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Contact toxicity of metals in sewage sludge: evaluation of alternatives to sodium chloride in the microtox® assay
Author(s) -
CarlsonEkvall C. E. Annika,
Morrison Gregory M.
Publication year - 1995
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620140103
Subject(s) - photobacterium phosphoreum , chemistry , chloride , extraction (chemistry) , potassium , sewage sludge , diluent , environmental chemistry , metal ions in aqueous solution , potassium phosphate , phosphate , nuclear chemistry , metal , sewage , inorganic chemistry , chromatography , toxicity , environmental engineering , organic chemistry , engineering
The presence of chloride ions in the Microtox® test can cause problems when testing metal toxicity, both due to extraction of metals from solid samples and formation of chloro complexes of metals in the liquid phase. To investigate alternatives to NaCl in the Microtox test, the toxicity of Cu, Cd, Pb, and Zn to Photobacterium phosphoreum was tested in 28 osmotic surrogates for NaCl. It was found that Na + must be present to keep the blank luminescence stable for 30 min. The results point to NaClO 4 as the most satisfactory surrogate solution as it has an inert behaviour and does not form complexes with any metal of environmental interest. Raw, digested, and reference sewage sludges were tested in the osmotic surrogates. The EC50 values for sludges were lower in solutions of NaNO 3 , Na 2 SO 4 , and NaClO 4 , and higher in sucrose, mannitol, and KCl, compared to NaCl. NaClO 4 can be recommended as an osmotic surrogate for sewage sludge testing. Another problem with the Microtox assay is the lack of pH control in the cuvette. Copper toxicity tests were carried out in Tris buffer and KH 2 PO 4 at two different concentrations and at pH 7 and 8. The results show that 1 mM phosphate buffer, pH 7.0, can be recommended for solid samples. However, owing to formation of KClO 4 a buffer containing potassium is not recommended in combination with NaClO 4 .