Nanoparticles offer multiple benefits to society in areas such as medicine, energy production and conservation, and pollution clean-up. Because nanoparticles is a relatively new technology area, we need to understand the dangers nanoparticles pose in the environment before their use becomes widespread. Environmental scientists are developing methods to assess nanoparticle distribution, fate, and toxicity in the environment. Naturally, a key part of the science relates to understanding how nanoparticles change once they interact with the environment.
A case study in the June 2009 issue of Environmental Toxicology and Chemistry, a publication of the Society of Environmental Toxicology and Chemistry, examines changes and transport in aluminum nanoparticles, currently used in energetics, alloys, coatings, and sensors, when they are exposed to relevant environmental conditions. In this study, nanoparticle suspensions were introduced into soil columns, where their concentration, size, agglomeration state, and particle charge were studied. Soil studies are important to understand exposure to plants and soil-dwelling organisms and the potential for nanoparticles to migrate into groundwater. A key finding was that characteristics of the nanoparticle and the environment interact to influence the distribution of the particles in the environment.
The present study demonstrated that the characteristics of nanoparticles are dynamic in the environment and that this is an important consideration for the design and interpretation of nanoparticle studies. The major factors influencing the transport of aluminum nanoparticles were agglomeration and surface charge. During this study, aluminum nanoparticles rapidly agglomerated, forming particles well outside the range of nanoparticles (i.e., micron size) especially when exposed to simulated groundwater. The increased size of the particles via agglomeration significantly reduced transport of the particles in soil columns.
Surface charges of the particles and the soil were also determining factors in the transport of nanoparticles in soil. Dramatic changes in the surface charge can be caused by changes in nanoparticle coating, surface treatment, and the characteristics of the media it is in. In this study, changing the water used in the soil columns from deionized water to simulated groundwater caused large changes in the surface charge of the aluminum nanoparticles and their ability to move through the soil columns. Typically, when particles have a surface charge similar to the matrix, they will be transported, and when the particle–matrix charges are opposite, the particles will remain in the matrix.
Studies like this will foster the development of models to predict the relationship between rates of agglomeration, size of the starting material, and charge of the nanoparticle and the matrix. This information is critical to determine how nanoparticles distribute in the environment and will help to explain uptake and toxicity to organisms in the environment and to man. Finally, identifying those factors that influence distribution in the environment can assist in designing nanoparticles that have limited transport potential and therefore limited impact on the environment.
The full text of this article, Nanoparticle Characteristics Affecting Environmental Fate and Transport Through Soil (Vol. 28, No. 6, June 2009) is available at http://www.allenpress.com/pdf/ENTC_28.6_1191-1199_.pdf