Chemistry Reference
In-Depth Information
chain, which can then be related to behavioral and other whole-organism responses
to neurotoxic pollutants.
In the first place, this approach can be adopted in field studies of polluted areas
where neurotoxic effects are suspected on the basis of circumstantial evidence, eco-
logical profiling, or the results of bioassays, or any combination of these (see Chapter
13, Section 13.4). Once a polluted area has been identified, “clean” indicator organ-
isms may be deployed from the laboratory into this area. For comparison, the same
indicator organisms can also be deployed to a reference area that is relatively unpol-
luted and can act as a control. Biomarker responses such as acetylcholinesterase
inhibition or changes in the electrophysiological properties of nerves can then be
measured in the deployed individuals. Thus, evidence may be sought for the opera-
tion of neurotoxic mechanisms—as explained in the foregoing text—and those pol-
lutants responsible for the toxic effects identified and quantified by chemical analysis.
Apart from investigations of this kind, this approach is also useful in field trials of
pesticides and other chemicals. Fish and other aquatic species have been studied in
this way (see Chapter 15 for examples).
Arguments are bound to be raised about the cost of such an approach, but the
important point is that much may be learned about the ecotoxicology of neurotoxic
pollutants from a few well-designed long-term investigations that can act as case
studies to give guidance when dealing with pollution problems with neurotoxic com-
pounds more generally. Knowledge gained in this way will be valuable—and should
be cost effective—in the longer term. A lot of money is spent on limited short-term
tests and short-term projects in ecotoxicology that contribute little or nothing to a
more fundamental understanding of the harmful effects of chemicals upon natural
ecosystems in the longer term.
In a similar way, an integrated biomarker approach has a role when carrying out
experiments in mesocosms. Under these controlled conditions, behavioral effects
of neurotoxic pollutants, acting singly or in combination, can be monitored and
compared with data on predator-prey relationships and effects at the population
level. The employment of mechanistic biomarker assays can facilitate comparisons
between results obtained in mesocosms and other data obtained in the field or in
laboratory tests. Here is one way of attempting to answer the difficult question—
“how comparable are mesocosms to the real world”?
There is a continuing interest in the development of biomarker assays for use in
environmental risk assessment. As discussed elsewhere (Section 16.6), there are both
scientific and ethical reasons for seeking to introduce in vitro assays into protocols
for the regulatory testing of chemicals. Animal welfare organizations would like
to see the replacement of toxicity tests by more animal-friendly alternatives for all
types of risk assessment—whether for environmental risks or for human health.
Considering risk assessment generally, Dewar (1983) and Atterwill et al. (1991)
have reviewed the subject of alternative procedures for testing neurotoxic com-
pounds. Atterwill et al. (1991) give details of a number of in vitro tests that might be
developed for this purpose and propose a stepwise scheme for neurotoxicity testing
that incorporates some of them. However, they and other authorities on the subject
stress the difficulty of devising a testing protocol based on in vitro assays alone
because of the complexity of the nervous system. More recently, in a report by the
Search WWH ::
Custom Search