Studies on the Distribution of

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Studies on the Distribution of

²¹⁰

Pb in Surface Sediments of Peninsular Malaysia during Monsoonal Season

Mohamad Arif Che Abd Rahim¹, Masni Mohd Ali¹, Wan Zuhairi Wan Yaacob¹, Abdul Hafidz Yusoff², Xuefa Shi³, Shengfa Liu³and Che Abd Rahim Mohamed¹*

1Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

2Faculty of Bioengineering and Technology, Universiti Malaysia Kelantan, 17600, Jeli, Kelantan, Malaysia

3First Institute of Oceanography, SOA, No.6, Xianxialing Road, Qingdao, China

Abstract

Thirty-three surface sediments samples were collected from the East and West coasts of Peninsular Malaysia by using the Van Veen Grab during Universiti Kebangsaan Malaysia – First Institute of Oceanography, China (UKM-FIO) Scientific Cruise.

Samples were collected during Southwest Monsoon events (August 2017) and Northeast Monsoon events (March 2018). The analysis of chemical and physical of the homogenised sediment sample, including sediment textural, loss of ignition, and ²¹⁰Pb concentration have been determined to investigate the effect of monsoonal changes to the physical and chemical characteristic of sediments in marginal sea area. The concentration of ²¹⁰Pb in surface sediment ranged from 80.33 ± 11.81 Bq/kg to 231.52 ± 25.95 Bq/kg. The result of statistical analysis shows significant negative correlation between organic matter (OM) and the content of silt (r = -0.519, p < 0.05) and positive correlation between OM and sand (r = 0.507, p < 0.05) during Southwest monsoon. However, no significant correlations detected between ²¹⁰Pb with the OM and sediments textural during both monsoons. Since the location of the sampling stations are located in the marginal sea area, it’s may suggest that the exposure to the boundary scavenging might leads to the fluctuated activity of ²¹⁰Pb and organic content in surface sediment, which occurred due to high particle flux within the water column.

Keywords: ²¹⁰Pb, monsoon, sediment, marginal sea

1. Introduction

Deltas are the primary source of fine-grained sediment to the coastal shelf where rivers are contributing a disproportionately a huge fraction of terrestrial flux, while important for sustaining the deltas. Moreover, riverine sediment is a key figure for carbon and nutrient deposition, therefore, playing a significant role in the biogeochemical cycle. Presence of climatic and hydrological variation would alter the sediment load along with the mobilizations. Identifying the sediment provenance and mobilization process from terrestrial to the open ocean enable users to predict the fate of pollutant release or sudden change in sediment delivery to marine environments. Furthermore, fine sediment as a pollutant carrier can move continuously through the drainage system that associated with cycles of deposition and resuspension during climatic and hydrological stages [1]. The importance of these pollutants is the magnitude of impacts in receiving areas such as oceans, and the relationship between drainage basin and the ocean is vital for active sediment bed quality and water quality [2].

The conditions of climatic and hydrological of the aquatic environment directly influence the deposition and mobilization of the fine-grained sediment onto the active sediment bed. Meanwhile, the climatic variation and hydrological movement were directly affected by the monsoonal season, thus triggering the weathering and erosion

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mechanism from the terrestrial source. A seasonal variation occurred in Southeast Asia namely southwest monsoon (June to August) and northeast monsoon (October to March) responsible for the rate of erosion and weathering thus the fluctuation of deposition in sediment by fine-grained sediment [3]. Similar hydrological action (e.g., upwelling, downwelling) occur in the aquatic environment would activate the resuspension on active sediment bed that increases the total volume of resuspended clay within the water column.

Further implication on resuspension also increases the volume of organic matter, as shown by [4] where sudden flooding would increase the overall volume of organic matter within the river channel.

Natural radionuclides can be utilized with success to investigate the movement of particulate matter and suspended sediment in the estuarine, coastal and aquatic environment. The uses of radionuclides as a tracer was well known among researcher, e.g., [5]–[7] to establish a baseline of mobilization of sediments, ingestion and doses of radionuclides onto marine organism and pollution tracer along the interest regions.

Furthermore, most of the naturally – occurring radionuclides such as uranium-thorium decay series which present in the marine ecosystem were sourced either from igneous rock or other types of minerals [8], [9]. To determine the distribution and sinks of particle behaviour, ²¹⁰Pb has been broadly used to study the dynamics, sources of suspended, and sinks of sediment while determining the fluxes and internal process in sedimentary compartment including coastal, river and oceans. The mechanism of ²¹⁰Pb was far more effective as a trace for sediment and soil due to higher affinity where sediment behaviour acted on ²¹⁰Pb was stronger binding on sediment and organic particle thus varying distribution is along with sediment particle-bound while under several physical processes such as erosion, water movement and wind [10]. In theory, the eroded solid would become a carrier of the fine-grained sediment as the large surface area and the affinity of the ²¹⁰Pb towards the Fe-rich organic matters. The objective of this study was to identify the sources of ²¹⁰Pb while assessing several factors that influence the distribution of ²¹⁰Pb along Peninsular Malaysia. Thus, the purpose of this study was to investigate the relationship of organic matter and sediment textural with ²¹⁰Pb concentrations.

2. Methodology

During UKM-FIO Scientific cruise on August 2017 and March 2018 (Figure 1), the collection of 33 surface sediment accomplished by using Veen Van Grab surrounding Peninsular Malaysia. Before the analysis, the sample was properly dried and homogenised. For loss of ignition, follow the published procedure [11]. The micropipette method was used to identify soil texture [12]. As for ²¹⁰Pb activity, an established method was obtained to study the activity of ²¹⁰Pb in Peninsular Malaysia [13]. First, a homogenised, dried sample of <63 µm was used and weighted around 0.25g to 0.30 g for total digestion. A combination of acids, HF+ HNO3 + H2O2 was used for 2 hours before being subjected to near dryness. Before being re-heated, the addition of with 2 ml of 0.5 M HNO3 and 0.5 g of boric acid onto the sample was to neutralise the fluoride ions and dilute with 50 ml of double-distilled water. The treatment of the liquid phase is using with FeCl3 and ammonia solution before running into a centrifuge for 3 minute at 4500 rpm.

The electrodeposition establishes at voltage range from 2.2 – 2.5 for one hour by using the platinum bucket as cathode and steel rod for anode. The captured of lead (II) was rinsed with 3M of nitric acid and 30% of H2O2 and heat treatment is used to evaporate the excess fluids. The sample, combined with 0.5M of HNO3 and H2SO4 left for overnight for so that a white precipitate of PbS04 appears. Using the filter paper of 0.45µm the collection of PbS04 salt done swiftly and ready for counting with β spectrometry by using Eclipse software from Canberra^® after 25 days of electrodepositing.

Table 1. Sampling station in Peninsular Malaysia during 2017 and 2018

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Year Station Longitude Latitude Sampling Date

Depth (m)

2017 (Southwest

Monsoon)

M2 103.0400 6.8000 18/9/2017 53.00 M10 104.6600 6.2600 19/9/2017 66.00 M13 103.5800 5.7200 21/9/2017 54.40 M15 104.6600 5.7200 21/9/2017 60.80 M17 105.7400 5.7200 27/9/2017 66.20 M19 104.1200 5.1800 21/9/2017 62.00 M20 104.6600 5.1800 21/9/2017 70.00 M22 105.7400 5.1800 24/9/2017 80.00 M29 104.6600 4.1000 24/9/2017 69.00 M34 104.1200 3.0200 27/9/2017 41.50 M35 104.6600 3.0200 24/9/2017 66.00 M39 104.6600 1.9400 28/9/2017 45.00 M40 104.6600 1.4000 28/9/2017 28.50 M41 99.1200 6.2600 2/10/2017 63.10 M43 98.0400 5.7200 2/10/2017 103.00 M45 99.1200 5.7200 2/10/2017 53.00 M49 99.1200 5.1800 1/10/2017 75.50

2018 (Northeast

Monsoon)

N53 104.3703 7.2886 22/4/2018 45.50 N61 103.3114 5.9983 24/4/2018 50.00 N64 104.9683 5.9981 24/4/2018 61.50 N72 103.8703 4.9281 25/4/2018 62.30 N75 105.5306 4.9111 26/4/2018 80.00 N80 104.1114 3.8564 27/4/2018 50.50 N84 104.9589 3.3072 28/4/2018 71.00 N87 104.9778 2.7714 29/4/2018 71.40 N90 104.4231 1.6781 1/5/2018 33.40 N94 99.4150 6.0261 1/5/2018 67.00 N95 99.9606 6.0069 1/5/2018 39.50 N97 98.8372 5.4350 2/5/2018 34.60 N99 99.9811 5.4428 2/5/2018 40.80 N103 100.4400 4.9433 2/5/2018 15.50 N106 100.4561 4.3733 2/5/2018 22.00 N108 100.4828 3.8247 2/5/2018 67.80

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Figure 1. Sampling stations of surface sediments during 2017 and 2018.

Samples were collected during Southwest monsoon and Northeast Monsoon in 2017 and 2018, respectively

3. Results and Discussion

The activities of ²¹⁰Pb within Peninsular Malaysia shown in Table 2 was ranging from 80.33 ± 11.81 Bq/kg to 231.53 ± 25.95 Bq/kg and averaging at 136.79 ± 16.20 Bq/kg. Total concentration in Peninsular Malaysia was different between sampling time where the collection of the sample during August 2017 of southwest monsoon (M station) exhibit a higher 55.04 % of the total concentration of ²¹⁰Pb than the March 2018 of northeast monsoon at 44 % of acquired concentrations (N station).

On the other hand, the acquired soil texture from the analysis saw a several variables ranging from 5.12 % to 92.9 % of pure sands averaging 60 % from total sands while silt varies from 3.33 % to 87.61 % with an average of 34.4% and acquire clay was ranging from 0.32 % to 13.24 % and averaging at 5.54 %. The sample collection during August 2017 lower clay output, 19 % compared to the collection during March 2018, 80.44 %. For silt and sand output throughout a season, collection of the sample during August was far higher compared to the March collection, where 51 % and 54 % for silt and sand collection while 48 % and 45 % for silt and sand on March 2018. The value of organic matter also saw a fluctuation with a lower percentage acquired in southwest monsoon (43%) opposed to the higher percentage in northeast monsoon (56 %) from the total organic matter obtained. Statistically, only southwest monsoon exhibits a significant difference between organic matter and the content of silt (r = -0.519, p < 0.05) and sand (r = 0.507, p < 0.05).

Seasonal variation acted on the sediment may altering the textural content where higher content of total silt and sand was found in August 2017 while clayey content dominating the surface sediment during March 2018. The presence of upwelling and downwelling acted on the surficial sediment for the rise of clayey content during northeast monsoon [14]. Furthermore, the shallow depth on Peninsular

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Malaysia coastal may ignite the resuspension onto the seabed sediment , thus increasing the content of clayey during northeast monsoon [15]. The high content of clay also suggests that the presence of the bioturbation lead to higher mixing rates during the monsoonal season; thus, redistribution of clay content may occur during the monsoonal season [16]. The lower content of silt and sand during southwest monsoon would suggest diminished terrestrial input from drainage basin, instead intensified southwest monsoon on seabed sediment might lead to higher in -situ resuspension [17]. Furthermore, continuous erosion on seabed sediment may be reducing the volume of clay within the sediment, thus lowering the content of clay during southwest monsoon [18].

The concentration of ²¹⁰Pb during both monsoonal season was highly variable, and no significant pattern exhibit on a complete cycle of monsoon. Moreover, there is no significant correlation between ²¹⁰Pb and clay, which occurred at the marginal sea. Wet and dry deposition onto the coastal of Peninsular Malaysia and the intensified boundary scavenging due to monsoonal season suggest the fluctuation of ²¹⁰Pb as the release of

222Rn from precipitation, and the transboundary of mineral dust leads to increment in ²¹⁰Pb concentrations [19]. Within the successive deposition into the water column, the scavenged ²¹⁰Pb might attach to the suspended matter as the release of dissolved Mn⁺ and Fe⁺ may re-precipitate to attain the additional ²¹⁰Pb on seabed sediment [20]. As deposition onto the seabed sediment, the adsorption onto porous sediment may yield the variety in ²¹⁰Pb concentration, which the dependency of ²¹⁰Pb was onto the grain size particles [21]. Furthermore, the variable of grain size acquired suggest that different level of compaction within seabed sediment, thus altering the concentration of ²¹⁰Pb, which it has an affinity with mineral contents [22]. Physical events such as wind cycle and tidal surges also play an important factor for the distribution of organic matter and residual of sediment texture as it interferes the fluctuations of ²¹⁰Pb which it has affinity properties towards grain size and organic matters [23].

Table 2. Concentration of ²¹⁰Pb and sediment properties

Year Station Clay (%)

Silt (%)

Sand (%)

Organic Matter

(%)

Pb-210 (Bq/kg)

2017 (Southwest

Monsoon)

M2 2.70 67.67 29.63 2.91 108.07 ± 15.5 M10 1.22 17.14 81.64 6.37 150.66 ± 17.1 M13 0.88 30.54 68.57 5.56 128.07 ± 16.11 M15 1.57 20.71 77.72 5.48 107.98 ± 13.09 M17 0.72 62.86 36.42 3.28 161.97 ± 16.86 M19 1.19 18.77 80.04 4.41 119.75 ± 13.6 M20 3.48 62.26 34.26 6.36 89.5 ± 14.7 M22 1.78 87.61 10.61 3.38 163.62 ± 16.63 M29 2.70 33.15 64.15 5.06 155.53 ± 17.27 M34 3.67 8.40 87.93 7.45 134.09 ± 16.55 M35 1.85 30.78 67.37 2.08 111.34 ± 13.66 M39 2.99 21.97 75.04 6.50 128.26 ± 17.88 M40 2.10 38.77 59.13 3.00 202.86 ± 21.12 M41 2.44 37.40 60.16 7.28 158.25 ± 16.44 M43 2.34 35.31 62.34 5.95 162.57 ± 16.59 M45 0.32 7.60 92.08 6.64 170.92 ± 17.55 M49 2.82 5.00 92.17 5.51 231.53 ± 25.96 2018

(Northeast Monsoon)

N53 6.97 9.51 83.53 7.57 108.45 ± 14.3 N61 9.91 43.16 46.93 6.33 128.31 ± 16.3 N64 10.71 27.74 61.55 5.74 186.01 ± 19.53

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N72 9.81 17.23 72.95 4.29 80.34 ± 11.82 N75 6.41 76.43 17.16 5.49 149.94 ± 16.26 N80 11.35 3.33 85.32 9.33 104.35 ± 14.67 N84 7.09 54.91 38.00 7.97 110.65 ± 15.87 N87 6.66 52.46 40.89 6.70 115.22 ± 14.73 N90 8.95 5.51 85.54 8.19 129.31 ± 15.87 N94 9.34 61.42 29.24 10.64 111.99 ± 13.42 N95 7.23 21.98 70.79 10.54 105.06 ± 14.54 N97 6.43 9.21 84.36 7.31 148.99 ± 16.92 N99 11.30 15.09 73.61 8.14 125.84 ± 14.71 N103 13.24 65.70 21.06 4.75 134.25 ± 15.82 N106 11.44 83.43 5.12 8.44 138.95 ± 14.38 N108 11.41 3.77 84.81 4.02 151.89 ± 19.17

4. Conclusion

The spatial distribution of ²¹⁰Pb in surface sediment from marginal sea area was fluctuated due to the boundary scavenging process alongside with dry and wet deposition, with the addition of monsoonal season, which ignites the physical force acting on surficial sediment. The further result is shown on sediment textural and organic matter exhibit constant changes during the presence of monsoonal season.

Acknowledgements

The authors would like to thank you to the First Institute of Oceanography (FIO), the People's Republic of China for providing the research grant (ST-2016-005) through the Universiti Kebangsaan Malaysia (UKM). Thanks also to the Ministry of Science Technology & Innovation (MOSTI) of Malaysia, Universiti Malaysia Terengganu and Universiti Kebangsaan Malaysia for their support during sampling. Lastly, thanks to the laboratory members for being an excellent research group and also to the staff of Pengajian Sains Sekitaran Dan Sumber Alam, Faculty of Science and Technology, UKM.

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