Environmental factors controlling potentially toxic element behaviour in urban soils, El Tebbin, Egypt

Ahmed Melegy,Samir Ahmed Awad,Yousria Samy,Andrew S Hursthouse,Salman Abd El-Raof Salman,Ibrahim Said

doi:10.1007/s10661-019-7388-1

Abstract

This study focuses on the assessment of surface soils from industrially polluted region (El Tebbin) of southern Cairo, Egypt. The impact of agricultural, residential and industrial land use on soils developed from Nile river sediments has significantly compromised their function. Previous evidence has shown that the food chain is contaminated and enhances risk of contaminant exposure of the residential communities. This study investigates factors controlling potentially toxic element (PTE) distribution (Co, Ni, Pb, Cd, Zn, Cr and Cu) in El Tebbin soils and provide estimates of their mobility and bioavailability. The PTE concentrations are characterised by high variability as result of the variety of natural and anthropogenic influences. Highest spatial variability is found for Zn, Cd, Pb and Cu (C.V = 260.0%, 280.4%, 140.8% and 159.6% respectively) and enrichment factors indicate strong anthropogenic inputs. For Co and Ni, relatively low spatial variability (C.V = 65.8% and 45.0% respectively) with depletion in Ni suggests a relatively minor contribution from anthropogenic sources. For Cr, a more uniform distribution pattern showing depletion to minimal enrichment across the study area (C.V = 19.2%) reflects almost exclusive lithogenic control. Using principle component analysis (PCA) to explore concentration data reveals that the major inputs affecting PTE distribution are modified by primary soil properties (texture and pH). Their relative bioavailability (identified through sequential chemical extraction) relates strongly to local input sources. Those elements dominated by lithogenic input (Ni and Co) were found predominantly in soil residual fractions (95.6% and 90.5% respectively), while elements with stronger anthropogenic contributions (Cd, Zn, Pb and Cu) showed much higher portion in the more mobile and bioavailable fractions obtained from sequential chemical extraction, with average proportions of the totals being 62.6%, 57%, 40.7% and 39.2% respectively. Those PTEs with strong anthropogenic influence are potentially much more mobile for bioaccumulation in food chain with increased health risk for exposed residents and are confirmed by elevated concentrations of Cd, Zn, Pb and Cu recorded in local plant species. The main pollution sources were further highlighted by cluster analysis and showed vehicle traffic and specific industrial activities but which varied significantly from site to site. The identification of sources through the approach developed here allows prioritisation of monitoring and regulatory decisions by the local government to reduce further environmental exposure of the local population.

Highlights

It is widely accepted that environmental contamination with potentially toxic elements (PTE) is one of the largest threats to human health
We focus on identifying factors controlling PTE distribution and availability in El Tebbin soil and estimating their mobility and bioavailability
Comparing our data with previous studies (Table 3) indicates that the Helwan is more contaminated with Cd and Pb than the opposite bank of the River Nile (Giza area), which we attribute to the dominance of heavy industries in Helwan compared to Giza

Summary

Introduction

It is widely accepted that environmental contamination with potentially toxic elements (PTE) is one of the largest threats to human health. The principle of the approach being that the expected availability/mobility generally reduces with increasing severity of extraction conditions, with a notional association with increasingly stable solid phases This depends very much on the nature of the soil medium— input parent materials, weathering and any disturbance or addition of anthropogenic materials and for surface soils makes it very spatially and temporarily variable. Elements associated with natural (silicate mineral) parent materials occur primarily in the residual fraction (F5) and have low biological availability which reduces their toxic risk. Despite the considerable history of human habitation in the region, this is relatively poorly documented and understanding the reactivity and availability of soil-based pollution sources is critical for future environmental management in the area and in zoning locations for detailed strategic development. We focus on identifying factors controlling PTE distribution and availability in El Tebbin soil and estimating their mobility and bioavailability

Materials and methods

Result and discussion

Findings

Conclusion