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The phytotoxicity due to nickel (Ni) and its accumulation in castor (Ricinus communis L.) plant of Euphorbiaceae family resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) was studied in a pot culture experiment. Nine levels of Ni (0, 10, 40, 80, 120, 160, 180, 200, 250 mg Ni kg−1 soil) were applied. Crop was harvested at 45 days after sowing. At the higher Ni levels, beyond 200 mg Ni kg−1 soil, reduced growth symptom was recorded. The concentration of Ni in plant parts increased with increasing dose of applied Ni. Nickel concentration in castor root ranged from traces (control) to 455 mg kg−1 and was directly related to soil Ni concentration. At 200 mg Ni kg−1 soil, dry matter yield of castor reduced to 10% of control plant. Significant changes were observed in the roots of castor treated with higher levels of Ni against control. The roots treated with Ni showed a decrease in number of cells in the cortex region. It also appeared that the cortex region consisted of elongated parenchymatous cells instead of the normal parenchymatous tissue as in the control plant. Regarding Ni accumulation capacity, castor plant was recorded as an accumulator (α = 0.11 and β = 1.10). A laboratory study was also conducted in the experimental soil to know the different operationally defined fractions of Ni, which control the availability of Ni to castor. Different fractions of Ni present in this soil followed this order: Residual > Fe-Mn oxides > carbonate > organic > exchangeable > water soluble Overall results depict that castor is a promising species which can be used as a potential plant for phytoremediation of contaminated soils and to improve soil quality and provide economical benefits. [ABSTRACT FROM PUBLISHER]

Phytotoxicity, due to chromium [Cr (VI)] additions from low to very high levels in a swell-shrink clayey soil (Haplustert), in maize and spinach was studied in a pot culture experiment. Six levels of Cr (VI) (0, 5, 10, 25, 50, and 75 mg kg-1 soil) for maize and five levels for spinach (0, 2, 5, 10, and 25 mg kg-1 soil) were applied singly and in combination with two doses (0 and 20 t ha-1) of city compost. At levels of more than 75 mg Cr (VI) kg-1 soil for maize there was virtually no growth after germination, whereas 25 mg Cr (VI) kg-1 soil hindered the germination of spinach crop. Initial symptoms of Cr (VI) toxicity appeared as severe wilting of the tops of treated plants. Maize plants suffering from severe Cr (VI) toxicity had smaller roots and narrow brownish red leaves covered with small necrotic spots. In spinach, severe chlorosis was observed in leaves. Higher levels of Cr (VI) inhibited the growth and dry-matter yield of the crops. However, application of city compost alleviated the toxic effect of Cr (VI). The concentration of Cr (VI) in plant parts increased when Cr (VI) was applied singly but decreased considerably when used in combination with city compost. There was evidence of an antagonistic effect of Cr (VI) on other heavy-metal (Mn, Cu, Zn, and Fe) concentrations in plant tops. Thus, when Cr (VI) concentration increases, the concentration of other beneficial metals decreases. Chromium (VI) concentration in maize roots ranged from traces (control) to 30 mg kg-1and were directly related to soil Cr (VI) concentration. At 25 mg Cr (VI) kg-1 soil, yield of maize was reduced to 41% of control plants, whereas in spinach, 10 mg Cr (VI) kg-1 soil caused a 33% yield reduction. Experimental results revealed that the maize top (cereal) is less effective in accumulating Cr (VI) than spinach (leafy vegetables). Laboratory studies were also conducted to know Cr (VI) sorption capacity of a swell-shrink clayey soil with and without city compost, and it was found that Cr (VI) sorption reaction was endothermic and spontaneous in nature. [ABSTRACT FROM AUTHOR]

The phytotoxicity due to cadmium (Cd) and its likely contamination of the food chain—resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) in spinach ( Spinacia oleracea L.)—was studied in a pot culture experiment. Twelve levels of Cd (0, 2, 4, 8, 10, 20, 40, 60, 80, 120, 160, 200 mg kg -1 soil) were applied singly and in combination with two doses (0 and 2.5 cm) of spent wash. Above 80 mg Cd kg -1 soil, there was very slow growth of spinach after germination. Spinach crop suffering from severe Cd toxicity had small roots and narrow yellowish leaves, covered in small necrotic spots. Higher levels of Cd inhibited the growth and biomass of the crop. However, application of spent wash alleviated the toxic effect of Cd to some extent. The concentration of Cd in plant parts increased when Cd was applied singly but decreased considerably when used in combination with spent wash. Cd concentration in spinach root ranged from traces (control) to 120 mg kg -1 dry matter and was directly related to soil Cd concentration. At 40 mg kg -1 soil, yield of spinach was reduced to 38% of control plants. A laboratory study was also conducted in the soils collected from treated pots after harvest in order to know the different operationally defined fractions of Cd that control the availability of Cd to spinach and that were correlated with dry-matter yield of spinach crop. [ABSTRACT FROM AUTHOR]