Earthworm Uptake Routes and Rates of Ionic Zn and ZnO Nanoparticles at Realistic Concentrations, Traced Using Stable Isotope Labeling

Abstract

The environmental behavior of ZnO nanoparticles (NPs), their availability to, uptake pathways by, and biokinetics in the earthworm Lumbricus rubellus were investigated using stable isotope labeling. Zinc isotopically enriched to 99.5% in (68)Zn ((68)Zn-E) was used to prepare (68)ZnO NPs and a dissolved phase of (68)Zn for comparison. These materials enabled tracing of environmentally relevant (below background) NP additions to soil of only 5 mg (68)Zn-E kg(-1). Uptake routes were isolated by introducing earthworms with sealed and unsealed mouthparts into test soils for up to 72 h. The Zn isotope compositions of the soils, pore waters and earthworms were then determined using multiple collector inductively coupled plasma mass spectrometry. Detection and quantification of (68)Zn-E in earthworm tissue was possible after only 4 h of dermal exposure, when the uptake of (68)Zn-E had increased the total Zn tissue concentration by 0.03‰. The results demonstrate that at these realistic exposure concentrations there is no distinguishable difference between the uptake of the two forms of Zn by the earthworm L. rubellus, with the dietary pathway accounting for ∼95% of total uptake. This stands in contrast to comparable studies where high dosing levels were used and dermal uptake is dominant.

Transformation kinetics of silver nanoparticles and silver ions in aquatic environments revealed by double stable isotope labeling

“…[27][28][29] The stable isotope labeling method has been used to detect the toxicity and bioaccumulation of several types of NPs with high sensitivity and reliability. 27,28,[30][31][32][33][34] In this study, we synthesized isotopically AgNO 3 and 3.7 mL of 34 mmol L −1 trisodium citrate dihydrate were added into 100 mL of boiling distilled water, and then 1 mL of 50 mmol L −1 sodium borohydride was added drop-wise into the solution with vigorous stirring. The solution turned from colorless to yellow immediately, and the color deepened with further addition of sodium borohydride.…”

Preparation and characterization of three-layer, isotopically labelled core-shell nanoparticles; a tool for understanding mechanisms of bioavailability

“…22,23 These labelled NPs enhance the signal to noise ratio of the NP from the background element by measuring the ratio of the enriched isotope against a non-enriched (background) isotope. This has allowed for a significant reduction in detection limits within organisms by up to two orders of magnitude.…”

Tracing multi-isotopically labelled CdSe/ZnS quantum dots in biological media

“…After the QDs were added to these media, all of the samples were agitated and then acidified to obtain 2% of nitric acid in the samples (in the case of the blood plasma samples, 1.5% of hydrochloric acid was used as complete digestion was not reached using nitric acid), and then left overnight prior to dilution and analysis. This acidification step is representative of the final step used in many studies prior to ENP analysis 15,19 . Simple acidification was sufficient to completely dissolve the QDs, and therefore complete acid digestion with HF/HNO 3 was not carried out.…”

“…2 open trace the QDs and to understand their behavior in biological environments at low concentrations (ppt-ppb level). In fact, isotopically labelled nanoparticles (NPs) are increasingly being used in the literature to better quantify manufactured NPs in biological matrices [15][16][17][18][19] . For instance, Khan et al showed the ability to conduct environmentally relevant exposures (20 µg 68 Zn/L) of spiked ZnO NPs in order to study their bioavailability to estuarine snails, whereas Bourgeault et al provided evidence for the critical use of spiked 47 TiO 2 NPs when studying the bioaccumulation of NPs at environmental concentrations (7-120 µg/L of 47 TiO 2 NPs) in zebra mussels in water.…”