Geography Reference
In-Depth Information
Table 11.4
Concentrations (µg
-1
) of selected
metals in roof, street and stormwater runoff
recorded in the Karlsruhe/Waldstadt region of
Germany.
chemical substances have been identified in lists
drawn up by the World Health Organization, the
US Environmental Protection Agency and the
European Community on the basis of toxicity,
persistence, biological accumulation and presence
in the environment (e.g. EEC 1982; WHO 1984).
Toxic organic substances enter freshwaters
through point and diffuse source inputs. The
former comprise effluents from major industrial
activities, such as petrol refining, coal mining and
the manufacture of synthetic products, while the
latter include organic pollutants carried in runoff
from urban and agricultural areas, often in
sediment-associated form. Organic
micropollutants originating from household and
industrial use include volatile organic substances
employed as extraction, degreasing and
drycleaning solvents and as aerosol propellants, the
halogenated derivatives of methane, ethane and
ethylene, and polycyclic aromatic hydrocarbons
(PAHs) from petroleum products and their
combustion. These substances have a high rate of
environmental dispersion compared with the
amount produced (Meybeck
et al
. 1989). Other
organic micropollutants originating from mainly
industrial processes have low rates of
environmental dispersion and include chlorinated
derivatives of benzene, naphthalene, phenol and
aniline, which are used in dyestuff manufacture,
and polychlorinated biphenyls (PCBs), which are
constituents of heat-exchange fluids and dielectric
substances.
Synthetic organic pesticides used in
agriculture and in horticulture have a high
potential to pollute water from direct runoff,
spray drift and their storage, handling and
disposal (Environment Agency 1997a). A wide
range of chemicals are employed in pesticides.
For example, about 450 active ingredients are
currently approved for use in the UK, and they
vary greatly in their physico-chemical
characteristics, including water solubility.
Pesticides have been grouped into
organochlorine insecticides, organophosphate
insecticides, herbicides of the plant hormone
type, triazines, substituted ureas and others
(Meybeck
et al
. 1989). Many countries ban or
Source:
Xanthopolous and Hahn 1993.
may be remobilised in the fluvial system at a later
date by, for example, channel reworking of
floodplain deposits (e.g. Bradley 1995).
Data on heavy metals in freshwaters are not
routinely collected in many countries (Meybeck
et al
. 1989) and few long-term records of river
concentrations exist. Information on sediment-
associated metal concentrations at sampling sites
on the Rhine and other rivers in the Netherlands
(Salomons and Förstner 1984) reveal a steady
increase during the twentieth century until 1975,
when controls on waste water inputs of metals led
to a decline. Reductions in atmospheric emission
of heavy metals from coal-burning power stations
and other sources over the last fifteen years in the
UK and elsewhere (e.g. Quality of Urban Air
Group 1993) may also be a significant cause of
lower freshwater concentrations in recent years in
some systems.
Organic micropollutants
It has been estimated that about 4 million
chemical compounds are in existence (Meybeck
et al
. 1989), and more than 100,000 commercial
chemicals are known or suspected of causing
health problems in humans, animals and plants
(Peters
et al
. 1998). Recently, there has been
growing concern that some chemicals in river and
drinking water may cause hormone disruption in
aquatic wildlife and adversely affect the
reproductive health of humans (Environment
Agency 1997a). Particularly hazardous organic
