The Role of Soil Organic Matter in Trace Element Bioavailability and Toxicity

Heavy metals in agricultural landscapes as hazards to human and ecosystem health: a case study on zinc and cadmium in drainage channel sediments

“…toxicity of Zn/Cd in the soil-plant-animal continuum. 10 For instance, the soil mobility and plant uptake of Cd and Zn are strongly dependent on their chemical speciation and distribution in the rhizosphere, principally on concentration of free metal forms (Cd 2+ , Zn 2+ ), although some inorganic and organic metallo-complexes (e.g. cadmium-chlorides, cadmium-fulvic acid complexes) may also need to be considered from the standpoint of food safety and security.…”

“…The cycling of Zn/Cd through agricultural eco-systems is complex and influenced by different factors, including soil pH, organic matter content, soil salinity and many other factors. 10 However, recent studies suggest agriculture on metal-contaminated land can increase a risk of toxic and nonessential elements such as Cd entering the human food chain at the expense of some essential metals such as Zn. [11][12][13]…”

Salinity decreases dissolved organic carbon in the rhizosphere and increases trace element phyto‐accumulation

“…DOC concentrations were significantly smaller in the rhizosphere solutions of the salt‐stressed treatments: such changes could be explained by effects on plant–microbe interactions. Plants and associated root microbes exude a wide range of low‐ and high‐molecular‐weight organic exudates, including acids, carbohydrates and proteins (van Hees et al , 2005), influencing biogeochemistry (through effects on acidification, redox potential and electrochemical gradients) and the organic C pool in the rhizosphere (McDowell et al , 2006; Ondrasek & Rengel, 2012). Similarly, Li et al (2007) reported significant negative correlations between soil salinity and total CO 2 ‐C emission (as a proportion of particulate organic soil C) and microbial biomass C (as a proportion of total or particulate organic soil C), concluding that salinity had an adverse effect on microbial biomass and activity.…”

“…Concentrations of trace metals in the radish rhizosphere solution were strongly altered by both NaCl and Cd treatments. Added salinity (20–60 m m NaCl) increased total concentration of dissolved metals in the radish rhizosphere in the highly organically‐enriched growing medium (>90% OM), which is important for controlling biogeochemical reactions (solubility, adsorption/desorption and bioavailability) of trace elements (Adriano et al , 2004; Ondrasek & Rengel, 2012). Particulate and dissolved soil OM containing negatively charged surfaces strongly competes with metals such as Cu and Cd, and inorganic ligands such as Cl − and SO, in adsorption and complexation reactions (Adriano et al , 2004).…”

“…Dissolved organic carbon is one of the most important soil properties affecting plant availability and phyto‐extraction of both non‐essential and essential metal elements (Ondrasek & Rengel, 2012). Complexation and chemisorption of free metal ions (the most bioavailable and potentially the most toxic forms) by humic substances could be significant for safe food production from metal‐contaminated soils (Ondrasek et al , 2009a).…”