Monday, January 12, 2015

Inhalation Model Research Needs

Hopefully the readers of this blog are now convinced of the importance of models that estimate the exposure potential of workers and other humans.    My sense is that we are only scratching the surface of the potential value of these models, however.   Indeed, many folks still reject the idea of modeling in favor of the direct approach of measuring which they consider the gold standard.  To the extent that we do not have the tools to feed our models with proper inputs, they are correct.   It is by now an old “Catch 22”:  it costs more to get the model inputs for any single question at hand than it does to directly measure, so we almost always directly measure.   The reality is that once what have the modeling input parameters we can use them in many different scenarios so that in the end it would generally be a much more cost-effective way forward.  
Please don't get me wrong, models are still very valuable tools but they could be so much more powerful and useful if properly developed with research done as a public works project in the general shared interest.  
Indeed, it was with this in mind that I spent quite a bit of time in Italy starting in 2004 in an effort to organize such an effort.  Given an introduction by my friend and colleague, Bert Hakkinen, I began working with Stylianos Kephalopoulos, who was head of the Physical and Chemical Exposure Unit of the Institute for Health and Consumer Protection (IHCP/PCE) at the Joint Research Centre (JRC) of the European Commission in Ispra which is just north of Milan.  
The REACh regulation was happening in Europe and it was obvious to many that exposure assessment tools needed to be developed to help with the implementation of this ground-breaking legislation.
Together we first organized a pre-workshop to setup the questions and issues and then  later a series of 5 simultaneous workshops on the general subject of modeling that happened in June 2005 in Intra Italy.   I was an organizer and moderator for the pre-workshop and the workshop on model “Source Characterization” since I had always seen this as vital research need.   For this workshop on Source Characterization, we invited and gathered modelers from all over the world with the following folks coming to the workshop:

Arvanitis A.   JRC/IHCP/PCE (EU) (Rapporteur)
Bruinen de Bruin Y    JRC/IHCP/PCE (EU)
Delmaar C.   RIVM (Netherlands)
Flessner C.   EPA (USA)
Hanninen O.   KTL (Finland)
Hubal E. Cohen   EPA (USA)
Jantunen M.   KTL (Finland)
Jayjock M.   The Lifeline Group (USA) (Moderator)
Kephalopoulos S.   JRC/IHCP/PCE (EU) (Co-ordinator)
Koistinen K.   JRC/IHCP/PCE (EU)
Little J.   Virginia Polytechnic Inst. (USA)
Mason M.   EPA (USA)
Matoba Y.   Sumitomo (Japan)
McKone T.   University of California (USA)
Nazaroff W.   University of California (USA)
Pandian M. (USA)
Price P.        The Lifeline Group (USA)
Shade W.     Rohm and Haas, Co (USA)
Sheldon L.   EPA (USA)
Sutcliffe R.  Health Canada (CAN)
Won D.        National Research Council (CAN)
Wu K.          University of Taiwan (Taiwan)
Zhang Y.     Tsinghua University (China)

Quite a few other fine modelers could not make this workshop but contributed to the report.

I must tell you that this was a remarkably talented and energetic group and it was all I could do to keep up with the ideas coming out of this critical mass of world-class modelers.   The main conclusions of our deliberations are presented below:

“It is the recommendation of the Workshop participants that the work products presented herein to be used in the systematic development of human exposure models for their use in a tiered approach to exposure/risk assessment. 
Given that the 5 bins presented herein represent a consensus taxonomy or universe of sources, the workshop participants advise that a reasonably representative subset of this comprehensive listing be selected for specific laboratory analysis and model development. It was further suggested that exposure models designed to describe these sources of exposure and the transport and fate of substances should be constructed using a step-wise approach as outlined in this report.”

In essence the group determined that there was no reasonably inclusive outline description of source types and certainly no systematic research effort to characterize them.   The two-day workshop resulted in the following primary work products: 
  • Identification of existing source sub-models: presented in the pre-workshop report and references
  • A defined Taxonomy of Sources
  • Identification and definition of the attributes and characteristics of First Principle, Mechanistic Source and Transport/Fate Models to be developed in a tiered approach 
All of the details of these outcomes are described in the 104 page workshop report which I will send to anyone requesting it:
This work and report are almost 10 years old.   From my perspective some progress has been made primarily from the work of Drs. Bill Nazaroff and John Little and their colleagues in the characterization of indoor air sources.    I think even Bill and John will admit that the vast majority of work that we outlined in this workshop has not been started.   From my perspective the effective implementation of REACh continues to limp along without these tools.  Any effective re-authorization of TSCA would also require the fruits of this research. 
As usual nothing really is going to happen without committed resources ($).   I simply plan to pull this report out every few years, dust it off and remind folks that it is here.   If we, as a society, are really serious about doing a comprehensive job of human health risk assessment to chemicals we will ultimately need to develop these cost-effective tools.

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