The Niagara River mussel biomonitoring program (Elliptio complanata): 1983-2009

The Ontario Ministry of the Environment has monitored the concentrations of contaminants in mussel (Elliptio complanata) tissue and bottom sediments at sites in the Niagara River since 1983 to describe the general contamination of the river and identify contaminant sources. More recently, the data have been used to document the effectiveness of remedial actions implemented at identified sources along the river. Results from Canadian sites and five U.S. sites at which remedial actions have been implemented [Bloody Run Creek (Hyde Park Hazardous Waste Site); Gill Creek; Occidental Chemical Company (Buffalo Avenue Plant); 102nd Street Hazardous Waste Site; and Pettit Flume Cove] are discussed. p,p′-DDE, PCBs and dioxins were the only contaminants detected at Canadian sites at concentrations probably representative of background. Results from the five sites showed the effectiveness of implemented remedial actions in reducing the flow of contaminants to the river ranged between very effective (Gill Creek: PCBs; and 102nd Street, CBs) to no effect (Bloody Run Creek: PCBs, CBs, and dioxins). Remedial actions at the Pettit Flume Cove (for dioxins/furans) initially appeared to be effective, but were subsequently shown to have missed a source to the cove. The effectiveness of the actions taken at these sites in improving contaminant conditions in the Niagara River since the 1980s as demonstrated by our mussel and sediment results is corroborated by the data from other fish and water quality monitoring programs. Additional remedial efforts are still required at these sites and other known sources of contaminants to the river.     

Compartmental Distribution of Organochlorine Contaminants in the Niagara River and the Western Basin of Lake Ontario

Ten chlorobenzenes, hexachlorobutadiene, and PCBs were measured in Niagara River water and suspended solids, and in western Lake Ontario sediments and benthic fauna. High levels of these contaminants were found on all fractions of the river suspended solids, but the larger particles contained much higher concentrations than the smaller particles. A portion of the CBs, HCBD, and PCBs present in the lake sediments was available to benthic organisms. A trend toward greater bioaccumulation for compounds having higher octanol-water partition coefficients was observed at all trophic levels.     

Studies of Trace Contaminants,Nutrients, and Bacteria Levels in the Niagara River

Sediment and water quality of the Niagara River were investigated during 1979 and 1980 to determine spatial and temporal differences in the levels of trace contaminants (heavy metals, phenolics, PCBs, and organochlorine pesticides) as well as nutrients and bacteria. Data from these studies as well as recent biomonitoring studies indicate that the Niagara River continues to be a source of such contaminants as PCBs, BHCs, mirex, and heavy metals to Lake Ontario. The major source of the contaminants is the highly industrialized and urbanized Tonawanda Channel area in the upper section of the river. Although a substantial improvement in phenolics levels was noted in the river since earlier surveys in 1971, bacterial and phosphorus levels show no significant changes, particularly near the U.S. mainland shore of the Tonawanda Channel and near the Buffalo River mouth.     

Biological Monitoring of Organochlorine Contaminants in the St. Clair and Detroit Rivers Using Introduced Clams, Elliptio Complanatus

Introduced clams (in cages) were effective biomonitors in determining the distribution, biological availability, and source areas of a number of chlorinated organic contaminants in the St. Clair River-Detroit River corridor during 1982 and 1983. In the St. Clair River, hexachlorobenzene (HCB), octachlorostyrene (OCS), pentachlorobenzene (QCB), hexachlorobutadiene (HCBD), 2,3,6-trichlorotoluene (TCT), and alpha-BHC were most frequently identified in tissues after 3 weeks’ exposure. When compared to other locations in the St. Clair and Detroit rivers, significantly (p<0.05) higher levels of QCB, HCB, OCS, and HCBD were found in clams exposed along the Sarnia to Corunna, Ontario, shoreline. Elevated concentrations of HCB and OCS were also detected in water samples from this section of the river. TCT was found in clams from most locations, at low levels, with no obvious source area. Low levels of polychlorinated biphenyls (PCBs) were restricted to clams from the Sarnia area. In the Detroit River, PCBs, HCB, and OCS were most frequently detected in clams. PCB levels were significantly (p<0.05) higher along the Michigan shore and the highest concentrations were found in the Rouge River area. PCBs were also detected in some water samples from urbanized areas of the river. HCB and OCS were found at near-detection levels in clams from most stations. Contaminant levels in clams from around Fighting Island were low or non-detectable, indicating an absence of biologically available organochlorine contaminants in this area of the river. In the St. Clair River, p,p-DDE was only detected in the Sarnia area, whereas it was found in clams from both sides of the Detroit River, also at low levels. Aldrin, chlordane, and DDT were only sporadically detected in both rivers.     

Chlorinated Organic Contaminants in Water and Suspended Sediments of the Lower Niagara River

Suspended sediment and raw water samples have been collected and analyzed for organochlorines and PCBs from a fixed location in the lower Niagara River at Niagara-on-the-Lake approximately weekly since 1979. Eight of the 19 organochlorine compounds measured were detected in more than 50% of the water samples analyzed, while 11 of the 19 compounds were detected in more than 50% of the suspended sediments collected at Niagara-on-the-Lake. Of the 10 chlorobenzene isomers measured, the one with the greatest usage (1, 4-dichloro) occurs in largest concentrations in the suspended sediments at Niagara-on-the-Lake. Other chlorobenzene isomers commonly occurring in suspended sediments are 1, 2 and 1, 3 dichloro, 1, 2, 4-trichloro, 1,2, 3, 4-tetrachloro, pentachloro, and hexachloro. All isomers of chlorobenzene occurred in more than 70% of the suspended sediment samples collected. Total loadings to Lake Ontario calculated from these data indicate that PCB loadings are about twice as high as previously reported, while mirex and total DDT hate decreased slightly. Although concentrations of contaminants in suspended sediments are usually higher than those measured in water samples, they are responsible for only about 40% of the total loadings for PCBs, DDT, and HCB, and significantly less for other organochlorine contaminants. Therefore, the data indicate that, to estimate total contaminant loadings, the water fraction must be sampled. Lake Erie is not the major source of such organic contaminants as PCBs and chlorobenzenes because contaminant levels in Lake Erie bottom sediments are 10 times lower for PCBs and 20 times lower for chlorobenzenes than in Niagara-on-the-Lake suspended sediments.     

Spatial Distributions of Legacy Contaminants in Sediments of Lakes Huron and Superior

The sediments of Lake Superior, Lake Huron, and Georgian Bay were sampled in 2001 and 2002 in order to evaluate the extent of surficial sediment contamination of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCs), polycyclic aromatic hydrocarbons (PAHs), and metals. Sediment concentrations of PCBs, OCs, PAHs, and mercury were generally low and up to 2 orders of magnitude less than in Lakes Erie and Ontario. In contrast, concentrations of metals such as arsenic, copper, and nickel were comparable to those in Lakes Erie and Ontario. These elevated Lakes Superior and Huron metal concentrations were attributed to naturally occurring metals within the bedrock, soil, and sediment of the study region. Concentrations of all contaminants were typically below the Canadian Sediment Quality Probable Effect Level (PEL) guidelines. With regard to spatial patterns, most contaminants were focused primarily in the depositional basins and atmospheric deposition was likely the major source of these chemicals to the lakes. The major exception was for metals (not including mercury) whose patterns were also influenced by natural sources as well as extensive mining activity. A comparison between surficial sediment contamination of samples collected as part of this survey and those collected in the late 1960s/early 1970s using similar methods showed that concentrations of DDT, PCB, lead, and mercury were generally similar between these two time periods. These results are not consistent with production and usage patterns that have declined substantially in the past 3 decades. We hypothesize that the lack of temporal trends is an artifact due to slow sediment accumulation rates as well as differences in analytical protocols between the two time periods.     

Monitoring metal and persistent organic contaminant trends through time using quagga mussels (Dreissena bugensis) collected from the Niagara River

Historically, the Niagara River received the discharge of persistent bioaccumulative and toxic chemicals from municipal and industrial outfalls and hazardous waste landfills. American and Canadian governments have coordinated investigations of chemicals entering the river and initiated remedial measures and monitoring programs with a goal to reduce loadings of toxic chemicals to the river. This study, a component of the Ontario Ministry of Environment Mussel Biomonitoring Program, compares contaminant concentrations in quagga mussels (Dreissena bugensis) collected from nine locations in the Niagara River in 1995 and 2003 to assess anticipated changes in tissue concentrations of contaminants in response to ongoing remedial efforts by government agencies and local industries. The concentrations of persistent organic compounds (e.g., PCBs, hexachlorobenzene, hexachlorobutadiene, octachlorostyrene) in quagga mussels in 2003 were lower than concentrations measured in 1995, consistent with a decrease in reported mean annual concentrations of these compounds in water. Significant differences in total PCB concentrations in mussels between stations (F = 4.6; P < 0.001) suggested sources of PCBs on the American side of the upper Niagara River. In general, highest concentrations of persistent organic compounds were found downstream of the Occidental Chemical Corporation Buffalo Avenue facility suggesting local sources of these contaminants notwithstanding remedial efforts. In contrast, metal concentrations in quagga mussels in 2003 were similar to concentrations found in 1995 and to values reported in the literature for mussels collected from industrialized areas in the Great Lakes. Overall, our results suggest that remedial efforts to improve water quality in the Niagara River have been successful.     

Anomalous Concentrations and Chlorination of Polychlorinated Biphenyls in Sediment Downwind of Lake Ontario

Relatively high concentrations (up to 98.5 ng/g dry wt) of polychlorinated biphenyls (PCBs) have been found in two cores penetrating fluvial sands east of Lake Ontario. One core was taken from the upper Salmon River reservoir on the Tug Hill Plateau and the other from Rice Creek near the lake at Oswego. In both instances, portions of the cores containing PCBs and other organochlorines (OCs) lack excess radiogenic ²¹⁰Pb and ¹³⁷Cs, implying depositional ages predating widespread OC commercial production, use, and release. Within each core there is little vertical variation in PCB composition and highly chlorinated congeners dominate the pattern. In addition, the PCB signature is analytically indistinguishable between cores despite collection over 50 km apart. This argues against local sources, and implies deposition and accumulation by processes operating over a substantial area and time period. Transport and introduction of a residual fraction of colloidal-bound PCBs to the sands via tannin-rich riverine waters is proposed.The PCB congener-specific pattern of air samples collected during the spring and summer of 1999 downwind of the lake at two locations (Rice Creek and Sterling) are similar to the sediments and display anomalous concentrations and chlorination with respect to other air sampling localities in the Great Lakes. A link between the residual fraction of PCBs observed in the sediment and air patterns via volatilization from the terrestrial surface is proposed. Elevated PCB concentrations and chlorination in non radiogenic fluvial sands and air may reflect regional accumulation and weathering processes operating over many decades and/or enhancement of contaminant deposition and partitioning downwind of the lake related to lake-effect precipitation.     

Maternal Transfer of Organochlorines to Eggs of Walleye (Stizostedion vitreum) in Lake Manitoba and Western Lake Superior

Gravid walleye were sampled from Lake Manitoba and western Lake Superior (St. Louis River) to measure the concentrations of organochlorine contaminants (OCs) in eggs and muscle and to assess the influence of maternal age and size on the transfer of OCs from mother to egg. Concentrations of most OCs in Lake Superior walleye eggs were 1 to 3 orders of magnitude greater than in Lake Manitoba eggs. Toxaphene (mean concentration (wet weight) ± 1 SE, 1580 ± 462 ng/g) and polychlorinated biphenyls (PCBs) (240 ± 24 ng/g) were the predominant OCs in Lake Superior walleye eggs, whereas DDT and metabolites (eggs 16 ± 1.5 ng/g, muscle 2.1 ± 0.36 ng/g) and PCBs (eggs 9.2 ± 0.83 ng/g, muscle 2.0 ± 2.4 ng/g) were the most common OCs in Lake Manitoba walleye eggs and female muscle. Egg size (dry mass) and the concentration of most OCs in Lake Manitoba walleye eggs were positively correlated with female length and age. This relationship was strongest for more hydrophobic OCs (e.g., PCBs) but was not significant for less hydrophobic OCs (e.g., hexachlorocyclohexanes (HCHs)). Neither egg size nor egg OC concentration of Lake Superior walleye were significantly correlated with female length or age. There was no relationship between OC concentrations in muscle tissue and female length or age of Lake Manitoba walleye. OC concentrations in Lake Manitoba walleye eggs were not correlated with concentrations in the muscle tissue of the mothers, suggesting that OCs in walleye eggs are derived from various tissues. A positive relationship between the egg:muscle ratio of PCB concentrations and the egg:muscle ratio oflipid in freshwater fish suggests that the maternal transfer of PCBs in freshwater fish is related to the relative amounts of lipid in the eggs and mother. The transfer of hydrophobic OCs from mother to eggs in freshwater fish appears to vary within and among fish species and with the hydrophobicity of the OC.     

Distribution of Mercury,Trace Organics,and Other Heavy Metals in Detroit River Sediments

In 1980 the Ontario Ministry of the Environment carried out a surficial bottom sediment survey of the Detroit River. The survey was designed to update changes in sediment mercury levels from a 1970 study, and to determine the spatial distribution of trace organics and other heavy metals as a baseline for future investigations. The contamination of sediments along the Ontario shoreline of the river was localized near known inputs such as Little River, the West Windsor sewage treatment plant, Turkey Creek, and Riviere aux Canards. Almost the entire U.S. shoreline sediments exhibited elevated levels (above provincial dredging guidelines) of contaminants such as heavy metals and PCBs. Levels of one order of magnitude higher than those on the Canadian shore were prevalent along the U.S. shore. Mercury levels exhibited a substantial decline during the period 1970–1980. Increases in chromium, copper, lead, and zinc in the vicinity of the mouth of the Rouge River along the U.S. shoreline during the same period suggest both recent and continuing inputs from industrial and municipal sources.     

A River-wide Survey of Polychlorinated Biphenyls (PCBs), Polycylic Aromatic Hydrocarbons (PAHs), and Selected Organochlorine Pesticide Residues in Sediments of the Detroit River—1999

The spatial distribution of hydrophobic organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and octachlorostyrene (OCS) in sediments of the Detroit River was established using data from a 1999 river-wide survey. The survey employed a stratified random sampling design that divided the river into six geostatistical zones consisting of upper, middle, and lower U.S. and equivalent Canadian river reaches. Organic carbon normalized OCS sediment concentrations demonstrated no significant differences between U.S. or Canadian sediments or upstream/downstream gradients suggesting that OCS is derived primarily from sources upstream of the Detroit River. In contrast, sum PCBs and sum PAHs were significantly elevated at U.S. as compared to Canadian stations and demonstrated significant increasing upstream/downstream gradients in organic carbon normalized sediment contamination. The upper and middle U.S. river reaches contained a number of near-shore stations with high localized PCB and PAH sediment concentrations suggesting multiple inputs along the upper U.S. portion of the river. Consistent with past surveys, wide-spread sediment contamination of PCBs and PAHs continues to be observed in the highly industrialized Trenton Channel and downstream of Grosse Isle. Threshold effect level (TEL) sediment quality guidelines for PAHs and PCBs were exceeded in 92.6 and 77.8%, respectively, of stations in Trenton Channel and downstream of Grosse Isle. This large reservoir of degraded sediments in the lower U.S. river reach has the potential to enter Lake Erie during sediment disturbance events and likely contributes to gentoxic stress and increased bioaccumulation of PCBs in resident benthos, fish, and wildlife.     

Assessment of Maternal Contaminant Burden by Analysis of Snapping Turtle Eggs

Snapping turtles (Chelydra serpentina serpentina) have been extensively used as an ecosystem and localized indicator of tissue contaminant bioaccumulation, and for monitoring the geographic and temporal trends of contaminants. The purpose of this study was to determine if any relationship exists in the pattern and quantity of select contaminants found in turtle tissues relative to egg contamination. Six gravid snapping turtle females were collected from within and outside the Great Lakes basin and analyzed for congener-specific polychlorinated biphenyls (PCBs), dichlorodiphenyl-dichloroethylene (DDE), mirex and hexachlorobenzene (HCB) distributions in the fat, liver, and eggs. Preliminary data collected from five sites indicates that the pattern of congener-specific PCBs and homologs, average chlorine/biphenyl, and total PCBs are significantly correlated among snapping turtle eggs and tissues. Significant correlations were also observed for DDE, mirex, and HCB. All six turtles in this study revealed a consistent, and enhanced lower-chlorinated PCB pattern in the eggs relative to maternal adipose and liver tissues. Although these preliminary results are based on a relatively small sample size (n = 6), the significance of the relationships observed indicate that the utilization of snapping turtle eggs provides a reliable indicator of maternal contaminant burdens found in the highest environmental trophic levels.     

Contaminant-associated health effects in fishes from the Ottawa and Ashtabula Rivers,Ohio

The health of resident fishes serves as a biologically relevant barometer of aquatic ecosystem integrity. Here, the health of the Ottawa River and Ashtabula River (both within the Lake Erie Basin) were assessed using morphological and immunological biomarkers in brown bullheads (Ameiurus nebulosus) and largemouth bass (Micropterus salmoides). Biomarker metrics were compared to fish collected from a reference site (Conneaut Creek). Data utilized for analyses were collected between 2003 and 2011. Fish collected from all three river systems had markedly different contaminant profiles. Total PCBs were the dominant contaminant class by mass. In bullhead, PCBs were highest in fish from the Ashtabula River and there were no differences in fish collected pre- or post-remediation of Ashtabula Harbor (median = 4.6 and 5.5 mg/kg respectively). Excluding PCBs, the Ottawa River was dominated by organochlorine pesticides. Liver tumor prevalence exceeded the 5% trigger level at both the Ashtabula (7.7%) and Ottawa Rivers (10.2%), but was not statistically different than that at the reference site. There was no statistically significant association between microscopic lesions, gross pathology and contaminant body burdens. Collectively, contaminant body burdens were generally negatively correlated with functional immune responses including bactericidal, cytotoxic-cell and respiratory burst activity in both species. Exceptions were positive correlations of HCB and heptachlor epoxide with respiratory burst activity in largemouth bass, and HCB with respiratory burst activity in bullhead and ΣBHC for all three functional assays in bullhead. Data here provide additional support that organochlorine contamination is associated with immunomodulation, and that species differences exist within sites.     

Distribution of Contaminants in Clams and Sediments from the Huron-Erie Corridor. I–PCBs and Octachlorostyrene

Samples of surficial sediments and the clam species Lampsilis radiata siliquoidea were collected from 102 sites covering all of Lake St. Clair and the Canadian shoreline of the St. Clair and Detroit rivers. The distribution patterns of both octachlorostyrene (OCS) and PCBs were mapped throughout this area. The mean level of PCBs in sediments of 3.9 μg kg^?1 (Aroclor 1254) was much lower than values for “total PCBs” reported in studies carried out in the early 1970s. This reduction does not appear to reflect a real decrease in PCB levels in the environment, but rather changes that have been made in sampling procedures and analytical techniques. Highest levels of PCBs in both sample types were found along the western shore of Lake St. Clair. Mean levels of OCS in whole clam tissue and surficial sediment (0–10 cm) were 43.0 and 5.1 μg kg^?1, respectively. The distribution pattern of OCS in the Huron-Erie corridor in both clams and sediments suggests that the primary source is in the St. Clair River. The mean chemical concentration factor was 59 for OCS, indicating considerable bioaccumulation in the biota of Huron-Erie corridor.     

Bioaccumulation Potential of Sediment-Associated Polychlorinated Biphenyls (PCBs) in Ashtabula Harbor,Ohio

Ashtabula Harbor, Ohio is designated as a Great Lakes Area of Concern contaminated by PCBs. Information on the bioaccumulation of PCBs from sediments is important for sediment management strategies such as dredging to restore navigable depths in the harbor. To ascertain the bioaccumulation of these PCBs, the aquatic earthworm Lumbriculus variegatus was exposed in the laboratory to contaminated sediments collected from 15 areas in the harbor. Data from these bioaccumulation experiments were used to determine the bioaccumulation potential of PCBs through the calculation of Biota- Sediment Accumulation Factors (BSAFs). The results showed that the mean values of the experimentally derived BSAFs for individual harbor areas ranged from 0.27 to 1.69. The median BSAF for sediments in the lower river sector of the harbor (0.38) was significantly lower than that for upper river sediments (1.34), indicating that the high adsorptive properties of coal soot particles constrained PCB bioavailability in the lower river sediments. These results indicate that the origin of total organic carbon (TOC) has a major influence on the bioavailability of total PCBs in harbor sediments. Moreover, the empirical BSAFs were well below the 4.0 default BSAF value recommended in joint USEPA/USACE protocols that are used to evaluate the Theoretical Bioaccumulation Potential, or bioavailability, of neutral organic chemicals in Great Lakes sediments. These empirical values should be used to more precisely predict the bioavailability of total PCBs in Ashtabula Harbor sediments.     

The Fate of Pentachlorophenol in the Bay of Quinte,Lake Ontario

Unfiltered water, surface film, sediment, and biota samples were collected from the Bay of Quinte between May and September 1978 and analyzed for chlorophenols (CPs). Sectioned sediment cores were dated using ²¹⁰Pb and ¹³⁷Cs analyses. Pentachlorophenol (PCP) was found at high concentrations adjacent to a point source and was detected in all compartments examined throughout the bay (a bioaccumulation factor of 10⁴ was observed for PCP in fish). The ratio of 2,3,4,6- and 2,3,5,6-tetrachlorophenols (TTCPs) to PCP increased with distance from the source in the water column and surface film. Photochemical reduction was proposed to account for the phenomenon. CP concentrations in sectioned cores suggested that settling particles adsorb CPs in similar proportion to that observed in the water column and little further change occurs after burial.     

Dynamics of PCBs in the Food Web of Lake Winnipeg

The bioaccumulation of polychlorinated biphenyls (PCBs) is examined in the food web of Lake Winnipeg using measured contaminant concentrations, stable isotopes of nitrogen, and a food web model. Measured concentrations of the sum of 103 PCB congeners are higher in south basin water, sediment, and biota compared with the north. The trophic positions of the top predators as well as the extent of biomagnification of PCBs per unit trophic level do not differ significantly between the north and the south basins. We therefore conclude that the higher PCB concentrations in the south basin are due primarily to higher PCB loadings via riverine sources to the south rather than food web processes. In contrast, the data from the north basin suggest lower total loadings of which a higher fraction is from atmospheric deposition. We find that rainbow smelt (Osmerus mordax) are not associated with elevated exposure of contaminants to top predators of the north basin. This surprising result is attributed to their reduced fitness in this relatively shallow and warm system, which may prevent them from feeding at an elevated trophic level compared with other forage fish. Finally, we hypothesize that high nutrient associated DOC in water decreases PCB bioavailability to lower trophic level organisms and hence the entire food web.     

Chlorinated Contaminants in Surficial Sediments of Lakes Huron,St. Clair,and Erie: Implications Regarding Sources Along the St. Clair and Detroit Rivers

Surficial sediments from southern Lake Huron, Lake St. Clair, and Lake Erie have been analyzed for a broad spectrum of chlorinated organics including PCBs, chlorobenzenes, and several pesticides. The differences between sediment contaminant concentrations in Lake Huron and Lake St. Clair indicated sources of hexachlorobenzene, hexachlorobutadiene, octachlorostyrene, and several other chlorinated benzenes along the St. Clair River. Similar differences between sediment PCB concentrations in Lakes Huron/St. Clair and Lake Erie indicated major PCB sources along the Detroit River. Specific PCB congener analysis revealed that PCBs discharged to the Detroit River contained especially high concentrations of highly chlorinated hexa-, hepta-, and octachloro-biphenyls which are major constituents of the industrial mixture Aroclor 1260. The analysis of individual PCB congeners made it possible to trace PCBs of Detroit River origin to the central and eastern basins of Lake Erie, and to estimate the contribution of the Detroit River to the PCB burden in sediments of these basins.     

秦淮河南京段水质变化过程及污染控制

从秦淮河南京段的水功能区划目标着手,运用污染指数法对秦淮河南京段2001--2010年的水质变化过程进行分析评价,指出秦淮河南京段污染源贡献大小依次为NH3-N、BOD、CODMn和石油类,主要超标污染物为NH3-N;秦淮新河的水质明显优于其他河段,内秦淮河的水质污染情况依旧严重。总结10年治污对秦淮河水质的影响,指出城市污水接管率、污染源、水动力条件等仍是影响秦淮河水环境的主要因素。在污染源综合整治、河道疏浚、生态修复、政策保障等方面提出了控制污染的措施及建议。     

Numerical research on the mechanism of contaminant release through the porous sediment-overlying water interface

After the pollutant discharged into the river or lake has been reduced, the release of the contaminant from the sediment to the overlying water may cause the river and lake be contaminated again. On the condition that the overlying water flow does not lead to sediment suspension, numerical researches are carried out for the mechanism of contaminant release through the sedimentoverlying water interface. The overlying water flow is calculated as turbulence. The sediment is regarded as isotropic homogeneous porous medium, therefore the seepage field in the porous sediment layer is obtained by solving Darcy＇s equations. Coupled two dimensional steady flows of the overlying water and the pore water in the sediment are calculated. Based on the flow fields obtained, the unsteady contaminant solute transportation process in the pore water in the sediment and the overlying water is numerically simulated, as the shapes of the sediment-overlying water interface are flat or periodic triangular respectively. Numerical results show that the exchange of the pore water and the overlying water is an important factor which decides the release flux of the contaminant from the sediment to the overlying water. The pressure distribution produced by the overlying water flow along the sedimentoverlying water interface, as it is not flat, may induce the seepage of the pore water in the sediment and through the sedimentoverlying water interface, which may increase the release flux of the contaminant from the sediment to the overlying water.