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International Journal of Marine Science 2014, Vol.4, No.52, 1-9
http://ijms.biopublisher.ca
2
Trivedi, 2009). Common mechanisms of genotoxicity
includes oxidative stress, impair DNA repair systems,
and interruption in signalling pathways, that are
related to cell proliferation. However, the intact
mechanism of metal carcinogenicity remains largely
unknown (Bolognesi et al., 1999).
Genotoxic studies on aquatic organisms exposed to
polluted waters containing heavy metals have
implicated DNA strand breakages (Kirsch-Volders et
al.,
2000; Pruski and Dixon, 2002). Micronuclei (MN)
can be produced from chromosomal fragments or
whole chromosomes that lag at cell division due to
lack of centromere, damage in centromere or defect in
cytokinesis. These small secondary structures of
chromatin are surrounded by membranes located in
the cytoplasm and have no detectable link to the cell
nucleus (Fenech et al.,
2003). T
he micronucleus assay
is one of the most widely used as biomarker for
genotoxicity testing in the aquatic organisms thus
providing an efficient measure of chromosomal DNA
damage occurring as a result of either chromosome
breakage or chromosome mis-segregation during
mitosis (
Bolognesi and Fenech, 2012)
.
Within the last
decade, micronucleus tests have played an important
role in assessing exposure to water pollutants, and
these tests have proved as appropriate tools to provide
an early warning of genotoxic threat to the aquatic
organisms, their ecosystem and finally to man (Cavas
and Ergene-Gozukara, 2005; Lah et al., 2005;
Bolognesi et al., 2006; Kim and Hyun, 2006;
Palanikumar et al.,
2012b). The micronucleus assay is
simple, reliable and sensitive for
in-vivo
evaluation of
genotoxic potential of xenobiotics and it does not
depend on any karyotypic characteristics of the test
animal (Lah et al., 2005).
Marine invertebrates, especially marine bivalves, are
used as test species for toxicity testing since these are
mostly benthic habitat and filter feeders and some are
found in the rocky shores. The marine mussels have
been used in assessment of cytogenetic damage
(Barsine et al.,
2004; Bolognesi et al.,
2004; Alink et
al., 2007; Sullivan et al., 2007; Bolognesi and Hayashi,
2011). Despite the considerable amount of information
available on the effect of heavy metal toxicity to
marine bivalves, the impact of heavy metals on
micronuclei formation to marine bivalves are quite
limited (Sommanee, 1980; Martin et al.,
1981; Arslan
et al., 2010; Bolognesi and Fenech, 2012). Therefore
the present study has investigated the acute and
cytogenetic effects (MN and BN) of metals to marine
bivalve mollusc,
Modiolus philippinarum
under
continuous flow through bioassay test method.
1 Materials and Methods
1.1 Experimental Animals
Healthy individuals of the mussel,
M. philippinarum
(9 ±2 mm length) (500 nos at a time) were collected
from the intertidal rocky shore at Pudumadam in the
Gulf of Mannar (N 09° 16’31” & E 079° 00’11”),
nearer to Mandapam, Southeast Coast, India. They
were transported to the laboratory immediately and
acclimated to room temperature (32.3±2°C) in glass
aquaria (60L × 30B × 30H cm) containing 20 L of
filtered seawater (salinity @ 30±1 PSU; Temperature
30±1°C). The collected animals were acclimated for a
period of 7 days in an ambient room condition. During
the acclimation period, mixed culture of phytoplankton
(
Chaetoceros
sp.,
Skeletonema
sp. and
Thallasiosira
sp.) was given as food and water was aerated
gently (4±1 ml.min
-1
.L
-1
). Physical and chemical
characterization of the filtered seawater were
estimated using standard protocol
(APHA, 1995) and
the values were given in Table 1.
Table 1 Physico-chemical characteristics of dilution seawater
collected at Pudumadam Coast, Gulf of Mannar, Southeast
coast of India
Parameter tested
Value (n=3)
Seawater Temperature (°C)
30.2 ±1.0
pH
8.1 ±0.1
Salinity (‰)
32.0 ±1.5
Dissolved Oxygen mg.L
-1
5.5 ±0.3
BOD mg.L
-1
119.3 ±5.4
COD mg.L
-1
3.50 ±0.2
Total Organic carbon %
0.25 ±0.040
Nitrite mg.L
-1
0.014 ±0.01
Nitrate mg.L
-1
0.043 ±0.01
Phosphate mg.L
-1
0.014 ±0.008
Silicate mg.L
-1
0.03 ±0.008
Copper µg.L
-1
0.25 ±0.07
Cadmium µg.L
-1
3.1 ±0.3
Lead µg.L
-1
13.1 ±2.14
Mercury µg.L
-1
BDL
Zinc µg.L
-1
8.37 ±2.63
Arsenic µg.L
-1
0.75 ±0.17
Note: BDL: Below Detection Limit; BOD – Biological Oxygen
Demand; COD – Chemical Oxygen Demand. Minimum
Detection Level for Mercury is 0.05 µg