Sediment Interstitial Water Research Articles

Submersed macrophytes of two habitats in Lake Constance (Untersee) and their relations to chemical composition of surface and sediment interstitial water

Summary Habitat conditions of two macrophyte stands in Lake Constance with different species composition were investigated to find out determinating factors. The results of surface water analyses hardly showed any differences. Marked differences were found in chemical composition of sediment interstitial water. This was explained by different wind exposition of the two habitats. One is exposed to the main wind direction and can be characterized as erosion shore, the other one is mostly protected against wind and can be characterized as sedimentation shore. In first case, locally produced organic matter is transported away from littoral zone by autumn storms onto the shore or to deeper sites of the lake, where decomposition of organic matter takes place. In the other case, decomposition of locally produced organic matter takes place directly at production site. This results in high concentrations of ammonium and sulfid in sediment interstitial water showing strictly anaerobic conditions, whereas at the wind exposed site only little concentrations of ammonium and no sulfid was detectable. Apart from different resistence against wave action of the macrophyte species, different sediment interstitial water quality is considered to be the reason for the differences in species composition of the two macrophyte habitats.

Toxicity of Cuyahoga River and Nearshore Lake Erie Sediments to Photobacterium phosphoreum

The Cuyahoga River Basin and Lake Erie (nearshore of Cleveland) sediments were assayed with Photobacterium phosphoreum during the summer of 1991. Of the 33 sediments tested, 23 exhibited toxicity using either interstitial or extract water. Nearly all (93%) of the “navigation channel” (i.e., the lower 8 km of the river) and nearshore lake samples were toxic. No statistical difference was observed between river sediment interstitial and extract waters. With the limited number of lake samples (seven), more toxicity was observed with extract water than with interstitial water.

Comparison of the enzyme inhibition effect of different humic substances in aqueous solutions

The enzymatic cleavage of the amide bond of l-leucine-4-nitroanilide by the proteolytic enzyme Pronase E releases 4-nitroaniline. The production of this molecule can be observed by the increasing UV absorption of the solution. A decrease in the rate of hydrolysis reaction was obtained in the presence of different humic substances isolated from water, sediment and soil. This result indicates that humic substances influence enzyme activity by interacting with the applied enzyme. A mathematical relation between the concentration of humic substances and their inhibition effect was used to calculate an effective concentration for which 50% of the maximum effect was observed. The obtained concentration was defined as the EC 50 value. The EC 50 values of the investigated humic substances were in the range 153 mg l −1 to 6360 mg l −1. The amounts of humic substances used in the experiment were higher than in most aquatic environments. However, in bog water or interstitial water of sediments and soils such large amounts of biologically and ecologically relevant natural organic matter can be expected.

Geochemistry and solid-phase association of chromium in sediment from the Calcasieu River and estuary, Louisiana, U.S.A.

Sediment samples were collected from the lower Calcasieu River and estuary, Louisiana, in a study of the release of metals from sediments to the overlying water column. Whole samples were characterized by analyses that included: (1) determination of total sediment ammonium concentrations; (2) determination of total sediment Cr, Mn and Fe concentrations; (3) extraction of sediment with hydrogen peroxide followed by dilute hydrochloric acid to obtain recoverable metals, including oxides; and (4) extraction of sediment with hydrogen peroxide plus pyrophosphate at a pH of 7–8 to recover organically-bound Cr but not metal oxides. Concentrations of Cr, Mn and Fe in sediment interstitial water were determined. The concentrations of Cr in interstitial water could not be predicted from total sediment concentrations of Cr. Degradation of organic matter appeared to be the mechanism that caused elevated Cr concentrations in the interstitial water. Concentrations of Cr in interstitial water were positively correlated with total concentrations of ammonium in sediment. Concentrations of Cr in interstitial water that exceeded water-column concentrations of Cr were found when the total concentrations of ammonium in sediment exceeded 1 μmol per gram wet weight. Concentrations of metals in interstitial water that are larger than metal concentrations in the water column create a potential for diffusive flux and metal enrichment of the overlying water column.

Arsenic speciation in aqueous samples using a selective As(III)/As(V) preconcentration in combination with an automatable cryotrapping hydride generation procedure for monomethylarsonic acid and dimethylarsinic acid

Differentiation between As(III) and As(V) is accomplished using earlier developed selective preconcentration methods (carbamate and molybdate mediated (co)precipitation of As(III) and As(V) respectively) follewed by AAS detection of the (co)precipitates. Apart from this, separation of methylated arsenic species is performed by an automatable system comprising a continuous flow hydride generation unit in which monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) are converted into their corresponding volatile methylarsines, monomethylarsine (MMA) and dimethylarsine (DMA) respectively. These species are cryogenically trapped in a Teflon-line stainless stell U-tube packed with a gas chromatographic solid-phase and subsequently separated by selective volatilization. A novel gas drying technique by means of a “Perma Pure” dryer was applied successfully prior to trapping. Detection is by atomic absorption spectrometry (AAS). MMAA and DMAA are determined with absolute limits of detection of 0.2 and 0.5 ng, respectively. Investigation of the behaviour of the methylarsines in the system was conducted with synthesized73As labeled methylated arsenic species. It was found that MMA is taken through the system quantitatively whereas DMA is recovered for about 85%. The opumized system combined with selective As(III)/As(V) preconcentration has been tested out for arsenic speciation of sediment interstitial water from the “Chemiehaven” at Rotterdam. The obtained concentrations are 28.5, 26.8 and 0.60 ng·ml−1 for As(III), As(V) and MMAA, respectively, whereas the DMAA concentration was below 0.16 ng·ml−1.

Bioavailability of Chlorocatechols in Naturally Contaminated Sediment Samples and of Chloroguaiacols Covalently Bound to C 2 -Guaiacyl Residues

Bacteria in anaerobic enrichment cultures that dechlorinated a range of chlorocatechols were used to examine the stability of endogenous chlorocatechols in a contaminated sediment sample and in interstitial water prepared from it. During incubation of the sediment sample for 450 days with or without added cells, there was a decrease in the concentration of solvent-extractable chlorocatechols but not in that of the total chlorocatechols, including sediment-associated components. In the presence of azide, the decrease in the concentrations of the former was eliminated or substantially decreased. Control experiments in which 3,4,5-trichlorocatechol was added to the sediment suspensions after 130 days showed that its dechlorination was accomplished not only by the added cells but also by the endemic microbial flora. It was concluded that the endogenous chlorocatechols in the sediment were not accessible to microorganisms with dechlorinating activity. On the other hand, microorganisms were apparently responsible for decreasing the solvent extractability of the chlorocatechols, and this effect decreased with increasing length of exposure time. Similar experiments carried out for 70 days with the sediment interstitial water showed that the chlorocatechols that were known to be associated with organic matter were also inaccessible to microbial dechlorination. Experiments with model compounds in which 4,5,6-trichloroguaiacol and tetrachloroguaiacol were covalently linked to C(2)-guaiacyl residues showed that these compounds were resistant to O demethylation or dechlorination during incubation with a culture having these activities. The only effect of microbial action was the quantitative reduction in 12 days of the C'1 keto group to an alcohol which was stable against further transformation for up to 65 days. The results of these experiments are consistent with the existence of chlorocatechols and chloroguaiacols in contaminated sediments and illustrate the cardinal significance of bioavailability in determining their recalcitrance to dechlorination and O demethylation, respectively. It is suggested that bioavailability is an important factor in determining the persistence of xenobiotics in natural ecosystems and that its omission represents a serious limitation in the interpretation of many laboratory experiments directed towards determining the persistence of xenobiotics in aquatic ecosystems.

The Effect of Changing Water Chemistry on Rates of Manganese Oxidation in Surface Sediments of a Temperate Saltmarsh and a Tropical Mangrove Estuary

The influence of changing water chemistry on manganese oxidation in surface sediments of a Sapelo Island, Georgia saltmarsh and an Andros Island, Bahamas mangrove swamp was examined. Surface sediment interstitial water salinities for sample stations in the mangrove swamp, and for saltmarsh creek bank sample sites on Sapelo Island were similar to that of the overlying waters. Intertidal sediments from high marsh sites on Sapelo Island were frequently exposed to the atmosphere on low tides, resulting in enhanced evaporation, and interstitial water salinities up to 105 were observed. Rates of microbial Mn oxide production were determined using the oxidation of leuco crystal violet in sediment/water suspensions. Sodium azide was added to some incubations to measure rates of abiotic Mn oxide formation. Overall, rates of Mn oxide production were much higher in saltmarsh sediments than in mangrove sediments. Within the mangrove swamp estuary, sediments approximately 15 km inland exhibited the highest rates of microbial Mn oxide production (station salinities of 0 and 8, 50 to 119 pmol mg dwt -1h -1, respectively), compared with sediments from the mouth of the estuary (station salinities of 24 and 34, 3 to 16 pmol mg dwt -1h -1, respectively). Suspension of mangrove sediments in water from different parts of the estuary, and in coastal seawater, had no affect on rates of Mn oxidation. In the saltmarsh rates of Mn oxidation were much higher for creek bank sediments than for sediments from high marsh sites (2·31 ± 0·28 SD and 0·45 ± 0·14 SD nmol mg dwt -1h -1, respectively). Suspension of creek bank sediments in coastal seawater diluted with distilled water had no affect on rates of Mn oxidation when compared with suspensions in natural saltmarsh creek water. Sediments from high marsh sites exhibited short-term enhancement of Mn oxidation when the coastal seawater used for suspensions was experimentally diluted to 24% of full strength with distilled water (final salinity 8). High marsh sediments experimentally exposed to hypersaline conditions, demonstrated decreasing rates of Mn oxidation as sediment suspension salinity reached 102. This inhibition of Mn oxidation appears to have been due to the effects of the concentrated bulk salts present in the water. Differences in organic or other trace components of the creek water appear to have had a negligible effect on rates of Mn oxidation.

An operative definition of alkalinity in interstitial waters

Vertical profiles of total alkalinity, pH, and salinity, as well as ammonia, silicate, sulphate, sulphur and borate concentration in the interstitial water of sediments from the Bay of Cadiz were measured. The results established which of those chemical species included in Dickson's (1981) definition have an influence on total alkalinity above the limits of accuracy of the analytical method. This enables an operative definition of alkalinity in interstitial waters to be proposed: A T =[ HCO 3 −]+2[ CO 3 2−]+[ B( OH) 4 −]+[ OH −]+[ HPO 4 2−]+2[ PO 4 3−]+[ SiO( OH) 3 −]+[ HS −]+[ NH 3] The main advantage is that with only a moderate amount of analytical work, the speciation of inorganic C in the interstitial water can be accurately determined. At the same time, the analytical method proposed by Van den Berg and Rogers (1987) for estuarine waters has been revised and adapted for the measurement of alkalinity in interstitial waters.

Transpiration by an emergent macrophyte: source of water and implications for nutrient supply

The contribution of sediment interstitial water and the water column to the transpiration stream of Myriophyllum aquaticum (Vellozo) Verdcourt was determined to estimate the significance of mass flow in supply of sediment nutrients for plant growth. Sediment interstitial water accounted for about 2% of the water transpired over a 37 day period. Because of the small volume of water that originated in the sediment we concluded that mass flow did not significantly enhance nutrient supply to the roots of M. aquaticum. Relative growth rate (RGR) of adventitious, water roots was greater than whole plant RGR, and RGR of sediment roots was not significantly different from zero, indicating a shift in the biomass allocation after emergence of the apical meristem into the air. Water use, measured by the transpiration coefficient, averaged 260 ml H2O mg DW-1, which is similar to C-4 terrestrial plants. M. aquaticum has leaf characteristics commonly associated with xerophytic habitats. These characteristics may be necessary if a high transpiration rate and a mechanical requirement for high cell turgor pressure, required by a reliance upon hydrostatic pressure for support of the aerial stems, are mutually exclusive because of morphological constraints on hydraulic conductivity.

Predicting the acute toxicity of copper in freshwater sediments: Evaluation of the role of acid‐volatile sulfide

AbstractAcid‐volatile sulfide (AVS) has been proposed as an important partitioning phase determining the bioavailability of cationic metals in sediments. The objective of this research was to evaluate the role of AVS in determining copper toxicity in sediments from two sites heavily contaminated with copper: Steilacoom Lake, Washington, and the Keweenaw Watershed, Michigan. Sediments from the two sites were used in 10‐d toxicity tests with the amphipod Hyalella azteca, and results of the toxicity tests were compared to bioavailability predictions based on copper and AVS concentrations in the test sediments, as well as copper concentrations in the sediment interstitial (pore) water. Normalization of sediment copper concentrations to AVS accurately predicted sediments that were nontoxic when molar copper‐to‐AVS ratios were less than one; however, toxicity also was frequently not observed in samples with molar copper‐to‐AVS ratios significantly greater than one. In contrast, measurement of pore‐water copper concentrations and subsequent comparison of these concentrations to water‐only copper toxicity data for Hyalella azteca resulted in accurate predictions of the presence and extent of copper toxicity in the test sediments. These results indicate that AVS alone is not an appropriate partitioning phase for predicting copper bioavailability in freshwater sediments.

Fixation of inorganic carbon from different sources and its translocation in Spartina alterniflora Loisel

The extent to which Spartina alterniflora Loisel. fixes lacunar CO 2 and utilizes dissolved inorganic carbon in the interstitial water of sediment was investigated, and the contribution of these two processes to total primary productivity was estimated and compared with photosynthesis in the leaf blades. Atmospheric CO 2 is primarily fixed in the leaf blades, and the resultant assimilates are rapidly translocated through the leaf sheaths to the below ground tissues and growing points above ground. Lacunar CO 2 is primarily fixed in the leaf sheaths and stem. The fact that these assimilates remain in the tissues around the lacunar spaces indicates that lacunar CO 2 does not diffuse freely into the leaf blades but is recycled in the lacunar spaces. Dissolved inorganic carbon taken up by the plant from the sediment is primarily fixed by a dark reaction in the root tissues. Some dissolved inorganic carbon in the interstitial water may collect as gaseous CO 2 in the lacunae and be fixed in the leaf sheaths and stem. In addition, dissolved inorganic carbon may be taken up in the transpiration stream and be fixed in the leaf blades by photosynthesis. However, internal CO 2 fixation and dissolved inorganic carbon utilization together are only about 10% of the rate of fixation of atmospheric CO 2 by leaves.

Alkylphenol ethoxylates in the environment

A comprehensive monitoring study, sponsored by the Chemical Manufacturers Association and designed in cooperation with the Environmental Protection Agency (EPA), measured the levels of nonylphenol (NP) and its ethoxylates (NPE) in 30 rivers. The sites, all receiving municipal or industrial wastewater, were selected at random from EPA’s United States river reach database by a statistical procedure. Water column and bottom sediment samples were collected along a perpendicular transect at each site. All samples were assayed for NP and NPE1, and the higher ethoxylates (NPE2 to NPE17) were determined in the water samples. Analysis was by high‐performance liquid chromatography (HPLC) with fluorescence detection of microgram quantities of NPE obtained by extractive steam distillation (NP and NPE1) or a dualcolumn extraction procedure (NPE2 to NPE17). Sample collection and analytical procedures were validated according to rigorous EPA guidelines, and quality assurance standards were met throughout the study. NP and NPE concentrations in river water were mostly (60 to 75% of the samples) below their detection limits (about 0.1 ppb for NP, NPE1, and NPE2; 1.6 ppb for NPE3–17). The highest levels found were about 1 ppb for NP, NPE1, and NPE2, 15 ppb for NPE3–17. A majority of sediment samples contained detectable amounts of NP and NPE1, ranging up to 3000 ppb for NP and 170 ppb for NPE1. Sediment interstitial water concentrations of NP were estimated to be similar to concentrations in the water column.

Seasonally induced separation of Mn and Fe in interstitial waters of exposed anoxic sediments from the dead sea

Though the geochemistries of manganese and iron have similar patterns there are environmental conditions under which Mn compounds become separated from Fe compounds. These conditions have been described at length in the literature [1-4] . Martin and Whitefield, for example [5], showed that the ratio of Fe/Mn in river water is 5, while in precipitates from nearshore marine waters this ratio is 0.1 [1]. In this study we report on dramatic chemical changes which occur between winter and summer to the Mn and Fe in the sediment interstitial waters. The migration of Mn and Fe in the interstitial water is one of the main diagenetic processes occurring in the newly exposed sediments of the Dead Sea shore [6]. Diagenesis started as a result of a drop in the Dead Sea water level [7] which exposes the anoxic bottom sediments to the atmosphere. This new environmental setting offers a unique opportunity to study the migration of iron and manganese in interstitial solutions during the transition from anoxic to oxic conditions. The reactions taking place since exposure to the atmosphere are the results of the draining, the flushing, and the drying of the sediments. The seasonal climatic range in a desert site like the Dead Sea shore varies between the extremes of cool with short periods of rains and floods in the winter to hot and dry in the summer. The research area is located on the floodplain of Wadi Ze'elim on the west-

U-series disequilibria in early diagenetic minerals from Lake Magadi sediments, Kenya: Dating potential

At the southern end of the Gregory Rift Valley, Lake Magadi occupies the bottom of a relatively large drainage basin. It is presently covered by a thick trona crust, which overlies two silty-clay units deposited during Late Pleistocene high lake stands. These units consist of a mixture of detrital grains (anorthoclase, amphiboles, quartz), clays (illite, authigenic zeolites), phosphates, and sedimentary sodium silicates and cherts. A late diagenetic calcite is occasionally observed. The authigenic and/or diagenetic mineralogical phases were extracted and analyzed for their uranium and thorium isotope contents. All yielded highly correlated ( 234U 232Th vs. 238U 232Th ) and ( 230Th 232Th vs. 234U 232Th ) isochrons defining two-component mixing systems (detrital and authigenic phases). The detrital component is characterized by large excesses of 230Th (over 234U) and by 230Th 232Th ratios carrying an imprint of the source rocks (e.g., Precambrian basement vs. volcanics) and indicating efficient uranium-leaching processes during the previous pedologic cycle. The slope of the isochrons defines the 234U 238U and 230Th 234U ratios of the authigenic component, i.e., the age of the uranium-uptake episode. Zeolites yield an age of 10.4 ± 0.6 ka. This age is in agreement with the 14C chronology already established for the most recent high lake level episode in the basin (10,000–12,000 yr Bp). Sodium-silicates and cherts yield distinct ages of 98.5 ± 20 and 6 ± 3 ka, respectively, for the lower and upper lacustrine units. These ages allow the conclusion that (1) sedimentary silicates are of late diagenetic origin, and (2) that the lower lacustrine unit was deposited during a former high Lake Magadi level, possibly during the lacustrine episode dated at 135 ± 10 ka from uranium-series measurements on littoral stromatolites. Finally, the late diagenetic calcite, which yields an age of about 5 ka, indicates a significant change in the sediment interstitial water chemistry. This is also shown by the occurrence of calcitic oncolites in flat deposits assigned to a mid-Holocene minor oscillation of Lake Magadi level on the basis of their 14C ages. It is concluded that uranium-series measurements in diagenetic minerals may give access to the age of their formation.

Sampling and measurement of transuranic elements in interstitial waters of sediments

The construction and installation of porous cup soil solution samplers and their operation in a saltmarsh is described. Levels of transuranic contamination in the saltmarsh sediments are relatively high (up to 930 kBq m −2 for 241Am and 500 kBq m −2 for 239,240Pu), but levels in the interstitial, or sediment-pore, waters are low, generally in the range 1 to 50 mBqL −1. Both 241Am/ 239,240Pu ratios and concentrations of dissolved transuranic elements are affected by the degree of inundation of the sampling site. These parameters also vary over time in an apparently unpredictable manner. The K d values (solid/solution distribution coefficients) for Pu and Am are comparable with those measured by other workers at this site.

Hydride-trapping techniques for the speciation of arsenic

The determination of arsenic species by the trapping of volatile hydrides prior to atomization in the light path of an atomic absorption spectrometer is described and its operation in the measurement of arsenic species in the marine environment are discussed. Examples are drawn from the analysis of Tamar estuary water and sediment interstitial (pore) waters and from studies of the temporal variation of dimethylarsenic in coastal waters. Improvements in both the design and operation of the technique have resulted in enhanced performance. Baseline resolution of inorganic arsenic, monomethylarsenic and dimethylarsenic is now possible and trimethylarsine is resolved. Ultraviolet photolysis of arsenobetaine and arsenocholine gives partial conversion to trimethylarsine oxide. This can be employed in the qualitative appraisal of the presence of trimethylarsenic species. Current detection limits (3 sigma) for inorganic, mono- and di-methylarsenic lie in the range 19 to 61 pg absolute, giving 19–61 ng/1 concentration detection limits for 1 ml samples. This can be improved even further by using larger sample volumes. The properties of the analysis system when presented with various arsenic species are described. A ca. 10% loss of arsenite occurs in samples stored at —20 °C and immediate freezing of samples in liquid nitrogen is recommended.

The contribution of ammonia, metals and nonpolar organic compounds to the toxicity of sediment interstitial water from an illinois river tributary

AbstractToxicity of Illinois River bulk sediment, sediment interstitial (pore) water and elutriates to the oligochaete Lumbriculus variegatus, fathead minnow (Pimephales promelas) and the amphipod Hyalella azteca was compared to determine the most representative aqueous fraction for toxicity identification evaluation (TIE) studies. Toxicity of pore water corresponded better than elutriates to bulk sediment toxicity. Subsequent TIE procedures conducted with the cladoceran Ceriodaphnia dubia indicated that ammonia, metals and nonpolar organic compounds (nonylphenols, polycyclic aromatic hydrocarbons, benzenes, long‐chain hydrocarbons) were responsible for toxicity of the sediment pore water. Results of TIE manipulations also suggested that methods for recovering pore water that include filtration may eliminate, a priori, a major component of the sediment contaminants responsible for toxicity.

Fate of Linear Alkylbenzenesulfonates in a Lake Estuary

The concentration of linear alkylbenzenesulfonates(LAS)in the Lake Teganuma estuary indicated a seasonal variation and a downstream decrease. The downstream decrease in the studied section varied between 28% and 100% seasonally, and the average was 66(±25)% during 1987-1988. As to explain the decrease, we investigated biodegradation of LAS in water, diffusive exchange of dissolved phase LAS through the sediment/water interface, and settling of adsorbed phase LAS. Adsorption experiments were performed between 0.3-9 ppm of the initial concentrations of LAS. The experimental equation used to estimate the adsorption coefficient of LAS was verified by using adsorption data from field observations. The averaged value 2.4×10−5 cm2 sec−1 for the diffusion coefficient in the sediment interstitial water was obtained from the experiments using the sediment core samples. The biodegradation rate constant (between 0.06 and 3.33 day−1) in water and the diffusive flux rate (between −0.157 and 0.022 mg m−2 hour−1) from water to sediment were obtained from field observations and experiments. Based on this information, a mathematical model was applied to simulate the downstream decrease of LAS in water. With this model, nearly 10% of the total LAS from the river was found to be transported to sediment both in summer and winter. The settling flux of LAS in the lake estuary was ten times greater than the diffusive flux. The settling flux was ten times smaller than the disappearing flux by biodegradation in summer but was the same level in winter.

The carbonate system in the Black Sea

We have measured both alkalinity and total carbon dioxide on a selected set of Black Sea samples from cruise 134 of R.V. Knorr, using gas extraction/coulometry techniques, and improved titration procedures that permit more accurate data than those obtained in earlier expeditions. Earlier results had shown an apparent excess in alkalinity, by a factor of 1.6, from the stoichiometric ratio predicted from the sequential oxidation of Redfield ratio organic matter by the species O 2, NO 3 − and SO 4 2−. Thus both the nature of the organic substrate and our fundamental knowledge of reaction stoichiometry in anoxic systems were called into question. We show that the total CO 2 balance is consistent, within narrower limits than found earlier, with oxidation of organic matter by sulfate: 2CH 2O+SO 4 2− → 2HCO 3 −+H 2S and consistent with work on sediment interstitial waters in anoxic conditions ( Berner et al., 1970, Limnology and Oceanography, 15. 544–549: Ben Yaakov, 1973, Limnology and Oceanography, 18, 86–94). The total CO 2 results are lower by 300 μmol kg −1 in surface waters, and 50 μmol kg −1 in deep waters, than data reported from the 1969 Atlantis II expedition. While changes in Black Sea hydrography have been documented, these CO 2 system changes are far too large to be accounted for by these processes and are more likely the result of improved technique, rather than geochemical evolution.

THE CONTRIBUTION OF AMMONIA, METALS AND NONPOLAR ORGANIC COMPOUNDS TO THE TOXICITY OF SEDIMENT INTERSTITIAL WATER FROM AN ILLINOIS RIVER TRIBUTARY

Toxicity of Illinois River bulk sediment, sediment interstitial (pore) water and elutriates to the oligochaete Lumbriculus variegatus, fathead minnow (Pimephales promelas) and the amphipod Hyalella azteca was compared to determine the most representative aqueous fraction for toxicity identification evaluation (TIE) studies. Toxicity of pore water corresponded better than elutriates to bulk sediment toxicity. Subsequent TIE procedures conducted with the cladoceran Ceriodaphnia dubia indicated that ammonia, metals and nonpolar organic compounds (nonylphenols, polycyclic aromatic hydrocarbons, benzenes, long-chain hydrocarbons) were responsible for toxicity of the sediment pore water. Results of TIE manipulations also suggested that methods for recovering pore water that include filtration may eliminate, a priori, a major component of the sediment contaminants responsible for toxicity.