Toxicity Assessment

In your tour through Tox Tutor you learned about the science of toxicology. Science is concerned with elucidating the laws of nature. Why do things happen? In this sub-module we will learn something about the application of the science of toxicology. Specifically, how do we express a risk due to a particular exposure? Here we are no longer concerned with the science, but rather the results. The history of engineering and technology has many stories of inventors who did not understand the science of their inventions or used incorrect science, but the result worked. The opposite also happens, the science is well understood, but the invention fails for some other reason, typically human problems or economics.

If the goal of our technology is to protect people from adverse heath effects, and we apply the technology and later find no adverse effects, we term the application a success. If adverse health effects are observed, we have failed. Using those definitions, science does not matter. If our goal is to protect people from cancer due to benzene in their water supply and we charcoal filter their water and later observe that their cancer rate is the same as communities that do not have benzene in their drinking water, we have succeeded. It does not matter if the benzene was really capable of causing cancer, or even if there really was any benzene in the water to start with, the charcoal filters have succeeded.

If the goal of an environmental law is to protect persons, and we protect them, it does not matter if they were actually (scientifically) threatened or not, the law has succeeded.

If you thought (or said) "Ouch!", please forgive me. There is often a large gap between science and its applications. As both an engineer and a scientist with years of practical experience trying to reconcile science with its practical limitations such as regulations, I have noted that at times the gap is so wide it seems there is little relation at all. [I wrote something about this for another course, which you are welcome to look at, but is not required here. Regulatory Toxicology. ] With that apology to philosophy, we continue.

In this sub-module we make a distinction between the toxic effect cancer and every other toxic effect. That is, we will divide the world of contaminants into carcinogens and non-carcinogens. In the case of the many chemicals that are both, we will separate the risk of cancer from the risk of the non-cancer harm, such as nerve damage. Typically the hazard identification at the beginning of the risk assessment has provided that information. Also, your SCEM and exposure analysis will provide you some information about the level and likely length of the exposure. What you want next are Toxicity Values that relate dose to response.

We will learn about the toxicity values for non-cancer effects, and cancer effects. NEXT

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