Distribution and behavior of trace metals in the sediment and porewater of a tropical coastal wetland

Vertical profiles (0-30 cm below surface) of four trace metals-Cadmium (Cd), Chromium (Cr), Lead (Pb) and Zinc (Zn)-in the sediment and sediment porewater of an ecologically important intertidal mudflat in the Mai Po and Inner Deep Bay Ramsar Site were thoroughly studied over a period of 10 months (from March 1999 to January 2000). Two surveys, one in summer and another in winter, involving a total of eight sampling stations were conducted to study the seasonal variation of the remobilization characteristics of these trace metals in the mudflat sediment. The range of depth averaged concentration of these trace metals in the mudflat sediment was: 0.3-0.8 microg/g (Cd); 9.8-91.0 microg/g (Cr); 7.3-69.1 microg/g (Pb); and 39.5-192.0 microg/g (Zn), while that in the sediment porewater was: 0.3-121.1 microg/l (Cd); 3.0-2704.1 microg/l (Cr); 2.6-105.6 microg/l (Pb); and 32.6-4238.3 microg/l (Zn). In general, levels of dissolved trace metals in the sediment porewater were much higher in the summer than in the winter while their concentrations in the sediment were more or less the same throughout the year. Enrichment of Cd, Pb and Zn in the sediment porewater of the upper oxic layer and that of Cr in the oxic-sub-oxic boundary was generally observed. Regions in the vicinity of the Mai Po mangroves and the river mouths of Shenzhen River and Shan Pui River were found to be hotspots of trace metal pollution. Benthic diffusive fluxes of trace metals from the mudflat sediment were also estimated. Of the four trace metals, cadmium showed the greatest tendency toward remobilization from the sediment phase to the more bio-available porewater phase.     

Heavy metal pollution status in surface sediments of the coastal Bohai Bay

Bohai Bay, the second largest bay of Bohai Sea, largely due to the huge amount of pollutants discharged into it annually and its geohydrologic condition, is considered to be one of the most polluted marine areas in China. To slow down, halt and finally reverse the environmental deterioration of Bohai Sea, some researchers have proposed to connect it with Jiaozhou Bay in the western coast of Southern Yellow Sea by digging an interbasin canal through Shandong Peninsula. In order to assess the heavy metal pollution and provide background information for such a large geoengineering scheme, surface sediments from 42 stations covering both riverine and marine regions of the northwestern coast of Bohai Bay were analyzed for heavy metal content and fractionation (Cd, Cr, Cu, Ni, Pb and Zn). Three empirically derived sediment quality guidelines were used to assess the pollution extent of these metals. The studied metals had low mobility except for Cd at all stations and Zn at some riverine stations. Although a high mobility of Cd was observed, it could hardly cause a bad effect on the environment owing to its low total concentrations. Anthropogenic influence on the accumulation of studied heavy metals in sediments of Bohai Bay was obvious, but their contents were relatively lower to date comparing with some other marine coastal areas that receive important anthropogenic inputs. Taking as a whole, surface sediments of northwestern Bohai Bay had a 21% probability of toxicity based on the mean effects range-median quotient.     

Heavy metal pollution in the Chao Phraya River estuary, Thailand

A study on heavy metal pollution in the Chao Phraya River estuary indicated that the accumulation of Cd, Cu, Cr and Pb in water in the river mouth vicinity was significant, which may have a long term impact on the aquatic environment through precipitation of heavy metals to the bottom sediments and bio-accumulation and bio-magnification of heavy metals in various food chains. Although the seasonal and spatial variations of heavy metals in the sediments and fish did not conform to a definite pattern, the heavy metal contents of samples were higher than those previously reported in the area and in some cases were higher than the mean world concentrations. Thus, Thai people may ingest Hg and Pb in fish in the Chao Phraya River estuary at quantities more than those reported for other countries.     

北京平谷西部矿集区附近土壤重金属特征

文章以平谷西部金属矿山及矿集区为研究区,采集土壤样品169个,开展区域土壤的重金属污染研究。采用X荧光光谱法、等离子原子发射光谱法等现代测试技术,分析了土壤中重金属(As、Hg、Cd、Cr、Zn、Cu、Pb、Ni)的含量;采用ArcGIS反距离权重插值数学模型和SPSS多元统计方法对土壤重金属空间分布及污染特征进行综合研究;运用潜在生态危害指数法进行生态风险评价。结果表明,研究区域土壤中重金属含量与背景值倍数大小依次是CdPbAsZnCuHgNiCr;重金属危害程度由大到小依次为CdAsPbHgCuNiZnCr;8种重金属潜在生态危害指数RI值在52.11～32 875.38之间。综上所述,研究区域的土壤重金属存在不同程度的风险。     

Mobilization of heavy metals from Le An River sediment

The release of sediment-bound heavy metals can have a significant influence on river water quality. Generally speaking, variations of pH and oxygen are among the most important chemical factors that affect the mobility of sediment-bound metals. Recent research has indicated that sulfide, measured as acid-volatile sulfide (AVS), is an important partitioning component of heavy metals. We determined the metal release potential of sediments from the Le An River which receives drainage from a major copper mining operation. We found that the in-situ Cu, Pb, Zn, Cd and As concentrations of the Le An River sediments below the mine are much higher than are the global background values, but that Ni was not elevated. There is potential for mobilization of bound metals to the overlying water, the order of metal release ratio in terms of pH dependencies is Zn > Cu > Cd approximately Pb. Sulfide is not a major binding component for metals in Le An River sediment. It is more likely that the iron and manganese oxides are the most important metal binding components in the sediments of the Le An River.     

Heavy metals in organisms of the River Guadalquivir estuary: possible incidence of the Aznalcóllar disaster

On the 25 April 1998, the giant holding pool of the Aznalcóllar mine, owned by the Canadian-Swedish Company Boliden Ltd burst its banks; 5 million cubic meters (6.7 million cubic yards) of sludge poured into the nearby River Guadiamar, which is a tributary of the River Guadalquivir (the main river of the south Iberian Peninsula). Within hours of the accident, approximately 2.5 Hm3 of acidic water with high concentrations of metals, especially Zn, had entered the River Guadalquivir. A biomonitoring program has been carried out to evaluate the incidence of this spill on the fauna of the River Guadalquivir. Six sampling stations within the estuary of were established and six species of molluscs (Crassostrea angulata, Scrobicularia plana), crustaceans (Palameon longirostris, Uca tangeri, Melicertus kerathurus) and fish (Liza ramada) were chosen for analysis. In the Portuguese oyster, Crassostrea angulata, Cd and Cu concentrations were above the maximum allowed by the Spanish legislation for bivalves for human consumption (60 micrograms.g-1 wet wt. for Cu and 1.0 microgram.g-1 wet wt. for Cd). The crustaceans Palaemon longirostris and Uca tangeri, also showed values above the legal limits for Cu (20 micrograms.g-1 wet wt.). An increase of the Zn levels was observed, as Zn concentrations in C. angulata were higher than those reported 30 years ago. The heavy metal concentrations in some of the organisms collected in the River Guadalquivir were higher than in the Bay of Cadiz or the Mediterranean Sea (clean sites), showing that this estuary was subjected to a heavy metal load. One month after the accident, concentrations of Zn were higher in C. angulata and in Palaemon longirostris compared with levels recorded on the 25 April. Nevertheless, some organisms did not show a clear tendency during the sampling period, probably due to the fluctuations of environmental (salinity, temperature) and physiological variables that affect bioaccumulation.     

Crab shell for the removal of heavy metals from aqueous solution

The ability of crab shell to remove heavy metals from aqueous solution was evaluated by comparing with that of several sorbents (cation exchange resin, zeolite, granular activated carbon, powdered activated carbon). All experiments were conducted using several heavy metal ion solutions (Pb, Cd, Cu, Cr). The orders of heavy metal removal capacity and initial heavy metal removal rate were found as crab shell > cation exchange resin > zeolite > powdered activated carbon>granular activated carbon. Therefore, crab shell is satisfactory as a good biosorbent for the heavy metal removal. The study indicates that the removal of these heavy metals is selective, with Pb and Cr being removed in preference to Cd and Cu. The sorption equilibrium of heavy metal ions on sorbents was modeled on the applications of Langmuir and Freundlich.     

Comparison of the feasibility of three extraction procedures for trace metal partitioning in sediments from south-west Spain

The feasibility of three sequential extraction schemes (a modification of the Tessier procedure, the scheme proposed by Meguellati and the protocol designed by BCR (now called the Standards, Measurements and Testing Programme, M&T) have been compared to study the distribution of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in sediment samples. The comparison has been performed by analyzing Certified Reference Material (CRM-601), a test material (S-12) and seven sediments from the Odiel Marshes Natural Park (located at the Atlantic coast of southern Spain). Samples were classified as sandy (with low iron oxide and organic matter contents) and clay-silty (with high iron oxide and organic matter contents) sediments. A higher metal mobility, especially under reducing conditions, was more properly assessed using the modified Tessier scheme compared to both the BCR and Meguellati procedures, these two later presenting comparative results for the reducible and residual phases. Significant Hg losses were found using the BCR procedure but the quantification of the acid phase for Cd, Cr and Ni was more reliable than that obtained with the modified Tessier and Meguellati schemes.     

Arsenic pollution at the industrial site of Reppel-Bocholt (north Belgium)

An industrial site, polluted with As and heavy metals, was investigated by combining chemical (sequential extractions and pHstat leaching tests), physical and mineralogical characterization of soil samples and slag fragments, and by the analysis of soil porewater aimed at assessing the distribution, speciation and mobility of heavy metals and As. On the site itself, arsenic concentrations up to 3.6% in surficial soil samples and up to 22% in slag fragments were found, together with elevated concentrations (percentage level) of Cu, Co, Ni, Zn and Pb. High concentrations of arsenic (up to 38,000 microg/l) and heavy metals (up to 1700 microg/l Cu and 4700 microg/l Zn) were also found in the in situ sampled soil porewater, highlighting the considerable availability of As, Zn and Cu for uptake by plants and leaching to the ground water. Sequential extractions also indicated a high availability of arsenic and copper in most samples and slag fragments of the industrial site, although poorly reactive phases were encountered as well. pHstat leaching tests confirmed that the present leaching of contaminants is alarming. Moreover, soil acidification will enhance the leaching of contaminants, emphasizing that remediation of the industrial site is urgent. Small scale variability of total metal concentrations and metal speciation, both in the horizontal and vertical direction, and the occurrence of a camouflage layer underline the importance of elaborate sampling for pollution assessment on an industrial site.     

Hydrogeochemical characteristics of the Tinto and Odiel Rivers (SW Spain). Factors controlling metal contents

The Tinto and Odiel Rivers are strongly affected by acid mine drainage (AMD) due to the intense sulphide mining developed in their basins over the past 5000 years. In this study the results obtained from a weekly sampling in both rivers, before their mouth in the Ría of Huelva, over three and a half years of control are analysed. In the Tinto River, the concentrations of sulphates, Al, Cd, Co, Li and Zn are double to those of the Odiel as a consequence of lower dilution. However, the concentration of Fe in the Odiel River is 20 times lower, since the precipitation of Fe oxyhydroxysulphates caused by neutralisation processes is more intense. Lower As, Cr, Cu and Pb concentrations are also found in the Odiel River as, to a greater or lesser extent, they are sorbed and/or coprecipitated with Fe. Other elements such as Be, Mn, Ni and Mg show similar values in both systems, which is ascribed to lithological factors. The seasonal evolution of contaminants is typical of rivers affected by AMD, reaching a maximum in autumn due to the dissolution of evaporitic salts precipitated during the summer. Nevertheless, in the Tinto River, Ca, Na and Sr show a strong increase during the summer, probably due to a greater water interaction with marly materials, through which the last reach of the river flows. Barium has a different behaviour from the rest of the metals and its concentration seems to be controlled by the solubility of barite. Iron, As and Pb show different behaviours in both rivers, those for Fe and As possibly linked to the prevalence of different dissolved species of Fe. The different Pb pattern is probably due to the control of Pb solubility by anglesite or other minerals rich in Pb in the Tinto River.     

Modeling heavy metal uptake by sludge particulates in the presence of dissolved organic matter

The uptake of the seven heavy metal ions Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) by sludge particulates in single-metal systems was investigated. Results showed that under acidic and neutral pH conditions, the uptake of all heavy metals by sludge particulates increases with the increase of pH. However, in the alkaline pH region, the uptake of Cu(II), Ni(II), and Co(II) decreases with the increase of pH, primarily due to the high dissolved organic matter (DOM) concentration in high pH conditions. Based on chemical reactions among heavy metal, sludge solids, and DOM, a mathematical model describing metal uptake as functions of DOM and pH was developed. The stability constants of metal–sludge and metal–DOM complexes can be determined using this model in conjunction with experimental metal uptake data. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on March 1997, the stability constants of Cu(II)–sludge complex (log K_S) and Cu(II)–DOM complex (log K_L) are 5.3±0.2 and 4.7±0.3, respectively; for Ni(II), they are 4.0±0.2 and 3.9±0.2, respectively. Results also showed that under neutral and low pH conditions (pH<8), the DOM effects on metal uptake for all heavy metals are insignificant. Therefore, the DOM term in the model can be ignored. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on December 1996, the estimated log K_S values of metal–sludge complexes for Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) are, respectively, 3.6±0.2, 3.0±0.1, 5.5±0.1, 4.8±0.1, 3.1±0.1, 5.1±0.1, and 4.4±0.3.     

兰州某铝厂旧址周围土壤重金属污染及分布特征

研究了兰州某铝厂旧址周围土壤重金属形态特征,找出了该土壤中重金属元素的形态分布及变化规律,分析了引起7种重金属元素形态变化的主要因子。结果表明,该铝厂周围土壤重金属Cu、Mn、Ni、Pb、Zn、Cr、Cd污染严重。各重金属元素的含量随样品采集半径的增加而减少,7种重金属的形态分析结果表明,重金属污染主要以残渣态为主,Cd、Mn和Cr的弱酸态占有较大的比例,其中Cd的生态风险性最高。同时对重金属的环境效应和生态风险作出一定的评价,为治理和改善该地区土壤环境质量积累科学数据。     

The Posidonia oceanica marine sedimentary record: A Holocene archive of heavy metal pollution

The study of a Posidonia oceanica mat (a peat-like marine sediment) core has provided a record of changes in heavy metal abundances (Fe, Mn, Ni, Cr, Cu, Pb, Cd, Zn, As and Al) since the Mid-Holocene (last 4470 yr) in Portlligat Bay (NW Mediterranean). Metal contents were determined in P. oceanica. Both, the concentration records and the results of principal components analysis showed that metal pollution in the studied bay started ca. 2800 yr BP and steadily increased until present. The increase in Fe, Cu, Pb, Cd, Zn and As concentrations since ca. 2800 yr BP and in particular during Greek (ca. 2680-2465 cal BP) and Roman (ca. 2150-1740 cal BP) times shows an early anthropogenic pollution rise in the bay, which might be associated with large- and short-scale cultural and technological development. In the last ca. 1000 yr the concentrations of heavy metals, mainly derived from anthropogenic activities, have significantly increased (e.g. from ~ 15 to 47 μg g^− 1 for Pb, ~ 23 to 95 μg g^− 1 for Zn and ~ 8 to 228 μg g^− 1 for As). Our study demonstrates for the first time the uniqueness of P. oceanica meadows as long-term archives of abundances, patterns, and trends of heavy metals during the Late Holocene in Mediterranean coastal ecosystems.     

Assessment of heavy metal levels in Almendares River sediments--Havana City, Cuba

The Almendares River watershed covers a large portion of Havana, Cuba and is centrally important to both recreational and other activities in the region. In order to assess current water quality conditions prior to planned remediation efforts, the spatial distribution of six heavy metals and other compounds were determined in river sediments at fifteen sampling stations in the watershed. Metal concentrations in sediments ranged from 86.1 to 708.8 for Zn, 39.3 to 189.0 for Pb, 71.6 to 420.8 for Cu, 84.4 to 209.7 Cr, 1.5 to 23.4 for Co, and 1.0 to 4.3 for Cd microg/g dry weight sediment. Calculated enrichment factors (EF; measured metal versus background mineral conditions) were almost always greater than 1.0, suggesting significant anthropogenic impact on metal levels in the river. The highest EF values were seen immediately below Cotorro (EF>10 for Pb, Cu, and Cd), a suburban town that has an active secondary smelter, and below the largest municipal landfill in Havana (EF>10 for Pb, Cu, Cd, and Zn). Further, three sampling stations had multiple metals at concentrations higher than probable effects concentrations (PEC), implying possible local ecotoxicological impacts. Finally, sequential extractions of the sediments indicated that heavy metals were largely associated with the organic fraction, and it was estimated that up to 62% of metals in the sediments would be susceptible to release back into the water column if hydraulic or other changes occurred in the river. These data are being used to prioritize decisions related to the remediation of the river system.     

Implication of heavy metals distribution for a municipal solid waste management system--a case study in Shanghai

Heavy metal contamination in municipal solid waste (MSW) is of increasing concern. The occurrence and distribution of heavy metals in MSW and their implications for the integrated MSW management system in mega-cities have been investigated by means of material flow analysis based on a case study of Shanghai in China. A good statistical basis was provided through a one-year monitoring program on the mass and metals composition of the waste from three MSW treatment facilities. The results showed that the main heavy metals in the MSW were Zn, Cr, Cu, and Pb (on average >100 mg kg(-1)), followed by Ni, Cd, and Hg. The MSW contained higher levels of Cu and Ni in metals, Cr and Pb in plastics, and Pb and Zn in the inorganic fractions. Regardless of the sources, the statistically similar heavy metal contents in the organic fractions indicated that effective blending and diffusion of heavy metals had taken place throughout the MSW collection, transfer, transportation, and storage, leading to cross-contamination of the waste fractions. PU (composed of putrescible waste and miscellaneous indistinguishable particles) contributed the majority of the heavy metals to the MSW, followed by plastics, as a result of the predominance in the overall composition of PU and plastics rather than from differences in their heavy metal contents. Therefore, manual or mechanical separation of some significantly heavy metal-rich fractions alone is not sufficient to reduce the heavy metal contents in the MSW. Source separation of organic waste and the diversion of tailored inorganic waste such as hazardous components, construction and demolition waste, etc., are proposed to control the heavy metal contamination in MSW. For the mixed MSW management system, physicochemical fractionation to exclude particles containing high levels of heavy metals can be conducted.     

Heavy metal contents in horticultural crops of a representative area of the European Mediterranean region

Heavy metal content (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) was analysed in the edible parts of two types of horticultural crops (leaf and inflorescence crops) from 30 agricultural fields in Castellón (Spain), a representative area of the European Mediterranean region. Selected soil properties relevant to control the mobility and bioavaibility of heavy metals were analysed for the general characterisation of these agricultural soils. The levels of clay, high percentages of organic matter and the presence of carbonate seem to suggest an important retention of heavy metals by these components in most of these soils. However, the high salinity in some fields (>4 dS/m) seems to facilitate the mobility of some heavy metals (e.g. Cu). The mean values of total contents of heavy metals in soils were similar to values obtained in other works on Spanish agricultural soils. However, there were some fields with a metal content (particularly Cu, Pb or Zn) higher than these works, reflecting an important anthropogenic source. In seven fields, the crop contents of Cd and/or Pb were higher than the maximum levels established by the Commission Regulation no. 466/2001 for horticultural crops. Heavy metal contents in leaf crops were higher than in inflorescence crops, except for Zn. The differences for Cd, Cr, Cu, Fe and Mn contents between these two types of crops were statistically significant. The analysis of crop heavy metal contents showed a higher absorption and/or accumulation of heavy metals in leaf crops than in inflorescence crops. Differences in crop characteristics seem to be responsible for the differential accumulation of heavy metals. Furthermore, agronomic practices and other sources of heavy metals (e.g. atmospheric deposition for Cd and Pb) may also have some influence on crop accumulation. Given the relevance of horticultural crops in the Mediterranean diet, it is highly necessary to extend the experience of this work to other areas of the European Mediterranean region.     

电渗析法去除未脱水污泥中重金属的试验研究

为了降低城镇生活污泥中重金属含量,采用三槽型电解槽研究了反应时间和NaClO预处理对未脱水污泥中重金属Zn、Cu、Cr和Ni去除率的影响。试验结果表明,延长反应时间可以提高未脱水污泥中重金属去除率。电渗析反应时间为14 h时,污泥中Zn、Cu、Cr和Ni的去除效果较好,去除率分别为52. 08%、27. 24%、31. 66%和46. 42%。污泥中重金属的初始非稳定态比例越大,电渗析反应后的去除率越高。NaClO/HNO_3组合预处理的污泥中重金属去除率最高,对Zn、Cu、Cr和Ni的去除率分别达到70. 32%、35. 39%、36. 80%和56. 78%。     

Heavy metals in the dump of an abandoned mine in Galicia (NW Spain) and in the spontaneously occurring vegetation

The concentrations of different forms of heavy metals (Fe, Mn, Zn, Cu, Cr, Ni, Cd and Pb) were determined in a mine dump material rich in chalcopyrite. The concentrations were compared with those of the natural vegetation colonising the dump. Samples taken from the dump are acid (pH(H(2)O) between 3.0 and 5.0), have carbon contents lower than 0.5%, N lower than 0.2%, effective cation exchange capacity between 0.74 and 4.96 cmol(+)kg(-1) and percent Al saturation in the exchange complex higher than 20% in 85% of the samples. Iron was the most abundant heavy metal, in both total and bioavailable forms, and the relative abundance of metals was: Fe>Cu>Mn>Zn>Cr. The total Fe concentrations ranged between 4315 and 31578 mg x kg(-1), the total Cu between 273 and 5241 mg x kg(-1), the total Mn between 294 and 2105 mg x kg(-1), the total Zn between 73 and 894 mg x kg(-1) and total Cr between 0.01 and 30 mg x kg(-1). Ni, Cd and Pb were below the analytical detection limits. The concentration of bioavailable Fe ranged between 40 and 1550 mg x kg(-1); Zn was the least abundant metal in this fraction (between 2 and 100 mg x kg(-1)). Copper was the most abundant heavy metal in the exchange complex and in the aqueous extracts, followed by Zn, Mn and Fe. Exchangeable Cu ranged between 17.7 and 1866 mg x kg(-1), whereas the maximum concentrations of exchangeable Zn, Mn and Fe did not exceed 140 mg x kg(-1). The Cu concentration in the aqueous extracts varied between 0.1 and 8.3 mg x l(-1) and the concentration of Fe was always less than 0.52 mg x l(-1). The heavy metal contents in the spontaneously occurring vegetation in the dump ranged between: 150 and 900 mg Fe x kg(-1), 84 and 2069 mg Mn x kg(-1), 20.5 and 106 mg Cu x kg(-1) and between 35 and 717 mg Zn x kg(-1), when considering all the plant samples analysed. Festuca sp. accumulated Fe, Salix atrocinerea accumulated Zn and Mn, and Frangula alnus and Quercus robur accumulated Mn. These native plant species may contribute to decrease the heavy metal contents in the dump material.     

Heavy metal pollution of soils affected by the Guadiamar toxic flood

Total heavy metal concentrations were determined in soil samples of seven selected areas along the Guadiamar river valley affected by the toxic flood, after removal of the deposited sludge. Mean total concentrations of nine elements (As, Au, Bi, Cd, Cu, Pb, Sb, Tl and Zn) out of the 23 (As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, In, Mn, Mo, Ni, Pb, Sb, Sc, Sn, Th, Tl, U, V, Y and Zn) analysed were higher in sludge-covered soils than in unaffected soils. Mean values of total As, Au, Pb, Sb, Tl and Zn in sludge-affected soils were higher than the upper limits for normal soils world-wide. Mean concentrations of Bi, Cd and Cu were within these ranges, although some individual values exceeded the upper limits. In all sampling areas, severe heavy metal pollution was observed in the superficial layers (0-20 cm) of most of the affected soils, which decreased downward in the soil profile. Generally, in soils with more than 25% of clay, concentration of heavy metals below the 20-cm depth decreased to values close to those of the background level of the Guadiamar valley soils, while in coarser soils, heavy metal pollution penetrated below this depth, being noticeable down to a depth of at least 50-80 cm.     

Localised remobilization of metals in a marine sediment

Trace metals and Fe and Mn were measured at vertical spatial resolutions of 2.5 and 5 mm in the top 35 cm of the profundal sediment of a Scottish sea-loch using DGT (diffusive gradients in thin films) technique. DGT probes lower adjacent metal concentrations in pore waters and induce a flux of metal from the solid phase to porewater. The concentrations of metals in porewaters at the interface of the probe were measured during its deployment in a box core. These measurements reflect porewater concentrations of metals and their rates of resupply from the local solid phase of a very small volume (25 microl) of sediment. There was pronounced horizontal and vertical structure in the interfacial concentrations. Horizontal variations were shown by results from adjacent DGT assemblies being markedly different in detail, while vertical structure was measured directly by the DGT-depth profiles. Iron and Mn varied systematically with depth, with both broad and detailed features of Co aligning with those of Mn. There was, however, evidence of additional localised sources of Co that were apparently unrelated to the redox behaviour that Mn typifies, but associated with the remobilization of Ni, possibly from mineral dissolution. Arsenic(III) was remobilized in well-defined zones. Detailed correspondence of As(II) with some Fe features suggest that its release is mechanistically-related to iron oxide dissolution, but the 3 orders of magnitude higher concentrations of Fe may sometimes obscure the association. These results demonstrate that, within sediments, metals may be released in discrete locations that are not measured by conventional porewater sampling techniques due to their horizontal averaging.