Interstitial Water Concentrations Research Articles

Extraction and analysis of low concentrations of DDT, DDE and DDD in small volumes of sediment pore water

As a result of effluent discharges by a previous chemical manufacturer, sediments in the Huntsville Spring Branch-Indian Creek (HSB-IC) near Huntsville, AL are contaminated with DDT and its metabolites. This area was selected as a field location at which to evaluate equilibrium partitioning theory (EqP) to predict the bioavailability of nonionic organic chemicals associated with sediments. An important component of the evaluation of EqP features determination of contaminant concentrations in the sediment interstitial (pore) water. The objective of our study was to develop an analytical method to measure o,p′- and p,p′-DDE, DDD and DDT at low concentrations (< 1 ng/mL) in small volumes (ca., 30 mL) of sediment pore water. Initially, pore water from a clean, uncontaminated (control) sediment was spiked with DDT and its metabolites and extracted with hexane. The extracts were applied to chromatography columns packed with acid silica gel or acid celite to remove interfering compounds. Gas chromatograms of extracts treated with acid celite exhibited lower background interferences and were easier to interpret than chromatograms for samples processed using acid silica gel. The acid celite technique was further assessed by spiking uncontaminated pore water over a range of DDE, DDD and DDT concentrations and evaluating recovery efficiencies for each target analyte. Polychlorinated biphenyl congener, 2,3,5,6-tetrachlorobiphenyl (PCB 065) was determined to be a good compound for monitoring method performance (e.g., analyte recovery). Pore water samples were obtained from nine sampling sites in the HSB-IC system and analyzed for DDT and its metabolites where concentrations ranged from 0.020 ng/mL (detection limit) to 8.200 ng/mL in 30 mL of pore water.

Effect of sediment organic carbon on the toxicity of a surfactant to Hyalella azteca

AbstractAccording to current sediment bioavailability models (e.g., equilibrium partitioning), toxicity of sorptive compounds in sediment depends on the free concentration in interstitial water. This free concentration may depend on both the characteristics of the compound and the sediment. For the sorption of anionic surfactants, sediment organic carbon content and cation exchange capacity have been shown to be important factors; however, it is not clear how these factors affect toxicity. Determining toxicity of these compounds in sediment using traditional batch sediment tests has not been entirely successful in the past due to excessive loss of parent material via biodegradation. In this study, effects of organic carbon on anionic surfactant toxicity were determined using highly branched alkylbenzene sulfonate (ABS) as the test compound in order to limit losses from biodegradation. Sediments were amended with peat moss to investigate the effects of organic carbon on surfactant sorption and toxicity to Hyalella azteca. Results support previous hypotheses regarding the effect of organic carbon on bioavailability and toxicity. Apparent sorption coefficients (Kapp) increased with higher organic carbon levels. Likewise, greater sediment concentrations of ABS were required to elicit toxic responses at greater organic carbon concentrations. Toxicity in sediment appeared to be due to interstitial water exposure.

Effects of In Vivo induction and inhibition of phase 1 and 2 enzymes on the toxicity of malathion to tilapia

A 42-d flow-through experiment was conducted to evaluate the effects of the organo-phosphate pesticide, chlorpyrifos, and microcosm size (small: 144 cm2; large: 400 cm2) on benthic estuarine macroinvertebrate colonization. Nested central and perimeter (outside margin) cores were used to assess animal distribution within microcosms. Fine-grained, organically-rich (approximately 4.0% organic carbon and 20% dry wt) sediments were nominally fortified with chlorpyrifos controls, low (1.0) and high treatments (10.0 μg−1 wet sediment). Large microcosms contained a significantly (p < 0.05) higher average taxa richness (10.9) than small microcosms (8.6) but small microcosms contained a significantly greater average animal density (295.8; numerical abundance adjusted to unit area) than large microcosms (120.5). Density of the polychaete, Neanthes succinea, the amphipod, Corophium acherusicum, and the barnacle, Balanus sp., was significantly greater in small microcosms but density of Ensis minor was significantly greater in large microcosms. In small and large microcosms, respectively, densities averaged significantly greater numbers in perimeter cores (e.g. 203.1 and 75.1) vs central cores (71.9 and 45.4). Average density decreased significantly with increasing chlorpyrifos concentration from controls (326.8), to low (123.8) and high (78.8) treatments. The density decrease was significantly related only to C. acherusicum whose densities decreased from controls (285.8) to low (88.5) and high (43.9) dosed microcosms. Application of an equilibrium partitioning model indicated that density of C. acherusicum was sensitive to an estimated interstitial water concentration of approximately 0.48 μg liter−1. Non-metric multidimensional scaling ordination analyses provided important insights into response patterns not available through ANOVA procedures. A permutation procedure (ANOSIM) detected a significant size effect (p < 0.0001) and a significant effect between controls and low (p < 0.042) and high doses (p < 0.013) but not between low and high chlorpyrifos treatments (p < 0.465). A single species, C. ascherusicum, as in the ANOVA analyses, dominated contributions to community average percent dissimilarity in most combinations of microcosm size and chlorpyrifos treatment effects (range: 8.4–21.9%). Community structure differed significantly in several combinations of microcosm size, core position and chlorpyrifos treatment. Results confirm earlier work that intrinsic design factors influence benthic macroinvertebrate community structure and determine taxa available to pesticide exposure in microcosms.

Voltammetric method for the determination of Zn, Cd, Pb, Cu and Ni in interstitial water.

To determine heavy metals in interstitial water from Baltic sea sediments a sampling method with subsequent voltammetric determination is described. Copper, lead, zinc and cadmium are determined in the UV-digested samples of interstitial water by differential pulse anodic stripping voltammetry while nickel is determined by adsorption voltammetry. The determination of five metals in one sample in a wide concentrations range is possible using a low cost apparatus. The profiles of the metal concentrations in interstitial water of subsequent layers of sediments, sampled from Puck Bay, Gdańsk Bay, the Bornholm area and the Słupsk area are presented.

Natural Organohalogens in Sediments

Recent fluvial, lacustrine and marine sediments were found to contain significant concentrations of organohalogens which cannot be explained by known anthropogenic halogen compounds. The assumption of a natural source for the major part of these organohalogens is strongly supported by the fact that in lacustrine sediments deposited some hundred years ago – where no industrial chlorinated organic compounds should be expected – concentrations between 30 and 100 mg/kg of adsorbable organic halogens (AOX, expressed as equivalent chlorine) were detected. In anoxic sapropels of the Black Sea, several thousand years old and having a high organic content (mainly derived from marine phytoplankton), organic bromine and iodine occur at levels up to 313 and 465 mg/kg, respectively. AOX concentrations in biogenic sediments from various epochs and representing different stages of coalification (peat – lignite – bituminous coal – anthracite) are clear evidence for naturally occurring organohalogens. Plant material has therefore to be considered as the most important primary source of high molecular weight organohalogens in sediments. In addition, natural low molecular organohalogens produced by bacteria, fungi, algae (such as haloalkanes, terpenes, amino acids and peptides, chlorophenols etc.) will also accumulate in the sediment and become part of its primary organohalogen content. As a secondary source of organohalogens in sediments their formation in the sediment itself has to be considered. Biotic halogenation of organic substrates by haloperoxidases (to occur in algae and other marine organisms but also in terrestrial lichens and fungi) leading to volatile organohalogens has been observed already. Only little knowledge exists on abiotic halogenation. In preliminary investigations in the system trichloroacetic acid – water – humic substances, chlorinated compounds could be identified. A transfer of (low molecular) organohalogens from the sediment into the interstitial water is obvious: If compared with the supernatant lake water, AOX concentrations in interstitial water of Lake Constance sediments are enriched by a factor of 20–70. Under anaerobic conditions bacterial decomposition of organohalogens leads to the release of halide ions into the interstitial water of the sediment. The results presented here fully confirm our previous conclusion [1], that the AOX value cannot be used exclusively as a sum parameter for anthropogenic organic halogen compounds.

A field investigation of the relationship between zinc and acid volatile sulfide concentrations in freshwater sediments

Understanding relationships between cationic metals such as cadmium, copper, nickel, lead and zinc, and amorphous iron sulfides, measured as acid volatile sulfide (AVS), is key to predicting metal bioavailability and toxicity insediments. The objective of the present study was to assess seasonal and spatial variations of AVS in freshwater sediments contaminated with zinc. Sediments were sampled from three streams with varying levels of zinc contamination at two different times, March and June of 1995, representing cold- and warm-weather situations. Interstitial (pore) water concentrations of zinc, and solid phase concentrations of AVS and zinc were measured in surficial and deep sediment horizons. Toxicity tests (10-d) with the amphipodHyalella azteca were conducted using intact cores. Sediment zinc concentrations from six sites within the primary test stream differed by about five-fold, and also varied seasonally. Acid volatile sulfide concentrations were generally lower than those of zinc, and pore water zinc concentrations typically were elevated. There was a positive correlation between solid-phase AVS and zinc concentrations, suggesting that the system was dominated by zinc, as opposed to iron sulfides. In contrast to expectations arising from some studies of seasonal variations of AVS in iron-dominated systems, AVS concentrations were smaller in June than in March. However, this was likely due to a major storm event and associated sediment scouring before the June sampling, rather than to seasonal processes related to variations in temperature and dissolved oxygen. Based upon an indirect analysis of depth variations in AVS, there was some indication that zinc sulfide might be less prone to oxidation than iron sulfide. There was a strong correlation between toxicity of the sediment samples toH. azteca and interstitial water concentrations of zinc; however, the possible contribution of other contaminants to sediment toxicity cannot be dismissed.

PREDICTING THE TOXICITY OF METAL-CONTAMINATED FIELD SEDIMENTS USING INTERSTITIAL CONCENTRATION OF METALS AND ACID-VOLATILE SULFIDE NORMALIZATIONS

We investigated the utility of interstitial water concentrations of metals and simultaneously extracted metal/acid-volatile sulfide (SEM/AVS) ratios to explain the biological availability of sediment-associated divalent metals to benthic organisms exposed in the laboratory to sediments from five saltwater and four freshwater locations in the United States, Canada, and China. The amphipod Ampelisca abdita or the polychaete Neanthes arenaceodentata were exposed to 70 sediments from the five saltwater locations, and the amphipod Hyalella azteca or the oligochaete Lumbriculus variegatus were exposed to 55 sediments from four freshwater locations in 10-d lethality tests. Sediment toxicity was not related to dry weight metals concentrations. Almost complete absence of toxicity in spiked sediments and field sediments where metals were the only known source of contamination and where interstitial water toxic units (IWTUs) were <0.5 indicates that toxicity associated with sediments having SEM/AVS ratios <1.0 from two saltwater locations in industrial harbors was not metals-related as these sediments contained <0.5 IWTU. Metals-associated toxicity was absent in 100% of sediments from the remaining three saltwater field locations, where metals were the only known source of contamination and SEM/AVS ratios were ≤1.0. Two-thirds of 45 sediments from seven saltwater and freshwater field locations having both IWTUs >0.5 and SEM/AVS ratios <1.0 were toxic. Toxicity was observed less often when SEM/AVS ratios >1.0 (39%) or IWTUs >0.5 (55%) were used alone. The difference between the molar concentrations of SEM and AVS (SEM – AVS) can provide important insight into the extent of additional available binding capacity, the magnitude by which AVS binding has been exceeded, and, when organism response is considered, the potential magnitude of importance of other metal binding phases. For these reasons, SEM – AVS should be used instead of SEM/AVS ratios as a measure of metals availability. Over all published experiments with both metal-spiked and field sediments, SEM – AVS and IWTUs accurately (99.2%) identified absence of sediment toxicity and with less accuracy (79.1%) identified the presence of toxicity.

ΣPAH: A Model to predict the toxicity of polynuclear aromatic hydrocarbon mixtures in field‐collected sediments

AbstractThe ΣPAH model estimates the probability of toxicity of PAH‐contaminated sediments using a combination of equilibrium partitioning, QSAR, toxic unit, additivity, and concentration‐response models. The sediment concentration of organic carbon and 13 PAH (polynuclear aromatic hydrocarbon) compounds were measured. Interstitial water concentrations (PAH1W) of the 13 compounds were predicted by equilibrium partitioning. The 10‐d LC50 of each compound in interstitial water (10‐d LC501W) was predicted by a QSAR regression of 10‐d LC501W (from spiked sediment tests) to Kow. Toxic unit concentrations of individual compounds (TU1) were predicted as PAH1w/10‐d LC501w. The total number of toxic units of the 13 compounds (ΣTU1) was calculated assuming the additivity of toxic effects of PAHs. ΣTU1 was used to predict the probability of toxicity to marine and estuarine amphipods using a concentration‐response model derived from spiked sediment toxicity tests. The ΣPAH model was verified by comparing predicted and observed toxicity in field‐collected sediment samples. There was 86.6% correspondence and no significant difference between predicted and observed toxicity at PAH‐contaminated sites. Ecological‐effect levels predicted by theΣPAH model correspond with several sediment‐quality guidelines.

Life habit of vesicomyid clam,Calyptogena soyoae, and hydrogen sulfide concentration in interstitial waters in Sagami Bay, Japan

In and around the beds of vesicomyid clam (Calytogena soyoae) located off Hatsushima Island in Sagami Bay, central Japan, hydrogen sulfide concentration in bottom water and interstitial water was measured every 10 cm from just above seafloor to 40 cm deep usingin situ separative dialysis bags. While hydrogen sulfide over 0.01 mmol/kg was not measured from the seawater just above the dense clam beds, the concentration of hydrogen sulfide increased rapidly below 10 cm deep. The results indicate that the habit of the clam is correlated with high concentration of hydrogen sulfide contained in pore waters of sediments between depths of 10 and 20 cm from the bottom surface. Concentrations of hydrogen sulfide ranging from approximately 0.05 mmol/kg to 0.6 mmol/kg might be suitable requirement for the habitat ofC. soyoae.

Assessing potential bioavailability of metals in sediments: A proposed approach

Due to anthropogenic inputs, elevated concentrations of metals frequently occur in aquatic sediments. In order to make defensible estimates of the potential risk of metals in sediments and/or develop sediment quality criteria for metals, it is essential to identify that fraction of the total metal in the sediments that is bioavailable. Studies with a variety of benthic invertebrates indicate that interstitial (pore) water concentrations of metals correspond very well with the bioavailability of metals in test sediments. Many factors may influence pore water concentrations of metals; however, in anaerobic sediments a key phase controlling partitioning of several cationic metals (cadmium, nickel, lead, zinc, copper) into pore water is acid volatile sulfide (AVS). In this paper, we present an overview of the technical basis for predicting bioavailability of cationic metals to benthic organisms based on pore water metal concentrations and metal-AVS relationships. Included are discussions of the advantages and limitations of metal bioavailability predictions based on these parameters, relative both to site-specific assessments and the development of sediment quality criteria.

Intraspecific variability of Zostera marina L. (eelgrass) in the estuaries and lagoons of the southwestern Netherlands. II. Relation with environmental factors

Habitat and tissue characteristics were assessed for four populations of Zostera marina L., ranging in life-history strategy from perennial to annual. Results are discussed in relation to previously reported data on population dynamics. Significant differences in turbidity existed between sites, and a possible frequent light limitation for growth during the growing season was suggested for one site. Nutrient concentrations in surface water varied between sites and seasons and were considered to play an important part in the different growth rates demonstrated. Despite relatively high nitrogen concentrations in interstitial water, possible nitrogen growth limitation was theoretically indicated for three populations.

Organic carbon partitioning as a basis for predicting the toxicity of chlorpyrifos in sediments

AbstractThe objective of this study was to evaluate an organic carbon partitioning model for predicting bioavailability of the organophosphate chlorpyrifos in sediments, in support of the development of a sediment‐quality criterion for the pesticide. Initial 10‐d water‐only toxicity tests were conducted with the midge Chironomus tentans to define the sensitivity of this species to chlorpyrifos. Two uncontaminated sediments with differing organic carbon contents (approximately 3 and 8.5%) were spiked with varying amounts of chlorpyrifos designed to result in equilibrium interstitial (pore) water concentrations that would bracket the effects concentrations observed in the water‐only exposures. Ten‐day toxicity tests with Chironomus tentans were conducted with the spiked sediments under conditions similar to those in the water‐only exposure. Based on predicted pore‐water concentrations of chlorpyrifos, results of the water‐only and sediment tests were in close agreement. The water‐only LC50 of chlorpyrifos to Chironomus tentans was 70 ng/L, whereas LC50 values based on predicted pore‐water concentrations in the two test sediments were 40 and 70 ng/L. Total concentrations of chlorpyrifos measured in pore water from the test sediments were always at least an order of magnitude greater than predicted pore‐water concentrations of the pesticide. However, upon correction for that fraction of the measured chlorpyrifos potentially bound to DOC in the pore water, measured and predicted chlorpyrifos concentrations were in much closer agreement, with the former typically about threefold greater than the latter. Overall, these results suggest that within the range of organic carbon tested in the present study, an equilibrium partitioning model based on organic carbon is appropriate for predicting the bioavailability of sediment‐associated chlorpyrifos to benthic invertebrates.

Effect of stormwater runoff on metal distribution in the sediment and interstitial waters of an urban river.

Metals were analysed in the interstitial waters and sediments of an urban river, receiving stormwater and combined sewer overflow, over a two month period and interpreted in terms of rain events. Depth profiles for metal concentrations showed the highest interstitial water concentrations in samples with low sedimentary organic material. Storm events can both resuspend sediments and associated metal-rich interstitial waters and alter the metal distribution between interstitial water and sediment. Metal profiles downstream of a combined sewer overflow showed elevated interstitial water concentrations compared to an upstream site. Downstream sites also reveal evidence of metal burial and resuspension processes during and between wet periods.

Development and evaluation of test methods for benthic invertebrates and sediments: Effects of flow rate and feeding on water quality and exposure conditions

In order to ensure among-laboratory comparability in the results of sediment toxicity tests, it is necessary to characterize the influence of variations in test regimes on organism responses and exposure conditions. The objective of these studies was to develop and document an optimized combination of overlying water renewal (flow) and feeding rates for sediment tests with three commonly used benthic species (midges, Chironomus tentans; amphipods, Hyalella azteca; oligochaetes, Lumbriculus variegatus). Optimal conditions were defined by a number of chemical and biological considerations including: (1) flow rate through the system, (2) amount of food added, (3) acceptable responses (survival, growth, reproduction) of the organisms over the course of a 10-day test, and (4) maintenance of an adequate concentration of dissolved oxygen in overlying water. The goal was to minimize factors (1) and (2), while maximizing criteria (3) and (4). The major reason for minimizing (1) and (2) was the concern that excessive water flow or addition of food could reduce exposure of the test organisms to sediment-associated contaminants. To evaluate this, interstitial (pore) water concentrations of contaminants (ammonia, zinc, copper, dieldrin) were measured over the course of 10 day tests conducted with a number of different sediments under various flow and feeding regimes. The different combinations of flow/feeding had variable effects upon pore water concentrations of contaminants; for example under our optimized regime, in some instances slight decreases in interstitial water contaminant concentrations were observed, whereas in other cases contaminant concentrations remained constant or even increased. Overall, the use of minimal water renewal and feeding rates should result only in small changes in exposure of benthic organisms to contaminants in pore water over the course of 10-day tests.

Bioavailability of sediment‐sorbed chlorinated ethers

AbstractThe equilibrium partitioning approach for developing numerical sediment‐quality criteria was tested in the laboratory using a mixture of chlorinated ethers/alcohols sorbed to sediments. The sorption behavior of the principal component of the mixture, tetrachloropropyl ether (TCPE), was determined on sediments with organic carbon contents ranging from 0.3 to 5.2%. Sorption was found to be a strong function of organic carbon with a log(Koc) of 2.9. Predictions of log(Koc) using Kow correlations and molecular connectivity indexes ranged from 2.9 to 3.3. Toxicity tests were then conducted on sediments spiked with the chlorinated ether mixture using the amphipod Hyalella azteca, the midge Chironomus tentans, and the water flea Daphnia magna. Sediment toxicity was highly dependent on the sediment organic carbon content, but there were differences in toxicity that could not be explained by differences in organic carbon. Interstitial water concentrations of total chloroether did not compare with effects between different sediments for either of the two sediment‐dwelling organisms, with LC50 values ranging from 1.6 to 10.5 mg dissolved chloroether per liter for Hyalella azteca and 1.5 to 9.3 mg dissolved chloroether per liter for Chironomus tentans. The effect of other sediment properties on the sensitivity of these two organisms may account for this difference. For Daphnia magna, there was a much closer correlation between interstitial water concentrations and effects, with the aqueous LC50 having a range of only 0.9 to 2.0 mg/L.

Benthic nutrient fluxes in Cadiz Bay (SW Spain)

During summer and autumn 1988, benthic fluxes of nutrients and oxygen were measured in the Bay of Cadiz. The study was carried out using benthic chambers and in addition by determining gradients of nutrient concentration in interstitial water. Fluxes ranged between 13.5–24.3, 3.4–7.8, 6.1–28.4 and (− 99.4)−(− 188.5) mmol m− 2 d−1 for NH4 + , o-P, SiO2 and O2 respectively. These values are far higher than those reported by other authors for locations at similar latitudes. The stoichiometry of O, N and P transference suggest that benthic degradation of principally allochthonous organic matter takes place mainly through anaerobic pathways.

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.

Bioavailability of fluoranthene in freshwater sediment toxicity tests

AbstractTo examine equilibrium‐partitioning model predictions of interstitial water concentrations of fluoranthene as part of the equilibrium‐partitioning (EqP) approach to sediment quality criteria development, the bioavailability (toxicity) of fluoranthene‐amended sediment (a nonpolar organic compound) to Hyalella azteca, Daphnia magna, and Chironomus tentans was determined. Fluoranthene was added to three freshwater sediments with similar organic carbon content (0.44‐0.50%). Although sediments were from divergent sources (Water Research Field Station [WRFS], Trinity River [TR], and Lake Fork [LF]), sediment physical and chemical characteristics did not vary appreciably, leading us to hypothesize (based on EqP theory) that fluoranthene‐amended sediment toxicity would not vary between sediments. Predicted interstitial water concentrations from the equilibrium‐partitioning model were similar to measured interstitial water concentrations for WRFS and TR sediment, but the model underpredicted measured values for LF sediment by a factor of two. EC50s for Daphnia magna, Hyalella azteca, and Chironomus tentans in interstitial water were a factor of two to five greater for LF than for WRFS and TR sediments. Factors other than organic carbon content of sediments (e.g., dissolved organic carbon content in interstitial water) probably contributed to the variability in bioavailability of fluoranthene. Based on 10‐d sediment toxicity tests with Hyalella azteca, Daphnia magna, and Chironomus tentans, organic carbon‐normalized sediment concentrations were better predictors of toxicity than interstitial water and bulk sediment fluoranthene concentrations. In 10‐d aqueous‐phase tests with fluoranthene, Chironomus tentans and Hyalella azteca were twice as sensitive as Daphnia magna. The response of freshwater organisms to fluoranthene‐amended sediment was similar to that of marine organisms exposed to fluoranthene in other studies. The EqP approach for sediment‐quality criteria accurately predicted sediment toxicity for WRFS and TR sediments but not for LF sediment, indicating the model may be overly protective for some bottom sediments. Factors other than organic carbon content may be important in affecting neutral organic compound bioavailability.

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.

The influence of organic matter quality on the toxicity and partitioning of sediment-associated fluoranthene

Organic matter in sediment is derived from many sources, including dead plants and animals, fecal matter, and flocculated colloidal organic matter. Chemical partitioning and toxicity of nonpolar organic contaminants is strongly affected by the quantity of sediment organic matter. The purpose of this study was to determine whether the quality of sediment organic matter affects partitioning and bioavailability of such contaminants. A base substrate, amended to a consistent organic carbon level (nominally 0.4%, measured 0.35% ± 0.11 sd POC [particulate organic carbon]) with five types of organic matter (a macrophyte, fecal matter of two invertebrate species, suspended particulate organic matter, and an organic-rich mud), was spiked with serial concentrations of the polynuclear aromatic hydrocarbon, fluoranthene. After a five-week equilibration period, the toxicity of the spiked substrates to an infaunal amphipod, Rhepoxynius abronius, was measured, and the distribution of fluoranthene between particulate and interstitial water phases (including total and freely dissolved interstitial water phases) was determined. The range of acute toxicity among organic matter–source treatments was small when based on total sediment concentrations (11.1–19.1 mg fluoranthene per kilogram dry sediment, nominal). Partitioning of fluoranthene between particulate-sorbed and interstitial water phases was not affected by organic matter quality, except when the source was fresh plant material. This variability may have been due to qualitative differences in the particulate/interstitial water partitioning in plant material as a source of sedimentary organic matter or an artifact in the method used to determine freely dissolved, interstitial water fluoranthene concentrations. Equilibrium partitioning models accurately predicted interstitial water concentrations of fluoranthene for the nonplant substrates once corrections were made for the solubility of fluoranthene in seawater. Our data suggest that equilibrium partitioning–based sediment quality criteria for fluoranthene may not need to correct for the quality of organic carbon in sediments and that these criteria can be applied to sediments with a particulate organic carbon content as low as 0.3%.