microwave assisted digestion followed by icp-ms for

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Microwave assisted digestion followed by ICP-MS fordetermination of trace metals in atmospheric andlake ecosystem

Manan Ahmed1, Ying Hui Chin1, Xinxin Guo1,⁎, Xing-Min Zhao2

1. Department of Environmental Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman,31900 Kampar, Malaysia2. College of Resource and Environment, Jilin Agriculture University, Changchun 130188, China

A R T I C L E I N F O

⁎ Corresponding author. E-mail: [email protected]

http://dx.doi.org/10.1016/j.jes.2016.06.0141001-0742/© 2016 The Research Center for Ec

A B S T R A C T

Article history:Received 3 April 2016Revised 2 June 2016Accepted 17 June 2016Available online 14 July 2016

The study of trace metals in the atmosphere and lake water is important due to their criticaleffects on humans, aquatic animals and the geochemical balance of ecosystems. Theobjective of this study was to investigate the concentration of trace metals in atmosphericand lake water samples during the rainy season (before and after precipitation) betweenNovember and December 2015. Typical methods of sample preparation for trace metaldetermination such as cloud point extraction, solid phase extraction and dispersive liquid–liquid micro-extraction are time-consuming and difficult to perform; therefore, there is acrucial need for development of more effective sample preparation procedure. A convectionmicrowave assisted digestion procedure for extraction of trace metals was developed foruse prior to inductively couple plasma-mass spectrometric determination. The resultshowed that metals like zinc (133.50–419.30 μg/m3) and aluminum (53.58–378.93 μg/m3) hadhigher concentrations in atmospheric samples as compared to lake samples beforeprecipitation.On the other hand, the concentrations of zinc, aluminum, chromium and arsenic weresignificantly higher in lake samples after precipitation and lower in atmospheric samples. Therelationship between physicochemical parameters (pH and turbidity) and heavy metalconcentrations was investigated as well. Furthermore, enrichment factor analysis indicatedthat anthropogenic sources such as soil dust, biomass burning and fuel combustion influencedthe metal concentrations in the atmosphere.© 2016 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences.

Published by Elsevier B.V.

Keywords:Trace metalsMicrowave digestionICP-MSAtmospheric environmentLake ecosystem

Introduction

The atmospheric environment contains numerous types of airpollutants from natural and/or anthropogenic sources. Tracemetals, particularly heavy metals, are gradually being intro-duced into the environment as contaminants and pollutants,byproducts of industry and human civilization. A significantenvironmental compartment in the biochemical cycles of

du.my (Xinxin Guo).

o-Environmental Science

trace metals is the atmosphere (Hu and Balasubramanian,2003). During the last decades, environmental pollution bytoxic heavy metals at trace levels has dramatically increased.Atmospheric deposition is considered to be the major sourceof toxic metals such as Hg, Cd, Pb and others to ecosystems.These trace metals are present in various forms in theenvironment (water, soil and air). There is an increasingneed to determine the natural background of trace metals

s, Chinese Academy of Sciences. Published by Elsevier B.V.

2 J O U R N A L O F E N V I R O N M E N T A L S C I E N C E S 5 5 ( 2 0 1 7 ) 1 – 1 0

(such as toxic heavy metals) to assess global environmentalpollution. These trace metals are considered some of the mostserious pollutants in the natural environment due to theirtoxicity, persistence and bioaccumulation, because they arebeing retained in plants, animals and nature in general (Gleyzeset al., 2002). The monitoring of trace metals in environmentalsamples is a keypart of analytical chemistry due to their negativeinfluence on human and environmental health (Najafi et al.,2010). Trace metal pollution not only affects the production ofcrops but also influences the quality of the atmosphere aswell aswater bodies, and threatens the health and life of animals,humans andmicroorganisms (Li et al., 2013). The environmentalpollution caused by trace metals is a long-term, irreversibleprocess and can be toxic even at low concentrations.

Trace metal pollution is a growing universal problem in theaquatic environment and currently it has reached an alarminglevel (Ogoyi et al., 2011). Many trace metals are regarded asserious pollutants of aquatic ecosystems because of their longenvironmental persistence, toxicity and ability to be incorpo-rated into food chains. There are many sources of tracemetals, however the most important sources of trace metalsin aquatic ecosystems are anthropogenic activities. Conversely,trace metals also arise in minor amounts naturally and mayenter into anaquatic system through leaching of rocks, airbornedust, vegetation and biomass burning (Fernandez and Olalla,2000). Their concentration usually depends on both natural andanthropogenic sources, amount of suspended particulate matterand composition, salinity, pH and redox potential (Adiana et al.,2011). In aquatic environments, trace metal concentrations areusually monitored by measuring their concentrations in waterand sediments such as those in lake ecosystems, and generallyare present at low levels in water and contribute to contamina-tion and pollution (Storelli et al., 2005).

Lakes are sensitive areas due to their potential exposure topollutants from several sources. Lake ecosystems also providean indication of climate variation, either directly or indirectlythrough their catchment. Pollutants enter the water body of alake through the connecting rivers, runoff water and fromatmospheric deposition. The limited water movement withinlakes influences the degree of pollution, and high concentra-tions of pollutants can decrease the biodiversity, as well asthe physical environment surrounding the lake ecosystems(Dudgeon et al., 2006). Atmospheric deposition is one of themajor sources of pollutants in a lake ecosystem (Vuorenmaaet al., 2014). The emissions from industry, motor vehicles andagricultural activities (biomass burning) are released to theatmosphere, blown by the wind; they then interact with waterand fall down to the ground through wet deposition. Thesepollutant particulates in air fall during rain as acid rain and asfine particles (particle size ≤ 2.5 μm) (Driscoll et al., 1995).These particles can bring nutrients and trace metals intoaquatic ecosystems, such as lakes, during their settling downto the surface of earth. It has been noted that the deposition ofsulfates and nitrates increases the acidity of a water body(Burton et al., 2013; Ding et al., 2014). Excessive amounts oftrace metals from atmospheric deposition are toxic to aquaticorganisms such as fish and microorganisms (Ashraf et al.,2011; Walraven et al., 2014). Trace metals deposited into lakesare usually sequestered in the layers of sediments on thebottom of the lake. Sediment quality is a good indicator of

pollution in the water column, because it tends to concentratethe heavy metals and other organic pollutants, which can berecycled into the water body by any disturbance.

Determination of trace metals in atmospheric and lakeecosystems is important for monitoring environmental pol-lution. In general, direct estimation of very low levels ofelements in environmental samples is often impossible due tothe presence of interfering compounds or the concentration ofanalytes being below the detection limit of instrumentation.The most commonly used analytical method for trace metaldetermination is the atomic absorption spectroscopy (AAS)technique, which offers multi-elemental analysis but suffersfrom poor sensitivity in the determination of trace metalsin environmental samples like lake water and atmosphericair samples, due to their low concentrations. Differentpre-concentration techniques such as cloud point extraction,solid phase extraction and the use of chelating agents beforesamples that are analyzed by AAS have been developed andsuccessfully applied in the determination of trace metals(Najafi et al., 2010; Soylak and Aydin, 2011; Gentscheva et al.,2012). However, these extraction techniques and methods ofanalysis are restricted for determination of trace metals insamples due to the usage of toxic organic solvents for extraction,and require extensive and complicated procedures. Inductivelycoupled plasma-mass spectrometry (ICP-MS) is consideredattractive and one of the most sensitive techniques for themulti-elemental analysis of tracemetals in various environmen-tal samples. This technique usually requires a transformation(extraction) of the samples into solution before analysis. UsingICP-MS apparatus, the detection limits for trace meals can bedown to sub-ppt or picomol/L levels in simple matrix solutions.Nowadays among the various pre-concentration procedures fortrace metals, digestion procedures using closed-vessel micro-wave sample preparation systems are used for various environ-mental investigations of trace metals due to their excellentcapabilities for multi-element concentration with minimumselectivity and sample manipulation.

The main objective of this investigation is to establish asimple and fast method of trace metals analysis in environ-mental samples, including atmospheric particulates and lakewater. The trace metals from atmospheric deposition and lakesamples were extracted using a combination of nitric acid(HNO3) and hydrogen peroxide (H2O2) with the help of 650 Wmicrowave energy, which is faster than other reported extrac-tion methods. This study also quantifies the effect of tracemetal concentration during rain fall in lake samples around thestudy area.

1. Materials and methods

1.1. Reagents and reference materials

For the preparation of reagents and standards, freshly preparedultrapure water (18.2 MΩ cm) from a TKA smart2plus ultrapurewater system (TKA, Germany) was used. Analytical gradereagent HNO3 (Fluka, France) and H2O2 (Merck, Germany) wereused for the digestion experiments. An ICP-MS multi-elementstandard was obtained from Perkin Elmer and used forcalibration of the equipment. Polyethylene bottles for water

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samples were obtained from Thermo scientific (Thermo scien-tific, Malaysia). All chemicals were of reagent grade and usedwithout further purification.

1.2. Description of sampling site

The sampling site for the determination of trace metals islocated around Kampar, within the state of Perak, which is onthe north coast of peninsular Malaysia. Kampar is located at4.3° North latitude, 101.15° East longitude and 63 m elevationabove sea level (Fig. 1). This city has a humid tropical climateand great deal of rainfall even in the driest month. Thisclimate is considered to be Af according to the Koppen–Geigerclimate classification. The average temperature is 27.3°C andaverage annual rainfall of 3133 mm has been recorded. Thisarea consists of a number of tin mine lakes and is at a greatdistance from local roads. The geographical location of thisarea is ideal to study the anthropogenic emissions fromSumatra, Indonesia and their chemical interactions.

1.3. Sampling techniques

To ensure accurate determination of low amounts of tracemetals, it is important to avoid contamination during all stagesof sample collection and preparation. The sample collectionfrom the lakewas performed from four different sampling spotswith fast moving water, at least 20–30 cm deep in 1000 mLpolyethylene bottles. The bottles were soaked in 10% nitric acidsolution and left for at least 24 hr, and then thoroughly cleanedwith ultrapurewater prior to sampling. These bottleswere filledwith acidified ultrapure water and transported to the lake. Atthe sampling site the acidified water was removed; all bottleswere rinsed 3 times by the lakewater prior to sample collection.Rinsingwas conducted downstreamof the sampling sites. Afterrinsing, the bottle was submerged below the water levelapproximately 15–20 cm from the surface to avoid contamina-tion and allowed to fill completely to the top. The lidswere then

Fig. 1 – Sampling location

tightly screwed on to prevent leakage. The samples wererefrigerated until analysis.

Atmospheric particulate samples were collected with apre-calibrated Thermo scientific total suspended particulate(TSP) high volume air sampler (Thermo Scientific, USA) andTisch environmental PM2.5 high volume air sampler (Tisch,USA). The samples were collected for 24 hr at flow rate of1.132 m3/min in order to collect sufficient mass for chemicalcharacterization. The accuracy of volume flow measurementwas ±2%. The filters had been pre-heated at 120°C overnightbefore weighing. At least three blank samples were also takenby placing clean filters in the sampler for 24 hr with thesampling flow switched off. After sampling, the filters werepacked in a clean aluminum foil until analysis.

1.4. Analytical methods

Sample pH values (Hanna Instrument, Romania) and turbidity(Lovibond, Germany) were measured immediately after col-lection. The samples were filtered through 0.45 μm, 47 mmglass microfiber filter paper using a vacuum pump in order toremove particulate matter. In filtered samples, a mixture of4 mL concentrated nitric acid and 2 mL hydrogen peroxidewas added and samples were digested in a microwave ovenfor 5 min at 650 W. After digestion the samples were allowedto cool and kept in the refrigerator at 4°C until furtheranalysis, normally conducted within one month.

The air filter samples were cut into small pieces and placedin borosilicate glass vessels capped with Teflon. The sampleswere treated with 4 mL of concentrated nitric acid and 2 mL ofhydrogen peroxide using the microwave oven for 15 min toensure complete digestion of particles. The microwave processconsisted of three steps with a power of up to 650 W. The firststep was heating to 450 W for 5 min; the second step washolding at 650 W for 10 min and the last cooling down to roomtemperature. The digested solution was diluted to 50 mL withultrapure water and carefully filtered using Membrane solution

around Kampar, Perak.


Polytetrafluoroethylene (PTFE) synergy filters (25 mm, 0.45 μm)prior to analysis, and stored at 4°C until further analysis.

1.5. Instrumentation

Determination of trace metal concentrations in the samples wasperformed with a Perkin Elmer NexION 300Q ICP-MS(Perkin-Elmer Inc., USA) equipped with a Perkin Elmer integratedauto-sampler, cross-flow nebulizer and a Quartz torch. Theinstrumental operating parameters for sample analysis are listedas following: nebulizer gas flow rate 0.90 L/min, auxiliary gas flowrate 1.20 L/min, plasma gas flow rate 16 L/min, deflector voltage−12 V, Inductive coupled plasma radio-frequency (ICP RF) power1150 W, analog stage voltage−1750 V, pulse stage voltage 1100 V,discriminator threshold 26, Alternating current (AC) rod offset −4,trace metalsm/zmeasurement 27Al, 52Cr, 66Zn, 75As, 111Cd, 118Sn,

202Hg and 208Pb, replicates 3, and rinse time 30 sec. The ICP-MSNexION instrument software was used to control all instru-ment operation including tuning, data acquisition and dataanalysis. Argon was used as the reaction gas in the collisioncell to reduce the polyatomic interference. ICP-MS calibrationsolutions were prepared by dilution of a commerciallyavailable 100 ppm multi-element standard (Perkin-Elmer) inultrapure water and three-point calibration (10, 500, 1000 μg/L)was performed for the 8 elements analyzed, and the regressioncoefficients were 0.998.

1.6. Enrichment factor (EF)

The EF is a way to characterize the chemical composition ofairborne particulate matter. The concept of EF was originallyintroduced by Menard and Chesselet (1979), and was used tocalculate the ratio of the concentration of metals in a samplewith that of a selected reference (such as aluminum) which isalmost entirely crustal in origin, compared with the corre-sponding ratio in the average composition of the earth crust.The EF value was calculated by Eq. (1):

EF ¼ X=Alð ÞsampleX=Alð Þcurst ð1Þ

where (X/Al)sample is the ratio of metal and Al concentration ofthe sample; (X/Al)crust is the ratio of metal and Al concentra-tion in the earth crust.

Table 1 – pH and turbidity Nephelometric Turbidity Units(NTU) of the lake samples before and after precipitation.

Sampling site November December

Precipitation Precipitation

Before After Before After

pH 1 7.86 6.89 7.88 6.832 7.71 6.85 7.79 6.813 7.63 6.87 7.71 6.884 7.68 6.86 7.69 6.82

Turbidity (NTU) 1 17.8 28.3 16.1 28.12 17.3 28.9 14.4 26.93 19.9 29.7 15.1 27.64 21.7 31.5 11.8 25.1

2. Results and discussion

2.1. Physicochemical parameters

The physicochemical parameters such as pH and turbidity ofwater samples were determined in the laboratory from thecollected lake samples.

2.1.1. pHThe basic physicochemical parameters of lakes including pHare given in Table 1. A lake pH fluctuates somewhat each dayand from season to season in response to photosynthesis byalgae, watershed runoff and other factors. Each sampling siteexhibited different pH values ranging between 7.63 and 7.88,which is slightly basic, and shifted to slightly acidic conditions

between 6.81 and 6.89 after precipitation. From the pHmeasurements, it was noticed that the pH of lake water wasacidic after precipitation when compared to that beforeprecipitation. This may be due to the possible reaction ofrainwater with atmospheric carbon dioxide to produce acidicrunoff water, which ultimately saturated the lake water,hence lowering the pH of water samples. It is suggested thatthe area under study is influenced by biomass burning thatemits particulate matter in the atmosphere, as well as greatquantities of acidity generating gases such as CO2, NOx andSO2, which contribute to the development of acid rain.

2.1.2. TurbidityTurbidity is produced due to suspended soil particles andorganic matter along with planktonic growth. The presentstudy result shows that the turbidity of lake samples rangedfrom a minimum of 17.3 Nephelometric Turbidity Units (NTU)(before precipitation) to 31.5 NTU (after precipitation). Thehighest turbidity levels were observed after precipitation in allsampling sites and the lowest before precipitation; thecorresponding data are shown in Table 1. Therefore, highturbidity may be attributed to the soil particles, inflow of silt,wood ashes, undesirable insoluble inorganic substances, andother particles in the atmosphere mixing during precipitationand subsequent runoff water. The study of Offem et al. (2011)reached a similar conclusion for Ikwori Lake in Nigeria. Theyreported that high turbidity due to flooding occurred duringthe wet season due to the rainfall and runoff fromnutrient-rich agricultural lands, which increased the level ofsome particles and debris in Ikwori Lake.

Turbidity can be used to detect the occurrence of pollut-ants such as trace metals because it is strongly influenced bythe properties of transported suspended solids, such as shape,size and mineral composition (Landers and Sturm, 2013). Ithas been reported that heavy metals are particle-boundpollutants in water, with suspended solids associated with60%–97% of total metals (Nguyen et al., 2005). During thisstudy it was also noticed that the concentration of tracemetalsdepended on the turbidity, and the relationship between theturbidity and trace metal concentrations is shown in Fig. 2.From the relationship it can be seen that the concentration oftoxic metals increases with increase in the turbidity, leading tothe conclusion that the trace metal concentrations are directlyrelated to the suspended solids, which could be supported bythe relationship to particulate matter.

Table 2 – Blank values and limits of detection.

Metals Limit of Detection (LOD)of blank atmospheric

samples (μg/m3)

Limit of Detection(LOD) of blank lakewater samples (μg/L)

Al 2.801 2.187Cr 0.006 0.001Zn 1.519 1.876As 0.002 0.001Cd 0.001 0.002Sn 0.003 0.015Pb 0.550 0.002Hg 0.088 0.001


2.2. Detection limits

The concentration of tracemetals in the filter andwater blankswas measured to establish a baseline. For the quantitativeanalysis no blank correction was necessary, as standards andsamples were treated exactly the same way, adding the sameamount of extraction solution. The detection limits wereestimated by using the equivalent concentrations correspond-ing to three times the standard deviation of measurement ofanalytes in a series of blanks treated the same way as thesamples. The detection limitswere evaluated on different datesto obtain their range. Overall the blank values and trace metaldetection limits generally ranged from 0.01–0.5 μg/L, exceptfor Zn and Al, and were sufficient to determine the metalconcentrations in samples. The detection limits are shown inTable 2.

2.3. Trace metals in lake water

In order to assess the water quality of Kampar lakes, 4samples on a bimonthly basis before and after precipitationwere collected from November to December 2015, from foursites around the study area as shown in Fig. 1, and analyzedfor total dissolved trace metals. Analysis of lake samples wasperformed by the procedure described above and the resultsare shown in Table 3. Among the trace metals, the highestconcentrations were recorded for Zn (19.777–43.289 μg/L) afterprecipitation, followed by Al, Cr, As, Hg, Pb, Sn and Cd. Theonly trace metal that showed no significant differencebetween seasons was Cd. A very interesting observationoccurred in sampling site 1, where all trace metals had theirhighest concentrations during the whole study. In our presentinvestigation, it was noted that the levels of trace metals suchas zinc and aluminum in the lake samples during precipita-tion were within allowable limits. Other than these tracemetals, others such as arsenic, chromium, tin, cadmium, leadand mercury were not within allowable limits recommendedby the Malaysian standard (NAHRIM, 2016). A study of

Fig. 2 – Relationship between turbidity and concentration of tr

Ismaniza and Saleh (2012) showed almost the same resultsthat the concentrations of some heavy metals in watersamples were beyond the detection limits of the Malaysianstandard.

The high concentrations of Zn and Al in lake samples fromthe study area are expected to originate from soil dust. Themajor ongoing land reclamation and construction activityaround the study area potentially contribute to the amount ofwind-blown dust, and appear to have contributed to theincreased concentration and deposition of the trace metalsassociated with soil dust, which contains a high amount ofzinc and aluminum. According to the agency responsible forthe toxic substance and disease registry, zinc and aluminumare naturally occurring elements found in the earth.Forest-clearing activities using slash and burn methodscould also have contributed to the amount of zinc- andaluminum-containing dust, since the emission of biomassburning pollutants from the upwind source from Sumatra,Indonesia was prominent. The study of Latif et al. (2015) foundthat the concentration of Zn was enriched when there iscontribution from biomass burning or wood combustion.Meanwhile, the concentrations of anthropogenic Pb and Cdlikely originated from vehicle emissions, such as from thetrucks and cars moving around the lake.

ace metals in lake samples before and after precipitation.

Table 3 – Trace metal concentrations in different sampling sites before and after precipitation in the months of Novemberand December (unit: μg/L).

Sampling site 1 Sampling site 2 Sampling site 3 Sampling site 4

Before After Before After Before After Before After

Nov. Al 10.897 22.398 5.925 14.051 7.738 23.534 6.096 17.392Cr 1.798 5.384 1.229 2.835 1.299 7.258 1.491 2.663Zn 27.779 40.868 21.223 22.795 19.607 40.596 14.128 21.742As 1.687 3.392 3.264 6.574 2.292 4.361 3.292 3.875Cd 0.502 0.259 0.112 0.741 0.057 0.264 0.048 0.807Sn 1.440 2.191 4.371 5.073 2.221 1.163 1.419 0.637Hg 2.256 3.869 2.772 3.173 1.802 2.185 1.332 2.133Pb 1.651 3.593 1.805 6.032 1.115 3.646 0.748 8.675

Dec. Al 6.856 21.767 5.529 16.139 8.056 27.479 5.234 27.47Cr 1.480 5.407 1.237 3.232 1.346 7.593 1.424 3.981Zn 15.137 23.27 18.126 19.777 19.593 43.289 11.964 34.067As 1.421 2.428 3.635 3.877 2.165 4.304 2.598 5.855Cd 0.394 0.479 0.088 0.307 0.061 0.264 0.054 1.244Sn 1.204 1.734 2.9928 1.095 1.833 1.094 1.175 0.819Hg 2.441 3.547 1.947 3.567 1.364 2.083 1.154 3.178Pb 4.068 5.281 1.410 4.379 0.971 3.857 0.694 5.672


However, the detected arsenic concentrations were alsohigher in this study than those in most of the previous reports(Taweel et al., 2013; Salim et al., 2008). The high concentrationof arsenic in lake water might be due to biomass burning andvolcano activity from the southern air mass and transferred tothe water bodies by wet deposition. Most toxic heavy metals intrace amounts released into the environment find their wayinto the aquatic system as a result of direct input, atmosphericdeposition and erosion due to rain water. In general, wet anddry atmospheric depositions are the major pathways ofaccumulation of heavy metals in lake ecosystems (Öztürk etal., 2009). It has been determined that approximately 80% ofthe atmospheric removal of toxic metals such as Pb, Cd, Zn,As and others to the aquatic medium takes place by wetdeposition, while 40% of removal for Al and Hg is related todry deposition (Kvietkus et al., 2011). Thus, the low concen-trations that were obtained for other metals may be attribut-ed to domestic and agricultural effluents. These pollutantscan change the natural conditions of an aquatic medium andcause behavioral changes as well as morphological imbal-ance in aquatic organisms.

2.3.1. Comparison of trace metal concentrations before and afterprecipitationMany studies in the literature have been reported on theseasonal variation of concentrations of trace metals duringwet deposition (Takeda et al., 2000; Kim et al., 2000; Pike andMoran, 2001). These studies have confirmed that differenttrace metals show different seasonal variation in wet depo-sition fluxes depending on the nature and strength of theircontamination source, major wind direction, mixing depth,hours of dry weather and monthly precipitation amount. Inthis study, there was no clear seasonal trend noticed in themetal deposition except that the highest deposition ratesoccurred after precipitation. Statistical analyses were con-ducted to test significant differences in the concentrations oftrace metals in lake samples as a function of the samplingtime before and after precipitation (Table 3). It is clear thatconcentrations of all the metals detected after precipitation

were highest, while low concentrations weremeasured beforeprecipitation. The variation in the concentration of trace metalsbefore and after precipitation is likely due to the difference in thesize distribution of atmospheric particles, and could be relatedto the source of pollutant emissions. This result can also beexplained by the fact that the heavy metals which arise fromanthropogenic sources (high temperature combustion-generatedaerosols) containing trace metals could be transported, collectedand concentrated during the no-rain time period, and thenwashed out of the air with the rain runoff and leached into theground-water through the soil and lake sediment.

2.4. Trace metals in atmospheric samples

The contents of the eight trace metals Zn, Al, As, Cd, Pb, Sn, Crand Hg in the ambient air samples collected over a period of2 months are shown in Fig. 3. The total number of ambient airsamples was 8, collected using two types of high volume airsampler (TSP and particulate matter smaller than 2.5 μmaerodynamic sizes (PM2.5)) before and after wet precipitation.The heavymetal concentrations of atmospheric samples wereanalyzed both before and after precipitation using ICP-MS.The result indicates that the recorded concentrations of heavymetals in the air samples before precipitation were high inboth types of samples (TSP and PM2.5), and were found to behigher than the World Health Organization guidelines (WHO,2000). The contents of heavy metals were as follows: Znranged from 133.50–419.30 μg/m3, Al: 53.58–378.93 μg/m3, As:2.83–5.43 μg/m3, Sn: 3.88–8.27 μg/m3, Cr: 5.15–17.32 μg/m3, Pb:7.15–37.41 μg/m3, Cd: 0.21–0.39 μg/m3 and Hg: 0.23–3.82 μg/m3.

The occurrence of heavy metals in the atmosphere andtheir distribution pattern in the study area suggest that someof the emittedmetals were transported viawind as aerosols tothis site from the city. The prevailing southwest wind in thisregion favors the transport of metals from Sumatra to thestudy area. As mentioned by a number of studies, metalsbound to aerosols can be transported over long distances,even over thousands of kilometers, before they return to theground surface (Barbante et al., 2001). For instance, the average

Fig. 3 – Trace metal concentrations before and afterprecipitation.


atmospheric residence time of particles is 3 to 7 days (Pleâowand Heinrichs, 2001).

In this study it is noted that the concentrations of tracemetals in TSP were higher than in PM2.5. The discrepancybetween TSP and PM2.5 is normal because TSP wouldinclude particles larger than PM2.5. In particular, SoutheastAsia biomass burning episodes greatly affect and increasethe mass concentration of coarse particles (Lee and Hieu,2011).

Of all the trace metals examined, Zn and Al showed higherconcentrations in both types of samples collected during theperiod under study, followed by Pb, Cr, As, Cd, Sn and Hg. Thehigh concentrations of Zn and Al in dry deposition indicatesources such as peat soil dust and strong emissions fromanthropogenic sources (fossil fuel and biomass burning) andalso attributed to elevated concentrations of these metals inthe atmosphere around the study area. The characteristics ofpeat soil, which is acidic with a high specific surface area,influence its capability to be a natural adsorbent (Kyziol, 2002).According to the study of Shah et al. (2012) Zn, Cd and Pb areproduced during biomass burning and anthropogenic activi-ties. Another study reported that the presence of Zn inambient air is due to the traffic emission originating fromengine oils, brake and exhaust systems (Bender and Lange,2011). The concentration of As in the atmosphere is usually

low, but as noted above, it was higher in this study. Arsenicenters the atmosphere through volcanic emission, winderosion, and low temperature volatilization from soil. Themost important anthropogenic source of arsenic is fossil fueland biomass combustion, and As is present in the atmosphereas As(III)2O3 dust particles. The Pacyna and Pacyna (2001)study estimated that anthropogenic sources of atmosphericAs contribute 30% of the global atmospheric As flux. However,it is accepted that these anthropogenic sources have animportant impact on airborne arsenic composition.

From the experimental results it can be clearly stated thatthe concentrations of the studied heavy metals were higherduring dry deposition. However, during wet deposition thevalues were in general low and fell within standard levels.This discrepancy might have occurred because of rainfall anddilution, which suggests that the amount or intensity ofrainfall may affect the dynamics of air quality (André et al.,2007). For Cd and Pb only, the concentration levels werealmost the same during dry and wet deposition. This might bedue to the high percentage of motor vehicles passing throughthe study area. The study of Othman and Latif (2013)supported the above conclusion that traffic emission andbiomass burning are the major sources of heavy metals andmajor contributors to the particulate matter in urban air.

2.5. Comparison between atmospheric and lake samples

The trace metal concentrations of lake and atmosphericsamples in ambient air were compared during the observationperiod. It was noted that the overall heavy metal concentra-tions in the lake samples in this study were much lower thanthe concentrations observed for the ambient air samples.According to the obtained results, it was also noted that thelake sample concentration increased with decreases in theconcentration of atmospheric samples during precipitation,and the results are shown in Fig. 4. This study supports otherreported observations (Kozak et al., 2015; Pan andWang, 2015;Lynam et al., 2015; Melaku et al., 2008) that precipitationactions can strongly influence the variability in concentrationof both atmospheric and lake samples.

2.6. EF analysis

In order to assess the origins of the trace metals accumulatedin atmospheric particulates, the results are often analyzedusing EFs. Measuring EF is an essential part of geochemicalstudies and is usually used to differentiate between metalsoriginating from anthropogenic (non-crustal) and geogenic(crustal) sources, and to assess the degree of metal contam-ination (Yongming et al., 2006). Fig. 5 shows EF values of Cr,Zn, As, Cd, Sn, Pb and Hg for the two sampling time periods(before and after precipitation). According to Zhang and Liu(2002), an EF value approaching 1 suggests that the elementoriginated from a crustal source, whereas the EF values inthe10 range (1–10) indicates that it mainly comes from anaturally occurring source and is not enriched. Moreover, avalue of (10–100) suggests that the element was moderatelyenriched, while an EF value >100 suggests that the elementwas highly enriched, with anthropogenic activities as themain sources, and hence termed as an enriched element.

Fig. 4 – Comparison between average concentrations of metals in atmospheric and lake samples before and after precipitation.


However, the types of crustal materials are unique in differentareas and not much is known about the uncertaintiesconcerning fractionation during weathering (Kaya and Tuncel,1997). Duan et al. (2002) stated that the reference element musthave the characteristics of being themost abundant element inthe earth's crust, very stable and not affected by pollution; andaccording to Al-Momani (2003), Al is derived almost exclusivelyfrom crustalmaterial, so this is the elementmost often used fornormalization.

Fig. 5 indicates that Cr, Zn, As, Cd, Sn, Pb and Hg have veryhigh EF values in both TSP and PM2.5, suggesting contributionsfrom various anthropogenic sources like fossil fuel combus-tion and industrial emissions (Kang et al., 2011; Gangwar etal., 2012). High EF values of metals indicate their contributionfrom emissions of non-crustal origin. The high values for Znand Cd obtained in this study are similar to results in the studiesby Latif et al. (2015). Another studydemonstrated thatZn is oneofthe indicators of biomass burning, and had a high EF value frompeat soil combustion during a haze episode in Southeast Asia(See et al., 2007). From the statistical results it was also noticedthat Cr had EF values greater than 10, suggesting that thiselement was moderately enriched, and might have originatedfrom airborne dust and also have significant contributions fromboth natural and anthropogenic sources. The EF value recorded

Fig. 5 – Enrichment factor values for the 8 analyzed heavymetals in atmospheric samples.

for Hg was the highest (more than 14,000) among all theelements, and may have originated from non-crustal sourcessuch as a forest fire near the sampling site. The results of thepresent study show that all the elements were significantlyenriched at the study locations since their EF values were greaterthan 100.

3. Conclusions

We have reported the measurement of 8 trace metals inlake water and atmospheric ambient air samples before andafter precipitation events, collected around Kampar, Perakduring the period of November to December 2015. Thetrace metal concentrations in lake water samples showedthe following trend, Zn > Al > Cr > As > Hg > Pb > Sn > Cd,while those in atmospheric samples showed the trendZn > Al > Pb > Cr > As > Sn > Hg > Cd. Higher values of thetracemetals were observed before precipitation in atmosphericsamples, except for cadmium and lead, which showed almostthe same concentrations before and after precipitation periods.It appears that the main reasons for the high concentrationlevels of the studied heavy metals in Kampar city are variousemission sources such as fossil fuel combustion, biomassburning and soil dust around the study area. A similar situationcan be observed when the data are expressed in terms of thecrustal enrichment, which refers to the composition of theearth's crust. When the trace metal data were compared withlake water samples after precipitation events, it should bementioned that the concentrations of metals decreased in theatmospheric samples because ofwashing by the rainwater,whilethe concentrations in the lake water increased. The results ofthis study also showed that an increase in turbidity of lakewater samples accompanied increases in the concentrations ofmetals.

Acknowledgments

This work was supported by the Universiti Tunku AbdulRahman under Universiti Research Grant (No. IPSR/RMC/UTARRF/C1-13/G03).


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