{"id":60,"date":"2008-12-05T10:10:36","date_gmt":"2008-12-05T18:10:36","guid":{"rendered":"http:\/\/blogs.edf.org\/nanotechnology\/2008\/12\/05\/clump-change-challenging-conventional-wisdom-about-nanoparticle-aggregation\/"},"modified":"2024-02-12T11:02:37","modified_gmt":"2024-02-12T16:02:37","slug":"clump-change-challenging-conventional-wisdom-about-nanoparticle-aggregation","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2008\/12\/05\/clump-change-challenging-conventional-wisdom-about-nanoparticle-aggregation\/","title":{"rendered":"Clump Change: Challenging conventional wisdom about nanoparticle aggregation"},"content":{"rendered":"

Richard Denison, Ph.D., is a Senior Scientist.<\/em><\/p>\n

In some nanotechnology circles, it is almost a mantra that, once released to the environment, nanoparticles will inevitably aggregate or agglomerate into larger masses and thereby lose their nanoscale-related properties and, by implication at least, any associated risks.<\/p>\n

But can we count on nanoparticles released to the environment to self-regulate their own risk so conveniently?<\/p>\n

For example, the National Nanotechnology Initiative prominently features on its website an article it commissioned, titled “Understanding Risk Assessment of Engineered Nanomaterials:\u00a0 How can we know what is a risk and what is not?<\/a>”\u00a0 In a section designed to lead readers to question published studies that suggest nanomaterials might pose risks, the article says: “In solution or in air, it’s quite difficult to keep nanomaterials separate, as they tend to clump in larger aggregates or agglomerates.”\u00a0 This is a point the author of this rather short article felt compelled to repeat twice more.<\/p>\n

An FAQ issued by Germany’s Federal Institute for Risk Assessment<\/a> states that “nanoparticles tend to aggregate into larger unions which are generally larger than 100 nm. The toxic effects of nanoparticles linked to their small size and higher reactivity are then no longer relevant.”<\/p>\n

And a recent post on the blog of the nanotechnology practice group at Porter and Wright<\/a> asserts that nanoparticles “have been shown to have fewer potential adverse health effects when they occur in cluster form (aggregates and\/or agglomerates).\u00a0 In the ‘good news’ department, scientists\u00a0studying aerosol dispersion of nanoparticles have found they tend to cling together when dispersed into the environment.”<\/p>\n

I won’t even begin to try to lay out here how much more complex and unpredictable than this nanoparticle aggregation and environmental fate and transport are in the real-world.\u00a0 Instead, let me just cite two excellent papers that do so:\u00a0 see Maynard<\/a> and Weisner et al.<\/a><\/p>\n

But I do want to briefly discuss and cite some recent studies supporting three reasons why we can’t count on nanoparticles released to the environment to self-regulate their own risk so conveniently:<\/p>\n

1.\u00a0 Some nanomaterials can be stabilized as nanoscale particles in solution under environmental conditions.\u00a0 <\/strong>A number of studies have found that carbon-based nanomaterials – despite their inherently very low water solubility – can be “solubilized,” that is, can enter and remain in stable suspensions upon interaction with water or with other common, naturally occurring substances.\u00a0 The latest study, authored by Salonen et al.<\/a> and published in the journal Small<\/a><\/em>, finds that C70<\/sub> fullerenes can form “stable, homogeneous suspensions” in water through interaction with ubiquitous phenolic acids that are present in and released from virtually all plant matter.\u00a0 It appears that individual C70<\/sub> fullerenes first become coated with the phenolic acid, and then form small, loose clusters with diameters on the order of a few nanometers.\u00a0 This study merited a “spotlight” on the Nanowerk website<\/a>.<\/p>\n

Earlier work has found similar behavior:\u00a0 Fortner et al.<\/a> identified the formation of stable suspensions of “nanocrystals” of C60<\/sub> fullerenes in water – nanoscale (25-500 nm diameter) aggregates they call “nano-C60<\/sub>” that have entirely shed the extreme hydrophobicity of the individual fullerenes.\u00a0 Hyung et al.<\/a> found that multi-walled carbon nanotubes could be stabilized as individual particles through interaction with natural organic matter found in river waters; the natural material actually worked better than commonly used surfactants selected to serve that same solubilizing function.<\/p>\n

2.\u00a0 For performance reasons, nanoparticles are being actively engineered not<\/span> to clump.<\/strong>\u00a0 For most nanomaterial applications, optimal performance depends on minimizing any disordered clumping or even maximizing dispersal, so that the properties of individual nanoparticles or highly ordered nanostructures can fully exert themselves.\u00a0 For this reason, researchers are working overtime to coat, cap, chemically modify or otherwise force nanoparticles not to aggregate or agglomerate.\u00a0 See, for example, Yang et al.<\/a>‘s use of special capping agents to prevent aggregation of platinum nanoparticles, and Nadagouda and Varma<\/a>‘s similar work with silver and palladium nanoparticles.\u00a0 Similar efforts have been mounted to chemically modify ceramic nanoparticles<\/a> to ensure dispersal.<\/p>\n

So even to the extent that native or current forms of nanoparticles do readily clump or retain their hydrophobicity, any assumption that engineered nanomaterials entering commerce and the environment will inevitably do so is wholly unwarranted.<\/p>\n

3.\u00a0 Even agglomerated or clumped nanoparticles can be toxic.<\/strong>\u00a0 The assumption that aggregated nanoparticles lose all of their nanoscale properties or become benign is also unwarranted. \u00a0Maynard and Kuempel<\/a> have amply demonstrated that even large aggregates on individual nanoparticles typically retain many of their nanostructural features and properties.\u00a0 But what about toxicity?<\/p>\n

Fortner et al.<\/a> found that their fullerene nanocrystals exhibited antimicrobial activity, suppressing bacterial growth and respiration.\u00a0 In addition to confirming nano-C60<\/sub>‘s antibacterial activity, a recent paper by Lyon and Alvarez<\/a> cited a number of studies demonstrating that the formation of these nanoscale aggregates in water yields a material with high toxicity to aquatic invertebrates, fish and the cells of higher organisms.\u00a0 The aggregates have also been shown to enter and accumulate in those cells and to adhere to lipids.<\/p>\n

Finally, Salonen et al.<\/a> showed that their phenolic acid-coated C70<\/sub> clusters could readily translocate across the membranes of human cells in culture and enter the membrane surrounding the cell nucleus.\u00a0 Moreover, they induced the contraction and ultimate death of those cells – ironically, apparently by aggregating into micro-sized particles through interaction with the cell membranes.<\/p>\n

Once again, we find that nanomaterials’ actual behavior confounds conventional wisdom and, when approaching their toxicology, forces us to question or abandon our assumptions and biases.<\/p>\n","protected":false},"excerpt":{"rendered":"

Richard Denison, Ph.D., is a Senior Scientist. In some nanotechnology circles, it is almost a mantra that, once released to the environment, nanoparticles will inevitably aggregate or agglomerate into larger masses and thereby lose their nanoscale-related properties and, by implication at least, any associated risks. But can we count on nanoparticles released to the environment …<\/p>\n","protected":false},"author":100,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[56087],"tags":[39211,39206,5017],"coauthors":[],"class_list":["post-60","post","type-post","status-publish","format-standard","hentry","category-nanotechnology","tag-carbon-nanotubes","tag-national-nanotechnology-initiative-nni","tag-risk-assessment"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts\/60","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/users\/100"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/comments?post=60"}],"version-history":[{"count":1,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts\/60\/revisions"}],"predecessor-version":[{"id":12949,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/posts\/60\/revisions\/12949"}],"wp:attachment":[{"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/media?parent=60"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/categories?post=60"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/tags?post=60"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/blogs.edf.org\/health\/wp-json\/wp\/v2\/coauthors?post=60"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}