- Bioaccumulation and Trophic Transfer
of Methylmercury in Long Island Sound
Chad R. Hammerschmidt and William F. Fitzgerald.
Archives of Environmental Contamination and Toxicology, Vol.
51, No. 3, Oct 2006, pp. 416-424.
Humans are exposed to methylmercury (MeHg) principally by
consumption of marine fish. The coastal zone supports the
majority of marine fish production, and may therefore be an
important source of MeHg to humans; however, little is known
about the bioaccumulation of MeHg in near-shore marine ecosystems.
We examined MeHg in microseston, zooplankton, a decapod crustacean,
and four representative species of finfish that differ in
trophic status and/or prey selection in Long Island Sound
(LIS), a large coastal embayment in the northeastern United
States. MeHg biomagnifies in LIS; levels in microseston were
10 super(4.2) greater than those in water and 2.3-fold less
than zooplankton. MeHg concentrations were related positively
to fish length for each species, but often varied considerably
among larger individuals. This may be due to differences in
the past dietary MeHg exposure of these fish, some of which
are migratory. Sedimentary production and mobilization can
account for most of the MeHg in microseston of LIS, and by
extension, other near-shore locations. Hence, much of the
MeHg in higher trophic levels of coastal marine ecosystems,
including fishes destined for human consumption, may be attributed
to net sedimentary production and dietary bioaccumulation.
- Daily intake of arsenic, cadmium, mercury,
and lead by consumption of edible marine species
Gemma Falcó, Juan M. Llobet, Ana Bocio and José L. Domingo.
Journal of agricultural and food chemistry, Vol. 54, No.
16, Aug 9 2006, pp. 6106-6112.
The daily intake of arsenic (As), cadmium (Cd), mercury (Hg),
and lead (Pb) through the consumption of 14 edible marine
species by the general population of Catalonia, Spain, was
estimated. Health risks derived from this intake were also
assessed. In March-April 2005, samples of sardine, tuna, anchovy,
mackerel, swordfish, salmon, hake, red mullet, sole, cuttlefish,
squid, clam, mussel, and shrimp were randomly acquired in
six cities of Catalonia. Concentrations of As, Cd, Hg, and
Pb were determined by ICP-MS. On the basis of recent fish
and seafood consumption data, the daily intake of these elements
was calculated for eight age/sex groups of the population.
The highest As concentrations were found in red mullet, 16.6
microg/g of fresh weight, whereas clam and mussel (0.14 and
0.13 microg/g of fresh weight, respectively) were the species
with the highest Cd levels. In turn, swordfish (1.93 microg/g
of fresh weight) and mussel and salmon (0.15 and 0.10 microg/g
of fresh weight) showed the highest concentrations of Hg and
Pb, respectively. The highest metal intake through fish and
seafood consumption corresponded to As (217.7 microg/day),
Cd (1.34 microg/day), and Pb (2.48 microg/day) for male seniors,
whereas that of Hg was observed in male adults (9.89 microg/day).
The daily intake through fish and seafood consumption of these
elements was compared with the provisional tolerable weekly
intakes (PTWI). The intakes of As, Cd, Pb, and total Hg by
the population of Catalonia were below the respective PTWI
values. However, the estimated intake of methylmercury for
boys, 1.96 microg/kg/week, was over the PTWI.
- The effect of fish consumption on blood
mercury levels of pregnant women
Euy Hyuk Kim, In Kyu Kim, Ja Young Kwon, Sang Wun Kim and
Yong Won Park.
Yonsei medical journal, Vol. 47, No. 5, Oct 31 2006, pp.
In the present study, we examined the relationship between
average fish consumption, as well as the type of fish consumed
and levels of mercury in the blood of pregnant women. We also
performed follow-up studies to determine if blood mercury
levels were decreased after counseling and prenatal education.
To examine these potential relationships, pregnant women were
divided into two groups: a study group was educated to restrict
fish intake, whereas a control group did not receive any prenatal
education regarding fish consumption. We measured blood mercury
level and performed follow-up studies during the third trimester
to examine any differences between the two groups. Out of
the 63 pregnant women who participated in our study, we performed
follow- up studies with 19 pregnant women from the study group
and 12 pregnant women from control group. The average initial
blood mercury level of both groups was 2.94 microg/L, with
a range of 0.14 to 10.75 microg/L. Blood mercury level in
the group who ate fish more than four times per month was
significantly higher than that of the group who did not consume
fish (p = 0.02). In follow-up studies, blood mercury levels
were decreased in the study group but slightly increased in
the control group (p = 0.014). The maternal blood mercury
level in late pregnancy was positively correlated with mercury
levels of cord blood (r = 0.58, p = 0.047), which was almost
twice the level found in maternal blood. Pregnant women who
consume a large amount of fish may have high blood mercury
levels. Further, cord blood mercury levels were much higher
than that of maternal blood. Because the level of fish intake
appears to influence blood mercury level, preconceptual education
might be necessary in order decrease fish consumption.
- Environmental controls on the speciation
and distribution of mercury in coastal sediments
E. M. Sunderland, F. A. P. C. Gobas, B. A. Branfireun and
Marine Chemistry, Vol. 102, No. 1-2, Nov 2006, pp. 111-123.
Methylmercury production by sulfate reducing bacteria in
coastal sediments leads to bioaccumulation of mercury in fish,
shellfish, and ultimately humans. Sulfur, organic carbon,
and sediment structure and composition can all affect methylmercury
production by changing the amount of bioavailable inorganic
mercury and by stimulating the activity of methylating microbes.
This study investigates total and methylmercury in solids
and porewaters relative to total sulfide concentration, redox
potential, sediment grain size, and total organic carbon in
a range of sediment types from the Bay of Fundy region of
Canada. Using these data, we construct a conceptual model
of the biogeochemical environment surrounding methylating
microbes in high sulfide, organically enriched sediments.
Whereas other studies of methylmercury dynamics measured porewater
sulfide concentrations in relatively low-sulfide systems (~20-300
mu M), we measured total sulfide levels using a method developed
to indicate organic enrichment across a much wider range of
sulfidic sediments (10-4000 mu M). We observed that higher
sulfide concentrations correspond to an elevated fraction
of mercury in methylated form suggesting higher net methylation
rates in these sediments. This relationship is strongest in
sediments that are moderately impacted by organic enrichment,
but weak in less impacted, aerobic sediments. Higher sulfide
concentrations in porewaters containing dissolved organic
matter appear to yield a geochemical environment that is conducive
to uptake of Hg(II) by methylating bacteria. Data collected
in this study imply that moderate levels of organic enrichment
through fish farming may enhance methylmercury production
in the Bay of Fundy.
- An examination of the factors influencing
the flux of mercury, methylmercury and other constituents from
R. P. Mason, E. H. Kim, J. Cornwell and D. Heyes.
Marine Chemistry, Vol. 102, No. 1-2, Nov 2006, pp. 96-110.
The flux of mercury (Hg), methylmercury (MeHg), other metals
(zinc (Zn), cadmium (Cd) and lead (Pb)), arsenic (As), nutrients,
dissolved organic carbon (DOC) and sulfide from sediments
collected in Baltimore Harbor, Maryland, USA were measured
over the period of approximately 5 days. Fluxes of the various
constituents changed over time and the magnitude and direction
of the fluxes of the major metals (Fe and Mn) correlated with
the extent of oxygen depletion and the presence or absence
of sulfide in the water column. It appeared that the heavy
metals, Zn, Cd, Pb, and Hg, were taken up into the sediment
under hypoxic/anoxic conditions but were released under more
oxic conditions. The fluxes of As and phosphate followed that
of Fe. Overall, the fluxes of these constituents confirmed
expectation based on thermodynamic considerations. For Hg
and MeHg, there appeared to be little relationship between
their flux and that of the major metals, or sulfide, or DOC.
For MeHg, there is a suggestion that processes occurring at
the sediment /water interface, including methylation, may
play a major role in determining the extent of the MeHg flux
to the water column.
- Japan remembers Minamata
Lancet, Vol. 367, No. 9505, 2006 Jan 14 2006, pp. 99-100.
- Methylmercury Concentrations in Fish
from Tidal Waters of The Chesapeake Bay
Robert P. Mason, Deborah Heyes and Auja Sveinsdottir.
Archives of Environmental Contamination and Toxicology, Vol.
51, No. 3, Oct 2006, pp. 425-437.
Striped bass (Morone saxatilis), white perch (Morone Americana),
and largemouth bass (Micropterus salmoides) were collected
in the Chesapeake Bay mainstem and tributaries and analyzed
for total mercury (Hg) and methylmercury (MeHg) content. Striped
bass are anadromous, whereas white perch and largemouth bass
are resident species, and the largemouth bass are also restricted
to the tidal fresh portion of the Bay. Total Hg and MeHg concentrations
in striped bass increased with fish size, and large fish (>7.5
kg wet weight) tended to have MeHg concentrations of 300 ng
g super(-1) or greater. On average, the striped bass MeHg
concentration was 120 plus or minus 100 ng g super(-1) and
the fraction of the total Hg as MeHg was 65 plus or minus
22%. Reasons for the lower relative MeHg content are discussed.
Otolith strontium/calcium ratios were also determined to examine
whether migration had a significant impact on MeHg content
in striped bass. Resident fish did appear to have a higher
MeHg burden than the more migratory fish of similar size.
Largemouth bass and white perch tended to have low MeHg content
(respectively, 14 plus or minus 7 and 13 plus or minus 11
ng g super(-1); all fish <1 kg wet weight), and the white
perch also had a low %MeHg (28 plus or minus 14%), reflecting
their mostly planktivorous lifestyle. A comparison of largemouth
bass and striped bass MeHg concentrations for the estuarine
fish with those of fish in Maryland reservoirs of similar
size showed that the estuarine fish have much lower MeHg burdens.
Differences in MeHg concentration in the estuarine waters
compared to the reservoir waters likely account for much of
this difference, although the importance of other factors
is also discussed.
- Recent Advances in Evaluation of Health
Effects on Mercury with Special Reference to Methylmercury:
Shun'ichi Honda, Lars Hylander and Mineshi Sakamoto.
Environmental Health and Preventive Medicine, Vol. 11, No.
4, 2006, pp. 171-176.
Mercury is a metal that has long been used because of its
many advantages from the physical and chemical points of view.
However, mercury is very toxic to many life forms, including
humans, and mercury poisoning has repeatedly been reported.
The main chemical forms of mercury are elemental mercury (Hg
super(0)), divalent mercury (Hg super(2+)) and methylmercury
(CH sub(3)-Hg super(+)), the toxicities and metabolisms of
which differ from each other. Methylmercury is converted from
divalent mercury and is a well-known neurotoxicant, having
been identified as the cause of Minamata disease. It bioaccumulates
in the environment and is biomagnified in the food web. Human
exposure to methylmercury is mainly through fish and seafood
consumption. Methylmercury easily penetrates the blood-brain
barrier and causes damage to the central nervous system, particularly
in fetuses. In this paper, we summarize the global mercury
cycle and mercury metabolism, toxicity and exposure evaluation,
and the thresholds for the onset of symptoms after exposure
to different chemical forms of mercury, particularly methylmercury.
- The Toxicology of Mercury and Its Chemical
Thomas W. Clarkson and Laszlo Magos.
Critical Reviews in Toxicology, Vol. 36, No. 8, 2006 Sep.
2006, pp. 609-662.
- Bioaccumulation Factors for Mercury
in Stream Fish
G. R. Southworth, M. J. Peterson and M. A. Bogle.
Environmental Practice, Vol. 6, No. 2, Jun 2004, pp. 135-143.
The bioaccumulation of methylmercury in fish is a complex
process affected by many site-specific environmental factors.
The US Environmental Protection Agency (USEPA) recently recommended
changing the basis for expressing the ambient water quality
criterion for mercury from an aqueous concentration to a measure
of the methylmercury concentration in fish. This change would
make the regulation of mercury in surface waters a site-specific
exercise in which fish-based bioaccumulation factors (BAF;
the ratio of mercury concentration in fish to the concentration
of mercury in water) are used to calculate aqueous concentration
limits for total mercury. These limits would then be used
to allocate mercury loading among various point and nonpoint
sources and guide regulatory actions. In order for this approach
to succeed, it is critical that the sitespecific BAFs and
methylmercury:total mercury conversion factors be independent
of aqueous total mercury concentration (Hg sub(T)). We investigated
this relationship by measuring aqueous methylmercury and Hg
sub(T)s and mercury in fish in ecologically similar warm-water
streams in the southeastern United States. Bioaccumulation
factors based on Hg sub(T) in water were found to decrease
with increasing Hg sub(T), primarily as a consequence of the
reduction in the ratio of aqueous methylmercury to total mercury
with increasing Hg sub(T). Methylmercury-based BAFs did not
vary as a function of Hg sub(T). The implication of this relationship
is that site-specific determination of aqueous Hg sub(T) limits
at contaminated sites may use BAFs that would be underestimates
of the appropriate BAFs to describe mercury bioaccumulation
in the system after mercury inputs have been reduced. In such
cases, regulatory limits set using site-specific BAFs might
not achieve their intended purpose of reducing mercury contamination
in fish to acceptable concentrations.
- Environmental mercury exposure in children:
South China's experience
Patrick Ip, Virginia Wong, Marco Ho, Joseph Lee and Wilfred
Pediatrics International, Vol. 46, No. 6, Dec 2004, pp. 715-721.
Background: Environmental mercury levels significantly increased
in the past decades following its increase in industrial applications.
In spite of an increasing concern on the potential harmful
effects of mercury on children, there is no reported data
for the Chinese population. The relationship between dietary
habit and environmental mercury exposure in Chinese children
was studied. Methods: The hair and blood mercury levels of
Chinese children aged above 3 years in 2000 March to September,
were studied. Sociodemographic data, dietary habits of the
past 6 months, and other risk factors for environmental mercury
exposure were collected. Those children with blood mercury
levels above the toxic range (i.e. > 45 nmol-L) and their
family members were further evaluated and their blood and
hair mercury levels were monitored before and after Fishing-Moratorium
period (June to August 2000) in South China Sea. Results:
Altogether, 137 Chinese children (mean age, 7.2 years) were
recruited. The mean hair mercury level was 2.2 p.p.m and the
mean blood mercury level was 17.6 nmol-L. There was a strong
correlation (r = 0.88) between hair and blood mercury levels
in our cohort. Frequency of fish consumption correlated with
hair (r = 0.51) and blood (r = 0.54) mercury levels. For those
children who consumed fish more than 3 times-week, hair and
blood mercury levels were twice as high as those who consumed
fish l-3 times-week and threefold of those who never consumed
fish. Five children and 12 family members had toxic blood
mercury levels. Their blood (P < 0.0001) and hair (P = 0.02)
mercury levels dropped significantly after reducing fish consumption
during Fishing-Moratorium period. Conclusion: Both blood and
hair (i.e. Tissue) mercury levels of children in Hong Kong
was elevated and correlated with the frequency of fish consumption.
- Fear of Fish: The Contaminant Controversy
Bioscience, Vol. 54, No. 11, Nov 2004, pp. 986-988.
- Health Effects of Methylmercury
Katherine M. Shea, Karen L. Perry and Mona Shah.
Physicians for Social Responsibility, 2004, pp. .
- Maternal and Fetal Mercury and n-3
Polyunsaturated Fatty Acids as a Risk and Benefit of Fish Consumption
M. Sakamoto, M. Kubota, X. J. Liu, K. Murata, K. Nakai and
Environmental science & technology, Vol. 38, No. 14, 15 Jul
2004, pp. 3860-3863.
Maternal fish consumption brings both risks and benefits
to the fetus from the standpoint of methylmercury (MeHg) and
n-3 PUFA (polyunsaturated fatty acids). MeHg is one of the
most risky substances to come through fish consumption, and
mercury concentrations in red blood cells (RBC-Hg) are the
best biomarker of MeHg exposure. Docosahexaenoic acid (DHA,
C22:6n-3), which is one of the most important fatty acids
for normal brain development and function, is also derived
from fish consumption. Our objective in this study was to
examine the relationships between RBC-Hg and plasma fatty
acid composition in mother and fetus at parturition. Venous
blood samples were collected from 63 pairs of mothers and
fetuses (umbilical cord blood) at delivery. In all cases,
fetal RBC-Hg levels were higher than maternal RBC-Hg levels.
The geometric mean of fetal RBC-Hg was 13.4 ng/g, which was
significantly (p < 0.01) higher than that of maternal RBC-Hg
(8.41 ng/g). While the average fetal/maternal RBC-Hg ratio
was 1.6, the individual ratios varied from 1.08 to 2.19, suggesting
considerable individual differences in MeHg concentrations
between maternal and fetal circulations at delivery. A significant
correlation was observed between maternal and fetal DHA concentrations
(r = 0.37, p < 0.01). Further, a significant correlation was
observed between RBC-Hg and plasma DHA in fetus (r = 0.35,
p < 0.01). These results confirm that both MeHg and DHA which
originated from fish consumption transferred from maternal
to fetal circulation and existed in the fetal circulation
with a positive correlation. Pregnant women in particular
need not give up eating fish to obtain such benefits. However,
they would do well to at least consume smaller fish, which
contains less MeHg, thereby balancing the risks and benefits
from fish consumption.
- Speciation and bioavailability of mercury
in well-mixed estuarine sediments
E. M. Sunderland, F. A. P. C. Gobas and A. Heyes, et al.
Marine Chemistry, Vol. 90, No. 1-4, 1 Nov 2004, pp. 91-105.
Despite regulations controlling anthropogenic mercury sources
in North America, high levels of mercury in coastal fish and
shellfish are an ongoing problem in Maritime Canada and the
Northeastern United States. This study presents sediment core
data from a macrotidal estuary located at the mouth of the
Bay of Fundy showing stratigraphic profiles of total and methylmercury
concentrations and potential methylation rates measured using
stable mercury isotopes. The results show that in contrast
to the expected methylmercury profile typically observed in
unmixed sediments, methylmercury production occurs throughout
the estimated 15-cm-thick active surface layer of these well-mixed
sediments. The resulting large reservoir of methylmercury
in these sediments helps to explain why mercury concentrations
in organisms in this system remain high despite emissions
reductions. Current management policies should take into account
the expected delay in the response time of well-mixed estuarine
systems to declines in mercury loading, considering the greater
reservoir of historic mercury available in these sediments
that can potentially be converted to methylmercury and biomagnify
in coastal food chains.
- Distribution of mercury over the Atlantic
Ocean in 1996 and 1999-2001
C. Temme, F. Slemr, R. Ebinghaus and J. W. Einax.
Atmospheric Environment, Vol. 37, No. 14, May 2003, pp. 1889-1897.
A series of measurements of total gaseous mercury (TGM) made
over the Atlantic Ocean in 1977-1980, 1990, and 1994 has been
continued by measurements made on board the research vessel
(RV) Polarstern during three cruises: from Bremerhaven to
Punta Quilla (October-November 1996), Bremerhaven-Cape Town-
Antarctica-Cape Town (December 1999-March 2000), and Antarctica-Punta
Arenas (February 2001). The data from these cruises are presented
and compared with the data from previous cruises. In both
hemispheres the average and median TGM concentrations in 1996
and 2000 were comparable to those measured in 1977-1980 but
substantially lower than those observed in 1990. TGM measurements
on board ships proved to provide a valuable complementary
information to measurements by a ground based monitoring network
since they show a large-scale distribution and can provide
information about sources of mercury and its long-range transport
in areas not covered by the present monitoring network.
- Potential for Increased Mercury Accumulation
in the Estuary Food Web
J. A. Davis, D. Yee, J. N. Collins, S. E. Schwarzbach and
S. N. Luoma.
San Francisco Estuary and Watershed Science, Vol. 1, No.
1, 2003, pp. .
Present concentrations of mercury in large portions of San
Francisco Bay (Bay), the Sacramento-San Joaquin Delta (Delta),
and the Sacramento and San Joaquin rivers are high enough
to warrant concern for the health of humans and wildlife.
Large scale tidal wetland restoration is currently under consideration
as a means of increasing populations of fish species of concern.
Tidal wetland restoration activities may lead to increased
concentrations of mercury in the estuarine food web and exacerbate
the existing mercury problem. This paper evaluates our present
ability to predict the local and regional effects of restoration
actions on mercury accumulation in aquatic food webs. A sport
fish consumption advisory is in place for the Bay, and an
advisory is under consideration for the Delta and lower Sacramento
and San Joaquin rivers. Mercury concentrations in eggs of
several water bird species from the Bay have exceeded the
lowest observed effect level. A variety of mercury sources,
largely related to historic mercury and gold mining, is present
in the watershed and has created a spatially heterogeneous
distribution of mercury in the Bay-Delta Estuary. Mercury
exists in the environment in a variety of forms and has a
complex biogeochemical cycle. The most hazardous form, methylmercury,
is produced at a relatively high rate in wetlands and newly
flooded aquatic habitats. It is likely that distinct spatial
variation on multiple spatial scales exists in net methylmercury
production in Bay-Delta tidal wetlands, including variation
within each tidal wetland, among tidal wetlands in the same
region, and among tidal wetlands in different regions. Understanding
this spatial variation and its underlying causes will allow
environmental managers to minimize the negative effects of
mercury bioaccumulation as a result of restoration activities.
Actions needed to reduce the uncertainty associated with this
issue include a long term, multifaceted research effort, long
term monitoring on local and regional scales, and careful
evaluation of individual restoration projects with regard
to potential increase of food web mercury.
- Variations in the isotope composition
of mercury in a freshwater sediment sequence and food web
T. A. Jackson.
Canadian Journal of Fisheries and Aquatic Sciences, Vol.
58, No. 1, Jan 2001, pp. 185-196.
Analysis of a sediment core and food-web animals from the
Niagara Basin of Lake Ontario yielded the first recorded evidence
for systematic variations in the stable-isotope composition
of mercury (Hg) in natural environments on Earth. The sediments
comprised younger strata enriched in Hg by recent pollution
overlying older strata containing background Hg only. Several
Hg isotope ratios, including super(199)Hg/ super(201)Hg, super(201)Hg/
super(204)Hg, and super(202)Hg/ super(204)Hg, varied significantly
with the Mn/Fe ratio of the extractable readily reduced oxyhydroxide
fraction of the sediment and with the concentrations of extractable
Mn or Fe fractions, or both, in the sediment, and the zone
of recent Hg pollution gave strikingly different results than
the zone of background Hg. Food-web animals displayed a progressive
increase in the super(202)Hg/ super(204)Hg ratio from lower
to higher trophic levels in the order crustaceans < forage
fish < trout; but superimposed on this trend were secondary
trends owing to systematic decreases in the ratio from planktonic
to benthic crustaceans and, correspondingly, from plankton-eating
to benthos-eating forage fish. The results of the research
suggest fractionation of Hg isotopes by natural processes,
including Hg methylation, with effects linked to temporal
variations in the oxidation-reduction potential of the sediments.
These findings show that Hg isotopes could provide valuable
but as yet untapped information about the sources and biogeochemical
cycling of natural and anthropogenic Hg.
- Understanding Minamata disease and
strategies to prevent further environmental contamination by
Pergamon, UK: Elsevier Science Ltd., 2000
Minamata disease is a neurological disorder caused by methylmercury
poisoning which originated from the discharge of wastewater
containing methylmercury from chemical plants in Japan. Residents
in the area who consumed large amounts of fish and other seafoods
suffered from the disease. The main symptoms consist of sensory
disturbance, ataxia, restriction of visual field and hearing
impairment. Various measures have been taken to deal with
Minamata disease, including environmental pollution control,
treatment for patients, and promotion of research activities.
Through the compensation law, 2,952 persons have been certified
as Minamata disease patients, and a total of approximately
144 billion yen had been paid in compensation by the responsible
companies as of March, 1999. Meanwhile, people who were not
certified as patients have filed suits against the Japanese
Government and local government challenging the diagnostic
criteria. The Japanese Government, patients and their supporters
reached an agreement in 1996, and Minamata disease legal issues
were finally resolved, 40 years after the outbreak. The Minamata
experience has left us with an invaluable understanding of
the importance of taking thoroughgoing measures to prevent
health damage from environmental pollution.
- Mercury in the Canadian Environment:
Current Research Challenges
L. M. Azzaria and R. G. Garrett.
Geoscience Canada [Geosci.Can.], Vol. 25, No. 1, Mar 1998,
Elevated methylmercury concentrations are common in fish
and other wildlife in ecosystems remote from any industrial
point sources. Concern about chronic exposure to methylmercury
for people who depend on fish as a dietary staple has focused
attention on mercury sources and cycling processes in rural
and remote areas, and on the potential for airborne mercury
to travel hundreds to thousands of kilometres. A number of
other studies have demonstrated that elevated concentrations
of mercury in fish may be attributable to local geological
sources. Compared to the large body of literature that is
emerging on anthropogenic sources, however, there is a relative
lack of research aimed at quantifying the contribution of
mercury from natural sources. This has resulted in a debate
over the relative significance of anthropogenic and natural
mercury inputs to rural and remote lakes. Geoscience research
is needed to improve our understanding of the biogeochemical
cycling of mercury species released from common sulphide minerals
and other crustal sources into soil, sediments, air, water,
vegetation and ultimately into the human food chain.
- Uptake, toxicity, and trophic transfer
of mercury in a coastal diatom
R. P. Mason, J. R. Reinfelder and F. M. M. Morel.
Environmental science & technology, Vol. 30, No. 6, Jun 1996,
The primary mechanisms controlling the accumulation of methylmercury
and inorganic mercury in aquatic food chains are not sufficiently
understood. Differences in lipid solubility alone cannot account
for the predominance of methylmercury in fish because inorganic
mercury complexes (e.g., HgCl sub(2)), which are not bioaccumulated
in fish, are as lipid soluble as their methylmercury analogs
(e.g., CH sub(3)HgCl). Mercury concentrations in fish are
ultimately determined by methylmercury accumulation at the
base of the food chain, which is governed by water chemistry,
primarily pH and chloride concentration. Our studies of mercury
speciation, toxicity, and phytoplankton uptake demonstrate
that passive uptake of uncharged, lipophilic chloride complexes
is the principal accumulation route of both methylmercury
and inorganic mercury in phytoplankton. The predominance of
methylmercury in fish, however, is a consequence of the greater
trophic transfer efficiency of methylmercury than inorganic
mercury. In particular, methylmercury in phytoplankton, which
accumulates in the cell cytoplasm, is assimilated by zooplankton
four times more efficiently than inorganic mercury, which
is principally bound in phytoplankton membranes. On the basis
of these results, we constructed a simple model of mercury
accumulation in fish as a function of the overall octanol-water
partition coefficient of methylmercury. Our model can explain
the variability of mercury concentrations in fish within,
but not among, different lake regions.
- Mercury in the Adriatic
J. Ui and S. Kitamura.
Marine Pollution Bulletin, Vol. 2, No. 4, 1971, pp. 56-58.
Environmental pollution by organic mercury compounds in Japan
and in Sweden is briefly discussed with particular regard
to Minamata disease and sources of contamination. Investigations
were carried out at the ANIC factory at Ravenna, Italy, which
synthesises acetaldehyde using a mercury catalyst. Elevated
mercury concs have been observed in fish in the large lagoon
near the waste discharge of the factory as well as in the
harbour channel and its mouth. Mercury pollution by factory
waste is suspected. However there is no remarkable mercury
pollution in samples of fish on sale in fishmarkets or caught
in districts far from the mouth of the harbours. Typical symptoms
of Minamata disease have never been recorded in the district.
The much higher conc of organic substances in sea water in
the Adriatic than in Japan or Sweden may be important since
it is known that the more advanced the state of eutrophication
of a water body, the less the accumulation of toxic material
into fishes because of the dilution effect of organic sub
stances in the water. The significance of a future ecological
investigation of the lagoon on the north side of the factory
is pointed out. Other possible mercury sources are discussed
and the need for further investigation stressed.