Potentially Toxic Element Availability and Risk Assessment of Cadmium Dietary Exposure after Repeated Croppings of Brassica juncea in a Contaminated Agricultural Soil

Diana Agrelli,Massimo Fagnano,Paola Adamo,Nunzio Fiorentino,Eugenio Cozzolino,Luigi Giuseppe Duri

doi:10.3390/agronomy10060880

Diana Agrelli, Massimo Fagnano + Show 4 more

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https://doi.org/10.3390/agronomy10060880

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Abstract

Phytoextraction of potentially toxic elements (PTEs) is eco-friendly and cost-effective for remediating agricultural contaminated soils, but plants can only take up bioavailable forms of PTEs, thus meaning that bioavailability is the key for the feasibility of this technique. With the aims to assess the phytoextraction efficiency on an agricultural soil contaminated by Cr, Zn, Cd, and Pb and the changes induced by plants in PTE bioavailability and in human health risk due to dietary exposure, in this work we carried out a mesocosm experiment with three successive croppings of Brassica juncea, each followed by Rocket salad as bioindicator. Brassica juncea extracted more Zn and Cd than Cr and Pb, significantly reducing, after three repeated croppings, the bioavailable element concentrations in soil as a result of plant uptake and soil pH changes. For Cd, this reduction did not bring the bioavailable amounts obtained by soil extraction with NH4NO3 below the trigger value of 0.1 mg kg−1 set by some European countries. Nevertheless, the Hazard Quotient for Cd in Rocket salad decreased across three repeated croppings of Brassica juncea. This indicated the beginning of a re-equilibration process between soil PTE forms of different bioavailability, that are in a dynamic equilibrium, thus stressing the need to monitor the possible regeneration of the most readily bioavailable pool.

Highlights

Soil contamination by potentially toxic elements (PTEs) is of great concern due to their harmfulness for the biota at certain concentrations and to their persistence in the environment [1]
After short-term phytoextraction, the readily bioavailable fraction of the respective element may be replenished through repartition between soil fractions and soil solution, and the kinetics of replenishment can change over time [9]. In view of these considerations, in the present work we report the results of a 3-year mesocosm experiment of PTEs phytoextraction from an agricultural soil polluted by illegal dumping of industrial wastes and by consecutive croppings of Brassica juncea L
The three sub-areas selected for this work showed neutral pH (7.1 ± 0.1 in A7, 7.0 ± 0.1 in C13 and 7.1 ± 0.1 in F4) and variable organic carbon content

Summary

Introduction

Soil contamination by potentially toxic elements (PTEs) is of great concern due to their harmfulness for the biota at certain concentrations and to their persistence in the environment [1]. When contaminant concentrations in a site overcome the screening values stated by the national legislations, the site has to be subjected to a site-specific risk analysis for calculating risk thresholds. When contaminant concentrations overcome risk thresholds, the site must be subjected to remediation projects [2]. In the case of agricultural soils, it is crucial to analyze the risks that a contaminant can enter the food chain, for this purpose chemical [3] and biological essays [4] have been proposed. Various soil remediation techniques exist, but many of them are complex and expensive. Much research has been done on soil phytoremediation because it is an in situ eco-friendly and Agronomy 2020, 10, 880; doi:10.3390/agronomy10060880 www.mdpi.com/journal/agronomy

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