Carbon nanotubes (CNTs) are currently incorporated into various consumer products, and numerous new applications and products containing CNTs are expected in the future. The potential for negative effects caused by CNT release into the environment is a prominent concern and numerous research projects have investigated possible environmental release pathways, fate, and toxicity. However, this expanding body of literature has not yet been systematically reviewed. Our objective is to critically review this literature to identify emerging trends as well as persistent knowledge gaps on these topics. Specifically, we examine the release of CNTs from polymeric products, removal in wastewater treatment systems, transport through surface and subsurface media, aggregation behaviors, interactions with soil and sediment particles, potential transformations and degradation, and their potential ecotoxicity in soil, sediment, and aquatic ecosystems. One major limitation in the current literature is quantifying CNT masses in relevant media (polymers, tissues, soils, and sediments). Important new directions include developing mechanistic models for CNT release from composites and understanding CNT transport in more complex and environmentally realistic systems such as heteroaggregation with natural colloids and transport of nanoparticles in a range of soils.

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.

Engineered nanoparticles, due to their unique electrical, mechanical, and catalytic properties, are presently found in many commercial products and will be intentionally or inadvertently released at increasing concentrations into the natural environment. Metal- and metal oxide-based nanomaterials have been shown to act as mediators of DNA damage in mammalian cells, organisms, and even in bacteria, but the molecular mechanisms through which this occurs are poorly understood. For the first time, we report that copper oxide nanoparticles induce DNA damage in agricultural and grassland plants. Significant accumulation of oxidatively modified, mutagenic DNA lesions (7,8-dihydro-8-oxoguanine; 2,6-diamino-4-hydroxy-5-formamidopyrimidine; 4,6-diamino-5-formamidopyrimidine) and strong plant growth inhibition were observed for radish (Raphanus sativus), perennial ryegrass (Lolium perenne), and annual ryegrass (Lolium rigidum) under controlled laboratory conditions. Lesion accumulation levels mediated by copper ions and macroscale copper particles were measured in tandem to clarify the mechanisms of DNA damage. To our knowledge, this is the first evidence of multiple DNA lesion formation and accumulation in plants. These findings provide impetus for future investigations on nanoparticle-mediated DNA damage and repair mechanisms in plants.