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The effects of silver nanoparticles (AgNPs) on terrestrial ecosystems need to be better understood and assessed. Cationic silver (Ag+) has well-documented toxicity against bacteria, but it is not clear what will be the effect of nanoscale Ag. In the present study, the potential effects of AgNPs were investigated in soils by measuring activity of the enzymes phosphomonoesterase, arylsulfatase, β-D-glucosidase, and leucine-aminopeptidase. The toxicity of AgNPs was compared with that of ionic Ag, and the ameliorating effects of soil organic matter were evaluated. To this end, 2 soils with different organic matter contents were artificially contaminated with either AgNPs or Ag-acetate at equivalent total Ag concentrations. In general, enzyme activities were inhibited as a function of the Ag concentration in the soil. In the AgNP exposures, only a small fraction of the AgNP was actually truly dissolved (found in the <1-nm fraction), suggesting that the particulate forms of AgNPs resulted in a significant inhibition of soil enzymes. The addition of organic matter to the soils appeared to enhance enzyme activities; however, the mechanism of organic matter action is not clear given that dissolved Ag concentrations were similar in both the organic-matter–amended and unamended soils. The present study shows that the AgNP produces significant negative effects on the soil enzyme activities tested. The Ag chemical speciation measurements suggested that the AgNP caused greater toxic effects to the soil enzymes at the low Ag concentrations. For the larger concentrations of total soil Ag, causes of the negative effects on enzyme activities are less obvious but suggest that colloidal forms of Ag play a role.

Single particle ICPMS (SP-ICPMS) is becoming a very promising technique for nanoparticle detection and characterization, especially at very low concentrations (~10(-12)-10(-10) M). Nonetheless, the ability of the technique to detect smaller nanoparticles is presently limited by the setting of threshold values for the discrimination of nanoparticles from the dissolved metal background. In this study, a new approach to attaining lower particle size detection limits has been developed by the online coupling of an ion exchange column (IEC) with SP-ICPMS (IEC-SP-ICPMS). The IEC effectively removes the continuous signal of dissolved metal, allowing for both lower detection limits and an improved resolution of solutions containing multiple particles. The feasibility and the efficiency of this coupling were investigated using silver nanoparticles in the presence of various concentrations of Ag(+) and other major ions (Mg(2+), Ca(2+), Na(+), K(+), and Cl(-)). The online elimination of the dissolved metal made data processing simpler and more accurate. Following the addition of 1 to 4 μg L(-1) of Ag(+) spikes, symmetric particle size distributions were obtained using IEC-SP-ICPMS, whereas the use of SP-ICPMS alone led to asymmetric distributions, especially for nanoparticle sizes below 60 nm. Although this proof of principle study focused on nanosilver, the technique should be particularly useful for any of the metal based nanoparticles with high solubilities.

Environmental context. The increasing use of nanomaterials in consumer products has led to increased concerns about their potential environmental and health impacts. TiO2 is a widely used nanoparticle found in sunscreens and electronic products. In order to understand and predict the mobility of TiO2 in the natural environment, it is essential to determine its state of aggregation under environmentally relevant conditions of pH, ionic strength, ion and natural organic matter content. Aggregation is likely to lead to both reduced mobility and bioavailability in soils and natural waters. Abstract. The physicochemical characterisation of nanomaterials is crucial to predict their environmental and health impacts. Ion adsorption is known to influence the surface properties of nano-metal oxides in natural systems. The role of calcium and phosphate adsorption on aggregation was examined in the presence and absence of natural organic matter. Fluorescence correlation spectroscopy (FCS) was performed in order to determine the diffusion coefficients of TiO2 nanoparticles having a nominal size between 3 to 5 nm. Based upon FCS and electrophoretic mobility measurements, the presence of calcium resulted in a destabilisation and aggregation of the TiO2 nanoparticles, even in presence of Suwannee River fulvic acid (SRFA). Conditions which favoured phosphate adsorption also resulted in a destabilisation of the TiO2 sample but for low SRFA concentrations only.

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