The sediment of Pattani Bay in Thailand and the Setiu Wetlands in Malaysia was investigated in the dry and wet seasons of 2014 to evaluate levels of trace metal concentrations (As, Cd, Cu, Pb, and Zn), sediment grain size, and organic matter. The mean concentrations of all the elements in both seasons (dry and wet) at Pattani Bay were higher than those in the Seitu Wetlands. High levels of As were detected in both seasons, but they were classified as moderately polluted in the dry season. The Enrichment Factor in relation to aluminum showed significant (Enrichment Factor >5 in the wet season) anthropogenic activity as related input for As in both areas and for Pb at Pattani Bay. Surprisingly, the metal concentrations (As, Cu, Pb, and Zn) were only significantly (p < 0.01, p < 0.05) correlated with clay content in the dry season at Pattani Bay. Silt-clay content and the amount of organic matter at Pattani Bay were higher than those of the Setiu Wetlands.
Sediment is considered to be a good indicator of metal pollution because it serves as a source, as well as an ultimate sink, of many pollutants in the aquatic environment. Trace metals could be transferred into estuaries via atmospheric and fluvial transportation, absorbed and preserved in the sediment, as well as enriched in the organism through the food chain (Dong et al., 2012). Metals may be brought by rivers to coastal areas by continuous, diffuse inputs, or during flood events, and they may accumulate in marine sediment (Oursel et al., 2014). Their input in the water column and in sediments may be a threat to the quality (such as water and sediment quality) of the coastal area (Oursel et al., 2014; Rocha et al., 2011; Weber et al., 2009). Many aquatic organisms are able to regulate the metal concentrations in their tissues. Metals could be released into the water column while the sediment resuspended or the environment changed (due to salinity, for instance, reducing the condition of the biogeochemistry process) (Wen and Allen, 1999; Kelderman and Osman, 2007; Murakami et al., 2009). Sediment-associated metals pose a direct risk to detritus and deposit-feeding benthic organisms and may also represent long-term sources of contamination to higher trophic levels (Mendil and Uluözlü, 2007).
In fact, during the last few decades industrial and urban activities have contributed to the increase of metal contamination in the marine environment and have directly influenced the coastal ecosystems (Buccolieri et al., 2006). Rapid development around Pattani Bay could produce a large quantity of pollutants, which may have adverse impacts on fisheries and human health. Aquatic fauna are part of the food chain, therefore toxic elements in the water and sediments may possibly be transferred to the humans who consume them (Maneepong and Angsupanich, 1999).Various studies have demonstrated that marine sediments from industrialized coastal areas are greatly contaminated by trace metals; therefore, the evaluation of metal distribution in surface sediments is useful for assessing pollution in the marine environment (Pradit et al., 2013; Buccolieri et al., 2006; Bellucci et al., 2002)
This research study of sediment covered the areas from Pattani Bay in Thailand and the Setiu Wetlands in Malaysia during two seasons. The study was carried out under the collaborative effort between the Universiti Malaysia Terranganu and the Prince of Songkla University, Thailand. The objective was to collect current sediment information. In a related paper by Pradit el al. (2016), an accumulation of trace metal (As, Cd, Cu, Pb, and Zn) in Blood Cockle form Pattani Bay and the Setiu Wetlands was investigated. Therefore it was beneficial if the concentrations of trace metals (As, Cd, Cu, Pb, and Zn) in sediment, sediment grain size, and organic matter were determined. The results of this study can be integrated into the existing data of the previous study to provide valuable information for the better understanding of aquatic ecosystems of those areas in the past and in the future.
Two coastal areas including, Pattani Bay (10 stations) and the Setiu Wetlands (5 stations) were selected for this study (Figure 1). These areas were chosen on the basis of the similarity in the geological location which both coastal areas face to the South China Sea, and are surrounded by with mangrove area with high in biodiversity such as Seagrass, Blood Cockle and birds etc. In particular Pattani Bay is a semi-enclosed estuarine bay, located on the east coast of Thailand, facing the Gulf of Thailand. The geographic location of the bay is between latitude 6° 51′ N and 6° 57′ N and longitude 101° 13′ E and 101° 25′ E. The International Union for Conversation of Nature identified Pattani Bay as a worthy coastal wetland conservation in Asia. It covers 74 km2. The average water depth is about 1.5 m, with a maximum depth of 5 m at the bay's mouth. Two major rivers, the Pattani River and Yamu River, drain into the bay. Recently, Pattani Bay has been affected by several land-use activities (such as industry, rubber fields, and aquaculture). Pattani Bay's population of about 70,000 is scattered throughout 18 villages; at present, most forms of waste around Pattani Bay are not treated. As such, solid waste or waste water contaminated with heavy metals from land-use activities around the bay may be harmful to the environment, especially to marine organisms (Sowana et al., 2011). The Setiu Wetlands are located along the coast, in the northern state of Terengganu, which belongs to the district of Setiu, on the east coast of the Peninsular Malaysia. The geographic location of the bay is between latitude 5° 39′ N and 5° 41′ N and longitude 102 °42′ E and 102 ° 44′ E. The study area covers about 13 km2 of the Setiu Wetlands' lagoon areas. Unlike Pattani Bay, the lagoon area of the Setiu Wetlands is enclosed, containing only a small opening to the South China Sea. It receives fresh water from the Setiu and Chalok Rivers. It is part of the Setiu River Basin and the larger Setiu-Chalok-Bari-Merang basin. The area comprises riparian forests lining the riverbanks, peat swamps, mangroves, brackish water lagoons with vegetated sand islands, Seagrass beds, and sandy beaches. The lagoon is a major aquaculture area, involving brackish water cage culture, pond culture, pen culture, and oyster farming. In addition, sand mining activities in the Setiu and Chalok Rivers have the potential to release heavy metals into the Setiu lagoon.
The sediments (up to a depth of 10 cm) were collected during the same period from the 10 stations in Pattani Bay and 5 stations in the lagoon of the Setiu Wetlands in February (dry season) and again in September 2014 (wet season), using a grab sampler. The approximate water depth of Pattani Bay sampling stations was approximately 0.60–1.00 m except station 10 the depth was approximately 2.5–3.00 m. The approximate water depth of Setiu Wetlands sampling stations was approximately 0.60–0.80 m. About 1 kg of sediment was placed in clean plastic bags, which were then placed on ice in coolers and transported to the laboratory. The samples were stored, frozen, until they were required for analysis.
Prior to analysis, the wet sediment samples were frozen, dried in the freeze dryer, homogenized, ground with a mortar, and sieved through a nylon sieve. The bulk sediment samples (about 0.1 g) were totally digested in an acid mixture (5 ml HCl: 8 ml HNO3: 2 ml HF) and analyzed for trace metals, according to the published methodologies of Noriki et al. (1980) and Loring and Rantala (1992), with some modifications (the Teflon vessels were heated in an oven instead of a microwave until complete digestion of the sample occurred). The trace metals were then measured by ICP-MS (Perkin Elmer Elan 9000). The reference material, MESS-2, was similarly analyzed to validate the accuracy of the analytical procedure. The analytical values were within 90% of the certified values, which demonstrates the validity of the applied methods.
The readily oxidizable organic matter of the sediment samples was determined by the Walkey-Black method, as described in Loring and Rantala (1992) and Schumacher (2002). The particle size analysis was determined using the hydrometer method (Gee and Bauder, 1986).
All calculations and statistics were carried out using MS Excel 2007. All comparisons were made at least at the 95% (p < 0.05) and 99% (p < 0.01) level of significant.
The enrichment factors (EF) were calculated in order to evaluate the anthropogenic activity related input of the toxic elements, using Al as a reference element. Al normalization has been shown to be applicable for coastal sediments in the Gulf of Thailand (Cheevaporn and San Diego, 1997).
Results and discussion
The As concentration in Pattani Bay and the Setiu Wetlands in February (Dry season) (Table 1) ranged 2.03–5.93 and 0.47–1.02 µg g−1 dry weight while As in September (wet season) (Table 2) was 6.90–11.70 and 1.07–2.34 µg g−1 dry weight. The Pb concentration in Pattani Bay and the Setiu Wetlands in February (Dry season) ranged 6.90–11.70 and 1.07–2.34 µg g−1 dry weight while Pb in September (wet season) was 2.40–11.48 and 0.63–1.56 µg g−1 dry weight. The other element concentration was shown in Tables 1 and 2.
Data for comparisons with the present findings are not generally available. The metal concentration detected at Pattani Bay and in the Setiu Wetlands is lower than the data reported for the Gulf of Thailand and mangrove sediments. The coarser sediments at Pattani Bay and the Setiu Wetlands are metal poor, with only the fine fraction (clay) having higher concentrations. Shazili et al. (1999) reported that the comparison of data for the Gulf of Thailand between the pre-NE monsoon and the post-NE monsoon indicated that concentrations of Zn were significantly higher in the pre-monsoon period, while those of Cu and Pb were significantly higher in the post-monsoon period. For the East Coast peninsular area, concentrations of Pb were higher in the post-monsoon period, while the concentrations of Cu were similar between the two periods (Shazili et al., 1999). Kamaruzzaman et al. (2008) reported that the average concentration of Pb, Cu, and Zn in the sediments collected from seven mangrove forests of Terengganu were 10.5 ± 7.12, 31.1 ± 16.5, and 20.8 ± 13.3 µg g−1 dry weight, respectively. Pradit et al. (2010) took the bottom sediments from 44 stations in Songkhla Lake, in southern Thailand, to study trace element contaminations in sediments. The trace element concentrations in the surface sediment ranged: it was 0.8–70.7 µg g−1 dry weight for As, 0.1–2.4 µg g−1 dry weight for Cd, and 8.2–131 µg g−1 dry weight for Pb. The results showed that the Outer Section of the lake, particularly the sediment at the mouths of Phawong, Samrong, and U-Taphao canals, was significantly enriched in trace elements, due to municipal, agricultural, and industrial discharges entering the lake through the canals.
The sediment in Pattani Bay is different from that of the Setiu Wetlands (Table 3). Pattani Bay is very likely to be under the direct influence of two major rivers; the Pattani River and the Yamu River draining into the bay. Meanwhile, the Setiu Wetlands' sediment is likely to be transported from and deposited under the influence of the South China Sea. Sand fraction is dominant in the Setiu Wetlands sediment, while in Pattani Bay, the sediment is composed of clay-sand. This result could be attributed to the sea conditions in the Setiu Wetlands. The roughness associated with the open sea would have caused the Malaysian waters to have less silt and clay, since water turbulence aids in dispersing the finer sediment further offshore, while the semi-enclosed condition of the gulf helps to reduce turbulence, thereby at the contain the rives discharges to the gulf (Husain, 1999). It has been suggested that the distribution of the sediment deposits is based upon the distribution of the different velocities of water masses and currents which are preliminarily influenced by wind velocity, direction, and the topography of the areas.
The dry season (February) showed a slightly high amount of organic matter than the wet season did, for both areas (Table 3). However the organic matter at Pattani Bay tended to be higher than that of the Setiu Wetlands, while the pattern was more variable for Pattani Bay, due to its larger area and greater population. The amount of organic matter deposited in sediment depends upon the rate of sedimentation, bioproductivity, and the input of organic matter. High sedimentation rates tend to dilute the organic matter with inorganic sediment.
Sediment quality guidelines (SQGs) for the assessment of sediment quality using chemical and biological effect databases have been established. These SQGs are summarized in Table 4. NOAA presents ERL (effects low range) and ERM (effects range median) guidelines for estuarine and marine environments which represent the 10th and 50th percentiles of adverse biological effects (NOAA, 1999).The US-EPA has also made classifications (non-polluted, moderately polluted and heavily polluted levels based on toxicity tests) (reported in Baudo et al., 1990 and Filgueiras et al., 2004). Mean value of As in Pattani Bay only dry season classified as a moderately polluted level suggested that As might flush away during wet season. Data for comparison with the present findings are not generally available. The metal concentrations detected in Pattani Bay and in the Setiu Wetlands were lower than data reported for the Gulf of Thailand and in mangrove sediments. The coarser sediments of Pattani Bay and Setiu Wetlands had low metal concentration, whereas the fine fraction (clay) possessed higher metal concentrations.
Two potential sources of Pb at Pattani Bay were lead as galena (PbS) and lead oxide (Pb3O4) released from boat repairing activity at the end of the Pattani River (Simachaya et al., 2003). At the Setiu Wetlands, potential sources of Pb would likely be the activities of boat repairing and sand mining (Kamaruzzaman et al., 2002). Several combination point sources contributing Cd and Pb into river outflow included waste water from industries and input of rock and mineral weathering as well as other local activities nearby. It is possible that sources of Pb contamination include the atmospheric input of Pb from the use of leaded petrol by motor vehicles, as well as considerable numbers of fishing boats surrounding the piers.
Regional background values assessed from core sediment samples were reported by Choi et al. (2008) and offshore sediments in the Gulf of Thailand by Shazili et al. (1999). Background levels varied from 10–25 µg g−1 dry wt. for Cu, from 55–115 µg g−1 dry wt. for Zn, from 5–9 µg g−1 dry wt. for As, from 0.03–0.2 µg g−1 dry wt. for Cd, from 15–30 µg g−1 dry wt. for Pb and 4–6% for Al. The EF value for As and Pb at Pattani Bay at stations 1, 4, 6, 9 and 10 is greater than 10 and 3, respectively. Stations 1, 9 and 10 were located at the mouth of the Bay, while stations 4 and 6 were located inside and near the main rivers. However, only a significantly high EF value (>5) is considered to denote enrichment by anthropogenic-related activities (Atgin et al., 2000). The EF value of As in the wet season is greater than 5 in both areas; the value ranged from 5.8 to 27.0. The EF value for Pb > 5 was only observed at Pattani Bay (wet season) for some stations, which ranged from 5.8 to 8.5.
The metals were significantly (p < 0.05) correlated with clay. Likewise, As and Pb were significantly correlated with silt (p < 0.01), and Cu, Zn, Pb (p < 0.01), and As (p < 0.05) were significantly correlated with the organic matter at Pattani Bay (Table 5). For the Setiu Wetlands, Cu was significantly correlated (p < 0.01) with As in the dry season. Cu, Zn, and As were significantly correlated with each other (p < 0.01) at Pattani Bay, as were Cu‒Pb‒Zn, As‒Cd‒Pb, and Cd‒Pb in the September samples in the same location. While the total concentrations of metals in the sediments of both water bodies were low, and thus, not polluted, the strong correlations of Cu, Zn, and As at Pattani Bay are indicative of their source: the use of agricultural fungicides. Likewise, Cd and Pb were indicative of fertilizers, boat activities, and gasoline. Surprisingly, the metals (As, Cu, Pb, and Zn) were only significantly (p < 0.05) correlated with clay in the dry season at Pattani Bay. This is because the fine particles or fine-grained sediments were charged, particularly the clay minerals, showing a high metal content. In contrast, in the wet season, there was no correlation among those elements and clay. We suggested that new clay had been introduced by the rivers, run-off, and rain during the wet season.
It was suggested by Pradit et al. (2016) that As could be a limiting element (BSAF < 1) of Cockles obtained from Pattani Bay. It would be that even the As concentration in sediment was high but it was limited to uptake by Cockle. The maximum values of Cd and Pb in Cockle (Anadara granosa and Anadara inaequivalvis) from both areas exceeded the permissible limits set by the Thailand Ministry of Public Health and the Malaysia Food Regulations for both areas (Pradit et al., 2016). Therefore it is important to monitor the concentration of Pb and Cd in the areas since it seemed like that Cockle could accumulate those metals unlimited. Apart from that Hajisamae et al. (2015) found that blue swimming crab (Portunus pelagicus) from Pattani bay feeding on a wide range of benthic invertebrates and the diets of P. pelagicus did not change with season but did vary with habitat. Therefore, P. pelagicus living associated with sediment for the whole year round has a high chance to obtained heavy metal especially As, Cd and Pb through their benthic food.
Pattani Bay and the Setiu Wetlands had low sediment metal concentrations, only As was classified as moderated polluted in the dry season. The As exceeded the enrichment factor, which showed a significant (EF > 5) anthropogenic activity related input for As in both areas. The new clay has been introduced by the rivers, run-off, and rain during the wet season of Pattani Bay. However in the Setiu Wetlands, the lack of correlation between clay and trace elements suggested that the clay was the same clay for both seasons. The differences between sediment characteristics in both areas could probably be attributed to the sea, since Pattani Bay is comparatively enclosed and protected by the Gulf of Thailand, as opposed to the conditions of the Setiu Wetlands, which are located in the exposed area of the South China Sea.
This work was supported by the budget revenue of Prince of Songkla University contact number COR560635S.