Short-Term Changes of Metal Availability in Soil. Part I: Comparing Sludge-Amended With Metal-Spiked Soils

Abstract

Sewage sludge application to soils is regulated by its total metal content. However, the real risk of metals is determined by the fraction that is biologically available. The available fraction is highly related to the strength of metal binding by the matrix, which is a dynamic process. The evaluation of the fate of metals in time can contribute increased accuracy of ecological risk assessment. Aiming to evaluate short-term changes in metal availability when metals were applied to soil directly (metal-spiked) or by way of an organic matrix (sludge-amended), a laboratory experiment was performed using open microcosms filled with agricultural soil. A concentration gradient of industrial sludge (11, 15, 55, and 75 t/ha) that was contaminated predominantly with chromium, copper, nickel, and zinc, or soil freshly spiked with the same concentrations of these metals, were applied on top of the agricultural soil. After 0, 3, 6, and 12 weeks, total (HNO(3) 69 %) and 0.01 M CaCl(2)-extractable metal concentrations in soil and metal content in the percolates were measured. Results demonstrated that comparison between sludge-amended and metal-spiked soils may give important information about the role of sludge matrix on metal mobility and availability in soil. In sludge-amended soils, extractable-metal concentrations were independent of the sludge concentration and did not change over time. In metal-spiked soils, metal extractability decreased with time due to ageing and transport of metals to deeper layers. In general, the sludge matrix increased the adsorption of metals, thus decreasing their mobility in soils.

Contribution of waste and biochar amendment to the sorption of metals in a copper mine tailing

“…Adding organic matter to these types of soils leads to a descent in the assimilable metal content, as this is capable of forming strong bonds with metals and therefore retain them firmly in the soil (Kabata-Pendias, 2001). Different studies have shown that adding amendments made of waste materials reduces the assimilable metal content in the soil (Brown et al, 2003;Natal-da-Luz et al, 2012). The increased content of organic matter provided by the residue causes an increase in the sorption capacity of heavy metals in soil (Kocasoy and Güvener, 2009).…”

Copper, Nickel and Zinc Speciation in a Biosolid-Amended Soil: pH Adsorption Edge, μ-XRF and μ-XANES Investigations

“…Due to the intensification of water quality requirements and more rigorous environmental laws in Europe, the production of biosolids has sharply increased in recent years. , The main management options include incineration, landfill sites, and application to agricultural lands as soil amendment . The use of biosolids in agriculture is widely practiced all over the world since it is the most economical option allowing the recycling of plant nutrients and organic matter. − However, this practice can be potentially harmful to the environment because biosolids contain high concentrations of toxic heavy metals. , Copper, nickel, and zinc are essential micronutrients required for plant nutrition and their addition with biosolids may be beneficial, but they are also potential environmental contaminants and will persist in the soil long-term if added in excess. , The fate of potentially toxic elements following short and long-term application of biosolids is well reported in the literature − but this issue remains strongly controversial within the scientific community. Some published data have shown that the long-term biosolid spreading would result in the release of metals into the soil due to organic matter mineralization; it is the “time bomb hypothesis”. ,, Other authors have suggested that the long-term application of biosolids would present no environmental risk, due to the high adsorption capacity of mineral phases within biosolids; it is the “protection hypothesis”. ,, Consequently, to better predict the environmental fate and mobility of contaminants, it is critical to study the speciation of heavy metals in biosolid-amended soils.…”