indicators such as corals which have yet documented
an anthropogenic enhancement, although it has been
estimated that Hg concentrations in the surface
ocean have increased from 0.5 to 1.5 pmol kg
À1
during the past century.
Other Anthropogenic Elements in the
Ocean
Several other elements have had significant anthropogenic enhancements of global fluxes, but in most
cases, the size of the oceanic reservoir of the elements
is too large for an observable shift in open-ocean
concentrations. A two- to three-fold increase in the
concentration of cadmium (Cd) has been observed in
corals near Bermuda during the past century. However, the concentrations of Cd in surface waters near
Bermuda are low even today (certainlyo10
À11 moles
kg
À1 and sometimes as low as 10
À12 moles kg
À1
; because concentrations in deep waters are two or three
orders of magnitude higher, the oceanic reservoir is
large compared with the anthropogenic enhancement
of Cd in surface waters. Although concentrations of
Zn in corals were not measured, a similar anthropogenic enhancement of emissions to the atmosphere
may well have caused slight enhancements to the Zn
concentrations of the surface ocean, but evidence of
such an increase has not been reported.
Because of the use of tributyl tin as a stabilizer
in PVC plastic (hence an incineration source for inorganic Sn) and as an antifouling agent in marine
paints, there has been some interest in the fate of anthropogenic Sn in the oceanic environment. Inorganic
Sn is very low in the surface waters of the Sargasso Sea
(B3 Â 10
À12 moles kg
À1
). Tributyl tin has been observed in enclosed harbors, but not in the open ocean.
On the whole, however, the size of the ocean
precludes major enhancements of oceanic trace metal
concentrations. Even where the enhancement is clear,
such as for Pb, the concentrations are quite low and
there is no reason to suppose that these enhancements pose a threat to marine biota.
Anthropogenic Trace Metal
Enhancements in Coastal Waters and
Embayments
As opposed to minimal evidence for anthropogenic
trace metal contamination of open-ocean waters, it is
clear that major impacts on the trace metal chemistry
of coastal sea water have occurred and that these
have sometimes had serious consequences. The discharge of untreated industrial and human wastes into
coastal waters, and the release of toxic metals and
metal compounds from antifouling paints have
clearly increased metal concentrations in shallow
ocean waters in many coastal regions.
One of the most notorious examples of coastal
pollution was in Minimata Bay, Japan where from
the 1930s until the 1960s a chemical company
dumped tonnes of mercury, which contaminated the
bay sediments. This Hg pollution entered the marine
food chain. Thousands of people developed severe
neurological symptoms as a result of eating Hgcontaminated fish. This is perhaps the most extreme
example where pollution in the marine environment
has demonstrably harmed humans directly.
More recently, it has been demonstrated that high
Cd, Zn, Cu, and Pb concentrations in Atlantic
coastal waters of southern Spain have risen by many
orders of magnitude due to acid mine drainage from
the Rio Tinto massive sulfides. As yet, little is known
about any human health effects from this trace
element pollution, although the region has an active
coastal fishing industry.
There is too much detail in the many local examples to discuss here, but there is little doubt that
many coastal embayments proximate to big cities
have elevated metal levels, and that an understanding
of the consequences of this pollution is still being
developed. Unfortunately, proper measurement capabilities did not exist until the past two decades, so
there is usually no direct evidence for the degree of
enhancement of dissolved metals relative to preindustrial times. One exception to this situation is in
San Francisco Bay, where the anthropogenic enhancement of dissolved cadmium has been documented by measuring the Cd content of benthic
foraminifera.
An anthropogenic impact on metals in coastal
marine sediments has been demonstrated repeatedly.
Lead has been shown to be enriched in coastal
sediments. Even more exotic elements such as silver
(photography) and osmium (electron microscopy)
are enriched in the sewage of some cities and can be
traced from their source.
Conclusions
The anthropogenic dominance of lead in the openocean environment has been conclusively demonstrated. Although there is evidence that the fluxes of
other elements to the ocean have been enhanced to a
significant degree, there is less direct evidence documenting their enhancements in the open-ocean environment. Coastal waters and sediments near major
278 ANTHROPOGENIC TRACE ELEMENTS IN THE OCEAN
an anthropogenic enhancement, although it has been
estimated that Hg concentrations in the surface
ocean have increased from 0.5 to 1.5 pmol kg
À1
during the past century.
Other Anthropogenic Elements in the
Ocean
Several other elements have had significant anthropogenic enhancements of global fluxes, but in most
cases, the size of the oceanic reservoir of the elements
is too large for an observable shift in open-ocean
concentrations. A two- to three-fold increase in the
concentration of cadmium (Cd) has been observed in
corals near Bermuda during the past century. However, the concentrations of Cd in surface waters near
Bermuda are low even today (certainlyo10
À11 moles
kg
À1 and sometimes as low as 10
À12 moles kg
À1
; because concentrations in deep waters are two or three
orders of magnitude higher, the oceanic reservoir is
large compared with the anthropogenic enhancement
of Cd in surface waters. Although concentrations of
Zn in corals were not measured, a similar anthropogenic enhancement of emissions to the atmosphere
may well have caused slight enhancements to the Zn
concentrations of the surface ocean, but evidence of
such an increase has not been reported.
Because of the use of tributyl tin as a stabilizer
in PVC plastic (hence an incineration source for inorganic Sn) and as an antifouling agent in marine
paints, there has been some interest in the fate of anthropogenic Sn in the oceanic environment. Inorganic
Sn is very low in the surface waters of the Sargasso Sea
(B3 Â 10
À12 moles kg
À1
). Tributyl tin has been observed in enclosed harbors, but not in the open ocean.
On the whole, however, the size of the ocean
precludes major enhancements of oceanic trace metal
concentrations. Even where the enhancement is clear,
such as for Pb, the concentrations are quite low and
there is no reason to suppose that these enhancements pose a threat to marine biota.
Anthropogenic Trace Metal
Enhancements in Coastal Waters and
Embayments
As opposed to minimal evidence for anthropogenic
trace metal contamination of open-ocean waters, it is
clear that major impacts on the trace metal chemistry
of coastal sea water have occurred and that these
have sometimes had serious consequences. The discharge of untreated industrial and human wastes into
coastal waters, and the release of toxic metals and
metal compounds from antifouling paints have
clearly increased metal concentrations in shallow
ocean waters in many coastal regions.
One of the most notorious examples of coastal
pollution was in Minimata Bay, Japan where from
the 1930s until the 1960s a chemical company
dumped tonnes of mercury, which contaminated the
bay sediments. This Hg pollution entered the marine
food chain. Thousands of people developed severe
neurological symptoms as a result of eating Hgcontaminated fish. This is perhaps the most extreme
example where pollution in the marine environment
has demonstrably harmed humans directly.
More recently, it has been demonstrated that high
Cd, Zn, Cu, and Pb concentrations in Atlantic
coastal waters of southern Spain have risen by many
orders of magnitude due to acid mine drainage from
the Rio Tinto massive sulfides. As yet, little is known
about any human health effects from this trace
element pollution, although the region has an active
coastal fishing industry.
There is too much detail in the many local examples to discuss here, but there is little doubt that
many coastal embayments proximate to big cities
have elevated metal levels, and that an understanding
of the consequences of this pollution is still being
developed. Unfortunately, proper measurement capabilities did not exist until the past two decades, so
there is usually no direct evidence for the degree of
enhancement of dissolved metals relative to preindustrial times. One exception to this situation is in
San Francisco Bay, where the anthropogenic enhancement of dissolved cadmium has been documented by measuring the Cd content of benthic
foraminifera.
An anthropogenic impact on metals in coastal
marine sediments has been demonstrated repeatedly.
Lead has been shown to be enriched in coastal
sediments. Even more exotic elements such as silver
(photography) and osmium (electron microscopy)
are enriched in the sewage of some cities and can be
traced from their source.
Conclusions
The anthropogenic dominance of lead in the openocean environment has been conclusively demonstrated. Although there is evidence that the fluxes of
other elements to the ocean have been enhanced to a
significant degree, there is less direct evidence documenting their enhancements in the open-ocean environment. Coastal waters and sediments near major
278 ANTHROPOGENIC TRACE ELEMENTS IN THE OCEAN