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Various applications of zinc oxide nanoparticles (ZnO NPs) can increase pollution in aquatic environments. Consequently, pollution can cause toxicity in fish as indicated by oxidative stress, hematotoxicity, and changes in gill and liver histology. Selenium is known for its antioxidant potential in scavenging the free radicals generated during ZnO NP-induced oxidative stress. This study tested the ameliorative role of selenium against ZnO NP-induced toxicity in freshwater fish Catla catla. Four groups of replicated fish, representing control, selenium-treated, ZnO NP-treated, and ZnO NPs+selenium-treated, were used in this study. The ZnO NPs (40 mg l−1) were given to fish in water whereas selenium (50 μg kg−1) was given as sodium selenite in feed. After 28 days of exposure, the fish specimens were processed to collect samples of blood, gills, and liver. The results demonstrated that the consumption of selenium containing feeds protected the C. catla from ZnO NP-induced toxicity and oxidative stress. The use of selenium containing feeds appeared to have reduced the contents of glutathione S-transferase (GST) and glutathione reduced (GSH), and increased the level of catalase (CAT) and superoxide dismutase (SOD). Furthermore, the consumption of selenium in feeds improved the hematological parameters in ZnO NP-treated fish. This study suggests that dietary selenium might be able to ameliorate ZnO NP-induced toxicity in fish.

This study assessed the protective effects of Cinnamomum cassia (cinnamon) bark extract in rats exposed to titanium dioxide nanoparticles or titanium dioxide bulk salt. For in vivo evaluation of the ameliorative role of the cinnamon extract, the experimental groups were orally administered with the cinnamon extract at different dose levels (50 or 100 or 150 mg/kg bodyweight) along with the subcutaneous injections of 150 mg/kg bodyweight titanium dioxide nanoparticles or titanium dioxide bulk salt. The extract showed significant ameliorative role on the antioxidant system in response to elevated levels of titanium dioxide nanoparticles or titanium dioxide bulk salt-induced oxidative stress. It aided in the recovery of the antioxidant system as well as protective role in histological damages and some haematological parameters in the rat liver treated with titanium dioxide nanoparticles or titanium dioxide bulk salt.

Although fish as a diet has many health benefits, metal accumulation in fish has been an increasing public health concerns across the world. The Cyprinus carpio samples were collected from Mangla Lake, Mirpur, Azad Kashmir, Pakistan, and analyzed for 18 essential and toxic trace metals. In edible muscles of the fish, average concentration (μg/g) of K (3002) was the highest, followed by Na (648), Ca (435), Mg (227), and Zn (161). Relatively lower levels (μg/g) were noted for Fe (16.9), Pb (6.05), Sr (4.01), Se (3.49), Co (2.90), Ni (2.37), Mn (2.29), As (1.48), and Cu (1.37), while least levels (μg/g) were found for Cr (0.61), Cd (0.52), Hg (0.15), and Li (0.09) in muscles. Majority of the metals revealed higher accumulation in gills compared with those in scales and muscles. Mean levels of Zn, Mn, Co, Pb, As, and Cd in Cyprinus carpio muscles were found to be exceeding most of the international permissible limits in muscles for safe human consumption. Estimated daily/weekly intakes and hazard quotients/index suggested a high risk related to the intake of Cyprinus carpio from Mangla Lake due to heavy metal contamination. Likewise, target cancer risk (TCR) also indicated significant lifetime carcinogenic health risks to the consumers.

The physicochemical and biological properties of metals change as the particles are reduced to nanoscale. This ability increases the application of nanoparticles in commercial and medical industry. Keeping in view this importance, Silver nanoparticles (Ag-NPs) were synthesized by reduction methods using formaldehyde as reducing agent in the chemical route and lemon extracts in the biological route. The scanning electron microscope (SEM) images of nanoparticles suggested that the particles were either agglomerated or spherical in shape with mean diameter of 16.59 nm in the chemical route and 42.93 nm in the biological route. The particles were between 5 and 80 nm with maximum frequency between 5 and 20 nm in the chemical route and between 5 and 100 nm with maximum frequency between 15 and 50 nm in the biological method. In the second phase of the study, the effect of Ag-NPs on the oxidative stress was studied. For this purpose, Labeo rohita (20 ± 2.5 g in weight and 12 ± 1.4 cm in length) were involved. Six treatments were applied in three replicates having five fishes in each replicate. The first treatment was used as control group, and the other five treatments were exposed to either 10 or 20 or 30 or 45 or 55 mg L−1 of Ag-NPs for 28 days. The treatment of Ag-NPs caused oxidative stress in the liver and gill tissues, which induced alterations in the activities of antioxidant enzymes. The level of catalase (CAT) was decreased in response to Ag-NPs concentration in dose-dependent manner. Ag-NPs treatment stimulated the liver and gill tissues to significantly increase the level of superoxide dismutase (SOD), which might be due to synthesis of SOD and addition in the pre-existing SOD level. The level decreases again due to depletion of SOD level. There was a sharp decline in the activities of glutathione S-transferase (GST) in both gills and liver tissues even at lower concentration, and this decrease in the GST activity was significantly different at each treatment after 28 days of treatment except 20 mg L−1. The malondialdehyde (MDA) levels of gills and liver tissues were increased with the increase in the concentration. The elevated levels of glutathione (GSH) showed that the liver started defensive mechanism against the oxyradicals. This study finds out the cheap eco-friendly and economical method of Ag-NP synthesis. It is further revealed that Ag-NPs caused oxidative stress in the aquatic animals if exposure occurs at high concentrations.

This study assessed the protective effects of Cinnamomum cassia (cinnamon) bark extract in rats exposed to titanium dioxide nanoparticles or titanium dioxide bulk salt. For in vivo evaluation of the ameliorative role of the cinnamon extract, the experimental groups were orally administered with the cinnamon extract at different dose levels (50 or 100 or 150 mg/kg bodyweight) along with the subcutaneous injections of 150 mg/kg bodyweight titanium dioxide nanoparticles or titanium dioxide bulk salt. The extract showed significant ameliorative role on the antioxidant system in response to elevated levels of titanium dioxide nanoparticles or titanium dioxide bulk salt-induced oxidative stress. It aided in the recovery of the antioxidant system as well as protective role in histological damages and some haematological parameters in the rat liver treated with titanium dioxide nanoparticles or titanium dioxide bulk salt.

Silver nanoparticles (Ag-NPs) have wide applications in the medical field; however, the toxicological effects are still poorly studied. The study was aimed to determine the effects of 15.78 nm spherical and amine-coated Ag-NPs on hematology and histology of gills and liver tissues in 28 days treated Labeo rohita (L. rohita). It was found that Ag-NPs induced alterations in the hematological parameters in a dose dependent manner. The Ag-NPs also induced histological alterations in a dose-dependent manner. In gill tissues, it induced fusion of secondary lamellae, separation of gill epithelium, fusion and necrosis of lamellar cells, hyperplasia, deformed cartilaginous skeleton, separation and lifting of epithelium, and curling of lamellae in a dose dependent manner. In the liver, Ag-NPs produced abnormalities in hepatic tissues by reducing the size of hepatocytes and nuclei, and stimulated the production of necrotic and apoptotic bodies. It was concluded that Ag-NPs are toxic to aquatic organisms and induce hematotoxicity and histopathological conditions in exposed fish.

Nano-titanium dioxide (TiO2) is one of the most commonly used materials being synthesized for use as one of the top five nanoparticles. Due to the extensive application of TiO2 nanoparticles and their inclusion in many commercial products, the increased exposure of human beings to nanoparticles is possible. This exposure could be routed via dermal penetration, inhalation and oral ingestion or intravenous injection. Therefore, regular evaluation of their potential toxicity and distribution in the bodies of exposed individuals is essential. Keeping in view the potential health hazards of TiO2 nanoparticles for humans, we reviewed the research articles about studies performed on rats or other mammals as animal models. Most of these studies utilized the dermal or skin and the pulmonary exposures as the primary routes of toxicity. It was interesting that only very few studies revealed that the TiO2 nanoparticles could penetrate through the skin and translocate to other tissues, while many other studies demonstrated that no penetration or translocation could happen through the skin. Conversely, the TiO2 nanoparticles that entered through the pulmonary route were translocated to the brain or the systemic circulation from where these reached other organs like the kidney, liver, etc. In most studies, TiO2 nanoparticles appeared to have caused oxidative stress, histopathological alterations, carcinogenesis, genotoxicity and immune disruption. Therefore, the use of such materials in humans must be either avoided or strictly managed to minimise risks for human health in various situations.