Keywords

Highlights

  • Activities of 210Pb along Sepang Besar River are widely varied.

  • Lower 210Pb activities at rivermouth; higher at inner course of Sepang Besar River.

  • Watershed’s geology and chemical weathering conditions affect the 210Pb activities.

Introduction

The radionuclides dating using 210Pb have been used for more than two decades to provide geochoronology of annually deposited sediment and to construct pollution histories (Benoit and Rozan 2001). Zulkifli et al. (2010a, b) has reported worlwide scientists concern on resuspension of bottom sediments (polluted layer) in recent years due to sediments dredging and coastal reclamations. The isotopes 210Pb (T1/2 = 22.3 yrs) is a decay product of 222Rn which escapes from the earth crust to the atmosphere. 210Pb short residence on atmosphere, falls into lake or river and tends to bury and permanently fixed on sediment particles as solid fallout (Althammer et al. 2010). 210Pb has been widely used as marine tracers of particles/water transport and particulate scavenging (Benoit and Rozan 2001). The usage of tracer such as 210Pb allows tracing the history and sources of pollution on studied area (Gelen et al. 2003).

The area around Sepang Besar River has been fully utilized for agriculture, animal farming, residential, aquaculture, ecotourism and power plant activities. The pollutants from anthropogenic activities could be accumulated in the sediments (Zulkifli et al. 2010a, b). Ismail and Ramli (1997) reported this river received high anthropogenic input of heavy metals in 1990s originated from massive pig farming activities. However, the outbreak of Japanese encephalitis (JE) in 1998 has caused pig farming activities to be closed. In order to understand the heavy metals enrichment in the sediments, geochronology of sediment should be studied. Thus, the aim of this study to investigate geochronological pattern of 210Pb in core sediments of the Sepang Besar River.

Materials and Methods

The Sepang Besar River is located at the state boundary of Selangor and Negeri Sembilan, Malaysia. The core sediments were collected from three locations along Sepang Besar River as shown in Fig. 45.1. The sediment core samples were collected by using the 1 m hand corer (6 cm inner diameter). The corer was hand-pushed into the bottom sediment, capped and retrieved. The core samples were directly brought back to laboratory and stored in a freezer at −20 °C to prevent any chemical or biological reactions prior further analyses. Laboratory analysis started by thawing the core sediments. Each core was sliced into 2 cm intervals from surface to bottom of the core. All core sections were dried in an air-circulating oven at 60 °C to a constant weight and homogenized through a 250 μm mesh size sieve for analysis 210Pb radionuclide dating. The digestion of sediment for radionuclide purposes was modified from Theng and Mohamed (2005). In general, about 5 g of homogenized core sediment sample was taken and spiked with 1.0 mL of PbNO3 (20 mg/mL) and 1.0 mL of FeCl3 (19.8 mg/mL). In the laboratory, samples were digested with a hot plate for 3 h. Then, the samples were filtered through membrane filter paper (0.45 μm pore size, 47 mm diameter) with a flow rate less than 10 mL.min−1. The filtreate was acidified with 65 % concentrated HNO3 till pH < 2 and spiked with iron carrier solution. The samples were centrifuge for 3 min at 4000 rpm. After that, the solution pH was increased to pH 10. The precipitate was filtered and redissolved in 1.0 M HNO3. The 210Pb was deposited on a platinum

Fig. 45.1
figure 1

Map of sampling locations along the Sepang Besar River, Malaysia

Full size image

bucket and redissolved with concentrated H2SO4 before filter with 0.45 μm filter paper. The precipitation of 210Pb effluence was counted with beta (β) spectrometry to determine the activity of 210Pb.

Results and Discussion

Three sampling locations have been selected, representing the behavior of the sediment. The activities of dissolved and particulate 210Pb from three stations of Sepang Besar River were measured and corrected for the recovery. The sampling location, sample intervals and 210Pb activity concentration are shown in Table 45.1. Based on the data shown in Table 45.1, the activities of 210Pb in Sepang Besar River estuary showed a wide variation and this was probably due to the geology of the watershed and chemical weathering conditions. In Station 1, the 210Pb activity concentration was varied between 6.16 ± 1.68 Bq/kg and 24.52 ± 7.64 Bq/kg. In Station 2, the 210Pb activity concentration was varied between 171.14 ± 111.90 Bq/kg to 595.19 ± 159.75 Bq/kg, whereas the 210Pb activity in Station 3 was between 185.56 ± 49.01 Bq/kg to 883.15 ± 303.55 Bq/kg. The activity of 210Pb was lower in Station 1 as it faces the river mouth of the river. The 210Pb activity in Station 1 was influenced by strong tides activities that occur daily as compared to 210Pb activity concentration in Station 2 and Station 3.

Table 45.1 Activities of 210Pb (Bq/kg) in the sediment cores of Sepang Besar River
Full size table

In Station 1, the 210Pb activites were higher on the surface layer (0–2 and 2–4 cm depth) of the core sediment. Based on personal observation, the sediment in this area was free from sheltered mangrove forest as compared to sediment collected from Station 2 and Station 3. The core sediment in Station1 received the highest amount was probably due to supply of deposition at atmospheric 210Pb originated from the decay of 222Rn (Yang and Lin 1992). Flying ashes from combustion of coals at the nearby power plant could potentially deposited into the sediment. The 210Pb activities in both surface layer (0–2 and 2–4 cm depth) of Station 2 and Station 3 were higher than in Station 1 but based on 210Pb count activities, it shows that 210Pb activities were lowest among the same station. The core sediment collected in this area was covered with sheltered mangrove plants, so the tendency of 210Pb particulate escape to the atmosphere to sink on sediment was low. The high 210Pb activities reported in this study was probably due to supply of 210Pb as these stations were in vicinity to the agricultural lands. The main agricultural activity that occurs in this area was oil palm plantation. Besides that, this area also received both domestic and industrial waste from nearby residential areas as the wastes released into this river. The 210Pb activities reported in this study was same as a study reported by Theng and Mohamed (2005) in Kuala Selangor estuarine.

Conclusion

Inner course of Sepang Besar River has higher 210Pb activities than rivermouth due to tidal actions. Further investigations are needed in order to related with deposition of pollutants.