Toxicity of gold nanorods on Ceriodaphnia dubia and Danio rerio after sub-lethal exposure and recovery.

Gold nanorods (AuNRs) are rod-shaped nanoparticles (NPs) with special optical properties that allow their application in several areas including photothermal therapy, diagnosis, drug and gene delivery, cellular imaging, and biosensors. Their high potential for many applications increases the possibility of release in aquatic environments, which can cause risks to organisms. In this study, we evaluated toxic effects of AuNRs on cladoceran and fish (Ceriodaphnia dubia and Danio rerio) and their recovery after post-exposure periods. The EC50 of 0.03 mg L-1 was found for C. dubia in the acute exposure. There was a significant decrease in the number of neonates produced and in the filtration rate of C. dubia after sub-lethal exposure to AuNRs. The toxic mechanism of these NPs to cladocerans was attributed to increases in the reactive oxygen species (ROS) generation. After 4 h of recovery in clean medium, C. dubia were able to reestablish the filtration rate. Enzymatic biomarkers for D. rerio showed significant increases in the activity of superoxide dismutase, catalase, and lipid peroxidation after sub-lethal exposure to AuNRs. These biomarkers were recovered after 168 h in clean water. These results are pivotal on the comprehension of AuNR toxicity to aquatic organisms and are useful in assessing this novel nanomaterial impacts on aquatic biota.

Antioxidant metabolism of zebrafish after sub-lethal exposure to graphene oxide and recovery.

Graphene oxide (GO) is a carbon nanomaterial with specific properties, which allow its use in several areas. Some studies have characterized the effects of GO on aquatic organisms, but the ability of recovery after exposure remains largely unknown. In this study, we evaluated the effects of GO on the antioxidant metabolism of zebrafish after 48 h of sub-lethal exposure, and the fish recovery after 168 h in nanoparticle-free water. After the sub-lethal exposure, superoxide dismutase (SOD) activity was significantly increased in 20 mg L-1, as well as catalase (CAT) activity in 2, 10, and 20 mg L-1, and the lipid peroxidation (LPO) had an increase in 2 mg L-1. On other hand, the glutathione peroxidase (GPx) activity was inhibited at 20 mg L-1. After 168 h of recovery in clean water, the SOD activity remained significantly increased in 20 mg L-1; the CAT activity was unchanged in all tested concentrations; the GPx activity was inhibited in 2, 10, and 20 mg L-1; and the LPO significantly decreased in 2 mg L-1. Our study suggests that GO exposure disrupts the antioxidant metabolism of adult zebrafish. Even after 168 h of recovery in clean water, homeostasis was not completely restored, although organisms developed mechanisms of recovery, and toxic effects were more subtle. Our results are pivotal to better understanding the physiological mechanisms involved in the detoxification process after GO exposure, and for strategies of protection on fish species.

Toxicity of copper oxide nanoparticles to Neotropical species Ceriodaphnia silvestrii and Hyphessobrycon eques.

The increase of production and consumption of copper oxide nanostructures in several areas contributes to their release into aquatic ecosystems. Toxic effects of copper oxide nanoparticles (CuO NPs), in particular, on tropical aquatic organisms are still unknown, representing a risk for biota. In this study, the effects of rod-shaped CuO NPs on the Neotropical species Ceriodaphnia silvestrii and Hyphessobrycon eques were investigated. We also compared the toxicity of CuO NPs and CuCl2 on these species to investigate the contribution of particles and cupper ions to the CuO NPs toxicity. Considering the low copper ions release from CuO NPs (<1%), our results revealed that the toxicity of CuO NPs to C. silvestrii and H. eques was mainly induced by the NPs. The 48 h EC50 for C. silvestrii was 12.6 ±â€¯0.7 µg Cu L-1 and for H. eques the 96 h LC50 was 211.4 ±â€¯57.5 µg Cu L-1 of CuO NPs. There was significant decrease in reproduction, feeding inhibition and increase in reactive oxidative species (ROS) generation in C. silvestrii exposed to CuO NPs. In fish H. eques, sublethal exposure to CuO NPs caused an increase in ROS generation in gill cells and an increase in cells number that were in early apoptotic and necrotic stages. Our results showed that CuO NPs caused toxic effects to C. silvestrii and H. eques and ROS play an important role in the toxicity pathway observed. Data also indicated that C. silvestrii was among the most sensitive species for CuO NPs. Based on predicted environmental concentration in water bodies, CuO NPs pose potential ecological risks for C. silvestrii and H. eques and other tropical freshwater organisms.

Chronic toxicity in Ceriodaphnia dubia induced by graphene oxide.

The unique physico-chemical properties of nanomaterials have allowed their application in different areas including electronics, energy storage, nanomedicine, environmental remediation and biotechnology. Graphene and its derivatives, in particular, have been commercially available, with prediction for increasing their production in the next years, in a way that their release into aquatic environments is very likely to occur, and the impacts of such situation on organisms are still not completely understood. In this context, we evaluated graphene oxide (GO) effects on the freshwater cladoceran Ceriodaphnia dubia through acute and chronic toxicity, feeding rates, and reactive oxygen species (ROS) generation. The mean effective concentration (EC50) estimated during acute exposure was 1.25 mg L-1 of GO. The chronic exposure resulted in significant decrease in the number of neonates. The feeding rates were also decreased by GO exposure. Sub-lethal concentrations of GO caused an increase in ROS generation in the organisms. Our results indicated that GO cause acute and chronic effects to C. dubia. In the presence of GO there was a shift in the available energy for self-maintenance rather than feeding or reproduction activities. This study provides useful information on GO concentrations that might impair the aquatic biota, and supports regulatory efforts concerning the environmental safety of this product.

Metabolic responses of channel catfish (Ictalurus punctatus) exposed to phenol and post-exposure recovery.

Metabolic adjustments were studied in channel catfish Ictalurus punctatus exposed to 1.5 mg L-1 of phe nol (10% LC50) for four days and recovered for seven days. Lower triacylglycerol (TGA) stores and increased muscle fat free acids (FFA) suggest fat catabolism in muscle. Remarkable liver FFA decrease (-31%) suggests liver fat catabolism as well. Increased muscular ammonia levels and ASAT (aspartate aminotransferase) and decreased plasma aminoacids suggest higher muscular amino acid uptake. Constant levels of glucose and increased liver glycogen stores, associated with lower amino acids in plasma, indicate gluconeogenesis from amino acids. This is supported by higher hepatic ALAT and ASAT. Higher hepatic LDH followed by lower plasma lactate may indicate that plasma lactate was also used as gluconeogenic substrate. Biochemical alterations were exacerbated during the post-exposure recovery period. Reduction in muscle and plasma protein content indicate proteolysis. A higher rate of liver fat catabolism was resulted from a remarkable decrease in hepatic TGA (-58%). Catabolic preference for lipids was observed in order to supply such elevated energy demand. This study is the first insight about the metabolic profile of I. punctatus to cope with phenol plus its ability to recover, bringing attention to the biological consequences of environmental contamination.

Metabolic effects of trichlorfon (Masoten®) on the neotropical freshwater fish pacu (Piaractus mesopotamicus).

Fish parasites are among the crucial limiting factors in aquaculture. The organophosphorous pesticide trichlorfon is widely used as an insecticide and against fish parasites worldwide. In this study, the effects of environmental trichlorfon on biochemical and physiological parameters were investigated in Piaractus mesopotamicus (pacu), a widely farmed fish in South America, through sublethal exposure (8 µg L(-1), 10 % of the LC50; 96 h) and recovery. The activity of brain acetylcholinesterase (AChE) was reduced after exposure (15.5 %) and remained decreased during the recovery (21.5 %). In white muscle, AChE activity decreased 31 % only after recovery. Alkaline phosphatase (ALP) and acid phosphatase (ACP) activities of the liver, muscle and plasma were steady during exposure. However, after the recovery period, ALP activity was increased in the liver and muscle and decreased in plasma, while ACP was increased in the liver and decreased in muscle. Intermediary metabolism was also affected by trichlorfon, depicting increase of energetic demand (hypoglycemia, neoglucogenesis and lipid catabolism), which remained even after recovery. These results indicate that P. mesopotamicus is adversely affected by sublethal concentrations of trichlorfon and are useful for assessing the impact as well as the pros and cons of its use in controlling fish parasites in aquaculture.