Delina Y. Lyon

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects

The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.

Antimicrobial nanomaterials for water disinfection and microbial control: Potential applications and implications

The challenge to achieve appropriate disinfection without forming harmful disinfection byproducts by conventional chemical disinfectants, as well as the growing demand for decentralized or point-of-use water treatment and recycling systems calls for new technologies for efficient disinfection and microbial control. Several natural and engineered nanomaterials have demonstrated strong antimicrobial properties through diverse mechanisms including photocatalytic production of reactive oxygen species that damage cell components and viruses (e.g. TiO2, ZnO and fullerol), compromising the bacterial cell envelope (e.g. peptides, chitosan, carboxyfullerene, carbon nanotubes, ZnO and silver nanoparticles (nAg)), interruption of energy transduction (e.g. nAg and aqueous fullerene nanoparticles (nC(60))), and inhibition of enzyme activity and DNA synthesis (e.g. chitosan). Although some nanomaterials have been used as antimicrobial agents in consumer products including home purification systems as antimicrobial agents, their potential for disinfection or microbial control in system level water treatment has not been carefully evaluated. This paper reviews the antimicrobial mechanisms of several nanoparticles, discusses their merits, limitations and applicability for water disinfection and biofouling control, and highlights research needs to utilize novel nanomaterials for water treatment applications.

Bacterial cell association and antimicrobial activity of a C60 water suspension.

Prior to the implementation of any new technology, possible environmental and health repercussions first must be researched. Fullerenes are to be produced soon on an industrial scale, with applications quickly following. To investigate the possible environmental impact of fullerenes, a C60-water suspension (nano-C60) was synthesized and then evaluated for cell-association and toxicity, using the bacteria Escherichia coli and Bacillus subtilis as indicator species. In a defined low-salts medium, nano-C60 associated with both the Gram-negative E. coli and the Gram-positive B. subtilis, albeit more strongly with the former. Nano-C60 also displayed antimicrobial properties against both E. coli and B. subtilis, with minimal inhibitory concentrations of 0.5 to 1 mg/ L and 1.5 to 3.0 mg/L, respectively. Media with higher salt contents result in the nano-C60 particles aggregating and falling out of suspension; thus, higher salt solutions reduced or eliminated the antimicrobial properties of nano-C60.

Antibacterial Activity of Fullerene Water Suspensions (nC60) Is Not Due to ROS-Mediated Damage

The cytotoxic and antibacterial properties of nC 60, a buckminsterfullerene water suspension, have been attributed to photocatalytically generated reactive oxygen species (ROS). However, in this work, neither ROS production nor ROS-mediated damage is found in nC 60-exposed bacteria. Furthermore, the colorimetric methods used to evaluate ROS production and damage are confounded by interactions between nC 60 and the reagents, yielding false positives. Instead, we propose that nC 60 exerts ROS-independent oxidative stress, thus reconciling conflicting results in the literature.

Effect of soil sorption and aquatic natural organic matter on the antibacterial activity of a fullerene water suspension

The present study investigated the association of a C60 water suspension (nC6) with natural organic matter, present as a soil constituent or dissolved in the water column, and its effect on the antibacterial activity of nC60. Sorption of nC60 to soil reduced its bioavailability and antibacterial activity, and the sorption capacity strongly depended on the organic content of the soil. Adsorption of aquatic dissolved humic substances onto nC60 and possible subsequent reactions also were found to eliminate nC60 toxicity at humic acid concentrations as low as 0.05 mg/L. These findings indicate that natural organic matter in the environment can mitigate significantly the potential impacts of nC60 on microbial activities that are important to ecosystem health.

Implications and potential applications of bactericidal fullerene water suspensions: effect of nC60 concentration, exposure conditions and shelf life

Stable fullerene water suspensions (nC(60)) exhibited potent antibacterial activity to physiologically different bacteria in low-salts media over a wide range of exposure conditions. Antibacterial activity was observed in the presence or absence of light or oxygen, and increased with both exposure time and dose. The activity was also influenced by the nC(60) storage conditions and by the age of the buckminsterfullerene (C(60)) used to make nC(60). These results reflect the potential impact of nC(60) on the health of aquatic ecosystems and suggest novel alternatives for disinfection and microbial control.

Nanotechnology-Enabled Water Disinfection and Microbial Control: Merits and Limitations

Several natural and engineered nanomaterials, such as silver (nAg), titanium oxide (TiO,), and carbon nanotubes (CNT), are known to have antibacterial properties and are under consideration as disinfecting agents for water treatment systems. Their antimicrobial mechanisms are diverse, including photocatalytic production of reactive oxygen species (ROS) that inactivate viruses and cleave DNA, disruption of the structural integrity of the bacterial cell envelope resulting in leakage of intracellular components, arid interruption of energy transduction. In order for a material to be used for water disinfection, it must exhibit potent antimicrobial activity while remaining harmless to humans at relevant doses. However, other factors can also hinder its viability as a disinfectant. For suspended nanoparticles, these factors include the presence of salts that promote coagulation and precipitation, natural organic matter that coats or sorbs on nanoparticles and reduces their bioavailability, and competing species that consume ROS. Similarly, the efficacy of antimicrobial coatings can be compromised by the deposition of debris (e.g., soluble microbial products, inorganic precipitates, or dead cells) that occlude antimicrobial surface sites and facilitate biofilm formation. Another potential limitation is the need to retain and recycle the nanoparticles to reduce cost and avoid potential health and environmental impacts. Despite these limitations, antimicrobial nanoparticles could overcome critical challenges associated with traditional chemical disinfectants (e.g., free chlorine and ozone) such as harmful disinfection by-products and short-lived reactivity, and they could enhance existing technologies such as ultraviolet inactivation of viruses, solar disinfection of bacteria, and biofouling prone membrane filtration. Furthermore, a potential growth in demand for decentralized or point-of use water treatment and reuse systems will likely stimulate further research and commercialization of nanoparticles to enhance water disinfection applications.