Ecological Risk Assessment
"...no adverse effect on human health or the environment." is the
mandate of several environmental laws. By now you have a good grasp on the basics
of human health risks. 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
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 Module 1. 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 are delivered in a day or two. Then they are tested with standard
EPA protocols. Similar to 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 the human species, 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, Fish and Game manages game populations this
way. For example, while for humans a one is 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 can demonstrate the population will spring back in a year or two, an LD
50 might be 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. You remember the pathways for the SCEM
on the PCP site. Here the approximate equivalent for an Ecorisk site.
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