replicates and the samples were incubated in the dark at 14°C for 6 months. At the end of the incubation time, the potential bioavailability of Cd in non-amended and amended soils was evaluated by extraction with DTPA and ethylenediamine tetraacetic acid (EDTA). Total Cd (CdT) and Pb (PbT) was extracted by aqua regia (HNO3 + HCl) extraction. The chemical fractions of Cd and Pb were determined by a sequential extraction method which is a five-step chemical fractionation based on the work of Tessier et al. (1979). All statistical analyses were performed using SAS software. Means of different treatments were compared using LSD (P ≤0.05) test.
Results and Discussion The results indicated that the additions of amendments to soils reduced the concentration of DTPA and EDTA-extracted Pb and Cd. The smallest concentration of Pb-extracted DTPA and EDTA was observed in organic amendments treated soil (biochar 640°C, and biochar 420°C) and treated with 5% biochar 640°C, respectively. The high sorbent capacity of the BI used in this study could be due to its high pH, high content of organic carbon and cation exchange capacity (CEC). The highest decreasing rate of DTPA and EDTA-extractable of Cd was observed in treated with 5% pumice and zeolite, respectively. Application of the amendments (except for 1% LE) decreased exchangeable fraction (F1) of Pb compared to the non-amended soil. Also, the amendments (except for 1% P, Z and BE) decreased exchangeable fraction (F1) of Cd compared to the non-amended soil. Although the biochar 640 (5%) showed the highest decreasing rate of exchangeable fraction (F1) of Pb and Cd, they increased the oxide (F3) and organic (F4) fractions, which might be due to its rich O-containing functional groups and high alkalinity leading to an increase in the binding of Cd and Pb to organic compounds and mineral oxides.
Conclusion Results indicated that application of amendments was successful in lowering the potential bioavailability of Pb and Cd soils. The 5% biochar 640 treatment had the greatest decrease in extractable Pb. Also, the 5% zeolite and pumice treatment had the greatest decrease in extractable Cd. Application of BI resulted in a significant decrease in both Pb and Cd exchangeable fraction (F1). This reduction in the exchangeable fraction (F1) of Cd and Pb in the soil was due to an increase in the fraction of heavy metals bound to the soil organic matter (F4) oxides (F3) after BI addition. Enhanced precipitation or co-precipitation and complexation of metals with amendments led to the reduction of the solubility of the metals. The P, LE, BE, and Z altered the exchangeable fraction (F1) of Cd and Pb to the oxide fraction (F3) and the carbonate fraction (F3), respectively. Application of BI amendment causes the highest decreasing rate of solubility Cd and Pb, suggesting this as the suitable amendment for the remediation of Cd and Pb in contaminated soils.

کلیدواژه‌ها [English]

  • Amendments
  • Bioavailability
  • Cadmium
  • Chemical fractions
  • Lead