Abstract
Although the development and application of nanomaterials is a growing industry, little data is available on the ecotoxicological effects on aquatic organisms. Therefore, we set up a workflow to address the potential uptake of weathered multi-walled carbon nanotubes (wMWCNTs) by a model organism, the pulmonary mud snail Lymnaea stagnalis (L. stagnalis), which plays an important role in the food web. It represents a suitable organism for this approach because as a grazer it potentially ingests large amounts of sedimented wMWCNTs. As food source for L. stagnalis, benthic biofilm was investigated by the use of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) after exposure with wMWCNTs. In addition, isotopic labeling was applied with 14C-wMWCNTs (0.1 mg/L) to quantify fate, behavior, and enrichment of 14C-wMWCNTs in benthic biofilm and in L. stagnalis. Enrichment in benthic biofilm amounted to 529.0 µg wMWCNTs/g dry weight and in L. stagnalis to 79.6 µg wMWCNTs/g dry weight. A bioconcentration factor (BCF) for L. stagnalis was calculated (3500 L/kg). We demonstrate the accumulation of wMWCNTs (10 mg/L) in the digestive tract of L. stagnalis in an effect study. Moreover, the physiological markers glycogen and triglycerides as indicators for the physiological state, as well as the RNA/DNA ratio as growth indicator, were examined. No significant differences between exposed and control animals were analyzed for glycogen and triglycerides after 24 days of exposure, but a decreasing trend is recognizable for triglycerides. In contrast, the significant reduction in the RNA/DNA ratio of L. stagnalis indicated an inhibition of growth with a following recovery after depuration. The described workflow enables a comprehensive determination of the fate and the behavior of wMWCNTs specifically and in general all kinds of CNTs in the aquatic environment and therefore contributes to a holistic risk assessment of wMWCNTs.
Highlights
Nanotechnology is an increasing sector in the industry with a wide range of applications such as drug delivery, healthcare products, or textiles (Baun et al 2008; Bianco et al 2005; Schwirn and Völker 2016)
The radioactivity decreased in the Relative amounts of 14C-weathered multi-walled carbon nanotubes (wMWCNTs) in snail tissue ranged from 1.9 ± 0.8% (4 h), 4.8 ± 2.4% (24 h), 5.0 ± 0.6% (48 h) to 1.6 ± 1.1% (72 h) (Fig. 4, left)
The enrichment of 14C-wMWCNT in L. stagnalis shows a maximum of 79.6 ± 34.7 μg wMWCNT/g dry weight at 24 h (Fig. 4, right), but decreased to 20.65 ± 12.50 μg wMWCNT/g dry weight (72 h)
Summary
Nanotechnology is an increasing sector in the industry with a wide range of applications such as drug delivery, healthcare products, or textiles (Baun et al 2008; Bianco et al 2005; Schwirn and Völker 2016). CNTs, especially MWCNTs, are described to be the star in the nanomaterials industry (Sebastian et al 2013). These groups are found in wastewater at concentrations between 3.69 and 32.66 ng/L, whereas a range of 0.001 and 0.8 ng/L has been detected in surface waters (Maurer-Jones et al 2013), but environmental concentrations of nanomaterials in general are widely unknown (Lawrence et al 2016). Environmental Science and Pollution Research and sedimentation, over time, CNTs deposit in water and cause higher concentrations in sludge and sediment (Chen et al 2010; Schierz et al 2014; Glomstad et al 2018; Gottschalk et al 2009; Sun et al 2014; Politowski et al 2021a). Reported CNT concentrations in sediment compartments range between 1 μg/kg and 1 mg/kg (Selck et al 2016)
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