Recombinant DNA, Synthetic Biology,and Nanotechnology, oh my!

There is an interesting article on Synthetic Biology in last week's New Yorker. Though I just gave it a skim, and didn't read the ending – the topic is intriguing and describes a field of science devoted to developing the capacity to build and manipulate biological systems as if they were Legos. According to SyntheticBiology.Org their goals begin with identification of the parts that “have well-defined performance characteristics and can be used (and re-used) to build biological systems” and end with “reverse engineer and re-design a ‘simple’ natural bacterium."

Wow. Should they succeed, they’d bear a hefty biological, ethical, environmental responsibility. Were these people nut jobs? Nascent Frankensteins? Or were they just being realistic about the future of their science? As I thought about what this all meant it dawned on me that Synthetic Biology, being an extension of Genetic Engineering, in some ways wasn’t so different or separate from nanotechnology.

I don’t mean that they’re similar in how the products of these technologies interact with living systems, all threats of “grey goo” (a worst-case scenario hypothesized by Eric Drexler, popularizer of nanotechnology, whereby nanobots run a muck, literally mucking up the world) aside - one science proposes to build biological systems while the other builds chemicals. Although, I suspect, as time goes on these two technologies will mingle if not marry (if they haven't run off to Las Vegas and done so already.) Biological systems after all are nothing more than chemical building blocks – so once those building blocks are better understood, and once we have the capability to not only engineer one cell at a time, but also to build chemicals one atom at a time, why not?

As a toxicologist observing the emergence of nanotechnology it has been easy to ask what nanotechnology can learn from past practices of chemical production, regulation, use and disposal. But beyond toxicology, biotechnology, has also laid some groundwork as to how to proceed with – or not-- development of a new technology that will impact all of our lives for better or worse, in ways we cannot fully understand.

Genetic engineering, the cornerstone of biotechnology, has been around since 1972 when scientists including Paul Berg of Stanford University first recombined pieces of DNA – the molecule which holds the secrets of all live on earth. Two years later, Berg and others raised serious concerns about unfettered recombinant DNA research, eventually calling for a temporary moratorium on certain types of research. Berg’s committee proposed that, “…until the potential hazards of such recombinant DNA molecules have been better evaluated or until adequate methods are developed for preventing their spread, scientists throughout the world join with the members of this committee in voluntarily deferring the following types of experiments....” the authors then listed specific research that they considered most risky, acknowledging that…”our concern is based on judgments of potential rather than demonstrated risk since there are few available experimental data…and that adherence to our major recommendations will entail postponement or possibly abandonment of certain types of scientifically worthwhile experiments.” A year later, the first conference on “Recombinant DNA molecules” widely referred to as Asilomar for the idyllic conference center by the sea, took place, and is still referred to, and reflected upon as a model of “self-regulation” by the scientific community (the meeting included scientists from around the world, lawyers, government officials and journalists as well.)

Of course the concept of self-regulation may be an oversimplification since the conference purposefully focused on health and environmental safety only. The ethics and legalities of recombinant DNA were not on the agenda, “This choice of agenda,” wrote Berg years later, “was deliberate, partly because of lack of time at Asilomar and partly because it was premature to consider applications that were so speculative and certainly not imminent.” Perhaps. I imagine, like my district’s school committee meetings which I’ve sometimes referred as “adults behaving badly” – if we stuck with the nuts and bolts rather than the deeper questions – we too might be more successful.

Berg revealed one other key to success on at a symposium celebrating the 25^th anniversary of Asilomar: molecular biologists weren’t yet heavily invested in the science and the public knew very little – so that there was still room for fluidity in the conversation. Positions on the recombinant DNA were not yet “hardened,” and scientists were primarily academic. This was a time when government funding was flush, when there was separation of academia and industry and the biotechnology industry with all its promises of the next million dollar drug was more “Jetsons” than reality.

Which brings me back to nanotechnology - a field developing under incredible public, government, and scientific scrutiny. Even industry, as I’ve read and heard, wishing to avoid the genetically modified foods fiasco (which is either ironic or inevitable considering Asilomar), seems willing to tread carefully when it comes to development of nanomaterials. A recent report by the DEEPEN (Deepening Ethical Engagement and Participation in Emerging Nanotechnologies) project – emphasizes a role for increased public participation in governance decisions related to nanotechnology development. In part because nanotechnology is poised to affect everyday life – so why not include all participants -- those who deliberately participant and those who are incidental nano-tourists in the conversation?

There's one caveat to suggestions by DEEPEN and others. There have been so many meetings, and project reports on how best to move forward conscientiously with nanotechnology, that there is some concern there’s too much talk and too little action. Meanwhile, nanomaterials find their way into more and more consumer products (1000 and counting,) and the body of research papers continue grow like a bacterial culture in log growth phase. But that's no reason not to broaden the conversation.

Perhaps comparisons between nanotechnology and Asilomar are unfair for nanotech.

As Berg noted, in 1975, neither Joe Public nor Joe the Plumber were invited members of the 'Recombinant DNA steering committee,' the focus of the meeting was strictly focused, and recombinant DNA was, and still is fairly easily defined. Isolating and rejoining segments of DNA – that was recombinant DNA. Today we have the world wide web of information where the public, if they wish can be informed, NGOs following and reporting on nanotechnology, a technology that is already in use, and scientists who can’t even agree on what constitutes a nanoparticle. Are they particles with one dimension measuring 100 nm or less? Or, should they be much smaller, encompassing particles in the 30 nm or smaller range, particles most likely to exhibit new and different physical-chemistry?

Then there are nanodots, nano-metals oxides, nanotubes and other nanos – all very different chemically although they may share some basic properties in terms of size, or increased reactivity as a result of decreased size, but how much do we know of their differences in terms of how nanoparticles will move and react inside a living being, or outside in the big wide world?

Our best hope right now, is that nanotechnology as a field is still young and flexible. Hopefully the talk with turn to action before nanotech’s arteries begin to harden before, as Berg observed twenty-five years after Asilomar – the issues become “chronic.”

(For the results of a recent poll on public understanding of nanotechnology and synthetic biology click here. )

A lot of information on a little topic: EPA's Nanotitanium Case Study

Still stuck in the sunscreen limbo? Wondering which to choose - "chemical" filters or "natural" filters like nanotitanium? While we know chemical filters tend to be absorbed into the skin, should we be concerned about absorption of nanotitanium as well? Or perhaps you're wondering when anyone is going to get around to really thinking about how best to evalute risks of nanomaterials? Well here's your chance to read all about it - at least all about the life and times of nanotitanium in one relatively complete report.

EPA has just releasee their Nanomaterials Case Studies: Nanoscale Titanium Dioxide in Water Treatment and in Topical Sunscreen DRAFT. I haven't read the section on water treatment, but this past winter I was involved in the review of the section on sunscreen - sure to be a hot topic even as summer is sadly winding down. While the report won't help you choose which sunscreen to use, it provides a fairly comprehensive review of nanotitanium.

The document, according to EPA is, "...a starting point to to identify what is known and, more importantly, what needs to be known about selected nanomaterial applications."

And, as they tackle the moving target (in the sense that research and publications just keep rolling in) that is nano from production to product, birth to afterlife they invite readers to:

....consider the questions listed throughout the document and offer specific comments on how individual questions, or research needs, might be more precisely or accurately articulated. If additional questions should be included or if information is already available to address some of the questions posed here, readers are encouraged to provide such comments as well. These or other comments on any aspect of the document should be submitted in writing in accordance with instructions, including the specified time period, stated in a Federal Register notice appearing on or about July 31, 2009 referring to Docket ID No. EPA-HQ-ORD 2009-0495.

So have at it. It'll be interesting to follow the further development of this report.

Musings of an obsolete toxicologist: nanotoxicology is a whole new world

This morning while walking across town to the Lady Killigrew , a small hipster café located just around the corner from home, I was thinking about a report I’d just begun to draft. The focus was how to evaluate the toxicity of nanoparticles. I was wondering if I’d been too strong in my dismal assessment of toxicology and had hoped that a good slap of cold air (the thermometer outside our kitchen window read -25C) would weed out the dramatic, and clarify the reality.

I’ve pasted some key points below, and while the topic and eventual report are confidential – there’s nothing confidential about the sentiment – I, and many others have been writing about it for a while:

1) The field of nanotoxicology is in its infancy, yet is ever expanding as newly created nanomaterials require assessment of potential health and environmental impacts. I’ve never before had the experience where I’ve considered research from 2006 as “old,” and where, the majority of literature cited is 2008 and 2009. Yet development of a new field within toxicology provides opportunity, and at the same time demands that toxicologists use both hindsight and foresight as they develop the methodology appropriate for these new materials.

2) Hindsight provides us with a glimpse of toxicology as a field, in large part, focused on application as a science catering to the need for rapid assessment and cost-effective regulation. Standardized toxicity testing methodology was developed and implemented as a result, quickly becoming a rigid set of test procedures, a good deal of which, over the years have become obsolete.

3) In part, because of the difficulties with changing test methodologies associated with a regulatory framework (check out the timeline for reproductive and developmental testing – “in development” for what, at least 10 years?) - standardized toxicity testing, useful for screening out the obvious is insufficient for detecting more subtle adverse effects or revealing the impacts of the complex mixtures of contaminants, drugs and naturally occurring chemicals to which we are all exposed.

4) We have an opportunity to consider the history of toxicology as we move forward. Many have expressed concern that “business as usual” may result in failure to adequately evaluate toxicity of nanomaterials. Oberdorster et al., (2005) representing the International Life Sciences Institute Research Foundation/Risk Science Institute (ILSI/RSI) writes “There is a strong likelihood that biological activity of nanoparticles will depend on physicochemical parameters not routinely considered in toxicity screening studies.” Additionally different physicochemical parameters may also affect behavior of particles in media typically used in preparing for traditional toxicity testing, the ability of researchers to adequately evaluate exposure concentrations, and particle behavior in the body. Problems only occasionally encountered in the past.

5) When it comes to some nanomaterials, such as quantum dots and functionalized particles we’re potentially dealing with multiple organic and inorganic materials that may, or may not, be released over a period of time. How do we assess that?

Well, as I wondered if I was getting a bit too dramatic, after grabbing a cup of decaf and ordering a breadboard with mustard I settled in and checked my emails. Bingo. There in the inbox was a link to Peter Montague’s recent article entitled "Can Chemicals be Regulated?" published in Rachel’s Democracy and Health News. Read it and weep.

Or, read it and be hopeful. I really do think that we’re at the proverbial crossroads. We’ve seen the consequences of becoming too rigid, of constrained linear thinking. But this is a new multitasking interconnected networked “wisdom of the masses” kind of world, not just for me and my Lady K compatriots (the majority of whom – to the dismay of the management - are more attentive to their electronics than to their stomachs) but also for those laboring away in research laboratories around the globe.

Maybe I need another slap of cold air, but if we can embrace this new fluidity in information, knowledge, and thinking, perhaps we can embrace a new way of not only evaluating health and environmental impacts of new chemical products, but a new way of using that information wisely.

Who's screening sunscreens?

A while back I wrote about sunscreens here and here. But that was already over a year ago - and as anyone who is confused by he says and she says in science knows - the reports just keep on rolling. Just yesterday the New York Times Science Section published an article by Tara Parker-Pope calling sunscreen safety into question, and based in large part on an Environmental Working Group (EWG) report on the stuff. In short, it seems that the EWG is concerned about chemicals like oxybenzone (or BP-3 )which are absorbed by the blood and can be detected in urine - the problem is - health impacts are unknown (although a recent news article in Environmental Health Perspectives reports that in animal studies BP-3 " effects in liver, kidney, and reproductive organs, and studies by other groups have shown endocrine-disrupting effects,") and some claim EWG's rating system for sunscreens lacks scientific rigor. Either way, there just aren't enough studies - though one would wonder maybe why consumers are allowed to slather products on themselves and their young ones when "there aren't enough data."

According to Parker-Pope, "Of nearly 1,000 sunscreens reviewed, the group recommends only 143 brands. Most are lesser-known brands with titanium and zinc, which are effective blockers of ultraviolet radiation. But they are less popular with consumers because they can leave a white residue." But many of the titanium and zinc sunscreens don't leave a residue, and the reason they don't is that titanium and or zinc in "micronized." In other words - really small - sometimes nanosized.

Those who remember smearing the white stuff on their noses in the summer - most likely were using zinc that scattered not only the undesirable UV light but also visible light (hence the clown effect.) Today's micro or nano zinc allow visible light to pass through them and so appear clear, while still scattering the sun’s shorter and harmful ultraviolet rays. Cool right?

Maybe. My friend Cal Baier-Anderson, blogging over at Environmental Defense just posted about a study initiated following an "...observation that installers of metal roofs who used these sunscreens inadvertently transferred the product onto the roofs. In places where the workers’ skin had touched the painted metal surfaces, the paint showed accelerated weathering. Why? Because the particular type of nanoscale TiO2 in the sunscreen (the anatase crystal form) is photoactive – when it absorbs UV light, it releases free radicals that speed up the oxidation of the underlying paint."

Cal wondered if the same might happen to our skin - inadvertently accelerating the weathering of our skin just as we are trying to stop any further damage. For more on the topic check out Cal's entry Nano on a Hot Tin Roof (rusted!) and her other entry on nanoproducts and sunscreen Burning Questions.

Nanothoughts

A while back I posted a few items about nanotoxicology. Back then, I must confess I didn’t know much beyond those few articles. Now that I’ve had some time to really review the nanotoxicology literature here are a few thoughts about the rapidly developing field.

The potential toxicity of nanomaterials or nanoparticles in either human or ecosystems is of concern to researchers, government, non-governmental organizations (NGOs), industry and consumers around the globe. However, even with all of the past experiences with developing and regulating chemicals – even with the knowledge that before new chemicals (or new formulations of old chemicals) blanket the earth we ought to understand their potential impacts – the health and environmental impacts of specific nanoparticles lags far behind nanoparticle technology.

I’ve also learned that although government agencies, research collaboratives and others are working to remedy this situation, the funding available for research on health and environmental effects of nanoparticles, or nanotoxicology, compared with money spent on R&D, is in the millions verses billions spent on development.

But before we despair that once again, the nanokitties have left the residents of Whoville holding the bag, nanotoxicology does have several advantages over other “ancestral” fields of toxicology including:

• Hindsight revealing flawed strategies of the past which led to inadequate prevention and protection (though this one is quickly slipping away.)

• The more global economy, where regulations in one country for example may impact development of a product in another (the newer EU requirements under REACH for example) in addition to greater potential for international collaboration may stretch resources beyond those that any one government might be able to contribute alone.

• Industries wishing to convince us that in addition to the “bottom line,” they really do care about health and the environment have shown some interest, and in some cases taken leadership in the field of nanotoxicology research – or entering partnerships with environmental NGOs (for example Dupont and Environmental Defense).

• These days, the internet provides a powerful mechanism for rapid distribution of government, NGO and academic reports, providing all stakeholders – even us peons who sit at home, our computers our only source of information - access to emerging data, technology, and publications. It will be interesting to monitor the impact of public oversight of the field as it develops.

Yet despite all of this potential, the “state of the science” on environmental and health effects research today is something of a hodgepodge. But more on that later!

A nanometer of regulation: EPA, TSCA and nanomaterials

I just came across a little blurb in this week’s issue of Science, noting that the EPA has finally made some decisions about regulating nanomaterials. A quick read indicates that 1) the EPA has decided that for chemicals already registered under their TSCA Chemical Substance Inventory (TSCA is the law enacted to protect us humans and the environment from nasty chemicals – and the inventory is a listing of all those chemicals from which we’re being protected) – nano-formulations of those chemicals will not require new registration (or registration as a new chemical) and 2) they are asking for voluntary submission of health and toxicity data, by manufacturers and users of nanomatierals. Huh.

So what does this mean? I was confused when I first read it. After reading and writing about nanomaterials, I thought one of the advantages of producing these things were specifically (in some cases) because they act differently than their bigger, larger, brothers and sisters. For example compounds like titanium dioxide and zinc oxide were nanoized in the first place was to take advantage of the differences between the larger forms and the smaller. So, I though, maybe the EPA didn’t really mean that.

Fortunately, EPA has an easily readable paper that explains these things – like how they define a new chemical - in great detail. According to their TSCA Inventory Status of Nanoscale Substances – General Approach (2008) paper, EPA focuses on “molecular identity.” In this case, chemicals that have the same molecular formulas, the same crystal structures, the same spatial arrangement of atoms – are the same chemical. That means, according to the EPA, and to borrow from Dr. Suess, titanium dioxide is titatinium dioxide no matter how small.

Why is it important to distinguish a chemical as “new?”

Normally, when a company manufactures a “new chemical,” unless it’s exempt – the company must submit a Pre-manufacture Notice, which then triggers some basic testing. That little bit about “exempt” can be important. In fact, you’ve likely got some of those “exempt” chemicals floating around in you right now. Remember all the hubbub about PFOA and PFOS? Those chemicals in Gore-Tex and Teflon and other products? Well perfluorinated chemicals involved in the production of PFOA and PFOS were granted exemptions, in this case because they were in commerce before TSCA came along. But look what happened. Now we’ve got those chemicals contaminating wildlife around the world. To be fair, it’s possible that would have happened anyway – who knows. But here’s the catch, the exemption was granted with the understanding that under TSCA, should any manufacturer realize that there might be health and safety issues, such information “ [would] be submitted to the Agency…when companies learn of it.” In the case of these products this didn’t happen, and Dupont ended up settling that account for $10 million dollars.

A steep price to pay; and an example which hopefully demonstrates for manufacturers that honesty really is the least expensive policy.

There are various ways a chemical might be exempt. If it’s used only for research and development, it might be exempt. If it’s produced in low volume, it might be exempt. And, if there’s some indication that it would be released in only small concentrations or that there would only be small exposures, it might be exempt.

Bottom line? There will be nanomaterials that will not be required to undergo testing.

Ah but rest assured, EPA has considered that some of these exempt or untested chemicals may have adverse health or environmental effects. You see, they recently announced their Nanoscale Materials Stewardship Program, where according to the program description, “Participants are invited to voluntarily report available information on the engineered nanoscale materials they manufacture, import, process or use,” should they happen to observe anything funky happening with their materials.

Let’s hope they do.

For a good readable explanation of TSCA and how it may or may not apply to nanomaterials check out the article “TSCA and Engineered Nanoscale Subtances,” by Lynn L. Bergeson and Ira Dassa and published in Sustainable Development Law and Policy.

New Report on EPA and Nanotech - just what I've been waiting for!

For those of us concerned with health and environmental impacts of new and old chemicals, the production and use of nanomaterials presents a fascinating opportunity to consider and then reconsider the mechanisms by which chemicals are tested and controlled in the United States. While I've been trying to keep up with the toxicology of nanomaterials, I've wondered about the adequacy of our current regulatory framework to evaluate and manage these materials. Fortunately for me and anyone else wondering the same thing, a recent report by Dr. Terry Davies entitled EPA and Nanotechnology: Oversight for the 21^st Century opens the door for us, by reviewing the principle laws and regulations developed to manage and control chemicals and considers the effectiveness of their application down in Whoville, where all things are nano.

As Davies notes, “In a few decades, almost every aspect of our existence….is likely to be changed for the better by nano. However, if the potential for good is to be realized, society must also faces nano’s potential for harm.”

One of the primary issues for toxicologists investigating nanomaterials, is my favorite, “It’s hard to find what you don’t know you’re looking for,” or it’s pretty difficult anyway…unless one is trained to expect the unexpected. And it seems that nanomaterials have the potential to behave quite differently not only from their non-nano counterparts, but also from different formulations of the same material. In some cases, as Davies notes, contrary to current underlying toxicological concept that smaller doses tend to be less toxic (in general – there’s a whole ‘nother discussion to be had about hormesis – the differential behavior of some chemicals at very low concentrations) in some cases nanomaterials may behave differently and potentially more toxic when present in lower concentrations than their non-nano counterparts. Just that issue alone has the potential to turn our current toxicity testing, assessment and regulatory practices upside down when it comes to nanomaterials!

But really the focus of Davies report is the “so what” question. Given where we are now – in terms of understanding the potential health and environmental impacts of these materials – what can be done in terms of regulation and management? As Davies points out, while some of EPA’s programs, as they are now, may provide adequate oversight of nanomaterials (he cites FIFRA – which has jurisdiction over all pesticides – as a program that has “strong legal adequacy” when it comes to nanomaterials) TSCA, the Toxic Substances Control Act, which has the greatest potential to cover the most nanomaterials, is “particularly deficient” for a number of chemical oversight functions. According to Davies “the Act desperately needs to be amended, both to deal with nano and to adequately address all types of chemicals.”

This is an informative and readable report, and if you’re at all interested in nanomaterials, you might want to take a look.

The full report is available free and online through the Project on Emerging Nanotechnologies, an initiative of the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts, www.nanotechproject.org.

What's Emerging in your Water?

There is a nice review of Emerging Contaminants, recently published in the journal Analytical Chemistry, by Susan Richardson. In it is a review of the "oldies" like PFOA, PFOS, and polybrominated flame retardants and newbies like nanomaterials and ethylene dibromide or EDB, a gasoline additive from back in the day when gasoline was leaded.

In the excerpt below she discusses the term “Emerging,” a term over which I sometimes stumble. Which chemicals fit into the category of emerging contaminants? Why are some chemicals which have been around for decades suddenly appear as “emerging” and, why are others, which have yet to be detected in major quantities (like the category of nanomaterials – which describes a type of chemical rather than any one specific chemical) on the list?

“Emerging environmental contaminants were the focus of a recent issue of Environmental Science & Technology (December 1, 2006), where current research on emerging chemical and microbial contaminants was highlighted. This is a must-read issue, and several of those papers will be discussed in this review. The guest editors of this issue also published an excellent perspective on "What is emerging?" as a lead-off editorial to this issue, which points out that the longevity of a contaminant's "emerging" status is typically determined by whether the contaminant is persistent or has potentially harmful human or ecological effects (2). It is often the case that emerging contaminants have actually been present in the environment for some time (in some cases, decades), but they are discovered through a wider search of potential contaminants (as in the case of ethylene dibromide, in this current review) or through the use of new technologies (such as LC/MS) that have enabled their discovery and measurement in the environment for the first time (as in the case of many pharmaceuticals).”

Although a bit technical in spots (this is Analytical Chemistry afterall,) the current literature for each emerging contaminant is reviewed in a readable manner, and there is an impressive list of over 200 citations for those looking to learn more.

New Journal, Nanotoxicology

For those interested in nanotoxicology, there is a new journal called Nanotoxicology, published by Informa Healthcare. It’s a quarterly and you can review the first issue (just published March 2007) for free, which allows you to access to the first issue. The first article, Toxicology of nanoparticles: A Historical Perspective, by Gunter Oberdorster, Vicki Stone and Ken Donaldson, provides an excellent review. They include some early studies of particles such as viruses and combustion particles that were around well before the age of intentionally manufactured nanomaterials but which fit the nano description, and provided scientists with insights into the movement and fate of very small particles in living systems.

I’d expect an explosive growth in our understanding of how nanoparticles interact with the environment and with living bodies, but it seems there is a long ways to got and an urgency to get there quickly. Notes Oberdorster and others, “There have been many conferences, meetings, and workshops….with as many calls for developing testing strategies, with only few proposals, followed through by far less action.”

This first sample issue is worth a read and the few moments it takes to register for your month-long free access. Other articles include: “Assessing exposure to airborne nanomaterials: Current abilities and future requirements” by Andrew D. Maynard; Robert J. Aitken; Characterization of the size, shape, and state of dispersion of nanoparticles for toxicological studies by Kevin W. Powers; Maria Palazuelos; Brij M. Moudgil; Stephen M. Roberts; and Cellular responses to nanoparticles: Target structures and mechanisms by Klaus Unfried; Catrin Albrecht; Lars-Oliver Klotz; Anna Von Mikecz; Susanne Grether-Beck; Roel P. F. Schins.

Stumbling Through Nanoparticle Definitions

I am still trying to understand the nano-world. It’s a big world and there are many different kinds of very small particles. But I’ve had some trouble finding good definitions of the inhabitants of this new world. What, for example, are quatum dots? And what makes metallic
nanoparticles different from other kinds of nanoparticles?

As discussed earlier down in Whoville, we know that not all nanoparticles (particles smaller than 100 nanometers) are created equally, and, even better -- or worse, depending on your viewpoint and the material -- many nanoparticles aren’t even equal to their larger counter parts. And that really, is just the point, or one of the points at least, of all this technology.

Fortunately for me, the EPA, in their recent Nanotechnology White Paper, organizes nanoparticles into four categories, and though there may be other ways to categorize nanomaterials I found these groupings helpful in understanding the different kinds of nanoparticles that might one day enter our world – if they haven’t already.

Below are EPA's catagorizes for nanomaterials along with some brief examples.

Carbon Based:

Carbon-based nanomaterials include things like fullerenes (cage-like carbon structures) which make up the single walled carbon nanotubes (those are the SWNTs I’ve referred to before) and buckyballs. All are made carbon. Just carbon. When there are 60 carbons involved, a sphere is formed, its a Buckyball. When there are more, the structure is tube – or cage-like, and is made of a single layer of carbons, almost like a tube of chicken wire, it’s a SWNT.

Metal Based:

Metal-base nanomaterials include quantum dots, metal oxides and pure metal nanoparticles. Quantum dots are structures so small that their properties are susceptible to the removal of a single electron. Every living creature depends on a kind of quantum dot for energy production, as electrons are moved around by proteins so the cell can store or use energy.

Manufactured quantum dots can contain a small number of atoms, for example, from tens of atoms to a few hundred. Some manufactured quantum dots are nanosized crystals of various elements (silicon and germanium or cadmium and selenium are a couple of examples), and emit light when excited. What most interesting is that the color of the light, which is based on wavelength, will vary with the size of the crystal or the type of crystal, with smaller particles of a particular crystal emitting light of shorter wavelengths (towards the blue end of the visible light spectrum) and larger particles emitting light of longer wavelengths (towards the red end.)

Titanium dioxide, which you can find in your sunblock lotion, is an example of a metal oxide that is now manufactured as a nano-metal oxide. As explained in an earlier article, it's the nano formulation of this material that allows us to smear the sunblock but avoid looking like a clown.

Metals can also exist as single ions, or larger bulkier structures think gold, or silver. But, as with many nanomaterials, it seems that when metals occur as nanoparticles they may exhibit different properties than their larger counterparts. Nanoized silver (or silver ions), for example, is a potent antimicrobial, but apparently aggregates of silver particles tend to loose their antimicrobial ability.

Dendrimers:

Dendrimers are branched polymers (a polymer is made up of repeating units or monomers. Monomers are molecules that can combine – or polymerize - with similar or identical molecules.) These can be manufactured so that they can carry other molecules within them, such as certain drugs.

Composites:

Composites refer to combinations of nanomaterials with other materials, for example DNA molecules may be combined with various nanomaterials to make a nanosized biocomposite.

These examples just scratch the surface of the world of nanomaterials. But this revolutionary technology is sure to present those charged with protecting human health and the environment a future filled with both opportunity, (providing new materials to clean up and reduce distribution and use of hazardous materials, and new drug formulations) and challenges as health and environmental scientists race to understand the impact of materials that play by new rules.

Length Matters: Nanotoxicity

Obviously size matters for nanoparticles, or the world wouldn’t be making such a big deal of them. Size also matters when it comes to toxicity of nanoparticles. A recent study published in Advanced Materials (Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes) by Matthew Becker and others, emphasizes that size (such as length and diameter of particles) matters particularly when deciphering toxicity studies. One source of size variation suggests the authors is dispersion of single-walled carbon nanotubes (SWNT) used in toxicity testing.

According to the article:

“Given a constant dosage, differences in dispersion ranging from macroscopic aggregates to micrometer-scale clusters bundles of multiple nanotubes or individually dispersed nanotubes will dramatically affect the absolute size and amount of nanotube surface area to which the cells will be exposed.”

Surfactants are materials used to increase water solubility and in some cases dispersion of a material, and are commonly used in studies of nanoparticle toxcity. Becker’s group used DNA as a surfactant, because they noted,

“These dispersions, in the case of DNA, are even stable enough to allow for the separation of the dispersed material into well-defined subpopulations of the SWNTs.”

Using this method to test the toxicity of SWNTs of varying length to muscle cells, the authors concluded that, “The assays determined an approximate uptake threshold of approximately (189+17) nm. Indicating that nanotubes shorter than this are consumed and likely induce more toxicity.”

Though they note that identifying an upper threshold for toxicity of nanoparticles is nothing earth-shattering or new, they do suggest that such behavior is likely to be a “general phenomenon,” though the actual size threshold is likely to vary depending on the type of cell.

For more information check out: Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes, by Becker et al, Vol 19:939-945.

Ingesting, digesting, and egesting oh my: nanoparticles and water fleas

Years ago when I first met my husband, I am ashamed to say, I may have belittled the importance of his research project. He was studying larval fish, and observing what they ate, how much they pooped and how quickly they grew. Who cared I wondered? I was a toxicologist I’d thought at least my work was somewhat applicable to….to something! That was almost twenty years ago and now he’s out saving wild fish populations, and I’m here typing at my desk! But recently I came across an article entitled “In Vivo Biomodification of Lipid Coated Carbon Nanotubes by Daphnia Magnia” by Aaron Roberts, et al., published in Environmental Science and Technology, which highlights the importance of ingesting and egesting (or eating and pooping) in an environmental context that even a toxicologist can appreciate.

Turns out that what little critters eat, digest and poop may have some important implications for nanomaterials. Roberts et al. reports on the fate (and to some extent toxicity) of single-walled carbon nanotubes or, SWNTs, in aquatic creatures known as Daphnia magnia, or better known as water fleas.

Alone, SWNTs are not water soluble, which apparently limits their utility. In this case, the authors first combined SWNTs with an amphiphilic coating, (that means it goes both way water loving and fat loving,) to render them soluble in water. Rendering SWNTs more water soluble, according to the authors will:

“..not only enable biological studies of cellular responses but also empower the development of next generation single-molucule chemical and biosensors and self-assembled nanodevices,.”

But, they noted, this new and improved water soluble nanomaterial comes with a caveat,

“Because of the large number of applications there may be great potential for discharge of coated, solubilized nanomaterials into the environment.”

Enter, the fleas.

Since solubilized nanomaterials might end up in watery environments, the authors exposed Daphnia to concentrations of coated SWNTs. They reported that up to a point, the Daphnia not only tolerated but (under conditions of starvation) may have even benefited from the coated materials. Daphia ingested the materials, stripped the coatings, and apparently used them as a food source (those in SWNT water survived to a greater extent than those without), and egested (pooped out) uncoated and now insoluble SWNTs. But we all know what happens when we over indulge. When exposed to higher concentrations, the Daphnia didn’t fare so well, and survival was reduced. Additionally the authors noted that coated SWNTs also accumulated on the outer surfaces of Daphnia (also not good.) I would also suggest that all food sources are not created equal. For example what keeps one generation going, might not be sufficient for producing the next, so that further studies of such materials might include life-cycle tests and more intensive investigation into the quality of "food" provided by similarly coated nanomaterials.

In conclusion, the authors note that:

“Our data show that biomodification of lysophospholipid-coated carbon nanotubes in vivo can occur and have dramatic effects on the physical properties of the nanomaterial. These modifications may result in unanticipated effects both on the materials properties as well as the organisms exposed to the nanomaterial. Biomodification is an important phenomenon that should be considered in studies on the biological applications, environmental fate, and toxicity of convalently and noncovalently functionalized nanomaterials.”

You can find the full article, by Aaron P. Roberts, et al., In Vivo Biomodification of Lipid Coated Carbon Nanotubes by Daphnia Magnia in Environmental Science and Technology, ASAP Articles, March 7, 2007.

More on Nanotech

Nanotechnology is an interesting field for a toxicologist because of the very public discussion about toxicity, regulation and the future of nanotechnology. Unlike other major technological advances in the past with the potential for health and environmental impacts, nanotechnology is developing under the virtual microscope of the internet – where citizens, researchers, regulators are able to access a great deal of information and can organize via the internet.

Below are a few new articles on the toxicology of nanomaterials and a link to a podcast "The Implications for Health, Safety and the Environment of the Nanotech Revolution."

This interesting and informative podcast sponsored by Nanotechnology Victoria (Austrailia), considers the ethics, toxicology, risk assessment, worker heath and safety. While those interviewed agree that there are data gaps in the toxicology and potential for environmental impacts of nanotechnology, they also note the potential benefits of future nanotechnology products. Views range from a moratorium on nanotechnology development, to greater government and industry resources to improve worker standards to avoid another potential “asbestos-like” disaster for workers in the field, to a call for all involved to recognize the broad range of materials to which the term nanotechnology refers.

For those interested in more technical articles on nanomaterials, below are three articles recently published in Environmental Health Perspectives describing recent toxicological research on nanoparticles.

Cardiovascular Effects of Pulmonary Exposure to Single-Wall Carbon Nanotubes by Zheng Li,¹ Tracy Hulderman,¹ Rebecca Salmen,¹ Rebecca Chapman,¹ Stephen S. Leonard,² Shih-Houng Young,² Anna Shvedova,² Michael I. Luster,¹ and Petia P. Simeonova concludes:

“Taken together, the findings are of sufficient significance to warrant further studies to evaluate the systemic effects of SWCNTs [Single-Wall Carbon Nanotubes] under inhalation exposure paradigms more likely to occur in the workplace or environment, such as low-level chronic inhalation exposure.”

Inhalation Exposure Study of Titanium Dioxide Nanoparticles with a Primary Particle Size of 2 to 5 nm by Vicki H. Grassian,^1,2,3, Patrick T. O'Shaughnessy,³ Andrea Adamcakova-Dodd,³ John M. Pettibone,² and Peter S. Thorne concludes:

“Mice subacutely exposed to 2–5 nm TiO₂ nanoparticles showed a significant but moderate inflammatory response among animals at week 0, 1, or 2 after exposure that resolved by week 3 postexposure.”

Finally, an interesting article entitled Effects of Aqueous C₆₀ Nano-Aggregates to Tetrahydrofuran Decomposition Products in Larval Zebrafish by Assessment of Gene Expression by Theodore B. Henry, Fu-Min Menn, James T. Fleming, John Wilgus, Robert N. Compton and Gary S. Sayler suggests that toxicity in this case was caused by chemicals used in the preparation of the nanomaterials, rather than the nanomaterials themselves.

Toxicology Down in Whoville: Who's testing nanoparticle toxicity?

My daughter is rehearsing to be a Who down in Whoville, a creature invisible and nonexistent to all but Dr. Suess’s Horton who first hear the Whos. This would make her and her fellow Whos, inhabitants of a world the size of a dust mote, nanoparticles I suppose, which according to at least one definition are particles smaller than 100 nanometers (or one billionth of a meter). Around the time Dr. Suess was envisioning the importance and potential of the nanosized Whos, Dr. Richard Feynman, the Nobel Prize winning physicist was also envisioning the technological potential of the very small, well before the term nano-anything even existed. Towards the end of a 1959 lecture, Feynman offered a $1000 reward to anyone who could figure out how produce a nearly Who-sized version of the Encyclopedia Britannica, shrinking the entire series so could fit on the head of a pin.

Though Feynman expected rapid progress, the technological breakthrough (and a legitimate claim for the reward) didn’t come for another thirty years. But since then, the production of nanoparticles, and the field of nanotechnology has blossomed. One institute, Foresite Nanotechnology offers a Feynman Grand Prize of $250,000 for “the first persons to design and build ...a nano-scale robotic arm and a computing device….” By some estimates, nanotechnology is now a billion dollar field, involving both government and industry dollars and it’s growing. The promise of nanotechnology includes both environmental and health applications including more effective drug delivery, potential applications for solar derived power, reduced use of industrial chemicals, and improved environmental cleanup methods.

Until researching this article I had thought the emerging field of nanotechnology would be a great opportunity to witness the fruits of over thirty years of experience with environmental standards, guidelines, laws and regulations. I had thought that development of nanoparticles and nanomaterials (made of nanoparticles) would go hand in hand with human health and environmental toxicity testing. That we would avoid yesterday’s and today’s problems like PCBs, lead paint, and climate change, so that today’s little Cindy-loo Whos won’t need to ask, “How did you let this happen, and how do we fix it?”

Unfortunately, it seems that the Whoville cats have already left the bag. According to Dr. John Balbus of Environmental Defense, the production of nanomaterials has already outpaced knowledge of human health and environmental impacts.

“The Wilson Center [Woodrow Wilson International Center for Scholars] notes 356 nanoparticle products on the shelves around the world,” says Balbus, “and most of them have virtually no in-depth toxicity testing done on the basic material in them…..There are huge knowledge gaps about how these materials will move about and persist, whether they will bioaccumulate, let alone their toxicity to humans or other animals.”

Whoops. What about those thirty years of regulations and guidelines and experience? What about all those toxicity testing techniques designed to protect human health and the environment? After decades of data on thousands of chemicals, one cannot argue that we’re not better off today than we were thirty years ago, but there are also plenty of chemicals that we still just don’t know enough about. And nanoparticles are like the new kid on the block who doesn’t play by the rules, and that’s what makes them so intriguing for industry. In many cases nanomaterials are just different from their counterparts (including both their basic atomic building blocks, and their larger composites – both of which may or may not have already been through all the toxicity testing hoops).

“Ordinary new chemicals go through a series of [initial] screens using computer-based structure-activity-relationships,” explains Balbus, meaning that to some extent researchers and regulators can predict the activity of a chemical based on its structure, comparing the similarity of that structure to chemicals of known toxicity, allowing regulators to determine the need for further more detailed toxicity testing.

“With nanomaterials, we don’t have the experience to be able to predict, so they can’t go through the same screening tests…the tools to use for regular chemicals don’t apply to nanomaterials.”

Titanium dioxide is an example of a chemical with a long history -- dating back to the early 1900’s -- of mass production (now millions of tons per year) in non-nano form, and a more recent history of mass production as a nanomaterial. Traditionally one of the most important white pigments in commerce, one new use for nano-sized titanium dioxide is as a next generation sunscreen, ironically labeled “non-chemical.” Ever wonder how those new sunscreens with titanium and zinc oxide protect you from the sun’s ultraviolet rays without making you look like a clown? Turns out that the typical white smear associated with titanium or zinc oxides result from the excellent light scattering properties of these chemicals. But nanosized particles of titanium dioxide allow visible light to pass through them and so appear clear, while still scattering the sun’s shorter and harmful ultraviolet rays. And, while many in the field agree that a sufficient number of studies on dermal or skin toxicity of nanosized titanium dioxide have been conducted, the same cannot be said of ecotoxicity studies evaluating the potential impacts on the environment.

Although the pending large scale production and potential release of nanoparticles like nanosized titanium dioxide is a recent development, nanoparticles or ultrafine particles have existed in our atmosphere ever since there were fires, volcanos and sea spray to produce them. More recently, manmade sources including traffic and industry have added to the suite of nano-sized particles in the atmosphere, and higher amounts of particulates in the air are consistently linked with adverse health impacts such as increased death rates and respiratory distress. The most recent studies suggest that ultrafine particles cause the greatest harm to the lungs.

In the lungs, says Dr. Vicki Stone, of Napier University, Edinburgh, Scotland, “Smaller particles almost always induce greater cellular response than larger particles of the same chemical composition. Such responses include cell death, and responses that cause activation of inflammation (immune response) and pathways that drive disease.”

In general as particle size gets smaller the toxicity increases, in part because of increased surface or reactive area, and in part because the behavior of the chemical in the environment or in living systems might change.

For example, nano-sized forms of chemicals that normally would not be able to cross into the brain (blocked by what is know as the blood-brain-barrier,) might be able to penetrate and gain access more easily. Similarly nano-sized particles may act differently in the environment. Perhaps becoming more easily dispersed than their counterparts, or perhaps just the opposite, sinking into sediments or settling on soils, making them more likely to be ingested by critters that make a living by stripping chemicals from sediment and soil particles.

However, cautions Stone, “Only a relatively small number of particles of different chemical composition have been tested…so many experiments are needed to verify whether this is a general phenomenon.”

In many cases, whether a product is tested for toxicity and how it is tested depends on the product, the potential for exposure, the amount in production, the proposed end use. For example, a product may be classified as a pharmaceutical, a food additive, a pesticide or a “device” such as a washing machine that sanitizes clothes as it washes, by releasing silver ions and perhaps some nanoparticles as well, (yes there is such a thing, and EPA is currently struggling with how to classify it.) The regulations, standards and guidelines that govern the use and release of a particular chemical may consider all of the above, and this is where a chemical, or an altered form of an existing chemical, may slip through the regulatory cracks.

Fortunately, the US EPA along with several other government agencies, acknowledging the different nature of nanoparticles and nanomaterials, have over the past five years, committed millions of dollars towards health and environmental effects research on nanomaterials; and they’re not the only ones.

“Large companies are certainly concerned about releasing toxic products and having liability risks,” observes Balbus, “so they have done some of the toxicity studies on nanoparticles…..but much of the development and commercialization is being done by small startups that don’t have the resources to do much toxicity testing or exposure testing.”

Stone agrees, “There appears to be huge variation in the way in which different companies are approaching the questions about testing nanoparticle hazard and risk – some have funded extensive research, others are waiting to see whether legislation will require testing, while others are avoiding using nanomaterials until they have a clear understanding of how they will be regulated.”

So, the question is, will the threat of regulation prompt responsible and meaningful health and environmental testing of nanomaterials by industry, heading off further involuntary regulation, or increased creativity in classification of nanoparticles? Let’s hope for all those Whos down in Whoville that it’s the former.

Nanoparticles

This week there was an interesting article by Barnaby J. Feder in the New York Times reporting on the regulation or non-regulation of nanoparticles. The article raises questions about regulating the release and use of chemicals produced as tiny particles (on the scale of nanometers - or one billionth of a meter.)

As a relatively new technology, it will be interesting to see if regulators and industry learn from past experiences with chemical releases and contamination. One lesson is precaution. I know that’s thrown around a lot lately. But, in terms of industry - take the perfluorinated chemical (PFOA/PFOS) example - where tons were realeased and they were exempted from regulation. Once it was noted as an environmental issue, industry has been able to cut back environmental release by large amounts. If only they had done that from the beginning.

Also these days we do have the capability to evaluate impacts of contaminants both on environment and on health (if you can make a distinction) on a finer scale than we could or did before. What we do with that information, could be based on what we’ve learned in the past - be cautious with chemicals that are persistant or that are constantly released into a system either by either consumer products or by industry – when we don’t know enough about the impacts on living things. I don’t know enough about nanoparticles just yet to know if they fall or would fall into either catagory but I’m not sure if anyone does at this point. I hope to learn more and write up a more detailed article on nanoparticles in the next week or so.

It will be interesting to observe the progress of nanotechnology and regulation of nanotech. Unlike previous technology or industrial chemicals/products, where many, even in the environmental health world, were unaware of a chemical’s widespread release or environmental dispersion many groups are watching this one closely. One group is the Project on Emerging Technologies.