Response to stress of mussels (Mytilus edulis) exposed in Dutch tidal waters.

1. Mussels were exposed in the Dutch coastal zone and the Western Scheldt estuary. After six weeks of exposure, trace metals, PCBs and PAHs were measured in the soft tissue. 2. Tissue concentrations of contaminants are high in the Western Scheldt and intermediate near the Rhine outflow, except for the lower PCB congeners. 3. Results show that the survival in air is significantly lower at higher tissue concentrations, in particular of the lower PCB congeners. 4. The clearance rate is reduced at the highest tissue concentrations.     

Dissolved and particulate trace metal geochemistry in the scheldt estuary,S. W. Netherlands (water column and sediments)

The geochemistry of dissolved and particulate trace metals has been studied in the water column and the sediments of the Scheldt estuary between 1987 and 1990. A strong seasonal influence on the behaviour of dissolved Cd, Cu and Zn is observed, related to the redox conditions in the upper estuary and phytoplankton activity in the lower estuary (which are both seasonally dependent variables). The dissolved trace metal concentrations in the fresh water end-member are remarkably low during spring and summer, due to metal sulphide precipitation in the anoxic Scheldt river. However, the dissolved concentrations increase rapidly with increasing salinity, due to oxidation of metal sulphides that are present in the suspended matter, accompanied by (e.g. chloro-)complexation of the released metals. Readsorption of Cd and Zn occurs in the lower estuary during the spring phytoplankton bloom. During winter, when the Scheldt river is not completely anoxic, much higher dissolved trace metal concentrations are observed in the fresh water end-member since metal sulphide precipitation in the water column is precluded. Rapid trace metal removal is observed in the low salinity, high turbidity zone, due to adsorption onto suspended matter and freshly precipitated iron and manganese oxyhydroxides. Upon further mixing, desorption is apparent, due to a similar oxidation-complexation mechanism as observed during spring and summer. Pore water infusion may also contribute to the enrichment of dissolved Cd, Cu and Zn in the mid-estuarine region. The trace metal contents of the suspended matter and the sediments show a continuous decrease with increasing salinity. This behaviour is to a very large extent due to physical mixing of contaminated fluvial particulates and relatively unpolluted marine particulates. Desorption of Cd, Cu and Zn can be identified but is of minor importance compared to the conservative mixing process. The distribution of dissolved Cd, Cu and Zn in the pore waters of the mid-estuarine region reflects the impact of early diagenetic processes. Trace metal peaks are observed near the sediment-water interface, and at greater depth in the manganese and iron reduction zones. These peaks are attributed to oxidation of reduced trace metal compounds (e.g. sulphides) and reduction of the (iron and manganese) oxide carrier phases, respectively. At greater depth, the dissolved trace metal concentrations are much lower due to metal sulphide precipitation in the sulphate reduction zone. Analysis of a large sediment dataset indicates severe trace metal pollution of the Scheldt estuary at the end of the fifties. A major reduction of the pollution by As, Cr, Hg, Pb, and Zn has occurred in the seventies, and of Cd and Cu in the eighties. The Ni pollution has increased over the time period considered. In spite of this improvement, the present-day pollution status of the Scheldt estuary is still reason for concern.     

Modelling of water and sediment quality in the Scheldt estuary

In 1987 the Tidal Waters Division (Ministry of Transport, Public Works and Water Management, The Netherlands) initiated the SAWES project (Systems Analysis WEstern Scheldt). In the framework of this project, a water quality model for the Scheldt estuary was made. The model aims to establish the relation between pollution inputs and the concentration of pollutants in the abiotic compartments and to establish the fate of wasted substances. The model includes oxygen, nitrogen and trace metals. Due to the low oxygen content of the upper Scheldt estuary, a new model approach for trace metals had to be developed, taking into account precipitated metal sulphides. The calibration, verification and sensitivity analysis of the model provided a good understanding of the chemistry of the estuary. Afterwards the model was used to support policy making by computing how the water and sediment quality in the estuary respond to reduced inputs of waste.     

Temporal and spatial trends in heavy metal concentrations in the marine mussel Mytilus edulis from the Western Scheldt estuary (The Netherlands)

Since the first North Sea Conference (1984, Bremen), all countries bordering the North Sea made commitments to reduce discharge of hazardous substances into the North Sea. From Belgium and The Netherlands, large reductions (upto 90) in heavy metal emissions from land-based sources have been reported between 1985 and 2000. Recently, some studies in the Western Scheldt estuary (WS) have shown that total metal concentration in the water, sediments and suspended particles have decreased compared to levels in the 70s. However, data on aquatic organisms is still very limited and it is therefore difficult to confirm whether the reductions in pollution input and generally improving water quality in the WS have a corresponding impact on the levels of heavy metals in aquatic organisms. The current study measured metal concentrations in the soft tissues of mussels, Mytilus edulis (known to be good indicators of environmental metal pollution) during the period 1996–2002. Spatial (salinity and pollution gradients), temporal and seasonal variations were also studied. Results showed a down-stream decreasing trend for the metals studied (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) during all sampling campaigns. There was also a significant seasonal effect on tissue metal concentrations, with a peak observed around spring in both WS and the nearby less polluted Eastern Scheldt (ES). On temporal trends, a clear drop of metals in mussels was observed in the early 80s coinciding with the start of the efforts to reduce chemical pollution input into the North Sea. Since those early reductions, metal concentrations in mussels generally remained unchanged upto mid 90s. However, in recent times metal concentration in mussels have increased significantly, for example Cd in 2002 was almost 10 times the values in 1983 and similar to levels seen during the peak in the 70s. Other metals also increased in the 90s also reaching levels seen in the 70s. As there is no indication of recent increase in metal input into the estuary, we suggest that increased metal concentrations observed in mussels in recent years especially in the upper estuary are most likely a result of changes in physical and chemical speciation and metal bioavailability. Such changes may be caused by changes in some water quality parameters in the estuary (i.e. increased dissolved oxygen, concentration of organic matter), resulting in conditions that favour releases of sediment-bound metals into the water column. The relationship between metal content and season showed very similar annual profiles in the polluted WS and less polluted ES. Thus, seasonal variations in metal concentrations appear to be largely controlled by biological processes, while total body burdens are dependent on environmental levels and bioavailability.     

Water quality modelling of the western Scheldt estuary

In 1987 the National Institute for Coastal and Marine Management (theNetherlands) initiated the SAWES project (Systems Analysis WEstern Scheldt).The main goals of the project were to acquire knowledge with respect to thepollution problems in the Scheldt estuary and to apply this knowledge tomanagement issues of the Scheldt on an operational level. The main interestwas to understand quantitatively the relation between inputs of pollutingsubstances and effects on the ecosystem. In the framework of the project, awater quality model for the Scheldt estuary was made. In 1995, the modelarea was expanded to include the Belgian coastal region at the mouth of theestuary. The model calculates the fate of discharged substances andestablishes the relation between pollution inputs and the resulting waterquality, including general water quality (oxygen, pH, alkalinity, major ionchemistry and nutrients) as well as pollutant concentrations. The modelincorporates all chemical processes which affect these concentrations,including the precipitation/dissolution of metal sulphides which to a largeextent controls the fate of trace metals. Based on calibration andverification exercises, it has been shown that the model provides a goodrepresentation of the physical and chemical processes taking place withinthe estuary and can therefore be used to support policy development for theestuary. For example, the model can compute how the water and sedimentquality in the estuary will respond to reduced inputs of waste or to suchhuman activities as dredging. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new index for assessing heavy metals contamination in sediments: A case study

In this study, heavy metals contamination in surface sediments of northwest Persian Gulf was investigated and a new index was formulated for assessing severity of heavy metal pollution in aquatic environments. The surface sediment samples were collected from 45 stations. The concentrations of 8 metals (Fe, Cu, Zn, Cr, Ni, Pb, Cd and V) were analyzed. According to the results of potential ecological risk index (RI), pollution load index (PLI) and modified degree of contamination (mCD), based on the average shale, considerable and intense pollution of heavy metals in sediments of study area was not observed. Based on the sediments quality guidelines the concentration of Ni at whole study area has frequently adverse biological effect on aquatic organisms. The mean effects range-median quotient indicated that surface sediments in the vicinity of petrochemical zone and Bahrekan pier with 49% probability of toxicity can be risky for the biota. The Consequence of the cluster analysis and principal component analysis/factor analysis indicated that Fe, Cu, Zn and Cr are mainly originated from natural sources and Ni, Pb, Cd and V are mostly derived from anthropogenic sources. Results of introduced index in this research (Contamination Severity Index) demonstrated that pollution of heavy metals in sediments at several sites is very intense. Assessment of results illustrated that proposed index is more reliable and logical compared with other investigated indices for evaluating heavy metals pollution in sediments of aquatic environments.     

Behaviour of selected PCBs,PAHs and γ-HCH in the Scheldt estuary,S.W. Netherlands

The behaviour of some organic micropollutants in the abiotic compartments water, particulate matter and bottom sediments of the Scheldt estuary, S.W. Netherlands, was studied between 1986 and 1989. Special attention was given to two individual PolyChlorinated Biphenyl congeners (PCB 52 and PCB 153), two Polycyclic Aromatic Hydrocarbons (PAHs) fluoranthene and benzo(a)pyrene and γ-HCH. Dissolved PCBs and γ-HCH behave conservatively during estuarine mixing. The concentration of γ-HCH in the fresh-water is extremely high in spring compared to the other seasons. Dissolved fluoranthene does not behave conservatively. The concentration of dissolved fluoranthene in the freshwater endmember shows a seasonal dependence with highest concentrations in winter and lowest in summer. Benzo(a)pyrene could hardly be detected in the dissolved phase with the methods used. PCBs and PAHs in particulate matter and sediments behave essentially conservatively as a result of the mixing of riverine particulates with high, and marine particulates with low organic micropollutant contents. Particulate fluoranthene is removed at low salinities under (nearly) anoxic conditions probably by microbial degradation. The rivers Scheldt and Rupel appear to be the major sources for the compounds studied. However, in particular the organic micropollutant contents of the sediments indicate that important emissions along the estuary were or are still present. Measurements of individual PCBs and PAHs in the <63 μm fraction of a dated sediment core from a salt marsh in the eastern part of the Scheldt estuary show that the recent input of PCBs and PAHs into the estuaryis probably 2–3 times lower than the maximum input in the mid-1960s. The PCB profile shows postdepositional congener-selective mobilization caused by advective transport. The PAH assemblage is remarkably uniform in the sediment core. The PAH ratios indicate that combustion of coal is the main source of PAHs in the Scheldt estuary.     

Contamination and environmental risk assessment of heavy metals in marine sediments from Tahaddart estuary (NW of Morocco)

Abstract

The distribution, contamination status, and ecological risks of heavy metals in Tahaddart estuary were investigated. 24 surface sediment samples and two cores were collected and analyzed for major (Al and Fe), heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn), and grain size composition. The heavy metals assessment was carried out using different environmental indices. The results indicated that the spatial distribution patterns of Al, Fe, and Zn were mainly determined by the distribution of the finer grained fraction (<63?μm) in the sediment. In contrast, As, Cd, Cr, Cu, Ni, and Pb concentrations were controlled by anthropogenic activities (vehicular traffic from Highway Bridge and thermal power plant). The distribution of heavy metals in sediment cores showed an upward enrichment in heavy metals with high concentration found in the uppermost may related to the increasing in human activities. The pollution indexes confirmed that the Tahaddart estuary sediment was considerably to high contaminated by heavy metals near to different anthropogenic inputs. Similarly, the potential ecological risk index and the biological risk index present 21% probability of toxicity posing potential risk to the aquatic organisms. These results provide basic information that can be used to protect and improve the quality of this ecosystem.     

Overview of trace metal contamination in the Scheldt estuary and effect of regulatory measures

Seasonally, dissolved and particulate metal concentrations in the Scheldt estuary were assessed over a period of 4 years (1995–1998). High quality data were obtained following stringent analytical protocols for each step: sampling, sample treatment, sample storage and analysis. Of the 5 trace metals, Ni showed the most conservative behaviour, while Cd and Cu were clearly transferred from the particulate to the dissolved phase in the middle estuary. A substantial part of the particulate metals entering the estuarine system are lost through sedimentation. General seasonal patterns are the following: lower concentrations in spring and higher ones in winter (sometimes late fall/early winter) for dissolved metals, while in summer a pronounced rise of the longitudinal concentration profile is observed for the particulate metals. A comparison of the trace metal concentrations (dissolved and particulate) at the mouth of the estuary in 1995–1998 with those from 1981 to 1983, reveal reductions between 30 and 58%. Reductions based on direct emission measurements for almost the same period suggest reductions (dissolved + particulate) between 42 and 64%. Biomagnification (BMF) is the accumulation of a compound through the food-chain. It is in our case expressed as the ratio of the metal concentration in the organism (g g^–1, d.w.)/the metal concentration in total suspended matter (g g^–1, d.w.). Almost all BMF-values of Periwinkle, Nereis diversicolor and Macoma balthica (3 bottom organisms in the Scheldt estuary) are negative meaning that these organisms contain less heavy metals than the particulate suspended matter. For all organisms log BMFs for Pb, respectively Ni, are around –1.8, respectively –0.7. For Cd, Periwinkle shows slight enrichment (0.05) and for Cu even more (0.45), while negative values were observed for Nereis diversicolour and Macoma balthica. The latter organisms are more enriched in Zn (–0.09) than Periwinkle (–0.43).     

Determination of water quality,and trace metals in endemic Sarotherodon linellii,Pungu maclareni and Clarias maclareni,in crater Lake Barombi Mbo,Cameroon

Considering water pollution as a potential threat to some endemic cichlids of Lake Barombi Mbo, Cameroon, an investigation was done in 2011 to determine trace metals in its water, linking their uptake in gills and liver of fish to water chemistry. ICP-MS and ICP-OES analyses of trace metals based on total concentration of unfiltered lake water samples showed the presence of trace metals. All fish species accumulated Al, Mn and Sr in the highest concentrations in their gills, with Cu, Cd, Co, Cr, Pb and U highest in the liver. Pungu maclareni accumulated Al, Cr, Co, Sr and Pb in the highest concentrations. The highest mean gill Al concentration of 140 µg g^?1 dry weight was measured in P. maclareni gills, this being one of the critically endangered cichlids of the lake. Stable isotope analyses of carbon δ¹³C and nitrogen δ¹⁵N showed that P. maclareni had the highest mean δ¹³C (?30.2‰) and highest concentrations of Cr, Co, Pb and U in liver, probably linking the carbon source to the accumulation of metals. Though trace metal levels in the lake water were low, their presence in fish tissues suggest they are bioavailable, bioaccumulate and may pose a threat to the aquatic biota, and therefore should be monitored.     

Environmental Risks of Inorganic Metals and Metalloids: A Continuing,Evolving Scientific Odyssey

Ecological risk assessment (ERA) of metals, metalloids, and inorganic metal substances (collectively referred to as metals) no longer focuses solely on persistence and bioaccumulation, but rather on solubility, toxicity, natural occurrence (concentrations above/added to background), essentiality (deficiency as well as excess), speciation, and bioavailability. Tolerance (both acclimation and adaptation) and possible resultant energetic costs are being considered, and realism is being increased in laboratory toxicity tests by the use of organisms pre-acclimated to natural levels of metals. The present status of ERAs for inorganic metals is summarized in terms of four key questions: (1) Do metals accumulate in biota above background levels? (2) Are these metals metabolically active? (3) If so, are they likely to result in adverse effects to individuals either alone or in combination with other stressors? (4) If so, are they likely to result in adverse impacts to populations? The most pragmatically useful future research will be that focused on the interactive risks of both complex chemical mixtures (metals and non-metals) and non-chemical stressors (both biotic and abiotic). Ideally this should occur in the context of continued metal loadings to terrestrial and aquatic ecosystems assessed holistically, including trophic food web relationships, metal transfer, and genetic diversity. Relationships between environmental concentrations and internal, metabolically active doses are the key to understanding and predicting environmental risks without excessive reliance on safety factors.     

Geochemical composition of sediments in the Scheldt estuary with emphasis on trace metals

Superficial sediments of the Scheldt estuary were collected with a Van Veen grab at 57 stations between Temse and Vlissingen. They were analysed for major elements (Si, Al, Fe, Ca, Mg, Na, K, Cinorg and Corg) and trace metals (Cd, Pb, Cu, Zn, Cr, Ni, Co, Mn and Li). Factor analysis indicates that 44% of the variance can be explained by one factor which exhibits a high saturation for trace metals, organic matter, Al and Fe, all variables typical of fine mud. The high scores of this first factor are almost exclusively present in the upper estuary except for one area in front of Terneuzen. The second factor, which explains 23% of the variance, is typical of the carbonates and the third one (19% of the variance) is representative of the clay minerals. These two factors are more evenly distributed over the estuary. As usual, a strong influence of granulometry on the distribution of trace elements in the sediments was observed. Intercomparison of their composition within the Scheldt or with those of other aquatic systems requires thus a normalization procedure. This problem has been studied in detail by analysing various size fractions (63–16, 16–8, 8–4, <4 m) obtained by elutriation of the sample or by using a parameter characteristic of the fine fraction such as the concentration of a typical element (Al, Fe, Li, Corg). The normalization of trace metals allowed us to evaluate an enrichment factor of the trace elements in the estuarine deposits due to mans activities. In addition, it demonstrates the decrease of the anthropogenic impact on the composition of sediments by comparing the composition of sediments collected in 1976 and in 1994.     

Average annual growth and condition of mussels as a function of food source

Prior to 1986, before completion of a storm surge barrier, the average annual condition of mussels at culture plots in the Eastern Scheldt was better in the western part near the North Sea, than in the central part of the estuary. No such difference was observed in 1986 and 1987.To predict the effects of the barrier on mussel culture, the condition of the mussels, which is an index of growth rate, is analysed and correlated with food sources for the period 1981–84. In the western and central part of the Eastern Scheldt, mussel condition correlates strongly with average annual primary production, but not with chlorophyll-a concentrations. This suggests a direct link between primary production and the growth of mussels.In the western part of the estuary, the relation between condition and primary production has a less steep slope than in the central part. Import of food from the North Sea is suggested to act as an additional food source in the west of the Eastern Scheldt; hence the better condition values of the mussels, also in years with relatively low primary production.The storm surge barrier reduces the water exchange with the North Sea. Reduced import of food and consequently lower mussel condition are expected in the western part of the estuary. Preliminary data from 1987 confirm this prediction.     

Importance of Clean Techniques and Speciation in Assessing Water Quality for Metals

Trace metals in aquatic and soil systems exist in a number of different soluble and particulate forms that impact the effect of the metals on these ecosystems. Appropriate methods of sampling and analysis are required to accurately determine the low concentrations present. Although assessment of metals in many regulatory programs is based on data for total metal concentrations, such values rarely correlate with effects. Consequently, other means are needed for the prediction of risk. Bioavailability of metals depends on their speciation, whose importance was first established for copper in aquatic systems where the toxicity of metals is related to the activity of the free metal ion. Small concentrations of natural organic matter strongly complex metals ameliorating toxicity. Several electroanalytical techniques are available that allow the assessment of metal species. Recently, a modeling approach, the Biotic Ligand Model (BLM), has been applied to the prediction of acute toxicity. The model accounts for the effects of natural organic matter, pH, and hardness and is able to predict toxicity over several orders of magnitude of soluble metal concentration using only easily determined site parameters. Total metal concentrations in sediment cover several orders of magnitude with no distinction of sediments that cause effects and those that do not except at low total metal concentrations. Relating the metal concentration to the concentrations of sulfide and organic matter binding sites enables the sediments containing higher concentrations of metals to be divided into those that do and those that do not have adverse effects. It is essential that metal speciation be considered to realistically evaluate the potential of metals to pose risk.     

A cohesive sediment balance for the Scheldt estuary

This article present a method to generate a cohesive sediment balance for the Scheldt estuary (The Netherlands and Belgium). In this balance the net transports have been determined on a regional scale. The complicated circulation patterns on a smaller scale are considered as a black box. The cohesive sediments in the balance are defined as the inorganic sediment with a particle size smaller than 63 μm. In the balance a distinction is made between the relatively ‘clean’ marine mud fraction and the more polluted fluvial fraction. The calculations are made on a basis of field data. The field data of the morphological changes in the estuary are based on the period of 1975–1985. The net natural transport of fluvial mud is estimated to reach beyond the mouth of the estuary. The net marine import of mud is estimated to reach beyond the brackish part of the estuary, located in Belgium. The sediment balance also provides the time scale for the response of an estuary. The time scale related to the reduction in pollution proves to be quite large. Calculations with a simple analytic model with typical values for the Scheldt estuary indicate that several decades will pass until a significant improvement in bottom sediment quality is reached even after a 100% reduction of the loading of pollutants. The presented balance is not the final answer. Improvements can be achieved by more accurate field data, smaller morphological units and verification by other methods (cf. tracer methods, mathematical models).     

A box-model of metal flows through the Scheldt estuary (1981–1983 and 1992–1995)

The behaviour of Cu, Zn, Cd and Pb in the Scheldtestuary was investigated in the periods 1981 to 1983and 1995. The Hg behaviour was studied between 1992and 1994. A box model was used to establish therelationship between the trace metal inputs and thefate of these pollutants in the Scheldt estuary.Annual budgets were calculated for particulate anddissolved trace metals. For Hg, seasonal budgets ofthe various species (inorganic Hg, methylmercury,Hg °) could also be calculated. These budgetsallow an evaluation of the consistency of eachindividual flux or process, such as the inputs of thevarious metals into the North Sea, the sedimentationflux of particulate metals in the area of highturbidity, the evasional fluxes and the formationrates of Hg °, etc. in relation to the other ones. This revised version was published online in July 2006 with corrections to the Cover Date.     

Elemental composition of seston and nutrient dynamics in the Sea of Marmara

The Sea of Marmara, an intercontinental basin with shallow and narrowstraits, connects the Black and Mediterranean Seas. Data obtained during1991–1996 have permitted the determination of the elementalcomposition of seston in the euphotic zone and the N:P ratio of thesubhalocline waters of the Marmara Sea. Since primary production is alwayslimited to the less saline upper layer (15–20 m), of the Marmara Sea,the subhalocline waters of Mediteranean origin are always rich in nutrients(NO₃ + NO₂ = 8–10 μm, PO₄ = 0.8–1.2 μm) but depleted in dissolvedoxygen (30–50 μm) throughout the basin, yielding an -O_{_2} : N : P ratio of 178 : 9 : 1. Pollution of the surfacewaters since the 60s has modified the subhalocline nutrient chemistryslightly. In the euphotic zone, the N : P ratio of the seston changes from5.9 to 9.5 between the less and more productive periods. Though the biologyof the Marmara has changed significantly during the previous two decades,the close relationship observed between the elemental composition of thesurface seston and the NO₃ : PO₄ ratio of thesubhalocline waters strongly suggests that during the whole year primaryproduction throughout the basin and POM export to the lower layer remainnitrogen-limited. This suggestion needs to be confirmed by bio-assays,biological studies and sediment trap data from the upper subhaloclinedepths. Nonetheless, the counterflows in the Marmara basin possessrelatively low N : P ratios in both dissolved and particulate nutrients andextend as far as the adjacent seas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding birds from reedbeds to alpine meadows

The main processes that determine the behaviour ofheavy metals in the Scheldt estuary are tidalhydrodynamics, sediment transport, and sorption ofheavy metals on suspended matter. The water qualitymodel WASP is applied to simulate the spatialdistribution of five heavy metals in the estuary,under average hydrodynamic and suspended sedimenttransport regimes. First, the hydrodynamical part ofthe model is constructed and the results are verifiedby comparison with measured water levels and flowvelocities. Secondly, a salt transport model is set upin order to evaluate the hydrodynamical dispersivemixing characteristics. Thirdly, a suspended sedimenttransport model is constructed and finally a transportmodel for heavy metals. The simulated distributions of the sorbedamounts of heavy metals, suspended sediment andsalinity in the estuary agree well with observations.The calculated profiles of dissolved and sorbedconcentrations of heavy metals in the water columnindicate an accumulation of heavy metals in the zoneof the turbidity maximum, while closer to the sea theconcentrations diminish due to mixing of the pollutedfluvial sediments with unpolluted marine sediments andbecause of sediment deposition in the estuary. It canbe concluded that only a small part of the heavymetals reaches the sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

汕头湾表层沉积物重金属污染与潜在生态风险评价

汕头湾作为华南地区重要的出海门户,汕头市主要的旅游区和水产养殖基地,其环境污染问题已成为制约当地经济发展的重要因素,为此2002年在此开展了重大科技术兴海项目,以海洋沉积物质量标准、单因子污染指数和潜在生态风险评价体系对汕头湾表层沉积物重金属污染现状和潜在生态风险进行了评价。结果表明:汕头湾表层沉积物中Cd,Cu,Pb,Zn的平均含量超过海沉积物质量标准(Ⅰ类);以单因子污染指数评价,Cd达到很强污染等级,Zn为强污染,Cu,Ni,Pb为中等污染;以单元素生态系数(E_rⁱ)评价,只有Cd的潜在生态风险达到很强等级,其它元素则只属于轻微潜在风险范畴;以多元素潜在生态风险指数(RI)评价,汕头湾的潜在生态风险水平处于中等强度;重金属含量分布特征与重金属污染及潜在生态风险的空间差异性一致,表现为由上游至下游呈波状递减趋势,其中以牛田洋和汕头港上游最为严重;这一污染特征主要是由集水区域内的产业结构特点、河流入海口及排污口的分布以及汕头湾的地理和水文特性所决定的。