Discharges
of heavy metals
ME-5
Marine
Environment & Coastal Zones
Pressure
1 Indicator
definition and unit of measurement
The
amount of heavy metals emitted directly or indirectly (via rivers) into the
coastal zone and marine environment. Unit: tonnes or grams depending on
metal/annum
.
2 Placement
in the framework
5EAP:
Calls
for a “r
eduction
of discharges of all substances which due to their toxic persistence or
accumulating impact could negatively affect the environment, to levels which
are not harmful...
”
Agenda
21:
Chapter
17
:
Protection
of the oceans, seas and coastal areas and the protection, rational use and
development of their living resources
.
Chapter
20
:
Environmentally-sound
management of hazardous wastes
.
International
conventions and agreements:
Reductions
of emissions to waters are agreed in
OSPARCOM
(Oslo, 1972 and Paris, 1974),
HELCOM
(Helsinki, 1994)
and
the North Sea
Ministerial
Conference (Esbjerg Declaration, 1995)
.
Individual heavy metal reduction and control laws e.g. Cadmium Directive
83/513/EEC and the Mercury directive 84/156/EEC, regulating the discharge of
respective metals from industrial processes and setting quality objective for
receiving waters
.
Ranking:
Core
ranking:
5
(34%)
Policy
Relevance:
9
(2.9)
Analytical
Soundness:
2
(3.1)
Responsiveness:
2
(2.8)
Most
appropriate related state indicator:
Heavy
metal concentrations in marine sediments and in
selected
bioindicator organisms.
3 Significance
Purpose:
•
Give politician
s/the
public
a picture of key heavy metal losses to the coastal and marine environment in
chosen areas or from
selected
sources
.
•
Review
additive effect of individual heavy metal emission licenses
.
•
If coupled with state indicator, should show effectiveness of legislation to
control heavy metal discharges
.
Relevance:
Heavy
metal is a category of metal elements with a specific weight exceeding 5 g/cm
3.
In
the
list
below, those heavy metals underlined are most commonly measured as widely
significant in the coastal and marine environment
:
Antimony,
Arsenic*,
Beryllium,
Cadmium,
Chromium,
Cobalt,
Copper,
Lead, Mercury, Molybdenum, Nickel, Selenium,
Silver, Tellurium, Thallium, Tin, Titanium, Uranium, Vanadium and
Zinc.
(*Often
arsenic, a non metal is discussed as though member of the group.)
Many
are needed in trace amounts, but become toxic to animals and plants in larger
doses, degree depending on metal. Heavy metals are persistent. Most can
accumulate in organisms and so even small amounts in sea water or sediment may
become significant to the top of the food chain. Some heavy metals of little
toxicity or problem in themselves - like tin - form complexes with organic
materials to produce highly toxic compounds like TBT (tributyltin) used as
antifowling paint.
Linkages
to other pressure indicators:
In
M
arine
Environment,
links to causes
,
ME-4: H
eavy
metal discharges associated with ore extraction.
In
Dispersion
of Toxic Substances,
TX-5:
Heavy
metal emissions to air and
TX-4:
H
eavy
metal emissions to water.
Targets:
In
EC Towards Sustainability 1997
:
Reduction
of discharges of all substances which due to their toxic persistence or
accumulating impact could negatively affect the environment, to levels which
are not harmful...
”
4 Methodological
description and underlying definitions
Underlying
definitions and concepts:
Specific
heavy metals such as cadmium, copper, mercury have been known to be toxic for
centuries. Losses to the marine and coastal environment can be noted during all
stages of a metal lifecycle, from mining, over
-use,
to component of waste. The metals
(though
not all complexes) can be measured accurately using standard methods and a
large amount of data has been collected on heavy metal concentrations and
effects. Heavy metals are naturally occurring. There are limit values set for
all metals in water discharges from various larger industries. There have been
several attempts to pool key heavy metal levels into one biotic index of
sediment quality - i.e. state indicators.
Measurement
methods:
Atomic
Absorption Spectrometry (for
selected
h
eavy
metals
additionally other or better, e.g. radio
-metric
for
uranium)
.
Limitations
of the indicator:
There
are considerable limitations to the use of heavy metal emissions to the marine
and coastal environment as pressure indicator. An aggregate
d
indicator made up of components with very different properties and toxicity
levels needs to be carefully assessed. Input of a gram of mercury may be
equivalent to a tonne of nickel. How will our indicator convey this
?
At minimum, one should be able to dismember the figure given for a set area
into component heavy metal levels and weigh component heavy metals according to
toxicity.
As
heavy metals can arise from so many sources and only some of these are licensed
and monitored, a significant part of the indicator value is likely to be a
guestemate if all input to the marine and coastal environment is to be included.
One
problem of heavy metal discharges in the marine environment is their relocation
from river estuaries and harbour muds to new sites as these areas are dredged
and the dredge spoil may be deposited in or near uncontaminated areas. If we
use the indicator too globally - total input per annum in a country, or sea
area, this very significant point will be lost. Close cooperation with state
indicators could tackle this weakness.
Alternative
definitions:
It
may be wiser to only include those heavy metal discharges which we can
calculate quickly and relatively accurately. In this way one would not give the
full picture but at least a sharper picture of a fraction of the total input.
Most data would come from monitoring licensed discharge, flue gas monitoring.
This could be augmented by indirect input such as riverine heavy metal loads
(some
of which will be natural) and mean heavy metal emissions calculated from
certain class
es
of vessels and vehicles per km journey in the marine and coastal area.
