The objective of this paper was to review the status of the Malaysian aquatic environment with respect to heavy metals. Much of the work on metals focused on measurements in biota and sediments, but very little research has been done on dissolved and particulate metals in water, metal speciation in sediments or on the bioavailability of metals. Cadmium (Cd), Copper (Cu), Lead (Pb) and Zinc (Zn) received much attention but due to technical difficulties, Arsenic, (As), Mercury (Hg), Tin (Sn) and other hydride elements have not been well studied.
The sources of metal pollution come from manufacturing, agriculture, sewage and motor vehicle emissions. The few reliable studies on metals in water indicate that some rivers were contaminated with Pb, Cu and Zn. Measurements in fish, bivalves and shrimp indicate no contamination of these resources by metals. However contamination by Cd and Pb was noted in some littoral shore molluscs such as Thais sp. as well as rock oysters (Saccostrea sp.) which may be due to non-anthropogenic sources.
Sediments of the Juru and Langat rivers are contaminated by Pb and Zn, while the Langat River was heavily contaminated by Cd. The concentrations of Zn and Pb in coastal sediments off Juru in Penang, and in the Johor Strait were two and three times higher than global shale values. The source of Pb pollution was thought to be derived from the use of leaded petrol. Metal levels in sediments of the Malacca Strait and the South China Sea were generally similar to global shale values.
Information on the levels of heavy metals in the Malaysian aquatic environment is scarce and limited to a few studies. Most of the coastal resources, agriculture and economic activities and human population, are concentrated on the west coast of Peninsular Malaysia, and as such most of the studies on heavy metals have been focused in this area (Abdullah et al., 1999). The Straits of Malacca on the west coast is a major international shipping lane and the related maritime activities may also contribute to the pollution of the marine environment of Malaysia. Oil and gas-related industries are developing rapidly along the east coast of Malaysia with most of the development located in the states of Pahang and Terengganu.
The objective of this paper is to describe the status of pollution in the Malaysian aquatic environment with regards to metals. Emphasis has been placed on reliable analytical data rather than report based studies where analytical methods have not been described in detail. Only sources with reliable data were used for this review. The criteria for acceptance were good spike recoveries of metals analysed, or good recoveries of standard reference materials used during metal analysis.
Sources of metals in the aquatic environment of Malaysia
The manufacturing sector is regarded as the major contributor of metal pollution in the environment. Of this, metal finishing processes such as electroplating, etching, and preparation of metal components for various industries, have been identified as a major source of wastes containing high concentrations of Cd, Cu, Zn, Nickel (Ni), Iron (Fe), Aluminum (Al), Zn, Manganese (Mn), Chromium (Cr) and Sn (Rahman and Surif, 1993). The electronic and semiconductor industries in several states of peninsular Malaysia contributed more than 69,000 m3 per annum of sludge containing heavy metals in 1992 (Hamid and Sidhu, 1993). The agricultural sector also contributes some wastes containing metals; for example, Cu from piggery wastes has been correlated to contamination of sediments and molluscs (Ismail and Rosniza, 1997). In the Malacca Strait, port and shipping activities contribute to pollution by tributyltin (TBT) as well as Pb, Cu and As (Abdullah et al., 1999). Mining of tin, iron, copper and gold (Yusof et al., 2001), may further contribute to contamination of waters by some metals, although not much work has been done in this respect.
Most of the manufacturing industries are located in the west coast of peninsular Malaysia and thus most of the studies on metal contamination have been focused there. Only a small number of studies have provided data for the east coast.
Heavy metals in sediments
The concentrations of heavy metals in sediment from the coastal and offshore waters of peninsular Malaysia have been extensively studied, while a small number of studies have provided some data for East Malaysia (Table 1). The rivers of peninsular Malaysia in areas with heavy industries and large human populations have also been studied.
The sediments of rivers receiving extensive pollution from industry, sewage and runoff in highly populated areas have been found to be polluted with Pb, Zn and Cu. Lead concentrations in the Juru River in Penang were up to 117 μ g g−1 dry wt. while Cu was up to 144 μg g−1 and Zn 483 μg g−1 dry wt. (Lim and Kiu, 1995). These metals came primarily from a sewage treatment plant that emptied into the river. Sequential analysis has been useful in identifying sediments that are anthropogenically contaminated. Lim and Kiu (1995) showed that non-residual Zn at one particular sampling point in the river accounted for > 80% while the proportions of non-residual Cu, Pb, Mn and Fe were also relatively high. The main pollution source was identified as the sewage treatment plant.
The Langat River in Negeri Sembilan was heavily polluted with Zn and Cd, with levels of 71–374 μ g g−1 dry wt. and 3.0–37.9 μg g−1 dry wt., respectively (Sarmani, 1989). In comparison with natural average global shale values (Mason and Moore, 1982), Pb in Juru River was about five times higher than natural values (20 μg g−1), while Cu was two times higher (shale value of 45 μ g g−1) and Zn was four times higher (shale value of 95 μg g−1). Natural Cd levels in shale were 0.3 μg g−1 and thus the Langat River was highly contaminated with Cd.
In marine sediments from the coastal environment of peninsular Malaysia, concentrations of Pb indicate some enrichment above the natural global value (in shale) in the coast of Kemaman (Ahmad, 1996), Tanjung Karang and off Juru, Penang (Wood et al., 1993). In the Johor Strait between Malaysia and Singapore (Wood et al., 1997) Pb and Zn were higher than global shale values, by a factor of three and two times respectively, at sampling sites closest to the causeway linking Malaysia and Singapore, which receives very high vehicle traffic. The Pb enrichment was probably due to the use of leaded petrol and Zn from tire wear (Wood et al., 1997).
The concentrations of most of the metals studied in coastal and offshore sediments of the Malacca Strait and of the South China Sea off peninsular Malaysia and East Malaysia were similar to global shale values and can be regarded as baseline values (Shazili et al., 1989, 1999a, 1999b; Mohamed and Shazili, 1998; Ahmad, 1996; Kamaruzzaman et al., 2002). Normalization of metal concentrations to Al have frequently been used to differentiate between anthropogenic enrichment and natural metal values (Din 1992; Wood et al., 1997; Shazili et al., 1999a, 1999b) and the use of this method showed that Zn was higher than the global shale value, while those of Cu, Cr and Ni in the South China Sea sediments were lower. Elevated levels of metals in coastal sediments may be attributed to anthropogenic input. When values are higher than global shale values in sediments from regions of the South China Sea far from the mainland (Shazili et al., 1999a, 1999b), it may be due to sediment grain size, mineralogy and organic matter content (Calvert et al., 1993).
Metal concentrations in water
Published data on trace metal concentrations in rivers and marine environments of Malaysia are especially scarce due to the difficulty of measuring the metals at the sub-ppb levels. Data from metals requiring hydride generation in their analysis such as Hg and As are scarce. The Department of Environment, Malaysia carries out regular monitoring of the water quality of rivers, but reliability of the data has not been reported. The few reliable studies on metal concentrations in rivers (Table 2) indicate that these rivers were possibly contaminated with Pb, Cu and Zn, although the values were still within the safe limits for drinking water.
Metal concentrations in biota
Unlike other environmental media, the use of biomonitors to study heavy metal pollution in the Malaysian environment has received widespread attention. Bivalves (Perna viridis and Saccostrea sp.) and gastropods (Thais sp.) were frequently used while fish were used mainly in relation to health concerns as a result of fish consumption rather than as indicators of heavy metal contamination. In these studies, Cd, Cu, Pb and Zn have received attention. However, due to difficulty in analysis, As, Hg, Sn and other hydride elements have received little attention.
The only reported data on metals in seaweeds were by Omar and Jemani (2000) and Ramachandran et al. (1994), but these have not been included in this review as standard reference materials or spikes were not used in their studies. For the same reason, data reported by Law and Singh (1986) for metals in fish from the Kelang River estuary, considered a major river receiving effluent from the major cities of Selangor State, has been rejected.
The results of measurements in fish, bivalves and shrimp (Table 3) indicated that there was very little cause for concern with respect to contamination by heavy metals. The levels of various metals were well within the safe limits set by the Malaysian Food Act of 1983. However, in gastropods such as the predatory Thais sp., levels of Pb and Cd were elevated as a result of transfer from the rock oysters (Saccostrea sp.) on which they feed (Shazili et al., 1995). In addition, Cd was elevated in rock oysters from some east coast locations and may not necessarily be due to metal pollution since some of the sampling sites were away from known sources of pollution. Thus natural levels may be above normally accepted “baseline” values.
Bioavailability and bioaccumulation studies of metals
Reports on the assessment of bioavailability of metals for bioaccumulation by aquatic organisms are very scarce. Bioavailability of metals may be estimated from reports where data for both water and specific biota is available. Bio-concentration factors of 132–12900(×103), 580–76000 and 481–17200 were estimated for Cu, Pb and Cr respectively, in rock oysters from Kalong Bay, Kemaman (Shazili et al., 1995). Lim et al. (1998) reported BCF values of 0.9 × 10−3 to 1.9 × 10−3 for Pb, 8.0 × 10−3 for Cu and 2.6 × 10−3 to 3.3 × 10−3 for Cd for the oyster Crassostrea belcheri and similar values for C. iredalei cultured for 9 months in the Merbok Estuary. Yap et al. (2002) studied metal speciation in sediments from the west coast of peninsular Malaysia and found significant correlations of Cd and Cu in the green-lipped mussel, Perna viridis with the ‘easily, freely leachable and exchangeable’ fractions in sediment. However their data were based on a small number of ten samples and P. viridis is normally found attached to substrates in the water column rather than on the sediment.
Studies on the fate and effect of metals in the freshwater and marine environments have unfortunately received no attention and thus need to be given attention in future in order to relate environmental levels with possible adverse effects on aquatic organisms. Toxicity tests with metals relating bioaccumulation and mortality of test organisms with metal speciation is limited to investigating effects of metal concentrations to lethal toxicity and few in relation to environmental parameters such as salinity (Shazili, 1995), water hardness, pH or temperature.
Industrial wastes were estimated to be more than 247,000 m3 in 1992 for all categories of scheduled wastes (Hamid and Sidhu, 1993) of which more than 71, 000 m3 may contain heavy metals. There is adequate legislation in place for the control of pollution of the aquatic environment in the form of the Environmental Quality (Sewage and Industrial Effluents) Regulations of 1979 and the Environmental Quality (Scheduled Wastes) Act of 1989 (Jaafar, 1991). There is a need to ensure that smaller manufacturing and waste generating industries are more compliant with these environmental acts and that there is better control of pollution from sewage (Jaafar, 1991). The gradual replacement of leaded petrol with unleaded petrol will also result in a decrease in environmental Pb contamination.
Prospects for the future
Although studies on Cd, Cu, Pb and Zn are already carried out in water, biota and sediments, reliable data are still lacking for elements such as Hg, As, Sn, Cr and others. There is a need to produce data for these elements due to their high bioavailability and potential toxicity. Although publications were available for all these metals, they have been left out of this study because the reliability of the data was not been tested against metal spikes or standard reference materials (SRMs). Recent studies in Malaysia have begun to include SRMs in their analytical methods for the analysis of metals and organic pollutants in various environmental media.
Aspects of metal toxicology in relation to speciation of metals in various environmental media, bioaccumulation and biomagnificaton have not been well studied due to the lack of scientists trained in ecotoxicology.
The results of the studies reviewed here showed that there was contamination by Pb and Zn in the sediments of coastal environments that receive wastes from areas of high human activities such as the Juru and the Johor Strait. The water of some rivers near major cities and townships, such as the Juru and Langat Rivers, were also contaminated. However fish have been shown not to be contaminated while some bivalves and seaweeds may have elevated levels of Pb and Zn. Thus Pb and Zn may be of primary concern in future environmental monitoring. As the hydride generation metals have not been extensively studied, the true extent of contamination by these metals has yet to be ascertained and thus should be given priority in future studies.