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Abstract Untreated industrial sewage and domestic wastewater irrigation has led to agricultural soil-crop system contamination by heavy metals and fluoride in Dongdagou and Xidagou stream basins, Baiyin city, China. A total of 36 pairs of soil and wheat samples (roots, stalks, leaves, husks, and grains) and 42 pairs of soil and maize samples (roots, stalk1, stalk2, stalk3, leaves, husks, corncobs and grains) were collected from Dongdagou and Xidagou stream basins to examine the accumulation, fractionation, correlation of heavy metals and F in soil-crop systems. Risks posed by heavy metals and F in this system to human health was also assessed. The total contents of F and heavy metals (Cd, Cu, Pb, Mn Zn, Cr and Ni), as well as the fraction distribution in soil, were determined. The total contents of F and heavy metals in crop tissues were also determined. The results indicated that the average contents of Cd, Cu, Pb, Mn Zn, F and Cr in Dongdagou and Xidagou stream basins exceeded the soil background value. Heavy metals and F more easily accumulated in the male inflorescence of maize. Correlation analysis showed that content of water soluble F positively were correlated with the contents of Cd, Cu, Pb, Mn Zn, Cr and Ni in exchangeable and carbonate fractions (P < 0.05). Stepwise discriminant analysis showed that the combined stresses of soil total Cu and Ni accounts for 100% effect on water soluble F accumulation in soil and crop roots. The hazard index indicated that noncancerous risk is likely to occur through maize grains and wheat grains consumption by children and adults. Graphical abstract Unlabelled Image Highlights • Water soluble F may increase the bioavailability of Cu, Mn, Zn, Pb, Ni, Cd and Cr. • The combined stresses of Cu and Ni may be the main factor that increases F bioavailability. • Contaminants easily accumulate in male inflorescence of maize except for roots and leaves. • Crop grains and shoots cannot be used for food and feed consumption. [ABSTRACT FROM AUTHOR]

It is not yet clear whether the carbon released from biochar in the soil solution stimulates biological activities. Soluble fractions (AQU) from wheat and maize biochars, whose molecular content was thoroughly characterized by FTIR, 13 C and 1 H NMR, and high-resolution ESI-IT-TOF-MS, were separated in dilute acidic solution to simulate soil rhizospheric conditions and their effects evaluated on maize seeds germination activity. Elongation of maize-seeds coleoptile was significantly promoted by maize biochar AQU, whereas it was inhibited by wheat biochar AQU. Both AQU fractions contained relatively small heterocyclic nitrogen compounds, whose structures were accounted by their spectroscopic properties. Point-of-Zero-Charge (PZC) values and van Krevelen plots of identified masses of soluble components suggested that the dissolved carbon from maize biochar behaved as humic-like supramolecular material capable to adhere to seedlings and deliver bioactive molecules. These findings contribute to understand the biostimulation potential of biochars from crop biomasses when applied in agricultural production. [ABSTRACT FROM AUTHOR]