Carboxymethyl chitosan is a hydrophilic modification of chitosan by carboxymethylation, which is a polysaccharide obtained from chitin through deacetylation. Chitin, the second most abundant polysaccharide, is a natural polymer made from chains of N-acetyl D-glucosamine and it is found in the exoskeletons of insects, the cell walls of fungi, and cephalopod beaks. As chitin is insoluble in all regular solvents such as water, organic solvents, mild acidic or basic solution, etc., it is deacetylated to obtain chitosan, which is soluble in dilute aqueous acidic solution (pH<6.5). Chitosan has wide biological applications due to its properties such as biocompatibility and biodegradability, thus the use of acids for the solubilization might induce a toxic effect of the chitosan. By carboxymethylation, chitosan becomes soluble in water at neutral pH, thus no acids are required for solubilization. Due to the potential pollution of the environment caused by the broad medical and pharmaceutical application of carboxymethyl chitosan, the assessment of its ecotoxicity is essential. The ecotoxicological effects of carboxymethyl chitosan (CMCS) were assessed using a growth inhibition assay on Lemna minor (duckweed) conducted according the OECD 221 guideline, followed by fresh and dry weight determination. Ten concentrations of CMCS (1%, 0.5%, 0.1%, 0.05%, 0.001%, 0.005%, 0.0001%, 0.0005%, 0.00001% and 0.00005%) were tested, with 35 duckweed fronds per replicate. After 7 days, the number of fronds (green and chlorosed) and colonies were assessed, the fronds were weighted, after blotting on paper for fresh weight determination, and were kept at 60˚C until no weight change was recorded, for dry weight determination. The results showed both green frond number and total frond number increased with decrease in CMCS concentration. The colony number and the number of fronds with chlorosis decreased with the concentration. Only the highest two concentration (1% and 0.5%) inhibited the growth of fronds, while the other concentrations showed no inhibition, on the contrary, promoting the growth. Regarding the dose-response curve, the calculated E50 value for CMC was 3000.6 mg/L, a high concentration that is not considered toxic.

ecotoxicity, common duckweed, carboxymethyl chitosan

biology

Presentation: poster