Potential Impact of Low-Concentration Silver Nanoparticles on Predator-Prey Interactions

Potential Impact of Low-Concentration Silver Nanoparticles on Predator-Prey Interactions between Predatory Dragonfly Nymphs and Daphnia magna as a Prey

Supporting Information

Lok R. Pokhrel,† and BrajeshDubey*,‡

†Department of Environmental Health, College of Public Health, East Tennessee State University, Johnson City, TN 37614-1700, USA.

‡Environmental Engineering Program, School of Engineering, University of Guelph, 50 Stone Road West, Guelph, Ontario, Canada.

*Corresponding author address: Environmental Engineering Program, School of Engineering, University of Guelph, 50 Stone Road West, Guelph, Ontario, Canada, Phone: 519-265-3304, Email: .

Total Pages: 12 (including cover page)

Total Figures: 4

Total Tables: 6

Figure S1. Schematic showing experimental setup designed for horizontal migration, 48-h survival, and 21-day reproduction tests.

Figure S2. An experimental setup designed for testing the potential interactions of citrate-nAg (2 µg Ag L-1) with Daphnia magna (as a prey) in the presence of the predatory Dragonfly (Anaxjunius) nymph for vertical migration test.

Synthesis of Citrate-nAg:1 mM AgNO3 solution was mixed with 10 mM Sodium citrate dihydrate in a volume ratio of 2:1, and heated for four hours at 70 °C in a water bath.1 Citrate capped Ag nanoparticles (citrate-nAg) thus formed were characterized using the dynamic light scattering (DLS), UV-Vis Spectrophotometry, and transmission electron microscopy (TEM). The characteristics of citrate-nAgare presented in Supporting Tables S1S2 and Figures S1 &S3 below. The ionic citrate carboxyl groups are known to electrostatically stabilize the particles.1-3

Figure S3. Representative TEM imagery of citrate-nAg.ImageJ 1.44 software was used to estimate the particle size distribution (PSD) of the nanoparticles, which is presented in Table S2 below.

Table S1. Purification (diafiltration) protocol used for cleaning as-synthesized Citrate-nAg using Tangential Flow Filtration (TFF) system.

* obtained as purified citrate-nAg suspension with electrical conductivity of 5 µS/cm and used for assessment of toxicity.

Table S2. Characteristics of citrate nanosilverparticles.

SD, Standard deviation of the sample;the Smoluchowski’s equation was used to estimate the mean ζ potential from the electrophoretic mobility of the particles; mV, millivolt.λmax represents maximum wavelength at which the peak was observed; n = number of particles analyzed for estimating particle diameter from Transmission Electron Microscopy (TEM) imagery; n = number of particles measured for estimating size from a TEM image using ImageJ 1.44.

Table S3.Stability of citrate-nAg in moderately hard water over a period of 21-days as determined by DLS method.

Data showed that the nanoparticles were stable in the test matrix (moderately hard water; without food)over the period of 21-days, with apparently no change in particle size. HDD, volume-weighted hydrodynamic diameter; SD, Standard deviation of the sample;the Smoluchowski’s equation was used to estimate the mean ζ potential from the electrophoretic mobility of the particles; mV, millivolt; M.U., mobility unit.

Table S4. Rate of silver dissolution from citrate-nAgduring the toxicity tests.

Method detection limit (MDL) for silver using GF-AAS was 0.54 µg/L(as total Ag). BDL denotes below detection limit, and the recovery was 98.2 – 101.2%.

*At 0.99% dissolution for comparable TEM size and organic coated AgNPs (ref. Table 1 of Ma et al. Environ Science Technol2012, 46 (2), 752–759).4

#At 5.5% dissolution with comparable pH (7.4) for Citrate-AgNPs (ref. Figure 2 of Liu and Hurt Environ Science Technol2010, 44, 2169-2175).5

§At 1% dissolution for carbonate coated AgNPs (ref. Navarro et al., Environ Science Technol2008, 42, 8959-8964).6

†At 0.45 – 3.7% dissolution for NanoAmor- and Sigma-AgNPs (ref. Laban et al., Ecotoxicology 2010, 19, 185–195).7

$At 1.3% dissolution for Citrate-AgNPs(ref. Huynh and Chen, Environ. Sci. Technol. 2011, 45, 5564–5571).8

¥At 0.1% dissolution for Citrate-AgNPs(ref. Fabrega et al., Environ. Sci. Technol. 2009, 43, 7285–7290).9

Figure S4.UV/Vis spectra of citrate-nAg (stock), silver ions (100 µg Ag+/L), nanopure water (as a blank), and supernatants obtained from 48-h and 21-day dissolution experiments. The overlapped spectra of the latter four suspensions are presented in the inset. Note thatthe UV/Vis spectrum of 48-h supernatant showed lower absorbance than nanopure water and that of 21-daysupernatant also showing absorbance below zero (a.u.). Thisindicated an absence of Ag nanoparticles and perhaps (null to) negligible amount of Ag+ ions in the 5 mL supernatants, supporting the analytical values obtained from GF-AAS, which were similar to the background (Moderately Hard Water with food) concentrations and below the detection limit of GF-AAS.

Table S5.Water quality parameters of moderately hard reconstituted water used as the test media for all toxicity bioassays.

NP, 2µg L-1citrate-nAg; NY, Predators; NP+NY, citrate-nAg+ Predators combined; Control indicates D. magna only (without NPs and Predators).

Table S6. Analytically determined citrate-nAgconcentrations for different treatments measured for a duration of 21-day.

Method detection limit (MDL) for silver using GF-AAS was 0.54 µg/L(as total Ag). BDL denotes below detection limit, and the recovery was 98.2 – 101.2%.

References for Supporting Information

(1)El Badawy, A. M.; Luxton, T. P.; Silva, R. G.; Scheckel, K. G.; Suidan M. T.; Tolaymat, T. M. Impact of environmental conditions (pH, ionic strength, and electrolyte type) on the surface charge and aggregation of silver nanoparticles suspensions. Environ. Sci. Technol. 2010, 44, 1260-1266.

(2)El Badawy, A. M.; Silva, R. G.; Morris, B.;Scheckel, K. G.;Suidan, M. T.; Tolaymat, T. M.Surface charge-dependent toxicity of silver nanoparticles. Environ. Sci. Technol. 2011,45, 283–287.

(3)Kimling, J.; Maier, M.; Okenve, B.; Kotaidis, V.; Ballot, H.; Plech, A. Turkevich method for gold nanoparticle synthesis revisited. J. Phys. Chem. B2006,110,15700-15707.

(4)Ma, R.; Levard, C.; Marinakos, S.; Cheng, Y.; Liu, J.; Michel, F. M.; Brown, G . E. Jr.; Lowry, G. V. Size-controlled dissolution of organic-coated silver nanoparticles. Environ. Sci. Technol.2012,46(2), 752–759.

(5)Liu, J.; Hurt, R. H. Ion release kinetics and particle persistence in aqueous nano-silver colloids. Environ. Sci. Technol.2010,44, 2169–2175.

(6)Navarro, E.;Piccapietra, F.; Wagner, B.; Marconi, F.;Kaegi, R.;Odzak, N.;Sigg, L.; Behra, R. Toxicity of silver nanoparticles to Chlamydomonasreinhardtii. Environ. Sci. Technol. 2008, 42, 8959–64.

(7)Huynh, K. A.; Chen, K. L. Aggregation kinetics of citrate and polyvinylpyrrolidone coated silver nanoparticles in monovalent and divalent electrolyte solutions. Environ. Sci. Technol.2011,45, 5564–5571.

(8)Laban, G.; Nies, L. F.; Turco, R. F.; Bickham, J. W.; Sepulveda, M. S. The effects of silver nanoparticles on fathead minnow (Pimephalespromelas) embryos. Ecotoxicol.2010,19, 185–195

(9)Fabrega, J.; Fawcett, S. R.; Renshaw, J. C.; Lead, J. R. Silver nanoparticle impact on bacterial growth: Effect of pH, concentration, and organic matter. Environ. Sci. Technol.2009,43, 7285–7290.

S1