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
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 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. 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, we do not what 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.
NEXT PAGE
EQE 693 Home Module
12 Index