今週ドイツで参加していた国際会議IPTC 2013 (10th International Particle Toxicology Conference @Dusseldorf, Germany) では、breakのときにある課題提起に対する私の答えで少し盛り上がりました。そこで、そのときの私の答え（考え）を書いておきたいと思います。
日本語に訳すのが面倒なこともあり、ほぼ原文のまま（英語の細かい間違いはご容赦ください）にします。
簡単に言うと、課題提起は「新規ナノ材料のリスク評価に際して予算が限られているとき、有害性評価、曝露評価、物理化学的性状評価の何を優先させたらいいのか」という問いでした。それに対して私は「（その前提であれば）曝露評価でしょ」と答えたというところです。
--- written by Masakazu Umezawa on June 9 ---
Q. If we do not have enough budget for risk assessment of (novel) nanomaterials (NMs), what do we have to evaluate: hazard, exposure or physicochemical characteristics?
A.
My answer to this question is “exposure.”
I talked (Oral-21 ->program) in the conference we need additional predicting & screening method for hazard characterization of NMs; however, I also think we have to utilize the knowledge of PM2.5 more. We have a lot of data on epidemiological studies of PM2.5. NM is not actually equal to PM2.5, but we should be able to use the human data. (Of course, the dose/exposure metric of NM needs to be optimized.) We need to start (to try) risk management based on current knowledge of NM toxicity and exposure.
I am sure we need to prepare budget for research on hazard assessment in addition. If we had enough budget for the research, we would conduct hazard and physicochemical characterizations of NMs to improve the risk assessment and to realize effective risk management of NMs.
If we could identify or predict hazard of NMs by in vitro and/or in silico techniques, we would not require in vivo testing. However, can anyone predict toxicity, including chronic and reproductive effects, of NMs by using in vitro or in silico model? My answer is no, therefore I think we need in vivo hazard assessment of NMs in a current condition.
Masakazu Umezawa (runner_fromgoka@yahoo.co.jp)
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*Definition of the term 'nanomaterial' posted by NanoTrust (Austrian Academy of Sciences) on June 6, 2013.
--> Definition of the term 'nanomaterial'
●岩波『科学』2012.10月号に「ナノ材料による次世代健康影響とリスク管理への課題」（2013年10月4日）
●岩波『科学』2013.4月号にPM2.5の特集（2013年4月5日）
●『市民研通信』2013.4月号に「ナノ粒子の健康リスク」（2013年4月16日）
