Nanotechnology Lawyer & Attorney : Porter Wright Morris & Arthur : Nanotechnology Law Report - Germanium nanobead image provided by UT-Battelle, which manages Oak Ridge National Laboratory for the Department of Energy

The NanoSafety Consortium for Carbon just submitted a proposed toxicity testing agreement to EPA under Section 4 of the Toxic Substances Control Act covering a range of nanoscale materials including multi-walled carbon nanotubes, double-walled carbon nanotubes, single-walled carbon nanotubes, and graphene. 

Key elements for the curious:

• The chemical substances to be tested may include representative (i) purified multi-walled carbon nanotubes ranging from 4 to 600 nanometers in diameter and less than 30 micrometers in length; (ii) purified double-walled carbon nanotubes ranging from 1.5 to 4 nanometers in diameter and less than 5 micrometers in length; (iii) purified single-walled carbon nanotubes ranging from .7 to 2 nanometers in diameter and less than 30 micrometers in length; and (iv) purified graphene nanoplatelets in flake/sheet form ranging from .5 nanometers to 100 nanometers thick. All test materials will be purified by the National Institute of Standards and Technology to be at least 99 percent pure. Final test materials will be approved by the EPA and will be selected to adequately represent the constituency of the final signatories to the testing agreement.

• The characteristic for which testing will be conducted is subchronic inhalation toxicity in rodents, or such other toxicity testing as may be approved by EPA to achieve the intent and purpose of the testing agreement. As appropriate, consideration will be given to using in vivo instillation rather than inhalation test methods. Test data will be developed under standards based on TSCA test guidelines in 40 CFR parts 796, 797, and 798, Organization for Economic Cooperation and Development (OECD) test guidelines, or other suitable test methodologies.  Specifically, the signatories will conduct a 90 day inhalation toxicity study in rats with a post exposure observation period of up to 3 months, including broncholaveolar lavage fluid analysis (OPPTS 870.3465 or OECD 413), or such other testing as may be approved by the EPA to achieve the intent and purpose of the testing agreement. Testing guidelines will be modified to account for nanoscale properties of the materials being tested. Such modifications are subject to EPA approval and will be incorporated into the below-referenced study plan.

If EPA decides to pursue the proposed testing agreement, it will initiate a six-month negotiation and comment period which will open to the public pursuant to 40 C.F.R. § 790.28.

Stay tuned.

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The NanoSafety Consortium for Carbon has recently posted a bibliography of in vivo tox studies on its website.  The bibliography is (obviously) a work in progress.  We would greatly appreciate it if our readers would bring to our attention any pertinent articles that are not already on the bibliography.  The articles will be used to inform and guide our attempt in crafting a representative toxicity testing regime with US EPA.  Many thanks in advance for your input.

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A recent in vivo study published in NanoLetters focuses on the impact of ultraviolet radiation on the ability of Quantum Dots (QD) to penetrate skin.

L. Mortensen, et al., "In Vivo Skin Penetration of Quantum Dot Nanoparticles in the Murine Model: The Effect of UVR," NanoLetters, Vol. 8, No. 9, pp. 2779-2787 (August 2008).

The article begins by noting that "[n]anoparticles (NP) are commonly used in sunscreens and other cosmetics, and since consumer use of sunscreen is often applied to sun damaged skin, the effect of UVR on NP skin penetration is a concern due to potential toxicity;" and "[t]he question of whether or not NP can penetrate the healthy stratum corneum skin barrier in vivo remains largely unanswered."

The authors note that there are conflicting results from recent studies in this area, which they attribute to different researchers using different nanoscale materials with different sizes/diameters. The authors point out that the inconsistent results of prior studies "highlight the need for standardization of experimental techniques in ex vivo skin models are to be useful."

Despite the authors’ stated concern with possible dermal penetration of NP contained in cosmetics and sunscreens, they chose to test a nanoscale material which is not used in any cosmetic or sunscreen – Quantum Dots.

The authors explain:

We selected to investigate QD, as they posses ideal characteristics for in vivo experimentation including broad excitability, narrow emission bandwidth, high fluorescence quantum yield, photostability, and ease of surface functionalization. Moreover, QD are of a similar size to TiO2 NP used in sunscreen applications, they intrinsically generate ROS species, and the carboxyl terminated QD have a similar negative oxide surface chemistry to the TiO2 and ZnO raw materials often used in sunscreen applications.

There are no lack of manufacturers selling the very type of nanoscale zinc oxide and titanium oxide used in consumer cosmetics and sunscreens. Quantum dots are very remote cousins to these particles.  Why not test the substances themselves rather than a surrogate?

Regarding the animals used in the experiment, the researchers selected 6-7 week old SKH-1 hairless, albino mice.  The QD mouse application vehicle was a solution of 75% glycerol/25% carboxyl QD Stock Solution (pH=9.0 borate buffer, 8μm QD).  One half of the mice received an acute single UVR dose, which was administered by using UVA Sun 340 lamps (320-400 nm (UVA)) (290-320 nm (UVB)). 

The scientists found increased QD penetration for 8 hr and 24 hr treatment conditions after UVR exposure.  However, "[m]ost strikingly, under no circumstances is there evidence for massive QD penetration, even for UVR exposed mice 24 hr after QD application." "[N]one of the penetration observed was at a very high level."

The scientists conclude that "[t]hese studies demonstrate the importance of skin condition to effect the penetration of QD nanoparticles . . . in the . . . mouse model.  We have shown that QD work their way between corneocytes of the stratum corneum and penetrate deep in the epidermis and dermis of an in vivo model with UVR penetration exacerbation." "The minimal QD penetration observed in our study on barrier intact (non-UVR exposed) skin suggests the preponderance of current literature suggesting TiO2 and ZnO NP used in commercial sunscreens exhibit limited penetration in layers below the lower SC."
 

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The December 4, 2006 on-line edition of the Proceedings of the National Academy of Sciences is set  to publish findings from a recent in vivo animal study researching the possible health effects of SWCNTs deliberately injected into the bloodstream.  Scientists at Rice University and the University of Texas are said to have found that carbon nanotubes are filtered from the bloodstream by the liver over one hour after injection.  The scientists are also said to have sampled tissue from various locations in the test animals and apparently found SWCNT deposits in the liver, and trace amounts in the kidney -- both of which were expected.  Preliminary reports believe the study supports the conclusion that there are no immediate adverse health effects from SWCNTs injected into the bloodstream.  Look for more information about this study in upcoming posts.

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