rapid radiochemical bacterial bioassay to evaluate copper toxicity in freshwaters

• Published in: Archives of environmental contamination and toxicology 2005-11, Vol.49 (4), p.471-479
• Main Authors: Rogers, N.J, Apte, S.C, Knapik, A, Davies, C.M, Bowles, K.C, Kable, S.H
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Australia; bacteria; Bacteria - drug effects; Bioassays; Biological and medical sciences; Biological Assay - methods; Copper; Copper - toxicity; Dissolved organic carbon; DNA, Bacterial - genetics; Ecotoxicology, biological effects of pollution; Environmental research; Erwinia - drug effects; Erwinia - genetics; Erwinia - metabolism; Fresh water; Fresh Water - analysis; freshwater; Fundamental and applied biological sciences. Psychology; General aspects; Glucose - analysis; Glucose - metabolism; Hydrogen-Ion Concentration; microbial growth; Nitrilotriacetic acid; radiolabeling; Speciation; Spectrophotometry, Atomic; Toxicity; toxicity testing; Water Microbiology; Water Pollutants, Chemical - toxicity; water pollution
• ISSN: 0090-4341; 1432-0703
• DOI: 10.1007/s00244-004-0179-9

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).