Toxicity of Metals to a Freshwater Snail, Melanoides tuberculata

Abstract

Adult freshwater snails Melanoides tuberculata (Gastropod, Thiaridae) were exposed for a four-day period in laboratory conditions to a range of copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), nickel (Ni), iron (Fe), aluminium (Al), and manganese (Mn) concentrations. Mortality was assessed and median lethal times (LT₅₀) and concentrations (LC₅₀) were calculated. LT₅₀ and LC₅₀ increased with the decrease in mean exposure concentrations and times, respectively, for all metals. The LC(50) values for the 96-hour exposures to Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn were 0.14, 1.49, 3.90, 6.82, 8.46, 8.49, 68.23, and 45.59 mg L⁻¹, respectively. Cu was the most toxic metal to M. tuberculata, followed by Cd, Zn, Pb, Ni, Fe, Mn, and Al (Cu > Cd > Zn > Pb > Ni > Fe > Mn > Al). Metals bioconcentration in M. tuberculata increases with exposure to increasing concentrations and Cu has the highest accumulation (concentration factor) in the soft tissues. A comparison of LC₅₀ values for metals for this species with those for other freshwater gastropods reveals that M. tuberculata is equally sensitive to metals.

Full text

The Scientific World Journal
Volume 2012, Article ID 125785, 10 pages
doi:10.1100/2012/125785
The cientificWorldJOURNA
L
Research Article
Toxicity of Metals to a Freshwater Snail,
Melanoides tuberculata
M. Shuhaimi-Othman, R. Nur-Amalina, and Y. Nadzifah
School of Environmental and Natural Resource Sciences, Faculty of Sc ience and Technology, National University of Malaysia (UKM),
Selangor, 43600 Bangi, Malaysia
Correspondence should be addressed to M. Shuhaimi-Othman, shuhaimi@ukm.my
Received 18 October 2011; Accepted 5 January 2012
Academic Editors: T. Brock, K. Kannan, J. Ruelas-Inzunza, and B. C. Suedel
Copyright © 2012 M. Shuhaimi-Othman et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Adult freshwater snails Melanoides tuberculata (Gastropod, Thiaridae) were exposed for a four-day period in laboratory conditions
to a range of copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), nickel (Ni), iron (Fe), aluminium (Al), and manganese (Mn)
concentrations. Mortalit y was assessed and median lethal times (LT
50
) and concentrations (LC
50
)werecalculated.LT
50
and LC
50
increased with the decrease in mean exposure concentrations and times, respectively, for all metals. The LC
50
values for the 96-
hour exposures to Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn were 0.14, 1.49, 3.90, 6.82, 8.46, 8.49, 68.23, and 45.59 mg L
−1
,respectively.
Cu was the most toxic metal to M. tuberculata,followedbyCd,Zn,Pb,Ni,Fe,Mn,andAl(Cu> Cd > Zn > Pb > Ni > Fe >
Mn > Al). Metals bioconcentration in M. tuberculata increases with exposure to increasing concentrations and Cu has the highest
accumulation (concentration factor) in the soft tissues. A comparison of LC
50
values for metals for this species with those for other
freshwater gastropods reveals that M. tuberculata is equally sensitive to metals.
1. Introduction
Metals are released from both natural sources and human
activity. The impact of metals on the environment is an
increasing problem worldwide. The impact of metals on
aquatic ecosystems is still considered to be a major threat
to organisms health due to their potential bioaccumulation
and toxicity to many aquatic organisms. Although metals are
usually considered as p ollutants, it is important to recognize
that they are natural substances. Zinc, for example, is an
essential component of at least 150 enzymes; copper is essen-
tial for the normal function of cytochrome oxidase; iron is
part of the haemoglobin in red blood cells; boron is required
exclusively by plants [1]. Malaysia, as a developing country, is
no exception and faces metals pollution caused especially by
anthropogenic activities such as manufacturing, agriculture,
sewage, and motor vehicle emissions [2–5]. Metals are
nonbiodegradable. Unlike some organic pesticides, metals
cannot be broken down into less harmful components.
Managing metal contamination requires an understanding
of the concentration dependence of toxicity. Dose-response
relationships provide the basis for the assessment of hazards
and risks presented by environmental chemicals. Toxicity
testing is an essential tool for assessing the effect and fate of
toxicants in aquatic ecosystems and has been widely used as
a tool to identify suitable organisms as a bioindicator and
to derive water quality standards for chemicals. There are
many different ways in which toxicity can be measured, and
most commonly the measure (end point) is death [1, 6, 7].
Metals research in Malaysia, especially using organisms as
a bioindicator, is still scarce. Therefore, it is important to
conduct studies with local organisms that can be used to gain
data on metal toxicity, to determine the organism’s sensitivity
and to derive a permissible limit for Malaysian’s water that
can protect the local aquatic communities.
The freshwater molluscs of the Malaysian region are
common, and most extant species are relatively easy to
collect. The snails are rich fauna, while bivalve are the
second. More than 150 aquatic nonmarine mollusc species
have been recorded from the Malaysian region. Melanoisdes
tuberculata (M
¨
uller 1774) is from class Gastropoda with
shells higher than wide (elongate), conical, usually light
brown in colour, and it is a cosmopolitan species [8].
M. tuberculata is a species of freshwater snail with an
operculum, a parthenogenetic, aquatic gastropod mollusc
in the family Thiaridae. The average shell length is about

2 The Scientific World Journal
20–27 mm and this species is native to subtropical and
tropical norther n Africa and southern Asia (Indo-Pacific
region, Southern Asia, Arabia, and northern Australia), but
they have established populations throughout the globe. The
snail has an operculum that can protect it from desiccation
and can remain viable for days on dry land [9]. It is a
warm-climate species, prefers a temperature range of 18
to 32
◦
C, and is primarily a burrowing species that tends
to be most active at night. This snail feeds primarily on
algae (microalgae) and acts as an intermediate host for
many digenetic trematodes. M. tuberculata is a viviparous,
gonochoric species with polyploid strains that reproduces by
apomictic parthenogenesis. Because meiosis usually does not
occur, offspring are identical to their mother. Females can be
recognized by their greenish coloured gonads while males
have reddish gonads. Under good conditions, females will
produce fertilized eggs that are transferred to a brood pouch
where they remain until they hatch. M. tuberculata will begin
reproducing at a size as small as 5 to 10 mm in length and
broods may contain over seventy offspring embryos which
develop in the mother [10–12].
Molluscs have long been regarded as promising bioindi-
cator and biomonitoring subjects. They are abundant in
many terrestrial and aquatic ecosystems, being easily avail-
able for collection. They are highly tolerant to many pollu-
tants and exhibit high accumulations of them, particularly
heavy metals [13, 14]. Little information exists in the
literatures concerning the toxic effects of metals for this snail.
So far, only a few studies have been reported on metal toxicity
to M. tuberculata [15, 16] and most of the studies were on the
accumulation of metals [14, 17, 18]. Therefore, the purpose
of this study was to determine the acute toxicity of eight
metals (Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn) to the freshwater
mollusc M. tuberculata and to examine the bioconcentration
of these metals in the body after four days of exposure.
2. Materials and Methods
Snails M. tuberculata were collected from canals in the
university in Bangi, Selangor, Malaysia. Identification of
the species was based on Panha and Burch [8]. Prior to
toxicity testing, the snails were acclimatized for one week
under laboratory conditions (28–30
◦
C with 12 h light : 12 h
darkness) in 50-L stocking tanks using dechlorinated tap
water (filtered by several layers of sand and activated
carbon; T.C. Sediment Filter (TK Multitrade, Seri Kem-
bangan, Malaysia)) aerated through an air stone. During
acclimation the snails were fed on lettuce. The standard
stock solution (100 mg L
−1
)ofCu,Cd,Zn,Pb,Ni,Fe,Al,
and Mn was prepared from analytical grade metallic salts
of CuSO
4
·5H
2
O, CdCl
2
·2.5H
2
O, ZnSO
4
·7H
2
O, Pb(NO
3
)
2
,
NiSO
4
·6H
2
0, FeCl
3
,Al
2
(SO
4
)
3
·18H
2
O, and MnSO
4
·H
2
O,
respectively (Merck, Darmstadt, Germany). The stock solu-
tions were prepared with deionized water in 1 L volumetric
flasks. Acute Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn toxicity
experiments were performed for a four-day period using
adult snails (shell length approximately 1.5–2.0 cm, mean
wet weight 22.5
± 1.6 mg) obtained from stocking tanks.
Following a range finding test, five Cu, Cd, Zn, Pb, Ni, Fe,
Al, and Mn nominal concentrations were chosen (Ta ble 1).
Metal solutions were prepared by dilution of a stock solution
with dechlorinated tap water. A control with dechlorinated
tap water only was also used. The tests were carried out
under static conditions with renewal of the solution every
two days. Control and metal-treated groups each consisted
of two replicates of five randomly allocated snails in a
500 mL glass beaker containing 400 mL of the appropriate
solution. No stress was observed for the snails in the solution,
indicated by 100% survival for the snails in the control
water until the end of the study. A total of 10 animals per
treatment/concentration were used in the experiment and
a total of 410 animals were employed in the investigation
[42, 43]. Samples of water for metal analysis taken before
and immediately after each solution renewal were acidified
to 1% with ARISTAR nitric acid (65%) (BDH Inc, VWR
International Ltd., England) before metal analysis by flame
or furnace Atomic Absorption Spectrophotometer (AAS-
Perkin Elmer model AAnalyst800, Massachusetts, USA)
depending on the concentrations.
During the toxicity test, the snails were not fed. The
experiments were performed at room temperature of 28–
30
◦
C with photoperiod 12 h light : 12 h darkness, using fluo-
rescent lights (334–376 lux). Water quality parameters (pH,
conductivity, and dissolved oxygen) were measured every
two days using portable meters (model Hydrolab Quanta,
Hach, Loveland, USA) and water hardness samples were fixed
with ARISTAR nitric acid and measured by flame atomic
absorption spectrophotometer (AAS—Perkin Elmer model
AAnalyst 800). Mortality was recorded every 3 to 4 hours
for the first two days and then at 12 to 24 hour intervals
throughout the rest of the test period. The criterion u sed
to determine mortality were failure to respond to gentle
physical stimulation. The death was further confirmed by
putting the snail on the glass petri dish for few minutes and if
it did not show any movement, it was considered dead. Any
dead animals were removed immediately.
At the end of day four, the live snails were used to
determine bioconcentration of the metals in the whole body
(soft tissues) according to the concentrations used. The
snails were cleaned with dechlorinated tap water, and soaked
in boiling water for approximately 3 min. Tissues of the
molluscs were removed from the shel l, rinsed with deionized
water, and each sample contained three replicates of three to
five animals in a glass test tube (dep ending on how many live
animals were left) and was oven-dried (80
◦
C) for at least 48
hours before being weighed [14]. Each replicate was digested
(whole organism) in 1.0 mL ARISTAR nitric acid (65%) in a
block ther mostat (80
◦
C) for 2 hours. Upon cooling, 0.8 mL
of hydrogen peroxide (30%) was added to the solutions.
The test tubes were put back on the block thermostat
for another 1 hour until the solutions became clear. The
solutions were then made up to 25 mL with the addition
of deionized water in 25 mL volumetric flasks. Efficiency of
the digestion method was evaluated using mussel and lobster
tissue reference material (SRM 2976 and TORT-2, National
Institute of Standard and Technology, Gaithersburg, USA
and National Research Council Canada, Ottawa, Ontario,

The Scientific World Journal 3
Table 1: Median lethal times (LT
50
)forM. tuberculata exposed to different concentrations for Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn.
Nominal (and measured)
concentration (mg L
−1
)
LT
50
(h)
95% Confidence
limits
Cu
0.075 (0.081)
0.1 (0.145)
0.32 (0.292)
0.56 (0.549)
0.87 (0.915)
163.42
134.97
98.89
75.87
55.42
63.60–419.91
53.22–342.28
44.35–220.50
26.88–214.15
25.36–121.11
Cd
0.56 (0.611)
1.0 (1.21)
5.6 (4.87)
10 (10.82)
32 (33.49)
283.44
114.89
57.21
22.34
7.82
85.46–940.12
52.78–250.09
30.29–108.05
11.03–45.27
4.63–13.23
Zn
1.0 (1.09)
5.6 (5.30)
10 (8.19)
32 (32.45)
56 (49.60)
216.96
96.71
61.83
32.44
12.34
630.53–1541.63
52.82–177.09
39.85–95.94
22.13–47.55
8.25–18.45
Pb
1.0 (1.02)
5.6 (5.42)
10 (10.95)
18 (17.16)
32 (31.18)
250.72
179.32
88.25
40.36
11.17
430.55–2057.69
38.42–837.02
30.24–257.71
13.91–117.15
6.71–18.57
Ni
5.6 (5.51)
10 (9.02)
32 (31.53)
75 (67.11)
100 (97.84)
105.96
92.38
58.11
36.84
16.26
59.28–189.40
48.25–176.87
39.82–84.80
21.66–62.67
12.50–21.17
Fe
5.6 (5.27)
8.7 (8.86)
10 (11.76)
32 (33.47)
56 (58.17)
134.97
102.06
79.72
34.71
20.04
53.22–342.28
40.17–259.29
28.18–225.53
13.36–90.15
7.5–53.51
Al
56 (88.38)
100 (160.83)
320 (362.83)
560 (884.34)
1000 (1229.91)
80.87
57.91
42.75
18.57
8.40
111.48–58.66
87.09–38.50
65.99–27.70
40.94–8.42
18.52–3.81
Mn
10 (12.98)
32 (31.60)
56 (57.81)
87 (85.61)
100 (97.01)
119.53
67.81
35.07
16.97
8.35
62.44–228.82
35.06–131.15
19.04–64.60
9.00–32.00
5.05–13.79
Canada, resp.). Efficiencies obtained were within 10% of
the reference values. To avoid possible contamination, all
glassware and equipment used were acid-washed (20%
HNO
3
) (Dongbu Hitek Co. Ltd., Seoul, Korea, 68%), and
the accuracy of the analysis was checked against blanks.
Procedural blanks and quality control samples made from
standard solutions for Cu, Cd, Zn, Pb, Ni, Fe, Al, and
Mn (Spectrosol, BDH, England) were analyzed in every ten
samples in order to check for sample accuracy. Percentage
recoveries for metals analyses were between 85–105%.
Median lethal times (LT
50
) and concentrations (LC
50
)for
the snails exposed to metals were calculated using measured

4 The Scientific World Journal
metal concentrations. FORTRAN programs based on the
methods of Litchfield [44] and Litchfield and Wilcoxon [45]
were used to compute the LT
50
and LC
50
.Datawereanalyzed
using time/response (TR) and concentration/response (CR)
methods by plotting cumulative percentage mor tality against
concentration and time, respectively, on logarithmic-probit
paper. Concentration factors (CFs) were calculated for whole
animals as the ratio of the metals concentrations in the
tissues to the metals concentration measured in the water.
3. Results and Discussion
In all data analyses, the actual (measured concentration)
rather than nominal Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn
concentrations were used (Ta ble 1). The mean water quality
parameters measured during the test were pH 6.68
± 0.22,
conductivity 180.0
± 46.0 µScm
−1
, dissolved oxygen 6.1 ±
0.27 mg L
−1
, and total hardness (Mg
2+
and Ca
2+
)18.72 ±
1.72 mg L
−1
as CaCO
3
.
One hundred percent of control animals maintained in
dechlorinated tap water survived throughout the experi-
ment. The median lethal times (LT
50
) and concentrations
(LC
50
) increased with a decrease in mean exposure concen-
trations and times, respectively, for all metals (Tables 1 and
2). However, the lethal threshold concentration could not
be determined since the toxicit y curves (Figures 1 and 2)
did not become asymptotic to the time axis within the test
period. Figures 1 and 2 show that Cu was the most toxic
metal to M. tuberculata,followedbyCd,Zn,Pb,Ni,Fe,Mn,
and Al. Other studies show different trends of toxicity with
different snails. According to Luoma and Rainbow [7] the
rank order of toxicity of metals will vary between organisms.
With Lymnaea luteola, Khangarot and Ray [28, 30] showed
that the order of toxicity was Cd > Ni > Zn; with Viviparus
bengalensis,Guptaetal.[27] and Gadkari and Marathe [34]
found that the order of toxicity was Zn > Cd > Pb > Ni;
and with Juga plicifera,Nebekeretal.[20] found that Cu was
more toxic than Ni.
The present study showed that LC
50
s for 48 and 96 hours
of Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn were 0.39, 11.85,
13.15, 10.99, 36.46, 21.78, 306.89, and 120.43 mg L
−1
,and
0.14, 1.49, 3.90, 6.82, 8.46, 8.49, 68.23 and 45.59 mg L
−1
,
respectively (Tab l e 1). A few studies had reported on the
acute toxicity of metals to M. tuberculata. Bali et al. [15]
and Mostafa et al. [16] showed that 96 h-LC
50
of Cu to
M. tuberculata were 0.2 and 3.6 mg L
−1
,respectively,which
were higher than the present study. In comparison with
other freshwater gastropods (Tab l e 3), this study showed that
in general LC
50
sforM. tuberculata were lower or similar
compared to other freshwater snails. Direct comparisons of
toxicity values obtained in this study with those in the litera-
ture were difficult because of differences in the char acteristics
(primarily water hardness, pH, and temperature) of the test
waters. With similar water hardness (soft water) and using
adult snails, Nebeker et al. [20] reported that 96 h-LC
50
of
Cu for Fluminicola virens was 0.08 mg L
−1
,andofZnfor
Physa Gyrina was 1.27 mg L
−1
, which was lower than the
present study. The toxicity reported by other studies (Ta ble 3 )
Log time (hours)
Cu
Cd
Zn
Pb
Ni
Fe
Al
Mn
Log LC
50
(mg L
−1
0.1
1
10
100
1000
10 100
1000
)
Figure 1: The relationship between median lethal concentration
(LC
50
)andexposuretimesforM. tuberculata.
0.1 1 10 100 1000
10
100
1000
1
0.01 10000
Cu
Cd
Zn
Pb
Ni
Fe
Al
Mn
Log concentration
Log LT
50
(hours)
(mg L
−1
)
Figure 2: The relationship between median lethal time (LT
50
)and
exposure concentrations for M. tuberculata.
differs from that reported in this study owing to the different
species, ages, and sizes of the organisms as well as varied test
methods (water quality and water hardness) as this can affect
toxicity [46–49 ]. In the present study, the water hardness
used was considered low (18.7 mg L
−1
CaCO
3
), and the water
was categorized as soft water (<75 mg L
−1
as CaCO
3
).
In comparison with other taxa, M. tuberculata shows
less sensitivity to metals. LC
50
s reported for other taxa from
this laboratory such as Crustacea (prawn Macrobrachium
lanchesteri [50]andostracodStenocypris major [51]), fish
(Rasbora sumatrana and Poecilia reticulata [52]), and Annel-
ida (Nais elinguis [53]) were lower than the LC
50
values of
M. tuberculata in the present study. Von Der Ohe and Liess
[54] showed that 13 taxa belonging to Crustacea were among

The Scientific World Journal 5
Table 2: Median lethal concentrations (LC
50
)forM. tuberculata at different exposure times for Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn.
Time (hour) LC
50
(mg L
−1
)
95% Confidence
limits
Cu
24
48
72
96
0.82
0.39
0.21
0.14
0.49–4.21
0.23–0.88
0.12–0.33
0.09–0.20
Cd
24
48
72
96
85.03
11.85
5.24
1.49
13.94–518.57
2.70–51.99
0.96–28.43
0.34–6.53
Zn
24
48
72
96
33.97
13.15
4.73
3.90
21.59–65.31
6.93–26.06
2.28–8.10
1.81–6.67
Pb
24
48
72
96
17.39
10.99
8.57
6.82
12.06–29.47
6.04–19.68
4.37–14.79
2.89–12.67
Ni
24
48
72
96
68.35
36.46
15.04
8.46
48.18–102.23
20.76–70.91
5.23–28.97
3.53–14.02
Fe
24
48
72
96
42.12
21.78
13.29
8.49
25.74–133.99
10.52–88.85
4.09–29.47
1.58–15.25
Al
24
48
72
96
880.78
306.89
130.22
68.23
553.91–2147.55
184.29–487.20
35.51–226.38
2.24–123.87
Mn
24
48
72
96
194.52
120.43
78.35
45.59
112.85–335.27
58.08–249.72
36.20–169.56
20.17–103.04
the most sensitive to metal compounds and concluded that
taxa belonging to Crustacea are similar to one another and
to Daphnia magna in terms of sensitivit y to organics and
metals and that Molluscs have an average sensitiv ity to
metals. Mitchell et al. [9] reported that the snail has a tightly
sealing operculum that allows it to withstand desiccation and
apparently also increases its tolerance to chemicals.
Bioconcentration of Cu, Cd, Zn, Pb, Ni, Fe, Al, and
Mn in surviving M. tuberculata is as shown in Figure 3.
Bioconcentration data for live snails were obtained from
five Cd (0.61, 1.21, 4.87, 10.82 and 33.49 mg L
−1
), Fe (5.27,
8.86, 11.76, 33.47, and 58.17 mg L
−1
), and Mn (12.98, 31.60,
57.81, 85.61 and 97.01 mg L
−1
) concentration exposures;
four Pb (1.02, 5.42, 10.95 and 17.16 mg L
−1
) concentration
exposures; three Cu (0.081,0145 and 0.292 mg L
−1
), Zn (1.09,
5.30 and 8.19 mg L
−1
), Ni (5.51, 9.02 and 31.53 mg L
−1
),
and Al (88.38, 160.83 and 362.83 mg L
−1
) concentration
exposures. In general, the Cu, Cd, Pb, Zn, Ni, Fe, Al, and Mn
bioconcentration in M. tuberculata increases with increasing
concentration exposure. Similar results were reported by
Moolman et al. [18]onCdandZnaccumulationby
two freshwater gastropods (M. tuberculata and Helisoma
duryi). Hoang and Rand [55] showed that whole body Cu
concentration of juvenile apple snails (Pomacea paludosa)
was significantly correlated with soil and water Cu concen-
trations. In other experiments, Hoang et al. [56] showed that

6 The Scientific World Journal
Table 3: Comparison of LC
50
values of freshwater gastropod M. tuberculata with other freshwater mollusc.
Metal Species
Water
hardness
(mg L
−1
)
Live stage
Tes t
duration
LC
50
(mg L
−1
)
Reference
Copper
M. tuberculata 18.7 Adult 96 h 0.14 This study
M. tuberculata 48 h 3.6 [16]
M. tuberculata Juvenile 24 h 0.2 [15]
B. glabrata 44 Adult 48 h 0.18 [19]
F. virens 21 Adult 96 h 0.08 [20]
J. plicifera 21 Adult 96 h 0.015 [20]
B. glabrata 100 — 96 h 0.04 [21]
P. palud o s a 68 60 d 96 h 0.14 [22]
P. jenkinsi — Adult 96 h 0.08 [23]
Cadmium
M. tuberculata 18.7 Adult 96 h 1.49 This study
Amnicola sp. 50 Adult 96 h 8.4 [24]
P. fontinalis ——96h0.08[25]
A. hypnorum 45 Adult 96 h 0.09 [26]
B. glabrata 100 — 96 h 0.3 [21]
V. b e n g a l e n s i s 180 — 96 h 1.2 [27]
L. luteola 195 Adult 96 h 1.5 [28]
Zinc
M. tuberculata 18.7 Adult 96 h 3.90 This study
P. g y r i n a 36 Adult 96 h 1.27 [20]
L. acuminata 375 — 96 h 10.49 [29]
L. luteola 195 Adult 96 h 11.0 [30]
V. b e n g a l e n s i s 180 — 96 h 0.64 [27]
P. heterostropha 20 Adult 96 h 1.11 [31]
P. heterostropha 100 Adult 96 h 3.16 [31]
Lead
M. tuberculata 18.7 Adult 96 h 6.82 This study
L. emarginata 150 — 48 h 14.0 [32]
E. livescens 150 — 48 h 71.0 [32]
Filopaludina sp. — Adult 96 h 190 [33]
V. b e n g a l e n s i s 165 — 96 h 2.54 [34]
A. hypnorum 60.9 — 96 h 1.34 [35]
Nickel
M. tuberculata 18.7 Adult 96 h 8.46 This study
Amnicola sp. 50 Adult 96 h 14.3 [24]
J. plicifera 59 Adult 96 h 0.24 [20]
L. luteola 195 Adult 96 h 1.43 [28]
V. b e n g a l e n s i s 180 — 96 h 9.92 [27]
L. acuminata 375 — 96 h 2.78 [29]
Iron
M. tuberculata 18.7 Adult 96 h 8.49 This study
P. g y r i n a 109 — 96 h 12.09 [36]
Planorbarius sp. ——48h7.32[37]
S. libertina — — 48 h 76.0 [38]
Aluminium
M. tuberculata 18.7 Adult 96 h 68.23 This study
Physa sp. 47 — 96 h 55.5 [39]
A. limosa PH 3.5 — 96 h 1.0 [40]
A. limosa PH 4.5 — 96 h 0.40 [40]
Manganese
M. tuberculata 18.7 Adult 96 h 45.59 This study
B. globosus 53 — 96 h 100.0 [ 41]

The Scientific World Journal 7
Control (Cu)
0.081 mgCu/L
0.145 mgCu/L
0.292 mgCu/L
Control (Cd)
0.611 mgCd/L
1.21 mgCd/L
4.87 mgCd/L
10.82 mgCd/L
33.49 mgCd/L
Control (Zn)
1.09 mgZn/L
5.3 mgZn/L
8.19 mgZn/L
Control (Pb)
1.02 mgPb/L
5.42 mgPb/L
10.95 mgPb/L
17.16 mgPb/L
Control (Ni)
5.51 mgNi/L
9.02 mgNi/L
31.53 mgNi/L
Control (Fe)
5.27 mgFe/L
8.86 mgFe/L
11.76 mgFe/L
33.47 mgFe/L
58.17 mgFe/L
Control (Al)
88.38 mgAl/L
160.83 mgAl/L
362.83 mgAl/L
Control (Mn)
12.98 mgMn/L
57.81 mgMn/L
85.61 mgMn/L
97.01 mgMn/L
31.6 mgMn/L
988
600
450
50
60
30
26
12
132
48
74
169
67
66
65
3
7
5
38
49
53
37
45
0.08
0.09
0.07
34
41
42
37
48
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Cu
Cd
Zn
Pb
Ni
Fe
Al
Mn
Metal concentration in body tissues (µgg )
−1
Figure 3: Bioconcentration of Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn (mean) in M. tuberculata soft tissues (µgg
−1
dry weight) after a four-day
exposure to different concentrations of Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn. Concentration factor (CF) is indicated at the top of each bar.
whole body Cu concentrations of juvenile snails (P. paludosa)
increased with exposure time and concentration and reached
a plateau (saturation) after 14 days of exposure. These results
are in agreement with the statement of Luoma and Rainbow
[7] who state that the uptake of trace metals from solution by
an aquatic organism is primarily concentration dependent.
The higher the dissolved concentration of the trace metal,
the higher the uptake of the metal from solution into the
organism will be, until the uptake mechanism becomes
saturated.
The present study shows that in gener al the highest
concentration factor (CF) was noted for Cu (988), Pb
(169), and Zn (132), and the lowest CF was for Al (0.07)
(Figure 3). Similar results were reported by Lau et al. [14]
who reported that M. tuberculata collected from the wild
(Sarawak River) accumulated higher amounts of Cu, Zn, and
As in the soft tissues compared to other metals. Adewunmi
et al. [17] showed that Cu, Pb, and Cd were the highest
metal accumulated in tissues of freshwater snails in dams
and rivers in southwest Nigeria, and metal concentrations
in the snails were varied with the seasons, especially for Cu
which was higher in the dry season compared to the rainy
season. According to Luoma and Rainbow [7] the factors
that affect the rate of uptake of metals affect the toxicity of
metal. This is in agreement with the results from the present
study which shows that Cu, which was the most toxic to
the snail, also has the highest CF in the soft tissues of M.
tuberculata. In explaining the toxicity of Cu, Hoang and Rand
[55] demonstr ate that the potential toxicity of Cu carbonate
to snails may be explained by the carbonate content in
the snails. The carbonate requirement for snails is more
than for fish because snails require it for shell development.
Copper may enter snails as Cu carbonate. After entering
snails, Cu carbonate may be disassociated through biological
and chemical reactions. Carbonate would be available for
shell development and Cu would be accumulated in soft
tissue.Hoangetal.[56] also reported that with the juvenile
apple snail (Pomacea paludosa), most of the accumulated
Cu was located in soft tissue (about 60% in the viscera and
40% in the foot) and the shell contained <4% of the total
accumulated copper. However, a comparison of the uptake
rate in aquatic organisms showed that in general the order
of the uptake rate constant is Ag > Zn > Cd > Cu > Co >
Cr > Se [7]. This discrepancy is probably due to short time
of exposure (four days) to metals in this study. Other factors
which may influence the bioaccumulation of heavy metals in

8 The Scientific World Journal
aquatic organisms has been suggested, such as their feeding
habit [57], growth rate and age of the organism [14, 58],
and the bioavailability of the metals, which greatly depends
on hardness of water, pH, and the acid-volatile sulphide
of the water [59]. Hoang and Rand [55] showed that the
apple snails (Pomacea paludosa) accumulated more Cu from
soil-water than from water-only treatments and this suggests
that apple snails accumulate Cu from soil (-sediment)/water
systems. Org anisms with higher growth rates also usually
have lower metal concentrations in their bodies as the rate
of increase in the weight of its tissue and shell will be higher
than the accumulated metals [14]. According to Lau et al.
[14], the shell of M. tube rculata would be most suitable
for monitoring Cu in the aquatic environment, which has
an approximately thirtyfold magnification capability and
with standard errors of less than 10%. Zn would be best
monitored by using the shell of M. tuberculata, whose
magnification capability was approximately 35 times and its
error was at approximately 15%. Both tissue and shell of M.
tuberculata could also be used for monitoring arsenic as it has
good magnification capabilities with moder ate irregularity
approximately 23%. However, it is important to note that
the Lau et al. [14] study was conducted in the field (long-
term exposure), while the present study was conducted in
the laboratory with short-term exposure, and differences in
accumulation trend and strategies (higher accumulation in
soft tissues or shell) may exist.
Aquatic molluscs possess very diverse strategies in the
handling and storage of accumulated metals, which include
being in the forms of metal-rich granules metallothioneins
(MT) or metallothionein-like proteins [60–62]. Accumula-
tion strategies of invertebrates vary intraspecifically between
metals and interspecifically for the same metal in closely
related organisms [62, 63]. Moolman et al. [18] showed that
M. tuberculata had a much higher uptake of Zn in the Zn
and in the mixed Cd/Zn exposures compared to Helisoma
duryi, and Zn was readily accumulated with increasing metal
concentrations. Lau et al. [14] also demonstrated that Zn
concentrations in M. tuberculata were significantly higher
than those in the molluscs Brotia costula and Clithon sp.
The present study shows that the CF of Zn was higher
than the Cd in the soft tissues of M. tuberculata. With the
juvenile apple snail, Hoang et al. [56] showed that the snails
accumulated Cu during the exposure phase and eliminated
Cu during the depuration phase. Metals accumulated in
animals can be stored without excretion leading to high
body concentrations (accumulators), or the metal levels
in the body can be maintained at a low constant body
concentration (regulators) by balancing the uptake with
controlled rates of excretion [64].
4. Conclusions
This study showed that M. tuberculata was equally sensitive
to metals compared to other freshwater gastropods. Cu
was the most toxic metal to M. tuberculata followed by
Cd, Zn, Pb, Ni, Fe, Mn, and Al. A comparison of the
bioconcentration of metals in soft tissues of M. tuberculata
showed that among the eight metals studied; Cu, Pb, and Zn
were the most accumulated and Al was least accumulated. M.
tuberculata is widely distributed in urban and suburban areas
which makes it easy to sample and very useful in ecotoxicol-
ogy studies. This study indicates that M. tuberculata could be
a potential bioindicator organism of metals pollution and in
toxicity testing.
Acknowledgments
This study was funded by the Ministry of Science and
Technology, Malaysia (MOSTI) under e-Science Fund code
nos. 06-01-02-SF0217 and 06-01-02-SF472. The a uthors do
not have any direct financial relation with the commercial
identity mentioned in this paper.
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