Silver nanotoxicity using a light-emitting biosensor Pseudomonas putida isolated from a wastewater treatment plant

► Three silver species tested for toxicity using a bacterial biosensor. ► Bioassays carried out with a pseudomonad bacteria from activated sludge. ► Silver ions are the most toxic species followed by nano and micro silver particles. ► Stabilized nano systems show higher toxicity than non stabilized. ► Biosensor suitable for toxicity monitoring in industrial wastewater treatment plant. The effect of silver ions, nano- and micro-particles on a luminescent biosensor bacterium Pseudomonas putida originally isolated from activated sludge was assessed. The bacterium carrying a stable chromosomal copy of the lux operon (luxCDABE) was able to detect toxicity of ionic and particulate silver over short term incubations ranging from 30 to 240 min. The IC 50 values obtained at different time intervals showed that highest toxicity (lowest IC 50) was obtained after 90 min incubation for all toxicants and this is considered the optimum incubation for testing. The data show that ionic silver is the most toxic followed by nanosilver particles with microsilver particles being least toxic. Release of nanomaterials is likely to have an effect on the activated sludge process as indicated by the study using a common sludge bacterium involved in biodegradation of organic wastes.