Автор неизвестен - Inter-annualdepth-dependent toxicity and bioaccumulation of cadmium in marine benthic protist communities - страница 10

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0.0. 0.0.   0.0. 0.0. 0.0. 0.0. 0.0. 0.0. 0.0.

-H-H-H-H-H-H-H-H -H-H-H-H-H-H-H-H-H-H

85 02    9   0 0  5 9   7 7  7 9   0 11 88

.2.9 .0.2    .4  .0 .1  .5 .1   .7 .9  .9 .4  .0 .0.0 .8.8

3.1. 0.2.    1.   1. 7.  0. 4.   8. 4.  0. 7.   6. 1.0. 0.1.

08        4    9   7 6   0 0   2 1   0 5   1 31 03

H H   H    CO H Н НЮ

50 00    0  0 0  5 0  7 0  2 5  0 00 00

.2.1 .0.0    .0  .0 .0  .2 .2  .2 .1   .1 .2  .2 .2.1 .2.2

0.0. 0.0.   0.0. 0.0. 0.0. 0.0. 0.0. 0.0. 0.0.

-н-н -н-н -н-н -н-н -н-н -н-н -н-н -н-н -н-н

65 00    0  0 0 4 0  2 7  0 6  5 03 67

.9.9 .0.0    .0  .0 .0  .1 .0  .4 .9  .6 .1   .6 .8.7 .0.0

7.1. 0.0.    0.   0. 0.  6. 5.   1. 0.   1. 2.   0. 8.3. 3.5.

02 8 6 2 8 0 2 1 65 61 02 0 7  5 1 7  3 4 11

Н н Н ПН

95 50 2  5 0  0     5  5 0  0    8  0 65 00

.1.1 .2.1 .1   .1 .2   .2      .1   .2 .2   .1    .1   .1 .1.2 .1.2

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69 07 4  0 4  0     8  2 6  1    9  3 61 95

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1.6. 5.9. 2.   4. 7.   9.      1.   1. 6.   7.    9.   9. 8.7. 0.1.

НСЛНСОГ-Г-НСЧ Ю  Ю СО HO«Dt-C0t-

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ооооооо оооооооооо .0   .0.0   .0.1   .0.0    .0.0   .0.1   .0.1   .0.0 .0.0 0.   0.0.   0.0.   0.0.    0.0.   0.0.   0.0.   0.0. 0.0.

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8        2        6 4        8        2 6

4       7       9 0       2       4       7 9

2 1

Table 7. Dominant protist groups (density) during the 2002 assay

CD 0h

cm

24h

48h

72 h

96h

0

AFLA, DIAT

HFLA, DIN

DIN, HFLA

HFLA, SARC

SARC, HFLA,

 

(73.95), 11.73

(36.10, 40.98)

(34.95, 27.42)

(35.72, 30.03)

DIAT, CIL

 

 

 

 

 

(30.80, 19.77,

 

 

 

 

 

19.01, 16.34)

4

HFLA, AFLA,

HFLA, DIN,

HFLA, SARC,

HFLA, DIAT,

CIL, HFLA

 

DIN, DIAT

DIAT

DIN, DIAT

HDIN

(52.94, 47.06)

 

(42.60, 20.22,

(31.42, 31.42,

(41.89, 21.62,

(31.09, 22.27

 

 

19.13, 18.05)

18.31)

20.27, 16.22)

20.17)

 

8

AFLA (100.00)

HFLA, DIN

HFLA, DIN,

CIL, HFLA

CIL, HFLA,

 

 

(60.50, 29.41)

DIAT (43.24,

(46.66, 21.33)

DIN (46.55,

 

 

 

21.62, 18.92)

 

29.31, 24.13)

12

HFLA, DIN

DIAT (100.00)

HFLA, DIN

HFLA, DIN

HFLA, CIL

 

(44.26, 38.25)

 

(43.88, 26.53)

AFLA, DIAT

(53.66, 46.34)

 

 

 

 

(35.00, 32.50,

 

 

 

 

 

17.50, 15.00)

 

CT 0h

cm

24h

0    AFLA, DIAT   DIAT, HFLA (37.36, 32.31)    (39.30, 29.62)

4     HFLA (74.36)    DIAT, HFLA,

AFLA (37.29, 24.03, 22.38)

8    HFLA, DIN    HFLA, CIL (36.84, 33.33)   DIN (31.00, 22.88, 15.87)

12   DIN, CIL       CIL, DIN HFLA (50.00,   (48.29, 43.59) 32.00, 18.00)

48h

SARC, HFLA DIAT (45.31, 28.98, 25.71)

CIL, DIAT, HFLA (36.36, 34.85, 18.18)

72 h

96h

SARC, DIAT, SARC, HFLA HFLA (59.48, (55.88, 35.29) 22.22, 18.30)

SARC, HFLA SARC, CIL

DIAT (32.33,    DIAT, HFLA

30.45, 20.30)   (50.00, 19.04, 16.67, 14.29)

HFLA, DIAT HFLA, AFLA SARC, DIAT (46.67, 28.00)   (52.99, 20.90)  (66.67, 33.33)

DIN (91.94)    DIN (100.00)   HFLA, CIL,

SARC (48.28, 31.03, 20.69)

whereas they were infrequent in the former. Also, ciliates were not dominant in the control, but were second highest in the treatments with cadmium.

2004 assay. Figures 7 and 8 show the percentages of each protist group in the mean values of biomass in the control and cadmium treatments respectively. In both microcosms heterotrophic flagellates were dominant (34-54%, mean 41.6% of the whole protist groups), except at the beginning of the assay, when autotrophic flagellates were the dominant group. Heterotrophic flagellates were followed in dominance by different protist groups according to the phase of the assay:   after 48 and 96 h ciliates were dominant,

0h 24 h 48 h 72 h

Fig. 7. Control dominant protist groups during the 2004 assay: HFLA, heterotrophic flagellates; AFLA, autotrophic flagellates; DIN, dinoflagellates; DIAT, diatoms; CIL, ciliates; SARC, sarcodines. The diameters are proportional to the biomass

0h 24 h 48 h 72 h

Fig. 8. Treatments with cadmium. Dominant protist groups during the 2004 assay: HFLA, heterotrophic flagellates; AFLA, autotrophic flagellates; DIN, dinoflagellates; DIAT, diatoms; CIL, ciliates; SARC, sarcodines. The diameters are proportional to the biomass

but after 72 h it was the turn of the dinoflagellates. In percentages of mean density, the most important groups after the heterotrophic flagellates were the autotrophic flagellates (17.8%), followed by the ciliates (14.4%), the dinoflagellates (12%), and the diatoms (10.8%). The protists with the

lowest percentage were the sarcodines (3.4%). The dominant group in the control during the experiment were the heterotrophic flagellates (28-52%, mean 42.2%, of all the groups of protozoa). In percentages of mean density, the dominant groups after the heterotrophic flagellates were the diatoms (16.6%), followed by the ciliates (13.6%). Other groups presented similar values (autotrophic flagellates, 9%; dinoflagellates, 9.8%; sarcodines, 8.8%).

It is important to note that in the control all protist groups were present during the assay, whereas in the treatments with cadmium, autotrophic flagellates and sarcodines were not found after 48 h. Figure 9 shows the mean density percentages of the protist groups at the different depths during the 2004 assay. In the control the dominant group at all depths were the heterotrophic flagellates (45-55%, mean 48.25% of the total protist groups). Various groups followed the heterotrophic flagellates in dominance: diatoms at the surface, autotrophic flagellates at 4 cm, sarcodines and ciliates at 8 cm, and ciliates at 12 cm.

ct cd

Fig. 9. Dominant protist groups density (HFLA, heterotrophic flagellates; AFLA, autotrophic flagellates; DIN, dinoflagellates; DIAT, diatoms; CIL, ciliates; SARC, sarcodines) at different depths in the sediment both in the control (ct) and the treatments with cadmium (cd) in the 2004 assay

Bioaccumulation.

Figure 10 shows the percentages of cadmium bioaccumulated in the protists during the 2004 assay. The values ranged from 0 to 167.84 /igCd g_1 d.w. At all depths the proportion of cadmium bioaccumulated increased

towards the end of the experiment. In the initial phases of the treatment the proportion of cadmium bioaccumulated decreased with depth (14.52% at the surface, 1.76% at 4 cm, after 24 h). At 8 and 12 cm depths bioaccumulation was clearly in evidence after 72 h (24.55% and 14.16%, at 8 and 12 cm depth, respectively). After 96 h bioaccumulation was at a maximum, ranging between 66.22% at the surface and 81.79% at 12 cm. It is important to indicate that there was a significant correlation between the cadmium bioaccumulated and the biomass of protozoans at all depths (0.91-0.99; p < 0.05).

4. Discussion

In most of the documented effects of cadmium on marine communities of protists (Fernandez-Leborans & Novillo 1994, Fernandez-Leborans & Olalla-Herrero 1999), the communities used were epibenthic. In these previous studies the effects on the biomass and density of protists were observed in surficial sediments after 24 h.

Although the concentration of cadmium in seawater is low, it can become concentrated in sediments in polluted areas. In the present work, the initial concentration in water was chosen to be very high (1000 ppm), since cadmium was added only once. Moreover, this concentration allowed for the loss of cadmium through adsorption to the glass walls of tanks.

Metal toxicity is dependent on various environmental factors: temper­ature, salinity, pH, concentration of free metal ions, metal complexation by inorganic and organic ligands, etc. (Rai et al. 1981). According to Larsen (1989), minor fluctuations of the pH do not affect the speciation of cadmium. In the microcosms of the present study, pH varied between 6.32 and 7.67, and there were no significant pH differences between the control and the treatment with Cd. Cadmium uptake decreases with increasing salinity. Generally, it is accepted that only free Cd2+ can be accumulated in organisms, whereas there is no uptake by organisms of cadmium chloro-complexes in seawater. This explains why cadmium is considered to be more toxic in freshwater, where its bioaccumulation is higher than in seawater (Stratford 1985).

Dissolved cadmium concentrations are extremely low in open ocean surface waters (< 1ngdm-3) and increase with depth to a maximum at the level of the nutrient maximum (about 900 to 1000 m), where total cadmium concentrations can reach 145 ng dm-3. Concentrations then decline slightly at greater depths (Pohl et al. 1993, De Baar et al. 1994, Yeats et al. 1995).

Effects of cadmium in the assay. In the present study, after 24 h there was an important decrease in density, number of species and biomass. These

effects of heavy metals on communities of protists are due to the effects of the metals at a cellular level. It is known that toxic metal ions are able to cross membranes either by non-bilayer metal-induced structures or by non-specific multivalent ion carriers, causing membrane depolarisation and cytoplasmic acidification (Cumming & Gregory 1990). Heavy metals can also alter membrane function through displacement of calcium present as a structural component of membrane phospholipids (Green et al. 1980). In fact, membrane injury is one important effect of metal ions that may lead to the disruption of cellular functions. Protist mortality may then lead to oxidation of labile organic matter and a corresponding decrease in dissolved oxygen. These chemical changes could reduce the toxicity of cadmium, especially in the final phases of the assay, in which the amount of organic matter is high and the cadmium can form complexes. Redox potential has an indirect effect on the forms of cadmium in sediments. In oxic sediments, cadmium is associated primarily with the carbonate plus Fe/Mn oxide fractions; meanwhile, in hypoxic or anoxic sediments, most of the cadmium is associated with the carbonate and sulphide/insoluble humic substance phases. The cadmium species in oxidised sediment layers are more exchangeable and bioavailable than those in the anoxic layers (Dive et al. 1982, Houba & Remacle 1982, Nilsson 1989, Fernandez-Leborans & Novillo 1995). Tables 1 and 2 showed that the redox potential rose during the assay and it was higher at the surface than at depth 12 cm. In summary, cadmium species were less exchangeable and bioavailable at the end of the assays and at the surface than at the beginning of the assays and at 12 cm depth.

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