Evaluation of nanosilver-induced toxicity in aquatic environment using the Chinese rare minnow

Abstract

Nanosilver, a popular disinfectant with excellent antibacterial activity, is used in a variety of fields, including the food industry, medical appliance maintenance, and water treatment. Given its widespread use, there is increasing concern regarding the biosafety of nanosilver. We evaluated the toxicity of a nanosilver-based disinfectant at the suggested effective doses for water treatment (1-20 mg/L) using the Chinese rare minnow ( Gobiocyprisrarus ). The silver nanoparticles were coated with polyvinylpyrrolidone (PVP) and dispersed in the water. TEM characterization revealed the particle size was within 10 nm. The hydrodynamic size was ~3.76 nm based on measurement of dynamic light scattering. The zeta potential was -5.5 mV and the UV absorbance was weak. High levels of both silver ion and nanosilver exposure were lethal to the fish. The 24-h half lethal concentrations (24 h LC 50 ) were 12.79 mg/L and 22 μg/L for nanosilver and silver ions, respectively, suggesting the toxicity of nanosilver was much lower than that of the silver ion. We conducted a total silver analysis using ICP-MS to evaluate the accumulation and depuration of silver in the exposed fish. Both nanosilver and silver ions were able to enter into fish tissues, the bioaccumulation was not high though. The liver, gill, and intestine contained relatively high levels of silver and the bioaccumulation was in a dose-dependent manner for nanosilver exposure. Silver levels increased slowly with exposure time and decreased rapidly during the depuration period. Silver ions were characterized by a higher bioavailability to the the Chinese rare minnow than nanosilver. The histological observations using scanning electron microscopy (SEM) revealed that both silver ions and nanosilver had obvious deleterious effects on the target tissues, including gill and liver. The ultrastructural alterations of the gill tissues included a fall-off of the flat epithelial cell, disappearance of the surface microridges, and distorted taste buds. Similarly, nanosilver and silver ion exposure resulted in obvious damages to the liver surface such as irregular hepatocyte shape. Silver ion exposure caused in much more severe effects on these target tissues than nanosilver, likely because silver ions were more readily taken up. Our results are consistent with observations in other fish species (e.g., rainbow trout and zebrafish), suggesting that the Chinese rare minnow is a good model for evaluating the aquatic toxicity of nanosilver. Ultrastructural observations using SEM also provided a sensitive approach for toxicological studies. Given that these subchronic deleterious effects were induced by nanosilver at the doses suggested for water disinfection, there is an urgent need for risk assessment on the potential aquatic toxicological effects of nanosilver.