1 Research Article DISTRIBUTION OF FIVE TOXIC HEAVY METALS IN BIOTIC AND ABIOTIC ...

14 Pages·2016·0.62 MB·English

by  Pamoda Ratnaweera

Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
Volume 1 Issue 1

Research Article Open Access

DISTRIBUTION OF FIVE TOXIC HEAVY METALS IN BIOTIC AND
ABIOTIC CONSTITUENTS OF THE NEGOMBO LAGOON, SRI LANKA

Sivanantha N.1, Wijesinghe M. R.2* and Wijesekera R. D.1
1Department of Chemistry, University of Colombo, Colombo 03, Sri Lanka.
2Department of Zoology and Environment Sciences, University of Colombo, Colombo 03, Sri Lanka.

Abstract

The presence of toxic metals in water has become a matter of national concern. This
situation is potentially more dangerous when it occurs in lagoons and estuaries which

are both highly productive and sensitive in comparison to other natural habitats. In this
study, the levels of five toxic heavy metals, As, Cd, Cr, Pb and Hg, present in several

abiotic and biotic constituents of the Negombo lagoon, Sri Lanka, were investigated with
the objective of assessing the potential risks of accumulation. Sampling, in five locations,
was conducted from December 2014 to April 2015. Water, sediment, soil, bark and
leaves of the mangrove Bruguiera gymnorhiza, and fauna of selected taxa were collected
and heavy metals were analyzed using ICP – OES following microwave digestion. Apart

from Cr which was detected at low levels, none of the other metals were detected in the
water. Nevertheless, the five heavy metals were present in relatively large amounts in

one or more of the other tested constituents, indicating lagoon pollution, depicting an
overall trend water < leaves < bark < snails < fish < crab < sediment < soil. Our

investigation suggests that As and Cd, due to their high levels of accumulation in soil and
sediment, impose the highest potential risks. Trends in accumulation suggest non-point
sources for Cd, Cr and Pb. Findings reported here call for continual monitoring and for
controlling discharge of contaminated effluents into productive lagoon ecosystems.

Key words: accumulation, abiotic, biotic, heavy metals, lagoon

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
Volume 1 Issue 1
1. Introduction been well documented. It has been shown
that the accumulated metal
Heavy metal contamination in the aquatic concentrations in organisms generally
environment is a matter of serious reflect, quantitatively or semi-
concern due to its adverse impact on quantitatively, the level of environmental
humans and other organisms. Although pollution (Dallinger, 1994), allowing them
heavy metals in the environment could to be used as bio-indicators of metal
arise from natural sources (Chibuike & pollution.
Obiora, 2014), the recent increases have,
to a large extent, been attributed to The Negombo lagoon in the western
anthropogenic activities such as the region of Sri Lanka (7º 09’N 79º 51’ E)
discharge of untreated industrial effluents receives fresh water from three sources:
and the intense use of agrochemicals the Ja-Ela, Dandugam Oya and the
(Dixit et al., 2015). Heavy metals that Hamilton Canal (Gammanpila, 2013). The
enter a water body are dispersed area mainly receives rainfall from the
throughout its biotic and abiotic southwest monsoon from May to
constituents, the levels of occurrence September, while convectional showers
being influenced by the condition of the occur during the remaining months of the
water at a given time. For instance, acidic year (CEA, 1994). The temperature varies
conditions cause heavy metal ions between 24 oC to 30 oC. The Negombo
adsorbed to soil and sediment to be lagoon is one of the most productive
released into the water increasing their brackish water ecosystems in Sri Lanka in
bioavailability in the aquatic medium terms of mangrove vegetation, fauna and
(Alghanmi, et al., 2015). Similarly, other inland fishery (Samarakoon & van Zon,
factors, such as temperature and the 1991; Jayasiri, 2004; Dahanayaka et al.,
amount of dissolved oxygen and organic 2008). Previous studies have assessed the
matter, also determine the fate of the status of the Negombo lagoon through
heavy metals within a water body accumulation of heavy metals in selected
(Kuwabara et al., 1996; Croteau et al., constituents (e.g. Indrajith & Pathiratne,
2002). 2006; Indrajith et al., 2008 – water,
sediment and fish; Asanthi et al., 2007 –
The heavy metals As, Cd, Hg, Pb and Cr water, sediment and algae; Mendis et. al.,
(VI) are non-essential elements, and they 2015a & b – water and fish). In this paper,
induce toxic impacts in biota even at trace the levels of the five heavy metals As, Cd,
levels (Tchounwou et al., 2012). The Cr, Hg and Pb were examined
potential hazard imposed by these metals simultaneously, in three abiotic (water,
to organisms is enhanced due to the bio- sediment and soil) and selected biotic
accumulative and non-biodegradable (mangrove, snails, fish and crabs)
nature of the elements (Cui et al., 2011; constituents of the Negombo lagoon. In
Yu et al., 2013). Furthermore, the ascertaining the levels of these elements
potential for accumulated heavy metals to the possibility of bio-concentration of
bio-magnify along food chains, ultimately these heavy metals was also investigated.
reaching high concentrations in
organisms at the top trophic level, has

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
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2. Material and Methods Faunal species were collected at four of
the stations only (other than from station
2.1 Collection of samples C). Collection of faunal species was based
on the available taxa. For instance,
The present study was conducted samples of Hydrobiid sp. (gastropod)
between December 2014 and April 2015 were collected from station A,
at five sampling stations: A – bordering Heteropneustus fossilis (Asian stinging cat
the National Aquatic Resources, Research fish) from B, Scylla serrata (mud crab)
and Development Agency (NARA) from D and Eutroplus suratensis
Conservation Centre, B – bordering the (Pearlspot Cichlid) from E. A total of ten
main bus station in Negombo, C – samples each of the different taxa, which
Dandugam Oya inlet, D – bordering a were sufficient for analysis, were
residential area and E – in close proximity collected from the four sampling stations.
to the airport (Figure 1). At each station, Snails were collected from the surface of
samples were collected at five random the soil/sediment while fish and crabs
points separated from each other by a were caught with the aid of fishermen in
distance of more than 20 m, yielding a the vicinity of the sampling stations. All
total of 25 sampling points. At each of samples were transported to the
these points, two samples each of water, laboratory and stored at 4oC until
sediment and soil were collected yielding analyses which were carried out typically
a total of 50 samples per component. The within 3 days of collection.
water was collected from 1 m beneath the
surface with a Ruttner Sampler and 2.2 Analysis of heavy metals
stored in polypropylene containers for
analysis. These containers were washed The procedure employed for analysis of
with 10 % HCl and then with de-ionized heavy metals in water was according to
water before use. Surface sediment (down APHA 3120 – B (US EPA, 2007). Samples
to around 3 cm from the bottom surface) of the water were digested with conc.
was scraped off with a scoop and HNO (10 cm3 conc. HNO for 50 cm3 of
3 3
collected into sealable polythene bags, each sample) and further concentration
with excess water being drained before was achieved by evaporation. In cases
sealing. Soil, within 5 m away from the where NaCl precipitated before the
water and to a depth of 3 cm from the soil concentration process, the solutions were
surface, was scooped using a deep spoon topped to different volumes using de-
and also stored in sealable polythene ionized water. After filtration the solutes
bags. Obtaining soil and sediment in this were analyzed using ICP – OES and tested
manner increased the likelihood of for heavy metals. Whenever necessary,
collecting recent deposits, as opposed to the solute was diluted. Soil and sediment
mainly material of geological origin. At (500 g each) and 20 g of each biotic
each point bark and mature leaves from a constituent, i.e. bark, leaves and faunal
minimum of three trees of the mangrove tissue, were also digested for analysis, as
Bruguiera gymnorhiza were collected. described in US EPA (2007).

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Figure 1. Map of the Negombo lagoon showing the five sampling stations

Following microwave digestion, the Calibration checks (20 μg/dm3 for Hg and
concentrations of As, Cd, Cr, Pb and Hg in 1.00 mg/dm3 for the other metals) were
each sample were determined using used for every 20 samples. Certified
inductively coupled plasma-optical aqueous reference standards of TMDA
emission spectroscopy (ICP-OES) (Varian 64.2 and ICP-OES wavelength calibration
720-ES, Australia). Recovery studies were solutions were obtained from an outside
done with spiked samples and certified source and analyzed according to
reference materials (CRM). Analyses were instructions provided. The generated
conducted in duplicate, and repeated if results were checked to ensure that they
the error exceeded 10 %. For the were within the acceptable range.
recovery procedure, a known amount of
the standard mixture of the five heavy 2.3 Potential risk factors
metals was spiked into conc. HNO (10
3
cm3) (blank sample) and digested. The The Contamination Factor (Cf) which
CRMs used were 2711a Montana II, 2976 describes the contamination of a given
muscle tissue, 1570a spinach and TMDA toxic substance in a water body as
64.2. ICP-OES and VGA. Calibration check suggested by Håkanson (1980) is useful
solutions were analyzed to ensure for assessing the potential dangers
instrument performance and to validate imposed by the heavy metal loads in a
calibration, using the same acid matrix. water body and is derived using the

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
Volume 1 Issue 1
formula Cf = CCurrent / CPre-ind. These noteworthy that, with the exception of Cr
indices were calculated for the Negombo (recording a maximum of 0.09 mg/ dm3),
lagoon. Since data on pre-industrial levels none of the other toxic heavy metals (As,
are lacking for any of the tested metals for Cd, Pb, and Hg) were detected in the
Sri Lankan systems, the values obtained water. Nevertheless, the detected levels of
for a range of European and American the five metals in the other constituents
water bodies prior to industrialization, i.e. sediment, soil and the biota, are
which have been also widely applied even indicative of heavy metal contamination
for tropical estuaries (e.g Vowotor et al., of the Negombo lagoon (Figure 3 and
2014), were used for this purpose. Table 1). Considering sediment and soil,
Additionally, the Ecological Risk Factor the highest metal levels recorded were for
(Er) based on the Toxicity Response Cr (34.3 and 49.8 mg/kg respectively).
Factor (Tr) assigned to each of the metals Both these constituents were also
(Håkanson 1980) was calculated using Er relatively rich in Pb, whilst As and Cd
= Tr x Cf. were present at low levels. It is significant
that Hg was not recorded in sediment or
3. Results soil at any of the sampling stations.
Considering heavy metal concentrations
The analyses revealed the presence of all recorded in the flora and fauna, apart
five toxic heavy metals i.e. As, Cd, Cr, Pb from Cd, all the other toxic heavy metals
and Hg in at least one of the biotic or were recorded in one or more of the
abiotic constituents analyzed from each of biotic constituents. From among these, as
the five sampling stations in the Negombo although not recorded in the mangrove,
lagoon. Figure 2 shows the mean levels was seen to reach high levels, with a
(+ standard errors) of the metals maximum of 22.5 mg/kg, in crabs. Cr, Hg
recorded in the different constituents, and Pb were recorded in comparatively
whilst the minimum- maximum ranges high concentrations in both floral and
detected for each of the metals are shown faunal components (Figure 2 and Table
in Table 1. Some of the salient features 1).
evident from the results are set out
below. The overall trends of the mean levels of
accumulation of the five metals recorded
3.1 Apportionment among constituents in water, sediment, soil, flora and fauna
are shown in Figures 3 (a) and (b). The
The mean + standard error of the pH graphs show that, apart from subtle
values in the water samples recorded for differences, there is a similar overall
the five sampling stations were A: 7.79 ± pattern of accumulation for As, Cd, Cr and
0.24, B: 6.55 ± 0.14, C: 5.65 ± 0.10, D: 7.78 Pb with concentrations increasing in the
± 0.04 and E: 7.85 ± 0.12. The one way order water < leaves < bark < snails < fish
ANOVA and Tukey pairwise comparison < crab < sediment < soil. Hg was only
test revealed significant station-wise recorded from the biotic constituents. Soil
differences in pH (p ≤ 0.05), with station C and sediment evidently function as sinks
having a significantly lower pH. With of these heavy metals.
respect to the heavy metals, it is

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
Volume 1 Issue 1
The C and T factors as well as the low (i.e. < 1) and in the order of Pb < Cr <
Pre-ind r
generated C and E values are given in As < Cd. The Ecological Risk Factors
f r
Table 2. Accordingly, both concentration increase in the overall order of Cr < Pb <
factors for sediment and soil are generally As<Cd.

Figure 2. Mean concentrations (± standard error) of the five tested heavy metals in the
different biotic and abiotic constituents in the five sampling stations (A to E). (Note: results
for water, where only Cr was detected at low levels, are not shown)

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Table 1. The minimum and maximum values of the five selected heavy metals in the
different biotic and abiotic constituents in the Negombo lagoon.
Constituent As Cd Cr Hg Pb

Water (mg /dm3) ND ND ND - 0.09 ND ND
(n=50)
Sediment (mg ND - 8.65 ND - 1.67 7.64 - 34.30 ND 2.53 - 19.61
/kg)
(n=50)
Soil (mg /kg) ND - 9.89 ND - 2.63 2.40 - 49.80 ND ND - 20.26
(n=50)
Bruguiera
Bark (mg /kg) ND ND ND - 1.93 ND - 0.15 ND - 4.09
(n=50)
Leaves ND ND ND - 0.69 ND ND
(n=50)
Snails (mg /kg) 3.46 - 6.25 ND ND - 1.76 0.07 - 0.22 ND
(n=10)
Fish (mg /kg) 2.90 - 9.23 ND 0.92 - 4.69 0.15 - 0.61 ND - 2.34
(n=20)
Crabs (mg /kg) 20.51 - 22.46 ND 1.41 - 2.48 0.05 - 0.26 ND
(n=10)
ND indicates metal levels below limits of detection; n indicates number of samples analyzed

3.2 Inter-site comparisons higher than the others (metals: p <0.001).
Nevertheless, the inter-site differences in
To interpret inter-site differences the total metal levels were not significant
combined results for water, sediment, (sites: p>0.05), indicating that the total
soil, and mangrove bark and leaves for metal loads between sites were
each of the metals were considered. somewhat comparable. The interaction
Results for fauna were not included due between sites and metals was also not
to the disparity in sample sizes between significant (metals x sites: p>0.05)
sites. A two way ANOVA indicated that, suggesting that the trends of
overall in the Negombo lagoon, there is a accumulation of each of the metals in the
significant metal-wise difference, with different sites were nearly consistent.
loads of some metals being markedly

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
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g) 40 g) 0.6
g/ k30 g /k0.5
m m0.4
n (20 n (0.3
o o
ntrati10 ntrati00..21
e e
nc 0 nc 0
o o
C Sed Soil C
Bark
Leaf
Snail
Fish
Crab
As Cr Pb Cd

(a) (b)
Figure 3. The patterns of accumulation of heavy metals (means) in the different biotic and
abiotic constituents of the Negombo lagoon, depicted in two concentration ranges (a) Pb,
Cr, As and (b) Cd, Hg.
The extent of consistency between sites to similar sources of inputs suggesting the
suggests similarity in the sources of likelihood of non-point sources for these
contamination and this was examined metals. On the other hand, As and Hg are
using the Pearson's correlation coefficient not significantly correlated with any of
matrix, following Vowotor et al. (2014). the other metals, nor with each other,
The correlation matrix for the five heavy suggesting that these two metals most
metals under consideration is given in likely arise from different sources. The
Table 3. Interestingly, the significant and localization of Hg also suggests a point
strong positive correlations between the source of input.
three contaminants; Cd, Cr and Pb, points

Table 2. Concentration Pre-industrial (C ), Toxic response factor (T ), Contamination
Pre-ind. r
Factor (C) and Ecological Risk Factor (E ) values for As, Cd, Cr and Pb. Note: Hg was not
f r
recorded in sediment and soil.
As Cd Cr Pb
T* 10 30 2 5
r
C Sediment 0.4 0.5 0.2 0.1
f
Soil 0.2 0.4 0.2 0.1
E Sediment 4.0 15.0 0.4 0.5
r
Soil 2.0 12.0 0.4 0.5
*Source - Håkanson (1980)

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Table 3. Pearson’s Correlation Coefficients showing the consistency in occurrence of the
five tested heavy metals in the five sampling sites.

Cd Cr Pb As
Cr 0.55*
p < 0.01

Pb 0.79* 0.90*
p < 0.001 p < 0.001

As 0.20 0.25 0.19
p > 0.05 p >0.05 p >0.05

H g -0.11 0.18 0.20 0.36
p >0.05 p >0.05 p >0.05 p = 0.05

*significant association (p<0.01)

4. Discussion transport of heavy metals is the
adsorption onto surfaces of solid
In the current investigation, the five particulate matter, which results in
tested heavy metals (As, Cd, Cr, Pb and lowering levels in the water medium
Hg) were recorded at relatively high (Rieuwerts et al., 1998). Usually in
levels in one or more of the biotic or lagoons, triggered by acidic conditions,
abiotic constituents in the Negombo heavy metals tend to precipitate with
lagoon. In the water, however, none of the sulphide, lowering bioavailability in the
elements, with the exception of Cr, was water (Simpson & Spadaro, 2016). Such
recorded, and that too at relatively low processes give the water body the ability
levels. The absence/low concentration of to regulate toxic metals between the biotc
the heavy metals in the water reported and abiotic components. In the present
here is in conflict with previously study there is some evidence for
documented values for the Negombo variability in pH levels across the
lagoon. For instance, values reported by sampling stations which may have
Indrajith & Pathiratne (2006) and contributed to some extent to the
Indrajith et al. (2008) for Cd and Pb, and observed differences in the metal loads
by Asanthi et al. (2007) for arsenic, in between the sites, although such
water, were as high as 5.70, 2.10 and 2.16 differences were not significant. Two
µg/L, respectively. The seemingly other factors that would seriously affect
contradictory results obtained in the concentrations of heavy metals and other
present study could be viewed in the light contaminants in the water at a given time
of the conditions and processes that is the rate of flushing and the residence
prevail in the lagoon. One of the most time of water, both of which would have a
important processes controlling the major impact on the rate of sedimentation
as well as on the water chemistry. The

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Sivanantha et al. Sri Lankan J. Biol. 2016, 1(1):1-14 Sri Lankan Journal of Biology
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rate of water exchange between the although Hg has been previously
lagoon and the adjacent ocean occurs recorded in sediment from the Negombo
mainly through tidal action and the lagoon (Indrajith et al., 2008), the present
quantity of freshwater discharge. The study did not detect this metal in any of
Negombo lagoon is reported to feature a the soil or sediment samples. Studies have
weak tide (maximum range is about 10 demonstrated that metal ions with similar
cm) but it has a strong and variable valance states compete for metal binding
freshwater discharge resulting in a sites, i.e. in this case for surfaces of
residence time of between 2-14 days organic matter. Thus, there is a possibility
(Rydberg & Wickbom, 1996; Rajapaksha, that Hg was displaced upon additional
1997). The intermittent showers in the loadings of other metals such as Pb
area during the study period and the high (Holmberg, 2006). The weak association
freshwater discharge into the lagoon noted between Hg and Pb observed in the
would have facilitated some flushing present study, however, does not provide
which most likely resulted in low persuasive evidence that displacement
accumulation of heavy metals in the occurred. The present investigation
water as observed here. highlights As and Cd as metals with the
highest potential to concentrate in soil or
In the present study the heavy metal sediment whilst Cd, due to its high
loads recorded in sediment and soil were prevailing levels and high potency to
much higher than those in water, with soil cause adverse health impacts, shows up
and sediment being near equally polluted, as the metal with the higher ecological
reiterating the function of these two risk. Although the risks associated with
constituents as heavy metal sinks. Soil individual metals are low accordingly to
and sediment generally act as sinks of the stated threshold values (see
heavy metals primarily due to the organic Hakanson, 1980), the ‘true risk’ to biota
fraction that has the capacity to adsorb may arise from the summation of risks
these elements, the process being posed by all metals (as well as other
considerably influenced by factors such as contaminants) present in the ecosystem
pH, metal speciation, ionic strength, and (Hakanson, 1980).
other properties that are inherent to the
target metal (Lin & Chen, 1998). Flushing What is of considerable interest is that,
and the re-suspension of metals through despite concentrations in water being
the disturbance of sediment or soil would beyond detectable limits for most of the
temporarily cause elevation of metal metals and for the majority of the
loads in water at a particular site sampling sites, there were relatively high
(Eisenreich et al., 1980). levels of accumulation of those metals in
the biotic elements. Usually living
Heavy metal levels observed in the organisms take up heavy metals from
present study for sediment in the abiotic constituents, i.e. from soil, water
Negombo lagoon are similar for Pb and and sediment. The level of accumulation
Cr, whilst Cd values are higher than also depends on the particular trophic
previously recorded values (Indrajith et position each organism occupies in the
al., 2008). It is also noteworthy that food chain. The heavy metals that are

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