Nanoparticle Risk Assessment – Where Shall We Begin?

Nanotechnology and molecular biology are, individually, powerful new approaches to exploiting nonliving substances and to understanding living organisms. The two fields emerged at approximately the same time (early 1970s). But now, in the early 2000s, it is evident that that the laws of nanotechnology – which are based in quantum mechanics – are relevant to assessment of the potential hazard associated with macromolecular substances. Nanotechnology has heretofore been considered as a tool with which to fulfill a given task. But risk assessment of nanotechnology uses and products may need to address not only the characteristics of individual nanoparticles but also their potential – intentional or inadvertent – to create, mend, disable, or destroy life. Possible impacts of nanoparticles on human and ecosystem health are largely unknown; and there are currently no methods for assessing potential risks associated with nanoparticles in wastewater, treated effluents, sewage sludge, or biosolids.Nanotechnology focuses on the construction of tiny molecules between 1 and 100 nanometers in at least one dimension, and their assembly into exquisitely small devices. The only previously-known nano-sized objects occurred naturally either as nonliving soot and crystals, which could aggregate to form colloidal particles; or as biomolecules (proteins, nucleic acids, and lipids), which could assemble into quasi-living matter (viruses, viroids, and prions) or actual living cells. The behavior of naturally-occurring organic compounds is formally described by environmental chemists who emphasize molecular aspects of living or nonliving substances.The fact that matter can be finely divided to yield crystals, powders, or dusts in the solid state, or to remain dissolved, suspended, or colloidal in liquid systems is well known. This presentation will focus on the latter, to emphasize that the nature of physical and chemical interactions between nano-substances and their solvent, or with other solutes or particles, is not known. Here, both aqueous and nonaqueous solvents (specifically, lipids) will be considered.Buckminsterfullerene (C60), a well-known nanoparticle, is the largest object demonstrated to have properties of both waves and particles – to be energy and matter simultaneously. This duality is thought to be shared by all particles, especially those of subatomic size, and characterizes the low (0.1-1 nm) end of the nano range. There, physics and chemistry meet.Nanotechnology has also made evident a second duality, at the high (≥100-1000 nm) end of the nano range. Biologists had established the cell theory (that a cell – microbial, plant, animal, or other – is the smallest form of life) in the early 19th century. By the end of the 20th century, unicellular bacteria, fungi, and protists were known, as were viruses, viroids, and prions.Macroorganisms had been recognized as multicellular beings. The biological distinction between life and death remained clear, though the status of subcellular agents has not yet been clarified. It is somewhere in this zone that chemistry and biology meet.Thermodynamic laws invoke a third and final duality – equilibrium vs. disequilibrium – that refers to the overall state of a system or its components. Physicochemical activities and engineering processes occur at rates controlled by energy availability, where energy is available in chemical, electromagnetic, or mechanical form or simply as heat. Thermodynamic analysis reveals stable, metastable, and transition states, and can establish the reaction kinetics within both engineered (anthropogenic) and natural systems. Quantitative analyses reveal the statistical probability of any reaction or engineering outcome, and can be predictive.Engineered nanosubstances – particles, rods, tubes, dots, and the like – are already in widespread use within consumer products and pharmaceutical preparations. Nanomachines and - structures – stents, drug-delivery vehicles, and specialty materials – are being considered for use within medical and environmental applications. Nanotechnology products are developed, and expected to perform, according to chemical and engineering principles characteristic of life's smallest unit, the cell. There is a clear potential for hazard at the cellular level simply because of the tendency of nano-sized substances to self-assemble and self-organize, to replicate, and to recognize (and react with) others of their kind. Products designed to interact with living tissues pose the greatest potential danger.This presentation will review the nanotechnology toxicological literature, describing known and possible risks posed to human and ecological health by the disposal of nano-sized substances to wastewater and their predicted association with sewage sludge. Particular emphasis will be placed on devising new methods or paradigms for recognizing and quantifying the potential nanotechnology hazard, leading to development of a quantitative hazard assessment for nanoparticles in land-applied biosolids.