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There is a strong need for the establishment of qualitative monitoring of channel sediment media in agro-ecosystems closely linked with complex pollution sources (intensive agriculture, industry, urban zones).

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Soil degradation processes, such as organic matter (OM) depletion, accompanied by metal contamination and salinization are becoming a serious threat to crop production and human food security. A glasshouse study was conducted to assess a factorial combination of salinity (0, 20, 40 and 60 mm NaCl) and cadmium (Cd) (0.3, 2.5 and 5.4 mg Cd kg−1) in organic soil (>90% OM) and their influence on dissolved organic carbon (DOC) in the rhizosphere and phyto‐accumulation in radish (Raphanus sativus L. var. sativus). A 34‐day exposure to increasing NaCl salinity significantly decreased DOC concentration in the radish rhizosphere solution and increased trace element (copper, Cu; zinc, Zn; and Cd) concentrations in the rhizosphere as well as in leaf/fruit tissues of radish. Soil contamination by Cd progressively raised concentrations in soil solution, but markedly reduced total concentration of Cu and Zn in the rhizosphere and leaves of radish. The NICA‐Donnan chemical speciation/distribution modelling confirmed the predominance of dissolved organic reactive surfaces (from fulvic acid for example) in Cu and Cd chemisorption/complexation processes over the whole range of applied NaCl and Cd treatments. In contrast, Zn speciation was dominated by an organically‐complexed pool at low salinity (0–20 mm NaCl), and free Zn2+ was the most important species at increased salinity (≥40 mm NaCl). In conclusion, because of the diminished pool of DOC under excessive salinity, the biogeochemistry of Cu, Zn and Cd in the rhizosphere can be affected in a way that would enhance solubility and phyto‐accumulation of these trace metals in food crops.

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To test an assumption that organic soil can ameliorate nutritional disorders associated with metal and salinity stresses, we exposed salt-sensitive strawberry and lettuce to four salinity (0–60 mM NaCl) and three contamination (0.3–5 mg Cd/kg) rates in peat (pHH2O = 5.5). The results showed that, even at 20 mM NaCl, salinity stress exerted a dominant effect on rhizosphere biogeochemistry and physiological processes, inducing leaf-edge burns, chlorosis/necrosis, reducing vegetative growth in crops; at ≥40 mM, NaCl mortality was induced in strawberry. Signifiacntly decreased K/Na, Ca/Na and Mg/Na concentration ratios with raising salinity were confirmed in all tissues. The combined CdxNaCl stresses (vs. control) increased leaf Cd accumulation (up to 42-fold in lettuce and 23-fold in strawberry), whereas NaCl salinity increased the accumulation of Zn (>1.5-fold) and Cu (up to 1.2-fold) in leaves. Lettuce accumulated the toxic Cd concentration (up to 12.6 mg/kg) in leaves, suggesting the strong root-to-shoot transport of Cd. In strawberry Cd, concentration was similar (and sub-toxic) in fruits and leaves, 2.28 and 1.86 mg/kg, respectively, suggesting lower Cd root-to-shoot translocation, and similar Cd mobility in the xylem and phloem. Additionally, the accumulation of Cd in strawberry fruits was exacerbated at high NaCl exposure (60 mM) compared with lower NaCl concentrations. Thus, in salinized, slightly acidic and organically rich rhizosphere, pronounced organo- and/or chloro-complexation likely shifted metal biogeochemistry toward increased mobility and phytoavailability (with metal adsorption restricted due to Na+ oversaturation of the caton exchange complex in the substrate), confirming the importance of quality water and soils in avoiding abiotic stresses and producing non-contaminated food.