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This content is taken from a chapter of A Small Dose of Toxicology by Steve Gilbert.

 

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Nanotoxicology: Quick Facts

 

Definition of nanomaterials: materials sized from 1 to 100 nanometers (a nanometer is one billionth of a meter)

Use: wide range of chemicals, pesticides, plastics, flame retardants, medicine, paints, cosmetics, sunscreens, clothing, baby toys, and much more

Source: synthetic chemistry, plants

Recommended daily intake: none (not essential)

Absorption: intestine, respiratory system (lungs), skin

Sensitive individuals: fetus and children, workers

Toxicity/symptoms: affects endocrine system, hormone levels, sexual characteristics, reproduction, and development; mimics estrogen; and anti-estrogenic

Regulatory facts: FDA and EPA are reviewing the use and potential hazards of nanomaterials

General facts: billions of pounds used every year in wide range of products

Environmental concerns: widely distributed in environment and can affect wildlife

Recommendations: minimize use, avoid exposure to children, consider alternatives, expand research into toxicity, adopt precautionary approach

 

Case Studies

 

Carbon Nanotubes

Scanning electron micrograph of carbon nanotubes

 

Carbon nanotubes (CNTs) are typically created from one-atom-thick sheets of carbon called graphene that are rolled to form a hollow structure. Carbon nanotubes can be either single-walled or multi-walled, with a typical single-walled tube having a diameter of about 1 nanometer. CNTs are attractive to industry because they have multiple extraordinary properties including great hardness and strength, thermal and electrical conductivity, and optical properties; they can have other capabilities depending on the manufacture method and other chemicals or elements that are added. CNTs are now commonly used in industrial processes and consumer products such as skis, baseball bats, golf clubs, car parts, and paints. There are concerns that CNTs may be hazardous to human and environmental health: the physical structure of nanotubes is similar to that of asbestos fibers, which appear long and sharp when magnified. Inhalation of asbestos can cause malignant mesothelioma, a fatal lung cancer that follows a latency period of 20 to 40 years. Approximately 18,000 people died from malignant mesothelioma between 1999 and 2005. Animal studies using rodents have reported lung damage from CNTs similar to that caused by asbestos, which has important implications for people working with CNTs. The great variety in CNTs’ size, shape, surface area, and chemical coatings makes toxicology studies difficult to design and replicate. Some studies indicate that CNTs can cross cell walls and cause cell death.

 

Nanosilver

Nanosilver has many interesting characteristics, but it was added to consumer products because of its antibacterial properties. Over two thousand years ago, Hippocrates (460 BC – 370 BC) acknowledged the antimicrobial and healing properties of silver. By the early 1900s the antimicrobial properties of silver were well known and silver was used in a number of medical treatments. The use of silver in medicine declined following the introduction of antibiotics, but the use of silver-impregnated wound dressing has recently increased, particularly for treating burns. Silver sulfadiazine, used successfully to treat external infections and as an antiseptic in the treatment of burns, is now being replaced by nanosilver products. The ability to more easily manufacture nanosilver particles has stimulated a range of applications in consumer products to take advantage of its antibacterial properties. Products impregnated with nanosilver include socks, baby toys, kitchen tools, paint, sunscreen, cosmetics, and water treatment equipment, to name just a few. Though nanosilver is increasingly used in industrial and consumer applications, a systematic evaluation of environmental or human health hazards has not been done. Cell-based studies clearly demonstrate that nanosilver can be toxic to a variety of organ cells, such as lung, liver, kidney, and brain. There is also evidence that nanosilver particles are readily absorbed through inhalation or skin contact. In addition, there are concerns about nanosilver entering the environment after particles are released down the drain. The toxic properties of silver are typical of those of heavy metals, but silver has appeared to be minimally toxic to humans, unlike other metals such as mercury, lead, or arsenic. Silver solutions, sometimes called colloidal silver, are marketed as alternative medicines with a variety of unsubstantiated beneficial effects.

 

Nanomaterials in Sunscreens

Sunscreens are made up of chemicals that absorb or reflect ultraviolet (UV) radiation, or a combination of the two. Typical sunscreens block UVB radiation that causes sunburn but do not always block UVA, so it is recommended to use broad-spectrum sunscreens that block both UVA and UVB. Inorganic particles such as zinc oxide and titanium dioxide reflect UV radiation, and many sunscreens use nanosized zinc or titanium in part because the material becomes transparent at the nanoscale, with titanium appearing clear instead of white. The effectiveness of the nanoparticles can be enhanced by applying additional chemicals to the particles. One concern is that the nanosized particles may be absorbed through the skin or swallowed, with unknown possible consequences. Another concern is that the material is washed off into the environment, which may have harmful effects on the biotic community.

Introduction and History

 

Nanometer: one billionth of a meter (10-9),

from the Greek nanos or ‘dwarf’

 

Nanoparticle: 1 – 100 nanometers

 

“Nanotechnology is the understanding and control of matter at dimensions between approximately 1 and 100 nanometers, where unique phenomena enable novel applications.”

(www.nano.gov)

 

Nanomaterials or nanoparticles are generally defined as being between 1 to 100 nanometers. At this scale, the physical and chemical properties of a material can change. For example, titanium, which is usually white, becomes clear at the nanoscale. The small size of nanoparticles results in a much greater surface area-to-volume ratio, which makes the material potentially more reactive. Nanoparticles can also be coated with chemicals that can react with the environment.


A Nanometer in Perspective

  • A sheet of paper is about 100,000 nm thick
  • A strand of human DNA is 2.5 nanometers in diameter
  • A human hair is approximately 80,000-100,000 nanometers in diameter
  • There are 25,400,000 nm in an inch
  • A single gold atom is about a third of a nanometer in diameter
  • A nanometer is a millionth (10-6) of a millimeter

 

The use of nanomaterials dates back many centuries; people unknowingly used nanomaterials in a variety of objects (see table below). For example, colloidal gold and silver was used to change the color of the glass in the Roman Lycurgus Cup, which looks opaque green but turns red when light shines from the inside. The famous steel of the Damascus swords was strengthened by carbon nanotubes that appeared during the rigorous shaping of the steel blade.

Steady advances in technology catalyzed our understanding of these interesting phenomena and led to the development of the new field of nanotechnology. In 1936 the field-emission microscope, which allowed the experimental observation of atoms, was invented by Erwin Müller (1911-1977). The next major advance was in 1981, when Gerd Binnig and Heinrich Rohrer, at IBM’s Zurich lab, invented the scanning tunneling microscope, which allowed imaging of surfaces at the atomic level and resulted in the ability to "see" individual atoms. In the intervening years nanotechnology was predicted by the physicist Richard Feynman in a 1959 lecture titled "There's Plenty of Room at the Bottom." He predicted that someday the technology would exist to manipulate individual atoms and molecules. In 1985 the “buckyball” was discovered. This is a structure of carbon atoms that resembles a soccer ball in shape, though much smaller, of course (see illustration). Shortly thereafter in 1991, carbon nanotubes were discovered; they were tubular in shape, very strong, and showed a range of interesting properties.

In the late 1990s, nanomaterials begin to appear in consumer products. The U.S. government took notice and established the National Nanotechnology Initiative (NNI) to coordinate federal research and development efforts and to promote nanotechnology (http://nano.gov/). Gradually, authoritative reports advocating the need to address potential health, environmental, social, ethical, and regulatory issues associated with nanotechnology began to appear. The challenge now is to assess the consequences of human and ecological exposure to nanomaterials and balance these with the benefits.

 

Milestones in Nanotechnology

YearEvent
~300 ADLycurgus Cup (Rome): dichroic glass looks opaque green but turns red when light shines from inside, the result of colloidal gold and silver in the glass
~600-1500Stained glass windows in European cathedrals contained nanoparticles of gold chloride and other metal oxides
~1200-1800“Damascus” saber blades contained carbon nanotubes and cementite nanowires
1857Nanogold solutions’ ability to appear as different colors depending on the lighting demonstrated by Michael Faraday (1791-1867)
1936Field-emission microscope allowing the experimental observation of atoms invented by Erwin Müller (1911-1977)
1959"There's Plenty of Room at the Bottom," first lecture on technology and engineering at the atomic scale by Richard Feynman (1918-1988) of the California Institute of Technology
1981Scanning tunneling microscope allows imaging of surfaces at the atomic level and permits scientists to "see" individual atoms; invented by Gerd Binnig and Heinrich Rohrer at IBM’s Zurich lab
1985Buckminsterfullerene (C60) or buckyball was discovered by researchers at Rice University; it is shaped like a soccer ball and composed entirely of carbon
1986Atomic force microscope, providing the ability to view, measure, and manipulate materials down to fractions of a nanometer in size, invented
1991Carbon nanotube (CNT) created; CNTs are very strong, have electrical and thermal conductivity, and entirely composed of carbon but in a tubular shape
1999-?Consumer products employing nanotechnology appeared, from cars to golf balls to paint to clothing and more
2000National Nanotechnology Initiative (NNI) started by President Clinton to coordinate Federal R&D efforts and promote nanotechnology
2004“Nanoscience and Nanotechnologies: Opportunities and Uncertainties” published by Britain’s Royal Society and the Royal Academy of Engineering; it advocates the need to address potential health, environmental, social, ethical, and regulatory issues associated with nanotechnology

2008,

updated 2011
“Nanotechnology-Related Environmental, Health, and Safety (EHS) Research Strategy” published by the US NNI (http://nano.gov/node/681)

*For a more detailed list see http://www.nano.gov/timeline

Nanomaterials in Use

There are over 1,300 identified consumer products employing nanomaterials, according to a list compiled by the Project on Emerging Nanotechnologies (see http://www.nanotechproject.org/). The products include baby toys such as a baby bear and baby blanket impregnated with nanosilver, sunscreens and cosmetics, kitchen utensils, socks and shirts, paint, computer products, golf clubs, and much more. Silver nanoparticles are being used in a wide variety of products to kill bacteria, being touted as natural and “clinically proven to fight against harmful bacteria, molds and mites.” Nanoparticles in paint are advertised as improving adhesion and providing anti-mildew properties.

Nanomaterials are also widely used in university and industry research labs studying the properties of nanoparticles and investigating new applications.  

A basic challenge is determining what products or facilities are using nanoparticles, what types of nanoparticles are being used, and in what quantity. As noted by the US EPA, “Currently, tracking products that contain nanosilver is getting to be difficult because the products are almost always packaged under numerous brand names, and current labeling regulations do not require that the nanomaterials be listed as an ingredient.”  Maps that detail nanomaterial use and consumer product information are available (http://www.nanotechproject.org/inventories/map/). Some organizations are working on a cradle-to-grave risk evaluation for products using nanoparticles, incorporating potential hazards across manufacture, use, and disposal (see U.S. EPA “State of the Science Literature Review: Everything Nanosilver and More,” August 2010, http://www.epa.gov/nanoscience/files/NanoPaper1.pdf). The European Union is implementing a new approach to nanomaterials called Classification, Labeling and Packaging (CLP) Regulation. CLP stipulates that if the form or physical state of a substance is changed, an evaluation must be done to determine if the hazard classification should be changed.

Health and Environmental Effects of Nanomaterials

Introduction

A basic principle of toxicology is that risk of harm is related to hazard, exposure, and individual sensitivity. The assessment of any of these parameters is complicated by the large variety of nanoparticles and nanomaterials, the unique characteristics related to nanoparticles’ small size and large surface area, and various additional chemicals that can be applied. Consideration must be given to nanoparticles’ characteristics including concentration, size, shape, surface charge, crystal structure, surface chemistry, surface transformations, and chemical coatings. Most importantly, the small size and the large surface area-to-volume ratio means that nanomaterials have unique physiochemical properties not found in materials of the same kind but larger.

The challenge is determining how the nanomaterials interact with biological systems. The classic questions of persistence and bioaccumulation in animals, humans, or the environment must be addressed. In addition, procedures for the analytical measurement of specific nanoparticles must be developed and validated for a variety of media such as air, water, soil, tissue, blood, and urine. The development of a standard set of procedures to assess the potential hazards of nanoparticles is urgently needed (see papers by Maynard et al. 2006 and 2011). Below are examples of the challenges associated with addressing the nanotoxicology of specific nanoparticles.

Distribution, Exposure, and Absorption

Given the wide range of products using or incorporating nanomaterials, there is increasing potential for exposure to nanomaterials through various exposure routes. In some products the nanomaterials are tightly bound or are a structural part of the product and thus not bioavailable. In products such as sunscreens, however, the nano-sized titanium dioxide or zinc oxide are applied to the skin where there is potential for dermal absorption or oral ingestion. A variety of cosmetics are now employing nanomaterials, which increases the possibility of absorption through the skin. Breaks in the skin and various skin conditions such as sunburn and eczema can accelerate absorption of nanoparticles into the bloodstream. There is also concern that these materials can be washed off the skin and enter the environment; a similar concern exists with nanosilver used as a bactericide because the nanomaterials must be bioavailable to be effective. Nanosilver particles may enter wastewater and affect sewage treatment.

The manufacture of nanomaterials and their use in product manufacturing present significant challenges for occupational exposure. For example, the inhalation of carbon nanotubes may result in damage to lung tissue and cause lung cancer, as occurs with the inhalation of asbestos fibers.  There have been calls for greater monitoring and control of potential exposure to nanotube materials. In addition, the unintended production of nanomaterials in diesel exhaust or soot (combustion-derived nanoparticles) can be a serious hazard to workers and others near the source of the exhaust, such as trucks, trains, or ships. The small size of these nanomaterials allows them to move deep into the lungs, resulting in acute effects such as asthma, or long-term damage. Also, these nanoparticles can carry other chemical contaminants on their surface, such as polycyclic aromatic hydrocarbons (PAHs), deep into the lungs.  

Ultimately, more information on the manufacture, use, fate, and transport of nanomaterials is needed in order to better assess human exposure and ecological distribution.

Health Effects

The potential health effects of nanoparticle exposure to humans and other organisms are just beginning to be understood. Studying the toxicity of nanoparticles is complicated by a host of factors such as the variety of substances, variation in size and surface area, chemical charge, and chemical coating. An additional challenge is developing the analytical methodology for measuring the amount of nanomaterials in the tissue or biological fluid, which would permit the assessment of tissue distribution or even cellular exposure. There are similar problems in evaluating distribution of nanoparticles in the environmental media of air, water, or soil.

It is known that once in the body, nanoparticles can distribute into all organs and cross cell boundaries. Once inside the cell, the nanoparticles may interact with cellular DNA or cell proteins, thus interfering with normal cell function or causing an inflammatory response. An area of some study is the ability of nanoparticles to increase the production of reactive oxygen species (ROS), including free radicals, which can cause oxidative stress, inflammation, and other cellular damage. It should be remembered that nanosilver is useful precisely because it kills bacterial cells. Little is known about potential immunological effects of nanoparticles other than some reports of allergic response to nanosilver particles. Studies of fish exposed to nanoparticles in water indicated that the nanoparticles were readily absorbed, caused brain damage, and affected the liver. The consequences of ecological exposure to small organisms is poorly studied and could be significant because for a small organism, a small exposure represents a big dose and potential serious consequences.

Persistence and bioaccumulation of the various nanomaterials in their many forms, shapes, and coatings is not well understood. There has been very little study on the potential developmental effects of nanomaterial exposure. In summary, there are many challenges to assessing the risks of nanomaterials to human health or the environment and a lot more research needs to be done. The history of toxicology is replete with incidents where the application of technology advanced more quickly than the understanding or regulation of its health and environmental effects. The results of some of these incidents have been devastating.

Evaluation Summary

The chart below from nano.gov provides a good summary of the challenges of assessing hazards and the areas of concern.

 

from: http://nano.gov/you/environmental-health-safety. The risk assessment paradigm (on left) integrated with nanomaterial life cycle stages (across top). (Design credit: N.R. Fuller of Sayo-Art.)

Reducing Exposure

Reducing exposure is predicated on knowing if there is exposure. It is currently very difficult to know which products contain nanomaterials. When they are present, their potential bioavailability may be unknown. As a result, exposure cannot be predicted or quantitatively evaluated.

Regulation of Nanotechnology

Currently there is no comprehensive regulation that addresses industrial processes or consumer products that use nanomaterials or nanotechnology. Despite the rapid increase in the use of nanoparticles in consumer products from socks to sunscreens and the potential for human and ecological exposure, there is no consistent approach or requirement to evaluate potential hazardous effects.

The US EPA is struggling to adapt the 1976 Toxic Substances Control Act (TSCA) to address the potential hazards of nanoparticles. The U.S. Food and Drug Administration (FDA) is challenged to address the use of nanomaterials in products it regulates, such as foods, cosmetics, drugs, medical devices, and veterinary products, and has released a draft guidance related to nanotechnology applications in cosmetics and food substances (see reference below). The laws governing the Consumer Product Safety Commission do not mandate pre-marketing product approval, thus the CPSC can only address potential risk after public distribution of the product. The CPSC statement below is a good reminder of the problems faced by regulatory agencies as they try to address the use of nanomaterials.

The workplace is an area of potentially high exposure to nanomaterials through inhalation, ingestion, or dermal exposure. The US Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH), which regulate and research occupational health and safety issues, attempt to address workplace exposures. For agencies and consumers, the failure to require adequate labeling of nanomaterials makes health assessments very difficult.

 

Consumer Product Safety Commission

“Evaluation of Consumer Products: The potential safety and health risks of nanomaterials, as with other compounds that are incorporated into consumer products, can be assessed under existing CPSC statutes, regulations and guidelines. Neither the Consumer Product Safety Act (CPSA) nor the Federal Hazardous Substances Act (FHSA) requires the pre-market registration or approval of products. Thus, it is usually not until a product has been distributed in commerce that the CPSC would evaluate a product’s potential risk to the public.”

 

The European Union is implementing a new approach to nanomaterials called Classification, Labeling and Packaging (CLP) Regulation. CLP stipulates that if the form or physical state of a substance is changed, an evaluation must be done to determine if the hazard classification should be changed.

Recommendation and Conclusions

Nanomaterials have interesting properties and tremendous potential in many areas. Their use in industrial processes and consumer products is expanding rapidly. The huge challenge is making sure we understand the potential risks and that we properly balance the risks and the benefits. More research is needed on the potential human and ecological effects of nanomaterials. It is critical that our understanding and mitigation of potential adverse effects does not fall substantially behind the use of these materials.

More Information and References

European, Asian, and International Agencies


  • Nanowerk. Food Safety. Information and news portal. Committed to educate, inform and inspire about nanosciences and nanotechnologies.

North American Agencies


  • The National Nanotechnology Initiative (NNI). US Government Nanotechnology Initiative is a federal R&D program established to coordinate the multiagency efforts in nanoscale science, engineering, and technology.
  • National Aeronautics and Space Administration (NASA). Ames Center for Nanotechnology. Started in early 1996, the research work focuses on experimental research and development in nano and bio technologies; includes great images.
  • US FDA. Nanotechnology: Science and Research. Website includes nanotechnology fact sheet, draft guidance related to nanotechnology applications in cosmetics and food substances, and "Draft Guidance for Industry: Considering Whether an FDA-Regulated Product Involves the Application of Nanotechnology"
  • US Department of Labor, Occupational Safety & Health Administration (OSHA). Nanotechnology. Addresses worker safety and health issues related to the use or production of nanomaterials.
  • US Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health (NIOSH). Nanotechnology. Conducts research on worker safety and issues related to the use or production of nanomaterials.
  • The Center for Integrated Nanotechnologies (CINT) at Sandia National Laboratories, a Department of Energy/Office of Science Nanoscale Science Research Center (NSRC). "Our vision is to become a world leader in nanoscale science by developing the scientific principles that govern the design, performance, and integration of nanoscale materials."

For-profit Organizations


  • Nanotechnology Now (NN). Nanotechnology Glossary. NN was created to serve the information needs of business, government, academic, and public communities with the intention of becoming the most informative and current free collection of "nano" reference material.

Non-government Organizations


  • The Project on Emerging Nanotechnologies. Established in April 2005 as a partnership between the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts, "The Project is dedicated to helping ensure that as nanotechnologies advance, possible risks are minimized, public and consumer engagement remains strong, and the potential benefits of these new technologies are realized."

References


  • Ahamed, M., Alsalhi, M. S., & Siddiqui, M. K. "Silver nanoparticle applications and human health." Clin Chim Acta 411, 23-24 (2010): 1841-1848.
  • Donaldson, K., Murphy, F., Schinwald, A., Duffin, R., & Poland, C. A. "Identifying the pulmonary hazard of high aspect ratio nanoparticles to enable their safety-bydesign." Nanomedicine (Lond) 6, 1 (2011): 143-156.
  • Feynman, Richard. "There's Plenty of Room at the Bottom" delivered as a lecture at the annual meeting of the American Physical Society at the California Institute of Technology (Caltech), December 29th, 1959. First published in the February 1960 issue of Caltech's Engineering and Science, available on their website with their permission.
  • Luoma, Samuel. "Silver Nanotechnologies and the Environment." Project on Emerging Nanotechnologies by PEW Charitable Trust (2008). Maynard, A. D., Aitken, R. J., Butz, T., Colvin, V., Donaldson, K., Oberdorster, G., et al. "Safe handling of nanotechnology." Nature 444,7117 (2006): 267-269.
  • Maynard, A. D., Warheit, D. B., & Philbert, M. A. "The new toxicology of sophisticated materials: nanotoxicology and beyond." Toxicol Sci 120 Suppl 1 (2011): S109-129.
  • Nanotoxicology journal from Informa Healthcare. "Addresses research relating to the potential for human & environmental exposure, hazard & risk associated with the use & development of nano-structured materials."
  • Walker, N. J., & Bucher, J. R. "A 21st century paradigm for evaluating the health hazards of nanoscale materials?" Toxicol Sci 110, 2 (2009): 251-254.

 

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