Spring 2013 Closure
**Q. Who determines the effectiveness of exposure routes? Do they post the ED/LD of toxins with respect to the different exposure routes, i.e. inhaling benzene vs. ingesting benzene vs. absorbing benzene.
A. For chemicals where the testing has been done and routes are relevant, you will find toxicity results for the routes. So, for benzene, you will find data for both the inhalation and ingestion. Dermal exposure is more difficult. For workplace exposures, the rules just say to indicate the dermal route is important. Presumably one can protect against dermal exposures by proper clothing – but emphasize the word “proper.” For a worker exposed to benzene, where all three routes are plausible, industry uses a “BEI” or biological exposure index, where chemicals in the blood or urine are used as a surrogate for exposures via all three routes.
Q. I am testing a substance to determine its concentration decline. The first order rate constant was used to model the situation. What are some indicators that the first order rate constant model is accurate (or inaccurate)? Is the graphical representation noticeable skewed or is it more subtle?
A. The issue is that usually you only have a few data points with which to judge your model. And often there are confounding factors. For example a soil model may vary enormously with batches of soil from slightly different locations taken at different times. Temperatures and rainfall will vary and so on. If you had enough data points, you could use a “bootstrap” technique to develop the model from the data. But the first order is a common default.