Behavioural response to the bioavailability of inorganic mercury in the hydrothermal mussel Bathymodiolus azoricus
IMAR Centre of the University of Azores, Department of Oceanography and Fisheries, 9900 Horta, Portugal
* Author for correspondence (e-mail: EnikoKadar{at}notes.horta.uac.pt)
Accepted 24 November 2004
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Summary |
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As a result of Hg exposure, significant increase in duration, as well as decline in frequency of shell gaping occurred, which did not recover to pre-exposure levels following 21 days of Hg-free treatment. An increase in the duration of open-shelled status may indicate the absence of an avoidance reaction in the vent mussel coming in contact with Hg, unlike other bivalves that normally close their shells in response to stress compounds. Alternatively, it may suggest that Hg had an inhibitory effect on the adductor muscle function that is responsible for closing the shells. As a result, elevated Hg levels were measured in the soft tissues (270±71 µg g-1 in gills, 245±52 µg g-1 in digestive glands, 93±25 µg g-1 in the mantle and 46±9 µg g-1 in the foot), in byssus threads (peak levels of 442±89 µg g-1) and in pseudofaeces (reaching levels as high as 1000 µg g-1). Overall, gills contributed 75% to the total Hg body burden followed by mantle (13%), digestive gland (7%), byssus (3%) and foot (2%). Tissue Hg levels remained elevated in mussels transferred to Hg-free seawater even after 21 days, despite the high concentrations persistently eliminated with pseudofaeces both, during and after, exposure.
This potential for bioaccumulation of inorganic Hg (concentration factors reached the order of magnitude of 104) by the vent mussel, which does not seem to prevent uptake by shell closure, suggests that the main Hg-handling strategy is elimination via mucus.
Key words: mercury, shell gaping, hydrothermal vents, bivalve, Bathymodiolus azoricus
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Introduction |
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Mercury is a ubiquitous element, which is highly toxic
(Florentine, 1991), and is
present in the environment under three main forms: elemental Hg, divalent
`inorganic' Hg and organo-Hg (methyl-, dimethyl-, aril-Hg, etc). Organic forms
of Hg have been previously considered as having a greater lipid solubility
than the inorganic forms, which allows them to more readily cross cell
membranes and be absorbed. However, the work over a decade conducted by Mason
and co-workers (Mason et al.,
1993
,
1994
,
1996
, 1997,
2000
;
Andres et al., 2002
)
contradicts the above reason for the bioaccumulation of methyl Hg (MMHg) over
inorganic Hg, and concludes that both MMHg and inorganic Hg uptake involves a
number of mechanisms, both passive and active (energy dependent), and the
importance of each is highly dependent on the particular organism and on the
specific tissue membrane. Thus the toxicity of Hg to aquatic organisms is
widely recognized (Hassett-Sipple et al.,
1997
) and occurs even at low concentrations (Amiardtriquet et al.,
1993; Bellas et al., 2001
;
Hill and Soares, 1987
;
Sheuhammer, 1987
;
Simas et al., 2001
). The
general mechanism of action of both Hg and MMHg are based on their relatively
non-specific ATPase inhibition that disturbs osmotic and ionic regulation
(Barradas and Pequeux, 1996
;
Pequeux et al., 1996
;
Pagliarani et al., 1996
;
Jagoe et al., 1996
).
Furthermore, while the presence of Hg in the external medium appears to
influence ion regulation, the Hg, once taken up, is sequestered throughout the
gill tissues and not in specific cells
(Jagoe et al., 1996
).
Histochemical examination of tissues after exposure showed localization of Hg
in the gill of the green crab Carcinus maenas and suggested that it
was bound to the cuticle/membrane complex whereas MMHg was distributed evenly
in the cell/cytoplasm (Laporte et al.,
2002
). Domouhtsidou and Dimitriadis
(2000
) found, in mussels, that
Hg was concentrated in the abfrontal part of the gill filament and in the
lysosomes and residual bodies of the gut tissue. Similarly, Jensen and Baatrup
(1988
) found that while Hg was
widely distributed, it was concentrated in the apical part of intestinal
epithelial cells and was mostly within cell lysosomes that are probably
responsible for the sequestration and elimination of the metal.
Hg levels increase as it is passed up the aquatic food chain, resulting in
relatively high levels of mercury in fish, where it is mainly (>80%) found
in the methylated form (Fergusson,
1990) and ultimately consumed by humans. Furthermore, there is
recent evidence suggesting that the high levels of methyl mercury in some
predators in the Atlantic most probably originate from hydrothermal vents and
deep ocean sediments, and not from increased pollution as previously thought
(Kraepiel et al., 2003
). Under
`hydrothermal' conditions, when the hot water interacts with the volcanic
rocks, mercury and other elements are leached out and remain in solution in
the thermal fluid until it reaches the sea floor
(Prol-Ledesma et al., 2002
)
giving rise to cinnabar deposits (Stoffers
et al., 1999
) or alternatively, undergo methylation being
transformed into organic forms by micro-organisms. However, in the water
surrounding mussel communities, because of the extreme reducing conditions and
sulphide load (Sarradin et al.,
1999
), formation of the stable HgS would prevent much of the
mercury from being methylated (Fergusson,
1990
) that may indicate preponderant presence of the metal in its
inorganic form. Acknowledging the problems associated with prediction of
chemical species of trace metals present under such dynamic ecosystems, we
cautiously make assumptions on putatively elevated levels of inorganic Hg. At
any rate, invertebrates here are exposed to the metal for periods with
geological time-scale, and thus may have developed effective detoxification
mechanisms that may have deeply rooted evolutionary significance. Typical
mechanisms of handling high levels of toxic elements in species inhabiting
this mixing zone at hydrothermal vents are unresolved to date.
The genus Bathymodiolus has 11 species known to date, having
world-wide distribution (Von Cosel et al.,
1999); Bathymodiolus azoricus is endemic at many of the
hydrothermal vents of the MAR. Its ecological success under the extreme
environment of the vent is due to simultaneous nutrient uptake from several
sources: firstly by harbouring endosymbiotic chemoautotrophic bacteria (both
methanotrophs and thiotrophs) within specialised cells of the gills
(Pond et al., 1998
), secondly,
by filter-feeding (Page et al.,
1991
; Le Pennec and Bejaoui,
2001
) and finally it can also absorb and incorporate dissolved
amino acids (Fiala-Medioni et al.,
1986
; Fiala-Medioni et al.,
1994
; Fiala-Medioni et al.,
2002
; Fisher et al.,
1988
).
B. azoricus has been chosen as a model organism for this study,
primarily because it naturally accumulates high levels of heavy metals,
including Hg. The main organs accumulating heavy metals are the byssus
followed by the gill and the digestive gland (E. Kadar, J. J. Powell, V. Costa
and R. S. Santos, unpublished) in agreement with results of other authors
(Rousse, 1998; Fiala-Medioni et al.,
2000). Mantle levels are lower, this organ being mostly devoted to
storage and secretion of the shell. We measured Hg levels in tissues of B.
azoricus from the MAR vent sites and highest total Hg was recorded in
gills of mussels collected from Rainbow (average 12 µg g-1 dry
weight) followed by those from Lucky Strike (8 µg g-1). Mussels
collected from Menez Gwen (MG) had lowest concentrations among vent sites of
the MAR (2.85±0.3 µg g-1 in the digestive gland,
2.4±0.7 µg g-1 in the gill, 1.6±0.4 µg
g-1 in byssus threads and 0.4±0.2 µg g-1 in
the mantle), possibly because of the local exposure levels linked to the
undiluted fluid chemistry (Charlou et al.,
2000
) and/or metal speciation. In spite of these relatively low Hg
concentrations in mussels, MG was chosen for experimental sampling because it
is the shallowest (870 m), and thus long-term laboratory maintenance of
mussels is possible without specialised pressure gear
(Kadar et al., 2005
). Another
reason for selecting this particular organism for our experiment was its
feeding flexibility that enables contact with both soluble and particulate
forms of the metal that would impose highly efficient detoxification
mechanisms. The extent of exposure and thus the potentially toxic effect of a
metal in a bivalve will depend primarily on the duration of direct contact
with the toxic agent, i.e. when the shell is open. The present study
therefore, examines duration and frequency of shell gaping activity,
indicative of filter feeding in other bivalves
(Kádár et al.,
2001
; Riisgård,
2003
), in order to assess the response of the vent bivalve B.
azoricus to inorganic Hg. In a filter feeder bivalve, under optimal
conditions of feeding, the adductor muscle is relaxed and the valves are open.
Extended periods of shell gape are interrupted by rest periods, giving a
continuous pattern of periodicity that may, however, be perturbed by changes
in environmental conditions, thus providing a measure of the impact of
pollutants (Salánki,
1992
; Kontreczky et al.,
1997
). In our experimental conditions, and based on our previous
finding on the total loss of endosymbiont bacteria in B. azoricus
following transfer to sulphide/methane-free seawater for up to 30 days, the
assumption is made that mussels were filter-feeding. Thus, shell gaping as
proportional to the time engaged in filtering of B. azoricus was
monitored following 21 days exposure to inorganic Hg followed by an additional
21 days in Hg-free seawater to look into recovery processes. Exposure
concentrations, i.e. daily addition of 100 nmol l-1 (20 µg
l-1) for 21 days, were above those encountered in its natural
habitat (an average of 0.18 nmol l-1 total Hg was measured in
discrete water samples from above mussel clumps at Menez Gwen; data not shown)
in order to induce a well assessable behavioural response. Total Hg in tissues
(gill, digestive gland, mantle, foot and byssus threads) were measured during
and after exposure in order to determine biological half life and
uptake/release dynamics. Water Hg concentrations were also monitored for
dosage evaluation. Specific Hg-handling strategies that enable these vent
bivalves to survive under the hostile hydrothermal environment are discussed
with emphasis on the metalorganism interactions in this unique
habitat.
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Materials and methods |
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Experimental design
The experiments carried out for this study complied with the current
pertinent laws in Portugal. A total of 80 adult Bathymodiolus
azoricus (Von Cosel) (shell length 711 cm) were used in the
experiment carried out between February and May 2003. Twenty individuals were
placed in each of the three replicate, 8 l volume experimental tanks (HDP
containers) containing sand-filtered seawater that was pumped into a reservoir
from an unpolluted bay in Horta, Azores (38.5°N 28.7°W). The
experiment lasted for 63 days and consisted of 21 days of control in Hg-free
seawater followed by exposure to Hg by the daily addition of 160 µl
HgCl2 from a commercial standard solution of 1000 mg l-1
at pH 2, yielding a final added concentration of 20 µg l-1,
followed by 21 days of recovery in Hg-free seawater. Full water changes were
completed at the end of each week. One additional aquarium hosted twenty
individuals in seawater with no Hg addition and served as control. Prior to
water changes, i.e. on a weekly basis, water samples were taken for total Hg,
both prior to and after filtration, and pseudofaeces was collected using
decontaminated Pasteur pipettes. We termed `pseudofaeces' the gelatinous,
mucus-bound material and care was taken to separate it from true faeces that
is darker and has a more consistent texture. On days 7, 15 and 21 (control,
exposure and post-exposure, respectively) five specimens from each replicate
tank (including the untreated control) were measured and dissected into the
main organs of suspected Hg metal storage (i.e. gill, digestive gland, mantle,
foot and byssus) and kept frozen until dehydration, acid digestion and
analysis. Animals removed for dissection were replaced by marked mussels, with
similar shell length in order to keep variations in the system's equilibrium
to a minimum.
Water parameters (pH, dissolved oxygen and temperature) were measured daily using portable sensors, and were maintained constant during the experiment: dissolved oxygen ranged between 65 and 80%, pH was 8±0.4 and temperature ranged between 7 and 9°C (same as the mussels' natural habitat at Menez Gwen). Average total Hg concentrations were measured both in the filterable and the filter passing fractions, prior to each weekly water change and were as follows: (a) during the 21 days of the pre-exposure period, referred to as control: not detectable (detection limit of the method employed was 6 ng l-1); (b) during 21 days exposure, water Hg ranged between 25 and 35 µg l-1 with a constant total/filter-passing Hg ratio around 1.5; (c) during recovery, while animals were kept in Hg-free seawater, total Hg decreased to values below 2 µg l-1.
Shell gape monitoring
The shell gaping activity of three animals (one in each replicate aquarium)
was recorded using a device called `mussel actograph'
(Veró and Salánki,
1969) which is shown schematically in
Fig. 1. This device permits
continuous monitoring of adductor muscle activity, without disturbing the free
movement of the mussels, using the magnetic field built up between the shells
while opening and closing. Duration of shell opening and closing was recorded
continuously over the 63-day experiment (21 days control, 21 days exposure and
21 days recovery). Using the signal analysis system Signalview (1994 Real Time
Devices USA, Inc.) calculation of average duration and frequency of shell
gaping was possible simultaneously for three animals. Based on the positive
correlation between shell gape and filtration rate [reviewed by Riisgård
(2001
) and experimentally
supported by Riisgård (2003)] when the shell is widely open, we only
considered the duration of shell gapes when shells were open to their maximum.
In order to see possible exposure-time-dependent effect of Hg, duration of
consecutive shell gaping was averaged for 7-day sub periods within each
treatment. This experimental design made it possible to compare the nine time
periods as well as the three treatments using analysis of variance in order to
demonstrate potential behavioural changes induced by Hg as well as its
exposure-time-dependent effect.
|
Water sampling for total and filter-passing Hg analysis
Aliquots of 10 ml were taken prior to each water change, on day 7, 15 and
21 (of the control, exposure and recovery periods respectively), from the
middle of the aquarium, 10 cm below the water surface. Samples were acidified
to pH 2 by adding concentrated HNO3 and kept refrigerated in HDP
vials until analysis. Identical samples were taken and filtered through 0.45
µm pore size Teflon membranes (Millipore, Iberica, Spain) and stored as
above for total Hg analysis in the filter-passing fraction that would
represent chiefly dissolved forms of the metal. Water samples were
post-digested by bromination and total Hg was analysed by Cold Vapour Atomic
Fluorescence Spectrometry on the PSA Millenium Merlin System (PSA Analytical,
Orpington, Kent, UK) using a tin (II) reductant (Millenium Merlin 2001 method
for total mercury in drinking, surface, ground, industrial and domestic waste
waters and saline waters). Standards were prepared in filtered and acidified
seawater using a commercially available 1000 mg l-1 Hg standard
solution (Merck), and ranged between 0 and 100 µg l-1. Accuracy
of the analytical method was monitored by analysing sample spikes and blank
spikes. Spike recoveries were between 86 and 115%.
Tissue partitioning of Hg
Whole tissues (gill, mantle, digestive gland, foot and byssus threads) and
pseudofaeces samples were acid digested prior to analysis as previously
described (Jugdaohsingh et al.,
1998). Briefly, 0.51 g of dry tissue (previously
lyophilised using a Savant refrigerated vapour trap system, overnight) was
digested with equal volumes (1 ml added to 0.1 g dry weight) of Aristar grade
concentrated (69% v/v) nitric acid and 30% hydrogen peroxide. Digested samples
were diluted 12x with high purity deionised water prior to analysis on
the previously described PSA for total Hg using a tin (II) reductant
(Millenium Merlin method for determination of total mercury in mussel
homogenate Mytilus edulis, Application note 019). Standards
were prepared in 4% HNO3 using 1000 mg l-1 Hg standard
solution, and ranged between 0 and 20 ppb (parts per billion) for control
animals, and between 0 and 200 ppb for mussels dissected during and after
exposure. The accuracy of the analytical method was monitored by analysing two
different certified reference materials: CRM 414 (plankton) and CRM 278R
(mussel tissue), sample spikes and blank spikes. For both reference materials
measured, Hg concentrations were within 10% variation from the certified
values. Spike recoveries were between 86 and 115%.
Statistical analysis
Factorial analysis of variance was used to test statistical significance of
differences in Hg concentration in tissues as compared to control values, as
well as differences in duration of shell gaping periods. Specific differences
between treatments were examined a posteriori using the
StudentNeumanKeuls (S-N-K) multiple range test
(Steel and Torrie, 1980).
Normal distribution of data was confirmed by the One-Sample
KolmogorovSmirnov test. Calculations were made using SPSS (SPSS Inc.
1989).
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Results |
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Concentration of Hg in pseudofaeces (samples pooled for all animals in individual aquaria) were one order of magnitude higher than in soft tissues and peaked on the second week of exposure with over 1000 µg g-1 that dropped to 800 µg g-1 by the end of the 21-days exposure and remained elevated (around 600 µg g -1) on day 21 of recovery (Fig. 3).
|
The effect of Hg on shell gaping activity
Duration of shell opening and closing was continuously monitored during the
63-day experiment 21 days under control with no Hg addition, followed
by 21 days exposure to Hg and a further 21 days of recovery in Hg-free
seawater. Sum of the consecutive shell gapes over 1-week sub-periods of the
control, exposure and recovery are shown in
Fig. 4A together with the
frequency of shell openings (Fig.
4B). The full statistical details are given in
Table 1. Under control
conditions mussels spent 54% of total time with their shells widely open
(average 5500 min per week), the average duration of consecutive shell gapes
being 37 min, i.e. frequency of 150 times/week. Exposure to Hg caused a
significant increase (P=0.001) in the total time that animals spend
with open shells as compared to pre-exposure. The frequency of consecutive
shell openings decreased significantly (P<0.001) as shown in
Fig. 4. Following placement of
animals in Hg-free seawater the time that mussels spent with open shells
further increased (P<0.001) as compared to during exposure, but no
significant difference was detected (P<0.05 level), in the
frequency of shell gaping, i.e. the consecutive shell gapes became longer.
Time of exposure as an influencing factor, per se, did not have
significant impact (P<0.05) on shell gaping as the 7-day sub
periods of the three treatments (control, exposure and recovery) were
similar.
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Discussion |
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Considering the individual mass of each organ it is notable the 75% of
total Hg body burden was found in the gills, followed by mantle (13%),
digestive gland (7%), byssus (3%) and foot (2%). Byssus thread concentrations,
otherwise highest among all organs, declined by the third week of exposure,
possibly because of renewal of threads. To prove this hypothesis however, a
more in-depth investigation on the physiology and renewal dynamics of this
organ is needed. However, Hg levels in byssus were consistently an order of
magnitude higher than in soft tissues, which is in agreement with our previous
results on several heavy metals, including Hg, being consistently principally
bioconcentrated in byssus threads of B. azoricus from various vent
sites of the MAR (E. Kadar, J. J. Powell, V. Costa and R. S. Santos,
unpublished). Byssus is a target for metallic elements such as
Zn2+, Cu2+ and Fe2+
(Gundacker, 1999) since they
play a significant role in the structural integrity of the thread and are
essential for the normal functioning of this organ
(Lucas at al., 2002
). Metal
chelate cross-links created with histidine were reported in other bivalves
(Lucas at al., 2002
) that may
have accounted for the high Hg concentrations measured in the byssus of
Hg-exposed B. azoricus in this study. Ultrastructural evidence, both
qualitative and quantitative, on the byssus-Hg interaction is in preparation
in order to assess its role in detoxification of Hg.
Tissue concentrations remained above control levels in all organs following
transfer of mussels to Hg-free seawater for 3 weeks, suggesting that the metal
is firmly bound and depuration requires a longer period. Biological half-life
of Hg was only reached in gills, while digestive gland and byssus still
maintained over 50% of the peak exposure levels by day 21 of recovery. This
however, approximates to the biological half-life obtained for littoral
bivalves (not exceeding 40 days when administered as inorganic Hg, according
to data reviewed by Jorgensen et al.,
2000). For instance, biological half life of Hg (acetate) in the
American oyster Crassostrea virginica exposed to two distinct
concentrations of Hg (10 and 100 µg l-1) for 40 days that
resulted in tissue concentrations of 12 and 92 µg kg-1 Hg (wet
weight), was 16.8 and 9.3 days (Cunningham
and Tripp, 1975
). In spite of these differences in exposure
conditions, there is similarity, to a certain extent, of the Hg half-life of
the vent mussel with that of its shore analogues, but there is no exact proof,
owing to the lack of exposure experiments focused on this aspect.
The range and form of Hg to which B. azoricus is exposed in its
natural habitat is virtually unknown because of the wide fluctuations of
temperatures, pressures and chemical conditions present in the mixing zone.
Owing to the reducing conditions and the sulphide ion load in water
surrounding mussel communities at Menez Gwen
(Sarradin et al., 1999),
formation of the low soluble HgS would prevent much of the mercury from being
methylated (Fergusson, 1990
).
This would indicate an unusual inorganic Hg bioavailability at hydrothermal
vents. Our experiment also confirms an enhanced Hg bioavailability to the vent
mussel in spite of its widely accepted low absorption rate (7-15%) because of
its limited membrane-crossing ability when present as inorganic salts, and it
is in agreement with conclusions reached by Andres et al.
(2002
), who compared the data
available in the literature with respect to limited bioavailability of
inorganic Hg as compared to MMHg. Additionally, our simplified experimental
system without inorganic sulphide supply, permitted calculations of
partitioning of the metal within the system. Thus, out of the total 3.36 mg
inorganic Hg (i.e. daily administration of 160 µl of 1000 µg
ml-1 standard solution) approximately 77.7% was bioaccumulated in
tissues, 2.7% was bound to mucus and 19.4% remained in the water column. Post
exposure tissue levels indicate slow depuration that is typical for MMHg
accumulation (Fergusson,
1990
). However, it is unlikely that in our system a significant
bacterial methylation took place in the water, even if it was not conducted in
sterile seawater. Endosymbiotic methylation can be ruled out since animals
were acclimatised for 2 weeks followed by 21-days control period in seawater
not supplied with inorganic nutrients that is long enough to lose their
natural endosymbionts (E. Kadar, J. J. Powell, V. Costa and R. S. Santos,
unpublished). Methylation is also possible in the digestive tract via
well-documented mechanisms involving CH3 donors such as
methylcobalamin (a derivative of vitamin B12)
(Fergusson, 1990
).
Nevertheless, until these mechanisms are shown in B. azoricus and
considering our experimental conditions, it is thought that what was largely
bioavailable was in its inorganic form and that bioaccumulation took place
without lethal consequences and/or shell closure as observed in other
bivalves. Therefore an efficient mechanism may have been responsible for
sequestering the metal and preventing its toxicity at these levels.
Metallothioneins are small, soluble, heat stable proteins known to be involved
in the detoxification of Hg, and other trace elements
(Ng and Wang, 2000
). Although
found in relatively high quantity in B. azoricus
(Rousse et al., 1998
;
Fiala-Medioni et al., 2000
),
their levels did not reflect the metal burden of the tissue especially in the
symbiont-bearing organ. In other words no relationship between metals and
total metallothionein levels was evident, which may also suggest the
prevalence of an alternative detoxification mechanism. Future in-depth
ultrastructural investigations on putative Hg-bearing organelles may answer
these questions.
The relatively unchanged total Hg concentration in the water column at the end of each consecutive week of exposure may suggest that duration of exposure did not have notable influence on the rate of uptake, which is consistent with the prolonged shell gapes. Up to one third of the total Hg from the water column was retained by 0.45 µm pore-size membranes, indicating the presence of Hg-hydroxipolymers and/or Hg adsorbed onto particles. However, a complete picture on Hg speciation during the experiment is beyond the scope of this study, and it would involve more frequent sampling, and also methyl-Hg analysis. We instead, provide evidence for the bioavailability of inorganic Hg to the vent bivalve that resulted in the increase in duration, with simultaneous decrease in frequency, of its shell gaping. In spite of high Hg levels recorded in tissues, no mortality was recorded during the 63-day experiment, which might indicate an efficient Hg-detoxification mechanism developed by the vent mussel, and which deserves further investigations.
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Acknowledgments |
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References |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Amiard-Triquet, C., Jeantet, A. Y. and Berthet, B. (1993). Metal transfer in marine food-chains bioaccumulation and toxicity. Acta Biol. Hung. 44,387 -409.[Medline]
Ando, T., Yamamoto, M., Tomiyasu, T., Hashimoto, J., Miura, T. Nakano, A. and Akiba, S. (2002). Bioaccumulation of mercury in a vestimentiferan worm living in Kagoshima Bay, Japan. Chemosphere 49,477 -484.[CrossRef][Medline]
Andres, S., Laporte, J. M. and Mason, R. P. (2002). Mercury accumulation and flux across the gills and the intestine of the blue crab (Callinectes sapidus). Aquatic Toxicol. 56,303 -320.[CrossRef][Medline]
Ballantine, D. and Morton, J. E. (1956). Filtering, feeding and digestion in the lamellibranch Lasaea rubra.J. Mar. Biol. Assn. UK 35,241 -274.
Barradas, C. and Pequeux, A. (1996). Uptake of mercury by the gills of the fresh water Chinese crab Eriocheir sinensis (MilneEdwards). Comp. Biochem. Physiol. 113C,157 -160.[CrossRef]
Bellas, J., Vazquez, E. and Beiras, R. (2001). Toxicity of Hg, Cu, Cd, and Cr on early developmental stages of Ciona intestinalis (Chordata, Ascidiacea) with potential application in marine water quality assessment. Water Res. 35,2905 -2912.[CrossRef][Medline]
Charlou, J. L., Donval, J. P., Douville, E., Jean-Baptiste, P., Radford-Knoery, J., Fouquet, Y., Dapoigny, A. and Stievenard, M. (2000). Compared geochemical signatures and the evolution of Menez Gwen 37 degrees 50' N and Lucky Strike 37 degrees 17' N hydrothermal fluids, south of the Azores Triple Junction on the Mid-Atlantic Ridge. Chem. Geol. 171,49 -75.[CrossRef]
Conrad, M. E., Umbreit, I. N. and Moore, E. G. (1991). A role for mucin in the absorption of inorganic iron and other metal-cations a study in rats. Gastroenterol. 100,129 -136.[Medline]
Costa, M. M., Peneda, M. C. and Leite, R. (1988). Heavy metals monitoring by the pixe technique in the coastal zone of Portugal. Environ. Technol. Lett. 9, 941-944.
Cunningham, P. A. and Tripp, M. R. (1975). Factors affecting the accumulation and removal of mercury from tissues of the American oyster Crassostrea virginica. Mar. Biol. 31,311 -319.[CrossRef]
Devi, V. U. (1996). Changes in oxygen consumption and biochemical composition of the marine fouling dreissinid bivalve Mytilopsis sallei (Recluz) exposed to Mercury. Ecotoxicol. Environ. Safety 33,168 -174.[CrossRef][Medline]
Domouhtsidou, G. P. and Dimitriadis, V.K. (2000). Ultrastructural localization of heavy metals (Hg, Ag, Ph, and Cu) in gills and digestive gland of mussels, Mytilus galloprovincialis (L.). Arch. Environ. Contam. Toxicol. 38,472 -478.[CrossRef][Medline]
Falkner, K. K. et al. (1997). Minor and trace element chemistry of Lake Baikal, its tributaries, and surrounding hot springs. Limnol. Oceanog. 42,329 -345.
Fergusson, J. E. (1990). The Heavy Elements: Chemistry, Environmental Impact and Health Effects, pp.429 -524. Oxford, UK: Pergamon Press.
Fiala-Medioni, A., McKiness, Z. P., Dando, P., Boulegue, J., Mariotti, A., Alayse-Danet, A. M., Robinson, J. J. and Cavanaugh, C. M. (2002). Ultrastructural, biochemical, and immunological characterization of two populations of the mytilid mussel Bathymodiolus azoricus from the Mid-Atlantic Ridge: evidence for a dual symbiosis. Mar. Biol. 141,1035 -1043.[CrossRef]
Fiala-Medioni, A., Metivier, C., Herry, A. and Lepennec, M. (1986). Ultrastructure of the gill of the hydrothermal-vent Mytilid Bathymodiolus sp. Mar. Biol. 92, 65-72.[CrossRef]
Fiala-Medioni, A., Michalski, J. C., Jolles, J., Alonso, C. and Montreuil, J. (1994). Lysosomic and lysozyme activities in the gill of bivalves from deep hydrothermal vents. CR Acad. Sci. III 317,239 -244.
Fiala-Medioni, A., Rousse, N., Cosson, R., Boulegue,?. and Sarradin, P. M. (2000). Bioaccumulation and detoxication of heavy metals in Bathymodiolus azoricus (Von Cosel et al., 1998) from Azores hydrothermal vents on Mid-Atlantic Ridge. Abstracts of the 7th FECS Conference [OP 3.2].
Fisher, C. R., Childress, J. J., Arp, A. J., Brooks, J. M., Distel, D., Favuzzi, J. A., Felbeck, H., Hessler, R., Johnson, K. S., Kennicutt, M. C., Macko, S. A., Newton, A., Powell, M. A., Somero, G. N. and Soto, T. (1988). Microhabitat variation in the hydrothermal vent mussel, Bathymodiolus thermophilus, at the Rose Garden vent on the Galapagos Rift. Deep-Sea Research Part a. Oceanographic Research Papers 35,1769 -1791.[CrossRef]
Florentine, M. J. (1991). Grand rounds: elemental mercury poisoning. J. Clin. Pharmacol. 10,213 -221.
Fretter, V. and Graham, A. (1976). Functional Anatomy of Molluscs. London, UK: Academic Press.
Gundacker, C. (1999). Tissue-specific heavy metal (Cd, Pb, Cu, Zn) deposition in a natural population of the zebra mussel Dreissena polymorpha, pallas. Chemosphere 38,3339 -3356.[CrossRef][Medline]
Geret, F., Jouan, A., Turpin, V., Bebianno, M. J. and Cosson, R. C. (2002). Influence of metal exposure on metallothionein synthesis and lipid peroxidation in two bivalve mollusks: the oyster (Crassostera Gigas) and the mussel (Mytilus edulis). Aquat. Living Res. 15,61 -66.[CrossRef]
Hassett-Sipple, B. (1997). Health effects of mercury and mercury compounds. Mercury Study Report to Congress. Environmental Protection Agency (EPA) V.
Hill, E. F. and Soares, J. H. (1987). Oral and intramuscular toxicity of inorganic and organic mercury chloride to growing quail. J. Toxicol. Environ. Health 20,105 -116.[Medline]
Jagoe, C. H., Shaw-Allen, P. L. and Brundage, S. (1996). Gill Na+,K+-ATPase activity in largemouth bass (Micropterus salmoides) from three reservoirs with different levels of mercury contamination. Aquat. Toxicol. 36,161 -176.[CrossRef]
Jensen, P. K. and Baatrup, E. (1988). Histochemical demonstration of mercury in the intestine, nephridia and epidermis of the marine polychaete Nereis virens exposed to inorganic mercury. Mar. Biol. 97,533 -540.[CrossRef]
Jorgensen, L. A., Jorgensen, S. E. and Nielsen, S. N. (2000). ECOTOX Ecological Modelling and Ecotoxicology. Elsevier Science, First electronic edition: www.elsevier-ecotox.com.
Jugdaohsingh, R., Campbell, M. M., Thompson, R. P. H., McCrohan, C. R., White, K. N. and Powell, J. J. (1998). Mucus secretion by the freshwater snail Lymnaea stagnalis limits the soluble aluminium concentration of water. Environ. Sci. Tech. 32,2591 -2595.[CrossRef]
Juniper, S. K., Thompson, J. A. J. and Calvert, S. E. (1986). Accumulation of minerals and trace elements in biogenic mucus at hydrothermal vents. Deep-sea Res. 33,339 -347.
Kádár E., Bettencourt, R., Costa, V., Santos, R. S., Cunha, A. L. and Dando, P. (2005) Experimentally induced endosymbiont loss and re-acquirement in the hydrothermal vent bivalve Bathymodiolus azoricus. J. Exp. Mar. Biol. Ecol. (in press).
Kádár, E., Salánki, J., Jugdaohsingh, R., McCrohan, C. R. and White, K. N. (2001). Avoidance reactions of the swan mussel Anodonta cygnaea to sub-lethal aluminium concentrations, Aquat. Toxicol. 55,137 -148.
Kádár, E., Salánki, J., Powell, J., White, K. N. and McCrohan, C. R. (2002). Effect of aluminium on the filtration activity of the freshwater mussel Anodonta cygnea L at neutral pH. Acta Biol. Hung. 53/4,485 -493.[CrossRef][Medline]
Kontreczky, Cs., Farkas, A., Nemcsók, J. and Salánki, J. (1997). Short and long term effects of deltamethrin on filtering activity of the freshwater mussel (Anodonta cygnea L.). Ecotoxicol. Environ. Safety 38,195 -199.[CrossRef][Medline]
Kraepiel, A. M. L., Keller, K., Chin, H. B. Malcolm, E. G. and Morel, F. M. M. (2003). Sources and variations of mercury in tuna. Environ. Sci. Technol. 37,5551 -5558.[CrossRef][Medline]
Laporte, J. M., Truchot, J. P., Mesmer-Dudons, N. and Boudou, A. (2002). Bioaccumulation of inorganic and methylated mercury by the gills of the shore crab Carcinus maenas: transepithelial fluxes and histochemical localization. Mar. Ecol. Progr. Ser. 231,215 -228.
Le Pennec, M. and Bejaoui, N. A. (2001). The conquest of reduced deep marine ecosystems by mytilid mussels. Bull. Soc. Zool. France 126,121 -127.
Lucas, J. M., Vaccaro, E. and Waite, J. H.
(2002). A molecular, morphometric and mechanical comparison of
the structural elements of byssus from Mytilus edulis and Mytilus
galloprovincialis. J. Exp. Biol.
205,1807
-1817.
MacGinitie, V. L. (1941). On the method of feeding of four pelecypods. Biol. Bull. 80, 18-25.
Martins, I., Costa, V., Porteiro, F., Cravo, A. and Santos, R. S. (2001). Mercury concentrations in invertebrates from Mid-Atlantic Ridge hydrothermal vent fields. J. Mar. Biol. Assn. UK 81,913 -915.
Mason, R. P. and Sullivan, K. A. (1997). Mercury in Lake Michigan. Environ. Sci. Technol. 31,942 -947.[CrossRef]
Mason, R. P., Fitzgerald, W. F., Hurley, J., Hanson, A. K. J., Donaghay, P. L. and Sieburth, J. M. (1993). Mercury biogeochemical cycling in a stratified estuary. Limnol. Oceanogr. 38,1227 -1241.
Mason, R. P., Fitzgerald, W. F. and Morel, F. M. M. (1994). The aquatic biogeochemistry of elemental mercury. Geochim. Cosmochim. Acta 58,3191 -3198.[CrossRef]
Mason, R. P., Laporte, J.-M. and Andres, S. (2000). Factors controlling the bioaccumulation of mercury, methylmercury, arsenic, selenium, and cadmium by freshwater invertebrates and fish. Arch. Environ. Contam. Toxicol. 38,283 -297.[CrossRef][Medline]
Mason, R. P., Reinfelder, J. R. and Morel, F. M. M. (1996). Uptake, toxicity, and trophic transfer of mercury in a coastal diatom. Environ. Sci. Technol. 30,1835 -1845.[CrossRef]
Ng, T. Y. T. and Wang, W. X. (2000). Detoxification and effects of Ag, Cd, and Zn pre-exposure on metal uptake kinetics in the clam Ruditapes philippinaipum. Mar. Ecol. Prog. Ser. 268,161 -172.
Page, H. M., Fiala-Medioni, A., Fisher, C. R. and Childress, J. J. (1991). Experimental-evidence for filter-feeding by the hydrothermal vent mussel, Bathymodiolus thermophilus. Deep-Sea Research Part a-Oceanographic Research Papers 38,1455 -1461.[CrossRef]
Pagliarani, A., Ventrella, V., Trombetti, F., Pirini, M., Triagari, G. and Borgatti, A. R. (1996). Mussel microsomal Na+-Mg2+-ATPase sensitivity to waterborne mercury, zinc and ammonia. Comp. Biochem. Physiol. 113C,185 -191.[CrossRef]
Pequeux, A., Bianchini, A. and Gilles, R. (1996). Mercury and osmoregulation in the euryhaline crab, Eriocheir sinensis. Comp. Biochem. Physiol. 113C,149 -155.
Pond, D. W., Bell, M. V., Dixon, D. R., Fallick, A. E.,
Segonzac, M. and Sargent, J. R. (1998). Stable-carbon-isotope
composition of fatty acids in hydrothermal vent mussels containing
methanotrophic and thiotrophic bacterial endosymbionts. Appl.
Environ. Microbiol. 64,370
-375.
Prol-Ledesma, R. M., Canet, C., Melgarejo, J. C., Tolson, G., Rubio-Ramos, M. A., Cruz-Ocampo, J. C., Ortega-Osorio, A., Torres-Vera, M. A. and Reyes, A. (2002) Cinnabar deposition in submarine coastal hydrothermal vents, Pacific Margin of Central Mexico. Econ. Geol. Bull. Soc. Econ. Geol. 97,1331 -1340.
Riisgård, H. U. (2001). The stony road to reliable filtration rate measurements in bivalves: a reply. Mar. Ecol. Prog. Ser. 215,307 -310.
Riisgård, H. U., Kittner, C. and Seerup, D. F. (2003). Regulation of opening state and filtration feeding bivalves (Cardium edule, Mytilus edulis, Mya arenaria) in response to low algal concentration. J. Exp. Mar. Biol. Ecol. 284105 -127.[CrossRef]
Rousse, N., Boulegue, J., Cosson, R. P. and Fiala-Medioni, A. (1998). Bioaccumulation of metals within the hydrothermal mytilidae Bathymodiolus sp. from the Mid-Atlantic Ridge. Oceanol. Acta 21,597 -607.[CrossRef]
Salanki, J., Farkas, A., Kamardina, T. and Rozsa, K. S. (2003). Molluscs in biological monitoring of water quality. Toxicol. Lett. 140,403 -410.[CrossRef]
Salánki, J. (1992). Heavy metal induced behaviour modulation in mussels: possible neural correlates. Acta Biol. Hung. 43,375 -386.[Medline]
Sarradin, P. M., Caprais, J. C., Riso, R., Kerouel, R. and Aminot, A. (1999). Chemical environment of the hydrothermal mussel communities in the Lucky Strike and Menez Gwen vent fields, Mid Atlantic ridge. Cah. Biol. Mar. 40, 93-104.
Sheuhammer, A. M. (1987). The cronic toxicity of aluminium, cadmium, mercury and lead in birds: a review. Environ. Pollution 46,263 -295.[CrossRef][Medline]
Simas, T. C., Ribeiro, A. P. and Ferreira, J. G. (2001). Shrimp a dynamic model of heavy-metal uptake in aquatic macrofauna. Environ. Toxicol. Chem. 20,2649 -2656.[CrossRef][Medline]
Steel, R. D. G. and Torrie, J. H. (1980). Principles and Procedures of Statistics A Biometrical Approach. pp. 399-409. London: McGraw-Hill Inc.
Stoffers, P., Hannington, M., Wright, I., Herzig, P. and De Ronde, C. (1999). Elemental mercury at submarine hydrothermal vents in the Bay of Plenty, Taupo Volcanic Zone, New Zealand. Geology 27,931 -934.[CrossRef]
Veró, M. and Salánki, J. (1969). Inductive attenuator for continuous registration of rhythmic and periodic activity of mussels in their natural environment. Med. Biol. Eng. 7,235 -237.[Medline]
Von Cosel, R., Comtet, T. and Krylova, E. M. (1999). Bathymodiolus (Bivalvia: Mytilidae) from hydrothermal vents on the Azores Triple Junction and the Logatchev hydrothermal field, Mid-Atlantic Ridge. Veliger 42,218 -248.