Comparative toxicity of bulk and nano zinc particles in Oreochromis niloticus: Accumulation and effect on oxidative stress-related gene expressions

Nanoparticles are very reactive due to their large surface areas compared to their very small volumes. High reactivity potential may cause toxicity due to the harmful relationship of nanoparticles with the biological system and the environment. The rapid increase in the use of metal oxide nanoparticles leads to the uncontrolled release of these particles into the environment. These particles affect the aquatic ecosystem and the organisms found there, thus causing risks in the food chain. For this purpose, in this study, the LC50 values of nano-ZnO (<50 nm) and bulk-ZnSO4 (2000 nm) particles in Oreochromis niloticus were determined, and the fish were exposed to the sublethal concentrations determined according to these values (5% and 10% LC50) on the 7th and 15th days. At the end of the day, samples of liver tissue were taken. In addition to examining zinc accumulation in liver tissues, the gene expressions of SOD, CAT, GPX, GST enzymes, which are the basic enzymes of the defense system, which play an important role in the detoxification of potentially genotoxic compounds, and HSP70, a heat shock protein, were examined, and β-actin gene expressions were used as the standard gene. As a result of 96-hour LC50 analyses, ZnONP had a lower concentration LC50 value (about 25%) than ZnSO4BP; it was determined that ZnONP accumulated in higher amounts in fish exposed to sublethal concentrations for 15 days. In O. niloticus exposed to the effect of 1 and 2 mg/L ZnONP and 4 and 8 mg/L ZnSO4BP, SOD, CAT, GST (in 1 mg/L ZnONP and 4 and 8 mg/L ZnSO4BP groups) (on the 7th day), HSP70 (in the 7th day 2 mg/L ZnONP and 4 mg/L ZnSO4BP groups) was observed that gene expressions were stimulated in a coordinatedly compared to the control group. In O. niloticus exposed to the effect of 1 and 2 mg/L ZnONP and 4 and 8 mg/L ZnSO4BP, GPX (on the 7th day and 15th day), GST (in the 2 mg/L ZnONP group on the 15th day) and HSP70 gene expressions (except for on the 7th day 2 mg/L ZnONP and 4 mg/L ZnSO4BP groups ) were observed to be suppressed in a coordinatedly compared to the control group (P<0.05). The results of this study showed that metal particles of different sizes accumulate in the liver tissue, cause toxic effects in living organisms, and particle sizes lead to different toxic responses. It also confirms previous findings showing that antioxidant enzymes SOD, CAT, GPX, GST and HSP70 in fish can be effectively used as biomarkers of toxicity of nano zinc oxide and bulk zinc sulfate particles.