Article Cite This: Anal. Chem. XXXX, XXX, XXX−XXX
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Extraction Method Development for Quantitative Detection of Silver Nanoparticles in Environmental Soils and Sediments by Single Particle Inductively Coupled Plasma Mass Spectrometry Lei Li,†,§ Qiang Wang,*,†,§ Yuan Yang,*,‡,§,∥ Li Luo,†,§ Ru Ding,†,§ Zhao-Guang Yang,†,§ and Hai-Pu Li†,§
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Center for Environment and Water Resources, College of Chemistry and Chemical Engineering, Central South University, No. 932 Lushan Nan Road, Yuelu District, Changsha 410083, PR China ‡ College of Resources and Environment, Hunan Agricultural University, Changsha 410128, PR China § Key Laboratory of Hunan Province for Water Environment and Agriculture Product Safety, Central South University, Changsha 410083, Hunan PR China ∥ International Joint Laboratory of Hunan Agricultural Typical Pollution Restoration and Water Resources Safety Utilization, Hunan Agricultural University, Changsha 410128, PR China S Supporting Information *
ABSTRACT: For understanding the environmental behavior and toxicity of Ag nanoparticles (Ag-NPs), a quantitative method for characterizing the AgNPs in soils and sediments is urgently needed. In this study, we validated a previously developed extraction method by optimizing the extraction of silver nanoparticles from soil and sediment samples to which engineered AgNPs had been added. The samples were analyzed by single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). Initially, different extraction conditions were evaluated to validate the optimal extraction procedure. Then the optimal extraction procedure was applied to environmental soil and sediment samples spiked with AgNPs. The extraction data for Ag-NPs with sizes below 30 nm was not shown due to the particle size detection limit of the SP-ICP-MS method (∼20 nm). The number concentrations of Ag particles extracted from different environmental soils and sediments matrices were in the range of (12 ± 1−23 ± 1) × 107 particles/g soil. Similarly, 53.4−100.0% of the particulate Ag mass was recovered. For the relatively low Ag mass recovery of Guiyu agricultural soil, the Ag mass recovery shows great improvement (from 53.4 to 105.8%) by the soil dilution using SiO2. The optimal method was validated to be feasible for extracting Ag-NPs from environmental soils and sediments, except for the soil with high soil organic matter (SOM) content. The SiO2 dilution of soil provides a promising way to promote the extraction of Ag-NPs in soil (or sediment) with high SOM content, which could further promote the study on the environmental behavior and toxicity of Ag-NPs in soil and sediment environment.
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and toxicity of ENMs in a soil environment is of paramount importance.7 Silver nanoparticle (AgNP), as a nanomaterial with superior antibacterial properties, has been increasingly used in medical products, agriculture, wastewater treatment, textile coatings, electrical and chemical equipment, the food packaging industry, etc.2,10,11 The exposure of AgNPs to the environment can cause environmental problems and subsequently affect human health.7 AgNPs could enter the environment through a variety of sources and pathways, and recent studies have shown
he widespread application of engineered nanomaterials (ENMs) in various fields increases the possibility of their release into the environment, which is potentially threatening the natural ecosystem and providing potential pathways for human exposure.1−3 To understand the fate, transport, behavior, and toxic effects of ENMs, several extensive research projects have been focused on the detection and characterization of ENMs in environmental and biological matrixes. Studies of uptake and accumulation of ENMs in plants have drawn great attention, and the evidence of ENMs’ accumulation indicates their potential adverse effects on crop health and food safety due to the entry of ENMs into plant tissues.4−9 Since soil plays a crucial role in maintaining plant growth in plant−soil ecosystems, evaluating the environmental behavior © XXXX American Chemical Society
Received: December 3, 2018 Accepted: June 28, 2019 Published: June 28, 2019 A
DOI: 10.1021/acs.analchem.8b05575 Anal. Chem. XXXX, XXX, XXX−XXX
Article
Analytical Chemistry
concentration of 833 μg AgNPs per gram soil and showed high recovery.38 However, the environmental concentration of AgNPs is usually very low (range from ng kg−1 to μg kg−1)42 and the AgNPs are often present in different sizes and coatings in environmental soil matrices. In addition, for the capacity to capture AgNPs in soil, SOM may play a key role.43,44 In this context, the use of the TSPP extraction method (Schwertfeger et al. 2017) needs to be further optimized and validated for extracting AgNPs at low environmental concentrations and for extracting AgNPs of different sizes and with different coatings. In this study, a previously developed extraction method was validated.38 Initially, the extraction conditions for the extraction of Ag-containing nanoparticles in soil are further optimized and validated. As naturally occurring Ag-containing nanoparticles are usually formed when Ag+ binds to soil constituents such as sulfides and organic matter, and when engineered AgNPs are added to the soil, they often undergo transformations, which depending on environmental conditions, may include dissolution and release of Ag+, and possibly formation of coprecipitates (i.e., Ag2S, Ag2O) on the engineered AgNPs surface; moreover, an optimal AgNP extraction procedure should not drive or encourage AgNP dissolution, the effect of Ag+ on the extraction results of Ag particles is investigated. Subsequently, Ag particles formed by the addition of Ag+ to environmental soils and sediments is investigated. Also, a soil dilution series test is conducted on a soil sample with high organic matter content to assess whether the soil dilution could promote the extraction of Ag nanoparticles. Then, the environmental soils and sediments that may be contaminated by AgNPs were analyzed, and the AgNPs-spiked samples were applied to evaluate the applicability of the proposed method. The quantification and size distribution characterization of the isolated Ag nanoparticles were evaluated by SP-ICP-MS.
that the soil application of sewage sludge was a primary source of AgNPs entering into the environment.12 It has been reported that AgNPs can adversely affect soil organisms13,14 and native plants15−19 after entering into the soil environment. Moreover, a significant correlation between the size of AgNPs and their toxicity has been confirmedsmaller AgNPs have higher toxicity.20 Since the assessment of the toxic risks of AgNPs relies on the understanding of their exposure, transport, and fate in the environment, the establishment of a method to detect and quantify AgNPs in soil and sediment environments is urgently needed. However, although great efforts have been made to develop analytical methods for ENMs,21−24 assessment of the distribution, transport, and impacts of AgNPs in soils and sediments still remains a significant challenge because of the lack of quantitative characterization methodology.25,26 A large number of methods have been adopted to detect and characterize the metallic ENMs in the environment.27 Typically, electronic microscopy (EM)28 and dynamic light scattering (DLS)29 have been applied for the size determination of ENMs, while energy dispersive X-ray spectroscopy (EDS), 30 X-ray adsorption near edge spectroscopy (XANES),31 and ultraviolet−visible spectroscopy (UV− vis),32 have been used for their composition analysis. However, although EM technology is convenient and effective in assessing the shape and size of ENMs, its sample preparation may result in artifacts and the results are often statistically limited.33 Moreover, due to the extremely low environmental concentration of ENMs (μg kg−1) and the complexity of the environmental matrixes, these methods are often limited by their high detection limits.34 Among all the characterization technologies, single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is the state-of-the-art technique, first developed by Degueldre et al.35 It could provide information on the elemental mass concentration, number concentration, and size distribution of a metallic nanoparticle and its corresponding dissolved counterparts at ng L−1 ∼ μg L−1 levels.36,37 However, the use of ICP-MS requires that the sample be in aqueous form and free of large particles (typically >1 μm). In this case, it is very meaningful to develop a method for efficiently extracting ENMs from a complex matrix (especially soils and sediments) into the solution phase prior to ICP-MS analysis.38 Separation of ENMs from soil and sediment matrixes remains a major challenge and has now become a barrier to the quantitative characterization of ENMs in environmental soil. Moreover, up to now, limited studies have focused on the separation of ENMs in soils and sediments. Ultrasonication and some chemical dispersants (e.g., sodium hexametaphosphate (SHMP), detergents, etc.) have been used to release ENMs from the soil matrixes; however, poor separation of the ENMs was usually obtained.39,40 Ultrapure water (UP water) has also been used to extract AgNPs from soils, but it only achieved low recovery of AgNPs (up to 46%).25 The cloud point extraction (CPE) method with low-cost surfactants (Triton X-100 (TX-100) and Triton X-114 (TX-114)) has been applied for separating AuNPs from soil extracts, but the cloud point extraction step is relatively complicated; especially the control of cloud point temperature needs to be accurate.33 Schwertfeger et al.41 used potassium nitrate (KNO3) to extract Ag+ and AgNPs from soil, but they found that the KNO3 solution only moderately dispersed soil particles and caused a large amount of AgNPs to dissolve. Tetrasodium pyrophosphate (TSPP) was also used to extract AgNPs from soil with a
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MATERIALS AND METHODS Chemicals. Nominal sizes of 30 nm, 50 nm, 80 nm, and 100 nm citrate-coated AgNPs and 60 and 100 nm polyvinylpyrrolidone (PVP) coated AgNPs were obtained from Nanocomposix (San Diego, CA, USA). Additionally, 50 and 100 nm commercial AgNPs stabilized with unknown reagent were purchased from Beijing DK nanotechnology Co. Ltd. (China), with nominal suspension concentration of 100 mg L−1. TEM and SEM images provided by manufacturer are displayed in Figure S1 in the Supporting Information. The nominal size of 60 nm citrate-stabilized gold nanoparticle standard reference material was obtained from Nanocomposix (NanoXact, San Diego, CA, USA). 1000 mg L−1 dissolved Ag standard solution (in 1 mol/L HNO3) purchased from China Iron & Steel Research Institute (China) was used to establish the calibration curve of Ag. Silver nitrate (AgNO3, 99.99%) used to investigate the interference of Ag+, nitric acid (HNO3, 70%, chromatographic grade) and guarantee-reagent grade hydrochloric acid (HCl, 36−38%) were purchased from Aladdin (Shanghai, China). Silica (SiO2, 99.99% metals basis, particle size
