This study investigated the adsorption of the heavy metal ions Pb(II), Cu(II), Cd(II), Zn(II), and Ni(II) on a lignin isolated from black liquor, a waste product of the paper industry. Lignin has affinity with metal ions in the following order: Pb(II) > Cu(II) > Cd(II) > Zn(II) > Ni(II). The adsorption kinetic data can be described well with a pseudosecond-order model and the equilibrium data can be fitted well to the Langmuir isotherm. Metal ion adsorption was strongly dependent on pH and ionic strength. Surface complexation modelling was performed to elucidate the adsorption mechanism involved. This shows that lignin surfaces contain two main types of acid sites attributed to carboxylic-and phenolic-type surface groups and the phenolic sites have a higher affinity for metal ions than the carboxylic sites.

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To date, knowledge gaps and associated uncertainties remain unaddressed on the effects of nanoparticles (NPs) on plants. This study was focused on revealing some of the physiological effects of magnetite (Fe(3)O(4)) NPs on perennial ryegrass (Lolium perenne L.) and pumpkin (Cucurbita mixta cv. white cushaw) plants under hydroponic conditions. This study for the first time reports that Fe(3)O(4) NPs often induced more oxidative stress than Fe(3)O(4) bulk particles in the ryegrass and pumpkin roots and shoots as indicated by significantly increased: (i) superoxide dismutase and catalase enzyme activities, and (ii) lipid peroxidation. However, tested Fe(3)O(4) NPs appear unable to be translocated in the ryegrass and pumpkin plants. This was supported by the following data: (i) No magnetization was detected in the shoots of either plant treated with 30, 100 and 500 mg l(-1) Fe(3)O(4) NPs; (ii) Fe K-edge X-ray absorption spectroscopic study confirmed that the coordination environment of Fe in these plant shoots was similar to that of Fe-citrate complexes, but not to that of Fe(3)O(4) NPs; and (iii) total Fe content in the ryegrass and pumpkin shoots treated with Fe(3)O(4) NPs was not significantly increased compared to that in the control shoots.

Time effect on the fractionation of Cu, Zn, Pb, and Cd in three typical Chinese soils was investigated. A total of 500 mg kg À1 of Cu, Zn, Pb and 2.5 mg kg À1 of Cd were added to soils as nitrates. Metals in the incubated soils were fractionated termly from 3 h to 8 weeks by the sequential extraction procedure, in which the metal fractions were experimentally defined as exchangeable, carbonate-, Fe-Mn oxide-, organic matter-bound and residual fractions. Results showed that the changes of Cu, Pb and Zn in fraction distribution were biphasic by an initial rapid step followed by a slow one. Metals in exchangeable fraction were increased in the first 3 h, and then decreased, such decreases could be simulated by a diffusion equation and the decrease rate followed the order PbNCuNZnNNCd. Metals bound to Fe-Mn oxides and organic matter increased consistently in the 8-week incubation. There were almost no changes for the metals in the residual fraction. After 3-h incubation most of Cd added to soils presented in the exchangeable fraction. The content of Cd in each fraction changed slightly in the 8-week incubation. Soil pH played an important role in metal fraction distribution patterns. Jiangxi soil, with low soil pH, tended to keep more metals added in exchangeable fraction and the changes of metals in each fraction were not as remarkable as in other two soils. High organic matter content resulted in the increased organic matter-bound fraction. D

Currently, several single extraction methods are used for the evaluation of the phytoavailability of metals using pot experiments. A systematic comparison, however, is lacking. It is especially true for the field studies. This study was to investigate the phytoavailability of trace elements to vegetables grown on metal-contaminated soils under the field conditions. All soils collected were typical calcareous soils in northern China. Four frequently used methods using CaCl 2 , diethylenetriaminepentaacetic acid (DTPA), CH 3 COOH, and water as extractants were compared for phytoavailability. The concentrations of metals extracted by these four extraction methods ranged from 3.42 to 815, 1.51-6965, 0.732-24 473, 0.688-7863, 0.246-685, 1.99-5337 0.203-4649 ng/g for Cr, Ni, Zn, Cu, Cd, Pb and REEs, respectively. Simple correlation analysis indicated that a significant correlation (Cr: r ¼ 0:5411 ÃÃ ; Zn: r ¼ 0:6352 ÃÃ ; Cd: r ¼ 0:6979 ÃÃ ; Pb: r ¼ 0:5537 ÃÃ and REEs: r ¼ 0:5185 ÃÃ -0:6684 ÃÃ ) was observed between the CaCl 2 -extractable metals in soil solution and that in Chinese cabbage. In addition, soil pH, organic matter (OM), and cation exchange capacity (CEC) also affect the phytoavailability. An empirical model was developed to express the combined effect of soil properties on the phytoavailability. The stepwise multiple regression analysis demonstrated that the phytoavailability of trace elements strongly correlated with the extractable fraction by CaCl 2 , total metal concentration in soils, and soil pH, OM, CEC. This model can describe approximately 75-95% of the variability of metal uptake and the r 2 values ranged from 0.741 ÃÃ to 0.954 ÃÃ , which were much better than the single correlation analysis. For celery and cole, a strong correlation was obtained for Cr, Ni, Zn, Cu, Cd, La, Ce, Pr and Nd. For spinach and Chinese cabbage, however, a positive correlation was only observed for 1 and 3 metals, respectively. Generally, the developed empirical model can integrate the combined effects of soil properties, extractable metal fractions in soil solutions and plant species on the phytoavailability of metals to vegetables in the field conditions.

Background and aims Perfluorinated compounds (PFCs) are of particular environmental concern. The migration of PFCs from soil to plants is a likely pathway for PFCs to enter the human food chain. This study aimed to investigate the uptake mechanisms of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) by maize (Zea mays L. cv. TY2).Methods Hydroponic greenhouse experiments were performed. Results The kinetics of PFOS and PFOA uptake fitted Mechaelis-Menten equation well, suggesting their carrier-mediated influx processes. Uptake of PFOS was insensitive to metabolic inhibitors (NaN 3 and Na 3 VO 4 ). In contrast, treated with NaN 3 and Na 3 VO 4 reduced the uptake of PFOA by 83 and 43 % respectively. PFOS uptake was decreased by 31 % and 25 % when plants were treated with aquaporin inhibitors, AgNO 3 and glycerol, respectively, while aquaporin inhibitors had no effect on PFOA uptake. Anion channel blockers, 4, 4′-diisothiocyanostibene-2,2′-disolfonate (DID) and 5-nitro 2-(3-phenylpropylamine) benzoic acid (NPPB) inhibited the uptake of PFOS by 33 % and 30 %, respectively. Anion channel blocker anthracene-9-carboxylic acid (9-AC) decreased the uptake of PFOA by 28 %. No competitive uptake was found between PFOS and PFOA. Conclusions Uptake of PFOS and PFOA by maize may have different mechanisms.

Effects of different concentrations of arsenite and arsenate (0-16 mg/l) on seed germination, relative root length and shoot height, arsenic accumulation in young seedlings, a-amylase, b-amylase and total amylolytic activity in wheat were investigated in order to elucidate the toxicity of arsenic in the early developmental stage. Germination percentages of different wheat varieties had different responses to arsenic species and decreased significantly with increasing arsenic concentrations except Duokang 1. Relative root length (RRL) and relative shoot height (RSH) of wheat seedlings decreased with increasing concentrations of arsenite and arsenate. The relative root lengths were correlated with the relative shoot heights for arsenite (r 2 = 0.79) and arsenate (r 2 = 0.77). Arsenic uptake by seedlings increased with the increasing concentrations of arsenite or arsenate and followed the Michaelis-Menten kinetics function. The average total amylolytic activity and b-amylase activity had no significant difference comparable to that of controls at the concentration 6 2 mg/l arsenite or arsenate, but decreased apparently when the concentration was higher than 2 mg/l. Whereas the a-amylase activity decreased with increasing concentrations of arsenite or arsenate over the whole concentration range. Arsenite decreased all the endpoints more remarkably than arsenate. In comparison, shoot height and root length were more sensitive to arsenic than other endpoints and might be used as indicators for arsenic toxicity.