chapter 4 heavy metal concentrations in seawater and...

Heavy metal concentrations in Seawater and Seaweeds

Baseline studies of select stable elements in marine organisms, 2009/Lenin Raj

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CHAPTER 4

HEAVY METAL CONCENTRATIONS IN SEAWATER AND

SEAWEEDS

4.1. INTRODUCTION

Water is the most abundant substance on the surface of earth.

Water pollution by heavy metals is an important factor in both geochemical

cycling of metals and environmental health. Water pollution is a large set

of adverse effects upon water bodies such as lakes, rivers, oceans, and

ground water caused by human activities.

Most of the earth’s water (94.2%) is present in oceans and only

4.13% in the ground. As man makes further progress into the

technological era, production of chemicals also increases multifold. This in

turn causes an increase in the production of unwanted and hazardous

wastes, leading to higher risk of water contamination as a result of

accidental spillage or careless use. In the recent past, instances of illegal

disposal of chemical wastes into water bodies have been widely reported

in the world press.

Macrophytes are considered as an important component of the

aquatic ecosystem not only as a food source for aquatic invertebrates, but

also as an efficient accumulator of heavy metals (Devlin, 1967; Chung and



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Jeng, 1974). They are biological filters and play an important role in the

maintenance of the aquatic ecosystem. Aquatic macrophytes are

taxonomically closely related to terrestrial plants, which live in a completely

different environment. Their characteristic of accumulating metals make

the macrophytes interesting research objects for testing and modelling

ecological theories on evolution and plant succession, as well as on

nutrient and metal cycling (Forstner and Whittman, 1979). Therefore, it is

very important to understand the functions of macrophytes in the aquatic

ecosystem.

Bioavailability and bioaccumulation of heavy metals in aquatic

ecosystems is gaining tremendous significance globally. Several of the

submerged, emergent and free-floating aquatic macrophytes are known to

accumulate and bioconcentrate heavy metals (Bryan, 1971;

Chow et al., 1976). Aquatic macrophytes take up metals from the water,

producing an internal concentration several fold greater than that of their

surroundings. Many of the aquatic macrophytes are found to be potential

scavengers of heavy metals from water and wetlands (Gulati et al., 1979).

The capacity of seaweeds to accumulate elements depends on a

variety of factors such as location, wave exposure, temperature, salinity,

light availability, pH, nitrogen availability, age of plant, metabolic processes

and the affinity of the plant for each element, among others (Bryan and

Hummerstone, 1973; Fuge and James, 1973, 1974; Gale and



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Wixson, 1979; Levine, 1984; Zolotukhina et al., 1990; Catsiki and

Papathanassiou, 1993; Malea, 1994). Moreover, seasonality can be a

significant factor influencing the seaweeds capacity to accumulate heavy

metals. However, the two most probable factors affecting the elemental

levels in aquatic plants are the bioavailability of metals in the surrounding

water and the uptake capacity of the algae (Seeliger and Edwards, 1977;

Karez et al., 1994; Haritonidis and Malea, 1999).

Many industrial and mining processes cause heavy metal pollution,

which can contaminate natural water systems and become a hazard to

human health. Therefore, colonization of macrophytes on the sediments

polluted with heavy metals and the role of these plants in transportation of

metals in shallow coastal areas are very important. The present

investigation was planned and executed considering the potential of

macrophytes as a biological filter of the aquatic environment.

The objectives of this study were:

(i) to establish the baseline data of heavy metals (Cr, Mn, Fe,

Co, Ni, Cu, Zn, Cd and Pb) in seawater and in 25 different

species of brown, green and red macroalgae from the

Kudankulam coast;

(ii) to evaluate the inter-elemental correlation, concentration

factors and pattern of elemental occurrence in seaweeds;



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(iii) to analyse the pollution load in seaweed species using Metal

Pollution Index; and

(iv) to compare the metal concentration obtained in this study

with global values.

4.2. MATERIALS AND METHODS

Seawater collection and analysis

Seawater samples were collected around Kudankulam coast and

analysed for metals such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb. To

estimate the metal concentration 1000 ml of seawater was transferred to a

pre-washed separating funnel and the heavy metals were extracted by

using APDC-MIBK solution. The concentrations of heavy metals were

measured by using an atomic absorption spectrophotometer. The

procedures involved in the collection and analysis of seawater are given in

detail in chapter 2. The data were compared with global values and were

also used to estimate the Concentration Factor in seaweeds.

Seaweed collection and analysis

Seaweed samples were collected from the coastal intertidal zone

around the Kudankulam Nuclear Power Project site. The important coastal

sites in this study area are Kanyakumari, Kootapuzhi, Perumanal,

Kudankulam, Idinthakarai and Kuthankuzhi. All the sites are situated about

30 km on either side of the Kudankulam Nuclear Power Project



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site. Totally, 101 samples belonging to 25 different species were collected

around the Kudankulam Nuclear Power Project site. The collected

samples were dried in a hot air oven and about 5 g sample was acid-

digested with a HNO3 and HCl mixture. The detailed procedure is given in

chapter 2.

Statistical analysis

Analysis of variance (ANOVA) was applied to verify the difference in

heavy metal concentrations between species. Relationships between the

heavy metal concentrations were tested by using Karl Pearson’s

correlation analysis.

The Metal Pollution Index (MPI) was calculated to compare the total

metal content in different seaweed species, using the following equation

(Usero et al., 1996, 1997).

MPI = (Cf1 × Cf2

× …× Cfn)1/n

where Cfn is the concentration of metals (n) expressed in µg g-1 d.w.

This index has been highly successful in a biomonitoring programme

involving bivalves (Usero et al., 1996), but has not yet been widely used

for seaweed species (Giusti, 2001).

In order to determine the quantitative proportion in which an

element occurs in seaweeds and in the surrounding environment, the

Concentration Factors (CF) can be evaluated.

CF = C1/C2



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where C1 and C2 are the average metal content in seaweeds and in

seawater, respectively. Values of CF calculated on the basis of one or a

few determinations can be misleading. Thus, in this study, CF were

calculated by dividing the mean concentration of a given metal in an algal

species by its mean concentration in seawater. Such approaches have

been recommended by IAEA (1985). Knowledge of the CF values permits

recognition of the relative ability of an organism to take up metals from the

medium in which it lives.

4.3. RESULTS AND DISCUSSION

The concentration of metals such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd

and Pb in the seawater and seaweeds around the Kudankulam Nuclear

Power Project site was studied. The average concentrations of heavy

metals in different species of seaweeds are given in table 4.1 and the

results are given on a dry weight (d.w.) basis.

Chromium

The concentration of chromium in seawater ranged between 0.14

and 0.26 µg l-1, with a mean value of 0.21 µg l-1. The global median value

for Cr in ocean waters is 0.3 µg l-1 (Reimann and Caritat, 1998).

The Cr concentration in green (Chlorophyta), brown (Phaeophyta) and

red algae (Rhodophyta) ranged from 1.38 ± 0.96 to 8.68 ± 1.21 µg g-1 d.w.,



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1.27 ± 1.35 to 17.07 ± 4.37 µg g-1 d.w. and 0.46 ± 0.22 to 9.07 ± 4 µg g-1 d.w.,

respectively. In general, the highest Cr concentration was observed in the

phaeophyte, Padina pavonica (17.07 ± 4.37 µg g-1 d.w.) followed by

Colpomenia sinuosa (16.58 ± 4.72 µg g-1 d.w.) and Padina tetrastromatica

(15.8 ± 4.05 µg g-1 d.w.). The rhodophyte Acanthopora muscoides

(9.07 ± 4 µg g-1 d.w.) had the next highest concentration. The lowest Cr

concentration was registered in the rhodophyte, Amphiroa sp. (Fig. 4.1).

Analysis of variance showed that the concentration difference of chromium

between species was statistically significant (F = 5.93, d.f. = 24, 100,

P < 0.05, table 4.4).

The average chromium concentration measured in all seaweeds in

this study is similar to that reported in a study conducted by

Rao et al. (1995) from Visakapatnam coast (16.4 µg g-1 d.w.). Chromium

was found to have a similar distribution pattern in Colpomenia sinuosa,

Padina pavonica and Padina tetrastromatica and their concentrations were

16.58, 17.07 and 15.8 µg g-1 d.w., respectively. Shiber (1980) reported that

the chromium level was higher in Colpomenia sp. from Lebanon coast

(28.7 µg g-1 d.w.).

In this study, the chromium concentration was higher in Padina

pavonica and Padina tetrastromatica, than in the related species, Padina

durvillaei from Mexican coast (Paez-osuna et al., 2000 and Sanchez-

Rodriguez et al., 2001; 1.2 and 4.63 µg g-1 d.w., respectively). However,



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the concentration of Cr in Padina tetrastromatica was noticeably lower

than that in the same species reported from the Vishakhapatnam area of

the Indian coast (20.3 µg g-1 d.w.; Rao et al., 1995). Of the seaweeds of

Kudankulam, Ulva fasciata concentrated the minimum chromium among

the green algae and its concentration was 1.38 µg g-1 d.w. This value was

similar (1.1 µg g-1 d.w.) to that reported in the same species from Septiba

Bay, Brazil (Karez et al., 1994). However, this concentration was lower

than that in a related species (Ulva lactuca) reported from Lebanon coast

(6.9 µg g-1 d.w.; Shiber, 1980), Thermaikos Gulf, Greece (5.4–7.5 µg g-1 d.w.;

Djingova et al., 1987) and Coast of Bos (2.95–7.82 µg g-1 d.w.; Guven

et al., 1993). In Black Sea the chromium concentration observed in Ulva

rigida ranged from 5.32 to 5.92 µg g-1 d.w. These values are higher than

the values obtained in the present study for the species, Ulva fasciata.

Manganese

The concentration of manganese in seawater ranged between 0.06

and 0.18 µg l-1, with a mean value of 0.13 µg l-1. The average

concentration observed in the present study was lower than the values

obtained for the Visakhapatnam coast (21.16 µg l-1; Subrahmanyam and

Kumari, 1990), coastal and offshore waters of western Bay of Bengal (4.04

and 3.97 µg l-1; Satyanarayana et al, 1990), Andaman Sea (10.4 µg l-1;

Sanzgiri and Braganca, 1981) and northern Bay of Bengal (3.5 µg l-1 for

coastal and 3.4 µg l-1 for offshore waters; Satyanarayana et al., 1987).



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Ambient Mn concentrations in seawater have been reported to range from

0.4 to 10 µg l-1, with an average of about 2 µg l-1 (ATSDR, 2000).

However, Reimann and Caritat (1998) calculated the median Mn

concentration in the world ocean waters as 0.2 µg l-1.

Manganese was found to be the second most abundant element in

all the seaweed species analysed. The concentration of Mn in green,

brown and red algae ranged from 1.74 ± 1.05 to 121.36 ± 91.75 µg g-1 d.w.,

8.28 ± 3.68 to 115.43 ± 15.8 µg g-1 d.w. and 9.45 ± 2.9 to

149.47 ± 30.36 µg g-1 d.w., respectively. In general, the rhodophyte,

Hypnea sp., had the highest manganese concentration followed by

chlorophyte, Valoniopsis pachynema (121.36 ± 91.75 µg g-1 d.w.). The

phaeophytes Padina pavonica and Padina tetrastromatica also had high

manganese concentration (115.43 ± 15.8 and 109.48 ± 51 µg g-1 d.w.,

respectively). The lowest manganese concentration was found in the

chlorophyte, Enteromorpha compressa (Fig. 4.2). Compared with other

algal groups, phaeophyte species registered more manganese

concentration. A significant difference was observed for manganese

concentrations between species (F = 5.03, d.f. = 24, 100, P < 0.05,

table 4.5).

The Mn concentration in Hypnea sp. reported in the present study

was higher than those reported from Visakhapatnam coast

(113 µg g-1 d.w.; Rao et al., 1995), Bahrain (50 µg g-1 d.w.; Basson and



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Abbas, 1992) and southern Ghana region (42 µg g-1 d.w.; Serfor-Armah,

2006). Manganese concentration in Chaetomorpha antennina in the

present study was similar to that of Ghana coast (20 µg g-1 d.w.) but lower

than the concentration reported from Vishakapatnam (66.2 µg g-1 d.w.;

Rao et al., 1995) In the present study the minimum level was observed in

Enteromorpha compressa and it was lower than the level reported in Gulf

of Aden (12.9 µg g-1 d.w.; Al-Shwafi and Rushdi, 2007).

Iron

The iron content of seawater ranged between 11 and 24.1 µg l-1,

with a mean value of 19 µg l-1. The average Fe concentration observed in

the present study was higher than the values recorded in the

Visakhapatnam coast (12.3 µg l-1; Subrahmanyam and Kumari, 1990),

coastal and offshore waters of western Bay of Bengal (5.48 and 4.84 µg l-1;

Rejomon et al., 2007), Andaman Sea (6.24 µg l-1; Sanzgiri and Braganca,

1981), and comparable with values recorded in northern Bay of Bengal

(16.9 µg l-1 for coastal and 15.5 µg l-1 for offshore waters; Satyanarayana

et al., 1987). However, in the present study the concentration was lower

than the world ocean range of 25–743 µg l-1 (Reimann and Caritat, 1998).

Iron concentration in green, brown and red algal species ranged

from 280.86 ± 165.27 to 2455.31 ± 1277.78 µg g-1 d.w., 248.5 ± 121.55 to

3471.67 ± 1289.29 µg g-1 d.w. and 97.59 ± 85.91 to 1717 ± 668.92 µg g-1

d.w. Generally, the iron content in all the 25 species under study was



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relatively high because it is an essential element for biological activity.

(O΄Kelly, 1968; El-Sarraf, 1995). According to the data observed in this

study, a wide fluctuation in iron content was noticed in different algal

species.

In general, Padina tetrastromatica (3471.67 ± 1289.29 µg g-1 d.w.)

had the highest concentration of iron, followed by Colpomenia sinuosa

(2869.91 ± 936.08 µg g-1 d.w.) and Padina pavonica

(2544.26 ± 735.76 µg g-1 d.w.). The chlorophyte, Valoniopsis pachynema

(2455.31 ± 1277.78 µg g-1 d.w.) also registered more iron concentration.

These four species had considerably higher iron concentrations than the

other species analysed. The rhodophyte Hypnea sp. (1717 ± 668.92 µg g-1 d.w.)

and the phaeophyte Stoechospermum marginatum

(1417.69 ± 505.77 µg g-1 d.w.) had the next highest concentration. The

high mean concentrations observed in Phaeophyta can be attributed to the

high concentrations observed in both the species of Padina and

Colpomenia sinuosa. The rhodophytes such as Sarconema filiforme and

Amphiroa sp. had the lowest concentrations (97.59 ± 85.91 and

120 ± 28.28 µg g-1 d.w., respectively) (Fig. 4.3). Analysis of variance

showed that iron concentration differed significantly between species

(F = 6.97, d.f. = 24, 100, P < 0.05, table 4.6).

The iron concentrations reported in Enteromorpha compressa, Ulva

fasciata, Chaetomorpha antennina and Caulerpa sertularioides from



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Visakhapatnam, east coast of India, were 1989, 683, 1249 and

2204 µg g-1 d.w., respectively. Species such as Padina tetrastromatica and

Gracilaria corticata concentrated this metal in higher levels than the

Visakhapatnam seaweeds (1675 and 789 µg g-1 d.w.; Rao et al., 1995).

Iron concentration measured in Colpomenia sinuosa was comparable to

those reported from the Bahrain coastline (2300 µg g-1 d.w.; Basson and

Abbas, 1992). But in the case of Sarconema filiforme, the concentration

was higher compared to values reported from the Bahrain coastline

(700 µg g-1 d.w.). When compared to other areas the concentration of Fe

in the algal species of the Kudankulam coast was considerably lower.

Cobalt

The concentration of cobalt in seawater ranged between 0.05 and

0.12 µg l-1., with a mean value of 0.09 µg l-1. The concentration was lower

than the value observed from the Visakhapatnam coast (0.5 µg l-1

Subrahmanyam and Kumari, 1990) and it was comparable with the values

in the western Bay of Bengal (0.084 for coastal and 0.078 µg l-1 for

offshore waters; Rejomon et al., 2007). In ocean waters, Co ranges from

0.001 to 0.02 µg l-1 (Reimann and Caritat, 1998) and in the north Pacific it

averages 0.001 µg l-1 (Nozaki, 2005). In waters of the Baltic Sea, Co

contents vary from 0.001 to 0.07 µg l-1 (Szefer, 2002).



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The concentration of Co in green, brown and red algae ranged from

0.09 ± 0.04 to 2.71 ± 2.2 µg g-1 d.w., 0.53 ± 0.2 to 1.2 ± 0.26 µg g-1 d.w.

and 0.42 ± 0.16 to 4.59 ± 0.91 µg g-1 d.w., respectively. In general, the

rhodophyte, Hypnea sp. had the highest cobalt concentration, followed by

the chlorophyte, Valoniopsis pachynema (2.71 ± 2.2 µg g-1 d.w.). Low

cobalt concentration was found in the chlorophytes such as Caulerpa

peltata, Enteromorpha compressa and Caulerpa scalpelliformis

(0.09 ± 0.04, 0.22 ± 0.19 and 0.29 ± 0.14 µg g-1 d.w., respectively). Except

Hypnea sp. and Valoniopsis pachynema, all the other species had low Co

concentrations (Fig. 4.4). Analysis of variance showed that the

concentration of Co differed statistically between species (F = 3.21,

d.f. = 24, 100, P < 0.05, table 4.7). Cobalt level in Hypnea sp. in the

present study was higher than that in Hypnea cornuta (0.93 µg g-1 d.w.)

reported by Al-Shwafi and Rushdi (2007) and Hypnea pannosa

(2.53 µg g-1 d.w.) reported by Sanchez-Rodriguez et al. (2001). There is

no available literature on Co in seaweeds of the Indian coast for

comparison.

Nickel

The concentration of nickel in seawater ranged between 0.5 and

1.14 µg l-1, with a mean value of 0.72 µg l-1. The average concentration of

Ni observed in the present study was lower than that recorded in the

Visakhapatnam coast (2.9 µg l-1; Subrahmanyam and Kumari, 1990),



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coastal and offshore waters of western Bay of Bengal (1.56 and

0.81 µg l-1; Satyanarayana et al, 1990) and northern Bay of Bengal

(2 µg l-1 for coastal and 0.8 µg l-1 for offshore waters; Satyanarayana et al., 1987).

The values were comparable with those observed for coastal and offshore

waters (0.054 and 0.047 µg l-1, respectively) of the western Bay of Bengal

(Rejomon et al., 2007). The world ocean concentration of 0.48–1.7 µg l-1

was reported by Reimann and Caritat (1998). Szefer (2002) reported the

world Ni concentration range as 0.09–1.08 µg l-1, with a mean value of

0.7 µg l-1.

The concentration of Ni in green, brown and red algae ranged from

0.67 ± 0.41 to 6.35 ± 0.42 µg g-1 d.w., 1.59 ± 0.47 to 4.54 ± 0.91 µg g-1 d.w.


rhodophyte Laurencia papillosa had the highest concentration of nickel

(10.6 ± 1.05 µg g-1 d.w.), followed by Hypnea sp. (7.05 ± 2.31 µg g-1 d.w.) and

Valoniopsis pachynema (6.35 ± 0.42 µg g-1 d.w.). These three species had

considerably higher nickel concentration than other species analysed. The

phaeophyte Colpomenia sinuosa (4.54 ± 0.91 µg g-1 d.w.), Stoechospermum

marginatum (4.42 ± 1.26 µg g-1 d.w.) and Padina pavonica (4.09 ± 1.2 µg g-1 d.w.)

had the next higher concentrations. The chlorophyte Caulerpa peltata and

rhodophytes such as Amphiroa sp. and Sarconema fililforme, had the

concentrations below 1 µg g-1 d.w. (Fig. 4.5). Analysis of variance revealed

that the Ni concentration between different species was statistically significant

(F = 11.25, d.f. = 24, 100, P < 0.05, table 4.8).



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The average nickel levels in seaweeds of the Kudankulam coast

were comparable with those of the Saurashtra coast (2.53 µg g-1 d.w.;

Kesava Rao and Indusekhar, 1986) and Visakhapatnam coast

(1.74 µg g-1 d.w.; Rao et al., 1995). But the concentration was lower than

the values reported from Maharashtra (13.4 µg g-1 d.w.; Agadi et al., 1984)

and Goa coast (12.72 µg g-1 d.w.; Zingde et al., 1976; Agadi et al. 1978).

The highest Ni concentration in this study was found in Laurencia

papillosa, which is about ten times lower than that recorded in the Mexican

coast (100 µg g-1 d.w.; Sanchez-Rodriguez et al., 2001).

Copper

The concentration of copper in seawater varied from 3.24 to

6.23 µg l-1; with a mean value of 4.74 µg l-1. The average concentration

observed in the present study was lower than that observed in the

Visakhapatnam coast (13.9 µg l-1; Subrahmanyam and Kumari, 1990) and

higher than that recorded in the coastal and offshore waters of western

Bay of Bengal (1.13 and 0.69 µg l-1; Rejomon et al., 2007), Andaman Sea

(2.61 µg l-1; Sanzgiri and Braganca, 1981) and northern Bay of Bengal

(2.3 µg l-1 for coastal and 1.8 µg l-1 for offshore waters; Satyanarayana

et al., 1987). However, the mean Cu concentration in the north Pacific

Ocean was estimated to be 0.15 µg l-1 (Nozaki, 2005) and the median for

world ocean waters was 0.25 µg l-1 (Reimann and Caritat, 1998).



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The element copper belongs to the group of biologically important

metal ions. It is required by all algae and not replaceable even in part by

other elements. It also appears that Cu has a role in photosynthesis in

some algae. The Cu concentration in green, brown and red algae ranged

from 3.41 ± 0.8 to 8.95 ± 4.62 µg g-1 d.w., 1.85 ± 1.26 to 6.22 ± 1.07 µg g-1

d.w. and 1.22 ± 0.31 to 5.5 ± 1.45 µg g-1 d.w., respectively. In the present

study, the chlorophyte, Chaetomorpha antennina had the highest Cu

concentration (8.95 ± 4.62 µg g-1 d.w.) followed by Valoniopsis pachynema

(7.46 ± 2.75 µg g-1 d.w.) and Caulerpa peltata (6.55 ± 1.51 µg g-1 d.w.).

Padina pavonica and Colpomenia sinuosa, both phaeophytes, also had

high Cu concentrations (6.22 ± 1.07 and 5.72 ± 2.46 µg g-1 d.w.,

respectively). The lowest Cu concentration was found in the rhodophyte

Amphiroa sp. (1.22 ± 0.31 µg g-1 d.w.) (Fig. 4.6). Analysis of variance

showed that the Cu concentration between species was statistically

significant (F = 3.08, d.f. = 24, 100, P < 0.05, table 4.9).

The average copper level in seaweeds of the Kudankulam coast

was lower than that recorded from the Saurashtra coast (12.2 µg g-1 d.w.;

Kesava Rao and Indusekhar, 1986), Maharashtra coast (14.4 µg g-1 d.w.;

Agadi et al., 1984) and Goa coast (13.3 µg g-1 d.w.; Zingde et al., 1976).

But the Cu concentration recorded in this study was slightly higher than

the value previously reported by Pillai (1956) from Mandapam coast

(3.25 µg g-1 d.w.). The maximum concentration of Cu observed in

Chaetomorpha antennina in this study was higher than the average levels



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reported from Bulgarian Black Sea (5.7 µg g-1 d.w.) by Strezov and

Nonova (2005) and Ghana coast (3.6 µg g-1 d.w.) by Serfor-Armah (2006).

The average copper concentration in Enteromorpha compressa in this

study was 5.74 µg g-1 d.w. This value was considerably higher than the

value observed for Enteromorpha sp. inhabiting an industry-free area

(Zbikowski et al., 2006). However, the concentration recorded was

noticeably lower than those reported for algae inhabiting a highly

industrialized area of Hong Kong (Ho, 1987), north-west coast of Spain

(7.48 µg g-1 d.w.; Villares et al., 2002) and Gulf of Aden (17.53 µg g-1 d.w.;

Al-Shwafi and Rushdi, 2007). The copper concentration in Ulva fasciata

(3.72 µg g-1 d.w.) in this study was lower than its concentration in related

Ulva sp. found during summer and winter seasons (4.65 and

9.25 µg g-1 d.w., respectively) in Spain (Villares et al., 2002). Among the

phaeophytes, the maximum concentration of Fe in Padina pavonica of this

study was about three times higher compared to the value in the related

Padina durvillaei from Mexico (Paez-Osuna et al., 2000).

Zinc

The concentration of zinc in seawater varied from 9 to 22.3 µg l-1,

with a mean value of 16 µg l-1. The average concentration observed in the

present study was lower than that observed in the Visakhapatnam coast

(245.95 µg l-1; Subrahmanyam and Kumari, 1990) and northern Bay of

Bengal (25.3 µg l-1 for coastal and 25.7 µg l-1 for offshore waters;



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Satyanarayana et al., 1987) and higher than the coastal and offshore

waters of western Bay of Bengal (1.82 and 1.04 µg l-1;

Rejomon et al., 2007) and Andaman Sea (5.6 µg l-1; Sanzgiri and

Braganca, 1981). The median Zn concentration range for world ocean

waters has been estimated to be 0.5–4.9 µg l-1 (Reimann and

Caritat, 1998).

Zinc plays essential metabolic roles in plants, being an active

component of a variety of enzymes, such as dehydrogenases,

proteinases, peptidases and phosphohydrolases. The concentration of Zn

in green, brown and red algae ranged from 5.84 ± 2.32 to

19.51 ± 7.56 µg g-1 d.w., 5.22 ± 3.38 to 22.32 ± 3.74 µg g-1 d.w. and

3.69 ± 0.69 to 20.51 ± 8.36 µg g-1 d.w., respectively. Among the six

species of phaeophytes analysed, four species had higher Zn

concentration. Padina pavonica had a Zn concentration of

22.32 ± 3.74 µg g-1 d.w. followed by Hypnea sp. (20.51 ± 8.36 µg g-1 d.w.)

and Colpomenia sinuosa (20.19 ± 7.9 µg g-1 d.w.). Valoniopsis pachynema

(19.51 ± 7.56 µg g-1 d.w.), Padina tetrastromatica (18.17 ± 5.53 µg g-1 d.w.) and

Stoechospermum marginatum (18.71 ± 6.52 µg g-1 d.w.) also had higher

Zn concentrations. The lowest concentration was found in the rhodophyte,

Polysiphonia sp. (3.69±0.69 µg g-1 d.w.) followed by Sargassum

linearifolium (5.22 ± 3.38 µg g-1 d.w.), Ahnfeltiopsis densus

(5.25 ± 1.4 µg g-1 d.w.), Caulerpa peltata (5.84 ± 2.32 µg g-1 d.w.) and



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Gracilaria fergusonii (5.85 ± 6.43 µg g-1 d.w.) (Fig. 4.7). The significant

difference in Zn concentration observed between species (F = 3.05,

d.f. = 24, 100, P < 0.05, table 4.10) is attributed to the high Zn

concentration registered in the most of the phaeophyte species.

The obtained results, expressed as mean values in different

species of seaweeds are compared to the average Zn levels from other

areas, indicating that the zinc level was lower than that observed from

Saurashtra coast (23.7 µg g-1 d.w.; Kesava Rao and Indusekhar, 1986),

Maharashtra coast (90.7 µg g-1 d.w.; Agadi et al., 1984), Goa coast

(27.9 µg g-1 d.w.; Zingde et al., 1976) and Mandabam area

(34.6 µg g-1 d.w.; Pillai, 1956). The levels of zinc in Enteromorpha

compressa (215 µg g-1 d.w.), Ulva fasciata (131 µg g-1 d.w.),

Chaetomorpha antennina (139 µg g-1 d.w.), Caulerpa sertularioides

(136 µg g-1 d.w.), Padina tetrastromatica (169 µg g-1 d.w.), Gracilaria

corticata (127 µg g-1 d.w.) and Hypnea sp. (125 µg g-1 d.w.) reported by

Rao et al. (1995) from Vishakapatnam, east coast of India, were higher

than those species in the present study. These authors suggested that the

high levels were due to the pollution along the Vishakapatnam coast.

Cadmium

The concentration of cadmium in seawater ranged between 0.02

and 0.08 µg l-1, with a mean value of 0.05 µg l-1. The average



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concentration observed in the present study was lower than the values

recorded in the Visakhapatnam coast (0.74 µg l-1; Subrahmanyam and

Kumari, 1990), coastal and offshore waters of western Bay of Bengal (0.9

and 0.35 µg l-1, respectively; Satyanarayana et al, 1990), Andaman Sea

(0.64 µg l-1; Sanzgiri and Braganca, 1981) and northern Bay of Bengal

(1 µg l-1 for coastal and 0.9 µg l-1 for offshore waters;

Satyanarayana et al., 1987). The median Cd concentration in world ocean

waters has been estimated to be in the range of 0.07–0.11 µg l-1 (Reimann

and Caritat, 1998).

Cadmium is considered as one of the most ecotoxic metals that

exhibits adverse effects on all biological processes of humans, animals

and plants. This metal has an adverse effect on the environment. Aquatic

plants take Cd from the aquatic environment and the body burden of Cd is

many times higher than its level in water. The Cd threat to aquatic plants is

not only due to its concentration in the surrounding medium but also due to

its uptake and accumulation (Prasad, 1995).

The concentration of Cd in green, brown and red algae ranged from

0.38 ± 0.2 to 4.86 ± 1.97 µg g-1 d.w., 3.38 ± 1.29 to 5.65 ± 1.37 µg g-1 d.w. and

1.04 ± 0.23 to 9.69 ± 1.06 µg g-1 d.w., respectively. The mean Cd concentration

was the highest in phaeophytes followed by that in rhodophytes and chlorophytes.

Analysis of variance revealed that the concentration of cadmium differed

significantly between species (F = 4.01, d.f. = 24, 100, P < 0.05, table 4.11).



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The red algae Hypnea sp. had the highest concentration of

cadmium (9.69 ± 1.06 µg g-1 d.w.) followed by Acanthopora muscoides

(5.85 ± 1.49 µg g-1 d.w.). All the species in the phaeophyte group had

considerable amount of Cd (>4 µg g-1 d.w.) than other groups (except

Sargassum wightii). Caulerpa peltata was the species which concentrated

Cd the least (0.98 µg g-1 d.w.; Fig. 4.8). The present data are in agreement

with those of Serfor-Armah (2006) who found that the cadmium

concentration was 0.95 ± 0.09 µg g-1 d.w. in the related species

(Caulerpa taxifolia) from Ghana coast. In Hypnea sp. cadmium

concentration was higher than that in other related species as reported by

Rao et al. (1995) and Al-Shwafi and Rushdi (2007) from Vishakapatnam

and Gulf of Aden, respectively.

Lead

Of the known environmental pollutants, Pb has few competitors as a

persistent pollutant, which causes harmful effects on the ecosystem. It occurs in

the environment mainly as Pb2+ and its compounds are mostly insoluble in water.

The toxicity of Pb is not only due to its total concentration but also due to its forms.

The concentration of lead in seawater varied from 0.02 to

0.06 µg l-1, with a mean value of 0.04 µg l-1. The average concentration

observed in the present study was lower than that observed in the

Vishakapatnam coast (7.06 µg l-1; Subrahmanyam and Kumari, 1990),



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coastal and offshore waters of western Bay of Bengal (2.64 and

3.05 µg l-1; Rejomon et al., 2007), Andaman Sea (2.02 µg l-1; Sanzgiri and

Braganca, 1981) and northern Bay of Bengal (6.7 µg l-1 for coastal and

9.4 µg l-1 for offshore waters; Satyanarayana et al., 1987). The median Pb

content in the ocean waters has been calculated to be 0.03 µg l-1

(Reimann and Caritat, 1998).

The concentration of Pb in green, brown and red algae ranged from

0.92 ± 0.49 to 5.19 ± 2.84 µg g-1 d.w., 0.93 ± 0.3 to 8.58 ± 7.72 µg g-1 d.w.


phaeophyte Padina tetrastromatica had the highest Pb concentration

(8.58 ± 7.72 µg g-1 d.w.) followed by Padina pavonica (6.63 ± 1.67 µg g-1 d.w.)

and Colpomenia sinuosa (6.5 ± 3.02 µg g-1 d.w.). The lowest Pb

concentrations was measured in Amphiroa sp. (0.69 ± 0.43 µg g-1 d.w.)

(Fig. 4.9). The higher mean Pb concentration observed in group

Phaeophyta, was due to the high Pb concentration present in the algae

Padina pavonica, Padina tetrastromatica and Colpomenia sinuosa. No

significant difference in Pb concentration was observed between species

(F = 1.65, d.f. = 24, 100, P > 0.05, table 4.12).

The present data for Halimeda macroloba (2.82 µg g-1 d.w.) and

Hypnea sp. (2.75 µg g-1 d.w.) were in good agreement with those of

Al-Shwafi and Rushdi (2007) from Gulf of Aden, who found that lead

concentrations were 3.2 and 2.8 µg g-1 d.w. in Halimeda tuna and



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Hypnea cornuta, respectively, but the authors found lower Pb concentration

in Padina boryana (0.9 µg g-1 d.w.).

Inter-elemental relationship in seaweeds

The correlation between the accumulation levels of heavy metals is

an important factor for evaluating the heavy metal behaviour in biota and

the determination of these correlations is a major task in all environmental

studies.

A significant linear positive correlation (P<0.05) was observed

between a total of 34 different pairs of elements (Fig. 4.10) (Cr and Mn; Cr

and Fe; Cr and Co; Cr and Ni; Cr and Cu; Cr and Zn; Cr and Cd; Cr and

Pb; Mn and Fe; Mn and Co; Mn and Ni; Mn and Cu; Mn and Zn; Mn and

Cd; Mn and Pb; Fe and Co; Fe and Ni; Fe and Cu; Fe and Zn; Fe and Cd;

Fe and Pb; Co and Ni; Co and Cu; Co and Zn; Co and Cd; Co and Pb; Ni

and Cu; Ni and Zn; Ni and Cd; Ni and Pb; Cu and Zn; Cu and Pb; Zn and

Cd; Zn and Pb) and some of them are highly correlated (Fe with Cr and

Mn, P<0.05). Similar relationships have been found by different authors;

e.g. Haritonidis and Malea (1995) found a significant correlation between

Ni and Cr, Riget et al. (1997) observed that Fe and Co were correlated,

whereas Sanchez-Rodriguez et al. (2001) observed that Fe, Cr, Co, Ni

and Zn were highly correlated with each other. These observations agree

well with the results of this study.



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Pattern of heavy metal occurrence

The pattern of heavy metal abundance in all the seaweed species

in this study is presented in table 4.2. The mean element concentration in

seaweeds determined in this study followed the same order as that

reported by Rao et al. (1995) for Cu<Zn<Mn, as well as Zn<Fe (Brix and

Lyngby, 1984; Rajendran et al., 1993; Haritonidis and Malea, 1999),

whereas Nicolaidou and Nott (1998) found the order Cr<Co<Ni<Zn<Fe,

which is essentially the same as that in this study, except in the case of Cr

and Co, where the reverse was noted.

Iron was consistently the most abundant element in all the analysed

seaweeds, followed by manganese. Zinc was the next abundant element,

except in the case of Caulerpa peltata, Enteromorpha compressa and

Acanthopora muscoides. Cobalt was generally the least abundant

element, except in Hypnea sp. Cobalt tended to be the least concentrated

metal and Ni, Cd, Pb, Cr, Cu and Zn were generally in the middle range,

and Mn and Fe showed the greatest concentration levels.

With regard to the pattern of occurrence of elements on a species

basis, no definitive trend could be established. In the case of Fe and Mn

the pattern of occurrence is relatively similar. This may be due to the

relatively similar physicochemical properties of the two metals. As

mentioned earlier, a highly significant correlation (P < 0.05) was observed

between Fe and Mn.



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Concentration Factor

The Concentration Factors (CF) for the heavy metals considered

are presented in table 4.3. The average heavy metals in the three groups

of seaweeds followed the given order.

Chlorophyta Mn>Pb>Cd>Fe>Cr>Co>Ni>Cu>Zn

Phaeophyta Mn>Pb>Fe>Cd>Cr>Co>Ni>Cu=Zn

Rhodophyta Mn>Cd>Pb>Fe>Cr>Co>Ni>Cu>Zn

It is evident that the order of CF of Cr, Co, Ni, Cu and Zn was same

in all the three classes of algae. Manganese showed highest CF in

Phaeophyta, Chlorophyta and Rhodophyta. On the other hand, Zn

recorded the lowest CF followed by Cu in all the three classes of algae,

inspite of the fact that its concentration in seawater was much higher than

that of Mn. It can be concluded that the accumulation of manganese, lead

and cadmium by algae does not depend on their relative concentrations in

the ambient medium.

Furthermore, the extent of accumulation varied from one species to

another as is evident from the higher CF of Cr, Fe, Ni and Cu in

Padina pavonica, Padina tetrastromatica, Laurencia papillosa and

Chaetomorpha antennina, respectively. Relatively high CF of Zn and Pb

were recorded in Padina pavonica and Padina tetrastromatica,

respectively. The CF of Mn, Co and Cd were high in Hypnea sp.



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Accumulation of higher manganese over zinc by algae growing in the

ambient medium with either similar or higher zinc than manganese

concentration may be due to their metabolic requirements (Munda and

Hudnik, 1991).

Metal Pollution Index

The Metal Pollution Index (MPI) was calculated to compare the total

metal load in seaweed species. The calculated MPI for 25 different

species of seaweeds collected from Kudankulam coast is shown in

Fig. 4.11.

The MPI in different species of seaweeds ranged from 3.1 to 18.1.

The rhodophyte Hypnea sp. had the highest metal pollution load index

followed by the chlorophyte Valoniopsis pachynema (17.2). Phaeophyte

species such as Padina tetrastromatica, Padina pavonica and Colpomenia

sinuosa also registered higher MPI (16.9, 17.1 and 16.4, respectively).

Rhodophyte and the chlorophyte species such as Amphiroa sp. and

Caulerpa peltata had the lowest metal pollution load (3.1 and 3.4,

respectively). Except Sargassum wightii and Sargassum linearifolium, all

the other phaeophyte species had higher MPI than the other two algal

groups.

The high MPI observed in phaeophytes may be due to the high

concentration of iron in the algal tissues. Compared to other groups,

phaeophyte species had considerably higher concentration of all



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the other metals. It has been reported that Phaeophyta (especially Fucus

vesiculosus) have a tendency to accumulate metals (Sueur et al., 1982;

Khristoforova et al., 1983; Forsberg et al., 1988; Riget et al., 1995; Muse

et al., 1995; Ostapczuk et al., 1997). Brown algae are unable to regulate

the uptake of trace elements due to the presence of a large number of

compounds with anionic groups such as alginic acid, proteins,

polysaccharide monomers, galacturonic acid, carboxylate groups and

polyphenols in their cell walls (Paskins-Hurlburt et al., 1976, 1978; Crist

et al., 1988, 1990).

According to Lobban and Harrison (1994), Ca, Sr and Mg

concentrations in brown seaweeds are largely the result of ion exchange

between seawater and alginate in the cell walls by a process of cation

adsorption called Donnan Exchange System. According to Levine (1984)

and Crist et al. (1988, 1990), uptake is generally represented by a two-

step process. The first one is an initial, fast surface reaction when metals

adsorb to algal surfaces by electrostatic attraction to negative sites, and

the second one is a much slower active uptake, where metal ions are

transported across the cell membrane and into the cytoplasm

(Xue et al., 1988; Gonzalez-Davila et al., 1995). Step one is initially

independent of factors influencing metabolism such as temperature, light,

pH, nitrogen availability or age of the plant, but it is influenced by the

relative abundance of elements in the surrounding water. In some algal

species, metal accumulation is more dependent upon metabolic processes



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and is subject to changes in temperature, light, pH, nitrogen availability or

age of the plant. For example, uptake of Zn by Ascophyllum nodosum and

uptake of Co by Laurencia corallopsis appear to be by active transport

(Lobban and Harrison, 1994). Metabolic factors appear to control the

concentrations of Mn, Cu, Zn and Ni (enzyme cofactors), and Zn (activator

of dehydrogenases, protein synthesis enzymes) (Lobban and

Harrison, 1994).

Since the investigation on the heavy metal accumulation in

seaweeds of Kudankulam is a pioneering study, the results could be useful

for environmental monitoring and for checking the health of water bodies.

This preliminary survey shows seaweeds as metal bio-concentrators and

provides baseline data on the distribution of heavy metals in common algal

species. The seaweeds were found to be potential accumulators of heavy

metals from water. Therefore, such studies should become an integral part

of the sustainable development of the ecosystems and pollution

assessment programme.

The average concentrations of heavy metals in the seaweed

species collected from the Kudankulam coast were lower than the global

value. Brown seaweeds generally showed the highest elemental

concentration than green and red seaweeds. The same trend was

observed for concentration factor also. The following seaweed species are

known to accumulate metals and can be used as indicators of metal



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pollution: Hypnea sp. (for manganese, cobalt and cadmium), Padina

pavonica (for chromium and zinc), Padina tetrastromatica (for iron and

lead), Laurencia papillosa (for nickel) and Chaetomorpha antennina (for

copper).

chapter 4 heavy metal concentrations in seawater and...

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