Investigating the management challenges of the EU Ecolabel through multi-stakeholder surveys

The International Journal of Life Cycle Assessment - The EU Ecolabel is a voluntary scheme that aims to reduce the overall environmental impact of organisations to boost sustainable consumption in...     

Arsenic speciation in marine sediments: A comparison between two sequential extraction procedures

ABSTRACT

Arsenic distribution and mobility in marine sediments was investigated by means of total extraction and two sequential extraction procedures i.e. a modified sequential extraction procedure proposed by the European Standard, Measurementand Testing (SM&T) program, formerly the Community Bureau of Reference (BCR) procedure and a five steps sequential extraction based on the Wenzel extraction procedure, called modified Wenzel extraction. Sediments were collected from Cagliari’s harbour and Cagliari’s gulf, in Western Mediterranean Sea, Italy. The modified Wenzel extraction provided a more detailed As binding pattern and turned out to be much more appropriate than the modified SM&T procedure for gaining information regarding the mobilization of As within marine sediments. In the harbour, the largest part of As is contained in the residual fraction. At the contrary, As concentration, which is higher in the Cagliari’s gulf, is primarily associated with amorphous and crystalline hydrous Fe(Mn, Al) oxide. Moreover, this study suggests the possibility to segregate different types of marine sediments depending of human or industrial activities and to trace As contaminated marine sediments to determine the origin of contamination following the percentile of As contained in each extraction steps.     

Deactivation of free and stabilized acid phosphatase by urea

Tests on acid phosphatase (E.G. 3.1.3.2) deactivation by urea have been performed at two pH values. Two conditions have been used: native enzyme operating batch-wise in dilute solution and stabilized enzyme in continuous flow ultrafiltration membrane reactor. Stabilization is achieved by confining the enzyme within a concentrated solution of a linear chain polymer that forms a polarization layer over the membrane. The results provide significant information on the kinetics and thermodynamics of the complex phenomena taking place during deactivation. Deactivation by urea is also compared with thermal deactivation.     

Acid phosphatase deactivation by a series mechanism

Acid phosphatase (E.C.3.1.3.2.) thermal deactivation at pH 3.77 has been investigated by monitoring the enzyme activity as a function of time in the hydrolysis of p-nitrophenyl phosphate. The experimental curves obtained show a two-slope behavior in a log (activity)versus-time plot, which indicates that deactivation occurs via a complex mechanism. From the dependence of the kinetic parameters on both deactivation and hydrolysis temperatures, it is inferred that the deactivation mechanism involves intermediate, temperature-dependent, less-active forms of the enzyme. This interpretation is confirmed by the results of additional tests in which the temperature was suddenly changed during the deactivation process.     

Series mechanism of enzyme deactivation. Characterization of intermediate forms

Acid phosphatase (E.C. 3.1.3.2) undergoes complex thermal deactivation phenomena, as revealed by the two-slope pattern of the enzyme logarithmic-specific-activity versus time curves. The native enzyme first decays toward an equilibrium distribution of less, but still active, intermediate structures and these, in turn, undergo a final degradation to a completely inactive form. The effect of the experimental conditions at which the enzyme is kept during the deactivation process on the characteristics of these intermediate enzymatic structures has been investigated. The kinetic parameters of p-nitro-phenyl phosphate hydrolysis, as catalyzed by some of these intermediate forms, have been determined and the results compared to those obtained with the native enzyme.