Elemental copper nanoparticle toxicity to anaerobic ammonium oxidation and the influence of ethylene diamine-tetra acetic acid (EDTA) on copper toxicity

doi:10.1016/j.chemosphere.2017.06.054

Chemosphere

Volume 184, October 2017, Pages 730-737

https://doi.org/10.1016/j.chemosphere.2017.06.054 Get rights and content

Highlights

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Cu⁰ nanoparticles (NP) are toxic to anammox bacteria.
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The concentration of uncomplexed soluble Cu is predictive of the toxicity.
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CuCl₂, a model of the soluble Cu⁰ corrosion products, is toxic to anammox bacteria.
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EDTA attenuates Cu⁰ NP toxicity to anammox bacteria.
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EDTA complexes CuCl₂ rendering it less bioavailable and less toxic to anammox.

Abstract

Soluble ions released by elemental copper nanoparticles (Cu⁰ NP) are toxic to key microorganisms of wastewater treatment processes. However, their toxicity to anaerobic ammonium oxidation (anammox) has not yet been studied. Chelating agents occurring in wastewater may decrease copper ions (Cu²⁺) concentration and consequently, decrease copper toxicity. This study evaluated Cu⁰ NP and CuCl₂ toxicity to anammox and the influence of ethylene diamine-tetra acetic acid (EDTA) on copper toxicity. Bioassays were supplemented with Cu⁰ NP or CuCl₂ with and without EDTA. Anammox activities were used to calculate inhibition constants (K_i). Results showed that Cu⁰ NP are toxic to anammox. K_i constants with respect to added copper were 1.8- and 2.81-fold larger (less toxic) in EDTA-containing assays for Cu⁰ NP and CuCl_2, respectively, compared to EDTA-free assays. Additionally, K_i constants calculated in EDTA-free assays with respect the measured dissolved copper concentration were 0.023 mM Cu⁰ NP and 0.014 mM CuCl₂. The similarity of these K_i constants indicates that Cu⁰ NP toxicity to anammox is caused by the release of Cu²⁺. Finally, severe toxicity caused by 0.315 mM and Cu⁰ NP 0.118 mM CuCl₂ was attenuated by 88–100% when 0.14 mM EDTA was supplied. Toxicity attenuation likely occurred because EDTA complexed Cu²⁺ ions, thus, decreasing their bioavailability. Overall, this study indicates that Cu⁰ NP and CuCl₂ are toxic to anammox, and furthermore, that EDTA attenuates Cu⁰ NP and CuCl₂ toxicity to anammox by complexing Cu²⁺ ions.

Graphical abstract

Introduction

Engineered nanoparticles (NP) are manufactured materials with at least one dimension smaller than or equal to 100 nm (Hansen et al., 2007). Copper-based NP are widely used for the production of wood preservatives, catalysts, conductive inks, printable electronics, and used in antimicrobial products (Youngil et al., 2008, Bondarenko et al., 2013, Wang et al., 2013). Elemental copper NP (Cu⁰ NP) are one of the most commonly used copper-based NP for technological purposes (Wang et al., 2013). Additionally, copper-based NP are a byproduct of chemical mechanical polishing (Golden et al., 2000).

The continuous use of NP in industrial and domestic activities has raised concerns regarding their fate and effect on the environment. Copper-based NP can potentially end up in industrial or municipal wastewater treatment plants. The discharge of effluent or land application of sludges from the treatment plants can lead to release of the NP to the environment in addition to unplanned inappropriate disposals (Clar et al., 2016). Life cycle assessment studies have shown that NP are likely to accumulate in sewage sludge, wastewater treatment plants, and incineration plants after being discarded (Gottschalk and Nowack, 2011). Particularly, accumulation of NP used in consumer products has been found in activated sludge waste water treatment plants (Kiser et al., 2009, Kiser et al., 2010, Ma et al., 2013).

Accumulation of NP in the activated sludge process may affect the performance of a variety of microorganisms involved with the treatment. The whole activated sludge system and additional biological treatment processes involve not only oxygen-utilizing microorganisms, but also a variety of cultures responsible for nutrient removal or sludge stabilization (Tchobanoglous et al., 2014). Thus, research has been conducted to investigate the toxic effect of NP on microorganisms involved in waste water treatment (Gonzalez-Estrella et al., 2015a).

Studies exploring copper-based NP toxicity to anaerobic wastewater treatment microorganisms have exhibited a strong inhibition to glucose fermentation, anaerobic propionate oxidation, methanogenesis, denitrification, and sulfate reduction (Luna-delRisco et al., 2011, Otero-González et al., 2014, Gonzalez-Estrella et al., 2015a, Gonzalez-Estrella et al., 2015b). Recent studies have also shown toxicity of Cu⁰ NP toxicity to aerobic microorganisms such as nitrifying bacteria (Clar et al., 2016). However, very limited information is available concerning the effect of copper-based NP on the anaerobic ammonium oxidation process (anammox) even though copper salts have shown to be toxic to anammox in other studies (Lotti et al., 2012, Yang et al., 2013, Li et al., 2014). Presence of copper in nitrogen rich waste water can be expected in supernatants from anaerobic digestion sludge, leachates from landfills, piggery and dairy slurries, streams from the production of nitrogenous fertilizers, and semiconductor manufacturing waste water effluents (Zhang et al., 2015).

Copper-based NP toxicity is mostly caused by the release of soluble ions as a result of dissolution due to corrosion (Clar et al., 2016, Gonzalez-Estrella et al., 2016). Recent studies have demonstrated that sulfide can attenuate Cu⁰ toxicity to methanogens by decreasing the concentration of free soluble Cu²⁺ ions released by Cu⁰ NPs (Gonzalez-Estrella et al., 2015b, Gonzalez-Estrella et al., 2016). This suggests that decreasing the availability of Cu²⁺ ions by other mechanisms may attenuate Cu⁰ NP toxicity as well. Chelating agents, for instance, are commonly applied to remediate soils contaminated with heavy metals (Dermont et al., 2008).

Chelating agents form a coordinate chemical bond with the metal (complexed metal) which facilitates and improves their solubility (Udovic and Lestan, 2010). Nonetheless, a complexed metal is not necessarily bioavailable (active); therefore, by complexing the metal and reducing its bioavailability the toxicity can be decreased (Rodea-Palomares et al., 2009). Ethylene diamine-tetra acetic acid (EDTA) is one of the most applied chelating agents to remove copper and other heavy metals from the soil (Udovic and Lestan, 2010). Thus, EDTA may decrease the toxicity of Cu⁰ NP by complexing ions released from Cu⁰ corrosion. The findings of Conway et al. (2015) indicated that copper ions released by Cu NP reached the maximum soluble concentration between 0 and 1 d after the NP were added to wastewater media. They also found that the ionic fraction represented up to 30% of total aqueous copper. Thus, EDTA may play an important role in controlling the concentration of the Cu²⁺ free ions release by Cu NP corrosion. It should be noted that the presence of high concentrations of EDTA, nitrogen and copper, and low concentrations of carbon sources can be expected in wastewater effluents from electroplating processes (Maketon et al., 2008). Soluble copper concentrations range from 5 to 460 mg L⁻¹ (Maag et al., 2000, Wong et al., 2003) while the chelating agent concentration, mostly attributed to EDTA, ranged from 10 to 200 mg L⁻¹ in semiconductor wastewater streams (Dakubo et al., 2012). Additionally, metal cleaning and printing inks industries, which use copper as part of their processes, represent 5 and 3% of the EDTA world market, respectively (Oviedo and Rodríguez, 2003). Such wastewater characteristics may be appropriate for the application of an anammox process if the toxic effect of copper is attenuated by the presence of EDTA already occurring in the wastewater.

This study evaluated the toxic effect of Cu⁰ NP on the anammox process and the influence of EDTA in attenuating copper toxicity.

Section snippets

Chemicals

Cu⁰-NPs (40–60 nm, 99%) were purchased from Sky-Spring Nanomaterials Inc. (Houston, TX, USA) CuCl₂·H₂O (99%) was acquired from Sigma Aldrich (St. Louis, MO, USA). He/CO₂ (80/20, v/v) gas mix was acquired from Air Liquid America (Plumstedsville, PA, USA). CuCl₂ was used in the experiments as a source of Cu²⁺ ions. EDTA (>99%) was purchased from Fisher Science (Waltham, MA, USA).

NP dispersions and metal solutions

Cu⁰-NP stock dispersions were sonicated (DEX^® 130, 130 Watts, 20 kHz, Newtown, CT, USA) at 70% amplitude for 5 min in

Inhibition of anaerobic ammonium oxidizing (anammox) consortium in presence and absence of EDTA

The inhibitory effect of Cu⁰ and CuCl₂ on an anammox consortium was explored in a series of batch experiments. Fig. 1 shows the normalized anammox activity as a function of increasing concentrations of added Cu⁰ NP and CuCl₂ in EDTA-containing (0.07 mM) and EDTA-free conditions of the second substrate feed. The experiment showed two main findings; first, Cu⁰ NP and CuCl₂ were toxic to anammox, and second, 0.07 mM EDTA decreased the toxicity effect from both forms of copper. Concentrations of

Main contributions

The findings of the present study indicated that Cu⁰ NP are toxic to anammox mainly by the release of Cu²⁺ ions (uncomplexed ions). Measurements of the soluble copper regardless the source indicated that similar soluble final concentrations imparted a similar inhibition to the anammox consortia at any given EDTA concentration. Results also indicated that EDTA decreased the toxicity effect of Cu⁰ NP and CuCl₂ on anammox. Assays supplied with 0.07 mM EDTA increased the K_i constants (decreased

Conclusions

This study demonstrated that Cu⁰ NP are toxic to anammox. Likewise, CuCl₂ were toxic to anammox activity. The results show that Cu⁰ NP toxicity was driven by the release of Cu²⁺ ions. K_i constants calculated with respect to the soluble concentration confirmed that Cu free soluble ions regardless their source (Cu⁰ NP or CuCl₂) affect anammox in a similar fashion at any given EDTA concentration. Additionally, this study demonstrated that EDTA attenuates the toxicity effect of Cu⁰ NP on anammox.

Acknowledgements

This work was supported by the Semiconductor Research Corporation (SRC)/Sematech Engineering Research Center for Environmentally Benign Semiconductor Manufacturing (426.036). This work was partly funded the National Institute of Environmental Health Sciences-supported Superfund Research Program (NIH ES-04940) and by the National Science Foundation (NSF CBET-1234211). Gonzalez-Estrella was also funded by CONACyT (308577).

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Elemental copper nanoparticle toxicity to anaerobic ammonium oxidation and the influence of ethylene diamine-tetra acetic acid (EDTA) on copper toxicity

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

NP dispersions and metal solutions

Inhibition of anaerobic ammonium oxidizing (anammox) consortium in presence and absence of EDTA

Main contributions

Conclusions

Acknowledgements

Bioresour. Technol.

J. Hazard. Mater.

Sci. Total Environ.

Sci. Total Environ.

J. Hazard. Mater.

J. Hazard. Mater.

Sci. Total Environ.

Water Res.

Water Res.

Environ. Pollut.

J. Hazard. Mater.

Environ. Pollut. A

Water Res.

Water Res.

Process Biochem.

Chem. Eng. J.

J. Hazard. Mater.

J. Hazard. Mater.

J. Hazard. Mater.

Bioresour. Technol.

Water Chemistry