Pollution and Pollution Control - Environmental Biotechnology: Theory and Application - page 68

Pollution Control Strategies
Dilution and dispersal
The concept of 'dilute and disperse' was briefly mentioned earlier in this discus-
sion. In principle, it involves the attenuation of pollutants by permitting them to
become physically spread out, thereby reducing their effective point concentra-
tion. The dispersal and the consequent dilution of a given substance depends on
its nature and the characteristics of the specific pathway used to achieve this. It
may take place, with varying degrees of effectiveness, in air, water or soil.
Air
In general terms, air movement gives good dispersal and dilution of gaseous
emissions. However, heavier particulates tend to fall out near the source and the
mapping of pollution effects on the basis of substance weight/distance travelled
is widely appreciated.
Wa t e r
Typically, there is good dispersal and dilution potential in large bodies of water
or rivers, but smaller watercourses clearly have a correspondingly lower capacity.
It is also obvious that moving bodies of water disperse pollutants more rapidly
than still ones.
Soil
Movement through the soil represents another opportunity for the dilute and dis-
perse approach, often with soil water playing a significant part, except where
excessive ecohydrologic separation becomes a limiting factor (Brooks et al .,
2010), and typically aided by the activities of resident flora and fauna. The
latter generally exerts an influence in this context which is independent of any
bioaccumulation potential.
Concentration and containment
The principle behind this is diametrically opposed to the previous approach, in
that instead of relying on the pollutant becoming attenuated and spread over a
wide area, it is an attempt to gather together the offending substance and prevent
its escape into the surrounding environment.
The inherent contradiction between these two general methods is an enduring
feature of environmental biotechnology and, though the fashion changes from
time to time, favouring first one and then the other, it is fair to say that there is a
place for both, dependent on individual circumstances. As with so much relating
to the practical applications of biotechnologies to environmental problems, the
idea of a 'best' method, at least in absolute terms, is of little value. The whole
issue is far more contextually sensitive and hence the specific modalities of