An assessment of the effect of contact time on cadmium phytoavailability in a pasture soil.

The length of time cadmium (Cd) is in contact with the soil has been recognised as a factor affecting phytoavailability, but the extent of this process is currently poorly understood. This study used isotopic dilution techniques (E and L values) to determine the effect of contact time on Cd phytoavailability from soil collected from a long-term phosphorus (P) fertiliser trial. Cadmium phytoavailability was determined in soil that was last fertilised with soluble Cd from P fertiliser 17 years prior to sampling (residual plots) and soil that received annual applications of P fertiliser until sampling (continuous plots). It was found that both E values and L values increased with P fertiliser (viz Cd) inputs and were significantly related to each other (r 2 = 0.82 P < 0.005). There was however no significant difference (P < 0.05) in the percentage of total Cd that was phytoavailable calculated using E values (E%) between the continuous (mean 51 %) and the residual plots (mean 51 %). There was also no significant difference (P < 0.05) in the percentage of total soil Cd that was phytoavailable calculated using L values (L%) between the continuous (mean 77 %) and residual plots (mean 87 %). These results suggest that despite Cd being in contact with the soil for 17 years, there was no difference in the size of the phytoavailable Cd pool compared to recent Cd inputs. This study should be repeated for other soil types and factored into any analysis for the long-term implications of ongoing Cd accumulation in soil on future landuse.

[Effect of continual application of two kinds sludge on enzyme activities and heavy metal concentrations in alluvial soil].

Pot culture experiments were conducted to study the effect of industrial and sewage sludge on some enzyme activities and heavy metal concentrations in alluvial soil. The results showed that the heavy metals in both industrial and sewage sludge were mainly non-exchangeable, and those in sewage sludge had a lower concentration but a higher bio-availability than in industrial sludge. The application of sludge could increase the activities of soil urease, polyphenol oxidase and neutral phosphatase, and the polyphenol oxidase and neutral phosphatase activities showed a reverse relationship with the concentrations of soil exchangeable Zn and Cu. Soil polyphenol oxidase and catalase activities could be used to indicate the Zn pollution in soil.

Fractionation of arsenic in soil by a continuous-flow sequential extraction method.

Batch sequential extraction techniques for fractionating metals or metalloids in soils are time consuming and subject to several potential errors. The development of a continuous-flow sequential extraction method for soil As is described and assessed, having the benefits of simplicity, rapidity, less risk of contamination, and less vulnerability to changes in extraction conditions compared with traditional batch methods. The validated method was used to fractionate soil As using water, NaHCO3, NaOH, and HCl, followed by digestion of the residue with HNO3 and HF acids. The extracts and digests were analyzed for As by graphite furnace atomic absorption spectrometry. Good recoveries of total soil As (97-115%) were obtained and fractionation data generally comparable with those obtained using conventional batch techniques. Soils from a tin-mining area in Thailand and soils from As-contaminated cattle (Bos taurus) dip sites in Australia were used to test the applicability of the method, and to demonstrate the usefulness of the extractogram obtained. The ability to produce detailed extractograms for As and other elements (Al, Fe, and Ca) enabled an examination of elemental associations in individual fractions. With the exception of As extracted with HCl, the extractograms generally support previous suggestions of the likely forms or associations of As present in the different soil fractions.

Fractionation of copper, nickel, and zinc in metal-spiked sewage sludge.

The enrichment or spiking of sewage sludge with heavy metals for experimental purposes is a fairly widely used, although sometimes controversial, technique. A study was undertaken, using a sequential fractionation scheme, to assess the degree of incorporation of Cu, Ni, and Zn into sewage sludge samples spiked with these metals and incubated for 6 mo. For all three metals, substantial proportions of the metals were incorporated into the sludge matrix, particularly as evidenced by their occurrence in the oxide-bound, organic-bound, and residual fractions. In particular, for Cu very little of the added copper remained in the sludge supernatant solution after 6 mo of incubation and, apart from at the highest level of Cu addition, there was very little difference in the fractional distribution of Cu between the Cu-spiked and non-Cu-spiked sludges. For Ni and Zn, however, although there was substantial incorporation of these metals into the sludge, the higher levels of Ni and Zn addition resulted in greater proportions of the metals in the most soluble fractions (soluble, exchangeable, specifically sorbed) compared with nonspiked sludges. The fractionation data for Ni also showed that large additions of Cu and Zn can affect the fractional distribution of Ni in the sludge. The drying of sewage sludge prior to analysis was shown to increase metal solubility in the sludge samples, and the potential implications of this finding for the prediction of sludge metal bioavailability are discussed.

Inline blood gas analysis by gas chromatography in patients during and after coronary artery surgery.

A system was evaluated of measuring Pao2 and Pao2 by an inline sensor in the brachial artery and gas chromatography. Eight patients having coronary artery vein grafts were studied during anaesthesia, operation, perfusion and for 24 hours afterward. Compared to conventional blood gas analysis by polarography (electrodes), the chromatographic method gave readings for Pao2 which were not significantly different during normothermia. During hypothermic perfusion, the chromatographic system read significantly higher than the bench electrode, due at least in part to a difference in temperature correction. For Pao2 the correlation between the two methods was close and differences were clinically insignificant. The Sentorr blood-gas analyser provides a sensitive, accurate indicator of changes in oxygenation, ventilation and circulation during anaesthesia and in the intensive care unit.