Immobilization of Cd, Pb and Zn through Organic Amendments in Wastewater Irrigated Soils

Kouser Majeed Malik,Mona S Alwahibi,Mohamed Soliman Elshikh,Motsim Billah,Saba Akbar,Subhan Danish,Abdullah Ahmed Al-Ghamdi,Shah Rukh,Khalid Saifullah Khan,Ahmad Khan,Saqib Bashir,Abd El-Zaher M A Mustafa

doi:10.3390/su13042392

Abstract

Due to the scarcity of water, raw sewage effluents are often used to irrigate arable suburban soils in developing countries, which causes soil contamination with toxic metals. Soil microorganisms involved in biochemical transformations are sensitive to heavy metals contamination. The study was designed to investigate the effect of organic amendments on the microbial activity of cadmium (Cd), lead (Pb) and zinc (Zn) fractions and their bioavailability in soils contaminated with wastewater irrigation. Three metal contaminated soils under wastewater irrigation were collected, ground, sieved and added to incubation jars. Two organic amendments: wheat straw and chickpea straw, were applied (1% w/w) to the soil before incubation for 84 days at 25 °C. The CO2-C evolution after 1, 2, 3, 5, 7, 10 and 14 days was measured and thereafter was also measured weekly. Soil samples collected at 0, 14, 28, 42, 56, 70 and 84 days after incubation were analyzed for microbial biomass carbon (MBC). Sequential extraction for metal fractionation of samples was carried out collected at 0, 28, 56 and 84 days. Three soils differed significantly in evolved MBC and ∑CO2-C. Chickpea straw addition significantly increased soil MBC as compared to the wheat straw. Organic amendments significantly increased ∑CO2-C evolution from the soils, which was higher from chickpea straw. The addition of crop residues did not affect total Pb, Cd and Zn contents in soils. The concentration of exchangeable, carbonate bound and residual fractions of Pb, Cd and Zn decreased (6–27%), while the organic matter bound fraction increased (4–75%) with straw addition. Overall, the organic amendments improved microbial activity and reduce the bioavailability of toxic metals in wastewater irrigated soils. Furthermore, organic amendments not only reduce economic losses as they are cheap to produce but also minimize human health risks from heavy metals by hindering their entry into the food chain.

Highlights

Toxic metals contamination in soils is a key environmental problem because it adversely affects humans, animals and soil health [1]
Of DH, DR-1 and DR-2 soils was in the range of 7.36 to 7.59 and EC was less than 0.7 dS m−1, which shows that soils were in the near-neutral range and agricultural salinity problem was not observed
The results showed that soils and organic amendments had a strong interaction (P< 0.0001)

Summary

Introduction

Toxic metals contamination in soils is a key environmental problem because it adversely affects humans, animals and soil health [1]. Sustainability 2021, 13, 2392 people have died worldwide from more than 100 diseases caused by unhealthy environments such as contaminated soils [2]. It is estimated that globally, approximately 20 million ha of land is irrigated with wastewater, and this practice has intensified in recent years due to scarcity of water [5]. Waste effluents contain substantial amounts of organic carbon (OC) and essential plant nutrients to benefit crops and possess organic and inorganic pollutants, including toxic metals which tend to accumulate in soil [6]. Crop plants grown in contaminated soils uptake metal and leads to their entry into the food-chain, resulting in serious health concerns [8]

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