Novel and Nontraditional Use of Stable Isotope Tracers To Study Metal Bioavailability from Natural Particles

Abstract

We devised a novel tracing approach that involves enriching test organisms with a stable metal isotope of low natural abundance prior to characterizing metal bioavailability from natural inorganic particles. In addition to circumventing uncertainties associated with labeling natural particles and distinguishing background metals, the proposed "reverse labeling" technique overcomes many drawbacks inherent to using radioisotope tracers. Specifically, we chronically exposed freshwater snails ( Lymnaea stagnalis ) to synthetic water spiked with Cu that was 99.4% (65)Cu to increase the relative abundance of (65)Cu in the snail's tissues from ~32% to >80%. The isotopically enriched snails were then exposed to benthic algae mixed with Cu-bearing Fe-Al particles collected from the Animas River (Colorado), an acid mine drainage impacted river. We used (63)Cu to trace Cu uptake from the natural particles and inferred their bioavailability from calculation of Cu assimilation into tissues. Cu assimilation from these particles was 44%, indicating that 44% of the particulate Cu was absorbed by the invertebrate. This demonstrates that inorganic particulate Cu can be bioavailable. The reverse labeling approach shows great potential in various scientific areas such as environmental contamination and nutrition for addressing questions involving uptake of an element that naturally has multiple isotopes.

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.…”

Isotopically modified silver nanoparticles to assess nanosilver bioavailability and toxicity at environmentally relevant exposures

“…At each concentration, 10 acclimated snails were exposed to diatoms amended with 109 Ag NPs for 3 h. Typically, L. stagnalis avidly graze films of deposited diatoms. [21,27,32] Exposure was shorter than gut residence time, [25] which minimises the confounding influences of efflux and isotope recycling. The short exposures also allow determination of food ingestion rates and Ag assimilation efficiency.…”

“…[25] A low-threshold particle-specific feeding inhibition, that is not concentration-dependent, has been observed whenever Cu-bearing Fe-Al particles were mixed in the diet of L. stagnalis. [21] A possible explanation for the discrepancy in the food IR estimates at low Ag NP concentrations for the labelled and non-labelled particles includes the difference in the detection limits of the two approaches. There is a 50-fold difference in the smallest amount of Ag that can be detected when a tracer is used or not (Table S3 of the Supplementary material).…”

“…[18,19] One option to circumvent the confounding influences of high metal exposures is application of tracer techniques. [20][21][22] The most common types of tracers are radioisotopes [23] and enriched stable isotopes. [20,24] Both share similar advantages such as low detection limits and the ability to discriminate tracer from background concentrations.…”

“…They have been employed to define metal bioaccumulation processes [20,25,26] and to evaluate bioavailability and toxicity. [21,[26][27][28] Recently, enriched stable metal isotopes have been used in the synthesis of nanoparticles composed of the essential metals Cu and Zn, which provided enhanced sensitivity when evaluating the rates at which these particles delivered Cu and Zn to humans, [29] and to invertebrates. [15,16,27,30,31] Here we describe for the first time stable isotope labelling for citrate-coated Ag nanoparticles using Ag that was 99.7 % 109 Ag ( 109 Ag NPs).…”