No abstract

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.

There are currently few studies on the dual effects of metal ions on the sorption of atrazine and conversely of atrazine on metal adsorption on multiwalled carbon nanotubes (MWCNTs). While a number of sorption models were considered to describe the sorption of atrazine on MWCNTs, the Polanyi-Manes model (PMM) fit the sorption isotherms well with the lowest mean weighted square errors. Atrazine was mainly adsorbed onto the surface and micropores of MWCNTs bundles or aggregates. Hydrogen bonding between azo and amino nitrogen of atrazine and functional groups on MWCNTs also occurred. Oxygenated functionalities, mainly carboxylic groups on MWCNTs surface, decreased the sorption of atrazine. Metal cations Cu 2+ , Pb 2+ , and Cd 2+ diminished the sorption of atrazine depending on the oxygenated functionalities densities. The mechanisms ascribed were due to the formation of surface or inner-sphere complexes of Cu 2+ , Pb 2+ , and Cd 2+ through carboxylic groups and hydration, which may occupy part of the surface of MWCNTs-O. The large hydration shell of metal cations may intrude or shield the hydrophobic and hydrophilic sites and indirectly compete with atrazine for surface sites, leading to the inhibition of atrazine adsorption around the metalcomplexed moieties.

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Summary• Organic acids play an important role in metal uptake by, and accumulation in, plants. However, the relevant mechanisms remain obscure.• Acetic, malic and citric acids increased the uptake of lanthanum (La) by barley ( Hordeum vulgare ) roots and enhanced La content in shoots under hydroponic conditions.• Concentration-dependent net La influx in the absence and presence of organic acids yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The saturable component followed Michaelis-Menten kinetics. The K m values were similar; however, the V max values in the presence of acetic, malic and citric acids were 4.3, 2.8, 1.5-times that of the control, respectively.• Enhanced uptake of La by organic acids was mediated mainly, but not solely, by Ca 2+ channels. X-ray absorption spectroscopic techniques provided evidence of La-oxygen environment and established that La(III) was coordinated to 11 oxygen atoms that are likely to be involved in the binding of La(III) to barley roots via carboxylate groups and hydration of La(III).

The coadsorption of ciprofloxacin (Cip) and Cu(II) on montmorillonite and kaolinite was studied between pH 4.0 and 9.5. At pH < 5.0, Cu

Cu(II)Multi IntroductionCarbon nanotubes (CNTs) are considered to be superior adsorbents of pollutants due to their unique properties and relative high reactivity. (Li et al., 2003a;Lu and Chiu, 2006;Wang et al., 2005). Oxidation removes impurities and hemispherical caps, hence increases surface area and introduces oxygen-containing functional groups (Li et al., 2003a;Lu and Chiu, 2006;Wang et al., 2005). Modification of the structure and surface properties of CNTs affected sorption capacity and sorption mechanisms of metals and organic chemicals (Li et al., 2003a;Lu and Chiu, 2006;Wang et al., 2005;Lu et al., 2005;Chin et al., 2007;Cho et al., 2008). The adsorption capacity of Cu 2þ at a given pH followed the order NaOClmodified CNTs > HNO 3 -modified CNTs > as-produced CNTs (Wu, 2007). The extraordinary increase in sorption capacity and decrease in desorption rate of w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 2 4 0 9 -2 4 1 8

Abstract-Evidence exists for significant metal enrichment in particulate organic matter (POM) compared to other soil constituents, but the relevant mechanisms are poorly understood. In the present study, adsorption of the heavy metals Pb, Cu, and Cd on a loamy soil and on POM separated from this soil was investigated. The adsorption kinetic data can be well described with a pseudo-second order model, whereas the equilibrium data are well fitted by a Langmuir model. Adsorption isotherms and kinetics data, in addition to the influence of pH on metal adsorption, showed that POM had a much higher adsorption capacity for Pb, Cu, and Cd compared to the whole soil. Ionic strength effects on metal adsorption, Fourier transform infrared spectroscopy, x-ray absorption spectroscopy x-ray absorption spectroscopy including x-ray absorption near-edge structure and extended x-ray absorption fine-structure spectroscopy were employed to elucidate the adsorption mechanisms. The results suggested that Pb and Cu adsorption on POM was mainly through inner-sphere complexes with carboxyl and hydroxyl groups. Cadmium was possibly adsorbed via outer-sphere complexation, indicated by the influence of ionic strength on Cd adsorption.