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G Allen Burton

Publications and source records attributed to G Allen Burton.

17 recordsLinked to original sources
PubMed2006

Applying adult emergence as an endpoint in a post-exposure laboratory test using two midge species (Diptera: Chironomidae).

Several approaches have been used to evaluate biological impairment in aquatic ecosystems which can be categorized as either laboratory or field. In the recent years, the laboratory toxicity test approach has been extended to field exposures where ambient factors are allowed to influence the test response. Field exposures of laboratory test organisms require method modifications. In this paper, a novel in situ method is described which measures growth, survival and emergence of sediment inhabiting insects (Diptera: Chironomidae) that are used in standardized laboratory toxicity testing. Two standard chironomid species (Chironomus riparius and Chironomus tentans) were used to test the suitability of the approach and to compare the performance of the species. The larvae were transferred to the laboratory for emergence after 7 days in situ exposure which was compared to laboratory responses. Growth, survival and emergence were significantly lower in the in situ pre-exposure than in the laboratory. Also, emergence success was significantly lower in one reference sediment (LMR) than in the other test sediments in both in situ and the laboratory treatment. These lower response levels likely resulted from sediment characteristics and artifacts related to the exposure in the in situ chamber. Feeding and water quality within the exposure chamber appear to be factors that may differ markedly from the laboratory exposure and may affect organism responses. C. riparius developed (growth, emergence time) faster than C. tentans in all treatments, otherwise the species responded similarly. C. riparius may be a better alternative for the chronic in situ exposures because of shorter exposure times and reduced feeding requirements.

Analysis of Variance↗
PubMed2006

Analysis of algorithms predicting blood:air and tissue:blood partition coefficients from solvent partition coefficients for prevalent components of JP-8 jet fuel.

Algorithms predicting tissue and blood partition coefficients (PCs) from solvent properties were compared to assess their usefulness in a petroleum mixture physiologically based pharmacokinetic/pharmacodynamic model. Measured blood:air and tissue:blood PCs for rat and human tissues were sought from literature resources for 14 prevalent jet fuel (JP-8) components. Average experimental PCs were compared with predicted PCs calculated using algorithms from 9 published sources. Algorithms chosen used solvent PCs (octanol:water, saline or water:air, oil:air coefficients) due to the relative accessibility of these parameters. Tissue:blood PCs were calculated from ratios of predicted tissue:air and experimental blood:air values (PCEB). Of the 231 calculated values, 27% performed within +/- 20% of the experimental PC values. Physiologically based equations (based on water and lipid components of a tissue type) did not perform as well as empirical equations (derived from linear regression of experimental PC data) and hybrid equations (physiological parameters and empirical factors combined) for the jet fuel components. The major limitation encountered in this analysis was the lack of experimental data for the selected JP-8 constituents. PCEB values were compared with tissue:blood PCs calculated from ratios of predicted tissue:air and predicted blood:air values (PCPB). Overall, 68% of PCEB values had smaller absolute % errors than PCPB values. If calculated PC values must be used in models, a comparison of experimental and predicted PCs for chemically similar compounds would estimate the expected error level in calculated values.

Adipose Tissue↗
PubMed2006

Interlaboratory evaluation of Hyalella azteca and Chironomus tentans short-term and long-term sediment toxicity tests.

Methods for assessing the long-term toxicity of sediments to Hyalella azteca and Chironomus tentans can significantly enhance the capacity to assess sublethal effects of contaminated sediments through multiple endpoints. Sublethal tests allow us to begin to understand the relationship between short-term and long-term effects for toxic sediments. We present an interlaboratory evaluation with long-term and 10-d tests using control and contaminated sediments in which we assess whether proposed and existing performance criteria (test acceptability criteria [TAC]) could be achieved. Laboratories became familiar with newly developed, long-term protocols by testing two control sediments in phase 1. In phase 2, the 10-d and long-term tests were examined with several sediments. Laboratories met the TACs, but results varied depending on the test organism, test duration, and endpoints. For the long-term tests in phase 1, 66 to 100% of the laboratories consistently met the TACs for survival, growth, or reproduction using H. azrteca, and 70 to 100% of the laboratories met the TACs for survival and growth, emergence, reproduction, and hatchability using C. tentans. In phase 2, fewer laboratories participated in long-term tests: 71 to 88% of the laboratories met the TAC for H. azteca, whereas 50 to 67% met the TAC for C. tentans. In the 10-d tests with H. azteca and C. tentans, 82 and 88% of the laboratories met the TAC for survival, respectively, and 80% met the TAC for C. tentans growth. For the 10-d and long-term tests, laboratories predicted similar toxicity. Overall, the interlaboratory evaluation showed good precision of the methods, appropriate endpoints were incorporated into the test protocols, and tests effectively predicted the toxicity of sediments.

Animals↗
PubMed2006

Determining stressor presence in streams receiving urban and agricultural runoff: development of a benthic in situ toxicity identification evaluation method.

Determining toxicity in streams during storm-water runoff can be highly problematic because of the fluctuating exposures of a multitude of stressors and the difficulty of linking these dynamic exposures with biological effects. An underlying problem with assessing storm-water quality is determining if toxicity exists and then which contaminant is causing the toxicity. The goal of this research is to provide an alternative to standard toxicity testing methods by incorporating an in situ toxicity identification evaluation (TIE) approach. A benthic in situ TIE bioassay (BiTIE) was developed for separating key chemical classes of stressors in streams during both low- and high-flow events to help discern between point and nonpoint sources of pollution. This BiTIE method allows for chemical class fractionation through the use of resins, and these resins are relatively specific for removing nonpolar organics (Dowex Optipore), ammonia (zeolite), and polywool (control). Three indigenous aquatic insects, a mayfly (Isonychia spp.), a caddisfly (Hydropsyche spp.), and a water beetle (Psephenus herricki), were placed in BiTIE chambers that were filled with natural substrates. Acute 96-h exposures were conducted at Honey Creek, New Carlisle, Ohio, USA (reference site), and Little Beavercreek, Beavercreek, Ohio, USA (impaired site). At both sites, significant (p < 0.025) stressor responses were observed using multiple species with polywool or no resin (control) treatments exhibiting < 80% survival and resin treatments with >80% survival. The BiTIE method showed stressor-response relationships in both runoff and base flow events during 96-h exposures. The method appears useful for discerning stressors with indigenous species in situ.

Agriculture↗
PubMed2006

A geographic information systems-based, weights-of-evidence approach for diagnosing aquatic ecosystem impairment.

A Geographic Information Systems-based, watershed-level assessment using Bayesian weights of evidence (WOE) and weighted logistic regression (WLR) provides a method to determine and compare potential environmental stressors in lotic ecosystems and to create predictive models of general or species-specific biological impairment across numerous spatial scales based on limited existing sample data. The WOE/WLR technique used in the present study is a data-driven, probabilistic approach conceptualized in epidemiological research and both developed for and currently used in minerals exploration. Extrapolation of this methodology to a case-study watershed assessment of the Great and Little Miami watersheds (OH, USA) using archival data yielded baseline results consistent with previous assessments. The method additionally produced a quantitative determination of physical and chemical watershed stressor associations with biological impairment and a predicted comparative probability (i.e., favorability) of biological impairment at a spatial resolution of 0.5 km2 over the watershed study region. Habitat stressors showed the greatest spatial association with biological impairment in low-order streams (on average, 56% of total spatial association), whereas water chemistry, particularly that of wastewater effluent, was associated most strongly with biological impairment in high-order reaches (on average, 79% of total spatial association, 28% of which was attributed to effluent). Significant potential stressors varied by land-use and stream order as well as by species. This WOE/WLR method provides a highly useful "tier 1" watershed risk assessment product through the integration of various existing data sources, and it produces a clear visual communication of areas favorable for biological impairment and a quantitative ranking of candidate stressors and associated uncertainty.

Bayes Theorem↗
PubMed2005

In situ exposures using caged organisms: a multi-compartment approach to detect aquatic toxicity and bioaccumulation.

An in situ toxicity and bioaccumulation assessment approach is described to assess stressor exposure and effects in surface waters (low and high flow), the sediment-water interface, surficial sediments and pore waters (including groundwater upwellings). This approach can be used for exposing species, representing major functional and taxonomic groups. Pimephales promelas, Daphnia magna, Ceriodaphnia dubia, Hyalella azteca, Hyalella sp., Chironomus tentans, Lumbriculus variegatus, Hydra attenuatta, Hexagenia sp. and Baetis tibialis were successfully used to measure effects on survival, growth, feeding, and/or uptake. Stressors identified included chemical toxicants, suspended solids, photo-induced toxicity, indigenous predators, and flow. Responses varied between laboratory and in situ exposures in many cases and were attributed to differing exposure dynamics and sample-processing artifacts. These in situ exposure approaches provide unique assessment information that is complementary to traditional laboratory-based toxicity and bioaccumulation testing and reduce the uncertainties of extrapolating from the laboratory to field responses.

Animals↗
PubMed2005

Field validation of sediment zinc toxicity.

A field study was conducted to validate concentrations of zinc in freshwater sediments that are tolerated by benthic macroinvertebrate communities and to determine whether a relationship exists with the acid volatile sulfide (AVS)-simultaneously extracted metal (SEM) model. In both the lake and riverine systems, one sediment type was high in AVS and one low in AVS, which resulted in zinc-spiked sediments that ranged from low to high SEM to AVS ratios. The colonization trays were sampled seasonally, ranging from 6 to 37 weeks of exposure, and were evaluated using several appropriate benthic indices. Results of the field evaluations at the four test sites confirmed the validity of the AVS-SEM model, predicting benthic macroinvertebrate effects correctly 92% of the time. In sediments where the SEM to AVS ratio or the AVS and organic (OC)-normalized fractions exceeded 8 and 583 micromol/g of OC, toxicity was observed from the zinc-spiked sediments. Conversely, when the SEM to AVS ratio or OC-normalized AVS fractions were less than 2 or 100 micromol/g of OC, no toxicity was observed. In the range of 148 to 154 micromol/g of OC, toxicity varied in two treatments. Total zinc concentrations in sediments showed no relationship to benthic effects. The most impaired benthic community occurred in the high-gradient stream sediments, which had low OC and AVS concentrations and SEM to AVS ratios of 33 and 44 in the spiked sediments. Five to six benthic metrics were depressed at SEM to AVS ratios of 8.32 and 9.73. The no-observed-effect level appeared to be near a SEM to AVS ratio of 2, with slight to no effects between ratios of 2.34 and 2.94. No sites with ratios of less than 2 showed any adverse effects.

Acids↗
PubMed2005

Desorption kinetics of fluoranthene and trifluralin from Lake Huron and Lake Erie, USA, sediments.

Desorption kinetics were determined for fluoranthene (FLU) and trifluralin (TF) spiked onto Lake Erie and Lake Huron, USA, sediments at three concentrations (10, 40, 100 mg/kg dry wt). Following four months of equilibration, desorption was measured by extraction with Tenax and the data were fit to a first-order three-compartment kinetic model. The rate constants of the rapidly (k(rap)), slowly (k(slow)), and very slowly (k(vs)) desorbing fractions were on the order of 10(-1)/h, 10(-2-3)/h, and 10(-4)/h, respectively. The t99.9 (time required for 99.9% of the FLU and TF to desorb from each pool value) for each compartment indicated that FLU and TF desorption from rapid, slow, and very slow compartments were on the order of hours, days, and years, respectively. Higher rates of desorption were observed for FLU and TF from the Lake Huron sediments and this was not apparently related to the total organic carbon (TOC), particle size distribution, or polarity (carbon-to-nitrogen ratio) of the sediments. In general, the total fraction of the initial contaminant amounts that desorbed over the time course was directly related to concentration, which we hypothesized was due to the combined effects of saturation of high-energy (slow and very slow) binding sites in the organic carbon matrix and hysteresis. In extrapolations to field conditions, FLU and TF were predicted to persist in the sediments for years due to the very slow desorption of an estimated 31 to 53% of the bulk concentrations. Based on the rapidly desorbing fractions, the bioavailable amounts of the contaminants were predicted to be between 31 to 55% of bulk sediment concentrations.

Adsorption↗
PubMed2005

Gene expression in caged fish as a first-tier indicator of contaminant exposure in streams.

The development of sensitive, biologically based indicators of contaminant exposure (i.e., biomarkers) is an ongoing topic of research. These indicators have been proposed as a first-tier method of identifying contaminant exposure. The primary objective of this research was to implement a biomarker-based method of exposure assessment using caged fish and real-time reverse-transcriptase polymerase chain reaction (rtRT-PCR) measurements of gene expression. Primers were developed for the CYPIA, metallothionein, and vitellogenin genes in rainbow trout (Oncorhynchyus mykiss), cutbow trout (Oncorhynchyus clarkii x mykiss), and Atlantic salmon (Salmo salar). Each of these genes has been shown to respond specifically to planar aromatic compounds, heavy metals, and environmental estrogens, respectively. Juvenile fish were placed in cages and exposed in situ at reference and contaminated sites on the Cache la Poudre River (CO, USA), the Arkansas River (CO, USA), the St. John River (NB, Canada), and two urban creeks near Dayton (OH, USA). Quantitative gene expression was determined using rtRT-PCR. Biomarker expression profiles were obtained that demonstrated differences in CYPIA, metallothionein, and vitellogenin mRNA production unique to each site, indicating that specific types of compounds were bioavailable and present in sufficient concentrations to elicit transcriptional responses in the organism. These findings support the use of a biomarker-based approach to exposure identification and assessment.

Animals↗
PubMed2004

Effect of 3,4,3',4'-tetrachlorobiphenyl on the reworking behavior of Lumbriculus variegatus exposed to contaminated sediment.

The reworking response (bioturbation) of the oligochaete Lumbriculus variegatus was measured by following the burial rate and spread of a 137Cs marker layer translating worm activity into a biological burial rate (Wb) and a biological diffusion rate constant (Db) for surficial sediment mixing. Reworking was measured at 10 and 22 degrees C in two sediments: a reference site sediment dosed with 3,4,3',4'-tetrachlorobiphenyl (TCBP) and a field-collected sediment from a polychlorinated biphenyl (PCB)-contaminated site in Dicks Creek (DCC, Middletown, OH, USA). The body residue associated with response to TCBP also was determined. Reduction in the temperature from 22 to 10 degrees C reduced both Wb and Db by a factor of approximately two. The internal TCBP concentration to reduce the Wb by 50% was 96 nmol/g (95% CI 45-225 nmol/g) and 124 nmol/g (40-547 nmol/g) (28 and 36 microg/g) wet weight at 22 and 10 degrees C, respectively, and was independent of temperature. The Wb for the DCC sediment was lower than observed for the highest TCBP treatment. The internal body residue for total PCB for worms exposed to DCC sediment was 20-fold lower than TCBP in worms exposed to the lowest TCBP treatment on a molar basis. Comparing body residues of total PCB to TCBP assumes that the PCB congeners act additively on a molar basis. The DCC site contained a higher proportion of coarse material and a lower organic carbon concentration. The difference in sediment characteristics was assumed to be responsible for differences in the Wb.

Animals↗
PubMed2004

Comparing behavioral and chronic endpoints to evaluate the response of Lumbriculus variegatus to 3,4,3',4'-tetrachlorobiphenyl sediment exposures.

The response of Lumbriculus variegatus to 3,4,3',4'-tetrachlorobiphenyl (TCBP) was examined with feeding behavior and changes in carbon assimilation by using stable carbon isotopes at 22 and 10 degrees C. The classical measure of feeding behavior determined on a subset of sediment for which the biological burial rate was determined in a companion study allowed direct method comparison. This comparison helped address relationships between biological burial rate, feeding rate, and bioaccumulation. The change in stable isotope composition reflects the total metabolic activity by measuring carbon assimilation rate and was compared to feeding rate, biological burial rate (as determined in the companion study), and reproduction. Decreasing the temperature from 22 to 10 degrees C resulted in a twofold reduction in feeding rate and carbon assimilation. The fractional decline in feeding rate relative to the control mimicked the decline in the biological burial rate with increasing TCBP concentration that was found in the companion study. The bioaccumulation factor declined with increasing TCBP sediment concentration, tracking the feeding rate decline. Stable isotope measures showed differences in metabolic rates between the exposure temperatures but did not distinguish a metabolic rate change at 22 degrees C among TCBP treatments. Likewise, reproduction declined from 22 to 10 degrees C, with no reproduction at 10 degrees C. Like the stable isotope measure, no dose response was found among TCBP treatments at 22 degrees C. The reduction in carbon assimilation rate tracked the reduction in reproduction with lower temperature.

Animals↗
PubMed2004

An in situ toxicity identification evaluation method Part I: Laboratory validation.

Identification of individual chemical groups is critical in evaluating sediment quality and fractionating these groups of chemicals in a mixture is important to determine the primary chemicals causing toxicity. The in situ toxicity identification evaluation (iTIE) is a novel method that was developed to fractionate chemicals in contaminated sediments and waters and assess toxicity organisms. The study objectives were to verify that the iTIE can help identify contaminant chemical classes and improve the toxicity assessment process; and compare the iTIE and U.S. Environmental Protection Agency's (U.S. EPA) toxicity identification evaluation (TIE) methods. The iTIE exposure chamber is powered by a portable air pump that suctions pore water, via a Venturi system, through selective sorption materials. After passing through the sorptive materials, the pore water passes into an exposure chamber containing Daphnia magna. The chemical sorption materials included Ambersorb 563 for nonpolar organic chemical adsorption, Chelex for metals chelation, and multiple zeolite types for ammonia adsorption. The laboratory studies were performed using water and sediments spiked with ammonia, cadmium, and fluoranthene. The laboratory validation of the iTIE approach showed that different classes of compounds readily could be separated via the resin treatments, resulting in significant differences in concentrations and thus exposures to in situ exposed organisms. Ammonia, cadmium, and fluoranthene were significantly removed by zeolite, Chelex, and Ambersorb, respectively. Although there was some cross-adsorption to the other nontarget resins, it was limited and allowed for treatment differences to be detected. Survival in the treatment resins exposed to the target compounds was as high as control survivals. A 24-h exposure period appeared optimal, allowing for replacement of initial culture water with pore waters, while longer exposures occasionally allowed for breakthrough of contaminants. The iTIE was more sensitive than the U.S. EPA TIE method, in that it detected toxicity more readily due to the greater loss of contaminant concentrations in the TIE manipulation process.

Adsorption↗
PubMed2004

An in situ toxicity identification evaluation method Part II: Field validation.

When sediments are found to be toxic usually there is a mixture of chemicals present. Often it is important to establish which chemicals contribute to the toxicity. Establishing causality can be difficult and often requires fractionation with subsequent toxicity testing. The sample collection and manipulation process can alter chemical bioavailability and toxicity. An in situ toxicity identification evaluation (iTIE) chamber is described that was placed in sediments and fractionated pore-water chemicals into nonpolar chemicals, metals, and ammonia-type groups. This method was field tested and compared to the laboratory-based, U.S. Environmental Protection Agency (U.S. EPA) toxicity identification evaluation (TIE) method. Field studies were performed at three sites contaminated primarily with polycyclic aromatic hydrocarbons (PAHs) (Little Scioto River, OH, USA), polychlorinated biphenyls (PCBs) (Dicks Creek, OH, USA), and chlorobenzenes (Sebasticook River, ME, USA). Both the iTIE and the U.S. EPA TIE methods used Daphnia magna in 24-h exposures. Although the iTIE and TIE were conducted on sediments from the same location, there was significantly more toxicity observed in the iTIE testing. The dominant chemical classes were separated by the iTIE method and revealed which fractions contributed to toxicity. The loss of toxicity in the TIE approach did not allow for subsequent fractionation and stressor identification. Advantages of the iTIE over the TIE method were greater sensitivity and ability to detect causative toxic chemical fractions; lack of sediment collection and subsequent manipulation; and, thus, reduction in potential artifacts, more realistic exposure with slow, continual pore-water renewal in situ, ability to evaluate pore waters in sandy or rocky substrates where pore waters are difficult to collect, and a quicker phase I evaluation. Limitations of the iTIE method as compared to the TIE methods were extensive pretest assembly process, fewer phase I fractionation possibilities, and restriction to shallow waters. The results of these studies suggest that the iTIE method provides a more accurate and sensitive evaluation of pore water toxicity than the laboratory TIE method.

Animals↗
PubMed2003

Investigating the role of desorption on the bioavailability of sediment-associated 3,4,3',4'-tetrachlorobiphenyl in benthic invertebrates.

Only a fraction of all sediment-associated hydrophobic organic contaminants are bioavailable, and a simple Tenax extraction procedure may estimate this fraction. Bioavailability is assumed to coincide with the rapidly and, possibly, slowly desorbing sediment-associated contaminant. River sediment was spiked with radiolabeled (14C) and nonradiolabeled (12C) 3,4,3',4'-tetrachlorobiphenyl (TCBP), and desorption kinetics using Tenax extraction were obtained at 10 degrees C and 22 degrees C. Bioaccumulation was measured in Lumbriculus variegatus, Chironomus tentans, and Hyalella azteca. Desorption of TCBP was triphasic at 22 degrees C and slowed at 10 degrees C to show only biphasic kinetics. The rapidly desorbing fractions decreased with increasing TCBP sediment concentration. The biota sediment accumulation factors, biota accumulation factors, and sediment clearance coefficients (ks) also decreased with increasing sediment TCBP concentration. The rapidly plus slowly desorbing fractions and the total TCBP desorbed when 99.9% of the rapidly desorbing fraction had desorbed were used to estimate bioavailable TCBP. These Tenax-based fractions did not explain the decreasing bioavailability with increasing TCBP load. Several factors, such as animal behavior and TCBP water solubility limitations, were evaluated to explain the concentration effect, but the most likely cause was severe diffusion limitations in whole sediment that were not predicted by the fully mixed Tenax extraction. Therefore, desorbing fractions determined by Tenax extraction overestimated the bioavailable fractions in sediments.

Adsorption↗
PubMed2003

Laboratory and field validation of multiple molecular biomarkers of contaminant exposure in rainbow trout (Oncorhynchus mykiss).

Novel primers for three different genes (CYP1A1, vitellogenin, and metallothionein) for use in reverse transcription-polymerase chain reaction (RT-PCR) were developed and tested in laboratory flow-through experiments using model compounds benzo[a]pyrene, estradiol, and cadmium. Field validations of the molecular biomarkers were performed using 8-d or 48-h in situ, cagedexposure of juvenile rainbow trout (Oncorhynchus mykiss). Expression levels of genetranscription(messengerRNA [mRNA]) were monitored in gill and liver tissue after exposure at sites downstream of a known source of creosote contamination in the Little Scioto River (Marion, OH, USA) and metals and hydrocarbon contamination in Dick's Creek (Middletown, OH, USA). Significant increases of liver cytochrome P4501A1 gene (CYP1A1) and vitellogenin were measured in both streams at sites downstream of contaminant sources. Significant increases of gill CYP1A1 were also observed. Significant increases of gill and livermetallothionein occurred in Dick's Creek. A sample of gill tissue taken from each fish prior to placement in the Little Scioto River provided a pre-exposure control measurement for each individual. Expression of CYP1A1 and vitellogenin in trout at both streams indicated that exposure to bioavailable hydrocarbons and endocrine-disrupting compounds had taken place. Previous to this study, estrogenic compounds had not been detected in the Little Scioto River. Metallothionein expression confirmed the presence of metals in Dick's Creek. These results suggest a mixed contaminant environment that poses physiological hazard to existing teleost populations. Multiple molecular biomarkers provided a sensitive, physiologically based method of determining contaminant presence and bioavailability to aquatic organisms.

Animals↗
PubMed2002

Optimizing interpretation of in situ effects of riverine pollutants: impact of upwelling and downwelling.

In situ toxicity and bioaccumulation tests with Ceriodaphnia dubia (48 h), Chironomus tentans (96 h), Hyalella azteca (96 h), and Lumbriculus variegatus (96 h) were conducted at three stations on a river that was contaminated primarily with chlorobenzenes (CBs), and results were compared to a nearby reference site. Exposures were characterized by using minipiezometers for contaminant profiling and determination of hydraulic heads and vertical flow direction within the sediments and measuring contaminants in sediment, surface water, and exposure chamber water samples. Localized zones of upwelling and downwelling existed in the exposure areas at contaminated sites 5 and 18, while site 23 was downwelling at all measurement positions. Pore-water samples from minipiezometers contained CBs at the three contaminated sites that were highest at site 23. However, sediment and water samples from exposure chambers at site 23 contained the lowest levels of CBs among the contaminated sites. The CBs were not detected at the reference site, but other organic contaminants and metals were detected at all sites, with the highest concentrations occurring at sites 5 and 18. In water column exposures, no significant (p > 0.05) differences were observed in species survival between the contaminated sites and the reference. Mean percentage survival of H. azteca, C. dubia, and C. tentans exposed to surficial sediments (SS) at sites 5 and 18 was significantly (p < 0.05) reduced compared to the reference, whereas only C. tentans survival was significantly reduced at site 23. Body residues of total CB congeners in L. variegatus exposed to SS were highest at site 18 (618 micromol/kg lipid) and lowest at site 23 (21 micromol/kg lipid). The data suggest that downwelling reduced the bioavailability of CBs in surficial sediments, most likely by mobilizing the freely dissolved and colloid-bound fractions to deeper sediments. Overall, downwelling conditions reduced the in situ exposure of organisms in surficial sediments and hence the toxicity and bioaccumulation of CBs. Hydrologic and chemistry data from nested minipiezometers improved the interpretation of exposure-effects relationships.

Animals↗