Abstract
The occurrence of silver (Ag) in urban effluents is partly associated with the increasing use of silver nanoparticles (Ag NPs) as an antiseptic agent in various consumer products. Distinction among Ag forms must be taken into account in the assessment of exposure and toxicological effects to aquatic organisms. Wastewater treatment processes effectively remove Ag particles and colloids (mostly > 95%), but this still leaves notable concentrations (in order of ng/L) escaping to effluent-receiving waters. Total suspended Ag concentrations in various studied effluents ranged from 0.1 to 6 ng/L. The purpose of this study was then to measure and characterize Ag NPs in urban effluents for their concentrations and size distribution using the single particle ICP-MS technique (SP-ICP-MS). Wastewater influents and effluents from various treatment plants—from aerated lagoons to advanced treatment technology—were collected for three sampling days. Our results showed the presence of Ag NP in all samples with concentrations reaching 0.5 ng/L on a mass basis. However, on a particle number basis, Ag NP concentrations (expressed in particle/mL) in the 20–34-nm fraction (up to 3400 particles/mL) were much more abundant (> 700%) than in the > 35-nm larger fraction. The proportion of Ag at the nanoscale (1–100 nm) represents less than 8% of the total suspended Ag for all effluent samples, regardless of their origins. A significant correlation (linear regression: r2 > 0.7) was observed between Ag NP and total suspended Ag concentrations in investigated effluents. Because Ag nanotoxicity is size dependent, the determination of size distribution and exposure concentration on a particle number basis is urgently needed for risk assessment of this class of nanoparticles.
Highlights
The presence of silver in urban effluents is associated with the increasing use of silver nanoparticles (Ag NPs) as an antiseptic agent (Musee et al 2011; Dale et al 2015)
Because the main goal of this study was to evaluate the discharge of Ag NP, the Ag fraction evaluated was what remained in suspension
The highest total Ag concentrations (0.025 μg/L) reported for the studied effluents were observed in an aerated lagoon
Summary
The presence of silver in urban effluents is associated with the increasing use of silver nanoparticles (Ag NPs) as an antiseptic agent (Musee et al 2011; Dale et al 2015). The majority of Ag NPs in consumer products go down the drain and reach wastewater treatment plants (Kaegi et al 2011). The toxicity of Ag NPs on aquatic organisms could change markedly upon passing through municipal wastewater treatment plants (WWTPs), as their specific properties can be modified by physical and chemical transformations in WWTPs (Kaegi et al 2011; Bruneau et al 2016). Alterations of Ag NPs can be caused by a number of possible transformation processes such oxidation and sulphidation (Kaegi et al 2011; Kraas et al 2017; Lowry et al 2012; Georgantzopoulou et al 2018). Dissolved ionic silver (Ag+) and small complexes are considered highly available Ag forms for aquatic organisms (Khan et al 2012; Gagne et al 2013)
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