In Lawrence Raab’s poem, “Attack of the Crab Monsters,” a biochemist bewails the fact that his research has outstripped his preparedness to deal with its potential hazards. “It’s the old story, predictable/as fallout,” the narrator opines, “the rearrangement of molecules.” The narrator’s molecules have been rearranged into the form of a crab-monster—“I’m not used to all these/legs, these claws, these feelers”—who is now facing his own destruction. It’s cinematic—it was also the subject of a 1957 Roger Corman film—but it couldn’t really happen. Right?
Well, no amount of molecular rearrangement is likely to turn humans into crab monsters, but it is true that working with substances at the molecular level is potentially hazardous. It is also true that our ability to create molecular-scale substances—called nanomaterials—quickly outstripped our preparedness to deal with their potential hazards. As a result, agencies that provide guidance on worker and product safety are scrambling to identify hazards and controls for these materials. In November and December 2017, three agencies—the U.S. Food and Drug Administration (FDA), the World Health Organization (WHO), and the European Chemicals Agency (ECHA) all published new or updated guidance for the manufacture, handling, and use of engineered nanoparticles.
The Rearrangement of Molecules
One difference between a particle and a nanoparticle is, as the prefix “nano” suggests, their size. Nanoparticles are very tiny particles, generally 1–100 nanometers in their greatest dimension. But when it comes to chemical behavior, size really does matter—very tiny particles of a material display very different chemical behaviors from their larger counterparts.
The effect was first noticed with naturally-occurring nanoparticles, like some of the particulates found in diesel exhaust. But those particles—now more commonly called “ultrafine particles”—are irregular in shape, size, and composition, making their biological effects inconsistent. More common now are engineered nanoparticles—nanoparticles broken down into individual molecules or atoms and reconstructed in very specific ways—whose consistent structure leads to consistent and often unique chemical behavior. When a common substance like carbon—found in big chunks as charcoal—is broken down into individual molecules and rebuilt into an extremely tiny structure, like a tube constructed of individual carbon “rings” (called “bucky tubes”), its chemical behavior is entirely different both from the charcoal and from ultrafine carbon found in products of combustion.
These differences in chemistry result in new and different applications for nanoparticles when compared with their larger counterparts. In fact, nanoparticles have a lot of uses—in consumer products alone, there are more than 1,000 products that contain engineered nanoparticles. Makeup and medications, dental treatments, bandages and tissue adhesives, sunscreen, food storage containers, appliances, clothing, electronics and optics, computers, sporting goods, paint, and coatings all incorporate engineered nanomaterials.
The differences in chemistry also mean that the hazards of nanoparticles to both humans and the environment are different from the hazards of larger particles. Nanoparticles may pass through membranes that would be impervious to larger particles—a property that can be either hazardous, or beneficial, or both. For example, a drug that could not cross the blood-brain barrier in larger form may be engineered as a nanoparticle in order to pass into the brain—but that same engineered nanoparticle may be far more potent than its larger-scale counterpart, and it may enter other areas of the body where its effects can cause harm.
One of the most widely used and thoroughly studied nanoparticles is titanium dioxide (TiO2). In its larger forms, TiO2 is known as “the environmental white knight” because of its extremely low toxicity both in the environment and to humans. Its nanoparticulate form (TiO2 NP) is turning out to be another story; evidence is mounting that TiO2 NPs have significant aquatic toxicity, and that they are neurotoxins and respiratory toxins as well.
Tomorrow, we’ll look at the latest guidance from the FDA, the WHO, and the EC on nanoparticles.