Distribution and Effects of Chemicals in Communities and Ecosystems - Organic Pollutants: An Ecotoxicological Perspective - page 97

and government laboratories, there is uncertainty about the interpretation of the
results obtained using them. Results coming from mesocosm tests are not yet of
much use in environmental risk assessment. However, refinement of techniques
used in mesocosm testing could make them more valuable for risk assessment in
the future (see Section 4.8).

4.8 new aPProacHeS to PredIctIng ecoLogIcaL

rISkS PreSented By cHemIcaLS

As discussed previously, current risk assessment practices do not deal with the fun-
damental question about possible effects at the level of population and above. In the
foregoing sections, consideration was given to ways in which effects at these higher
levels might be identified—and even predicted—by using data from field studies,
laboratory studies, and mesocosms. At the fundamental level, the use of popula-
tion models that can predict population growth rate (r) has obvious attractions. The
incorporation of data from field and laboratory studies into such models should, in
principal, allow reasonable predictions to be made of the effects of defined environ-
mental levels of chemicals upon populations. The critical role of biomarker assays
and/or residue data in establishing (1) the relationship between dose and toxic effect,
and (2) the relationship between toxic effect and population change has already been
emphasized here and in the wider literature (Peakall 1992; Peakall and Shugart 1993;
Huggett et al. 1992; Fossi and Leonzio 1994; Walker et al. 1998). In the forthcoming
chapters, examples will be given where this approach has already been successful
in the retrospective investigation of pollution problems. The effects of TBT on dog
whelks (Chapter 8, Section 8.3.4), dieldrin on sparrow hawks (Chapter 5, Section
5.3.5.1), and p,p ′-DDE on peregrines and bald eagles (Chapter 5, Section 5.2.5.1) are
all cases in point.
The more difficult thing is to develop models that can, with reasonable confi-
dence, be used to predict ecological effects. A detailed discussion of ecological
approaches to risk assessment lies outside the scope of the present text. For fur-
ther information, readers are referred to Suter (1993); Landis, Moore, and Norton
(1998); and Peakall and Fairbrother (1998). One important question, already
touched upon in this account, is to what extent biomarker assays can contribute to
the risk assessment of environmental chemicals. The possible use of biomarkers
for the assessment of chronic pollution and in regulatory toxicology is discussed
by Handy, Galloway, and Depledge (2003).
Another issue is the development and refinement of the testing protocols used in
mesocosms. Mesocosms could have a more important role in environmental risk
assessment if the data coming from them could be better interpreted. The use of bio-
marker assays to establish toxic effects and, where necessary, relate them to effects
produced by chemicals in the field, might be a way forward. The issues raised in
this section will be returned to in Chapter 17, after consideration of the individual
examples given in Part 2.