RESEARCH ARTICLE

Evaluation of distribution and sources of sewage molecularmarker (LABs) in selected rivers and estuariesof Peninsular Malaysia

Sami M. Magam1& Mohamad Pauzi Zakaria2 & Normala Halimoon1

&

Ahmad Zaharin Aris1 & Narayanan Kannan1& Najat Masood1

& Shuhaimi Mustafa3 &

Sadeq Alkhadher1 & Mehrzad Keshavarzifard1& Vahab Vaezzadeh1

&

Muhamad S. A. Sani3 & Mohd Talib Latif4

Received: 27 July 2015 /Accepted: 11 November 2015# Springer-Verlag Berlin Heidelberg 2015

Abstract This is the first extensive report on linearalkylbenzenes (LABs) as sewage molecular markers in sur-face sediments collected from the Perlis, Kedah,Merbok, Prai,and Perak Rivers and Estuaries in the west of PeninsularMalaysia. Sediment samples were extracted, fractionated,and analyzed using gas chromatography mass spectrometry(GC-MS). The concentrations of total LABs ranged from 68to 154 (Perlis River), 103 to 314 (Kedah River), 242 to 1062(Merbok River), 1985 to 2910 (Prai River), and 217 to329 ng g−1 (Perak River) dry weight (dw). The highest levelsof LABs were found at PI3 (Prai Estuary) due to the rapidindustrialization and population growth in this region, whilethe lowest concentrations of LABs were found at PS1 (up-stream of Perlis River). The LABs ratio of internal to externalisomers (I/E) in this study ranged from 0.56 at KH1 (upstreamof Kedah River) to 1.35 at MK3 (Merbok Estuary) indicatingthat the rivers receive raw sewage and primary treatment ef-fluents in the study area. In general, the results of this paper

highlighted the necessity of continuation of water treatmentsystem improvement in Malaysia.

Keywords Linear alkylbenzenes (LABs) . I/E ratio . PerlisRiver .MerbokRiver . Prai River . Malaysia

Introduction

Pockets of Malaysian aquatic environments, especially rawsurface water, become contaminated as a result of excessiveand indiscriminate discharge of wastewater directly fromhouseholds or factories to drains and into rivers with minimalor no treatment. Organic contaminants such as LABs are in-troduced into aquatic environments from untreated domesticwastewater and industrial effluents (Islam and Tanaka 2004;Oller et al. 2011).

LABs with a C10–C14 normal alkyl chain are the raw ma-terials for linear alkylbenzenesulfonate (LAS) production.LASs are synthesized by sulfonation of LABs with H2SO4

or SO3 (Ricking et al. 2003). As a result of this incompletesulfonation, LABs have been discharged into the environmentas a by-product of LAS detergents. They are constituentswhich are found everywhere in many aquatic environmentsuch as treated and untreated domestic wastewater in riverwater and sediments (Takada and Ishiwatari 1987; Wei et al.2014; Dauner et al. 2015).

LABs are minor constituents in commercial LAS deter-gents and more stable markers than LAS. Moreover, LABshave been proposed as molecular markers of wastewater be-cause of their widespread occurrence in the aquatic environ-ment (Ishiwatari et al. 1983; Takada and Ishiwatari 1987;Hartmann et al. 2000). Once LABs are introduced into the

Responsible editor: Hongwen Sun

* Mohamad Pauzi Zakariampauzi57@um.edu.my

1 Environmental Forensics Research Center (ENFORCE), Faculty ofEnvironmental Studies, Universiti Putra Malaysia, 43400 UPM,Serdang, Selangor, Malaysia

2 Institute of Ocean and Earth Sciences, University of Malaya,16310 Bachok, Kelantan, Malaysia

3 Halal Products Research Institute, Universiti Putra Malaysia, 4300UPM, Serdang, Selangor, Malaysia

4 School of Environmental and Natural Resource Sciences, Faculty ofScience and Technology, Universiti Kebangsaan Malaysia,43600 Bangi, Selangor, Malaysia

Environ Sci Pollut ResDOI 10.1007/s11356-015-5804-9

environment, they can undergo aerobic microbial degradationover few days, and they may persist for many years underanaerobic conditions (Hartmann et al. 2000). For this reason,LABs have been considered as one of the most useful markersfor tracing organic contaminants from point source and non-point source because of their stability in sediments and bio-degradation processes during transport (Chalaux et al. 1995;Luo et al. 2008; Ni et al. 2009). LABs are characterized ashydrophobic compounds and associate with particulate matterin sewage and water column which are subsequently incorpo-rated into bottom sediments (Isobe et al. 2004; Magam et al.2012). It was suggested that the rate of sedimentation is 2 mmper year in aquatic environment of Peninsular Malaysia; there-fore, 4–5-cm layer of the surficial sediment indicates around20 years of modern inputs of organic contaminants, and theconcentrations of contaminants might decrease in deeperlayers of sediment (Ibrahim 1989). Martins et al. (2010) re-ported maximum concentrations of total LABs for a sedimentcore at 3 cm of sediment (near surface layers).

LABs have been ubiquitously detected in various environ-mental matrices, such as sediment (Eganhouse et al. 1983;Zhang et al. 2012; Liu et al. 2013a; Masood et al. 2015),municipal wastewater effluent (Eganhouse et al. 1983;Peterman and Delfino 1990), river runoff (Takada andIshiwatari 1987; Ni et al. 2008), and biota (Tsutsumi et al.2002). In addition, LABs were reported to be toxic, wherethe acute toxicity of LABs to Caenorhabditis elegans in soilwas reported at a lethal concentration of 1550 ng g−1 causing1 % fatality in 24 h, with the 95 % confidence limits in therange of 80–3360 ng g−1 (Johnson et al. 2007). LABs are goodindicators of human activities uniquely associated with sew-age contamination in different regions around the world(Eganhouse et al. 1983; Ni et al. 2009; Venkatesan et al.2010; Martins et al. 2012; Rinawati et al. 2012; Wei et al.2014; Alkhadher et al. 2015a, b).

LABs with external isomers (i.e., isomers whose phenylsubstitution positions are near the terminal end of the alkylchain) are more susceptible to aerobic microbial degradationthan those with internal isomers (i.e., isomers whose phenylsubstitution positions are near the center of the alkyl chain).Therefore, the isomeric distribution of LABs provides infor-mation related to the degree of biodegradation of LABs(Takada and Ishiwatari 1990). Furthermore, the isomer distri-bution of LABs can be used for obtaining information aboutthe various types of sewage discharged into the aquatic envi-ronment such as raw sewage and secondary effluents(Tsutsumi et al. 2002).

LABs have been studied by several researchers in manydeveloped countries. However, studies on the levels and dis-tribution patterns of LABs in the west Malaysian Rivers arestill limited. Public health risks have risen due to increasinginputs of untreated domestic wastewater to rivers and coastalenvironment in the west of PeninsularMalaysia resulting from

the rapid population growth, industrialization, and urbaniza-tion over the past decades. The increasing discharges intorivers and coastal areas have also posted a major concern tothe aqueous environment and have not been sufficiently ad-dressed so far. Diverse discharge sources release various typesof contaminants into the marine environment, especially un-treated municipal wastewater, domestic sewages, and urbanrunoff resulting in rising levels of marine pollution. Despitethe increasing use of molecular markers to trace domesticwaste inputs in several developed countries (Takada andEganhouse 1998), the use of molecular markers is yet to beimplemented in Malaysia (Magam et al. 2012; Alkhadheret al. 2015b; Masood et al. 2015).

Isobe et al. (2004) reported that the organic compoundsincluding LABs from anthropogenic inputs affected the westcoast of Peninsular Malaysia where the Klang River had thehighest concentrations of LABs and was categorized as thehot spot, while the Teluk Intan River in Perak had the lowestLABs concentrations and were classified as the clean site.

Previous studies demonstrated the association of humanactivities with environmental pollution using LABs as theindicators. These results indicated that the local socioeconom-ic development appeared to be the major cause of regionalenvironmental pollution. At the same time, these studies sub-stantiated the utility of certain LABs as appropriate indicatorsfor domestic wastewater (Ni et al. 2008).

The present study was conducted at selected riverine areasin the Perlis, Kedah, Merbok, Perak, and Prai Rivers andEstuaries in the west part of Malaysia. This study aimed to fillthe gap of information about the concentrations of LABs inthe surface sediments of above rivers and explore their distri-butions as well as their potential utilization as molecularmarkers of sewage contamination in the aquatic environment.Moreover, the results of this study will estimate the qualityand type of sewage treatment based on the information obtain-ed from the isomer distribution of LABs.

Methodology

Sampling and study area

Surface sediment samples were collected from 15 stations ofthe Perlis, Kedah, Merbok, Perak, and Prai Rivers andEstuaries, located in the west of Peninsular Malaysia, inJanuary 2013. The locations of the sampling sites are shownin Fig. 1 and Table 1. All samples comprised top 4 cm ofsediment cakes (to indicate modern input of target contami-nants) which were collected using an Ekman dredge. Thesediment samples were transferred into previously cleanedaluminum foil and double pre-cleaned Ziploc bag, and thenplaced in the cooler box with dry ice (Masood et al. 2014).

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After that, the samples were transported to the laboratory andfreeze-dried and stored at −20 °C until further analysis.

Chemical, extraction, and separation

The extraction, purification, and fractionation procedureswere described elsewhere (Vaezzadeh et al. 2015a;Keshavarzifard et al. 2014; Zakaria et al. 2002). This methoddepends on homogenization, extraction, two-step silica gelcolumn chromatography, and gas chromatography mass spec-trometry (GC-MS). Briefly, 10 g of freeze-dried sediment was

precisely weighed and then placed in a cellulose thimble in thesoxhlet glass chamber. Each sediment sample was spiked with50 μL of 1-CnLAB mixture (n=8–14) in isooctane as surro-gate internal standard (SIS) containing n-octylbenzene, n-nonylbenzene, n-decylbenzene, n-undecylbenzene, n-dodecylbenzene, n-tridecylbenzene, and n-tetradecylbenzenefor the recovery correction calculations of LAB compounds.Then, each sample was extracted using 300 mL high-puritydichloromethane (DCM) with a soxhlet extractor for 8–10 h.The activated copper treatment was done to remove the ele-mental sulfur, and the extracted sample was rotary evaporated

Fig. 1 Location of sampling areas: a Perlis River (PS), b Kedah River (KH), c Merbok River (MK), d Perak River (PK), and e Perai River (PI)

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followed by a gentle drying with pure nitrogen gas until neardryness.

The extract was then carefully transferred into the top of thefirst step glass column (0.9-cm i.d.×9-cm height), which werepreviously packed with 5 % H2O-deactivated silica gel (60–200 mesh size, Sigma Chemical Company, USA) to removepolar compounds. By this step, the nonpolar compounds in-cluding hydrocarbons were eluted by using 20 mL of hexane/DCM (3:1, v/v). Then, the eluent from the first step columnwas sequentially fractioned by second-step column chroma-tography using a fully activated silica gel column (0.47-cmi.d×18-cm height). The second high-purity hexane (4 mL)fraction was conducted to obtain LABs fraction. The n-alkanes and hopanes fractions were not analyzed in this study.The LABs fraction was concentrated to approximately 1 mLusing a rotary evaporator and then transferred into a 2-mLamber vial. Subsequently, the LAB fraction was further con-centrated to near dryness using a gentle stream of pure nitro-gen gas (N2). The fraction was then redissolved in 200 μL ofisooctane containing a 10 μg/g internal injection standard(Biphenyl-d10). LABs were analyzed using GC-MS.

GC-MS analysis of LABs

The 26 LABs were performed by GC–MSD using a 7890ASeries gas chromatograph interfaced with a C5975MSD split/splitless injector. One-microliter aliquot of purified sampleswas introduced into the GC-MS injector. The carrier gas washelium (99.999 purity), which was controlled using the con-stant flow mode at 1.2 mL/min. The injections were per-formed at 70 °C for 2 min, with a ramp of 30 °C/min until150 °C. The temperature was further increased to 310 °C with

an increasing rate of 4 °C/min for 15 min. The analysis wasperformed using the selected ion monitoring (SIM) mode withsplitless injection. Individual LABs were monitored in SIMmode at (mass/charge ratio) m/z=91, 92, and 105. The capil-lary column DB-5MS (30 m, 0.25-mm i.d., containing a0.25-μm film thickness) was interfaced directly to the ionsource of the mass spectrometer. The mass spectrometer wasscanned repeatedly at an ionization potential of 70 ev with thesource at 200 °C and electron multiplier voltage at ∼2000 ev.We used LABs mixture standards as analytical standards.

Quantification of target compounds of LABs was carriedout based on external calibration curves using standard mix-tures of LABs. Determination of the target compounds wasachieved based on matching their compound ionization andretention times with the standard mixture of LABs.Nondetectable compounds (<0.2 ng g−1) were treated as novalue in calculation of the total LABs. All of LABs in thesediment samples were calculated based on dry weight. Thedetails of the method were described previously by Hartmannet al. (2000) and Zakaria et al. (2002).

Quality assurance and quality control

The quality control and quality assessment were performedduring the analysis of the samples. Quality control for theLABs analyses was conducted by monitoring the recovery ofSIS prior to extraction. The recovery of surrogates was >83 %of the spiked concentration. The samples with the recovery ofthe surrogate standards lower than the accepted range werereanalyzed. The LAB concentrations were recovery-correctedagainst the surrogate standards spiked (Cortazar et al. 2008).All standards were freshly prepared prior to the actual analysis,

Table 1 Detailed water quality data of sampling sites

Sampling location Station code Latitude (°N) Longitude (°E) DO (mg/L) Conductivity(ms/cm)

Turbidity (NTU) Salinity (ppt) Temperature (°C) pH

Perlis River PS1 6° 24′ 100° 7′ 6.8 9.2 16.1 5 30.1 7.6

Perlis River P2S 6° 24′ 100° 8′ 5.8 19 20.3 19 29 8

Perlis Estuary PS3 6° 26′ 100° 9′ 5.5 45.5 19.7 29.3 30 8

Kedah River KH1 6° 6′ 100° 16′ 2.2 13.1 10.3 7.0 31.0 6.8

Kedah River KH2 6° 6′ 100° 19′ 2.1 25.5 14.5 15.5 29.8 7.0

Kedah Estuary KH3 6° 7′ 100° 20′ 4.9 39.7 17.4 25.2 31.1 7.5

Merbok River MK1 5° 39′ 100° 24′ 7.8 25.5 13 14.0 30.3 7.3

Merbok River MK2 5° 38′ 100° 26′ 14.1 37.1 5.0 23.4 31.0 8.4

Merbok Estuary MK3 5° 41′ 100° 29′ 12.1 39.2 3.5 24.9 30.0 8.5

Prai River PI1 5°24' 100°24' 1.5 4.4 10.5 4.2 31.2 6.5

Prai River PI2 5°23' 100°23' 1.4 11.4 14.9 6.4 30.7 7.1

Prai Estuary PI3 5°22' 100°22' 7.4 44.6 19.7 28.6 31.0 7.9

Perak River PK1 4° 0′ 100° 45′ 4.5 2.0 2.3 0.9 30.1 7.4

Perak River PK2 4° 2′ 100° 51′ 5.4 6.3 12.3 3.1 31.5 7.7

Perak Estuary PK3 3° 57′ 100° 55′ 5.1 40.1 6.4 22.6 32.1 7.5

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and procedural blanks for LABs were run with every batch ofsamples (Arias et al. 2009). The analysis of a reagent blankdemonstrated that the analytical system and glassware werefree of contamination. Statistical tests and analyses were per-formed using the Statistical Package for the Social Sciences(SPSS) v.12.0. Analysis of variance (ANOVA) was undertakento evaluate the significance of the differences between LABconcentrations in different stations.

TOC analysis

Dried sediment was homogenized and ground to fine powderusing mortar and pestle. Acidification procedure was used inorder to eliminate inorganic carbon (carbonates) existing in thesamples. One to two grams of each sample were weighed, and1–2 mL of 1MHCLwere added drop by drop until the samplecompletely moist with HCl. The samples were dried at 100 °Cfor 10 h to remove the hydrochloric acid. Aliquots of eachsample were reweighed and then analyzed using LECO CR-412 CarbonAnalyzer (LECOCorporation, USA) at 1350 °C todetermine total organic carbon (TOC) percentage (Nelson andSommers 1996; Masood et al. 2015; Vaezzadeh et al. 2015b).

Results and discussion

Distribution and composition of LABs

As shown in Table 2 and Fig. 2, the concentrations of LABswere 68 (Perlis River), 314 (Kedah River), 1062 (MerbokRiver), 2910 (Prai River), and 329 ng g−1 (Perak River) withan arithmetic mean of 505 ng g−1. There was a significantdifference between the concentrations of the total LABsamong sampling stations (p<0.05) where the maximum con-centrations of LABs were detected in PI3 (2910 ng g−1), whilethe minimum concentrations were observed in PS1(68 ng g−1). In general, the Prai River was the most contam-inated river by LABs among the study sites, followed by theMerbok River, Perak River, and Kedah River. The PerlisRiver, however, had the lowest LAB levels among the rivers.

The present study revealed that the Prai River has thehighest LABs concentrations in sediments among all the riv-ers in this study area. To determine the trend of LABs concen-trations in sediments from the Prai River, the findings of thisstudy were compared to previous studies. LAB concentrationsin the Prai River were higher than those found by Isobe et al.(2004) in the same area (25 ng g−1) (Table 3). A significantincrease was observed in the levels of LABs in the sedimentsamples of the present study compared to those of otherworkers in Malaysia such as Zhang et al. (2012), Alkhadheret al. (2015b), and Masood et al. 2015, where the concentra-tions of LABs were in the range of (1.5–410), (7.1–41.3),and (25–90)ng g−1, respectively. Two reasons can be

mentioned to explain this increment. Firstly, the sedimentationinput from the land-based activities such as land-clearing hasincreased since the time of the previous studies, and conse-quently, more inputs of contaminants have been carried by thesuspended sediments from upper and middle areas of the PraiRiver. Secondly, Malaysia has experienced a remarkable in-crease in population, industrialization, and urbanization lead-ing to a significant increase of the sewage pollution load intothe rivers. For example, the Prai River runs through thePenang State, Malaysia, where population and also industrial-ization have evidently increased over the last few decades.Therefore, continuous monitoring of LABs is needed in thisarea. Furthermore, waste pollution plants and sewage treat-ment plants need careful maintenance.

On the other hand, the concentrations of LABs in this studywere lower than those of the Port Klang (8590 ng g−1) andPenang Estuary (3000 ng g−1) (Isobe et al. 2004).Furthermore, the LAB concentrations in the Perlis River wereclose to those of Kim Kim River (Isobe et al. 2004) (Table 3).More data is needed to evaluate the trend of LABs inMalaysia.

A number of previous researchers have reported on LABslevels in sediments from around the world (as shown atTable 3). The LAB concentrat ions in Prai River(2910 ng g−1) were relatively higher than those observed inthe Tokyo Bay Estuary, Japan (1720 ng g−1) (Takada et al.1992), Thames, UK (2300 ng g−1) (Raymundo and Preston1992), Zhujiang River, China (2330 ng g−1) (Luo et al. 2008),Tokyo Bay, Japan (1109 ng g−1) (Rinawati et al. 2012), andDongjiang River, China (410 ng g−1) (Zhang et al. 2012), butlower than those of the Sumidagawa River, Japan(12110 ng g−1) (Takada and Ishiwatari 1987), SouthernCalifornia Bight, USA (19000 ng g−1) (Macías-Zamora andRamírez-Alvarez 2004), Chaohu Lake, China (5270 ng g−1)(Wang 2012), Jakarta Bay (86745 ng g−1) (Rinawati et al.2012), and Jakarta River, Indonesia (155937 ng g−1)(Rinawati 2013) (Table 3). On the other hand, the total LABsconcentrations in Merbok River were consistent with those ofTokyo Bay, Japan (1109 ng g−1) (Rinawati et al. 2012).

Higher concentrations of LABs with 13 carbon atoms or C13-LAB (tridecylbenzene) were observed, followed by the C11-LABs (undecylbenzene) and C14-LAB (tetradecylbenzene)(Fig. 2). These results corroborated the results reported in a pre-vious study byMartins et al. (2010) where the C13-LAB isomerswere found to be more abundant than the C12-LABs in surfacesediments of Santos Estuary. On the other hand, the results ofthis study are inconsistent with results obtained and reported byMedeiros and Bícego (2004) which showed that the C12-LABisomers were slightly more abundant than the C13-LABs in sur-face sediments of Santos Estuary. This variation between oursedimentary data and those reported by Medeiros and Bı́cego(2004) could reflect compositional changes in prevailinginputs of LABs. Gustafsson et al. (2001), in Boston Harboureffluents (USA) and Colombo et al. (2007) in the settling

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material from the sewage impacting the Buenos Aires coastalarea (Argentina), also found the abundance of C12-LAB isomersamong LABs which is different from the results obtained in thiswork.

Correlation ofΣLAB concentrations and other pollutants

LABs are hydrophobic compounds with the octanol/waterpartition coefficient (KOW) ranging from ∼7 to ∼9 showing

the strong partitioning behavior of LABs to sewage particles.The sampling stations with higher levels of LABs are expect-ed to have higher contributions of wastewater to the river flow(Sherblom et al. 1992). Pearson correlation analysis was car-ried out to test the relationship between total LABs in thesediment and TOCs. A good correlation between LABs andorganic matter content could be anticipated. As shown inFig. 3, the concentrations ofΣLABs were negatively correlat-ed with TOC contents in sediments from the Perlis, Kedah,

Table 2 LABs in selected main rivers of the Malaysian surface sediments

River Perlis Kedah Merbok Prai Perak

Stations PS1 PS2 PS3 KH1 KH2 KH3 MK1 MK2 MK3 PI1 PI2 PI3 PK1 PK2 PK3

C10-LABsa 4.43 5.11 12.1 53.3 13.1 25.3 16.8 132.7 82.2 231.1 323.4 302.75 43.3 28.3 31.7

C11-LABs 8.75 22.1 27.5 56.1 22.3 39.4 63.4 224.2 201.1 550 562.5 768.8 62.7 32.3 60.9

C12-LABs 17.6 19.6 26.2 53.5 26 35.8 51.3 185.9 102.8 201.6 338.5 406.6 48.9 36.7 53.4

C13-LABs 29.6 41.1 66.1 98.7 29.2 63.9 78.3 331 195 599.8 590.1 810.4 81.3 65 110.5

C14-LABs 7.83 6.7 22 51.7 12 27.9 31.6 188.2 134.4 402.5 399 621 64.2 55 72

LABs 68 95 154 314 103 192 242 1062 715 1985 2214 2910 301 217 329

I/Eb 1.02 0.92 0.82 0.56 0.74 0.71 0.84 0.71 1.35 0.75 0.75 0.73 0.59 0.60 0.78

LAB degradation (%)c 14.5 10.8 6.68 7 2.99 1.50 7.54 1.50 24.57 3.47 4.88 2.50 5.14 4.54 4.88

L/Sd 2.80 2.45 2.27 0.96 1.55 1.7 1.84 1.42 0.75 1.14 1.03 1.37 1.12 1.27 1.76

C13/C12e 1.67 2.10 2.53 1.84 1.12 1.79 1.52 1.78 1.90 2.98 1.74 1.99 1.66 1.77 2.07

TOC (%)f 2.44 5.53 2.17 1.64 1.9 2.19 7.06 2.04 3.31 1.97 2.47 1.74 5.97 1.82 1.26

a C10-LABs, sum of the 26 LAB congenersb I/E=(6-C12LAB+5-C12LAB)/(4-C12LAB+3-C12LAB+2-C12LAB)c LAB degradation(%)=81×log (I/E ratio)+15d L/S=(5-C13LAB+5-C12LAB)/(5-C11LAB+5-C10LAB)e C13/C12=(6-,5-,4-,3-and 2-C13)/(6-, 5-, 4-, 3-, and 2-C12LAB)f TOC (%)=total organic carbon

Fig. 2 Total concentrations ofLABs in sediments collected fromthe Perlis, Kedah, Merbok, Prai,and Perak Rivers

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Prai, and Merbok Rivers (r=−0.29, −0.55, −0.98, and −0.56;p<0.05). On other hand, the results showed poor correlationbetween the concentration of total LABs in the Perak Riverand the TOC (r=0.170; p>0.05). This poor correlation isprobably due to the differences in sources of LABs andTOC inputs (Vaezzadeh et al. 2015b). This is consistent withthe results of Keshavarzifard et al. (2014, 2015), who reportedno positive correlation between concentrations of polycyclicaromatic hydrocarbons (PAHs) and TOC in sediments fromthe Perak Rivers. Organic carbon content is generally relatedwith the amount of silt and clay found in sediments. Finesediment particles have relatively larger surface areas andcan absorb colloidal and dissolved organic matter formingsedimentary complexes (Kowalska et al. 1994; Martins et al.2010). LABs have found to be positively correlated with

PAHs in a study by Zhang et al. (2012), while PAHs werefound to stem from sources other than wastewater dischargesuch as atmospheric sources, dry deposition, and surface run-off in the Dongjiang River (Zhang et al. 2011). In addition, thetotal concentrations of 16 PAHs reported previously from thesame area (Keshavarzifard et al. 2014) were weakly correlatedwith LABs of present study (r=0.13; p<0.05).

Evaluation of LABs degradation and wastewatertreatment efficiency

The LAB homologues consist of isomers with different phe-nyl substitution positions on the alkyl chain. If the phenylposition is less than or equal to four, the LAB homologue isdescribed as an external isomer; otherwise, it is classified as an

Table 3 Total LABs concentrations in sediments from different locations around the world

Location Total LABs (ng g−1) I/E L/S C13/C12 Reference

Sumidagawa River, Japan 560–12110 1.09–1.74 (Takada et al.1987)

Tamagawa River, Japan 10–15790 1.29–1.85

Tokyo Bay Estuary, Japan 720–1720 1.7–2.0 (Takada et al. 1992)

Tokyo Bay Coastal, Japan 2750 3.1

Thames, UK 100–2300 2.0–3.1 (Raymundo and Preston (1992))

Southern California Bight, USA <MDL–19000 0–31.9 (Zamora et al.2004)

Japan 3–5860 1.2–6.0 (Isobe et al. 2004)

Thailand 3–14100 0.3–5.9

Malaysia 4–8590 0.7–4.8

Philippines 56–13000 0.6–2.9

Cambodia 2–4200 0–1.7

Vietnam 3.0–8650 0.6–2.2

Indonesia 3.0–42600 0.9–2.1

India 2–4450 0–2.1

Zhujiang River 58.5–2330 0.9–1.5 (Luo et al. 2008)

Dongjiang River 96.9–566 0.7–1.9

Xijiang River 20.5–69.4 0.6–1.0

Pearl River Estuary 5.8–25.8 0.6–1.5 1.2–1.9 1.2–1.4

South China Sea 2.5–23.1 0.2–0.9 1.2–4.6 0.7–4.0

Chaohu Lake 18–5270 0.8–2.12 1.3–3.4 0.7–1.4 (Wang 2012)

Dongjiang River 1.5–410 0.6–1.4 1.0–4.1 0.6–1.8 (Zhang et al. 2012)

Jakarta Bay 235–86745 0.92–2.88 (Rinawati et al. 2012)

Tokyo Bay 394–1109 2.78–4.80

Jakarta River 6171–155937 0.9–1.3 (Rinawati 2013)

Brunei Bay 7.1–41.3 0.56–2.17 (Alkhadher et al. 2015a)

Selangor River 25–90 0.15–1.02 0.6–5.4 1.1–2.7 (Masood et al. 2015)

Perlis River, Malaysia 68–154 0.82–1.02 2.3–2.8 1.7–2.5 This study

Kedah River, Malaysia 103–314 0.56–0.74 1.0–1.7 1.1–1.8 This study

Merbok River, Malaysia 242–1017 0.71–1.35 0.8–1.8 1.5–1.9 This study

Prai River, Malaysia 1985–2910 0.73–0.75 1.0–1.4 1.7–3.0 This study

Perak River, Malaysia 217–329 0.59–0.78 1.1–1.8 1.6–2.1 This study

MDL method detection limit

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internal isomer. The internal to external isomer ratio (I/E ratio)can be used to determine the degree of LABs degradation. I/Eratio=(6-C12LAB+5-C12LAB)/(4-C12LAB+3-C12LAB+2-C12LAB), C13/C12=ΣC13-LAB/ΣC12-LAB, and L/S=(5-C13+5-C12)/(5-C11+5-C10) have been applied broadly as in-dicators of LAB degradation (Gustafsson et al. 2001; Luoet al. 2008; Wang 2012; Wei et al. 2014; Dauner et al.2015). I/E ratio is around 0.7 in synthetic detergents and rawsewage. A high I/E ratio indicates higher degradation of LABswhich results in greater depletion of external isomers and viceversa (Takada and Eganhouse 1998; Takada and Ishiwatari1990). The I/E ratios in primary effluents are generally low,ranging from 0.5 to 0.9, since primary treatment is essentiallya physical removal of sewage particles, and therefore, theopportunity for aerobic microbial degradation during thisphase of treatment is limited. However, the secondary efflu-ents show a much higher I/E ratio ranging from 2 to 7 which isbecause of the fact that the secondary treatment involves bio-logical removal of waste where bacteria use oxygen to con-sume the sewage sludge (Takada and Eganhouse 1998).Whenreleased into the environment, the LABs will undergo micro-bial degradation naturally by microbial attack in rivers and

estuaries. Part of these LABs is deposited in the sediments,and the other part is taken up by aquatic organisms.

The relative abundances of LAB isomers in the commercialdetergents and raw sewage are stable (Takada and Ishiwatari1987). However, the I/E ratio systematically changes duringthe LAB degradation under aerobic conditions (Takada andIshiwatari 1990). Thus, this ratio has been applied (Takada andIshiwatari 1990; Isobe et al. 2004; Zamora et al. 2004) as anindicator of the extent of LAB degradation in aquatic environ-ment. Regarding C13/C12 and L/S, they have been widelyemployed as indicators of LAB degradation (Gustafsson et al.2001; Luo et al. 2008). According to the results from an incu-bation experiment by Takada and Ishiwatari (1990), it was sug-gested that the degradation percentage of LABs (D%) exponen-tially increased with increasing I/E. Similarly, the values of C13/C12 and L/S in detergent and untreated sewage were significant-ly lower than those in river water (Ni et al. 2008) and sediment(Luo et al. 2008) due to the selective degradation of long-chainalkylbenzenes relative to short-chain ones. I/E, L/S, and C13/C12 ratios in sediments from the study area are shown in Fig. 4.

As shown in Table 2, the I/E ratios in all stations in thepresent study ranged from (0.56 to 1.35) indicating that the

Fig. 3 Correlation betweenLABs and TOC in the study area

Environ Sci Pollut Res

raw sewage and primary effluents were discharged into river-ine and estuarine waters (Fig. 3). Significant differences in I/Eratios (p<0.01) were identified among sediment samples fromvarious stations. These results are similar to those in commer-cial detergents from southern China (Luo et al. 2008; Ni et al.2008), and significantly lower than those found in sludge (Luoet al. 2008) and suspended particles from wastewater (Takadaand Ishiwatari 1987). There may be two possible explanationsfor low I/E values found in the study area. First, the study areamay have received recent inputs of untreated or inadequatelytreated wastewater effluent. Secondly, weak biodegradation ofLABs occurred in sediment of some study areas due to itsanaerobic conditions. A previous study showed that anaerobicconditions suppressed the degradation of LABs (Takada andIshiwatari 1990). Generally, eutrophication encouragesphytoplankton and algal growth and decay, depleting thelevels of oxygen. In previous studies, high I/E ratios oftenwere observed in the samples with low concentrations ofΣLABs implying significant degradation (Chalaux et al.1995; Raymundo and Preston 1992). On the other hand, theLAB biodegradation value (D %) in this study ranged from1.5 to 24.6 %.

The findings of this study showed the existence of sewageinputs from the areas with different treatment efficiency.Typically, wastewater is discharged without treatment in ruralareas in Malaysia, and some wastewater is treated before dis-charge in urban area (Isobe et al. 2004; Magam et al. 2012).Yet, there is limited data for sewage treatment around thestudy areas. Therefore, LABs in sediment from the rivers ofwestern Peninsular Malaysia with higher I/E ratio were com-pared to other sampling locations (Table 3). L/S ratios ranged

from 0.8 to 2.8 inMK3 and PS3 and from 1.1 to 3 in KH2 andPI1, respectively, which were slightly higher than those foundin commercial detergents (Luo et al. 2008; Ni et al. 2008) andsignificantly lower than those in riverine runoff from the PearlRiver Delta (Ni et al. 2008). These results strongly suggestedthat long-chain alkylbenzenes were better preserved in sedi-ment of the study area relative to short-chain alkylbenzenes.

LABs transport

Different LAB homologues have various physicochemicalfeatures which affect the fate of LAB in the aquatic environ-ment. The homologue with the phenyl group located on ex-ternal position is more susceptible to undergo degradation inthe aquatic environment. The composition profiles of LABs(the average values of different carbon chain in three samplingstations of each river) are described in detail in the collectedsurface sediments (Table 2). As shown in Fig. 5, LABs in thePerlis River were predominated by C13 LABs (43 %), follow-ed by C12 LABs (20 %), while LABs in the Merbok Riverwere dominated by C13 LABs (30 %), followed by C11 LABs(24%). Similarly, the Prai River sediments were dominated byC13-LABs (28 %), followed by C11-LABs (27 %). C10-LABshad the smallest portion of LABs (12 %) in the sedimentsamples of Prai stations. This was because of the fact thatLABs chain length in all rivers and estuaries relatively variedaccording to the river and estuary locations. For example, theC10 was depleted in the estuaries PS1 of the Perlis, Kedah,Merbok, and Perak Rivers, while C12 was depleted in PI3 ofthe Prai River. This depletion can be related to the high tem-perature and low velocity of the water in the estuaries

Fig. 4 I/E, L/S, and C13/C12ratios in sediments collected fromthe Kedah, Merbok, Perak, Perlis,and Prai Rivers

Environ Sci Pollut Res

(Table 1), which may have increased the degradation of short-chain LABs. Hence, depletion of these compounds occurredin the estuaries. Among all carbon homologues (Fig. 5), therewere significant differences (p<0.05) for values of C11-LABsand C12-LABs among the Perlis and Perak Rivers, for C10-LABs among Prai and Kedah Rivers, for C13-LABs amongthe Merbok and Prai Rivers, and for C14-LABs betweenKedah and Perak. Overall, both long-chain and short-chaincompounds were representative of the total LAB compoundsin the collected sediments.

A previous study detected similar compositional profiles ofLABs for commercial detergents commonly used inGuangdong Province, which implicated a quite unanimoussource of LABs in the study region (Ni et al. 2008).However, LAB compositions varied among different environ-mental compartments of the Pearl River Delta (PRD), i.e.,detergent (Ni et al. 2009), soil (Wei et al. 2014), wastewater(Zhang et al. 2012), river water (Ni et al. 2008), and surfacesediments (present study). Probably, this suggests congenerspecificity of transfer mechanisms, in addition to subsequentphase partitioning and degradation potentials, for LAB com-ponents from sources to receptors. Different LAB homo-logues have various physicochemical features which affectthe fate of LABs in the aquatic environment. For example,the homologue with phenyl group located on external positionis more susceptible to undergo degradation in the aquaticenvironment.

Hydrodynamic flow and lateral transport are considered asthe dominant input routes for hydrophobic contaminants insediments (Wania et al. 1998; Jones and de Voogt 1999). Niet al. (2009) observed the extensive occurrence of LABs inriverine runoff of PRD and estimated that irrigation with pol-luted river water was a key pathway for LABs in agriculturallands.Moreover, direct wastewater discharge from paper millsaround Dongguan (Zhang et al. 2012) was suggested as apoint source for soil LABs, but it might be confined in a smallarea. Although 45 % of the produced sewage sludge was uti-lized in agricultural soils in China (Chen et al. 2012), the

extremely poor correlation of ΣLAB levels and TOC(Fig. 3) dismissed the application of composted sewage sludgein soils as the main input route for soil LABs. A previousstudy (Takada et al. 1992) on hydrodynamic transport ofLABs in riverine zones demonstrated that hydrophobicLABs were connected with lower-density particles and couldbe transported greater distances than PAHs. All these findingsfavor lateral transport and sediment deposition as the predom-inant mechanisms for the widespread occurrence of LABs ona riverine scale.

Conclusions

This study applied both qualitative and quantitative measure-ments of LABs in sediment samples from the Perlis, Kedah,Merbok, Perak, and Prai Rivers, located in the west ofPeninsular Malaysia using GC-MS. According to the results,the concentrations of LABs in the sampling stations variedbroadly. It can be concluded that the Prai River is the mostpolluted area by sewage pollution, followed by the Merbok,Perak, Kedah, and Perlis Rivers. Additionally, the results il-lustrated that the distribution of LABs in sediment samplestaken from the five rivers and estuaries can be determinedby the level of wastewater treatment in the surrounding areas.The high total LAB concentrations detected herein may be theresult of an insufficient wastewater treatment plants which arenot capable of serving the extremely large population in thesurrounding areas. Hence, because of the overloading of treat-ment plants, untreated or partially treated sewage may bedischarged into these rivers. The present paper was part of acomprehensive study on sewage pollution in the rivers of thewest Peninsular Malaysia.

The high concentrations of LABs with low I/E ratiosshowed that the rivers in west Peninsular Malaysia are heavilyaffected by untreated sewage. The results also highlighted thatsewage will continue to be a problem, considering increase ofpopulation in the study area. In the coming years, the total

Fig. 5 Compositional profiles oflinear alkyl benzenes in surfacesediments collected from thePerlis, Kedah, Merbok, Perak,and Prai Rivers

Environ Sci Pollut Res

amount of sewage discharged into the rivers and coastal wa-ters in Peninsular Malaysia is expected to progressively in-crease. In view of the current data and evidence of the impli-cations of sewage pollution, this paper highlights the necessityfor continuation of water treatment system improvement.Therefore, continuous assessment of the extent of sewage pol-lution in rivers and coastal waters can indicate the improve-ment brought by the upgraded sewage systems. Hence, furtherresearch concerning sewage and other anthropogenic pollut-ants is critical to reduce the health risks in PeninsularMalaysia.

Acknowledgments The research was funded by Inisiatif PutraBerkumpulan Grant (IPB) through Universiti Putra Malaysia (Grant no.9412401). The authors are very grateful to the chief editor and the re-viewers of this article for their valuable contribution.

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