Abstract: In the present study, available herbal resources among the 96 villages around Pulicat Lake have been isolated, identified and located using global positioning system. Nearly 34 species of herbal plants belonging to 24 families have been observed in these villages. Analysis of 27 plant and 27 soil samples for concentrations of toxic heavy metals (cadmium, chromium and lead) reveals relatively higher concentrations of cadmium (4.81 μg mL-1) and chromium (1.472 μg mL-1) in the plants when compared with the soil samples. In addition to this, 22 water samples were collected and their physiochemical parameters like pH, salinity, chloride, carbonate and bicarbonate were analyzed. The results obtained indicate that pH and chloride do not seem to influence the bioavilability of toxic heavy metals. Further work is required to establish the relationships among physiochemical characters of the water, soil, accumulation of heavy metals in plants and their physiology.
INTRODUCTION
The use of herbal medicines in therapeutics as well as in dietary supplement has increased vastly in the last decades (Khan et al., 2001; WHO, 2002; Wojcikowski et al., 2004). This has rapidly increased the demand for medicinal herbs but the lack of adequate regulation laws has led to decline in the quality of herbs and increase in the marketing of contaminant herbs. Poisoning associated with the presence of toxic heavy metals in herbal medicinal products was reported in Asia and European countries (Abou-Arab et al., 1999; Ernst, 2002; Chan, 2003). Plants accumulate these toxic heavy metals from the soil, water and some times from air (McLaughlin et al., 1999). However, high concentration of toxic heavy metal can occur in medicinal products, if the plants were grown in polluted areas or when toxic heavy metals were used as active ingredients in herbal medicinal preparation. In addition, several other factors that enhance the heavy metal contamination in plants are, (I) Environmental condition in which the plants were grown (ii) Application of toxic metals-containing fertilizers, fungicides and insecticides (iii) Processing and storage conditions and (iv) Type of industrial effluents released (Abou-Arab et al., 1999).
Pulicat Lake is the second largest brackish water lagoon in India, which runs parallel to the Bay of Bengal, bordering the east coast in Nellore District of Andhra Pradesh, with a portion of it extending into Thiruvallur District of Tamil Nadu. The lake is about 360 sq km and contains diverse natural resources. Catharanthes roseus, Pedalium murex, Argemone mexicus and other plants is the most dominant flora in the coastal regions of Pulicat Lake. The local people regularly harvest the plants and distribute them to the vendors. The improperly treated industrial effluents, including those from two coal based power plants and petrochemical industries from the Ennore Creek and Buckingham Canal, ultimately reach the Pulicat Lake through its bar mouth from the Bay of Bengal. Earlier studies in soil and sediment samples of the Lake have recorded elevated levels of heavy metal concentrations, especially cadmium, arsenic and mercury (Padma and Periakali, 1998, 1999; Periakali and Padma, 1998; Kamala Kannan and Krishnamoorthy, 2006). Hence, the present research has been undertaken to acquire information about the available herbal resources in Pulicat Lake with special emphasis on toxic heavy metals present in the plant as well as soil samples. In addition physico-chemical parameter of the water samples were also analyzed to study their influence on bioavilability of metals.
MATERIALS AND METHODS
In all, 96 villages were covered in two phases of fieldwork (November 2003 to November 2004) around Pulicat Lake and the available herbal plants in villages were isolated and identified. The exact locations were fixed with the help of a global positioning system. Twenty-two water samples were collected (15 during pre monsoon and 7 during monsoon) and analyzed for physiochemical parameters like pH, salinity, chloride, carbonate and bi-carbonate. Soil samples were taken randomly at the locations of plant sampling in 27 inner lake and outer villages.
Salinity, carbonate, bicarbonate and chloride were estimated titrimetrically following the procedure of Strickland and Parsons (1960). Dry ashing methods were followed for the digestion of plant samples (Tuzen, 2003) and the soil samples were digested according to Loring and Rantala, 1992. The toxic metals were analyzed using an Atomic Absorption Spectrophotometer (Perkin Elmer, AA 700). Instrument is calibrated with standard solutions prepared from commercial materials. Analytical blanks were run in the same way as the samples and concentrations were determined using the standard solutions prepared in the same acid matrix. The standard reference material (Merck) was used to check the accuracy of present results.
RESULTS AND DISCUSSION
Thirty-four species of herbal plants belonging to 24 families were isolated and identified from the 96 villages (Table 1). A total of 22 water samples were collected during the pre monsoon and post monsoon seasons. Among these, 11 were ground water and the other 11 backwater samples. The various physiochemical parameters analyzed in the samples are presented in the Table 2.
Bioaccumulation of heavy metals in plants depends upon several factors such as pH, chloride and other ions present in the soil. Soil pH exerts major control on the solubility and ability of the metals to form chelates in the soil. Acidic soils enhance the mobility and availability of the toxic heavy metals present in the soil (Ledin, 2000). The presence of high chloride concentration in soil or sediment, however, inhibits bioavailability by bonding with the metals (Craig and Moreton, 1985). Other ions like sulfide may also have the same effect (Gilmour and Capone, 1987). Bioavailability of metals also depends upon plant physiology, exposure time, metal concentration and species of chelators. Some times plants uptake toxic heavy metals similar to nutrients in chemical form or behavior; cadmium and arsenic enter the plant system because of their similarity to calcium and phosphate (Pierzynski et al., 1994). It is obvious from Table 2 that none of the ground water samples is acidic and their chloride content is also too low (maximum of 0.70 mg L-1) to influence the bioavailability of heavy metals.
Three toxic heavy metals were analyzed in the soil and plant samples collected at twenty-seven sites. The entire samples exhibit a relatively high concentration of at least one of the three heavy metals analyzed (Table 3).
| Table 1: | List of available herbals around the coastal regions of Pulicat Lake |
| Table 2: | Analytical results of water samples |
At some locations-Edamanikuppam, Pulicat Lake, Agaram, Kallur, Bottakuppam, Kuppam, Pamulumitta, Irakam and Sulurpet chromium concentrations are higher in plant samples when compared to soil samples. Januz et al. (1994) reported high concentration of heavy metals in plants growing in industrial areas. The variations in heavy metal concentration in plant samples, however, may be due to differential uptake by plant species, selective absorption of heavy metals and their varying residence times in plant system.
Previous research in the sediments of Pulicat Lake shows high concentrations of cadmium and arsenic (Padma and Periakali, 1998, 1999). The average concentration of cadmium during pre monsoon was 6.25 μg g-1 and in post monsoon it was 7.38 μg g-1. When compared with our results, the soil samples collected even from inner lake villages contain a maximum of only 7.350 μg mL-1 of cadmium, 7.55 μg mL-1 of chromium and 0.945 μg g-1 of lead which is several times less. Plants that grow in the metal contaminated soils have the ability to accumulate metals (Baker, 1981). Baker (1995) also reported that 400 species of plants have the ability to accumulate high levels of metals.
| Table 3: | Heavy metal concentration in plants and soil samples |
| a - Below Detection Limit | |
The presence of a higher number of plants in lake villages may, therefore, play an important role in the reduction of heavy metal pollution in inner lake soil samples.
Water samples indicate that pH and chloride concentration do not seem to play major role in the bioavailability of heavy metals in plants. Cadmium, chromium and lead concentrations in soil and plant samples at twenty seven locations in both the inner and outer lake villages reveal that at least one of the three heavy metals has higher concentration in all the plant samples than in soil samples. At eighteen locations, chromium concentrations are relatively higher in soil samples. This preliminary study reiterates the need for regular monitoring of water, soil and plant samples of Pulicat Lake and its environment for heavy metal concentrations, more so in view of the availability of medicinal herbal resources in this region.
ACKNOWLEDGMENTS
Authors are grateful to the authorities of University of Madras for financial support under UGC-University with Potential for Excellence (UWPFE) programme for the funding support to carry out this work and also for the teaching and fellowships to the research scholars (S.K, B.P and P.D). Authors also acknowledge the DST-FIST-AAS Instrumentation facility available at the Department of Applied Geology, University of Madras.