Heavy Metals Contamination in Water and Aquatic Plants in the Tha Chin River, Thailand

Transcription

1 Kasetsart J. (Nat. Sci.) 46 : (2012) Heavy Metals Contamination in Water and Aquatic Plants in the Tha Chin River, Thailand Oning Veschasit 1, Shettapong Meksumpun 1, 2 * and Charumas Meksumpun 3 ABSTRACT Evaluation of the distribution of heavy metals (cadmium: Cd, lead: Pb, copper: Cu and zinc: Zn) in water and two varieties of aquatic plants in the Tha Chin River, Samut Sakhon, Thailand, was performed in March and November, The results ranged from ND (not detected) to 0.05, ND to 1.04, 0.01 to 1.20 and 0.16 to 7.47 mg.l -1 for Cd, Pb, Cu and Zn, respectively. Although most of these heavy metals were within the range of standard values, some stations were higher than standard for lead and copper. The highest contamination of these heavy metals was found at stations near the river mouth during the wet season. Concentrations of Cd, Pb, Cu and Zn in Ipomoea aquatica ranged from ND to 0.22, ND to 2.42, 0.69 to 8.42 and to mg per kilogram dry weight, respectively. Results for Neptunia oleracea ranged from ND to 0.30, ND to 1.50, 2.00 to and to mg per kilogram dry weight, respectively. The concentration of zinc in water, as well as lead in I. aquatica, showed significant seasonal differences (P < 0.05). Analysis revealed that copper in I. aquatica positively correlated with copper in water, indicating a potential use of these plants for pollution monitoring. Both I. aquatica and N. oleracea offer potential for bio-remediation, reducing the heavy metal pollution of the water body in which these plants are grown. Keywords: heavy metal, aquatic plants, Ipomoea aquatica, Neptunia oleracea, Tha Chin River INTRODUCTION The Tha Chin River is one of the most important large waterways of Thailand. Covering a distance of 325 km, it passes through four provinces: Chai Nat, Suphan Buri, Nakhon Pathom, and Samut Sakhon, then flows into the inner Gulf of Thailand. This river basin is an important source of water for agriculture, agro-industry and local community residents. Pollution of this river by heavy metals is a serious problem, because many such pollutants are both highly toxic and not biodegradable in the natural environment (Morillo et al., 2002). Heavy metal contamination in aquatic and soil environments threatens aquatic ecosystems, agriculture and human health (Overesch et al., 2007). In addition, these elements can be accumulated in sediment and in the tissues of living organisms in the river. Aquatic plants absorb heavy metals from the water column and pore water. These heavy metals can be incorporated into the food chain, and their levels can increase through biological magnification (Cardwell et al., 2002). 1 Department of Marine Science, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand. 2 Center for Advanced Studies in Tropical Natural Resources, National Research University-Kasetsart University, Kasetsart University, Bangkok 10900, Thailand (CASTNAR, NRU-KU, Thailand). 3 Department of Fishery Biology, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand. * Corresponding author, ffisspm@ku.ac.th Received date : 01/06/12 Accepted date : 27/09/12

2 932 Kasetsart J. (Nat. Sci.) 46(6) Aquatic macrophytes have great potential to accumulate heavy metals inside their tissues. These plants can accumulate heavy metal concentrations 100,000 times greater than in the associated water (Mishra et al., 2008). Aquatic macrophytes are thought to remove metals by three patterns: metals are restricted from entering the plant and attach to the cell wall; metals are accumulated in the root, but translocation to the shoot is constrained; and hyperaccumulation, in which metals are concentrated in the plant parts. The hyperaccumulative capacities of aquatic macrophytes are beneficial for the removal of heavy metals (Mishra and Tripathi, 2008). Aquatic plants, including Ipomoea aquatica and Neptunia oleracea are common to wetlands in the tropical and subtropical regions of the world, and are found in many ponds, streams and rivers in Thailand. These plants uptake heavy metals into their organelles quite efficiently. Ipomoea aquatica can accumulate significant amounts of toxic metals (such as cadmium, copper and lead) in its roots, stems and leaves (Kashem and Singh, 2002; Gothberg et al., 2004). Rai et al. (1996) reported high accumulations of toxic metals such as Pb and Cd in I. aquatica found in the waters of eastern India. Fonkou et al. (2005) reported Cd of up to 590 mg.kg -1 in the whole body of I. aquatica. Wang et al. (2008) reported Cd accumulations in I. aquatica of 375 2,227 mg.kg -1 in roots, and mg.kg -1 in shoots, and suggested that I. aquatica was a potential aquatic plant to remediate Cd-contaminated wastewater. Pip and Stepaniuk (1992) investigated some aquatic plants as possible pollution indicators, due to their abilities to absorb and tolerate heavy metals. They determined that Ipomoea aquatica is an important aquatic plant which can grow in contaminated surface water. Huang et al. (2006) tested 18 plant species for the ability to accumulate arsenic; among these, Ipomoea aquatica was ranked third. During the last decade, I. aquatica has been widely used for wastewater treatment (Rai and Sinha, 2001). Since I. aquatica and N. oleracea are favorite vegetables in Thailand, it is very important to determine the contamination of heavy metals in these aquatic plants, especially any contamination found in the edible parts, which could be dangerous for human consumption. The current study was undertaken to determine the extent of such contamination, and the relationship between Cd, Pb, Cu and Zn in these aquatic plants and the associated water. This information will assist local authorities to develop better strategic plans for Thai public health. MATERIALS AND METHODS Water and plant sampling in Tha Chin River The study area was located in Samut Sakhon, Nakhon Pathom, Suphan Buri and Chai Nat provinces, in central Thailand, which has a tropical monsoonal climate with an annual average rainfall of 1,075 mm.yr -1 ([Available from: html]. [Sourced: 29/10/12]). Thirty-eight sampling sites were selected along the Tha Chin River, including sites in the estuary and sites in upstream areas (Figure1). The sampling was carried out during both the dry (March 2006) and high-loading (November 2006) seasons. Water samples were collected in each season from all sampling sites. Samples of the plant I. aquatica were collected at station 29 in October 2005 and were examined to determine the heavy metal content in separate parts namely, the leaf, stem and root. Although I. aquatica and N. oleracea could not be found at some study sites, additional I. aquatica and N. oleracea samples were collected at 33 and 15 sampling sites in March 2006 (dry season) and November 2006 (wet season), respectively. Only edible parts of these plants (leaf and stem) were analyzed for heavy metal contents. Sample preparation and analysis Plant The plant edible part (leaves and stem)

3 Kasetsart J. (Nat. Sci.) 46(6) 933 samples were washed thoroughly with tap water before being rinsed with de-ionized water, then dried at 70 C in an oven. The samples were ground into fine powder in an agate mortar. Plant tissue was digested with concentrated HNO 3 and HClO 4 (5:5, volume/volume; v/v). The extracted samples were then analyzed using a flame-atomic absorption spectrophotometer (Z-8200 Polarized Zeeman; Hitachi, Ltd.; Tokyo, Japan). Water All water samples were filtered through Chai Nat Suphan Buri Upper zone Whatman glass-fiber filters (GF/C). The resulting extracts were then extracted again with 2% APDC:MIBK:4N HNO 3 (10:10:10, v/v) (Sukasem, 1989). The concentrations of heavy metal in the final extracts were determined by use of the flameatomic absorption spectrophotometer. Statistical analysis Statistical analyses of the resulting dataset were performed using the SPSS Version 11 (SPSS Inc.; Chicago, IL, USA) statistical software package. The means of sampling and the evaluation of significant differences among sampling sites or plant species were determined using descriptive statistics and analysis of variance, followed by use of the Mann-Whitney U test. Correlations between metal concentrations in the plant and water samples were evaluated using Spearman s rank correlation coefficients. RESULTS AND DISCUSSION Gulf of Thailand Intensively cultivated Ipomoea aquatica Nakhon Pathom Samut Sakhon Middle zone Lower zone Figure 1 Map of numbered sampling sites in Tha Chin River. Concentration of heavy metals in river water The concentrations of heavy metals in the water are given in Figures 2 and 3. In March, the concentrations of cadmium, lead, copper and zinc in the water ranged from 0.01 to 0.05, not determined (ND) to 0.10, 0.02 to 0.10 and 0.16 to 2.38 mg.l -1, respectively. November results for the same metals ranged from ND to 0.04, ND to 1.04, 0.01 to 1.20 and 0.82 to 7.47 mg.l -1, respectively. Most results for cadmium, lead and copper were within the range of standard values (0.05, 0.05, and 0.10 mg.l -1, respectively) developed by the Pollution Control Department of Thailand (1997), except for some stations (St. 11, 21 and 31) where lead and copper concentrations were higher than the standard, especially at station 11, which is near an industrial area. During the wet season, some results were 3 to 20 times higher than the standard level. Lead is known to be extremely toxic to living organisms and human health (Peng et al., 2008). Zinc concentrations higher than the standard value (1.0 mg.l -1 ) were

4 934 Kasetsart J. (Nat. Sci.) 46(6) observed at most stations, during both the wet and dry seasons. Statistical analysis also showed a significant (P < 0.05) difference between March and November concentrations of Zn in the water. The overall results from heavy metals in these water samples indicated that the water quality of the Tha Chin River has been affected by urban communities, agriculture and agro-industrial activities. In the current study, concentrations of heavy metals found in the water were higher than Figure 2 Concentrations in water column in March and November 2006 of: (A) cadmium; and (B) lead, the horizontal line indicate a standard value for fresh water (developed by the Pollution Control Department of Thailand, 1997).

5 Kasetsart J. (Nat. Sci.) 46(6) 935 those found by previous studies. Somsiri et al. (1991) reported concentrations of cadmium, lead, copper and zinc in the Tha Chin River of 0.01 to 0.13, 0.01 to 0.20, 0.02 to 0.29, 0.20 to 0.61 mg.l -1, respectively. Petpiroon and Rungsritsuk (2000) found concentrations of cadmium, lead, copper and zinc in the Tha Chin River of ND to 0.02, ND to 0.02, to , and to mg.l -1, respectively. The results of the current study suggest that pollution is causing Figure 3 Concentrations in water column in March and November 2006 of: (A) copper; and (B) zinc, the horizontal line indicate a standard value for fresh water (developed by the Pollution Control Department of Thailand, 1997).

6 936 Kasetsart J. (Nat. Sci.) 46(6) increased heavy metal concentrations which are reducing the water quality of the Tha Chin River. An appropriate strategic management plan is needed to halt or reverse this deterioration. Concentrations of heavy metals in Ipomoea aquatica and Neptunia oleracea growing in Tha Chin River In this study, only Ipomoea aquatica was studied to determine the heavy metal content in separate plant parts, as a representative of the aquatic plants in the study area. Concentrations of Cd, Pb, Cu and Zn in the roots of Ipomoea aquatica were markedly higher than those in the stems or the leaves (Table 1). Fritioff and Greger (2006) also suggested that although all plant parts may accumulate heavy metals, the ability to concentrate metals from the external medium varies between both plant parts and metals. However, there was no marked difference between the levels of concentration in the various edible parts of these plants (Table 1). The concentrations of heavy metal found in Ipomoea aquatica are shown in Figures 4 and 5. In March, the levels of cadmium, lead, copper and zinc in these plants ranged from ND to 0.16, 0.41 to 2.42, 1.45 to 8.42 and to mg per kilogram dry weight, respectively. In November, these values ranged from ND to 0.22, ND to 0.95, 0.69 to 6.27 and to mg per kilogram dry weight, respectively. The March values for Neptunia oleracea ranged from 0.10 to 0.15, 0.52 to 1.50, 4.04 to and to mg per kilogram dry weight, respectively. In November, the concentrations of these heavy metals ranged from ND to 0.30, ND to 1.42, 2.00 to and to mg per kilogram dry weight, respectively. Most of the heavy metals found in N. oleracea (Figures 6 and 7) were still within the range of standard values established by the Ministry of Public Health, Thailand (1986) of 0.8, 1.0, 20.0 and mg per kilogram dry weight, respectively, except for some stations (St. 9, 10 and 21) where the lead concentrations in this aquatic plant were higher than the standard value during the dry season (Figure 6). In I. aquatica, lead contamination in the tissues was even more serious during the dry season. The concentrations of this heavy metal in plant tissues were higher than the standard levels at the collection sites near the gulf and at some sites farther upstream (Figure 4). Lead is extremely toxic to humans. In the plant, accumulated amounts of the different heavy metals varied in the following order: Zn > Cu > Pb > Cd. This corresponded to the findings reported by Zhang et al. (2009) and Hu et al. (2010). Zurera et al. (1989) reported that changes of the metal contents observed in vegetables depend on the physico-chemical nature of the soil (or water bodies) and the absorption capacity of the plant, which may be different for various metals. The levels of heavy metal contamination found by the current study were markedly higher than those found by Hu et al. (2010) who determined the cadmium, lead, copper and zinc contents as , , and mg.kg -1, respectively of I. aquatica in eutrophic water (Huajia pool) which has not been contaminated by these heavy metals. Table 1 Concentrations of Cd, Pb, Cu and Zn in stem, leaf and root of Ipomoea aquatica at Station 29. Cd Pb Cu Zn (mg.kg -1 ) (mg.kg -1 ) (mg.kg -1 ) (mg.kg -1 ) Stem 0.37 ± ± ± ± 3.07 Leaf 0.30 ± ± ± ± 1.78 Root 0.45 ± ± ± ± 5.79

7 Kasetsart J. (Nat. Sci.) 46(6) 937 The current study found that concentrations of Cd in the two plant species ranged from ND to 0.30 mg per kilogram dry weight. Cadmium is a highly toxic, non-essential element. The concentration of Cd in normal plants from uncontaminated soils usually ranges from 0.05 to 0.20 mg.kg -1 (Kabata-Pendias and Pendias, 1992). Reeves and Baker (2000) reported that a few plant species could accumulate Cd concentrations of more than 100 mg.kg -1 dry Figure 4 Concentrations in Ipomoea aquatica in March and November 2006 of: (A) cadmium; and (B) lead, the horizontal line indicate a standard value for food (established by the Ministry of Public Health, Thailand, 1986).

8 938 Kasetsart J. (Nat. Sci.) 46(6) weight in the shoot. Cadmium concentrations from 0.11 to 0.85 mg.kg -1 have been reported in the leaves of 13 plant species from contaminated urban streams (Cardwell et al., 2002). This study found Pb concentrations in the two plant species ranging from ND to 2.42 mg per kilogram dry weight. Peng et al. (2008) reported that aquatic plants might accumulate large amounts of Pb in their tissues. The concentration of Cu found by this study in the two plant species Figure 5 Concentrations in Ipomoea aquatica in March and November 2006 of: (A) copper; and (B) zinc, the horizontal line indicate a standard value for food (established by the Ministry of Public Health, Thailand, 1986).

9 Kasetsart J. (Nat. Sci.) 46(6) 939 ranged from 0.69 to mg per kilogram dry weight. This study found a wide range of variation in the amount of Zn observed in the two plant species from to mg per kilogram dry weight. Significant (P < 0.05) differences were found in the concentrations of Pb in Ipomoea aquatica between March and November. In general, the concentrations of Cu and Zn in the downstream region were significantly (P < 0.05) Figure 6 Concentrations in Neptunia oleracea in March and November 2006 of: (A) cadmium; and (B) lead, the horizontal line indicate a standard value for food (established by the Ministry of Public Health, Thailand, 1986).

10 940 Kasetsart J. (Nat. Sci.) 46(6) higher than those in the upstream region. A significant (P < 0.05) positive correlation was found between Cu in I. aquatica and Cu in water as shown in Table 3. The results indicated that Neptunia oleracea has more ability to accumulate heavy metals than does I. aquatica (based on the average values from these aquatic plants during March and November 2006), especially for Cd, perhaps because N. oleracea has a longer, twig-like root, giving this plant more surface area than that of I. aquatica (Table 2). The root was thought to be important for element uptake in free-floating Figure 7 Concentrations in Neptunia oleracea in March and November 2006 of: (A) copper; and (B) zinc, the horizontal line indicate a standard value for food (established by the Ministry of Public Health, Thailand, 1986).

11 Kasetsart J. (Nat. Sci.) 46(6) 941 plants as well (Sharma and Gaur, 1995). Most metal ions are both metabolically and passively taken up by roots and transported into shoots (Marschner, 1995). Zhang et al. (2009) suggested that heavy metal distributions among the two compartments were significantly different, with the following order: plant > water. Interestingly, the concentration of lead in the water in the middle zone was markedly low while the concentration of this heavy metal was high in I. aquatica cultured in this area. This phenomenon may have been due to the efficiency of heavy metal accumulation of this plant. The current study clearly shows that the two plant species tested can be valuable for bio-remediation of metal pollution of the water body, and might be used to remove such metals from any contaminated water body. CONCLUSION The concentrations of lead and copper in the river water in some areas of the Tha Chin River were found to be higher than the standard values. During the wet season, high concentrations of zinc, in excess of standard values, were observed also. The native aquatic plant species Ipomoea aquatica and Neptunia oleracea were found to accumulate high concentrations of the same heavy metals. Statistical analysis revealed that copper in I. aquatica had a positive correlation with copper in the surrounding water. The overall results demonstrated that I. aquatica and N. oleracea can be used to remediate heavy metal pollution in water. ACKNOWLEDGEMENTS The authors gratefully acknowledge Assoc. Prof. Saran Petpiroon and the helpful suggestions provided by Assoc. Prof. Sangtien Ajjimangkul. This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission. Table 2 Average concentrations of Cd, Pb, Cu and Zn in Ipomoea aquatica and Neptunia oleracea along Tha Chin River from two observations. Cd Pb Cu Zn (mg.kg -1 ) (mg.kg -1 ) (mg.kg -1 ) (mg.kg -1 ) Ipomoea 0.06 ± ± ± ± Neptunia 0.10 ± ± ± ± Table 3 Relationships between the concentrations of Cd, Pb, Cu in Water (W) and Cu in Ipomoea aquatic (P). Cd Pb Cu Cu (W) (W) (W) (P) Cd Correlation Coefficient (W) p-value. Pb Correlation Coefficient 0.427* (W) p-value Cu Correlation Coefficient ** (W) p-value Cu Correlation Coefficient * (P) p-value Correlation was evaluated using Spearman s correlation coefficients; * = P < 0.05; ** = P < 0.01

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