Influence of Extracellular Polymeric Substances on the Long-Term Fate, Dissolution, and Speciation of Copper-Based Nanoparticles

Abstract

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...

Environmental Stresses Increase Photosynthetic Disruption by Metal Oxide Nanomaterials in a Soil-Grown Plant

“…In addition to its surface charge, the tendency of Cu(OH) 2 to dissolve at low pH, 30,31 such as is found in the soil used in this study (Table 2), likely also contributes to its uptake behavior. Rhizosphere pH tends to be more acidic than the surrounding soil due to the release of protons by roots to stimulate and counterbalance the uptake of ions from the soil; 32 one effect of this acidity may be to dissolve a portion of the Cu(OH) 2 .…”

Heteroaggregation of nanoparticles with biocolloids and geocolloids

“…It is very likely that the large amount of production of ENMs will lead to their release into the environment through production, application, and disposal processes [1,22,23]. For example, titanium dioxide nanoparticles (TiO 2 NPs) were modeled and predicted to be discharged to the wastewater treatment plant, landfill and other environments [4,17,24].…”

“…NOM is mainly the residual from plants and animals materials, as well as some of the biocolloids mentioned before [15,22,58]. NOM has been shown to interact strongly with ENMs [59], modifying their surfaces and in general making them more bioavailable [60,61].…”

“…NOM is a complex heterogeneous mixture of organic compounds, covering a wide range from largely aliphatic to colored aromatic hydrocarbon structures that possess attached functional groups [55,[62][63][64]. These functional groups include amide, carboxyl, hydroxyl, ketone, and various others [22,62]. NOM contains various complex polyelectrolytes with different molecular weights, mainly resulted from the decomposition of plant and animal residues, soluble microbial products, and extracellular polymeric substances [65][66][67][68][69][70].…”

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“…Although our data are from experiments in which we only considered the mitigating ability of algal-produced DOC, studies have shown that algal-produced DOC and natural organic matter share a lot of similarities in their composition and functional groups. 50,51 We defined "remediation" as the Cd and FeSSi concentrations either having no effect on the algae (exposure growth pattern was similar to the controls) or causing a "growth delay" ≤30 days. We explored the sensitivity of these remediation boundaries to model parameters by simulating the model 600 times with variations of parameters ±15% of the best fit parameter value and recorded the outcome (see SI Section 4 for details and Figures S16 and S17).…”