Health risk assessment for nanoparticles: A case for using expert judgment
Journal of Nanoparticle Research
Vol. 9, Num. 1
In conventional quantitative risk assessment, uncertainties are linked to the values of the parameters used. But environmental contaminants typically have multiple components, and to cope with multiple effects, some of which are hard to quantify, analysts used default assumptions and extrapolations. Kandlinkar et. al. note that the "estimation of a biologically relevant dose from exposure information is...often very dificult and requires fairly detailed knowledge of the toxicokinetics of the pollutant in the human body."
Nanoparticles form a new challenge because not only is there a lack of data, there is also a lack of information about the basic nature and environmental interaction of these particles. Parameters of effect are not the only point in question: basic cause and effect mechanisms are in question. Particle size in PM2.5 pollution studies is linked to toxicity, but the mechanisms of effect are uncertain. Exposure mechanisms for nanoparticles (in air, in water) may change the end results for those exposed. Moreover, because of their extremely narrow specifications and interactions, a study done one one nanoparticle may not be generalizable to all nanoparticles.
Kandlikar et al. proposes to supplement regular risk assessment techniques, ineffective in the case of nanoparticles, with expert judgment approaches. These approaches elicit judgments from a wide range of experts on different parts of the risk causal chain and look for consensus. "Often, and especially in early stages of a scientific issue when uncertainty is high, expert assessment is used to structure problems, to indicate key variables, and to examine relation ships and influences between variables by building influence diagrams." Kandlikar et. al. describe the method for developing these expert consensus judgments: "The expert judgment process begins with a set of qualitative questions administered in an open-ended interview format to a small group of experts....These interviews lay the groundwork for developing expert assessment protocol to be administered to a larger group of experts. We call this a protocol rather than a survey because of the effort to provide structure and detail in setting out the relevant questions.It is not a survey of overall opinions on nanoparticle risks,but a tool to identify judgments and provide diagnostic guidance." To ensure balance, experts should meet a variety of standards and be drawn from a variety of backgrounds.
Kandlikar et al also use examples to illustrate how studying expert consensus/disagreement helps in research prioritization and budget allocation exercises by risk managers or managers of funding agencies.