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Zinc in the Ocean

Authors:
  • Battelle Memorial Institute, Duxbury, MA

Abstract and Figures

Reported concentrations of zinc in seawater vary widely, probably due both to variability in concentrations actually present and to sample contamination. Zinc and iron often seem to co-occur in seawater samples. The concentrations of zinc in seawater are anomalously high. A large fraction of the zinc entering the oceans of the world is derived from aerial deposition. Between 11,000 and 60,000 metric tons of dissolved and particulate zinc is deposited from the air into the ocean each year. An additional 6,000 tons of dissolved zinc enters the oceans each year in river flows. Flux rates of zinc from the atmosphere vary widely in different geographic regions. Zinc concentrations in estuaries and coastal waters frequently are much higher than those in the ocean, with concentrations often as high as 4 μg/L and occasionally as high as 25 μg/L. A large fraction of the zinc in contaminated and uncontaminated sediments is residual, rendering it non-bioavailable. The residual zinc may be associated with the mineral lattice of clays or with a variety of heavy minerals.
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10.1 ZINC IN SEAWATER
A large fraction of the zinc entering the oceans of the world is derived from aerial
deposition. Between 11,000 and 60,000 metric tons of dissolved and particulate zinc is
deposited from the air into the ocean each year (Jickells, 1995). An additional 6,000 tons
of dissolved zinc enters the oceans each year in river flows. Flux rates of zinc from the
atmosphere vary widely in different geographic regions from 24 to 58 µg/m2/y in the
South Pacific to nearly 80,000 µg/m2/y in the North Sea (Chester and Murphy, 1990).
More recent estimates of the flux of zinc from the atmosphere to coastal waters of north-
ern Europe are in the range of 2681 to 16,414 µg/m2/y (Cabon and Le Bihan, 1996).
Estimated fluxes of zinc from the atmosphere to the land in Florida are in the range of
5320 to 11,920 µg/m2/y (Landing et al., 1995). Average dissolved and particulate zinc
concentrations in the Mississippi River are 0.2 µg/L and 180 µg/g dry wt, respectively
(Trefry et al., 1986). Based on these concentrations, the Mississippi River contributes
approximately 38,000 metric tons/y of zinc, most of it particulate, to the Gulf of Mexico.
Reported concentrations of zinc in seawater vary widely, probably due both to vari-
ability in concentrations actually present and to sample contamination. Zinc and iron
often seem to co-occur in seawater samples as a result of laboratory contamination from
metal surfaces in the field and laboratory (Martin et al., 1993; Bruland et al., 1994).
Thus, many reported concentrations of zinc in seawater are anomalously high.
Examples of recently published concentrations of zinc in marine and coastal waters
of the world are summarized in Table 66. Zinc concentrations in surface waters of the
North Atlantic and North Pacific Oceans are in the range of 0.006 to 0.12 µg/L and
increase to more than 0.5 µg/L in the deep sea (Pohl et al., 1993; Bruland et al., 1994).
Zinc concentrations in surface waters tend to decrease with increasing distance from
shore. For example, the concentration of zinc in surface waters of the mid-Atlantic
southwest of Great Britain is about 0.02 µg/L; the concentration increases to about
0.10 µg/L in the English Channel (Ellwood and van den Berg (2000). Zinc concentra-
tions are higher in Antarctic waters than in ocean waters at lower latitudes (Nolting and
CHAPTER 10
Zinc in the Ocean
175
de Baar, 1994; Löscher, 1999). Zinc concentrations range from 0.09 to 0.81 µg/L in sur-
face waters of the Scotia and Weddell Seas and increase to 0.46 to 0.98 µg/L at a depth
of 300 m. Concentrations tend to increase toward the south and the ice edge and co-vary
with silicate concentrations. The high concentrations of zinc in Antarctic waters are
derived from upwelling of zinc-rich deep-ocean water.
Zinc concentrations in estuaries and coastal waters frequently are much higher than
those in the ocean, with concentrations often as high as 4 µg/L and occasionally as high
as 25 µg/L (Morse et al., 1993; Law et al., 1994). Waters of the Tay River Estuary,
Scotland, contain 0.6 to 3.6 µg/L dissolved zinc; in most seasons, the concentration is
highest in the low-salinity reaches of the estuary (Owens and Balls, 1997). Waters of
estuaries receiving drainage from metal mining areas or metal smelters may contain
more than 1,000 µg/L zinc (Bloom and Ayling, 1977). Some of this water-borne zinc
may be present as microparticulate zinc sulfide (sphalerite: ZnS). Sacrificial anodes and
base paints for submerged steel surfaces, used frequently on offshore platforms and in
ports and marinas, release zinc to the ambient waters. Zinc concentrations in the water
of open, well-mixed marinas may be 2 to 4 µg/L higher than in open coastal waters and
may be as high as 20 µg/L in the water of enclosed marinas, due to leaching from sacri-
ficial anodes (Bird et al., 1996).
A significant fraction of the total zinc in seawater may be adsorbed to particles or
complexed with dissolved organic matter. More than 90 percent of the zinc in waters of
Galveston Bay, TX, is complexed to colloidal organic matter (Wen et al., 1999). The
binding to colloids is much stronger than to suspended particles. Less than 10 percent of
the total zinc in surface waters of the central Pacific is particulate (Bruland et al., 1994).
Most of the adsorbed zinc is leached with weak acid, indicating that it is weakly bound.
176 Bioaccumulation in Marine Organisms
Table 66.
Concentrations of dissolved zinc in oceanic and coastal waters of the world based on recent
(>1990) determinations. Concentrations are µg/L.
More than 98 percent of the dissolved zinc in surface waters of the central Pacific is com-
plexed strongly with dissolved organic ligands, resulting in a free zinc ion concentration
of approximately 0.0001 to 0.0009 µg/L (Bruland, 1989; Bruland et al., 1994). Between
96 and 99 percent of the zinc in surface waters of the North Atlantic Ocean is complexed
to an organic ligand (Ellwood and van den Berg, 2000). The zinc binding ligand is pres-
ent in surface waters at a concentration of 0.4 to 2.5 nM; the concentration does not
change much with depth. Because of the high affinity of the organic ligand for zinc, most
of the dissolved zinc in seawater is complexed, leaving very little as free ionic zinc
(Zn+2). Ellwood and van den Berg (2000) estimate that the concentration of free Zn+2 in
the surface waters of the open North Atlantic Ocean is 0.0004 to 0.001 µg/L; the con-
centration increases to about 0.01 µg/L in surface coastal and deep offshore waters.
About 26 percent of the total zinc in surface waters of the Irish Sea and 54 percent of
the total zinc in surface waters of the southern North Sea is adsorbed to suspended parti-
cles (Jones and Jeffries, 1983). These particles contain averages of about 210 and 1,160
µg/g zinc, respectively. The concentration of particulate zinc in surface waters of the
North Atlantic Ocean containing 0.032 to 0.447 mg/L suspended particulate matter is
0.004 ± 0.003 µg/L (Kuss and Kremling, 1999). The suspended particles contain an aver-
age of 28 ± 16 µg/g zinc. Luther et al. (1986) showed that 4 to 50 percent of the dissolved
zinc in seawater from Newark Bay, New Jersey, is non-labile, and probably is associated
with inorganic and organic colloidal material. The dominant inorganic colloidal phase
consists of particles (<0.04 µm) of zinc sulfide. The organic colloidal phase includes zinc
complexes with humic acids and organic material from municipal sewage discharges.
Zinc complexes with dissolved or colloidal organic matter generally are quite stable
(Piotrowizc et al., 1982; Muller and Kester, 1991), and so are not bioavailable or toxic.
Zinc forms a variety of inorganic complexes in seawater, the relative proportion of
different complexes depending on seawater salinity and pH (Zirino and Yamamoto,
1972; Bernhard et al., 1975; Turner et al., 1981; Amdurer et al., 1983). Uncomplexed
zinc (Zn+2), the most bioavailable species, may represent 17 to 46 percent of the total dis-
solved zinc at the pH of seawater. The quantitatively most important dissolved or
microparticulate zinc complexes or compounds in seawater at a pH of 8.1 are Zn(OH)2,
ZnCl,+ ZnCl2, and ZnCO3. Complexes with S-2 or HS-and microparticulate ZnS also
may be present in anoxic waters (Al-Farawati and Van den Berg, 1999).
10.2 ZINC IN MARINE SEDIMENTS
Concentrations of zinc in marine and estuarine sediments vary widely. Zinc concen-
trations in surficial sediments from the continental shelf of the southeastern United
States are in the range of 3 to 10 µg/g (Bothner et al., 1980a). Concentrations of zinc in
surficial sediments from Georges Bank off the New England coast range from 1.2 to
71 µg/g, with the highest concentrations being associated with the finest-grained
sediments (Bothner et al., 1985). Zinc concentrations may be high in uncontaminated
sediments remote from human activities. The <63 µm fraction of sediments from Terra
Nova Bay, Antarctica, contains 75 to 155 µg/g dry wt. zinc (Giordano et al., 1999). The
zinc may be associated with natural heavy mineral particles in the sediments.
Zinc concentrations in nearshore marine sediments from the central Maine coast are
higher, ranging from 53.8 µg/g to 287 µg/g (Larsen and Gaudette, 1995). Sediments
from San Francisco Bay contain 140 to 1,890 µg/g zinc (Luoma and Phillips, 1988).
Chapter 10 – Zinc in the Ocean 177
Mean zinc concentrations in sediments from the Bilbao Estuary, Spain, vary seasonally
from 536 to 5261 µg/g dry wt (Ruiz and Saez-Salinas, 2000). High concentrations of
sediment zinc are associated with drought and low river flows. Very high concentrations
of zinc may be found in sediments near major point sources. Zinc concentrations up to
100,000 µg/g are present in sediments near the wharf of a zinc refining company on
the Derwent Estuary, Tasmania (Bloom and Ayling, 1977). Zinc concentrations up to
10,000 µg/g in sediments extend for several kilometers downstream from the wharf. The
“high” concentration of zinc in National Status and Trends Program sediments from the
U.S. coasts is 135 µg/g (Table 24).
Zinc concentrations in sediments from Galveston Bay, TX, are in the range of 6 to
116 µg/g (Morse et al., 1993). Most of the zinc is associated with the clay fraction and
about 44 percent is non-residual. Sediments from the coastal zone of Louisiana contain
52 to 133 µg/g zinc (Pardue et al., 1988). Concentrations of zinc in surficial sediments
near six produced water discharges to coastal and offshore waters of the northwestern
Gulf of Mexico are in the range of 24.3 to 268 µg/g (Neff et al., 1989b; Trefry et al.,
1995, 1996). The produced water discharges do not seem to contribute to the zinc con-
centrations in sediments near the platforms. A major source of zinc in these sediments
probably is the Mississippi River; suspended sediments in the river contain an average
of about 160 µg/g zinc (Trefry et al., 1996).
A large fraction of the zinc in contaminated and uncontaminated sediments may be
residual (part of the mineral lattice of sediment particles or present in heavy minerals),
rendering it not bioavailable (Warren, 1981; Loring, 1982). The residual zinc may be
associated with the mineral lattice of clays or with a variety of heavy minerals. Chromite,
ilmenite, and magnetite contain up to 8,000, 2,400, and 800 µg/g zinc, respectively
(Baker, 1962). From 86 to 91 percent of the total zinc (18 to 104 µg/g) in Bay of Fundy
sediments is residual (Loring, 1982). Sphalerite (ZnS) and zincite (ZnO) are important
detrital carriers of zinc in these sediments. Zinc in noncarbonate pelagic sediments
(Förstner and Stoffers, 1981) and surficial sediments from the Fraser River Estuary,
Canada, (Grieve and Fletcher, 1976) is associated with the silicate (predominantly clay)
fraction. Non-residual zinc in many oxidized hemipelagic sediments (Shimmield and
Pedersen, 1990) and sediments from estuaries and coastal waters of southwest England
(Luoma and Bryan, 1981) and southern Louisiana (Feijtel et al., 1988; Guo et al., 1997)
is associated primarily with the reducible iron and manganese oxide fractions. Organic
material is also an important carrier of zinc in these sediments. Because of the associa-
tion of non-residual zinc with clay-sized particles and iron/manganese oxides (usually
coating clay particles) in oxidized layers of sediment, there is a good correlation in most
relatively uncontaminated sediments between concentrations of zinc and aluminum or
iron (Windom et al., 1989; Schropp et al., 1990; Schiff and Weisberg, 1999; Weisberg et
al., 2000).
In reducing sediments from Corpus Christi Channel, Texas, heavily contaminated
with zinc (mean of 4,550 µg/g total zinc), 35 percent of the zinc is adsorbed to iron and
manganese oxides, 48 percent is in the organic/sulfide fraction, and 17 percent is resid-
ual (Neff et al., 1978). Between 40 and 70 percent of the total zinc in sediments from
Mobile Bay, Alabama, and False Bay, South Africa, is associated with the organic/sul-
fide fraction and tends to increase with depth in the sediment (Brannon et al., 1977;
Rosental et al., 1986). It is uncertain whether this zinc is complexed to organic matter or
precipitated as zinc sulfide. Nissenbaum and Swaine (1976) quantified the fraction of
178 Bioaccumulation in Marine Organisms
total zinc associated with humic substances in marine sediments and concluded that vir-
tually all the non-residual zinc in reducing sediments is associated with organic matter.
However, other investigators have identified significant quantities of zinc sulfide in
reducing sediments (Loring, 1982). At Eh values below about –150 mV in anoxic sedi-
ments from coastal Louisiana, most of the non-detrital zinc is associated with sulfides
and organic matter (Guo et al., 1997). A small fraction is associated with carbonates.
Concentrations of zinc in solution in sediment pore waters vary over a wide range
(Campbell et al., 1988) and often are higher than concentrations in solution in the over-
lying water (Brannon et al., 1977). Pore water of surficial sediments (0 to 15 cm) from
Mobile Bay, Alabama, contains 26 to 35 µg/L zinc, compared to 4 to 8 µg/L in the over-
lying water column (Brannon et al., 1977). Concentrations of zinc in pore water from
these sediments increase with depth in the sediment core from 40 µg/L at the surface to
56 µg/L at 45 to 60 cm. Virtually all the pore water zinc (5 to 20 µg/L) in reducing sed-
iments from Saanich Inlet, Canada, is complexed with organic matter. Pore water from
intertidal mud flat sediments from Hong Kong contains 10 to 66 µg/L zinc; the highest
concentration is at 1.25 cm below the sediment surface (Yu et al., 2000).
However, as the sulfide concentration in reducing sediments increases, the solubility
of zinc in the pore water increases, presumably by formation of polysulfide complexes
(Zn(HS)2, ZnHSS-, etc.) (Salomons et al., 1987). Lu and Chen (1977a,b) predicted that
the dominant form of inorganic zinc in solution in pore water of reducing sediments
would be Zn(HS)3-. In oxidized sediments, most of the inorganic zinc in pore water is in
the form of Zn+2, Zn(OH)2, ZnHCO3-, and, and ZnCO3(Lu and Chen, 1977a,b;
Salomons, 1985).
There often is a net flux of dissolved zinc from zinc-contaminated sediments into the
overlying water column (Ciceri et al., 1992; Wood et al., 1995). The total flux of zinc
from sediments into the waters of the whole of southern San Francisco Bay is approxi-
mately 298 kg/day (Wood et al., 1995). The estimated flux of zinc from intertidal mud
flat sediments in Hong Kong is 4.45 mg/m2/y (Yu et al., 2000). Flux of zinc is faster from
oxidized than from anoxic sediments. When anoxic sediments are resuspended, up to
about 1 percent of the particle-bound zinc is mobilized into solution (Petersen et al.,
1997).
10.3 BIOACCUMULATION OF ZINC BY MARINE ORGANISMS
Zinc is an essential micronutrient in all marine organisms, being a cofactor in nearly
300 enzymes (Vallee and Auld, 1990). Because it is an essential micronutrient, numer-
ous species of marine animals appear to be able to regulate tissue zinc at concentrations
in seawater and sediments from normal ambient levels to incipient lethal levels (Luoma
and Bryan, 1982; Amiard et al., 1985; Vale and Mendes, 1986; Ahsanullah and Williams,
1991). For example, intertidal snails Polynices sordidus maintain a relatively constant
internal zinc concentration in sediments with zinc concentrations up to 10,000 µg/g
(Ying et al., 1993). Crabs Carcinus maenas and barnacles Elminius modestus maintain
relatively constant body residues (mean 83.2 ±19.4 µg/g dry wt) of zinc in the presence
of dissolved zinc concentrations up to about 400 µg/L (Rainbow, 1985). At higher dis-
solved zinc concentrations, there is a net bioaccumulation. Uptake rates of zinc by
benthic amphipods Orchestia gammarellus from clean and metal-contaminated sites in
Great Britain and France range from 406 to 2769 ng/g/d (Rainbow et al., 1999). Uptake
Chapter 10 – Zinc in the Ocean 179
rates are not related to zinc concentrations in the sediments in which the amphipods
reside. The amphipods from sediments containing widely varying concentrations of zinc
contain 120 to 392 µg/g dry wt zinc in their tissues.
Some species of marine animals have the ability to regulate tissue zinc concentrations
at very high levels. Zinc is stored in the hemolymph of shore crabs Carcinus maenas
tightly bound to organic compounds in the blood (Martin and Rainbow, 1998). Zinc bio-
concentrated from the ambient water does not replace the bound zinc in the hemolymph,
except at very high ambient zinc concentrations. Hemolymph zinc has a half-life of
about 21 days and is maintained at a concentration of about 35,000 µg/L. Barnacles
Balanus amphitrite contain up to 16,000 µg/g dry wt zinc in their tissues (Wang et al.,
1999). The barnacles are able to assimilate the zinc very efficiently from their food and
release it very slowly to the environment. Most of the zinc is stored in the midgut epithe-
lium in zinc phosphate granules. Female, but not male, squirrelfish (family
Holocentridae) store large amounts of zinc in their livers (Hogstrand et al., 1996;
Hogstrand and Haux, 1996). Livers of female squirrelfish may contain more than 5,000
µg/g dry wt zinc. The zinc is stored in the liver complexed to two zinc-binding proteins,
metallothionein in hepatocyte nuclei and female-specific zinc-binding protein in the
cytosole of liver cells. The ovaries of female squirrelfish also contain high concentrations
of zinc. When the females are administered estrogen, the concentration of zinc in the
liver decreases and the concentration in the ovaries increases, indicating that the females
store zinc in the liver for use in egg formation and development.
Dissolved zinc that is complexed to organic ligands in the water is less bioavailable
to mussels Mytilus edulis than dissolved ionic zinc (Vercauteren and Blust, 1996). The
bioavailability of ionic and complexed zinc is higher in the digestive system than in the
gills. This may be due to facilitated zinc transport across the gut epithelium.
Bioaccumulation of zinc by black mussels Septifer virgatus is an active process medi-
ated by SH-containing ligands in cell membranes (Wang and Dei, 1999). Zinc uptake
decreases with increasing ambient seawater salinity, probably due to complexation by
other cations in seawater.
Marine organisms can accumulate zinc from water, food, and sediments. Polychaete
worms Neanthes arenaceodentata are able to bioaccumulate dissolved, free ionic zinc
but not organically complexed zinc from seawater (Mason et al., 1988). Highest con-
centrations of zinc in the deposit-feeding clam Scrobicularia plana are found in the
digestive gland, indicating that ingested sediments are the primary source of the zinc
(Bryan and Uysal, 1978). Scrobicularia plana and Neries diversicolor from the Bou
Regreg Estuary, Morocco, readily accumulate zinc from sediments contaminated with
effluents from a sewage treatment plant (Cheggour et al., 1990).
Baltic clams Macoma balthica also bioaccumulate zinc primarily from sediments on
which they feed (Harvey and Luoma, 1985a,b). Bioaccumulation is most efficient when
the zinc is adsorbed to iron oxide particles. Clams accumulate less zinc from algal foods
than from solution in seawater during long-term high-concentration exposures. However,
Macoma does not bioaccumulate any zinc when exposed for two days to dissolved zinc
concentrations up to 600 µg/L (Bordin et al., 1994). The algal food of the periwinkle
snail Littorina obtusata and the animal food of the predatory dogwhelk Nucella lapillus
are the major sources of zinc in their tissues (Young, 1975, 1977). However, much of the
zinc in the snails (the preferred food of the dogwhelks) is sequestered in phosphate gran-
ules and is not absorbed efficiently from the gut of the whelks (Nott and Nicolaidou,
180 Bioaccumulation in Marine Organisms
1993). Marine snails Cerithium vulgatum eliminate accumulated zinc in fecal pellets
which may contain more than 400 µg/g zinc (Nott and Nicolaidou, 1996)
The assimilation efficiency of zinc from ingested natural seston by mussels Mytilus
edulis ranges from 32 to 41 percent (Wang et al., 1996). Assimilation efficiency of zinc
from solution in the ambient water is 0.89 percent. The relative contribution of zinc in
the dissolved phase to total bioaccumulation of zinc ranges from 17 to 51 percent,
depending on the concentration and zinc binding capacity of the food. The relative
importance of water and food for zinc bioaccumulation in mussels is not influenced by
mussel size (Wang and Fisher, 1997). This is because the influx rates of zinc from water
and food both decrease in a similar fashion with increasing size.
Assimilation efficiency of zinc from food varies in different species of marine ani-
mals and with differences in the zinc concentration and quality of the food. Zinc assim-
ilation efficiencies for several species of marine animals fed different natural foods
ranges from 16 to 93 percent (Wang and Fisher, 1999). Green mussels Perna viridis
assimilate 21 to 36 percent of the zinc from ingestion of five species of marine phyto-
plankton; clams Ruditapes philippinarum assimilate 29 to 59 percent of the zinc from the
same five species of algae (Chong and Wang, 2000). The assimilation efficiency of zinc
by the benthic amphipod Leptocheirus plumulosus ranges from 5 to 33 percent and is
highest for phytoplankton food (Schlekat et al., 2000). Assimilation efficiency of zinc
from iron oxide coatings on sediments is low; assimilation from whole sediment is
between 10 and 20 percent. The amphipod can process up to three times its body weight
per day of sediment; thus, they can accumulate large amounts of zinc by this route.
Polychaete worms Capitella capitata accumulate several metals from their algal and
detrital foods (Rice et al. 1981, Windom et al. 1982). Accumulation of zinc increases
with increasing food quality (measured as nitrogen concentration) and decreases with
increasing ration size of the algal foods, Gracilaria and Ascophylum. Juvenile silverside
minnows Menidia spp. are able to absorb only about 6 percent of the zinc in their cope-
pod food (Reinfleder and Fisher, 1994). The fraction of the zinc that is associated with
the exoskeleton of the copepods is not bioavailable, whereas that associated with the soft
tissues is.
Shrimp Lysmata seticaudata and crabs Carcinus maenas, when exposed for three
months to 65Zn in water or a combination of water and food, accumulate equal amounts
of zinc from water alone as from water plus food (Renfro et al., 1975). However, a fish,
Gobia sp., accumulates 2.5 times more zinc from the combined food/water pathway than
from the water pathway alone. Crabs Pugetta producta are able to assimilate more than
65 percent of the zinc in their macroalgal food (Boothe and Knauer, 1972).
Highest levels of zinc in bottom-feeding fish Platichthys flesus, are found in the skin
and the gills suggesting uptake from seawater due perhaps to surface adsorption (Amiard
et al., 1985). Skin of five species of tropical fish from Trinidad contain higher concen-
trations of zinc than underlying muscle tissues (Singh et al., 1991). This may be due to
sorption of zinc from seawater by skin mucus.
In exposures lasting 120 days, mosquitofish Gambusia affinis and spot Leiostomus
xanthurus accumulate 78 and 82 percent, respectively, of their body burdens of 65Zn
from food (Artemia contaminated by ingestion of 65Zn-labeled algae) (Willis and Sunda,
1984). Similar results were obtained by Baptist and Lewis (1969) for postlarval Atlantic
croakers Micropogon undulatus and mummichogs Fundulus heteroclitus. Juvenile plaice
Pleuronectes platessa accumulate zinc more efficiently from food (Artemia nauplii or
Chapter 10 – Zinc in the Ocean 181
polycheates, Nereis diversicolor) than from water (Pentreath, 1973; Milner, 1982). Only
about 10 percent of the zinc in the plaice tissues is derived from the water. In a closely
related flatfish, the winter flounder Pleuronectes americanus, a zinc-binding metalloth-
ionein is readily induced in intestinal cells by parenteral injections of zinc (Shears and
Fletcher, 1984). However, high levels of zinc metallothionein in intestinal mucosa have
no effect on the rate of uptake of zinc from food, suggesting that intestinal metalloth-
ionein does not play a role in controlling absorption of metals from the gut. However,
the assimilation efficiency of zinc in two tropical marine fish, the pelagic glassy
Ambassis urotaenia and the intertidal mudskipper Periophthalmus cantonensis, is quite
low, ranging from 5 to 31 percent (Ni et al., 2000). The zinc in the copepod prey may
have been in non-bioavailable forms.
Zinc concentrations are highest in animals at the lowest trophic level in the Palos
Verdes (Southern California Bight) food web examined by Young and Mearns (1979)
and Young et al. (1980). Schafer et al. (1982) observed an inverse relationship between
trophic level and tissue residues of zinc in three marine food webs in the eastern Pacific
Ocean.
Zinc is relatively uniformly distributed in the tissues of annelids, crustaceans, and fish
from two locations in the Loire River estuary, France, with highest concentrations in
worms and copepods (Amiard et al., 1980, 1983; Metayer et al., 1980). Concentrations
of zinc are nearly always much higher in the stomach contents than in the intestinal tract
contents of the top carnivore fish from the estuary. The mean transfer factors (concen-
tration in fish tissues/concentration in fish food) for zinc in five species of carnivorous
fish from the estuary usually are less than one, indicating that the metals are not being
biomagnified by the fish.
10.4 CONCENTRATIONS OF ZINC IN
TISSUES OF MARINE ORGANISMS
Zinc concentrations in tissues of marine plants and animals usually are much higher
and more variable than concentrations of other metals. Concentrations of zinc in oysters
Crassostrea virginica collected as part of the National Status and Trends Mussel Watch
Program from coastal waters of the U.S. south Atlantic and Gulf of Mexico range from
1.8 to more than 28,000 µg/g dry wt (Table 53). Some oysters C. rhizophorae from
Puerto Rico and Ostrea sandvicensis from Hawaii also contain high concentrations of
zinc in soft tissues. Oysters from elsewhere in the world also may contain high zinc con-
centrations (Table 67). Natural concentrations of zinc, like copper, are much higher in
tissues of oysters than in mussels. The “high” concentration of zinc in tissues of oysters
and mussels, based on the Mussel Watch data, is 6,500 and 210 µg/g, respectively
(O’Connor and Beliaeff, 1995).
Mussels Mytilus edulis and M. californianus from Mussel Watch sites along the U.S.
Atlantic and Pacific coasts contain much lower concentrations of zinc than oysters (Table
53). Zinc concentrations in the soft tissues of the mussels range from about 50 µg/g to
nearly 400 µg/g. Highest concentrations are in mussels from the coasts of California and
Washington. Mussels from elsewhere in the world contain zinc concentrations similar to
those in mussels from U.S. waters (Table 67).
182 Bioaccumulation in Marine Organisms
Chapter 10 – Zinc in the Ocean 183
Table 67.
Representative concentrations of zinc in tissues of marine organisms from throughout the
world. Concentrations are µg/g dry wt of whole soft tissue or muscle.
Zinc concentrations in marine organisms from the south Texas outer continental shelf
food chain and estuarine organisms from the Calcasieu River estuary food chain are in
the range of 14 to 7,800 µg/g (Tables 54 and 55). Highest concentrations are in oysters
from the northern end of Calcasieu Lake (Ramelow et al., 1989). Some periphyton and
mixed zooplankton from the Calcasieu River estuary also contain elevated concentra-
tions of zinc. With the exception of blue crabs and some gulf menhaden from the
Calcasieu River, all other plants and animals in the two food webs contain less than 100
µg/g zinc. Viscera of squid and shrimp and skin of flatfish contain higher concentrations
of zinc than other tissues. The liver of sand sea trout also contains a higher concentra-
tion of zinc than the muscle does.
Concentrations of zinc in marine plants and animals from throughout the world are
highly variable and usually fall in the range of concentrations found in plants and ani-
mals from the Gulf of Mexico (Table 67). Marine plants generally contain relatively low
concentrations of zinc, except near point sources of zinc contamination. The brown alga
Fucus vesiculosus from the Fal Estuary in southwest England, heavily contaminated
with metal mine drainage, contains more than 1,300 µg/g zinc. The same species from
western Greenland rarely contains less than 26 µg/g zinc.
An Antarctic sponge Tedania charcoti contains a very high concentration of zinc,
comparable to zinc concentrations in contaminated oysters (Table 67). This sponge, pre-
sumably from an uncontaminated environment, also contains a very high concentration
of cadmium (Capon et al., 1993). The metals seem to impart a strong anti-bacterial activ-
ity to crude ethanol extracts of the sponge. Nemerteans sometimes contain high concen-
trations of zinc, part of which is complexed with the abundant mucus they produce.
Snails Littorina littoralis from British estuaries contain zinc concentrations that reflect
the concentration of zinc in their algal foods. Snails with the highest body burdens of
zinc are from the Fal Estuary where brown algal foods and sediments are heavily con-
taminated with zinc.
Bivalve mollusks, other than oysters of several species, usually contain low concen-
trations of zinc, rarely exceeding about 250 µg/g (Table 67). Oysters, on the other hand,
rarely contain less than about 200 µg/g zinc, irrespective of species. However, zinc con-
centrations in soft tissues of the deposit-feeding clam from the Bilbao Estuary, Spain,
vary seasonally between 1700 and 4140 µg/g dry wt (Ruiz and Saez-Salinas, 2000).
Digestive gland of the clams may contain up to 8000 µg/g zinc, suggesting that the clams
are ingesting and retaining zinc-contaminated sediment particles.
Among the crustaceans, barnacles appear to be the exceptional accumulators of zinc.
Some barnacles from Hong Kong contain nearly 20,000 µg/g zinc (Phillips and
Rainbow, 1988). Barnacles Balanus improvisus from the Gulf of Gdansk, Poland (Baltic
Sea) contain 5,000 to 11,000 µg/g dry wt zinc (Rainbow et al., 2000). Most other crus-
taceans contain less than 100 µg/g zinc. Zinc in the gills of crabs Pacygrapsus
marmoratus and Carcinus maenas is associated primarily with insoluble granules
(Legras et al., 2000). Muscle tissues of sharks and teleost fish also contain low concen-
trations of zinc. Concentrations rarely exceed 50 µg/g.
However, in teleosts but apparently not in sharks, zinc concentrations in some organ
tissues may be very high (Table 68). Kidneys and ripe ovaries, in particular, may contain
several hundred parts per million zinc. Testes contain much lower zinc concentrations
than ovaries. Liver generally contains lower concentrations of zinc than kidney.
184 Bioaccumulation in Marine Organisms
However, the liver of rabbitfish Siganus oramin from Hong Kong contains up to 1,175
µg/g zinc (So et al., 1999). This distribution of zinc in fish tissues undoubtedly reflects
the distribution of requirements for zinc as a cofactor in several important enzymes.
Much of the zinc in organ tissues of fish appears to be bound to metallothionein
(Hogstrand and Haux, 1996).
The distribution of zinc in the tissues of marine turtles, birds, and mammals is some-
what different than that in fish (Table 60). Zinc concentrations usually are slightly higher
in liver than in kidney. Lowest concentrations usually are in muscle. However, muscle
tissue of marine birds and mammals often contains more than 100 µg/g zinc. Liver and
kidney often contain more than 200 µg/g zinc. Blubber of marine mammals usually con-
tains relatively little zinc. Zinc is relatively evenly distributed among liver, kidney, and
muscle of walrus Odobenus rosmarus (Wagemann and Stewart, 1994). Tissues of polar
bears Ursus maritimus from central east Greenland contain relatively high concentra-
tions of zinc, possibly reflecting zinc levels in the ringed seals upon which they feed
(Dietz et al., 1995). Highest concentrations of zinc are in liver and muscle. The zinc con-
centration in kidney, but not other tissues, increases with age of the bears (Dietz et al.,
2000a). There are no differences in zinc concentrations in tissues of polar bears from dif-
ferent regions of Greenland.
Chapter 10 – Zinc in the Ocean 185
Table 68.
Typical concentrations of zinc in different tissues of marine fish. Concentrations are µg/g dry wt.
10.5 TOXICITY OF ZINC TO MARINE ORGANISMS
Because marine organisms can regulate tissue residues of zinc over wide ranges of
zinc concentrations in the ambient water, sediments, and food, it is only moderately toxic
to some marine organisms. The toxic species of zinc is the free ion, which represents
only a small fraction of the total zinc in natural seawater. Acutely lethal concentrations
of total zinc in solution usually are in the range of 100 to 50,000 µg/L. Fish are the most
tolerant; phytoplankton and some larval crustaceans and mollusks are the most sensitive.
Growth of coastal strains of the microalgae Thalassiosira pseudonana and T. weiss-
flogii is inhibited at concentrations of dissolved, ionic zinc lower than 0.00065 µg/L
(Sunda and Huntsman, 1992), indicating that zinc is an essential micronutrient for
microalgae. Maximal growth occurs between concentrations of 0.00065 µg/L and 0.65
µg/L; growth is inhibited at higher concentrations. However, growth of another species,
Emiliania huxleyi, is not affected at concentrations of ionic zinc up to at least 6.5 µg/L.
Most of the zinc in seawater is complexed or adsorbed, maintaining free ionic zinc con-
centrations below this level, except in heavily contaminated estuaries, such as the Fal
Estuary, England (Bryan and Langston, 1992). Zinc ion concentrations in surface waters
of the open ocean, but not in coastal waters, may be low enough to limit phytoplankton
growth (Torell and Price, 1996; Ellwood et al., 2000). Growth of diatoms Nitzschia
closterium is inhibited at total dissolved zinc concentrations of 20 µg/L (Stauber and
Florence, 1990). Carbon fixation in mixed natural populations of marine phytoplankton is
inhibited at a concentration of total dissolved zinc of 15 µg/L (Davies and Sleep, 1979).
Marine macroalgae are slightly less sensitive than phytoplankton to zinc. Growth is
inhibited in six species of seaweeds from Brazil at a concentration of 20 µg/L (Filho et
al., 1997). All six species are killed at a zinc concentration of 5,000 µg/L; Ulva latuca
and Enteromorpha flexuosa are killed at a zinc concentration of 1,000 µg/L and Hypnea
musciformis died at 100 µg/L.
Concentrations of total dissolved zinc in the range of 5 to 20 µg/L interfere with nor-
mal fertilization and early development of some mollusks, crustaceans, and fish (Ojaveer
et al., 1980; Verriopoulos and Hardouvelis, 1988; Hunt and Anderson, 1989). Embryos
of oysters Crassostrea gigas and mussels Mytilus edulis undergo abnormal development
at a dissolved zinc concentration of 119 and 175 µg/L, respectively (Martin et al., 1981).
Growth of the amphipod Allorchestes compressa is decreased at zinc concentrations of
100 µg/L or higher (Ahsanullah and Williams, 1991). Chronic exposure to 166 µg/L zinc
causes reduced survival and interferes with reproduction of mysids Mysidopsis bahia
(Lussier et al., 1885). Exposure of male Norway lobsters Nephrops norvegicus to 40
µg/L zinc in the presence of 5 µg/L copper and cadmium inhibits gill Na,K-ATPase
activity (Canli and Stagg, 1996). The 48-hour median lethal concentrations of zinc for
juvenile grass shrimp Palaemonetes pugio and killifish Fundulus heteroclitus are 11,300
µg/L and 96,500 µg/L, respectively (Burton and Fisher, 1990). The 96-hour LC50 for
zinc in juvenile white shrimp Penaeus setiferus is 43,870 µg/L (Vanegas et al., 1997).
The marine acute and chronic water quality criteria for zinc are 95 and 86 µg/L, respec-
tively (Table 30).
Concentrations of zinc in contaminated estuarine and coastal waters sometimes are
higher than concentrations shown to cause adverse effects in sensitive species, particu-
larly some phytoplankton and invertebrate embryos. Therefore, it is possible that zinc
pollution is causing harm to some nearshore marine and estuarine environments.
186 Bioaccumulation in Marine Organisms
However, much of the zinc in coastal and estuarine waters is complexed with inorganic
and organic ligands or adsorbed to suspended particles, rendering it less bioavailable and
toxic than free zinc ion. Therefore, it is uncertain how frequently zinc represents an envi-
ronmental hazard to marine environments.
The effects range-low (ERL) and effects range-median (ERM) sediment quality
guidelines for zinc are 150 and 410 µg/g, respectively (Table 24). The “high” concen-
tration in National Status and Trends sediments is 135 µg/g. Sediments from 22 percent
of the sites monitored in various government monitoring programs in the U.S. contain
more than 135 µg/g zinc (Daskalakis and O’Connor, 1995). Probably less than 5 percent
of the sites have sediments containing more than the ERM guideline concentration.
Therefore, zinc contamination of coastal marine and estuarine sediments in the United
States is only a moderate problem. Zinc contamination in sediments rarely contributes
substantially to environmental degradation in coastal habitats in the U.S.
Watzin and Roscigno (1997) studied the effects of added zinc on benthic communi-
ties at two locations in Mobile Bay,AL. At zinc concentrations above about 600 µg/g dry
wt, total abundance and diversity of benthic macro- and meiofauna in sediments is
decreased. Several families of polychaetes, harpacticoid copepods, and ostracods are
sensitive to zinc. However, some species of gastropods and bivalve mollusks are tolerant
and their abundances increase in the zinc contaminated sediments, even at zinc concen-
trations higher than 8,000 µg/g. Thus, zinc in sediments is moderately toxic to some
benthic marine animals.
It is not possible to estimate a concentration of zinc in tissues of marine animals that
would be expected to be associated with adverse effects in the animals themselves or
their consumers, including man. This is because presumably natural concentrations of
this essential trace nutrient vary so widely in apparently healthy marine animals, as dis-
cussed above. Frequently, much of the zinc in the tissues of marine animals is
sequestered in relatively inert concretions (Simkiss and Taylor, 1989). The zinc in these
concretions may not be bioavailable to consumers of fishery products (Nott and
Nicolaidou, 1993).
Dillon and Gibson (1987) identified tissue residues of 100 to 510 µg/g dry wt that are
associated with various adverse reproductive effects in some species of freshwater and
marine invertebrates and fish. Marine amphipods Allorchestes compressa experience
decreases in growth when tissue residues of zinc exceed 139 µg/g (Ahsanullah and
Williams, 1991). However, oysters Crassostrea virginica containing 4,100 to 7,000 µg/g
dry wt zinc have normal growth and condition and apparently are healthy (Frazier, 1976;
Abbe and Sanders, 1986). These tissue residues associated with adverse effects in marine
animals seem reasonable for most invertebrates and fish, with the exception of oysters
and barnacles. Apparently healthy marine birds and mammals may have higher concen-
trations than these of zinc in liver, kidney, and ovaries. It is uncertain but doubtful that
the high concentrations of zinc found in some shellfish products pose a health hazard to
avian and mammalian consumers.
The RBC for zinc in edible tissues of marine animals consumed by man is 811 µg/g
wet wt (4,055 µg/g dry wt) (Table 30). International standards for zinc in shellfish con-
sumed by man are in the range of 200 to 500 µg/g dry wt (Melzian, 1990). Zinc is bio-
accumulated naturally to high concentrations by oysters (NOAA, 1995). The form of
zinc in oyster tissues and its bioavailibility to consumers of oysters are not known. Most
other marine animals frequently consumed by man, including fish, usually do not
Chapter 10 – Zinc in the Ocean 187
contain zinc concentrations exceeding the RBC. Thus, frequent consumption of oysters
heavily laden with zinc could pose a health risk to human consumers. Consumption of
other marine animals probably does not pose a serious risk of zinc poisoning.
10.6 ENVIRONMENTAL EFFECTS OF
ZINC IN PRODUCED WATER
The concentration of zinc in produced water from the Gulf of Mexico is higher than
the concentration of zinc in clean ocean water. Concentrations as high as 200,000 µg/L
have been reported in produced water from some sources (Table 1). Some of the reported
high concentrations may be due to sample contamination during sampling, storage, or
analysis, or they may be due to the presence of zinc-particles (e.g., flakes of galvanized
steel or microcrystals of sphalerite) in the samples. Zinc is difficult to analyze accurately
in environmental samples because of the multiple sources of zinc in the human environ-
ment. Samples of produced water from four offshore platforms in the Gulf of Mexico
and North Sea, analyzed by advanced analytical methods, contained 10 µg/L to 340 µg/L
total zinc (Table 3). These concentrations probably are more typical of the actual con-
centrations of zinc in produced water.
Although zinc is fairly abundant in coastal marine waters (1 to 5 µg/L), nearly all
produced waters discharged to offshore waters of the Gulf of Mexico and North Sea are
enriched with zinc, compared to concentrations in ambient seawater, by factors ranging
from just over 2 to about 1,000. Dilution of produced water with the highest reliably ana-
lyzed zinc concentration by 1,000-fold, which usually happens within a few hundred
meters at most from the outfall, reduces the zinc concentration to background. Dilution
of the produced water by 100-fold brings the concentration down below the marine
chronic value (81 µg/L). Zinc from produced water probably is complexed rapidly with
organic and inorganic ligands in ambient seawater, reducing the effective concentration
of the more bioavailable and toxic ionic forms even more rapidly. Thus, zinc from
produced water does not pose a significant risk to marine organisms living in the water
column near an offshore produced water discharge.
Concentrations of zinc in sediments from the vicinity of produced water discharges
occasionally are slightly elevated above natural “background” concentrations that vary
widely depending on sediment texture and mineralogy. Zinc concentrations in surficial
sediments near four produced water discharges to the Gulf of Mexico range from 96 µg/g
dry wt 2,000 m down-current from a discharge to 800 µg/g 50 m from another discharge
(DOE, 1997a). Zinc concentrations in sediments near reference platforms not discharg-
ing produced water are in the range of 35 to 85 µg/g. It is uncertain what fraction of the
zinc comes from produced water. Other sources of anthropogenic zinc near offshore plat-
forms include leaching from sacrificial anodes and antifouling coatings on submerged
platform structures and zinc-rich particles from galvanized platform structures. Water
base drilling muds often discharged from offshore platforms to waters of the Gulf of
Mexico often contain high concentrations of zinc that may contribute to slightly elevated
zinc concentrations in sediments near platforms (Neff, 1987; Boothe and Presley, 1989).
Zinc in sediments has a low bioavailability and toxicity to marine organisms. The
ERL and ERM for zinc in marine sediments are 150 µg/g and 410 µg/g, respectively. The
extent of the elevation, when detected, usually is not sufficient to represent a significant
188 Bioaccumulation in Marine Organisms
hazard to the local marine communities. Therefore, it is unlikely that zinc from produced
water is adversely affecting marine organisms near produced water discharges.
Zinc is an essential micronutrient and concentrations are regulated or excess zinc is
sequestered in inactive forms in tissues of marine animals. Natural concentrations of zinc
in tissues of many healthy marine animals, particularly oysters, are very high. There is
little evidence of bioaccumulation of excess zinc by marine organisms near offshore pro-
duced water discharges.
Oysters Crassostrea virginica from the vicinity of produced water discharges off
Louisiana contain means of 1,610 to 2,150 µg/g zinc in soft tissues (Table 62). This con-
centration range is slightly but not significantly higher than the mean zinc concentration
in oysters from a nearby reference site (no produced water discharge) and well below the
“high” concentration for Mussel Watch oysters. Zinc concentrations in soft tissues of
clams Chama macerophylla from the vicinity of the produced water discharges are about
one-tenth the concentrations in oysters. There is no difference in zinc concentrations in
clams from the vicinity of the discharges and from a reference location. Zinc concentra-
tions in oysters from the vicinity of high-volume produced water discharges to Bayou
Rigaud and Port Fourchon, Louisiana, are in the range of 2,142 to 3,857 µg/g dry wt
(Boesch et al., 1989a), slightly higher than the geometric mean concentration of zinc in
Mussel Watch oysters (2,100 µg/g) from Louisiana. Oysters from the vicinity of a
produced water discharge at East Tambalier Island, Louisiana, contain approximately
905 µg/g zinc. The differences in zinc residues in oyster tissues probably is due more to
effects of salinity on zinc bioaccumulation (Bryan and Uysal, 1978) than to effects of
produced water discharges.
Concentrations of zinc are low in muscle tissue of red snapper Lutjanus campechanus
and triggerfish Balistes capriscus from the vicinity of offshore produced water dis-
charges; zinc concentrations in the edible muscle tissues range from 13 to 23 µg/g (Table
62). Concentrations are similar in the muscle of fish from produced water discharge and
reference sites (Trefry et al., 1996). Therefore, the bivalves and fish are not accumulat-
ing significant amounts of zinc from the produced water discharges.
Chapter 10 – Zinc in the Ocean 189
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