Pectin and modified pectin differ in the structure of the chains in which the modified version of pectin is shorter in length, non-branched, and galactose-rich. These differences in structure may be exploited for the removal of heavy metals. Durian (Durio zibethinus) rind, that is regarded as agri-food waste was processed into durian rind pectin (DRP) and modified durian rind pectin (mDRP). DRP and mDRP were evaluated as biosorbent for removal of toxic heavy metals (Pb(II), Cd(II), Cu(II), Zn(II) and Ni(II)) and were compared with two commercial products; citrus pectin (CP) and modified citrus pectin (MCP). In general, the order of removal of heavy metals by all biosorbents was Cu(II) > Pb(II) > Ni(II) > Zn > Cd(II). Except for the removal of Pb(II), the order of effectiveness of heavy metal removal of the biosorbents was MCP > mDRP > CP > DRP. MCP, a commercial biosorbent showed the best biosorbent ability, and mDRP a waste product from durian was also a favorable sorber that should be considered for sorption and removal of heavy metals.
In this study, a polluted site at Kg. Pasir Puteh was assessed for heavy metal pollution by using
transplanted caged mussel (Perna viridis) from a relatively clean population, Sg. Melayu; both are located in the Strait of Johore. For control purposes, the P. viridis from Kg. Pasir Puteh were also simultaneously transplanted in Sg. Melayu at the same time. It was found that Zn was the metal which got accumulated fastest in the transplanted mussel while Cd was the slowest. This study indicated that the byssus of Perna viridis was most effective for biomonitoring of Cd, Ni, Pb and Zn, while the shell could be used for the biomonitoring of Cu, Ni and Pb and the total soft tissue for the biomonitoring of Ni since they were able to accumulate and eliminate the respective metals well. By using mussel as a biomonitor, the present study found that Kg. Pasir Puteh, which is located in the eastern part of the Strait of Johore, had significantly higher contamination and bioavailabilities of Cd, Cu, Fe, Ni, Pb and Zn. Therefore, the use of the transplanted caged mussels is very useful for heavy metal assessment purposes since it can increase the validity of data interpretation by minimizing ecological factors.
The present study was carried out to determine the concentrations of selected metal elements (lead, copper, manganese, zinc and iron) in 51 samples of commercial drinking water and tap water available in Malaysia. The results indicated that low metal elements were found in the studied water samples. Lead, manganese, zinc and iron were not detected in some of the studied samples, except copper. The concentrations of the metal elements in the studied samples were well below the maximum permitted concentrations as recommended. Therefore these drinking water are safe for consumption and do not pose adverse effect to the health of consumers due to metal toxicity.
This study was conducted using crab shells as a biosorbent to remove Cu and Cd with different initial concentrations of 1, 5, 10, 15, and 20 mg/L in a biosorption treatment process. Crab shells were selected as biosorbents due to their abundance in the environment and ready availability as waste products from the market place. This study aimed to determine the ability of Scylla Serrata shells to remove Cu and Cd in an aqueous solution, as well as to provide a comparison of the removal rate between the two metals. The data were incorporated into hydrochemical software, PHREEQC, to investigate the chemical speciation distribution of each heavy metal. The shells of S. serrata were found to have a significant (p< 0.05) ability to remove Cu and Cd following the treatment. After six hours of treatment, the crab shells had removed 60 to 80% of both metals. However, the highest removal percentage was achieved for Cu with up to 94.7% removal rate in 5 mg/L initial Cu concentration, while 85.1% of Cd was removed in 1 mg/L initial solution, respectively. It can be concluded that the shells of S. serrata could remove Cu and Cd better with significant results (p
The objectives of this review are to determine the types of indices to use, to assess the current sediment quality index (SQI) of a mangrove forest and to select the appropriate index to describe the mangrove sediment quality index. Amongst the many indices considered in this review are the enrichment factors (EFs), the geo-accumulation index (Igeo), the pollution load index (PLI), the marine sediment pollution index (MSPI) and sediment quality index (SQI). The different indices give diverse perspectives of the status of mangrove sediment quality. This review also highlights the appropriate parameters that need to be used in assessing sediment quality, such as the physical, chemical and biological properties. As the comparison review, the sediment quality can be utilized for Mangrove quality index (MQI) development like to assess the heavy metal, complete laboratory parameters and a classification following the Interim Sediment Quality Guidelines ISQG, PCA and HACA. For the heavy metal content of sediment, the suggested parameters are Pb, Zn, Cu, Co and Mn. Lastly, for the indices, the enrichment factor (EFs), geo-accumulation index (Igeo), pollution load index (PLI) and marine sediment pollution index (MPSI) are used in develop SQI on mangrove forest.
Radon and toxic elements (Pb, Cd, Co, Cu, Cr, Zn and Ni) were measured in different water samples in Cameron Highlands, Pahang. RAD7 and rad H20 were used to estimate the radon concentration. The average values for radon concentration were found to vary from a minimum of 0.21 Bq/L to a maximum of 0.297 Bq/L. Heavy metals concentration were measured using an atomic absorption spectrometer. The mean concentrations of Pb, Cd, Co, Ni, Cu, Zn and Cr were 0.07, 0.009, 0.009, 0.043, 0.076, 0.079 mg/L and ND, respectively. Comparing the results with the literature, shows that the concentrations obtained were within the allowed limits of the agricultural and domestic use.
Kandungan logam-logam berat Pb, Zn, Ni, Co dan Cd pada empat bahagian tumbuhan Nepenthes sp. (akar, batang, daun dan periuk) serta substrat tanih yang menyokong pertumbuhannya dari kawasan bekas lombong bijih timah dan besi di Lombong Pelepah Kanan, Kota Tinggi, Johor telah ditentukan. Komposisi logam-logam berat dalam sampel tanih diekstrak menggunakan campuran asid nitrik pekat dan asid perklorik. Pengekstrakan logam berat dalam tumbuhan pula dilakukan menggunakan kaedah penghadaman basah. Kandungan logam berat di dalam ekstrak larutan tanih dan tumbuhan ditentukan menggunakan Spektrofotometer Penyerapan Atom kaedah nyalaan (FAAS-model Perkin Elmer 3300). Nilai koefisien Penyerapan Biologi (BAC) yang merupakan nisbah kandungan logam berat dalam tumbuhan kepada kandungan logam berat dalam tanih ditentukan secara kiraan. Hasil kajian menunjukkan bahawa tanih di kawasan kajian adalah berasid dan didominasi oleh pasir. Kandungan bahan organik dan kepekatan garam dalam tanih pula adalah rendah, manakala nilai pH adalah berasid. Logam Zn (698.5 mg/kg) menunjukkan kepekatan yang tinggi di dalam substrat tanih diikuti oleh logam Co (182.9 mg/kg), Pb (58.2 mg/kg), Ni (12.2 mg/kg) dan Cd (2.09 mg/kg). Kepekatan logam berat di dalam tumbuhan mengikut kepekatan menurun adalah Ni>Co>Cd>Pb>Zn. Kepekatan logam di dalam bahagian-bahagian tumbuhan tidak menunjukkan perbezaan signifikan bagi semua logam. Tumbuhan Nepenthes sp. didapati menumpukkan logam Ni dalam kepekatan yang tinggi sebagaimana yang ditunjukkan nilai BACnya yang tinggi. Tumbuhan ini mungkin boleh digunakan sebagai bio-penunjuk bagi kehadiran Ni dalam kepekatan yang tinggi di dalam tanih.
This study was carried out at an ultrabasic area, Selaru and Felda Rokan Barat, Kuala Pilah, Negeri Sembilan. Eighteen samples of plant and its substrates were collected for determination of heavy metal contents such as Ni, Co, Cr, Mn and Fe in soils and plants. The plants were separated into different portion such as root, stem and leaf and extracted for their heavy metal content by wet digestion method whereas the soils heavy metal available and resistant content were extracted by sequential extraction. Heavy metals content in soil and plant extract was determined using Flame Atomic Absorption Spectrophotometer. The result showed that total content of heavy metals for Ni, Cr, Co, Mn and Fe was at 84.13 - 740.36 mg/kg, 23.51 - 135.53 mg/kg, 188.23 - 848.92 mg/kg, 245.00 - 545.33 mg/kg and 1176.77 - 1243.90 mg/kg, respectively. Bio-available heavy metals content in soil is at 0.09-6.32 mg/kg for Ni, 0-0.51 mg/kg for Co, 0 mg/kg for Cr, 7.78-21.07 mg/kg for Mn and 2.23-4.47 mg/kg for Fe. Based on BAC, Mn and Fe were detected to have a high concentration in plant parts compared to other heavy metals.
A preliminary study on the concentration and distribution of heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) was carried out for the whole of Ranau District. Topsoil samples (0-15 cm depth) were collected randomly in accordance with the distribution of soil associations in the area. It was found that only three of the heavy metals (Ni, Cr, and Cu) were present above the threshold of toxicity level, whilst the others were below this level. These higher levels of heavy metal concentration were most likely associated with the mining activities in the headwater of the study area and also to the occurrence of serpentinite parent material. The area affected is confined only to the northern part of the study area.
Kajian awal bagi menentukan taburan dan kepekatan logam-logam berat (Cd, Co, Cr, Cu, Ni, Pb dan Zn) telah dijalankan bagi seluruh daerah Ranau. Sample tanah atas (kedalaman 0-15 cm) telah dikutip secara rawak bergantung kepada taburan asosiasi tanah di kawasan tersebut. Didapati bahawa hanya tiga daripada logam berat ini (Ni, Cr dan Cu) melebihi had keracunan, sementara yang lain berada di bawah paras keracunan. Kepekatan logam berat yang tinggi di dalam sampel kajian' dapat dikaitkan dengan aktiviti pelombongan tembaga di kawasan punca air dan juga dengan batuan serpentinit yang menjadi bahan induk tanah. Kawasan yang terlibat terhad di bahagian utara kawasan kajian sahaja.
The sorption parameters of two heavy metals (i.e. Pb and Cu) in clay soils from Selangor were studied using batch equilibrium test. The test was conducted in two separate systems, i.e. single and mix solutions. The sorption isotherms data from this test were then used to calculate the sorption parameters, i.e. distribution coefficient (Kd) and maximum adsorption capacity (Am). Langmuir sorption equation was used to model the sorption data with the correlation coefficients (r2) higher than 0.6. The study has revealed that different soils have different sorption capacity for different heavy metals. The Kd values are proportional to the sorption capacity of the soils. The sorption of Pb and Cu in single solution is higher than in mix solution, due to the competition for sorption sites among heavy metals in mix solution. The Kd values for Pb in single solution ranging from 36.18-334.48 L/g and for Cu is 9.29-66.19 L/g. In mix solution, the Kd values for Pb and Cu are much smaller, ranging from 23.13-31.79 L/g and 3.95-18.53 L/g respectively. The Am values in single solution for both Pb and Cu are ranging from 0.48-1.09 mg/g dan 0.18-0.70 mg/g respectively. While in mix solution, the values of Am for Pb ranging from 0.20-1.11 mg/g and Cu within 0.18-0.60 mg/g.
Kajian kandungan logam berat Cd, Co, Cr, Ni, Pb, dan Zn telah dilakukan ke atas tumbuhan Arundina graminifolia daripada kawasan Lombong Pelepah Kanan, Kota Tinggi, Johor. Kandungan logam berat yang sama turut ditentukan ke atas substrata tanih di tempat di mana tumbuhan itu diambil. Kandungan logam berat dalam tiga bahagian tumbuhan iaitu akar, batang dan daun telah diekstrak secara penghadaman basah manakala kandungan logam berat tersedia dan resistan dalam tanih diekstrak dengan kaedah pengekstrakan berjujukan. Kandungan logam berat jumlah didapati dengan menjumlahkan logam berat tersedia dengan logam berat resistant. Kandungan logam berat di dalam larutan ekstrak tanih dan tumbuhan ditentukan menggunakan Spektrofotometer Serapan Atom Nyalaan. Kandungan logam berat Cd, Cr, Ni dan Pb adalah setara kandungannya dalam semua bahagian tumbuhan manakala kepekatan Co dan Zn adalah tiga hingga lima kali lebih tinggi berbanding tumbuhan kawalan. Bagi kandungan logam berat di dalam bahagian tumbuhan yang berbeza didapati kepekatan Cd adalah lebih tinggi dalam akar (2.03 mg/kg) diikuti oleh daun (1.67 mg/kg) dan batang (1.49 mg/kg). Kepekatan Co adalah lebih tinggi dalam daun (9.26 mg/kg) diikuti oleh akar (9.18 mg/kg) dan batang (6.94 mg/kg). Kepekatan Cr mengikut susunan menurun adalah akar (0.46 mg/kg) > daun (0.19 mg/kg) > batang (0.08 mg/kg). Kepekatan Ni adalah lebih tinggi dalam daun (2.78 mg/kg) diikuti oleh akar (2.71 mg/kg) dan batang (1.66 mg/kg). Kepekatan Pb mengikut susunan menurun adalah akar (10.34 mg/kg) > daun (4.18 mg/kg) > batang (3.75 mg/kg). Kepekatan Zn lebih tinggi dalam daun (44.03 mg/kg) diikuti oleh akar (32.30 mg/kg) dan batang (13.21 mg/kg). Kandungan logam berat jumlah dalam tanih adalah masing-masing 2.07-5.59 mg/kg, 8.72-39.93 mg/kg, 1.81-2.14 mg/kg, 2.66-6.87 mg/kg, 23.02-51.56 mg/kg and 0.64-2.61 mg/kg bagi Ni, Zn, Cd, Pb, Co dan Cr. Didapati bahawa kandungan fraksi tersedia dalam tanih adalah 21.9% bagi Ni, 15.3% bagi Zn, 49.9% bagi Cd, 19.3% bagi Pb, 45.7% bagi Co and 0% bagi Cr. Koefisien penyerapan biologi tumbuhan ke atas logam berat yang dikaji adalah rendah keculai bagi Zn yang nilainya lebih daripada 1. Tumbuhan ini tidak sesuai digunakan sebagai agen fitoremediasi untuk logam-logam di atas.
Kajian ini dijalankan di kawasan tanih ultrabes di Felda Rokan Barat (FRB), Negeri Sembilan. Sebanyak dua puluh sampel cili, kunyit, pandan dan serai serta substratnya telah diambil secara rawak untuk penentuan kandungan logam berat Fe, Cd, Co, Cu, Mn, Ni, Pb, Cr dan Zn. Kandungan logam berat dalam tumbuhan diekstrak secara penghadaman basah, manakala kandungan logam berat resistan dan tersedia dalam tanih diekstrak dengan kaedah pengekstrakan berjujukan. Kandungan logam berat jumlah diperoleh dengan menjumlahkan kandungan logam berat rintang dan tersedia. Kandungan logam berat di dalam larutan ekstrak tanih dan tumbuhan ditentukan dengan menggunakan Spektrofotometer Penyerapan Atom Nyalaan (FAAS). Hasil kajian menunjukkan logam Fe adalah dominan di dalam tanih di kawasan kajian manakala kepekatan logam Cd paling rendah dengan nilai < 10 mg/kg. Sela kepekatan logam-logam berat dalam tanih ialah Fe (2618.4 hingga 4248 mg/kg), Mn (240.9 hingga 741.9 mg/kg), Zn (81.9 hingga 324.8 mg/kg), Cr (46.8 hingga 438.7 mg/kg), Cu (15.7 hingga 81.7 mg/kg), Pb (14.9 hingga 116.8 mg/kg), Ni (10.1 hingga 545.6 mg/kg), Cd (5.6 hingga 10.6 mg/kg) dan Co (0.8 hingga 126.1 mg/kg). Nilai kepekatan Fe tersedia mencatatkan nilai tertinggi bagi semua substrat tumbuhan, diikuti oleh Mn, Zn, Pb, Ni, Cr, Cu, Co dan Cd. Berdasarkan peratusan tersedia Mn, Pb dan Zn merupakan logam berat yang paling banyak tersedia diambil oleh tumbuhan dengan nilai 8 hingga 10%. Kepekatan Fe, Mn, Ni dan Zn menunjukkan purata kepekatan yang tinggi pada bahagian tumbuhan yang dikaji berbanding dengan logam lain. Nilai koefisien penyerapan biologi (BAC) bagi cili, kunyit, pandan dan serai masing-masing dalam julat 0.02-0.36, 0.03-0.41, 0.03-0.63 dan 0.03-1.15. Boleh disimpulkan bahawa penyerapan logam berat oleh tumbuhan adalah normal walaupun kepekatan logam berat dalam tanih ultrabes adalah tinggi.
The concentrations of the heavy metal in Pacific white shrimp (Litopenaeus vannamei) purchased from the local wet markets throughout the state of Selangor were investigated using flame atomic absorption spectrometry. The order of the heavy metal concentrations were Zn>Cu>Pb>Cd, whereby the metal concentrations in most samples exceeded the limits of the Malaysian Food Regulation, 1985 and the guidelines set by the Food and Agriculture Organisation (1983). A health risk analysis based on the mean target hazard quotient (THQ) yielded values <1 for all metals for average and maximal consumers. The total THQ (tTHQ) which measures the aggregated risk due to heavy metal uptake via the ingestion of L. vannamei was 0.124 and 0.372 for average and maximal consumers, respectively. This suggests that although the metal concentrations are exceeding the limit, there is no calculated significant risk from metal toxicity by the consumption of shrimp.
The concentrations of arsenic, cadmium, chromium, copper, mercury, nickel, lead and zinc in surface sediments collected from the east coast of peninsular Malaysia, along the South China Sea, were measured by two methods instrumental neutron activation analysis and inductively coupled plasma mass spectroscopy. The obtained results were use to determine the areal distribution of the metals of in the east coast of peninsular Malaysia and potential sources of these metals to this environment. The geochemical data propose that most of the metals found in the east coast of peninsular Malaysia constitute a redistribution of territorial materials within the ecosystem. Then, the metal concentrations can be considered to be present at natural background levels in surface sediments.
Waste plastics contain a substantial number of valuable chemicals. The wastes from post-consumer as well as from industrial production can be recycled to valuable chemical feedstock, which can be used in refineries and/or petrochemical industries. This chemical recycling process is an ideal approach in recycling the waste for a better environment. Polymer cracking using a laboratory fluidized bed reactor concentrated on the used highly contaminated catalyst, E-Cat 2. Even though E-Cat 2 had low activity due to fewer acid sites, the products yielded were similar with amorphous ASA and were far better than thermal cracking. The high levels of heavy metals, namely nickel and vanadium, deposited during their lifetime as an FCC catalyst, did not greatly affect on the catalyst activity. It was also shown that E-Cat 2 could be used with and without regeneration. Although there was more deactivation when there was no regeneration step, the yield of gases (C(2)-C(7)) remained fairly constant. For the first time, these results indicate that "waste" FCC catalyst (E-Cat) is a good candidate for future feedstock recycling of polymer waste. The major benefits of using E-Cat are a low market price, the ability to tolerate reuse and regeneration capacity.
Present study was conducted to evaluate current status of trace elements contamination in the surface sediments of the Johor Strait. Iron (2.54 +/- 1.24%) was found as the highest occurring element, followed by those of zinc (210.45 +/- 115.4 microg/g), copper (57.84 +/- 45.54 microg/g), chromium (55.50 +/- 31.24 microg/g), lead (52.52 +/- 28.41 microg/g), vanadium (47.76 +/- 25.76 microg/g), arsenic (27.30 +/- 17.11 microg/g), nickel (18.31 +/- 11.77 microg/g), cobalt (5.13 +/- 3.12 microg/g), uranium (4.72 +/- 2.52 microg/g), and cadmium (0.30 +/- 0.30 microg/g), respectively. Bioavailability of cobalt, nickel, copper, zinc, arsenic and cadmium were higher than 50% of total concentration. Vanadium, copper, zinc, arsenic and cadmium were found significantly different between the eastern and western part of the strait (p < 0.05). Combining with other factors, Johor Strait is suitable as a hotspot for trace elements contamination related studies.
This paper presents a preliminary result carried out in the Besut River basin, Terengganu, Malaysia to determine the selected trace metal concentrations. Concentrations of dissolved Pb, Cu, and Fe during the present study were in the range of 3.3-8.3 microg/L Pb, 0.1-0.3 microg/L Cu, and 1.1-12.3 microg/L Fe. For the particulate fraction concentrations of Pb, Cu, and Fe ranged from 1.0 to 3.6 microg/L, 0.3 to 2.8 microg/L, and 114 to 1,537 microg/L, respectively. The concentrations of metals in this study area, in general, were lower than those reported for other study areas. Higher metal concentrations measured in the wet monsoon season suggest that the input was mainly due to terrestrial runoff.
Concentrations of Cd, Cu, Pb, Zn, Ni and Fe were determined in the surface sediments to investigate the distributions, concentrations and the pollution status of heavy metals in Dumai coastal waters. Sediment samples from 23 stations, representing 5 different site groups of eastern, central and western Dumai and southern and northern Rupat Island, were collected in May 2005. The results showed that heavy metal concentrations (in microg/g dry weight; Fe in %) were 0.88 (0.46-1.89); 6.08 (1.61-13.84); 32.34 (14.63-84.90); 53.89 (31.49-87.11); 11.48 (7.26-19.97) and 3.01 (2.10-3.92) for Cd, Cu, Pb, Zn, Ni and Fe, respectively. Generally, metal concentrations in the coastal sediments near Dumai city center (eastern and central Dumai) which have more anthropogenic activities were higher than those at other stations. Average concentration of Cd in the eastern Dumai was slightly higher than effective range low (ERL) but still below effective range medium (ERM) value established by Long et al. (Environmental Management 19(1):81-97, 1995; Environmental Toxicology Chemistry 17(4):714-727, 1997). All other metals were still below ERL and ERM. Calculated enrichment factor (EF), especially for Cd and Pb, and the Pollution load index (PLI) value in the eastern Dumai were also higher than other sites. Cd showed higher EF when compared to other metals. Geo-accumulation indices (I(geo)) in most of the stations (all site groups) were categorized as class 1 (unpolluted to moderately polluted environment) and only Cd in Cargo Port was in class 2 (moderately polluted). Heavy metal concentrations found in the present study were comparable to other regions of the world and based on the calculated indices it can be classified as unpolluted to moderately polluted coastal environment.
The purpose of this paper are to determine the concentration of heavy metals namely cadmium (Cd), copper (Cu) and lead (Pb) in water and sediment; and to investigate the effect of sediment pH and sediment organic matter on concentration of cadmium, copper and lead in sediment at oxidation fraction. For this purpose the concentration of heavy metals were measured in water and sediments at 15 sites from Tasik Chini, Peninsular Malaysia. The sequential extraction procedure used in this study was based on defined fractions: exchangeable, acid reduction, oxidation, and residual. The concentration of heavy metals in residual fraction was higher than the other fractions. Among the non-residual fractions, the concentration of heavy metals in organic matter fraction was much higher than other fractions collected from all sampling sites. The pH of the sediment in all sites was acidic. The mean pH ranges from 4.8 to 5.5 with the higher value observed at site 15. Results of organic matter analysis showed that the percentage of organic matter present in sediment samples varies throughout the lake and all sites of sediments were relatively rich in organic matter ranging from 13.0% to 34.2%. The highest mean percentage of organic matter was measured at sampling site 15, with value of 31.78%.
Concentrations of heavy metals were determined in the water column (including the sea-surface microlayer, subsurface, mid-depth and bottom water) and sediments from Singapore's coastal environment. The concentration ranges for As, Cd, Cr, Cu, Ni, Pb and Zn in the seawater dissolved phase (DP) were 0.34-2.04, 0.013-0.109, 0.07-0.35, 0.23-1.16, 0.28-0.78, 0.009-0.062 and 0.97-3.66 microg L(-1) respectively. The ranges for Cd, Cr, Cu, Ni, Pb and Zn in the suspended particulate matter (SPM) were 0.16-0.73, 6.72-53.93, 12.87-118.29, 4.34-60.71, 1.10-6.08 and 43.09-370.49 microg g(-1), respectively. Heavy metal concentrations in sediments ranged between 0.054-0.217, 37.48-50.52, 6.30-21.01, 13.27-26.59, 24.14-37.28 and 48.20-62.36 microg g(-1) for Cd, Cr, Cu, Ni, Pb and Zn, respectively. The lowest concentrations of metals in the DP and SPM were most frequently found in the subsurface water while the highest concentrations were mostly observed in the SML and bottom water. Overall, heavy metals in both the dissolved and particulate fractions have depth profiles that show a decreasing trend of concentrations from the subsurface to the bottom water, indicating that the prevalence of metals is linked to the marine biological cycle. In comparison to data from Greece, Malaysia and USA, the levels of metals in the DP are considered to be low in Singapore. Higher concentrations of particulate metals were reported for the Northern Adriatic Sea and the Rhine/Meuse estuary in the Netherlands compared to values reported in this study. The marine sediments in Singapore are not heavily contaminated when compared to metal levels in marine sediments from other countries such as Thailand, Japan, Korea, Spain and China.