Chemistry Reference
In-Depth Information
4
Distribution and
Effects of Chemicals
in Communities
and Ecosystems
4.1 IntroductIon
In Chapter 3, the distribution of environmental chemicals through compartments of
the gross environment was related to the chemical factors and processes involved, and
models for describing or predicting environmental fate were considered. In the early
sections of the present chapter, the discussion moves on to the more complex question
of movement and distribution in the living environment—within individuals, com-
munities, and ecosystems—where biological as well as physical and chemical factors
come into play. The movement of chemicals along food chains and the fate of chemi-
cals in the complex communities of sediments and soils are basic issues here.
Ecotoxicology deals with the study of the harmful effects of chemicals in ecosys-
tems. This includes harmful effects upon individuals, although the ultimate concern
is about how these are translated into changes at the levels of population, community,
and ecosystem. Thus, in the concluding sections of the chapter, emphasis will move
from the distribution and environmental concentrations of pollutants to consequent
effects at the levels of the individual, population, community, and ecosystem. The
relationship between environmental exposure (dose) and harmful effect (response) is
fundamentally important here, and full consideration will be given to the concept of
biomarkers, which is based on this relationship and which can provide the means of
relating environmental levels of chemicals to consequent effects upon individuals,
populations, communities, and ecosystems.
4.2 moVement of PoLLutantS aLong food cHaInS
The pollutants of particular interest here are persistent organic chemicals—com-
pounds that have sufficiently long half-lives in living organisms for them to pass
along food chains and to undergo biomagnification at higher trophic levels (see Box
4.1). Some compounds of lesser persistence, such as polycyclic aromatic hydrocar-
bons (PAHs) (Chapter 9), can be bioconcentrated/bioaccumulated at lower trophic
levels but are rapidly metabolized by vertebrates at higher levels. These will not be
discussed further here, where the issue is biomagnification with movement along the
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