Nanoparticles and Health Michael T. Kleinman Department of Community and Environmental Medicine University of California, Irvine
Particle Scale PM 10 Ultrafine Respirable PM 2.5 Nanoparticles 10 mm 1 mm 1 nm 10 nm 100 nm
Definitions- Particle Size • Nano = Ultrafine = < 100 nm (Conventional) • Nano = <10 nm (suggested by unique quantum and surface-specific functions) • Fine = 100 nm - 3 m • Respirable (rat) = < 3 m (max = 5 m) • Respirable (human) = < 5 m (max = 10 m) • Inhalable (human) = ~ 10 - 50 m
Much of our thinking about nanoparticles stems from our knowledge of traffic-related particulate matter (EPA, 2004) • The four polydisperse modes of traffic-related ambient particulate matter span approximately 4 orders of magnitude from below 1 nm to above 10 μm. • Nucleation and Aitken mode particles are defined as ultrafine particles (<~100 nm). • Source-dependent chemical composition is not well controlled and varies considerably. • In contrast engineered nanoparticles (1-100 nm) have well controlled chemistry and are generally monodispersed. • The particles < 10 nm have surface properties that are quantum dominated and may represent a separate class of materials.
Interparticle Forces And Surface Chemistry Will Be Influenced By Size And Whether Particles Are Individual or Aggregates & Agglomerates Mechanical interlocking Single particle Capillary (surface tension) Van der Waals (cohesive force α 1/d**2) Chemical bonds Equivalent dia. ~2 x Settling velocity ~3-4 x Equivalent diameters of 10-1000x are common
These properties influence lung deposition as well as toxicity. • Ultra-fine or nanoparticles may deposit as aggregates due to high Van Der Waals forces, rather than discrete particles. • If an inhaled particle with a diameter of 50–100 nm forms an aggregate of 5–10 particle types, in terms of deposition it may have the properties of a 200–500 nm particle • Inhaled agglomerates may dissociate when in contact with lung surfactants.
Engineered Nanoparticles • There are four basic categories of nanoscale materials that are being sold as commercial products and materials that may need to be regulated. • Metal oxides—ceramics from oxides of zinc, iron, cerium, and zirconium; • chemical polishing agents from semi-conductor wafers; • scratch resistant coatings for glass; and • cosmetics and sunscreens which are the biggest group of current commercial nanomaterials. • Nanoclays—naturally-occurring plate-like clay particles; • improve strength, hardness, heat resistance and flame retardancy of materials • produce barrier films in plastic beverage bottles, paper juice cartons, and tennis balls. • Nanotubes and spheres—used in coatings • to dissipate and minimize static electricity in fuel lines and hard disk handling trays; • can also be found in electrostatically paintable car exterior components, flame-retardant fillers for plastics, and field emitter sources in flat panel displays. • Quantum dots—used in exploratory medical diagnostics and therapeutics and self assembly of nanoelectronic structures.
Engineered nanoparticles will have a variety of applications in the environment and in people • Nanoscale sensors are being investigated for detection of biological compounds such as algal toxins in the marine environment or mycobacteria present in drinking water. • Fluorescent dendrimers displaying spatially resolved microdomains on polymer beads can detect different algal (or other) toxins. • The binding of different toxins results in specific fluorescence wavelengths, depending upon the spatial resolution of the dendrimers on the polymer beads.
NANOTECHNOLOGY, HUMAN HEALTH, AND MEDICINE Nanoparticles are far to useful NOT to enter the human environment! Once an early biomarker of a disease or dysfunction is identified, then scientists can use targeted pharmaceutical or gene therapy to correct the faulty components. —Kenneth Olden
INTERACTIONS WITH BIOLOGICAL SYSTEMS • The challenge that nanomaterials pose to environmental health is that they are not one material. • It is difficult to generalize about them because, similar to polymers, they represent a very broad class of systems. • Many engineered nanomaterials have precisely controlled internal structures, which are structures of perfect solids. • Over a third of the atoms in a nanoparticle are at the surface, and these are extremely reactive systems, which in some cases can generate oxygen radicals; • Nanoparticles can also be tied up very tightly in covalent bonds and wrapped with a polymer. • Because of the size of nanostructures, it is possible to manipulate the surface interface to allow for interactions with biological systems. • With the correct coating, particles below 50 nm can translocate into cells relatively easily and are able to interact with channels, enzymes, and other cellular proteins. • Those particles above 100 nm, based primarily on size of the particles, have more difficulty. • Through the interactions with cellular machinery, there is potential for medical uses, such as drug delivery and cellular imaging.
SIZE ISN’T EVERYTHING • In most cases, nanoscale systems will alter in physical size upon interaction with an aqueous system. • For example, it is very common for many nanostructures to adopt a different chemical form simply through relatively minor interactions; consequently, size is not a constant factor in biological interactions. • The surface area can make up a sizeable fraction of these materials. • they can be derived to make many different biomedical systems. • by changing surface coatings the nanomaterial toxicity can almost be completely altered. • For example, changing the surface features of the materials can change a hydro-phobic particle into a hydrophilic one. • Hypothetically, surface coats could, for instance, make it possible to eat nanoscale mercury if it has the right surface coating, while it may be dangerous to eat nanoscale table salt if the surface coating was not correct. • The scientists’ typical view of toxicology, which is driven by the composition of an inorganic particle, may have to be modified for nanoscale materials, because surface characteristics are going to affect different dimensions of environmental and health effects
Carbon Nanotubes Will Be Used In Electronics Applications • Transistors and diodes • Field emitter for flat-panel displays • Cellular-phone signal amplifier • Ion storage for batteries • Materials strengthener Source: Scientific American- Illustration: RICHARD E. SMALLEY, Rice University
Manufactured Nanotubes are Similar to Combustion-Generated Nanotubes • Assays on a murine lung macrophage cell line to assess cytotoxicity of commercial, single wall carbon nanotubes (ropes) and two different multiwall carbon nanotube samples; utilizing chrysotile asbestos nanotubes and black carbon nanoaggregates as toxicity standards. • These nanotube materials were characterized by transmission electron microscopy. • and observed to be aggregates ranging from 1 to 2 microm in mean diameter, with closed ends. • The cytotoxicity data indicated a strong concentration relationship and toxicity for all the carbon nanotube materials relative to the asbestos nanotubes and black carbon. • These results implicate NP’s as triggers of asthma and related respiratory or other environmental health effects. • Indoor number concentrations for multiwall carbon nanotube aggregates is at least 10 times the outdoor concentration • Virtually all gas combustion processes are variously effective sources of Nanotubes. • These results also raise concerns for manufactured carbon nanotube aggregates, and related fullerene nanoparticles. • From: Mur et al., Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment (2005).
Electron micrographs demonstrating effects of different sized particles in RAW 264.7 cells treated with USC-Jan 02 CAPs for 16 hr. (A) and (B) Untreated RAW 264.7 cells. (C) and (D) RAW 264.7 cells exposed to coarse particles. (E) and (F) RAW 264.7 cells exposed to fine particles. (G) and (H) RAW 264.7 cells exposed to UFPs. Notice damage to cristae as well as the presence of particles (P) inside mitochondria (M) in UFP- or fine + UFP-exposed cells.
USE OF QUANTUM DOTSQDs can be used for long-term tracking of primary liver cells without compromising liver-specific function Hepatocytes were labeled by endocytosis of EGF-coated red QDs A & B Labeled Hepatocytes on Day 1. C & D Hepatocytes were reorganized by Day 7 but still identified by label. D Albumin production (marker for hepatocyte function) same as controls.
THE ENVIRONMENT CAN INFLUENCE THE TOXICOLOGY OF NANOMATERIALS • We do not have testing procedures equivalent to drug delivery devices in place for some NP applications (Eva Oberdörster, Southern Methodist University). • Coating or modifying the outer surfaces of nanomaterials can alter the toxicity of most particles. TOPO (trioctylphosphine oxide) is used to control the magnetic and electronic properties of nanoparticles. • Questions remain about the effects of environmental conditions—as opposed to laboratory conditions. • Drefus et al. (2004) suggests that air exposure and nanoparticle dose are important for cytotoxic effects. • Toxicity of CdSe quantum dots in a liver culture model changes when they are exposed to air or ultraviolet light. LESSON LEARNED: Nanomaterials may be safe under laboratory conditions but not under some environmentally relevant conditions. (A) Hepatocyte viability assessed by mitochondrial activity of QD-treated cultures vs. untreated controls. Thirty minutes of exposure to air while TOPO-capped renders QDs highly toxic at all concentrations tested. Ultraviolet light exposure increases toxicity with increasing time and QD concentration
POTENTIAL MECHANISM • Surface oxidation leads to release of cadmium ions. • (A) Proposed mechanism of Cd release from the QD surface via either TOPO-mediated or UV-catalyzed surface oxidation. • (B) Inductively coupled plasma optical emission spectroscopy (ICP/OES) measurements of free cadmium in 0.25 mg/mL solutions of QDs, indicating higher levels of free cadmium in all oxidized samples. • Increasing Cd levels with UV exposure time, correlate with cytotoxicity observed in previous figure
Exposure to carbon nanotube material: Aerosol release during the handling of unrefined SWCNT- Andrew Maynard et al. • Laboratory study and field-based study • Field study – assessed airborne and dermal exposure to SWCNT while handling unrefined material. • Lab studies – SWCNT can release fine particles with sufficient agitation. • Field studies – concentrations generated while handling material were very low- always < 53 g/m3.
Handling nanotube material Raw single walled nanotube material
Characteristics of airborne ‘nanotube’ particle Expected Morphology Predominant Morphology (Field Samples)
Preliminary Study at Rice University: SiO2 Nano-SiO2 is less inflammatory than Min-U-Sil
Toxicity of TiO2 Pigmentary & Nano-TiO2 are not different
Are Nanoparticles More Toxic Than Projected From Studies of Larger Particles? • Some current hypotheses suggest that nanoparticles are more toxic (inflammatory, tumorigenic) than fine-sized particles of identical composition. • This concept is based on a systematic evaluation of only three particle types: titanium dioxide, carbon black, and diesel particles. • Thus, the current hypotheses are based on a paucity of data.
On the hopeful side---- • Nanotechnology is a revolutionary scientific and engineering concept that will have a large impact on our life. • A core piece of this technology is the production of nanomaterials for electronic, chemical, medical, pharmaceutical, and environmental applications. • Natural and modified natural nanomaterials would be good reference points for comparison of the functionality, cost, and potential ecological implications of synthetic nanomaterials. • While the environmental impact and health effects of synthetic nanomaterials are essentially unknown and their use is of concern, natural nanomaterials have been part of human existence since antiquity. • Many of these NPs do not appear to pose much risk either to the physical environment or to human health.
On the other hand, there are many unanswered questions • Where are the impacts of products that have nanomaterials in them? • Where in the life cycle are their impacts going to fall? • Are there any impacts in the use stage like automobiles; the disposal stage, like electronic equipment; or the extraction stage like some of our mining endeavors? • How will the move to nanotechnology change a material’s flow within a particular sector? • What is the correct metric for nanoparticles?
PERHAPS AN HOLISTIC APPROACH COULD BE USED TO HELP US UNDERSTAND THE POTENTIAL HEALTH IMPLICATIONS
Most of the initial reports (in the media) have been positive; however, we should not forget that given the nature of nanoparticles, not all nanomaterials will be benign. —Kenneth Olden WHERE DO WE STAND?