Abstract
Sewage sludge improves agricultural soil and plant growth, but there are hazards associated with its use, including high metal(loid) contents. An experimental study was conducted under greenhouse conditions to examine the effects of sewage sludge on growth of the invasive tree Prosopis glandulosa, as well as to determine its phytoremediation capacity. Plants were established and grown for seven months along a gradient of sewage sludge content. Plant traits, soil properties, and plant and soil concentrations of N, P, K, Cd, Pb, Cu, Ni, Zn, Cr, Co, As, and Fe were recorded. The addition of sewage sludge led to a significant decrease in soil pH, and Ni, Co, and As concentrations, as well as an increase in soil organic matter and the concentrations of N, P, Cu, Zn, and Cr. Increasing sewage sludge content in the growth medium raised the total uptake of most metals by P. glandulosa plants due to higher biomass accumulation (taller plants with more leaves) and higher metal concentrations in the plant tissues. P. glandulosa concentrated more Cd, Pb, Cu, Zn, and Fe in its below-ground biomass (BGB) than in its above-ground biomass (AGB). P. glandulosa concentrated Ni, Co, and As in both BGB and AGB. P. glandulosa has potential as a biotool for the phytoremediation of sewage sludges and sewage-amended soils in arid and semi-arid environments, with a potential accumulation capability for As in plant leaves.
Highlights
Sewage sludge, a biological by-product of sewage treatments, increases organic matter and macronutrients in agricultural and degraded soils, and is widely used for plant fertilization since it offers the opportunity to recycle organic matter to soil [1,2]
Plants can be used as biotools to reduce metal loads in soils enriched with sewage sludge or even directly in municipal sewage sludges before they are added to the soil [6]
Metals accumulate and distribute in plant tissues depending on the plant species, the concentration of metals in the soil, and the element species and its bioavailability, which depends on soil pH, organic matter content, and other factors [15]
Summary
A biological by-product of sewage treatments, increases organic matter and macronutrients in agricultural and degraded soils, and is widely used for plant fertilization since it offers the opportunity to recycle organic matter to soil [1,2]. Concern has increased about the application of municipal sewage sludge for plant fertilization because of the high metal(loid) concentrations in some sewage-amended soils, with potentially deleterious impacts on the ecosystem and human health [3,4,5]. Phytoremediation refers to the use of plants and associated microbes in soil to reduce pollutant concentrations and/or their toxic effects on the environment [9]. Those plants taking up higher concentrations of metals by their roots and their accumulation in the above-ground biomass (AGB) are suitable biotools for phytoextraction, while those species reducing the mobility and bioavailability of metals in the environment represent biotools for phytostabilization [10]. The potential use of trees as a suitable solution to remediate metal-contaminated soils has received increasing attention [16,17,18], especially when it is costly to use other treatments or there is no time pressure to reuse the land [19]
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