Ecological Risk Assessment

"...no adverse effect on human health or the environment." is the mandate of several environmental laws. From 8B you have a good grasp on the basics of human health risk assessment. From that base we will talk a little about adverse effects on the environment. Here are the main differences between the two types of risk assessment:

Let's discuss each:

• You realize by now that our estimation of low dose effect on humans is at least one step removed from science for most chemicals, although it is the best we can do. In any given meso-environment or ecosystem there are hundreds or thousand of species, from whales to microorganisms. It is rare we know anything about the toxicity of any particular chemical to more than one or two of these species. If there is a species that is both convenient and relevant, it could be tested, just like Cheeech did to the fish back in Submodule 1E. By convenient I mean amenable to laboratory testing. Relevant means important to the ecosystem in question, recognized by the public, sensitive to the chemical. These are often impractical to find, so standard indicator species are used. These you order from a supply house and they are delivered in a day or two. Then they are tested with standard EPA protocols. As for human dose-response estimates, the indicator species are about the best you can do, given normal limitations of time and budget. The resulting dose-response numbers may or may not be relevant.
• For human receptors, we do not want to hurt anybody. Now or ever. For animals in an ecosystem, we can accept some mortality, as long as the population stays healthy. On a macroscale, the Fish and Game Department manages game populations this way. For example, while for humans a one in one million or one in ten thousand chance of harm is acceptable to some. (Note this is computed harm, it may not hurt anyone.) For damage to an ecosystem, a LD10 might be acceptable. That is, it will kill 10% of the animal species population. As long as the PRP ("Potentially Responsible Party, i.e., the polluter) can demonstrate the population will spring back in a year or two, an LD 50 might be acceptable.
• For humans we sometimes separate male and females. We always separate children. But that's about it. For ecosystems we must consider trophic levels, i.e., the food chain. Ducks eat lead shot from the bottom of the lake, foxes eat the ducks. Some contaminants increase as they are passed up the food chain
• Effects are impossible to test in humans, but often can be tested in at least some animals.
• Pathways. We looked at some pathways for human receptors a few pages back . The next page has the approximate equivalent for an Ecorisk site.

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