Environmental Assessment of Metal Pollution in Manila Bay ......(Velasquez et al. 2002) to measurements in sediments (Duyanen 1995), it showed enrichment in sediments by a factor of

Keywords: elemental analysis, Manila Bay, Pb-210, sediment, trace metal, XRF

Environmental Assessment of Metal Pollution in Manila Bay Surface Sediments

1Department of Science and Technology – Philippine Nuclear Research Institute (DOST-PNRI) Commonwealth Ave., Diliman, Quezon City 1101 Philippines

2Department of Environment Systems, Graduate School of Frontier Sciences University of Tokyo, Kashiwa 277-8583 Japan

Ryan U. Olivares1,2*, Efren J. Sta Maria1, and Elvira Z. Sombrito1

Philippine Journal of Science149 (S1): 183-195, Special Issue on Nuclear S&TISSN 0031 - 7683Date Received: 18 Jun 2019

The impact of human activities on the sediments of Manila Bay was evaluated through elemental analysis to determine the trace metal element concentration and calculate the corresponding metal enrichment factor (EF). The samples were analyzed using the X-ray tube-excited XRF (X-ray fluorescence) with Ag secondary target to quantify elements Mn to Pb, while the Fe target was used to quantify elements Na to Cr. The radioisotope-excited XRF with 241Am was used for Cd and Hg. The normalized EF has been calculated against baseline values to estimate the environmental impacts of human activity on the bay. In an attempt to provide a better understanding of sediment movement and reworking in the bay, spatial distribution of metals was correlated with the obtained 210Pb radioactivity levels in Manila Bay sediments. Overall, heavy metal and other trace elements are low in Manila Bay sediments, mostly ranging from deficient or minimal to moderate enrichment except for some stations where enrichment of Mn and Cu is significant. Nevertheless, there is a need to estimate the enrichment levels in marine sediments to effectively understand the risk and impact of heavy metals to support management and decision making for the rehabilitation, protection, and maintenance of a healthy ecosystem along the bay.

*Corresponding Author: [email protected]

INTRODUCTIONManila Bay is one of the important coastal marine ecosystems in the country. The bay has served as a major avenue for trade and commerce and considered to be the second most productive fishing ground in the country (Perez et al. 1999). Now, however, it is an ecosystem threatened and adversely affected by exploitation and pollution. The rapid urban growth and industrialization are contributing to a decline in water quality and deteriorating marine habitats. Recently, events associated with accidental oil spills, releases of industrial effluents,

mining operations, urban runoff, and atmospheric depositions have intensified public concern to assess the impact of pollution on health and the environment. More importantly, the interest over heavy metal pollution in the marine environment has become a rising concern due to human activities that contribute significantly to the release of agricultural, domestic, and industrial wastes along the coastal areas of Manila Bay.

Metals are one of the major anthropogenic inputs into the coastal areas (Prudente et al. 1994, Skejelkvale et al. 2001). Some of these metals are essential biological elements; some are not essential and can be toxic even at very low concentrations. Those that are essential to

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organisms can also have the potential to be toxic if present above a certain threshold concentration. Because of their potential toxicity, heavy metals – arsenic, cadmium, chromium, lead, and mercury – rank among the priority metals that are of public health significance and are usually monitored in the water column in marine and freshwater systems in the Philippines. There is substantial evidence of heavy metal enrichment in the bottom sediments of coastal waters and the concentrations of toxic metals in many ecosystems are reaching unprecedented levels (Prudente et al. 1994, Silva and Shimizu 2004). Heavy metals – particularly total Cd, total Pb, and total Cr – were evident in the waters, fish, and macro-invertebrates in Manila Bay and significant differences on the total Cd and total Pb in the water column were noted for both wet and dry seasons (Su et al. 2009). In Manila Bay, comparing the levels of selected elements in the water column (Velasquez et al. 2002) to measurements in sediments (Duyanen 1995), it showed enrichment in sediments by a factor of 103–105. Enrichment has been a function of grain size, being greatest with clay and silt particles. Heavy metals, in particular, have a high affinity for fine sediment particles. High concentrations of heavy metals have also been correlated with a higher content of organic matter (Palanques et al. 1995).

The transport and ultimate fate of heavy metals in the marine environment are needed in understanding marine processes and assessing the magnitude and impact of pollution. Numerous published data have indicated that heavy metals such as As, Cd, Cr, Pb, and Hg occur naturally. However, anthropogenic activities contribute significantly to environmental contamination (Birch et al. 1996, Birch and McCready 2009). Despite this situation, at present, there is very limited information on the levels and distribution of dissolved metals in Manila Bay especially in sediment samples (Vicente-Beckett 1992, Duyanen 1995, Hosono et al. 2010). The writ of continuing mandamus issued by the Supreme Court in the years 2008 and 2011 responded to the challenges posed by the environmental pollution and environmental destruction pursuant to RA No. 9275 or the “Philippine Clean Water Act of 2004.” To ensure the complete rehabilitation, restoration, and conservation of Manila Bay, AO No. 16 was enforced in February 2019.

In this study, elemental analysis via the XRF spectrometry was undertaken to determine the presence and distribution of heavy elements in Manila Bay sediment samples collected and processed in 2005. The spatial distribution of metals will be correlated with existing 210Pb radioactivity levels in the bay sediments (Sta, Maria et al. 2011) to provide information on sediment movement and reworking in the bay. From the perspective of a sustainable marine and coastal management, and in line with the

efforts to address marine pollution in the coastal areas, the potential impact of this problem – particularly the adverse implications on public health and safety – should be recognized and properly documented. The results presented here will benchmark the levels of trace metals as well as fill the gap in metal contamination data in the bay’s sediment historical records. These will help in the establishment of the much-needed sediment quality guideline in the country and provide a valuable resource for future studies, against which monitoring of and future studies in the bay can be assessed.

MATERIALS AND METHODS

Description of the Study AreaManila Bay is a semi-enclosed estuary that is connected to the West Philippine Sea and the larger South China Sea via a 16.7-km-wide entrance (Figure 1). The Regional Program on Partnerships in Environmental Management for the Seas of East Asia (PEMSEA) has identified Manila Bay for the development and implementation of a strategic environmental management plan, as it is one of the pollution hot spots in the region. Manila Bay receives drainage from approximately 17,000 km2 of watershed consisting of 26 catchments areas – with main tributaries such as Pasig, Bulacan, and Pampanga Rivers (Silvestre et al. 1995). The surface area of the bay is 1,800 km2 contained by a shoreline approximately 220 km from a reference point in Mariveles, Bataan ending at a point in Maragondon, Cavite. It consists of a gently sloping basin with depth increasing from the interior to the entrance. The mean depth of the bay is 25 m and the volume is 31 km3 (PRRP 1999, Wolanski 2006).

Freshwater inflow has been estimated at approximately 25 km3 yr–1. Seasonal and annual variations in discharges are pronounced, with the largest input occurring in August (rainy season) and the lowest in April (dry season). The typical retention time for freshwater in the bay is between 2 wk and 1 mo depending on the season (PRRP 1999). Manila Bay current is believed to be initiated by three interacting factors – winds, tides, and freshwater currents. Different seasonal wind blow controls the circulation in the bay (de las Alas and Sodusta 1985). There are northeasterly winds from October to January, southeasterly winds from February to May and southwesterly winds from June to September.

Sediment SamplingThe Integrated Environmental Monitoring Program for Manila Bay (IEMP-MB) included the collection of sediment samples (grab samples) in nine geographically-

Olivares et al.: Assessment of Metal Pollution in Bay Sediments

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spaced locations in Manila Bay. The surface sediment samples were collected for the preparation of the pilot study report for Manila Bay implemented by the Sub-technical Working Group under the Manila Bay Environmental Management Project of the Department of Environment and Natural Resources (DENR) and the International Maritime Organization – PEMSEA.

Nine grab samples were collected from the pilot study stations during the pilot study cruise of the IEMP-MB team onboard RPS Corregidor and MV Nueva Vizcaya on 10–11 Feb 2005. The collection of samples was done in the same sampling sites, as presented in Table 1. The sediment grab samples were sub-sampled and were analyzed for selected elements at the DOST-PNRI.

XRF AnalysesEnergy-dispersive XRF spectrometry is a powerful tool in the trace analysis of some heavy metals, as well as in the analysis of concentration profiles of the different sampling stations in the Manila Bay area. Sediment samples collected from nine stations within the bay were prepared for XRF analysis. Weighed amounts of each of the dried samples were pressed into 1-in disks. The samples were then analyzed in tube-excited XRF systems using secondary targets Ag and Fe and in a radioisotope excited XRF using a 241Am source. The X-ray tube-excited XRF (KEVEX ED-771 brand) with Ag secondary target was used to quantify elements Mn to Pb, while the Fe target was used to quantify elements Na to Cr. To determine the presence of other heavy elements like Cd and Hg, the radioisotope-excited XRF was used employing the 241Am as the excitation source. Spectra were fitted and results were calculated against the IAEA standard reference material.

The X-ray tube-excited XRF with Ag secondary target was operated with a tube voltage of 30 kV and a tube current of 0.5 mA while for the Fe secondary target, the tube voltage was 20 kV and the current was 0.7 mA. For the Fe target, the analysis was done under vacuum conditions. The lithium-drifted silicon detector was used for all analyses.

X-ray Fluorescence TechniqueXRF spectrometry is a well-established analytical technique widely used in industrial and research applications for elemental composition analysis (IAEA

Table 1. Sampling location coordinates and depth.

Station Latitude Longitude Depth (m)

1 14.6667 120.8424 10

2 14.68311 120.7612 14

3 14.67143 120.6248 10

4 14.57835 120.634 22

5 14.4525 120.6261 36

6 14.45305 120.7599 26

7 14.46786 120.8411 16

8 14.58444 120.7621 25

9 14.59082 120.8473 18

Figure 1. Study site and sampling stations.



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2005). The accuracy, precision, and performance of this technique have been evaluated for the determination of metals in marine sediments in several studies (Stallard et al. 1995, Baranowski et al. 2001). In XRF spectrometry, a sample is bombarded with radiation (source). If the source has high enough energy to eject electrons from their orbitals, only then can XRF emissions (called K- or L- lines) be emitted and detected by the detector. These X-ray lines are characteristics of the elements in the sample and it is in the presence of these lines that the elements present in the samples are determined.

L-lines are generally weaker than K-lines. For trace levels (ppm and below), the L-lines are not generally strong enough to be seen in the spectrum. For the case of Fe- and Ag-secondary targets, the K-lines are beyond the energy range that can be seen in the spectrum, thus only the L-lines are in the energy range of the spectrum. However, at very low levels of concentration, these L-lines can be very weak to be seen as peaks in the spectrum. The intensity of the XRF line is approximately proportional to the concentration of the emitting substance in the sample (Blair 1962).

Estimating Pollution ImpactNumerous methods to estimate pollution impact in marine sediments have been published. The most common approach to estimate the anthropogenic impact on sediments is to calculate a normalized EF for metal concentrations above uncontaminated background levels (Dickinson et al. 1996, Loska et al. 1997, Çevik et al. 2008). This method normalizes the measured heavy metal or any trace elements with respect to a sample reference metal (Callender 2005). The degree of metal enrichment in Manila Bay sediments has been calculated to evaluate the spatial variation of trace element levels based on the following equation (Loska et al. 1997, Çevik et al. 2008):

EF = (Csample / Xsample) / (Coffshore/ Xoffshore) (1)

where Csample represents the concentration of the given element in the sediments, Xsample represents the concentration of the reference element in the sediments, while Coffshore and Xoffshore are those of offshore sediments. In this study, titanium has been used as a conservative tracer (sample reference metal) to differentiate natural from anthropogenic components (Loring 1991). Titanium is a very conservative element that is associated with crustal rock sources. Normalization with respect to Ti compensates for the relative percentage of various diluents (non-crustal rock sources) and allows anyone to identify clearly metal enrichment due to anthropogenic inputs (Callender 2005). The metal concentration that will be used for offshore sediments was considered as those from the reference environment. Several tables of

crustal abundances have been published (Turekian and Wedepohl 1961, Bowen 1979) i.e., the world’s sediments and earth’s crust, and compiled in this study to obtain the average metal values for purposes of comparison as reference materials. Although this compilation can be subject to great uncertainties, these reference values can always be amended or debated. However, in the absence of reference values for Manila Bay sediments that were age-dated back to pre-industrial sediment deposition, this database for reference values can represent a good approximation for geogenic metal concentrations in the marine sediment. The enrichment level is classified as defined by Loska et al. (1997).

RESULTS AND DISCUSSIONQuantitative results of the elemental analysis of the nine sediment samples using XRF spectrometry are summarized in Table 2 and the calculated limits of detection (LODs) for each of the analytical systems used are given in Table 3. Detection limits were generally five to several tens parts per million (ppm), and the variation of analytical values were influenced by the type of elements and matrix composition. The error value ranges for most elements from 6–12% except for elements, Ni, Mg, and Pb, whose error ranges up to 31% for some locations. The measurement using XRF indicated that accuracy was within an order of magnitude for common elements. Although fluorescence intensity derived from 22 elements was monitored, it was difficult to quantify some elements due to the absorption of fluorescence X-ray by ambient air.

Spatial Distribution of Trace Elements in Surface SedimentsTrace elements enter the environment and the bay area through natural processes and anthropogenic activities. In this study, the range of concentration of trace elements showed variation among all the sampling sites. Cr and Zn were higher in the northern part of the bay (Station 1) whereas Cu, Fe, Ti, Ca, Mg, and K were higher in the eastern and southeastern (Stations 6 and 7) coastal sites. The spatial distribution profiles of selected trace elements are shown in Figure 2. Unlike these elements, Pb is higher in the central part of the bay (Station 8). Mn was found higher in the southwestern site (Station 5) while Ni was higher in all except in Stations 6, 7, and 8. The variation among the stations may be due to different sources of metals discharged from the land through the river. High concentrations of heavy metals have been attributed to local point sources and direct deposition due to precipitation (Skejelkvale et al. 2001) and the increasing river influx during the wet seasons (Su et al. 2009). In tropical areas like the Philippines, water quality is heavily



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influenced by high suspended load particularly during rainy months which contributes to the accumulation of a significant volume of sediments (Olivares et al. 2016). A previous water quality study reported that levels of certain trace metals found in surface sediments from inflowing rivers were substantially higher than the levels in Manila

Bay, especially near the mouth of Pasig River, as compared with offshore sediments (Prudente et al. 1994). While it is expected that the Metro Manila side has more population and possibly more domestic and industrial waste as compared to other coastal areas along Manila Bay, it appears that Station 9 (eastern side of the bay) generally obtained lower metal concentration levels. It could be due to several factors e.g., sampling was conducted during the dry season with no recent inputs coming from major rivers draining into that part of the bay, and hydrodynamic behavior predominating during the time of sampling.

Heavy MetalsThe sources of heavy metal contamination vary from natural abundance to contamination from non-point sources of pollution – domestic sewage, toxic industrial effluents from factories and shipping operations, combustion emissions, mining operations, leachate from garbage dumps, and runoff from chemical agriculture. In 1995, 12 oil spills were recorded in Manila Bay (Jacinto et al. 2006) and the increased presence of oil and grease was

Table 2. Elemental contents in surface sediments from Manila Bay.

Elementconc. (ppm)

Sampling station

1 2 3 4 5 6 7 8 9

Na 458000 450000 448000 624000 552000 22000 101000 588000 562000

Mg 5310 6060 -- 1050 1910 28180 11400 975 4210

Al 29500 30600 32600 16200 16000 53400 68200 17800 22000

Si 85300 82120 75890 35520 36500 137640 152000 41200 59800

S 8160 7460 7150 7700 7920 5005 5790 7910 7530

Cl 140000 162000 210000 262000 200000 111000 45300 200000 189000

K 4660 4830 4960 2200 1750 6788 6380 2432 3246

Ca 11700 8062 8220 5090 6030 94450 28200 5570 10200

Ti 3550 3430 3140 2060 1780 4071 5410 3000 3130

Cr 139 127 107 67 52 58 49 72 71

Mn 896 909 1020 841 1810 1288 1100 1250 1050

Fe 45100 43400 43300 37200 38200 51400 56600 44300 38700

Ni 16 17 17 17 18 9.9 12 10 18

Cu 66 57 70 74 85 76 90 71 77

Zn 124 102 86 75 84.5 104 86 122 80

Pb 13 14 16 8.7 18 14 13 27 20

Br 144 176 131 171 182 106 139 192 217

Rb 25 21 23 37 33 30 25 20 20

Sr 124 111 126 100 129 1350 200 102 119

Y 14 12 13 11 9.3 14 12 11 9.5

Zr 54 47 51 49 53 62 81 62 54

Mo 0.65 1.7 1.7 2.4 1.9 1.2 2.1 2.1 2

Table 3. Computed LODs of XRF systems used in analyzing Manila Bay sediments.

Secondary target: Fe Secondary target: Ag

Element LOD (ppm) Element LOD (ppm)

Na 2010 Mn 114

Mg 318 Fe 78

Al 192 Ni 7.4

K 11 Cu 10.6

Ca 6.8 Zn 17

Ti 4.4 Rb 4.7

Cd 350 Sr 9.3

Pb 7.5



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attributed to maritime activities at the harbors, together with the presence of oil terminals and discharges from industries (PEMSEA/DENR 2002). Aside from oil spills, trace metals such as Cu, Cd, and Zn at the surface of the water were found at the bay coming from sea-based and land-based sources (Velasquez et al. 2002). The prevalence of varying land uses around Manila Bay makes this marine environment a potential sink for heavy metals. Table 4 summarizes the quantitative results for the heavy elements detected, as well as the corresponding dry bulk density of the sediment samples.

Among the heavy metals, Cd and Hg were not detected in the Ag- and Fe-secondary target set-ups. From the basic concepts of XRF, the detections of heavy elements like

Cd and Hg were difficult using the Ag- and Fe- secondary target set-ups because these are high-Z elements. Only their L-lines are detectable using this system since its highest energy secondary target is Ag (22.101 keV). L-lines are weaker than K-lines and for Cd, L-lines are in the low energy region of the spectrum where most of the low-Z elements in high concentrations are located. The presence of a low concentration of Cd is difficult to detect even with Fe as the secondary target. The use of radioisotope-excited XRF using 241Am as the excitation source was conducted to further verify the presence of Cd and Hg. However, 241Am spectra of the sediments did not yield any significant peak corresponding to Cd and Hg. The LOD for Cd using this system is 1050 ppm, higher than that obtained using the tube excited XRF (350 ppm). Thus, Cd cannot be measured

Figure 2. Spatial profile of trace metal concentrations (ppm) in Manila bay sediments.



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probably because XRF has a higher LLD (lower limit of detection) than the usual concentrations of Cd on marine sediments. Hg, on the other hand, is easily vaporized especially by heat during the process with XRF.

Other elemental analytical methods must be employed to verify the absence or presence of Hg and Cd. Nonetheless, studies on high-resolution trace element distribution in mussel shells (Perna viridis) collected from Manila Bay did not indicate heavy elements like Pb, As, and Cd (Samson 2012). Gabriel and Salmo (2014) studied the trace metal concentrations in both sediments and plant tissues along Manila Bay and contamination were below threshold levels, with Cd having the lowest concentration in all compartments and in all sites. Cd concentration was found to be low and uniformly distributed throughout the bay below the surface and suggests that the cadmium source in the bay is largely anthropogenic (Velasquez et al. 2002). Cd is widely distributed in the Earth’s crust at about 0.1 ppm and the highest level of Cd compounds in the environment is found in sedimentary rocks, and marine phosphates contain about 15 mg Cd kg–1 (GESAMP 1987). If indeed Hg and Cd were not present in the sediments in this study, it is likely that Cd was frequently used in the past for various industrial activities, where its major applications include alloys, pigments, and batteries (Wilson 1988). Recently, its commercial use has declined in response to environmental concerns. Hosono et al. (2010) suggested the rate of decline in heavy metal pollution increased dramatically in the latter part of the ‘90s due to stricter environmental regulations being enforced by the Philippine government. Likewise, the industrial demand for mercury sharply declined in 1994 as a result of prohibiting mercury additives in paints, pesticides, and the reduction of its use in batteries (USEPA 1997).

Table 5 lists the comparison of values for heavy metal concentrations in surface sediments collected from Manila Bay in 1992 (Prudente et al. 1994) and 2005 (this study) with reference to other places.

Except for Mn and Fe, the range of metal concentration

values in sediments obtained in this study appears to be lower than the previous study conducted by Prudente et al. (1994). The range of metal concentrations is comparatively in the same magnitude as to several reference areas e.g., Bohai Bay, China (Zhan et al. 2010); Mediterranean Sea, France (Fernex et al. 2001); Jakarta Bay, Indonesia (Rochyatun and Rozak 2008); and Harbour and Mytilene coast in Greece (Aloupi and Angelidis 2002). The same trend of declining tributyltin concentrations has been observed in green mussels conducted in Manila Bay (Olivares et al. 2013) in comparison with the results obtained from a previous study in 1994 by the Asia–Pacific Mussel Watch Program (Tanabe et al. 2000). It was deduced that the enactment of the Administrative Order No. 42 in 2002 – a law to regulate water quality, air pollution, and industrial wastes – is behind this decline in connection with the Manila Bay Declaration 2001, recognizing Manila Bay as a source of food, employment, and income for the people as well as the gateway for tourism and recreation (Hosono et al. 2010).

EFs for Selected Heavy Metals Although the number of samples taken from each grid is quite limited (one sample per grid), it is of interest to compare these values with the shale values listed in Table 6 to estimate the possible environmental consequences of metals analyzed.

Shale values represent a good approximation for geogenic metal concentrations in sediment in the absence of cores age-dated back to pre-industrial sediment deposition. This published baseline values for the distribution of many elements in various units of the Earth’s crust have been compiled for general use (Bowen 1979, Turekian and Wedepohl 1961). This baseline value is being used as a reference before the advent of industrial releases. In these dated sediment cores, initial results suggest that Manila Bay concentrations of metals in the sediments approximate those of the average shale and significantly higher in some stations relative to the average shale concentration except for Ni, which yielded a lower concentration in all sampling stations.

Table 4. Concentration of heavy metals (ppm) in Manila Bay sediments by XRF.

Stn. Depth (m) Dry bulk density (g mL–1) Cr Cu Zn Pb Ni Mn Fe (%) Ti Al (%)

1 10 0.31 139 65.9 124 13.0 16.0 900 4.51 3550 2.95

2 14 0.28 127 56.7 102 14.1 16.6 910 4.34 3430 3.06

3 10 0.34 107 69.6 85.7 15.7 17.4 1020 4.33 3140 3.26

4 22 0.27 67.6 73.9 74.6 8.69 17.1 841 3.72 2063 1.62

5 36 0.27 52.2 84.7 84.5 18.2 18.7 1810 3.82 1780 1.60

6 26 0.51 58.4 75.5 104.3 14.3 9.92 1290 5.14 4070 5.34

7 16 0.41 49.9 90.3 86.1 13.1 12.0 1100 5.66 5410 6.82

8 25 0.22 71.5 71.2 122 26.6 10.2 1250 4.43 2990 1.78

9 18 0.25 71.4 77.2 80.4 20.4 18.0 1050 3.87 3130 2.42



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To estimate the anthropogenic impact on sediments, a normalized EF for metal concentrations has been calculated relative to the reference environment. Table 7 lists the sediment EF for selected metals. The EFs obtained for many elements (> 2) fall under deficient or minimal enrichment, which may imply that these elements

are depleted relative to crustal abundance in the study area. However, it is evident that some samples exhibited an EF value classified to have moderate and significant enrichment (<2 – >5, <5 – >20, respectively) and may reveal sediment contamination.

Stations 1, 2, and 3 located on the northern part of the bay and coastal areas of Bulacan and Pampanga exceeded the reference values for chromium. Although based on the obtained enrichment ratio based on the EF classification, Stations 1 and 2 are considered moderately enriched. Other sampling sites for Cr fall under deficient to minimal enrichment. The distribution profile of the EF of trace metals in Manila Bay is shown in Figure 3. The coastal area of Bulacan (Station 1) and associated rivers draining into the bay are an area associated with tanneries, which is a potential Cr source. These stations also receive drainage from major contributory rivers and watershed areas coming from the north, which contribute sediment with high metal loads into the bay.

Table 5. Ranges of heavy metal concentrations (ppm) in surface sediments of Manila Bay collected in 1992 and 2005 in comparison with other reference areas.

Station Cd Cu Zn Pb Ni Mn Fe Co Reference

Manila Bay 139.0–0.0 32.0–118.0

60.0–329.0 6.0–95.0 10.0–

19.0291.0–1200

11440–40900

8.0–17.0

Prudente et al, 1994

Manila Bay

Jakarta Bay

–

–

56.7–90.3

10.8–107.0

74.6–124.0

85.0–845

8.69–26.6

13.0–106.0

9.92–18.7

–0

841.0–1810

37200–56600

–This study

Riyadi et al. 2011

Bohai Bay, China

Mediterranean Sea, France

0.04–0.84

0.15–1.57

7.2–44.0

14.0–82.6

56.3–308.5

29.4–503.4

5.9–97.0

20.1–393.7

–0

–0

Zhan et al, 2010

Fernex et al. 2001

Harbour and Mytilene Coast,

Greece0.05–0.49 9.4–86.2 38.8–

230.0 30.5–93.0 –0 201.0–360.0

7700–28100

Aloupi and Angelidis 2002

Alexandria Coast, Egypt 3.7–53.41 6.94–

192.516.61–166.54

49.9–109.77

13.48–1384.3 124–36869 El Nemr et al.

2007

Table 6. Comparison of shale values and Manila Bay sediments.

Element World’s sediment

Earth’s crust

This study(ppm)

Cr 72.0 100.0 50–140

Cu 33.0 50.0 57–90

Pb 19.0 14.0 13–27

Ni 52.0 80.0 16–19

Zn 95.0 75.0 75–124

Mn 770.0 950.0 841–1810

Fe (%) 4.10 4.17 3.72–5.66

Table 7. Sediment EF.

Station Depth (m) Dry bulk density (g mL–1) Cr Cu Zn Pb Ni Mn Fe Al

1 10 0.31 2.1 2.1 1.9 1.0 0.3 1.4 1.4 0.5

2 14 0.28 2.0 1.9 1.6 1.2 0.3 1.4 1.4 0.5

3 10 0.34 1.8 2.5 1.5 1.4 0.4 1.8 1.6 0.6

4 22 0.27 1.8 4.0 2.0 1.2 0.6 2.2 2.0 0.4

5 36 0.27 1.6 5.3 2.6 2.9 0.7 5.5 2.4 0.5

6 26 0.51 0.8 2.1 1.4 1.0 0.2 1.7 1.4 0.7

7 16 0.41 0.5 1.9 0.9 0.7 0.2 1.1 1.2 0.7

8 25 0.22 1.3 2.7 2.2 2.5 0.2 2.3 1.7 0.3

9 18 0.25 1.2 2.8 1.4 1.8 0.4 1.8 1.4 0.4

*Enrichment level: < 2 – deficient to minimal; 2–5 – moderate; 5–20 – significant



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Ni concentrations are all below the criteria values, and enrichment levels were categorized as low. According to previous studies done in Oahu, high levels of nickel were found in highly cultivated soils. Possible sources for these high levels are agricultural fertilizers, fungicides, and pesticides primarily used in the sugarcane and pineapple industries (McMurtry et al. 1995). In addition, industrialization, intensive fishing and ferry services, sewage, and other commercial activities along the coast of Manila Bay may be potential sources for Cr and Ni. These activities are contributors to the elevated concentrations of Ni, Cr, Cu, Zn, Al, and Fe in the Hugli Estuary in Bengal (Chatterjee et al. 2007). Although the coastal areas of Bulacan, Pampanga, and Bataan (Stations 1, 2, 3) are among areas being cultivated and farmed, it could be that the sources of Ni in the bay are lithogenic since it did not exceed all criteria values. Another possibility that can be inferred may be due to the eruption of Mt. Pinatubo and dilution from lahars. It is interesting to note that there are recent studies on the influence of microorganisms on the removal of nickel in tropical marine sediments (New Caledonia) and the removal of Ni (2+) was strongly enhanced by the presence of bacteria (Pringault et al. 2010).

For Cu, all sites generally exceeded the reference values – particularly high on Stations 5, 6, and 7 located southern part of the bay (near coastal areas of Bataan and Cavite).

However, most of the stations are considered moderately enriched except that Station 5 obtained an EF ratio of 5.3, which is categorized as having significant enrichment. Cu in the bay may be coming from industrial effluents and from agricultural activities in the provinces surrounding the bay. Likewise, Station 5 exhibited the highest value for Mn and Pb having an EF of 5.5 and 2.9, believed to have had significant and moderate enrichment, respectively. All other stations were classified to be deficient or having minimal enrichment for Cu, Mn, and Pb except for some stations, which registered a moderate enrichment in sediments. Stations 1, 2, 6, and 8 exceeded the shale value for Zn. However, computation of the EF revealed that Stations 4, 5, and 8 have experienced moderate enrichment and the rest below minimal. The primary anthropogenic sources of Zn in the environment (air, water, soil) come from discharges related to mining and metallurgic operations, and the use of commercial products such as fertilizers and wood preservatives. In Manila Bay, it may be due to intensive shipping activities that serve as a transit site for incoming and outgoing ships in the bay. In addition, the navy shipyard is situated in Cavite, which may be utilizing materials that are high in Zn. In the Manila Bay Refined Risk Assessment (2002), it was reported that the risk quotient (RQ) for Cu and Zn exceeded one (RQ > 1) in sediments (< 2 μm) for

Figure 3. Distribution of EF of trace metals in Manila bay sediments.



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the coastal Metro Manila area. Station 5 has the highest EF concentration for Fe while Al fell under deficient enrichment, as observed in all sampling sites.

One of the potential pathways of enrichment in Manila Bay is the discharge of domestic waste, suggesting that the contribution of land-based human activities which lead to the release of metals which, in turn, are eventually transported into the bay through the rivers is a major source of metals in the bay. This is supported by the findings showing that the near-shore marine environments had higher levels of heavy metals compared to offshore sediments, inferring that these originate in the marine environment from river discharges (Prudente et al. 1994, Urase et al. 2006). The EF results give an indication of the extent of pollution from these sources.

Lead-210 (210Pb) Distribution in Manila Bay SedimentIn an undisturbed environment, changes in the radioactivity concentration levels have been a useful indicator of pollution input from land-based sources. In an ideal open ocean situation wherein there is a constant rate of sediment accumulation and very low sediment reworking by physical or biological activities, the level of 210Pb activity in the entire bay should nearly be constant. 210Pb is a radionuclide from the decay of naturally occurring 238U. It has a half-life of 22.3 years and is used to date sediments up to 100 years old (Smith and Walton 1980). Most of the radioactivity, if released into the coastal system, will travel through the water column and attach to suspended particles before they eventually sink into sediments. Figure 4 shows the spatial distribution of 210Pb activity throughout the bay area. The profile revealed that

Figure 4. Spatial profile of 210Pb activity (in Bq kg–1).

the general trend is increasing radioactivity towards the bay entrance i.e., Stations 5, 6, 7, and 8 (Sta. Maria et al. 2011). Likewise, the enrichment of metals in Stations 4, 5, and 8 was higher based on the EF spatial distribution profile. These stations are considered the deepest portions in the bay, and the obtained sediment samples in these areas have the lowest dry bulk densities. Normally, bulk density decreases as sediment becomes finer in texture. Consequently, as grain size decreases, the concentration of metals adsorbed onto sediment components increases. Station 8 is located in the middle part of the bay. Station 5 is located near the shore of Bataan and runs through the upper mouth of the bay, where flushing out is believed to occur.

In Manila Bay, the deeper portions tend to have higher 210Pb activity, which may indicate that the area is less disturbed and could be a potential sink for metals released to the bay. This is one possible indication of the sediment dynamics in the bay; the water tends to carry the sediments to the deeper parts of the bay, carrying with them particulates embedded with several types of matter (Mouret et al. 2010), possibly trace metals. On the other hand, shallow areas i.e., Stations 1, 2, 3, and 9, have lower 210Pb radioactivity. These stations are believed to be experiencing sediment mixing due to high physical and biological activity. Sediments lying under shallow areas in the bay are subjected to strong current movement and current variability is influenced by the prevailing wind (de las Alas and Sodusta 1985, Villanoy and Martin 1997).

Simulation of currents in Manila Bay confirms that southeast winds (northeast monsoon – dry season) predominating during the time of sampling produce counter-clockwise circulation in the bay (Villanoy and Martin 1997, de las Alas and Sodusta 1985). This counter-clockwise movement predominating in the bay may be influencing the horizontal transport, thereby depositing suspended matter upon flushing out near the bay entrance.

CONCLUSIONThe results based on the computed EF showed that most of the metals suggest that sources are anthropogenic and, to a limited extent, the origin may be geogenic. Major rivers draining to the bay have been used as an artery for transportation and have varied land uses along its tributaries, which are potentially discharging effluents into the waterways. Several pieces of research corroborate these findings and have identified urban runoffs and wastewater discharges as the sources of these contaminants. Although the analysis of sediments showed spatial variability, the results generally revealed that high enrichment of metals was observed in the northern and western parts of the bay, while the levels tend to decrease near the bay entrance. The



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distribution of metals can be deduced from the movement of the prevailing wind and hydrodynamic behavior (counter-clockwise gyre) of the bay during the time of sampling, which transports suspended sediments from the eastern coast of Manila to the northern and western coasts of Bulacan, Pampanga, and Bataan. Overall, heavy metal and elemental contamination is low in Manila Bay sediments and is comparatively lower by global standards. However, such observation may still be subject to debate. Continuous monitoring is therefore encouraged to effectively understand the risk and impact of heavy metals on the environment and on the general public’s welfare with the advent of increasing agriculture, housing, and industrial development. Moreover, the data obtained on surface sediments may help in the establishment of the first sediment quality guideline in the country and provide a valuable resource for future studies, against which monitoring of and future studies in the bay can be assessed.

ACKNOWLEDGMENTSThe sediment sampling was done under a collaborative effort among different agencies involved in the pilot study for the IEMP-MB, a project of the DENR and PEMSEA. The XRF analysis was done by the DOST-PNRI as part of its commitment to the IEMP.

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Environmental Assessment of Metal Pollution in Manila Bay ......(Velasquez et al. 2002) to measurements in sediments (Duyanen 1995), it showed enrichment in sediments by a factor of