Adsorption of heavy metals and redox reactions of Cr(W) ions on Fe-Mn nodules from five soils of China were investigated by chemical analysis, equilibrium adsorption/redox, and X-ray photoelectron spectroscopy (XPS). Results show that Mn is mainly present as Mn3+and Mn4+ forms in Fe-Mn nodules. The maximum adsorption amounts for different heavy metal ions follow the order Pb2+≈Cu2+>Zn2+>Co2+>Ni2+>Cd2+. The adsorption capacity for heavy metals by Fe-Mn nodules from calciaquert in Shandong province (N5-1) is the highest, while that from hapludalf in Shandong province (N6-1) is the lowest. About 44-100% of the heavy metals adsorbed on Fe-Mn nodules were dissolved in 0.1 mol/L hydroxylamine hydrochloride (HAHC). The maximum amounts of Cr(VI) production by Fe-Mn nodules follow the order of N1-1 (69 mmol/kg)>N4-1 (57 mmol/kg)>2-1 (52 mmol/kg)>N5-1 (44 mmol/kg). Based on the content of MnO2 in Fe-Mn nodules dissolved in HAHC, the amount of Cr(VI) production by Mn oxides in N1-1, N2-1, N4-1, and N5-1 is 326, 624, 726, and 482 mmol/kg (MnO2), respectively. We propose that the amounts of Cr(VI) production through oxidation Cr(III) by Mn oxides are related to the types of Mn oxides in Fe–Mn nodules.

To obtain a better understanding of the enzymatic properties of soils from tropical and subtropical areas polluted with heavy metals, the effect of zinc on the activities and kinetics of acid phosphatase immobilized on variable-charge soil constituents was investigated. Both free and immobilized enzymes were inhibited significantly in the presence of 0.1 to 4 mM Zn (as ZnCl2), and the inhibition increased with an increase of pH from 5.0 to 6.0. The enzymes immobilized on the Latosol clay and kaolin mineral were as sensitive as free (i.e. soluble) enzymes to Zn toxicity. The inhibitory effect of Zn was reduced when acid phosphatase was immobilized on goethite. Various inhibition patterns by Zn were observed for free and immobilized acid phosphatase at different pH values. Zinc showed uncompetitive inhibition for the goethite-enzyme complex at pH 5.0, 5.5 and 6.0. The inhibition of free enzyme and Latosol clay-enzyme complex by Zn changed from an uncompetitive type at pH 5.0 and 5.5 to a mixed type at pH 6.0. However, the inhibition model of the kaolin-enzyme complex was mixed type at the three pH levels. Variation of inhibition model seems to be related to the degree of deactivation of the enzyme by the Zn. Zinc addition also increased the affinity of free and immobilized enzymes for the substrate (i.e. reduced Km values). The high affinity of goethite-enzyme complex for the substrate induced a substrate inhibition at pH 5.0, which was enhanced by the presence of Zn.

The effects of montmorillonite (Osage, Wyoming) with different interlayers on the adsorption, activities, and kinetic properties of acid phosphatase were examined. Hy-droxy polymers of aluminum or chromium (200 cmol kg-1 clay) were intercalated in montmorillonite in the absence or presence of citric acid (citrate/Al or Cr=0.1 and 0.5). The activities of acid phosphatase in the presence of different amounts of clay at three pH values (5.0, 5.5, and 6.0) were de-termined, and the Michaelis-Menten kinetic parameters were calculated. The amount of enzyme adsorbed by interlayered montmoril-lonite was considerably lower than that by pure montmorillonite and increased as the citrate/Al or Cr ratio increased. The type of interlayer (A1 or Cr) influenced the ease with which enzymes could be removed by washing. Complete adsorption of the enzyme led to the formation of clay-enzyme com-plexes, which had lower activities than the free enzyme. The order of activity of en-zymes following adsorption was Cr-montmo-rillonite>Al-montmorillonite>montmoril-lonite. The effect of citrate on enzyme activity in the clay-enzyme complexes was significant only at the higher ratio. Factors that caused a reduction in enzyme activity were adsorption by clay, amount of clay, and increase in pH. These effects were modified by the type of interlaycrs (AI or Cr), the ci-trateYAI or Cr molar ratio, and the strength of adsorption. In the presence of clay, the Michaelis-Menten affinity constant (K.,), in-creased, whereas the luaxinlnnl eazyme reaction velocity (Vmax), decreased compared with the free enzyme. The change of the enzyme kinetics by A1- and Cr-interlayered montmorillonite can be described as partial noncompetitive inhibition.

Heavy metal pollution presents a major hazard to the soil environment. Studies have shown that the activities of a variety of soil enzymes are inhibited by heavy metals. However, little information is available concerning the effect of heavy metals on the activity of enzymes immobilized by different soil constituents. The main objective of this work was to investigate the effects of copper on the activity and kinetic properties of acid phosphatase both free and immobilized on two variable-charge soil clays and the minerals kaolin, goethite and manganese oxide. The effect of different forms of copper on enzyme activity was also examined. In the presence of copper chloride, the activity of free and immobilized enzymes was inhibited at copper concentrations of 0.005-0.8 mM at pH 5.0 and inhibition increased at pH 6.0. The inhibitory effect of copper chloride was greater on the enzymes bound by the two soil clays and kaolin than those by goethite and MnO2. Addition of copper chloride decreased both the Km values and the Vmax/Km ratios of free and all forms of immobilized enzymes, and showed mixed type inhibition kinetics. Comparing the effect of different forms of Cu, the residual activities of free enzyme and soil clay-enzyme and kaolin–enzyme complexes were higher when copper citrate was used than with copper chloride. The reverse was true for the enzymes immobilized on goethite and MnO2. These results indicate that the inhibition by Cu of enzymes immobilized on soil components are influenced by the properties of the adsorbent and the form of Cu, as well as pH.

DNA is the genetic material of various organisms. Extracellular DNA adsorbed or bound on surface-active particles in soils has been shown to persist for long periods against nucleases degradation and still retain the ability to transform competent cells. This paper reviews some recent advances on the binding and transformation of extracellular DNA in soils, which is fundamental to understanding the nature of the soil, regulating biodiversity, and assessing the risk of releasing genetically engineered microorganisms (GEMs) as well as being belpful for development of the genetic evolutional theory of bacteria. Several inlluencing factors, such as soll pH, ionic strength, soll surface properties, and characteristics of the DNA polymer, are discussed. To date, the understanding of the type of molecular binding sees and the confirmation of adsorbed and bound DNA to soil particles is still in its infancy.