Search

Chemical analyses and biological methods were combined to investigate oxidative stress, hormesis effect and concerned mechanism in roots of Viciafaba seedlings grown in 0-2000 mg kg(-1) of Pb-treated soils after germination of 20d. The results showed that U-shaped dose response curves were displayed in superoxide radical (O2-) radicals, guaiacol peroxidase (POD) and ascorbate peroxidase (APX) activities, malondialdehyde (MDA) and carbonyl groups as well as activities of endoproteinase (EP) isoenzymes in the roots at low doses of extraneous Pb, indicating reduced oxidative stress and toxic effect. The inverted U-shaped curves were also exhibited in growth height, superoxide dismutase (SOD) and EP activities as well as inducible heat shock protein70 (HSP70) with the increasing extraneous Pb, indicative of enhanced oxidative stress. The enhancement in HSP70, carbonyl groups and EP activities confirmed intracellular proteotoxicity and proteolytic activity in the roots at higher doses of soil Pb. More interestingly, levels of inducible HSP70 were well correlated with those of growth heights (r=0.809, p<0.05), implying that HSP70 induction may be one of the mechanisms underlying the U-shaped growth curve of V. faba seedlings in the experiment. The results suggest that traditional threshold models ought to be combined with hormesis effect in assessment of Pb-polluted soils and the threshold dose range of Pb-treated soils is proposed rudimentally as 25-125 mg kg(-1)., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Lead arsenates were the most extensively used arsenical insecticides in the past. Their residues, especially the water-soluble fractions in environment may pose a potential human health risk. The solubility products (K(sp)) and free energies of formation (Delta G(f) degrees) of PbHAsO(4).2H(2)O(c), Pb(5)(AsO(4))(3)OH.H(2)O(c), Pb(3)(AsO(4))(2)(c) and Pb(8)As(2)O(13)(8PbO.As(2)O(5))(c) at 25 degrees C were determined by precipitation and dissolution experiments. The composition of precipitates depended on the Pb/As molar ratios and pH values. The solid precipitates were lamellar PbHAsO(4).2H(2)O(c) at pH = 3-5 and Pb/As = 1.0, columnar Pb(5)(AsO(4))(3)OH.H(2)O(c) at pH = 12-13 and Pb/As = 1.5, Pb(5)(AsO(4))(3)OH.H(2)O(c) with little amounts of Pb(8)As(2)O(13)(c) at pH = 12-13, Pb/As = 1.67 and 2.0. The mixture of PbHAsO(4).2H(2)O(c) and Pb(3)(AsO(4))(2)(c) formed at pH = 6.51 and Pb/As = 1.5. Based on the analytical results, the solubility products (K(sp)) of PbHAsO(4).2H(2)O(c), Pb(5)(AsO(4))(3)OH.H(2)O(c), Pb(3)(AsO(4))(2)(c) and Pb(8)As(2)O(13)(c) were calculated by the computer program PHREEQC as 10(-10.70)(10(-7.81)-10(-14.32)), 10(-81.75)(10(-74.37)-10(-84.83)), 10(-33.83)(10(-32.05)-10(-34.49)) and 10(-174.24)(10(-156.64)-10(-178.35)), respectively. Correspondingly, the free energies of formation (Delta G(f) degrees) of these lead arsenates were calculated to be -1274.36 kJ/mol, -2928.33 kJ/mol, -1563.12 kJ/mol and -3909.69 kJ/mol.

Stress proteins (HSP70 and HSP60) and other related biological parameters were investigated in leaves of Vicia faba L. seedlings subjected to soil lead stress. The seedlings were cultivated outdoors in pots for five weeks. Results showed that total lead content, superoxide radical (O2*-) and lipid peroxidation productions in the leaves increased with the increase of extraneous lead in soils. Significant correlation was found between the O2*- and lipid peroxidation productions (r = 0.973, p < 0.01). Activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were activated. Moreover, HSP70 and HSP60 increased more sensitively than the other parameters in response to lead stress. This indicates lead might cause lipid peroxidation in the leaves by mediation of O2*-. The activated antioxidative enzymes alleviated the stress and damage of reactive oxygen species. HSP70 and HSP60 are potential biomarkers for early warning of lead-contaminated soils. Additionally, concentrations of soil lead and related biological parameters should be combined.

Chemical analyses and biological measurements were investigated in leaves of Vicia faba seedlings exposed to extraneous lead (Pb) at 0 to 2,000 mg/kg of soil for a month. The results showed that superoxide radical (O*(2)(-)) production, increased along with total Pb in leaves and available Pb in soil, resulted in enhancement of malondialdehyde and carbonyl groups. Antioxidant enzymes, including corresponding isoenzymes and heat shock protein 70 (hsp 70), were also enhanced to some extent. Significant changes were detected in the patterns and intensities of guaiacol peroxidase isoenzymes, while superoxide dismutase, catalase, and ascorbate peroxidase isoenzymes only changed intensities. Superoxide dismutase activities increased with the increase of extraneous Pb at 0 to 500 mg/kg of soil and tended to decline thereafter, which might be responsible for the decrease of hydrogen peroxide and accumulation of O*(2)(-). Guaiacol peroxidase and ascorbate peroxidase enzymes were upregulated to become major scavengers of excess hydrogen peroxide on the condition of decreased catalase activities. Levels of hsp 70 were well correlated with Pb contents in leaves (r=0.777), O*(2)(-) accumulation (r = 0.985, p<0.01), and carbonyl groups (r=0.920, p<0.01) under extraneous Pb at 0 to 250 mg/kg of soil, suggesting that hsp 70 induced by O*(2)(-) was possibly involved in disposal of denatured proteins. The results showed that O*(2)(-), hsp 70, and guaiacol peroxidase isoenzymes had the most sensitive responses in the seedlings and these parameters could be potential early biomarkers of soil Pb contamination.