Biological Uptake and Depuration of Carbon Nanotubes by Daphnia magna

Abstract

It is inevitable that carbon nanotubes (CNTs) will be released to and widely dispersed in environmental ecosystems, given their numerous expected applications. Determination of their potential for bioaccumulation by ecological receptors is thus critical. Previous, research involving several different terrestrial and benthic organisms has indicated that CNTs spiked to soils or sediments do not bioaccumulate. Conversely, we report here distinctly different uptake and depuration behaviors for an aquatic organism, Daphnia magna, in a water-only system. After 48 h of exposure of this organism to a 0.4 microg/mL solution of dispersed nanotubes, the CNTs comprised 6.3 +/- 1.5% of the residual organism dry mass. Moreover, these organisms were unable to excrete the nanotubes to either clean artificial freshwater or filtered Lake Kontiolampi water after 24 h depuration periods, even though the lake water had a substantial concentration of natural organic matter. Addition of algae to the water during the depuration period did result however in release of a significant fraction (approximately 50-85%) of the accumulated CNTs within the first few hours, but little thereafter. Light microscopy results suggest that the vast majority of the accumulated CNTs remained in the organisms' guts and were not absorbed into cellular tissues.

Ecotoxicity test methods for engineered nanomaterials: Practical experiences and recommendations from the bench

“…The data so far suggest that invertebrates such as Daphnia and earthworms do not readily take up and accumulate CNTs. Furthermore, the CNT may remain in the gut lumen, also making it difficult to purge the gut contents so that accurate internal body burdens can be obtained [62,103,104]. Similar observations have been made in the gut of Daphnia for TiO 2 [105].…”

Methodological considerations for testing the ecotoxicity of carbon nanotubes and fullerenes: Review

“…Substantial differences are found among different sonicators, so researchers are encouraged to test their instrument calorimetrically to facilitate comparisons among research groups [83]. Nevertheless, several techniques are available for quantifying CNT in aqueous suspensions: UV/vis spectroscopy [84,85], spectrofluorimetry [86][87][88], thermal optical transmittance [89], and radioactivity measurements for radioactively labeled nanotubes [75,90]. Perhaps the most straightforward approach is to assess the concentration of suspended nanotubes gravimetrically.…”

“…Another specialized technique used to quantify CNTs in soils, sediments, and biological tissues and fullerenes in biological tissues is radioactive labeling [27,41,42,90,[96][97][98][99]. Some studies have indicated that biological oxidation of MWNTs and SWNTs in soils, sediments, and tissues was needed to avoid artifacts related to the self-quenching: beta emissions from 14 C were absorbed by the NP aggregates [41,42], whereas another study did not find this effect [27].…”

“…Although large numbers of studies have investigated the ecotoxicity of CNTs, CNT absorption has not been observed consistently for organisms tested in terrestrial, sediment, and aquatic conditions [27,41,42,69,90,96,100]. In the four studies that investigated the extent to which SWNTs and MWNTs would accumulate in organisms in sediments, researchers found negligible absorption into tissues of oligochaetes [42,96], two estuarine invertebrates [27], and a lugworm [100].…”

Effects of suspended multi-walled carbon nanotubes on daphnid growth and reproduction

“…Diameter may play a part in determining the degree to which NOM acids can stabilize tubes. Lin and Xing (2008) tested adsorption and stability of tannic acid to SWNTs and MWNTs of mean outer diameters from about 9 nm to 70 nm (Table 2) Obligate fine mesh grazing zooplankton, such as in the case of two cladocerans, Ceriodaphnia dubia and Daphnia magna, have been shown to ingest suspended CNT aggregates (Roberts et al 2007, Petersen et al 2009). In the pelagic zone, grazing zooplankton are the main primary consumer.…”