Elevated concentrations of As and Sb impact environmental quality and human health. In this study total and bioavailable As and Sb were measured from recently and historically contaminated soils and the phytotoxicity of these soils was evaluated with Ipomoea aquatica (35-d exposure from germination) using biomass, length of plant tissues and photosynthetic efficiency. As and Sb were both present within the soil (co-contaminated). The bioavailable As and Sb in soils were determined by a Sequential Extraction Procedure (SEP) and compared to total soil concentrations and bioaccumulation in the edible parts of I. aquatica. For both As and Sb, bioavailable concentrations increased proportionally with the total soil concentrations and greater bioavailability in recently contaminated soil was observed. Tissue dry mass and length drastically reduced with increasing total and SEP-bioavailable As and Sb soil concentrations. The total soil concentration was a less sensitive measure of the phytotoxicity of As and Sb than the bioavailable fraction. Shoot length was inhibited by 50% (EC50) at bioavailable As concentrations of 80-96 mg kg-1 in both recently and historically contaminated soils; however, bioavailable Sb EC50 for shoot length was achieved at lower bioavailable concentrations, 96 (42-219) and 12 (7-19) mg kg-1 in recently contaminated soils and historically contaminated soils, respectively. Shoot biomass was inhibited by 50% (EC50) at bioavailable As concentrations of 11 (4-30) and 49 (37-65) mg kg-1 in recently and historically contaminated soils, respectively whereas this occurred at much lower bioavailable Sb concentrations, 2-5 mg kg-1 in both recently and historically contaminated soils. Aging is important in contaminated soils, it decreases the lability of As and Sb and hence their bioavailability to agricultural plants, thus posing a lower risk of exposure of these metalloids to humans through agricultural plants grown in contaminated soils.

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Fertilizers containing phosphate (PO43−) are commonly used within the agricultural industry and are known to increase the bioavailability and mobility of metalloids like arsenic (As). This may increase plant uptake of As and hence pose a risk to human health. Arsenic and antimony (Sb) often co‐occur in contaminated soils; however, little is known about the interactions between As and Sb with PO43− on their bioavailability, accumulation, and toxicity in plants. The present study investigated individual and combined As and Sb–contaminated soils across 2 soil PO43− concentrations using a commonly consumed leafy vegetable, choy sum (Brassica chinensis var. parachinensis). Increased soil PO43− had no clear influence on the bioavailability of As or Sb (derived from a sequential extraction procedure). At high PO43− concentration, B. chinensis accumulated higher amounts of As in the shoots and roots in both individual and co‐contaminated soil, whereas Sb accumulation increased only when Sb was the only contaminant. When As was the only contaminant, the translocation of As from roots to shoots decreased as soil PO43− increased. Increased soil PO43− had no influence on Sb translocation from root to shoot. Although As was toxic (impaired growth) at low PO43− soil concentration, no toxicity was observed in the high‐PO43− soil. No toxicity was observed for Sb in either low‐ or high‐PO43− soils. Increased soil PO43− concentration ameliorated or masked As toxicity to plant growth and led to higher As concentration in the plant's edible parts. The addition of high soil PO43− concentrations ameliorated or masked As toxicity to plant growth in both individually and As + Sb co‐contaminated soil; however, the plant's edible parts accumulated higher As and Sb concentrations. Environ Toxicol Chem 2020;39:1233–1243. © 2020 SETAC

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