Genotoxic evaluation of silver nanoparticles in catfish Clarias gariepinus erythrocytes; DNA strand breakage using comet assay

Abstract

In the present study, the neutral comet assay was applied for determination DNA double strand breakage in the African catfish Clarias gariepinus exposed variable concentrations and size of silver nanoparticles and ions. The parameters, tail % DNA; tail length, tail area; tail intensity; tail moment, olive tail moment, head mean intensity exhibited variability in the treatment and recovery periods. The silver small sized nanoparticles affect significantly (P < 0.0001) all the comet parameters in comparison to other treatments. In the case of recovery, the high sized nanoparticles with high concentration exhibited the significant effects in all parameters in comparison to other treatments. Moreover, correlation between exposure and recovery periods for each parameter was found to be significantly lower (P < 0.05). A positive insignificant correlation (R = 0.79) was recorded between % TDNA of the exposure period and erythrocyte alterations of the same period. On the other hand, such %TDNA was positively correlated (0.81–0.96) with more biochemical and histopathological parameters and negatively correlated (-0.85—0.88) with some other parameters. No micronuclei were recorded in association with AgNPs or Ag-induced DNA damages and other erythrocytes alterations. DNA damage was identified as follows: undamaged (%TDNA 0–10%), low damaged (%TDNA >10–20%), moderate damaged (%TDNA ≥20–40%) and sever damaged (%TDNA ≥ 40%). The undamaged DNA exhibited more or less decline with Ag and AgNPs whereas the damaged DNA increased with fluctuation especially with Ag and all concentration of AgNPs except for 40 nm/100 µg/L. After 15-day recovery, fluctuation in undamaged and damaged DNA was evident due to insufficient period of DNA repair with individual variations. No hedgehogs (%TDNA <85%) were recorded in both periods of exposure and recovery since low percent of severe damage was recorded. These findings emphasize on the adverse impacts of AgNPs especially those of small size and/or of high concentration on fishes.