ABSTRACT:The influence of phytoplankton-derived soluble extracellular polymeric substances (EPS), pH, and ionic strength (IS) on the dissolution, speciation, and stability of nano-CuO, nano-Cu, and Kocide (a micron sized Cu(OH) 2 -based fungicide) was investigated over 90 days. EPS improved the stability of commercial copper-based nanoparticles (CBNPs) in most conditions, in addition to influencing their dissolution. The dissolution rate was pH 4 ≫ pH 7 > pH 11. The presence of EPS correlated with higher dissolved Cu at pH 7 and 11, and lower dissolved Cu at pH 4. More dissolution was observed at higher IS (NaCl) due to complexation with Cl − . Dissolution of nano-CuO at pH 7 increased from 0.93% after 90 days (without EPS) to 2.01% (with 5 mg-C EPS/L) at 10 mM IS. Nano-CuO dissolved even more (2.42%) when IS was increased to 100 mM NaCl (with EPS). The ratio of freeCu 2+ /total dissolved Cu decreased in the presence of EPS, or as pH and/or IS increased. On a Cu mass basis, Kocide had the highest dissolved and suspended Cu at pH 7. However, dissolution of nano-Cu resulted in a higher fraction of free Cu 2+ , which may make nano-Cu more toxic to pelagic organisms. ■ INTRODUCTIONGlobal production of copper-based nanoparticles (CBNPs) was estimated at ∼200 t/yr in 2010, and is increasing. 1 CBNPs have found use in cosmetics, pigments, paints and coatings, electronics, and pesticides. 2−4 These applications may lead to direct exposure of CBNPs to the environment due to normal use, product wear-and-tear, and/or end-of-life disposal. 1 Toxicity of CBNPs and composites to organisms has been demonstrated. 2,5−8 It is therefore important to understand the long-term fate and transformations of these materials in aquatic systems in order to predict exposure to at-risk organisms.Stability and dissolution of engineered nanoparticles (ENPs) depend on ionic strength (IS), pH, and natural organic material (NOM). 9−12 Rapid aggregation of nano-Cu was reported in freshwater by Griffitt et al. 5 The authors also found that less than 0.1% of the nano-Cu dissolved in 48 h in the freshwater media used (pH 8.2). 98% dissolution of nano-Cu was however reported at pH 6 in "uterine-fluid" after a week, 13 demonstrating the importance of pH and media composition on CBNPs' dissolution. Mudunkotuwa and co-workers 14 reported increased dissolution of aged and new CBNPs in the presence of organic acids. Similarly, Worthington et al. 15 showed that the chitosan improved stability and dissolution of nano-Cu. To our knowledge, no studies have previously investigated the effects of naturally occurring NOM such as extracellular polymeric substances (EPS) on the stability and dissolution of CBNPs. EPS are synthesized by microorganisms, which are abundant in natural aquatic systems. EPS are mainly composed of polysaccharides, proteins, nucleic acids, and other polymers; and their composition may vary spatially and temporally even within the same species. 16 EPS may interact with ENPs, thus affecting their fate and transformation. 17 Additional...

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