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.
Highlights
The novel properties exhibited by engineered nanoparticles (NPs) have resulted in these materials becoming increasingly prevalent in consumer products
The soil samples dosed with 68ZnO NP and dissolved 68Zn had initial measured dry weight 68Zn isotope (68Zn-E) concentrations of 3.58 ± 0.75 (1 sd, n = 3) and 3.51 ± 1.13 mg kg−1 (1 sd, n = 3), respectively (Table S5)
These concentrations are identical, within uncertainty, and show a recovery of >70% for the 68Zn-E that was added to the soils at 5 mg kg−1
Summary
The novel properties exhibited by engineered nanoparticles (NPs) have resulted in these materials becoming increasingly prevalent in consumer products. Zinc oxide (ZnO) NPs, for example, have found use in sunscreens, cosmetics and paints due to their UV absorbance properties.[1,2] The increased manufacture and use of engineered NPs will inevitably lead to a corresponding rise in their release into natural environments.[3] Engineered NPs are likely to end up in water treatment plants and be removed as part of the water treatment sludge. In places where such sludge is applied to agricultural land, it is expected that soils will be a major sink. For sewage treatment sludge and sludge treated soils Boxall et al.[5] modeled PECs of 2.2−22 mg kg−1 and 3.2−32 mg kg−1, respectively, assuming between 10% and 100% market penetration for ZnO NPs in sunscreens
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