Measuring the bioavailability of two hydrophobic organic compounds in the presence of dissolved organic matter

Bioavailability of benzo[a]pyrene (BaP) and 3,3',4,4'-tetrachlorobiphenyl (TCB) was studied in natural lake water containing dissolved organic matter (DOM). Lake water was diluted to give a dissolved organic carbon (DOC) range of 1 to 20 mg/L. Partition coefficients for the model compounds were assessed at different DOM concentrations and over time with three different methods, namely equilibrium dialysis and reverse-phase and liquid-liquid extraction. In addition, biological partition coefficients were estimated from the difference in the bioconcentration of the model compounds in Daphnia magna in the presence and absence of DOM. Results showed that bioavailability of the model compounds was reduced by the presence of DOM. The equilibrium dialysis method gave the best estimates for bioavailability of the model compounds when compared with biologically determined values. Both the reverse-phase and the liquid-liquid extraction overestimated the bioavailable fraction. The more pronounced overestimation of bioavailable fraction of TCB suggested that the sorption of TCB was not only lower but the interaction was also weaker than that of BaP. Increasing DOM concentration produced lower partition coefficients and the effect seemed to be more pronounced when measured by the reverse-phase and the extraction methods.     

Dissolved organic matter modulating the uptake, biotransformation, and elimination rates of pyrene in Daphnia magna

In the current study, the toxicokinetics of pyrene in Daphnia magna was determined in detail, and the role of dissolved organic matter (DOM) in these processes was investigated. Uptake, biotransformation, parent compound and metabolite elimination rates (k(u), k(m), k(ep), k(em)), depuration rates, bioconcentration factors (BCFs), and biological half-lives were studied in one natural humic water, in two waters made from DOM isolates, and in DOM-free artificial fresh water. The daphnids were exposed to pyrene for 24 h and depurated for another 24 h. To analyze the data, the two-compartment model was used to obtain toxicokinetic parameters, and the depuration data were analyzed by linear regression. Extensive biotransformation of pyrene resulted in high metabolite concentration in the organisms (83% of total radioactivity) after 24 h exposure. Depuration of the parent compound seemed to be biphasic: at first, depuration was rapid, but after 4 to 10 h in uncontaminated water, the disappearance rate came close to zero. After a 24-h depuration time, 7.8% of the pyrene accumulated remained in the organism. Overall, the elimination of parent compound was faster than the elimination of metabolites, which might imply inefficient excretion of water-soluble biotransformation products from daphnids. The effect of DOM on accumulation of pyrene was seen in a decreased uptake rate, indicating lower bioavailability of the compound in waters that contain high-aromaticity DOM. In the same waters, DOM significantly accelerated pyrene biotransformation and overall elimination. Altogether, DOM appears to be able to affect toxicokinetics through mechanisms that are connected to interaction with the contaminant but also directly through interaction with biotransformation systems.     

Effects of XAD-8 fractions of dissolved organic carbon on the sorption and bioavailability of organic micropollutants

The dissolved organic carbon (DOC) from a stream water near a peat deposit was fractionated into hydrophobic-acid (HbA), hydrophobic-neutral (HbN), and hydrophilic (Hl) subcomponents by XAD-8 chromatography. The capacity of these fractions and the total (unfractionated) water to bind hydrophobic organic contaminants was measured by equilibrium dialysis, and the effect of binding on contaminant bioavailability was measured inDaphnia magna. Model contaminants were the poly cyclic aromatic hydrocarbons, naphthalene (NPH) and benzo(a)pyrene (BaP), and the polychlorinated biphenyl, 2,2,5,5-tetrachlorobiphenyl (TCB).Both BaP and TCB exhibited high partition coefficients (Kp's) for binding to both the total DOC and the hydrophobic components of the DOC. BaP had a higher affinity for binding to the HbA fraction, while TCB (and 3 other PCB's had a higher affinity for the HbN fraction. The K_p's for binding to the Hl fraction were twofold to tenfold lower than for binding to the hydrophobic fractions. The less hydrophobic compound, NPH, had a much lower K_p, and little difference was seen between the fractions. The total water and the different DOC fractions reduced the uptake and accumulation of BaP and TCB byD. magna in proportion to the capacity of the DOC for binding the contaminants. Data were consistent with the hypothesis that a contaminant bound to DOC (total water or any of the fractions) is unavailable for uptake by biota. Uptake of NPH was not substantially affected by the DOC, consistent with its lower K_p.     

Atrazine uptake, elimination, and bioconcentration by periphyton communities and Daphnia magna: effects of dissolved organic carbon

The bioconcentration and toxicokinetics of atrazine in three different periphyton communities and in laboratory reared Daphnia magna were studied in natural and artificial waters with different dissolved organic carbon (DOC) concentrations and qualities. The exposure concentrations were similar to those short-lived peak concentrations found in contaminated waters. Atrazine uptake and elimination were very fast, and the bioconcentration was low both in periphyton and D. magna. The bioconcentration factors in D. magna were approx. 16% of those in periphyton. The uptake and elimination rates were also higher in periphyton than in Daphnia. The periphyton properties affected the bioconcentration of atrazine more than the DOC concentration and water quality. A steady state was reached within a few hours of uptake by the periphyton and within 24 h by D. magna. A residue of atrazine was left in the periphyton and D. magna after an 8-h biphasic depuration with clearly distinct fast and slow phases. In D. magna, atrazine may be eliminated during the normal life span of the organism. These results suggest that DOC has a minor influence on the toxicokinetics of atrazine.     

Effect of dissolved organic matter of various origins and biodegradabilities on the bioaccumulation of polycyclic aromatic hydrocarbons in Daphnia magna

As a preliminary study of the influence of urban organic matter on the bioavailability of polycyclic aromatic hydrocarbons (PAHs), the effect of different types of dissolved organic matter (DOM) on the bioaccumulation of fluoranthene, pyrene, or benzo[a]pyrene in Daphnia magna was studied. Commercial humic substances, DOM from the aeration basin of a wastewater treatment plant, and highly biodegradable DOM (algae or animal extracts) were tested. The bioaccumulation of benzo[a]pyrene was reduced by each DOM (up to 80% reduction with humic substances). Pyrene bioaccumulation was also decreased by each DOM to a lesser extent. Fluoranthene bioaccumulation was affected by the presence of humic acids only. In each experiment, the solution containing humic DOM led to the lowest bioaccumulation. Supposing that only dissolved PAHs were bioavailable, the reduction of bioaccumulation allowed a biological estimate of the partition coefficients of DOM and PAH, K(DOC). The estimated coefficients were positively related to the aromaticity of DOM and negatively related to its biodegradability.     

The ability of dissolved organic matter (DOM) to influence benzo[a]pyrene bioavailability increases with DOM biodegradation

The biodegradation of two substrates and the ability of dissolved organic matter (DOM) to influence benzo[a]pyrene bioavailability as DOM biodegradation progressed were monitored in reactors. Substrates were composed of algae extracts and an artificial substrate that mimics raw wastewater, which were considered to be autochthonous and anthropogenic allochthonous models for DOM, respectively. The soluble microbial products formed during biomass activity were also studied. The aromaticity of DOM was investigated with specific ultraviolet absorbance. Partitioning coefficients between DOM and benzo[a]pyrene, K(DOC)(biol), were biologically determined by means of 4-h bioaccumulation experiments on Daphnia magna. Parent and degraded substrates always significantly reduced the bioaccumulation of benzo[a]pyrene at environmental DOM concentrations. Soluble microbial products also significantly affected the benzo[a]pyrene bioaccumulation. K(DOC)(biol) ranged between 2 x 10(4) and 4 x 10(5) L/kg. As the artificial wastewater biodegraded, DOM aromaticity increased, as did K(DOC)(biol). During the biodegradation of algae extract DOM, K(DOC)(biol) increased, whereas their aromaticity slightly decreased.     

Assessing the biological relevance of exposing freshwater organisms to atrazine and molinate in environmentally realistic exposure test systems

Assessing the toxicity of chemicals in treated laboratory water may not accurately represent the toxicity of chemicals in natural aquatic systems. In natural water, dissolved organic matter, suspended particulate matter, and sediment play key roles in the sorption of contaminants from the water. Our previously published series of papers illustrated that the presence of sediment in aquatic toxicity testing systems significantly (p < 0.05) reduced the bioavailability of the herbicides atrazine and molinate to five Australian freshwater organisms. It is not clear whether the reduced bioavailability means that the trigger values (TVs) in the current Australian and New Zealand water quality guidelines, which are calculated using toxicity data from water-only toxicity tests, provide appropriate environmental protection. Several new sets of TVs were derived in the present study and were compared to each other and to the current Australian and New Zealand TVs for atrazine and molinate. The current Australian and New Zealand TVs for atrazine and molinate provided appropriate protection to Australian freshwater species. Australian freshwater species have a sensitivity distribution similar to those of overseas species to atrazine and molinate.     

Polycyclic Aromatic Hydrocarbons in Freshwater Isopods and Field-Partitioning Between Abiotic Phases

An assessment was made of the in situ bioaccumulation of 13 polycyclic aromatic hydrocarbons (PAHs) in freshwater isopods in relation to their partitioning between sediments, particulate matter (>0.7 μm), and dissolved phases in eight different water systems of The Netherlands. Large differences in total (Γ PAHs) concentrations and in relative abundance of individual PAHs were observed between organisms and abiotic compartments and among sampling stations. Principal component analysis revealed distinct differences between PAH profiles in sediments and water. High molecular weight PAHs dominated in the sediments, fluoranthene and pyrene in the isopods, and naphthalene in water. Apparent lipid-based bioconcentration factors (BCFs) increased with increasing hydrophobicity (n-octanol/water partition coefficient; K_ow). The total range of the BCFs varied only one order of magnitude, ranging from 10^5.1 (naphthalene) to 10^6.1 (benzo[a]pyrene). For PAHs with log K_ow > 6.1 lower BCFs than expected were observed, which was attributed to reduced bioavailability, to the operational definition of the dissolved phase, and to growth dilution preventing equilibrium to be reached within the lifetime of the isopods. Abiotic partitioning coefficients, such as K_oc (organic carbon normalized sediment–water partition coefficient) and K_pm (particulate matter–water distribution coefficient) increased with hydrophobicity for PAHs having a log K_ow < 6.1. Sediment-water partition coefficients (K_d) increased with the organic carbon content of the sediments for most PAHs. It is concluded that isopods have a marked ability to accumulate PAHs and that their tissue residues tend to reflect spatial and temporal variations in the bioavailability of PAHs in littoral freshwater environments. Received: 9 April 1997/Accepted: 3 January 1998     

UV-B-Induced acute toxicity of pyrene to the waterflea Daphnia magna in natural freshwaters

The effects of various water characteristics in natural freshwaters on the acute toxicity of one polycyclic aromatic hydrocarbon (PAH), pyrene, to a pelagic invertebrate Daphnia magna was studied under ultraviolet B (UV-B) radiation and in the dark. Pyrene was photoactivated and was more toxic to D. magna in the presence of UV-B radiation. Dissolved organic material (DOM), measured as dissolved organic carbon (DOC), significantly reduced the photoenhanced toxicity of pyrene. Under UV-B radiation the EC(50) values were lower and in relation to the amount of DOM, ranging from 3.0 to 30.0 microg/L pyrene, whereas in the dark they were between 29.2 and 54.8 microg/L and not related to the amount of DOM in the waters. Although the condition and mortality of the daphnids in the control groups were not affected by UV-B irradiation, the increased toxicity was considered to be either an additive or a synergistic effect of both the photomodified pyrene and the stressing light conditions of UV-B. The measured binding of pyrene to DOM was low, although it was related to the amount of DOC. Despite the relatively high intensity of UV-B used, humic substances in the waters remained undegraded. It was thus concluded that with their brownish-yellowish color, waters rich in humic substances decreased the photomodification of the freely dissolved parent compound simply by diminishing the light penetration in these waters and, by implication, contact with the intact compound. These results suggest that DOM in surface waters plays an important role in protecting against the photoinduced toxicity of PAHs.     

Chemical and biological availability of sediment-sorbed benzo[a]pyrene and hexachlorobiphenyl

This study examined the chemical and biological availability of two nonpolar organic compounds, benzo[a]pyrene (BaP) and hexachlorobiphenyl (HCBP), from a spiked sediment that was aged for varying amounts of time. Chemical availability was evaluated using four different solvent combinations to extract chemicals from the sediment. The extractability of BaP and HCBP from sediment using traditional solvents was then compared to the transfer efficiency (TE) of a benthic invertebrate (Lumbriculus variegatus) to relate chemical extractability to bioavailability in the organisms. Results indicated that water was the solvent that best approximated bioavailability for BaP, whereas comparisons for HCBP were inappropriate, because TE values exceeded 100%. The inability to obtain a reasonable TE estimate for HCBP was most likely due to the fact that the oligochaetes received a major portion of their uptake from interstitial water instead of ingestion of sediment particles, which invalidated an important assumption of the TE model. Overall, the results of this study indicate that exhaustive chemical extractions may be an inaccurate representation of the bioavailable fractions for some contaminants.     

Toxicity of cadmium and copper on larval and juvenile stages of the estuarine crab Chasmagnathus granulata (Brachyura, Grapsidae)

The binding and bioavailability of pyrene was studied in the laboratory in two humic fresh waters and in a reference water without dissolved organic material (DOM), measured as dissolved organic carbon (DOC). The uptake of pyrene by Daphnia magna in short-term (24 h) accumulation experiments was fitted to a first-order rate-kinetic equation to calculate simultaneous uptake and elimination rates. The partition coefficients of pyrene to DOC (K_DOC) were 37.1 × 10³ in Pielisjoki River (9.4 mg DOC L⁻¹), and 34.9 × 10³ in Lake Kontiolampi (17.4 mg DOC L⁻¹) waters, indicating similar binding affinities of pyrene for both humic waters. The uptake clearance of pyrene (k_u) in the DOC-rich Lake Kontiolampi water was 290.4 ml g wet weight⁻¹ h⁻¹, which was lower than those in Pielisjoki River and DOC-free waters (395.8 and 346.0 ml g wet weight⁻¹ h⁻¹, respectively). Pyrene elimination (k_e) was in average 0.2 h⁻¹ with no significant differences between the waters. The observed bioconcentration factors of pyrene in Pielisjoki River and Lake Kontiolampi waters were 84% and 46% of that in the DOC-free reference water, respectively, thus indicating that a high concentration of DOC is needed to decrease the bioavailability of waterborne pyrene to D. magna. Received: 15 May 2000/Accepted: 8 November 2000     

Toxicity of Atrazine and Molinate to the Cladoceran <Emphasis Type="Italic">Daphnia carinata</Emphasis> and the Effect of River Water and Bottom Sediment on Their Bioavailability

Atrazine and molinate are widely used herbicides and concern has been raised about their potential deleterious impacts on aquatic ecosystems. Although there have been some studies on the toxicity of herbicides to aquatic organisms using laboratory or natural water, information on the effect of sediments, suspended particulates, and dissolved organic matter on their bioavailability is quite limited. This study aims to provide toxicity data that considers these factors and the effect that these factors have on bioavailability. In this study, the toxicity of the test chemicals was calculated following the Organisation for Economic Co-operation and Development (OECD) methods, whereas change in bioavailability was measured using EC₅₀ values based on measured initial concentrations of the test chemicals. The acute (48-h) static toxicity of atrazine and molinate to the freshwater cladoceran Daphnia carinata was determined in cladoceran water and river water in the absence and presence of sediment. The 48-h EC₅₀ (immobilization) values of atrazine to D. carinata ranged from 22.4 to 26.7 mg/L, while the corresponding values for molinate ranged from 18.3 to 33.6 mg/L, respectively. Both chemicals were classed as having low acute toxicity to D. carinata. The presence of dissolved organic matter and suspended particles in river water did not significantly (p > 0.05) reduce the bioavailability (measured as toxicity) of atrazine to D. carinata compared to that tested in cladoceran water. The presence of sediment, however, signifi- cantly (p < 0.05) reduced the bioavailability (48-h EC₅₀) of atrazine in cladoceran water, from 24.6 to 30.7 mg/L, and in river water, from 22.4 to 31.0 mg/L. Similarly, the presence of sediment in cladoceran water, significantly (p < 0.05) reduced the bioavailability (48-h EC₅₀) of molinate, from 26.6 to 46.4 mg/L, and in river water, from 22.5 to 45.6 mg/L.     

Effect of suspended solids on bioavailability of pyrethroid insecticides

Runoff and surface-water effluents commonly contain suspended solids. Adsorption to suspended particles and the associated dissolved organic matter (DOM) may significantly decrease the freely dissolved concentration of a hydrophobic compound and, hence, its availability to aquatic organisms. In the present study, we evaluated phase distribution and bioaccumulation of two synthetic pyrethroids, bifenthrin and permethrin, in water samples containing suspended solids from different source sediments. Uptake of [14C]bifenthrin or [14C] permethrin by Daphnia magna after 24 h consistently decreased with increasing levels of suspended solids in the range of 0 to 200 mg/L. The trend of decrease was closely mimicked by pesticide accumulation on polydimethylsiloxane (PDMS) fibers exposed under the same conditions, and the ratio of body residues in D. magna to the concentration detected in the PDMS fiber was consistently around 2.4. Regression analysis showed that the pesticide adsorbed on particles or DOM was completely unavailable to D. magna for uptake during the 24-h exposure. The relative contribution of particles and DOM to the reduced bioavailability depended on the organic matter content and the texture of the source sediment. The influence from particles was predominant for sandy sediments, but contribution from DOM became comparable to or even greater than particles when the organic matter content of the source sediment was 1% or greater. The inhibitory effects of suspended solids on bioavailability should be considered when monitoring runoff and surface-water effluents for synthetic pyrethroids. The proposed PDMS method is simple and inexpensive, and it may serve as an effective option for obtaining ecotoxicologically relevant concentrations.     

Oxygen consumption rates of grunion (Leuresthes tenuis) embryos exposed to the petroleum hydrocarbon, benzo[a]pyrene

Bioconcentration of [14C]benzo[a]pyrene and effects of unlabeled benzo[a]pyrene (BaP) accumulation on the routine oxygen consumption of embryonic grunion (Leuresthes tenuis) were studied. At Day 15, bioconcentration factors over dissolved BaP levels ranged from 249 to 466. Weight-specific respiration rates at Days 14-15 were significantly increased (P less than or equal to 0.05) at a mean BaP body burden of 0.51 ppm wet wt. Oxygen consumption rates of embryos containing 0.70 to 12.80 ppm BaP were not significantly different from control rates. Because in a previous study embryos containing 0.51 ppm BaP exhibited hatching and developmental rates similar to those of controls, their metabolic response to low-level hydrocarbon exposure may be an example of hormesis, an overcompensating metabolic regulation to inhibitory challenges.     

Influence of dissolved organic matter on the complexation of mercury under sulfidic conditions

The complexation of Hg under sulfidic conditions influences its bioavailability for microbial methylation. Neutral dissolved Hg-sulfide complexes are readily available to Hg-methylating bacteria in culture, and thermodynamic models predict that inorganic Hg-sulfide complexes dominate dissolved Hg speciation under natural sulfidic conditions. However, these models have not been validated in the field. To examine the complexation of Hg in natural sulfidic waters, octanol/water partitioning methods were modified for use under environmentally relevant conditions, and a centrifuge ultrafiltration technique was developed. These techniques demonstrated much lower concentrations of dissolved Hg-sulfide complexes than predicted. Furthermore, the study revealed an interaction between Hg, dissolved organic matter (DOM), and sulfide that is not captured by current thermodynamic models. Whereas Hg forms strong complexes with DOM under oxic conditions, these complexes had not been expected to form in the presence of sulfide because of the stronger affinity of Hg for sulfide relative to its affinity for DOM. The observed interaction between Hg and DOM in the presence of sulfide likely involves the formation of a DOM-Hg-sulfide complex or results from the hydrophobic partitioning of neutral Hg-sulfide complexes into the higher-molecular-weight DOM. An understanding of the mechanism of this interaction and determination of complexation coefficients for the Hg-sulfide-DOM complex are needed to adequately assess how our new finding affects Hg bioavailability, sorption, and flux.     

Enhanced kinetics of solid-phase microextraction and biodegradation of polycyclic aromatic hydrocarbons in the presence of dissolved organic matter

The uptake kinetics of fluorene, phenanthrene, fluoranthene, pyrene, and benzo[e]pyrene by solid-phase microextraction fibers was studied in the presence of dissolved organic matter (DOM) obtained from sediment pore water and resulted in increased fiber absorption and desorption rate coefficients. Compared to the control without DOM, these rate coefficients were increased at a DOM concentration of 36.62 mg/L by a factor of 1.27 to 2.21 and 1.31 to 2.10 for fluorene and benzo[e]pyrene, respectively. The calculated values for the fiber absorption and desorption rate coefficients show that diffusion through an unstirred boundary layer (UBL) surrounding the fiber probably forms the rate-limiting step of the process. The mineralization of aqueous-phase phenanthrene and pyrene by a representative polycyclic aromatic hydrocarbon (PAH)-degrading bacterium (Mycobacterium gilvum VM552) also was found to be enhanced by DOM. The initial degradation rates of phenanthrene (9.03 (microg/L) and pyrene (1.96 microg/L) were significantly higher compared to the control values and were enhanced by a factor of 1.32 and 1.26 at a DOM concentration of 43.14 and 42.15 mg/L, respectively. We suggest that such an enhancement results from the combination of faster uptake kinetics of the water-dissolved compounds in the UBL surrounding microbial cells and direct access of the bacteria to DOM-associated PAHs. These enhanced kinetic effects of DOM may have strong implications in sediment processes like desorption, nonequilibrium exposure, and biodegradation.     

Effects of dissolved organic carbon concentration and source, pH, and water hardness on chronic toxicity of copper to Daphnia magna

The effects of pH (5.3-8.7), water hardness (CaCO3 at 25-500 mg/L), dissolved organic carbon (DOC) concentration (1.6-18.4 mg/L), and DOC source on the chronic toxicity of copper to Daphnia magna were investigated by using a multifactorial, central composite test design. Natural dissolved organic matter (DOM) was collected at three sites in Belgium and The Netherlands by using reverse osmosis. For a total number of 35 toxicity tests performed, 21-d no-observed-effect concentrations (NOECs) of copper based on reproduction ranged from 29.4 to 228 microg/L and 21-d concentrations of copper causing 50% reduction of reproduction (EC50s) ranged from 41.5 to 316 microg/L. Statistical analysis revealed that DOC concentration and pH had a significant effect on copper toxicity but hardness (at the levels tested) did not. In general, an increase in pH or DOC resulted in a linear increase of 21-d NOEC and EC50 values. All DOMs (originating from three different sources) reduced copper toxicity to the same extent. Multiple linear regression analysis on the results of all 35 toxicity tests revealed that DOC concentration is the most important factor for chronic toxicity of copper to D. magna, explaining about 60% of the observed variability, whereas pH only explained about 15% of the observed variability. Regression models were developed (with DOC and pH as parameters) that were capable of predicting NOECs and EC50s within a factor of 1.9 from observed NOEC and EC50 values obtained with eight natural surface waters spiked with copper. Until future research further elucidates the mechanisms underpinning the observed bioavailability relations, these empirical regression models can become a first simple tool for regulatory applications.     

Toxicokinetics of 2,4,5-Trichlorophenol and Benzo(a)pyrene in the Clam Pisidium amnicum: Effects of Seasonal Temperatures and Trematode Parasites

Several biotic and abiotic stress factors may affect aquatic organisms simultaneously. However, not much is known about the effects of, e.g., low temperatures and parasite infections on the toxicokinetics of organic hydrophobic chemicals. Here we studied the accumulation and depuration of [¹⁴C]2,4,5-trichlorophenol (TCP) and [³H]benzo(a)pyrene (BaP) in the sediment-dwelling freshwater clam Pisidium amnicum. Experiments were made in October (+15°C), April (+4°C), and July (+15°C) both with uninfected clams and clams infected with Bunodera luciopercae (Trematoda). The accumulation rate for both chemicals was slower at 4°C than at 15°C. The depuration of TCP was biphasic, and the slowest depuration occurred at 4°C. For BaP, the depuration was very slow and monophasic at all temperatures. The highest BCFs for both chemicals were found in July at 15°C. Surprisingly, the BCFs for TCP were higher in April at 4°C than in October at 15°C. For BaP, no steady-state was reached in April. Differences in chemical toxicokinetics between the infected and uninfected clams were only minor. However, for both chemicals a trend of slightly lower BCFs in the infected clams was found. In conclusion, low temperatures modify the toxicokinetics of organic chemicals in P. amnicum and the effects depend on hydrophobicity of the chemical. The effects of parasites on toxicokinetics seem to be small. Received: 4 November 1999/Accepted: 29 March 2000     

Role of participate organic matter in decreasing accumulation of polynuclear aromatic hydrocarbons byDaphnia magna

Accumulation of benzo[a]pyrene (BaP) and anthracene (A) byDaphnia magna in the presence of suspended yeast cells was analyzed using multicompartment models. The rate coefficient for uptake of polynuclear aromatic hydrocarbon (PAH) due to ingestion of yeast cells laden with sorbed chemical was only 3 to 15% of the rate coefficient for uptake of dissolved PAH. Uptake and accumulation of BaP was reduced 97% due to sorption of PAH to naturally occurring organic matter (humic acids). Accumulation of hydrophobic chemicals in aqueous systems appears to depend on the amount of chemical in solution and on the amount of chemical sorbed to particles entering the food chain. Chemicals sorbed to suspended organic matter, including dissolved or colloidal organic matter, have greatly reduced availability.Research sponsored by the Office of Health and Environmental Research, U.S. Department of Energy, under contract W-7405eng-26 with Union Carbide Corp. Publication No. 2127, Environmental Sciences Division, ORNLBy acceptance of this article, the publisher or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering the article     

Examining the role of temperature and sediment-chemical contact time on desorption and bioavailability of sediment-associated tetrabromo diphenyl ether and benzo(a)pyrene

The effects of temperature and sediment-chemical contact time on desorption and bioaccumulation of sediment-spiked (14)C-labelled 2,2',4,4'-tetrabromo diphenyl ether (BDE-47) and benzo(a)pyrene (BaP) were examined. Experiments were performed after 2 or 6 weeks and 23 or 24 months sediment-chemical contact time at 10 and 20 degrees C. Desorption was measured in a sediment-water suspension using Tenax extraction, and bioaccumulation was measured by exposing Lumbriculus variegatus (Oligochaeta) to BDE-47 and BaP-spiked sediments in a 10d kinetic study. Biota-sediment accumulation factors (BSAFs) ranged between 2.9 and 4.3 for BDE-47 and between 0.5 and 0.9 for BaP. Thus, temperature and aging had a minor effect on bioavailability estimates. On the other hand, the difference between the chemicals was clear and could not be interpreted solely by reference to the size of the desorbing fractions, although the rapidly desorbing fraction-revised estimate clearly reduced the difference. The remaining discrepancy may be related to methodological (Tenax extraction vs. worm exposure) and/or biological (digestive extraction) causes. However, the data support the role of diffusional forces in the bioavailability of sediment-associated organic contaminants. Therefore, desorption-revised bioavailability estimates would lead to more precise bioavailability estimates than the traditional sediment organic carbon-organisms' lipids-based equilibrium partitioning approach.