Influence of nanotube preparation in Aquatic Bioassays

Abstract

Knowledge gaps in nanomaterial fate and toxicity currently limit the ability of risk assessments to characterize the environmental implications of nanomaterials. This problem is further complicated by the lack of standardized characterization and preparation methodologies for researchers to gain the needed information to assist risk assessors. In the present study, data were generated to determine if multiwalled nanotube (MWNT) fate and toxicity are altered by engineered surface modifications or by different dispersal methods. While dissolved organic matter was a good dispersing agent of MWNTs in water, the humic acid fraction was a more effective dispersant than the fulvic acid fraction. When stabilized in organic matter, the functional group attached to the MWNT controlled its toxicity. Underivatized MWNTs induced relatively moderate toxicity to Ceriodaphnia dubia after 96 h (25 +/- 19% survival at 26 mg/L), while hydrophilic groups (hydroxyl, carboxyl) reduced this toxicity (93 +/- 12% survival at 48 mg/L). However, other functional groups (alkyl, amine) increased toxicity (0 +/- 0% survival at <15 mg/L). In dispersal method studies, sonication of MWNTs increased fragmentation relative to magnetic stirring. The sonication treatment of MWNTs also slightly reduced the mortality of C. dubia in the water column but increased toxicity in the sediment to Leptocheirus plumulosus and Hyalella azteca. Findings in the present study indicate that nanotubes engineered for specific applications need to be managed independently and that laboratory methods to disperse and test nanotubes in bioassays need to be standardized to obtain repeatable results for comparison of materials.

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

“…Functionalized CNPs may be the starting material for ecotoxicity tests, and these characteristics should be verified prior to testing; alternatively, changes in surface functionalization may occur during testing and should be evaluated when possible. Evidence exists that surface chemistry can influence toxicity in test organisms, including Ceriodaphnia dubia [61], in which alkyl and amino functional groups on CNTs dramatically increased toxicity, whereas hydrophilic groups made the CNTs less toxic. Likewise, various types of surface-modified fullerenes have also exhibited substantially different toxicities to Daphnia pulex and Daphnia magna compared with underivatized fullerenes [62,63].…”

“…This includes leached metal ions, polycyclic aromatic hydrocarbons, and toxic chemicals included in or formed by the dispersion process (THF byproducts for fullerenes). Many of these potential artifacts can be identified by thoroughly analyzing the materials in the test media prior to initiating ecotoxicity experiments (see Kennedy et al [61] for an example of a thorough characterization of potential byproducts after CNP modifications). Additionally, it is typically possible to filter solutions used for the toxicity testing to remove the CNPs and then test the toxicity of the filtrate.…”

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

“…The optimal sonication time depends on the suspended ENM concentration, but it is usually less than 1 h [35]. In addition, sonication can introduce artefacts in toxicity studies because it fragments multiwalled carbon nanotubes [36] and possibly alters the coatings on ENMs [37] or increases reactive oxygen species (ROS) production (see later discussion). Sonication settings and procedures should therefore be reported carefully at all times.…”

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

“…This can further be complicated by surface functional groups. Kennedy et al (2009) exposed C. dubia over 96 hours to (1) pristine, (2) alkyl functionalized, (3) amine functionalized, and (4) hydroxylated MWNTs (Table 1).…”