Environmental context A Cu ion-selective electrode is potentially an excellent tool for cupric ion measurements in salt water, but it is prone to poor reproducibility. We show that dramatic improvements can be obtained by using a Cu ion-selective electrode and a one-point calibration method that corrects for electrode fouling. The method shows promise to be used to collect data on toxic cupric ion concentrations in saltwater environments. Abstract Free Cu is often used as an indicator for potential Cu toxicity. Free ionic Cu2+ was measured using a flow-through ion-selective electrode (ISE). Four different marine samples were collected from various locations and analysed during a fixed-pH Cu titration using an external standard calibration ISE method. Free cupric determinations in the range 10–12 to 10–7molL–1 were consistent with published literature but replicate measures showed up to four orders of magnitude variability. To improve reproducibility, an internal calibration method was developed. The new method was validated using artificial seawater with added tryptophan as the model ligand. The free Cu measured using the improved method showed the same trends as the external calibration data but reproducibility increased to an order of magnitude or better. The potential applicability of this new method was also highlighted in that it matches, in the environmentally and regulatory significant range of total Cu, with a fluorescence quenching method applied to one of the four samples. The ISE data do not agree with free ion concentrations estimated from anodic stripping voltammetry (ASV) though. This suggests that, at least for these samples, ASV responded to a larger fraction of total Cu than simply the inorganic complexes. Caution should be exercised when using ASV as a proxy for bioavailability because the trends in ASV-derived free Cu did not match the free Cu as estimated by ISE. This ability to more reliably measure free Cu is significant for predicting and measuring toxicity on Cu exposure.
The CanaDian Journal of ChemiCal engineering 929 INTRODUCTIONO dours from intensive hog operations result in highly adverse publicity, especially during land disposal of liquid hog manure. Odour results from the action of anaerobic bacteria in the anoxic environments of the porcine gut and liquid manure tank, with the production of reduced sulphurand nitrogen-containing organic compounds. We previously showed (Bejan et al., 2005) that an electric current can ameliorate the odour of liquid hog manure, using electrochemical oxidation at anodes such as Ti/IrO 2 or boron-doped diamond (BDD), a novel electrode material known for stimulating the formation of reactive hydroxyl radicals under anodic polarization (Marselli et al., 2003;Panizza and Cerisola, 2004;Cañizares et al., 2004;Foti and Comninellis, 2004).Electrochemical remediation of waste offers prospective advantages of relatively simple equipment, oxidative or reductive chemistry, operation at ambient temperature and pressure, as well as the low cost of electricity compared with chemicals -typically < 0.5 ¢ per mol of electrons (Rajeshwar and Ibanez, 1997 current efficiency, formation of insulating deposits on the electrode surface, and the need for inexpensive electrode materials.Many types of waste have been treated electrolytically, with some attention given to animal wastes. Electrolysis of manure at copper anodes (Muller, 1987;Ranalli et al., 1996;Zanardini et al., 2002) is unsatisfactory because it relies on the toxicity of dissolved Cu 2+ towards the odour-causing bacteria, making the treated manure inappropriate for land-disposal. Other sacrificial metal anodes such as iron and aluminum form hydroxides that remove manure solids by coagulation (Marconato et al., 1998). Moniwa et al. (2003) treated fowl slaughterhouse waste using the electroFenton reaction, which employs a combination of oxidation and coagulation. Oxygen supplied to the cathode generates hydrogen peroxide, which reacts with Fe 2+ dissolved from a sacrificial iron anode to form reactive hydroxyl radicals (Fe 2+ + H 2 O 2 → Fe 3+ + OH + OH -). The resulting Fe(OH) 3 acts as a coagulant for the manure solids.Electrolysis of liquid hog manure under direct current achieved amelioration of odour, in terms of both odour quality and odour intensity, and simultaneously reduced the population of odour-causing bacteria by two orders of magnitude. A comparison of anode materials indicated that hydroxyl radical-forming anodes (boron-doped diamond and Ebonex) were the most effective, but unfortunately these materials are not yet available commercially in large size format. Dimensionally stable anodes composed of Ti/IrO 2 were found to be satisfactory; lead-based anodes leached unacceptable quantities of inorganic lead into the treated manure, and graphite anodes tended to disintegrate on long-term use. The mechanism of action of the bactericidal effect involves a combination of toxicity by O 2 that is released at the anode and hypochlorination due to the chloride ion that is present in manure. The pro...
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