The adverse effects of metals on human health were
recognized in the 1950s and 1960s following catastrophic events involving mercury. Inorganic mercury is normally excreted by humans and poses little
hazard to the general public. However, organic
mercury compounds, such as methylated forms, are
not readily excreted. Methylated mercury compounds can pass to all tissues in the body after absorption from the gastrointestinal tract. They can
cross diffusion barriers and penetrate membranes,
such as the blood–brain barrier (causing irreversible
brain damage) and the placenta (rendering methylated mercury concentrations in fetal blood higher
than those in the mother). The most significant outbreak of neurological, and often fatal illnesses occurred among the residents of Minamata in Japan.
Chemical companies had discharged or dumped
tonnes of mercury compounds into Minamata Bay
for decades and these accumulated in the tissues of
shellfish and fish. Consequently, large doses were
passed onto the local, fish-eating population. Eventually the Bay was sealed off with nets to prevent
organisms contaminated with mercury from escaping
and affecting other areas. Over several decades biogeochemical processes and hydrodynamic flushing of
mercury from the Bay have resulted in concentrations of mercury falling below government
standards. Presently, the World Health Organization
(WHO) regards a tolerable daily intake of total
mercury (inorganic þ organic) to be 50 mg d
À1 for an
adult of 70 kg.
Human exposure to high concentrations of cadmium are rare and current concern centers around
the chronic toxicity caused by long-term exposure to
low levels of the metal. Bone disorders are one
manifestation of chronic cadmium exposure. Cadmium is present in all tissues of adults, with the most
significant amounts found in the liver and kidney,
and the concentrations tend to increase with age. The
WHO regards a tolerable daily intake of cadmium to
be 70 mg d
À1 for an adult of 70 kg.
Conclusions
Despite coastal waters in the vicinity of urban and
industrial regions being contaminated with metals,
there exists no evidence of significant pollution that
poses a threat to human health, except on a local
scale (and usually in shellfish) or where control has
been poor. Since the dominant temporary or ultimate
sink for metal contaminants is the sediment, an important goal of current research is to understand
the mechanisms and extent to which contaminants
are extracted by organisms (i.e., contaminant
bioavailability) and transferred within the marine
food chain.
Glossary
Advection Horizontal water motion.
Bioavailable metals Dissolved and particulate
metals that are accessible to organisms during
normal metabolic activity.
Bioaccumulative metals Metals that can be
regulated and reside in the organism and are
added to over its life.
Biomagnified metals Metals that are not regulated
by organisms that can acquire an even larger body
burden of metals.
Bioturbation Reworking of bottom sediment by
burrowing marine organisms.
Diagenesis Release of particulate metals into the
dissolved phase under suboxic conditions.
Flushing time The time required for an existing
body of water to be exchanged with surrounding
water.
Upwelling Vertical, upward movement of water at
the shelf break, often tidally induced.
See also
Anthropogenic Trace Elements in the Ocean.
Atmospheric Input of Pollutants. Land–Sea Global
Transfers. Metalloids and Oxyanions. Pore Water
Chemistry. Refractory Metals. River Inputs.
Transition Metals and Heavy Metal Speciation.
Further Reading
Baeyens W (1998) Evolution of trace metal concentrations
in the Scheldt estuary (1978–1995). A comparison with
estuarine and ocean levels. Hydrobiologia 366:
157--167.
Clark RB (1998) Marine Pollution 4th edn. Oxford: Clarendon Press.
Ebinghaus R (ed.) (1997) Regional and Global Cycles of
Mercury: Source, Fluxes and Mass Balances. NATO
Series, Amsterdam: Kluwer Press.
GESAMP: Group of Experts on Scientific Aspects
of Marine Pollution (1990) The State of the Marine
Environment. Nairobi, Kenya: United Nations Environment Programme.
Langston WJ and Bebianno MJ (eds.) (1998) Metal Metabolism in Aquatic Environments. London: Chapman
and Hall.
Lowry R, Cramer RN, and Rickards LJ (1992) North Sea
Project CD ROM and Users Guide. Swindon: British
Oceanographic Data Centre, Natural Environment
Research Council of the United Kingdom.
METAL POLLUTION 271
recognized in the 1950s and 1960s following catastrophic events involving mercury. Inorganic mercury is normally excreted by humans and poses little
hazard to the general public. However, organic
mercury compounds, such as methylated forms, are
not readily excreted. Methylated mercury compounds can pass to all tissues in the body after absorption from the gastrointestinal tract. They can
cross diffusion barriers and penetrate membranes,
such as the blood–brain barrier (causing irreversible
brain damage) and the placenta (rendering methylated mercury concentrations in fetal blood higher
than those in the mother). The most significant outbreak of neurological, and often fatal illnesses occurred among the residents of Minamata in Japan.
Chemical companies had discharged or dumped
tonnes of mercury compounds into Minamata Bay
for decades and these accumulated in the tissues of
shellfish and fish. Consequently, large doses were
passed onto the local, fish-eating population. Eventually the Bay was sealed off with nets to prevent
organisms contaminated with mercury from escaping
and affecting other areas. Over several decades biogeochemical processes and hydrodynamic flushing of
mercury from the Bay have resulted in concentrations of mercury falling below government
standards. Presently, the World Health Organization
(WHO) regards a tolerable daily intake of total
mercury (inorganic þ organic) to be 50 mg d
À1 for an
adult of 70 kg.
Human exposure to high concentrations of cadmium are rare and current concern centers around
the chronic toxicity caused by long-term exposure to
low levels of the metal. Bone disorders are one
manifestation of chronic cadmium exposure. Cadmium is present in all tissues of adults, with the most
significant amounts found in the liver and kidney,
and the concentrations tend to increase with age. The
WHO regards a tolerable daily intake of cadmium to
be 70 mg d
À1 for an adult of 70 kg.
Conclusions
Despite coastal waters in the vicinity of urban and
industrial regions being contaminated with metals,
there exists no evidence of significant pollution that
poses a threat to human health, except on a local
scale (and usually in shellfish) or where control has
been poor. Since the dominant temporary or ultimate
sink for metal contaminants is the sediment, an important goal of current research is to understand
the mechanisms and extent to which contaminants
are extracted by organisms (i.e., contaminant
bioavailability) and transferred within the marine
food chain.
Glossary
Advection Horizontal water motion.
Bioavailable metals Dissolved and particulate
metals that are accessible to organisms during
normal metabolic activity.
Bioaccumulative metals Metals that can be
regulated and reside in the organism and are
added to over its life.
Biomagnified metals Metals that are not regulated
by organisms that can acquire an even larger body
burden of metals.
Bioturbation Reworking of bottom sediment by
burrowing marine organisms.
Diagenesis Release of particulate metals into the
dissolved phase under suboxic conditions.
Flushing time The time required for an existing
body of water to be exchanged with surrounding
water.
Upwelling Vertical, upward movement of water at
the shelf break, often tidally induced.
See also
Anthropogenic Trace Elements in the Ocean.
Atmospheric Input of Pollutants. Land–Sea Global
Transfers. Metalloids and Oxyanions. Pore Water
Chemistry. Refractory Metals. River Inputs.
Transition Metals and Heavy Metal Speciation.
Further Reading
Baeyens W (1998) Evolution of trace metal concentrations
in the Scheldt estuary (1978–1995). A comparison with
estuarine and ocean levels. Hydrobiologia 366:
157--167.
Clark RB (1998) Marine Pollution 4th edn. Oxford: Clarendon Press.
Ebinghaus R (ed.) (1997) Regional and Global Cycles of
Mercury: Source, Fluxes and Mass Balances. NATO
Series, Amsterdam: Kluwer Press.
GESAMP: Group of Experts on Scientific Aspects
of Marine Pollution (1990) The State of the Marine
Environment. Nairobi, Kenya: United Nations Environment Programme.
Langston WJ and Bebianno MJ (eds.) (1998) Metal Metabolism in Aquatic Environments. London: Chapman
and Hall.
Lowry R, Cramer RN, and Rickards LJ (1992) North Sea
Project CD ROM and Users Guide. Swindon: British
Oceanographic Data Centre, Natural Environment
Research Council of the United Kingdom.
METAL POLLUTION 271