Toxicity of copper in the presence of organic substances in sewage sludge

The toxicity of Cu to Photobacterium phosphoreum was studied in the presence of both model substances and organic substances that have been identified as sludge components. Copper toxicity increased in the presence of LAS, caffeine, myristic acid, palmitic acid, nonylphenol, ethyl xanthogenate and oxine, with a steep toxicity gradient for the latter two compounds. Other substances, including complexing agents, ameliorated Cu toxicity. Synergistic/antagonistic effects of organics and Cu in sludge were tested through comparison of the toxicity of Cu added to three sludge types with the concentration of electrochemically available Cu at different sludge/Cu proportions. The toxicity of Cu in raw and digested sludge was much higher than could be explained by the concentration of electrochemically available Cu alone and was attributed to synergism and potentially the formation of lipid-soluble Cu complexes.