Search

Dihydrogenarsenate [H(2)AsO(4)(-), As(V)] or dichromate [Cr(2)O(7)(2-), Cr(VI)] at pH=4.0 showed to be sorbed on a Fe(OH)(x)-polymerin complex and ferrihydrite to a greater extent than on polymerin, the organic polymeric fraction of olive oil mill wastewater (OMW). In particular, the maximum amount (x(m)) of arsenate sorbed on Fe(OH)(x)-polymerin complex was similar to that on ferrihydrite (880.26 and 743.02 mmol kg(-1), respectively), and was much greater than that sorbed on polymerin (384.25 mmol kg(-1)). The sorption of dichromate was to a comparable extent on Fe(OH)(x)-polymerin complex and ferrihydrite (205.90 and 254.88 mmol kg(-1), respectively). Cr(III), a less toxic chromium form, mainly, and Cr(V) were indeed the effective forms sorbed on polymerin (200 mmol kg(-1)), as a consequence of the redox reaction of the strongly toxic Cr(VI) with the CH(2)OH groups of the polysaccharide moiety of this bio-sorbent, according to the data deriving from XPS and DRIFT analyses. The potential exploitation of the selected sorbents for the removal of As(V) or Cr(VI) from aqueous effluents is briefly discussed.

This study investigated the sorption of paraquat and 2,4-D on polymerin, the humic acid-like fraction of olive mill wastewater. Effects of pH, contact time, initial concentration and sorbent dosage on the sorption of both herbicides were studied. The sorption mechanism of paraquat on polymerin was consistent with the ion exchange of this herbicide with Ca, Mg and K natively occurring in the sorbent; in contrast, 2,4-D was bound to polymerin by hydrogen bonding. Simulated wastewaters contaminated with paraquat were purified after three sorption cycles on polymerin renewed at each cycle, at a solid/liquid ratio of 0.5, whereas those containing 2,4-D showed a maximal residue removal of 44% after two sorption cycles at the same ratio. The possible application of this model to other water-soluble herbicides, as well as the possible exploitation of polymerin as a bio-filter for the decontamination of pollution point sources is briefly discussed.

The transformation by an oxidoreductase (a laccase from Rhus vernificera) of a mixture of four phenols (catechol, methylcatechol, m-tyrosol and hydroxytyrosol) that simulates a typical wastewater derived from an olive oil factory was investigated. Results achieved in this study confirm that laccase-mediated transformation of phenols depends on the nature and the initial concentration of the involved phenol, the time course of the reaction, and mainly, on the complexity of the phenolic incubation mixture. Actually, the four phenols each have a completely different response to enzyme action both in terms of quantitative and kinetic transformation. For example, after 24-h incubation, methylcatechol was completely removed, whereas 30% of untransformed hydroxytyrosol and catechol and more than 65% of m-tyrosol were still present in the reaction mixture. A reduction of enzyme activity occurred for all phenols after enzymatic oxidation. No correspondence between phenol transformation and disappearance of enzymatic activity was observed, thus suggesting that different mechanisms are probably involved in the laccase-mediated transformation of the four phenols. The behavior of phenols became more complex when an increasing number of phenols was present in the reaction mixture, and even more so when different concentrations of phenols were used. Competitive effects may arise when more than one phenol is present in the reaction solution and interacts with the enzyme.

The interactions between 2,4-D and simazine with inorganic and organic soil colloids affected by adsorption (abiotic) and enzymatic mechanisms (biotic) were investigated. Complex model systems which closely simulate those encountered in soils [i.e. pure montmorillonite, montmorillonite covered by different amounts of OH-Al species (chlorite-like complexes)], were used as adsorbents. 2,4-D gave a negligible adsorption on pure montmorillonite, whereas it was significantly adsorbed on chlorite-like complexes. The larger the OH-Al amounts on clay surfaces, the greater the quantity of 2,4-D adsorbed. An opposite behaviour was observed with simazine, which adsorbed much more on montmorillonite than on chlorite-like complexes. A well characterised laccase from the fungal strain Cerrena unicolor was used as biotic catalyst. The enzyme displayed a lower ability to oxidise 2,4-D and simazine whereas it was extremely efficient in the oxidation of 2,4-DCP (a derivative of 2,4-D) and catechol. The presence of soil colloids or reactive co-substrates differently influenced the enzymatic transformation of 2,4-DCP. The results obtained in this study provided useful information for predicting the behaviour of a xenobiotic substance when entered into soil.

The kinetics and stability of a laccase isolated and purified from the fungal strain Cerrena unicolor were studied. The enzyme was produced in a great yield without inducers. Kinetic parameters were determined by using 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) as substrate. At high ABTS concentrations (> 10 mM) a substrate inhibition phenomenon appeared and an inhibition constant Ki of 24 mM was determined. The pH- and temperature-profiles as well as the sensitivity of the enzyme to several deactivation agents were almost similar to those observed with laccase from different origins. Freezing-thawing treatment, high temperature, acidic pH (< 3.0) and acetonitrile strongly affected laccase activity. The laccase showed a good ability to oxidize different phenolic substances; a significant enhancing effect was showed by ABTS acting as co-substrate. These results seem to suggest that this new laccase preparation may be suitable for environmental purposes.

The effects of atrazine, carbaryl, glyphosate and paraquat on the activity of jack bean urease, free in solution or immobilized on a clean clay (montmorillonite), an organic compound (tannic acid) or a synthetic organo-mineral [Al(OH) x -tannate and Al(OH) x -tannate-montmorillonite] complexes were studied. For comparison, pesticide influence on urease activity in some soils and soil extracts was investigated, under laboratory conditions. Urease was affected by pesticides to different degrees, depending on its physical state, i.e. if free, immobilized or as total activity in soils or soil extracts. Glyphosate and paraquat enhanced the urease activity of soils (by 1.1–1.4-fold) and soil extracts (by 2.59–6.73-fold). No significant effects were detected on the activity of jack bean urease, either free in solution or absorbed on montmorillonite. Similarly, no influence on the activity of urease immobilized on synthetic organo-mineral complexes was observed with paraquat. Since atrazine and carbaryl, which have low solubility in water, were applied in methanol, the effect of this solvent on urease activity was investigated. The activity of urease in soils and soil extracts was strongly increased by methanol (by 1.48–7.47-fold and by 1.42–11.62-fold, respectively) and carbaryl (by 1.73–2.91-fold). Atrazine partly reduced the increasing effect of methanol. Free and immobilized urease were generally inhibited by methanol and both pesticides (on average −40%), but the extent of inhibition greatly depended on the nature of immobilizing support.