title: A rapid radiochemical bacterial bioassay to evaluate copper toxicity in freshwaters.
abstract: A rapid, highly sensitive bacterial bioassay to determine copper toxicity in freshwaters was developed based on the inhibition of cellular assimilation of radiolabeled glucose. The test used a copper-sensitive bacterium isolated from a freshwater stream. Employing sensitive radiochemical techniques enabled environmentally relevant concentrations of the test bacterium (10(5) cells mL(-1)) and a short incubation period (4 hours) to be used, which minimized the potential for changes in copper speciation during the test. The 4-hour median effective concentration (EC(50)) for inorganic copper at pH 7.5 in synthetic freshwater was 0.6 microg L(-1) (95% confidence limits 0.4 to 1.0 microg L(-1)). This compared well with chronic growth inhibition of this bacterium in minimal medium (48-hour EC(50) of 0.9 microg L(-1) [95% confidence limits 0.7 to 1.0 microg L(-1)]). MINEQL + software (Environmental Research Software) was used to calculate copper (II) ion concentrations in synthetic freshwater at pH 7.5, giving an EC(50) value of pCu(2+) 8.8. However, using nitrilotriacetic acid metal-ion buffers (Cu-NTA), 50% inhibition occurred at a pCu(2+) of 9.7, suggesting this bacterium was markedly more inhibited by copper in these Cu(2+)-buffered solutions. This may indicate that the Cu-NTA species was contributing to toxicity. The radiochemical bioassay was evaluated further using freshwater samples from both copper-impacted and pristine environments. Measured EC(50) values ranged from 3.4 to 34.0 microg L(-1)inorganic copper and were strongly correlated with dissolved organic carbon (DOC) concentrations (r = 0.88, p < 0.05).
authors.affiliation: Centre for Environmental Contaminants Research, CSIRO Energy Technology, Private Mail Bag 7, Bangor, NSW 2234, Australia. nicola.rogers@csiro.au
authors.forename: N J
authors.initials: NJ
authors.lastname: Rogers
authors.forename: S C
authors.initials: SC
authors.lastname: Apte
authors.forename: A
authors.initials: A
authors.lastname: Knapik
authors.forename: C M
authors.initials: CM
authors.lastname: Davies
authors.forename: K C
authors.initials: KC
authors.lastname: Bowles
authors.forename: S H
authors.initials: SH
authors.lastname: Kable
mesh_terms: D001315:Australia; D001419:Bacteria / Q000187:drug effects*; D001681:Biological Assay / Q000379:methods*; D003300:Copper / Q000633:toxicity*; D004269:DNA, Bacterial / Q000235:genetics; D004885:Erwinia / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D005618:Fresh Water / Q000032:analysis*; D005947:Glucose / Q000032:analysis / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D013054:Spectrophotometry, Atomic; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D004269:DNA, Bacterial; D014874:Water Pollutants, Chemical; D003300:Copper; D005947:Glucose