Abstract
The extensive use of engineered nanomaterials, such as graphene oxide (GO), is stimulating research about its potential environmental impacts on the aquatic ecosystem. This study is aimed to comprehensively assess the acute toxicity of a well-characterized GO suspension to Daphnia magna. Conventional ecotoxicological endpoints (lethality, immobilization) and more sensitive, sublethal endpoints (heartbeat rate, feeding activity, and reactive oxygen species (ROS)) production were used. The possible normalization of the heartbeat rate and feeding activity in clean test medium was also investigated. The fate, time-dependent, and concentration-dependent aggregation behaviour of GO was followed by dynamic light scattering, UV-Vis spectroscopy, and zeta potential measurement methods. The EC20 value for immobilization was 50 mg/L, while, for physiological and behavioural endpoints, it ranged from 8.1 mg/L (feeding activity) to 14.8 mg/L (immobilization). The most sensitive endpoint was the ROS production with EC20 = 4.78 mg/L. 24-h recovery experiments revealed that feeding activity was restored only up to a certain level at higher concentrations, indicating that the potential environmental health effects of GO cannot be neglected. Alterations of normal physiology (heart rate) and feeding activity may be associated with increased risk of predation and reproductive decline, highlighting that GO may have impacts on population and food web dynamics in aquatic ecosystems.
Highlights
The growing use of carbon-based nanomaterials (CNMs) and their mass production have raised questions about their safety and environmental impact
graphene oxide (GO)-induced significant inhibition of the heartbeat rate, which was normalized after 4 h of a recovery period in a clean test medium
Our results clearly demonstrate that, in the aquatic environment, GO may result in adverse effects on water flea physiology, behavior, and biomarker responses
Summary
The growing use of carbon-based nanomaterials (CNMs) and their mass production have raised questions about their safety and environmental impact. Investigation of the potential adverse effects of an important CNM, graphene, on the aquatic ecosystem has attracted great attention, considering the likeliness of its release into the environment at significant levels due to its extensive production and use [1,2]. Graphene oxide may be introduced into the environment through its application as adsorbent for wastewater and drinking water treatment, material for solid-phase extraction, membrane for desalination, catalyst for aqueous organic pollutant oxidation and degradation, and coating material for filtration or even during the waste disposal of GO-containing products [5]
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