INTRODUCTION:

The long history of seaweed utilization for a variety of purposes has led to the gradual realization that some of their constituents are more superior and valuable in comparison to their counterparts on land [1]. In the search for nutritional supplements, the people of maritime countries found the seaweeds as the potential repositories of essential nutrients which lead to cultivation and consumption of seaweeds. While the seaweeds, in other words the marine macro algae, are used as multiple forms of food in certain countries, it is used as food only in a limited form in India. In the Indian Ocean region, countries like Malaysia, Indonesia, Singapore, Thailand, Korea, etc. seaweeds are used in salad, jelly and soup. The seaweed consumption in India is negligible except in the preparation of porridge from Gracilaria sp. and Acanthophora sp. in coastal States of Kerala and Tamil Nadu [2]. Seaweeds contain high amounts of carbohydrates, protein, minerals and low fat.

Mineral content is generally high (8-40%) and the essential minerals and trace elements needed for human nutrition are present in macro algae [3]. The levels of trace elements in soil largely depend on some factors such as P^H, cation exchange capacity, chemical structure, calcium carbonate equivalent and micro organisms [4].

Trace elements get accumulated in the marine macro algae from the surrounding marine water. The trace element load depends upon the quantum of these elements disposed into the marine water either through natural or anthropogenic causes. Assessment of trace metal concentration in the coastal waters can be made by using marine algae as indicator organism [5,6] which accumulate pollutants proportionally to their environmental concentration [7,8]. The accumulation of trace elements may depend on the combination of factors such as membrane permeability, mobility, valency, affinity of metal to the protein binding group in the cell wall, ambient seawater concentration and growth of the algae [9]. Certain trace elements are considered essential for the plant system and it is further considered a threat when it crosses the threshold as the macro algae are consumed by human. For instance, selenium is recognized as an essential micronutrient in animal and humans, playing important biological roles as antioxidant, as a regulator of thyroid hormone metabolism or as anti-carcinogenic. However, higher concentration of selenium is toxic [10]. The indispensable organic integration of living beings with the life support systems in environment essentially implies absorption of trace elements by humans through food channel. Essential trace elements will contribute to human health while indiscriminate consumption of non-essential trace elements may harm the health. In this context, the present study has been conducted with the specific objective of estimating the accumulation level of selected trace elements in G. edulis and to analyse the level and potential influence of independent factors such as season and location.

MATERIALS AND METHODS:

The selected marine macro algae G. edulis was collected for four seasons in 2011 from four different coastal locations viz: Arockiapuram, Kadiapattinam, Kurumpanai from the coast of Kanyakumari district and Mandapam from the coast of Ramanathapuram district in the State of Tamil Nadu, India. The state of Tamil Nadu extends between the 8º 08’N latitude and 78 º 0’ E longitudes. The selected coastal areas are located in the following geographical coordinates viz: Kurumpanai: 8.18 N, 77.22 E, Kadiapattinam: 8.13 N, 77.30 E, Arockiapuram: 8.08 N, 77.54 E and Mandapam: 9.27 N, 79.12 E respectively. Kanyakumari district lies between 77^o – 15’ and 77^o – 36’ of the eastern longitude and 8^o– 35’ and 8^o – 35’ of the northern latitude. This district enjoys the unique feature of being bordered by the three oceans viz: the southeast coast bordered by the Gulf of Mannar, south by the Indian Ocean and the southwest by the Arabian Sea. The data were grouped on the basis of four distinct seasons (Southwest monsoon: May to July; Post southwest monsoon: August to October; Northeast monsoon: November to January; Post northeast monsoon: February to April).

The trace elements in the seaweed powder were estimated using the methodology proposed in AOAC [11]. 0.2g of oven dried seaweed powder was taken in conical flasks. To this 10 ml of diacid mixture (2:5 of Nitric acid and Perchloric acid) was added. This was kept overnight for cold digestion. The conical flasks were then placed on a hot plate and the contents were digested by increasing the temperature (90⁰C). The digested materials were filtered through Whatman No.40 filter paper by repeatedly washing the conical flasks with a small volume of distilled water. The filtrates collected were made up to a suitable volume (20 ml). The filtrates obtained were fed into Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-Perkin Elmer Mayer Optima Z100 DV). The data thus obtained were analysed with the help of SPSS software.

RESULTS AND DISCUSSION:

Table 1. Locational variation of trace elements (µg/g ± S.D.) in G. edulis.

Trace Elements

Locations

Arockia-puram

Kadia-pattinam

Kurum-panai

Manda-pam

Aluminium

8.020±

4.560

14.345±

4.694

9.580±

6.226

33.218±

27.979

Cadmium

0.031±

0.023

0.024±

0.010

0.031±

0.026

0.043±

0.017

Cobalt

0.032±

0.012

0.041±

0.016

0.041±

0.022

0.057±

0.026

Chromium

0.540±

0.175

0.757±

0.091

0.412±

0.123

0.480±

0.106

Copper

0.489±

0.318

0.655±

0.169

0.423±

0.140

0.292±

0.186

Manganese

1.000±

0.794

1.095±

0.831

0.772±

0.347

3.630±

1.146

Nickel

0.246±

0.036

0.377±

0.125

0.360±

0.232

0.248±

0.043

Table 2. Seasonal variation of trace elements (µg/g ± S.D.) in G. edulis

Trace Elements

Seasons

Northeast Monsoon

Post Northeast Monsoon

Southwest Monsoon

Post Southwest Monsoon

Aluminium

19.650±

6.417

8.818±

6.113

15.363±

2.445

21.333±

11.069

Cadmium

0.030±

0.012

0.050±

0.023

0.024±

0.005

0.024±

0.024

Cobalt

0.061±

0.027

0.039±

0.005

0.034±

0.006

0.037±

0.025

Chromium

0.527±

0.147

0.496±

0.250

0.654±

0.184

0.511±

0.123

Copper

0.314±

0.155

0.510±

0.248

0.489±

0.283

0.546±

0.258

Manganese

1.701±

1.096

1.337±

1.003

1.762±

0.733

1.697±

1.025

Nickel

0.331±

0.135

0.404±

0.222

0.243±

0.034

0.253±

0.036

Lead

0.079±

0.072

0.091±

0.076

0.169±

0.072

0.082±

0.029

Zinc

2.119±

1.286

2.441±

1.192

2.215±

0.638

1.445±

0.364

Aluminium was observed in varying levels in G. edulis between the different locations. The lowest mean value of 8.020 ± 4.560 µg g^-1 dry weight was observed in the sample from Arockiapuram while the highest mean value of 33.218 ± 27.979 µg g^-1 dry weight was registered in Mandapam (Table 1). Among the three locations on the coast of Kanyakumari District, the samples from Kadiapattinam indicated relatively higher level of Aluminium (14.345 ± 4.694 µg g^-1dry weight). The reported bio-concentration of aluminium which ranged from 8.3 to 76.00µg g^-1dry weight in G. acerosa [12] and the range was comparable with the aluminium concentration in the present study. Concentration of aluminium in G. edulis also showed a marginal seasonal variation. The highest level of mean concentration of 21.333 ± 11.069 µg g^-1 dry weight was observed during the post south west monsoon season while the lowest mean concentration of 8.818 ± 6.113 µg g^-1dry weight was observed during post northeast monsoon season (Table 2). Seasonal variation is attributable to multiple factors in the specific marine environment. The concentrations of different elements in an organism can vary with season, independently of environmental concentrations; for example, the contents of certain elements may be diluted during the periods of maximum growth in an organism [13].

Cadmium has a long biological half-life and it is especially insidious for humans. Therefore cadmium has been ranked as one of the major potential heavy metal hazards with acute toxicity to humans and aquatic organisms [14]. The concentration of cadmium in the samples of G. edulis showed only a marginal variation between different locations as the highest mean concentration of 0.043 ± 0.017 µg g^-1 dry weight was observed in Mandapam and the lowest mean concentration of 0.024 ± 0.010 µg g^-1 dry weight was found in the samples of Kadiapattinam. Similar observation of mean concentration of cadmium is also indicated between different seasons and hence no statistically significant seasonal variation was observed between samples (P> 0.05).

The mean concentration of cobalt in the samples of G. edulis was the lowest in Arockiapuram (0.032 ± 0.012µg g^-1 dry weight) and the highest mean value was observed in the samples of Mandapam (0.057 ± 0.026 µg g^-1 dry weight). Kadiapattinam and Kurumpanai recorded the same mean concentration of cobalt. Similar finding was also recorded in terms of seasonal variation in the mean concentration of cobalt in the present study. These observations conform to the trace metal concentrations in red seaweeds from different coastal areas of Karachi region [15]. The marginal variation in the observed mean concentration of cobalt did not indicate any statistically significant variation between locations and also seasons in the present study.

Chromium in the samples of G. edulis collected from the four distinct locations indicated varying levels of mean concentrations. The highest mean concentration was observed in the samples of Kadiapattinam (0.757 ± 0.091µg g^-1 dry weight) and the lowest mean concentration of chromium from Kurumpanai (0.412 ± 0.123 µg g^-1 dry weight). The locational variation is found statistically significant (P < 0.05) and this conforms with similar variations in the mean concentration of chromium in the edible seaweeds collected from seven different locations of the central west coast of India [16]. The observed mean concentration of chromium in G. edulis in the present study falls below the highest level of concentration (4.16 ± 0.28 ppm) in brown seaweed [17].

Presence of copper in G. edulis from the sampling sites showed the highest mean concentration of 0.655 ± 0.169 µg g^-1 dry weight at Kadiapattinam and the lowest mean concentration of 0.292 ± 0.186 µg g^-1 dry weight at Mandapam. The observations from other two locations viz: Arockiapuram and Kurumpanai recorded a moderate mean concentration of 0.489 ± 0.318 and 0.423 ± 0.140 µg g^-1 dry weight respectively. Variations in bioaccumulation of copper in seaweeds collected from different coastal regions of Gujarat, India were also observed [12]. Distribution of mean concentrations in terms of seasonal variation indicated that higher peaks were observed during post southwest and post north east monsoon seasons (Table 2). The absolute variations observed in mean concentration of copper in different locations is marginal and hence there is no statistically significant variation (P > 0.05).

The Manganese concentration in the samples of G. edulis collected from different locations varied significantly as the samples from Mandapam indicated the highest mean concentration of 3.630 ± 1.146 µg g^-1 dry weight while Kurumpanai recorded the lowest mean concentration of 0.772 ± 0.347 µg g^-1 dry weight. The mean concentrations of manganese in the samples from Arockiapuram and Kadiapattinam were 1.000 ± 0.794 and 1.095 ± 0.831µg g^-1 dry weight respectively (Table 1). The observed locational variation in the mean concentration was statistically significant at 99 per cent (P < 0.05). However, the mean concentration of manganese did not show significant variation in terms of seasons. Significant regional variation in manganese in marine green algae is also reported[18].

Nickel is present in the marine environment both as natural and anthropogenic factors. The mean concentration of nickel showed only a marginal variation between locations viz: Arockiapuram, Kadiapattinam, Kurumpanai and Mandapam with a mean value of 0.246 ± 0.036, 0.377 ± 0.125, 0.360 ± 0.232, 0.248 ± 0.043 µg g^-1 dry weight respectively. The mean concentration of nickel in the present study falls much below the minimum concentration of nickel (1.76µg g^-1) in different sea grasses of Andaman Islands [19].

Lead is a classical chronic or cumulative poison. In humans, lead can result in a wide range of biological effects depending upon the level and duration of exposure. In addition, lead has been shown to have effects on bone and on the immune system in laboratory animals. Children are more vulnerable to the effects of lead than adults [20]. The present study has observed a highest mean concentration of lead from the samples of Kadiapattinam (0.153 ± 0.057 µg g^-1 dry weight) and the lowest mean concentration from Arockiapuram (0.029 ± 0.026 µg g^-1 dry weight ). The locational variation of lead was observed statistically significant at 99 per cent level (P < 0.05). Similar variation in terms of season is also observed in lead (Table 2). It was observed that the concentrations of zinc and cadmium in food crops increased with the degree of contamination of the soil.

Presence of zinc was observed in the selected samples in all the sampling locations. The highest mean concentration of zinc was observed in the samples collected from Kurumpanai (2.630 ± 0.874 µg g^-1 dry weight) which is followed by Kadiapattinam (2.550 ± 1.239µg g^-1 dry weight) Arockiapuram (1.723 ± 0.520 µg g^-1 dry weight) and Mandapam (1.317 ± 0.377 µg g^-1 dry weight) respectively. The locational variation of mean concentration showed only a marginal statistical significance (P = 0.061). However, the variation between different seasons was not found significant in the study area. It was observed that the concentrations of zinc and cadmium in food crops increased with the degree of contamination of the soil [21]

Table 3. Permissible intake of toxic trace elements in daily dose of G. edulis

Elements	Permissible daily dose (µg)	*Recommended daily intake of G. edulis* (g/day)**	Reference
Cadmium	150	4.83	Phaneuf et al.,1999
Lead	250	22.62	Phaneuf et al.,1999
Chromium	350	190.92	IOM, 2001
Copper	900	418.27	IOM, 2001
Manganese	3300	1340	IOM, 2001
Nickel	1000	307.75	IOM, 2001
Zinc	1100	2260.5	IOM, 2001

The permissible intake of toxic trace elements such as cadmium, lead, chromium, copper, manganese, nickel, zinc [22,23] and recommended daily dose of edible marine macro algae G. edulis are presented in Table 3. It is observed that the dietary intake of more than 4.83g dry weight of G. edulis is not recommended to be used as spice as it indicates the upper limit for toleration of cadmium. If 4.83 g dry weight of G. edulis is consumed, the daily intake of Pb, Cr, Cu, Mn, Ni and Zn would be 53.38, 8.85, 10.39, 122.607, 15.69, 2.35 µg/day, respectively and this is within the permissible limits proposed by the FAO/WHO [20].

CONCLUSIONS:

The present study has brought to light the presence of various trace elements in the marine macroalgae G. edulis in varying levels in terms of locations and seasons. Among the four locations, the highest concentration of Al, Cd, Co and Mn was recorded for the samples collected from Mandapam while the samples from Kadiapattinam registered the highest concentration of Cr, Cu, Ni and Pb. The highest level of Zn was observed in the samples of G. edulis collected from Kurumpanai. Use of this macro alga in different forms of human diet necessitates the estimation of trace elements in relation to its tolerable human intake. The trace elements such as Al, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn in the study locations were found in the order of Al > Zn > Mn > Cr > Cu > Ni > Pb > Co > Cd. The locational variation of trace elements such as lead, manganese and chromium were found to be statistically significant while cadmium, cobalt, copper and zinc did not show significant variation. In the present study, it is recommended to use not more than 4.83g dry weight of G. edulis as spice daily. The mean concentrations of trace elements except cadmium were also recorded much below the quantity of daily intake recommended by FAO/WHO specifications [20]. This study suggested that G. edulis could potentially be used as raw material or ingredients to improve nutritive value in human diet and animal feed.

ACKNOWLEDGEMENT:

The corresponding author thanks the University Grants Commission for granting teacher fellowship to undertake the present study. Thanks are also due to the Management, Holy Cross College, Nagercoil.

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Received on 19.12.2014 Modified on 19.01.2014

Asian J. Research Chem. 7(3): March 2014; Page 295-299