Carbon nanotubes

Various forms of nanotubes are added to a variety of products during their manufacture and biomedical applications to increase the strength of the materials without adding much weight. Nanotube manufacturing waste products and bio-solids that result from such applications as in water purification may find their way into wastewater treatment plants. These bio-solids cannot be released into water bodies and so they are often discarded by spreading on land.

Similarly both carbon nanotubes and functionalized carbon nanotubes (with modifications to create chemical or biological changes to the nanotubes) are often used in medicines. Majority of the wastes emanating from these sources may also be disposed into soil.

Data on the effects of the release of these nano materials on environment, particularly in high or low organic soils remains sparse.

Effect on soil

Results indicate that repeated applications of as-produced SWNTs can affect microbial community structures and induce minor changes in soil metabolic activity in the low organic matter systems.

Researchers have studied soils with either low or high organic matter contents as well as pure cultures of E. coli by treating with either raw as-produced SWNTs or SWNTs functionalized with either polyethylene glycol (PEG-SWNTs) or m-polyaminobenzene sulfonic acid (PABS-SWNTs).

AP-SWNTs were found to suppress metabolic activity of the E. coli, whereas the two functionalized SWNTs were less toxic. The metals released from the raw forms of SWNTs did not play a role in the effects seen in soil or the pure culture but sorption to soil organic matter played a controlling role in the soil microbiological responses to these nano materials.

Study at Purdue University showed that some types of carbon nanotubes used for strengthening plastics and other materials had an adverse effect on soil microbiology and soil microbial processes.

The raw, non-functionalized single-walled carbon nanotubes damage the active microbiology in low-organic soil due to carbon and nitrogen cycling, which are critical processes to ensure a fully functional soil.