ANTHROPOGENIC TRACE ELEMENTS IN THE
OCEAN
E. A. Boyle, Massachusetts Institute of Technology,
Cambridge, MA, USA
Copyright & 2001 Elsevier Ltd.
Introduction
Human activities have increased the fluxes of several
chemical elements into the ocean above natural
levels. Despite convincing evidence for this enhancement of elemental fluxes (see Further Reading
section for references relevant to the discussion in
this article), there is only one element – lead (Pb) –
where abundant evidence proves that open-ocean
seawater concentrations are substantially higher than
they were in preindustrial times. For a few other
elements – e.g. cadmium (Cd) and mercury (Hg) –
there is some evidence suggesting a detectable anthropogenic impact (or models indicating that an
anthropogenic enhancement must exist even if it has
not been observed). For most other elements, the size
of the oceanic reservoir of these elements overwhelms relatively large anthropogenic fluxes, and it
may require centuries of further inputs before the
human impact can be discerned.
Anthropogenic Lead in the Ocean
Sampling and analysis for Pb have been difficult because of low concentrations and abundant contamination sources: lead paint, lead weights, and gasoline
exhausts. The latter source is now substantially reduced, so perhaps the current Pb contamination
problem is less serious than it was in the 1980s.
Patterson and co-workers were the first to call attention to the overwhelming anthropogenic augmentation of Pb fluxes into the environment,
particularly that resulting from alkyl leaded gas utilization. Patterson’s evidence began with the demonstration that Pb deposition in remote Greenland
snows had increased by two orders of magnitude. In
the late 1970s/early 1980s, his laboratory obtained
the first valid data (uncontaminated and properly
analyzed) for the vertical distribution of Pb in water
sample profiles from the North Atlantic, North
Pacific, and South Tropical Pacific (Figure 1). These
data demonstrated that the highest concentrations of
Pb occurred in the surface ocean and that
concentrations decreased with increasing depth in the
water column. At that time, the highest Pb concentrations were found in the North Atlantic Ocean
(160 Â 10
À12
moles kg
À1 at the surface decreasing to 26 Â 10
À12
moles kg
À1 at 3000 m water depth). The high Pb
concentrations in this basin are emitted from the
major industrial nations surrounding the basin.
Lower Pb concentrations were seen in North Pacific
surface waters (60 Â 10
À12 moles kg
À1 at the surface
decreasing to 5 Â 10
À12 moles kg
À1 at 3500 m depth),
and the lowest concentrations in the south tropical
Pacific (20 Â 10
À12 moles kg
À1 at the surface decreasing to 4 Â 10
À12 moles kg
À1 at 4000 m). In Patterson’s view, this evidence proved the anthropogenic
origin of Pb in the modern ocean.
The lead industry attempted to discredit Patterson’s evidence on environmental Pb pollution by
many spurious arguments. Although they were not
clever enough, they might have attempted to discredit Patterson’s interpretation of his oceanic Pb
data by pointing out that similar comparative concentration variations occur for aluminum (Al) in the
ocean, even though oceanic Al is entirely of natural
origin. Al is released from terrestrial dusts blown
into the ocean and ‘scavenged’ onto sinking biologically produced particles that remove it from the
deep ocean. Therefore Al is high in the surface ocean,
highest downwind of major dust sources such as
north-west Africa, and lowest in the South Pacific
because of low dust inputs to the surface and cumulative scavenging in the deep waters.
Lead was phased out of gasoline in the USA (followed soon by Canada and Japan, and somewhat
later by western Europe and a few other countries)
beginning in 1970 when the US Environmental Protection Agency mandated emissions controls on gasoline exhausts. Originally, controls on lead emissions
were not the goal of the regulations; the regulations
were formulated to minimize emissions of hydrocarbons, nitrogen oxides, and carbon monoxide. As it
turned out, the technological fix for those problems
was to use catalytic converters on the exhaust stream,
and the activity of the catalysts was destroyed by lead
exhausts. Hence leaded gasoline could not be used
with catalytic converters, and regulations mandated
the elimination of leaded gasoline. Later, regulations
specifically directed at minimizing lead emissions into
the environment were also enacted.
273
OCEAN
E. A. Boyle, Massachusetts Institute of Technology,
Cambridge, MA, USA
Copyright & 2001 Elsevier Ltd.
Introduction
Human activities have increased the fluxes of several
chemical elements into the ocean above natural
levels. Despite convincing evidence for this enhancement of elemental fluxes (see Further Reading
section for references relevant to the discussion in
this article), there is only one element – lead (Pb) –
where abundant evidence proves that open-ocean
seawater concentrations are substantially higher than
they were in preindustrial times. For a few other
elements – e.g. cadmium (Cd) and mercury (Hg) –
there is some evidence suggesting a detectable anthropogenic impact (or models indicating that an
anthropogenic enhancement must exist even if it has
not been observed). For most other elements, the size
of the oceanic reservoir of these elements overwhelms relatively large anthropogenic fluxes, and it
may require centuries of further inputs before the
human impact can be discerned.
Anthropogenic Lead in the Ocean
Sampling and analysis for Pb have been difficult because of low concentrations and abundant contamination sources: lead paint, lead weights, and gasoline
exhausts. The latter source is now substantially reduced, so perhaps the current Pb contamination
problem is less serious than it was in the 1980s.
Patterson and co-workers were the first to call attention to the overwhelming anthropogenic augmentation of Pb fluxes into the environment,
particularly that resulting from alkyl leaded gas utilization. Patterson’s evidence began with the demonstration that Pb deposition in remote Greenland
snows had increased by two orders of magnitude. In
the late 1970s/early 1980s, his laboratory obtained
the first valid data (uncontaminated and properly
analyzed) for the vertical distribution of Pb in water
sample profiles from the North Atlantic, North
Pacific, and South Tropical Pacific (Figure 1). These
data demonstrated that the highest concentrations of
Pb occurred in the surface ocean and that
concentrations decreased with increasing depth in the
water column. At that time, the highest Pb concentrations were found in the North Atlantic Ocean
(160 Â 10
À12
moles kg
À1 at the surface decreasing to 26 Â 10
À12
moles kg
À1 at 3000 m water depth). The high Pb
concentrations in this basin are emitted from the
major industrial nations surrounding the basin.
Lower Pb concentrations were seen in North Pacific
surface waters (60 Â 10
À12 moles kg
À1 at the surface
decreasing to 5 Â 10
À12 moles kg
À1 at 3500 m depth),
and the lowest concentrations in the south tropical
Pacific (20 Â 10
À12 moles kg
À1 at the surface decreasing to 4 Â 10
À12 moles kg
À1 at 4000 m). In Patterson’s view, this evidence proved the anthropogenic
origin of Pb in the modern ocean.
The lead industry attempted to discredit Patterson’s evidence on environmental Pb pollution by
many spurious arguments. Although they were not
clever enough, they might have attempted to discredit Patterson’s interpretation of his oceanic Pb
data by pointing out that similar comparative concentration variations occur for aluminum (Al) in the
ocean, even though oceanic Al is entirely of natural
origin. Al is released from terrestrial dusts blown
into the ocean and ‘scavenged’ onto sinking biologically produced particles that remove it from the
deep ocean. Therefore Al is high in the surface ocean,
highest downwind of major dust sources such as
north-west Africa, and lowest in the South Pacific
because of low dust inputs to the surface and cumulative scavenging in the deep waters.
Lead was phased out of gasoline in the USA (followed soon by Canada and Japan, and somewhat
later by western Europe and a few other countries)
beginning in 1970 when the US Environmental Protection Agency mandated emissions controls on gasoline exhausts. Originally, controls on lead emissions
were not the goal of the regulations; the regulations
were formulated to minimize emissions of hydrocarbons, nitrogen oxides, and carbon monoxide. As it
turned out, the technological fix for those problems
was to use catalytic converters on the exhaust stream,
and the activity of the catalysts was destroyed by lead
exhausts. Hence leaded gasoline could not be used
with catalytic converters, and regulations mandated
the elimination of leaded gasoline. Later, regulations
specifically directed at minimizing lead emissions into
the environment were also enacted.
273