Factors affecting fate and behaviour of chemicals
in the environment
This Section summarises the key variables that
must be considered when assessing projects affecting
water quality. Their role and significance are considered
only briefly here, for a fuller account staff should
refer to the separate reports for nutrients, metals
Impact of Nutrients in Estuaries - Phase 2
(CCRU and CEFAS, 1999).
Turbidity in England and Welsh Tidal Waters
Assessment of Risks Posed by List II Metals
and Adequacy of Existing Environmental Quality Standards
(EQSs) for SMA Protection (WRC, 1999).
Chemicals introduced to the marine environment
as a result of an activity or a discharge include
toxic and non-toxic substances. Toxic substances
generally exert their effects on organisms through
direct toxicity and the extent of the effect is
dependent on the chemical form of the substance
(e.g. dissolved forms of metals are most toxic),
the concentration and the period of exposure. Non-toxic
substances generally exert their effects on organisms
through direct or indirect means by changing the
natural balance of the physico-chemical environment
through a series of chemical and biological transformations.
For example, nutrients stimulate growth of planktonic
algae which, in turn, affects the light regime in
the water column.
The fate and behaviour of a substance once discharged
to the marine environment is determined to a large
extent by its physico-chemical properties. However,
the concentration and period of exposure of toxic
substances and the chemical and biological transformations
of non-toxic substances are affected by a number
of important processes in the receiving environment.
The effects of each of these on the behaviour and
hazard posed by chemicals introduced into the marine
environment are considered in turn.