Toxicity of Silver-Chitosan Nanocomposites to Aquatic Microcrustaceans Daphnia magna and Thamnocephalus platyurus and Naturally Luminescent Bacteria Vibrio fischeri .

All novel materials should be analyzed for their potential environmental hazard. In this study, the toxicity of different silver-chitosan nanocomposites-potential candidates for wound dressings or antimicrobial surface coatings-was evaluated using environmentally relevant aquatic microcrustaceans Daphnia magna and Thamnocephalus platyurus and naturally luminescent bacteria Vibrio fischeri . Three silver-chitosan nanocomposites (nAgCSs) with different weight ratios of Ag to CS were studied. Citrate-coated silver nanoparticles (nAg-Cit), AgNO 3 (ionic control) and low molecular weight chitosan (LMW CS) were evaluated in parallel. The primary size of nAgCSs was ~50 nm. The average hydrodynamic sizes in deionized water were ≤100 nm, and the zeta potential values were positive (16-26 mV). The nAgCSs proved very toxic to aquatic crustaceans: the 48-h EC 50 value for D. magna was 0.065-0.232 mg/L, and the 24-h LC 50 value for T. platyurus was 0.25-1.04 mg/L. The toxic effect correlated with the shedding of Ag ions (about 1%) from nAgCSs. Upon exposure of V. fischeri to nAgCSs for 30 min, bacterial luminescence was inhibited by 50% at 13-33 mg/L. However, the inhibitory effect (minimum bactericidal concentration, MBC) on bacterial growth upon 1 h exposure was observed at higher concentrations of nAgCSs, 40-65 mg/L. LMW CS inhibited bacterial luminescence upon 30-min exposure at 5.6 mg/L, but bacterial growth was inhibited at a much higher concentration (1 h MBC > 100 mg/L). The multi-trophic test battery, where D. magna was the most sensitive test organism, ranked the silver-chitosan nanocomposites from 'extremely toxic' [L(E)C 50 ≤ 0.1 mg/L] to 'very toxic' [L(E)C 50 > 0.1-1 mg/L]. Chitosan was toxic (EC(L) 50 ) to crustaceans at ~12 mg/L, and ranked accordingly as 'harmful' [L(E)C 50 > 10-100 mg/L]. Thus, silver-chitosan nanocomposites may pose a hazard to aquatic organisms and must be handled accordingly.