1
|
Hiki K, Fischer FC, Nishimori T, Endo S, Watanabe H, Yamamoto H. Influence of water exchange rates on toxicity and bioaccumulation of hydrophobic organic chemicals in sediment toxicity tests. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2023; 25:609-620. [PMID: 36779546 DOI: 10.1039/d2em00462c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
In standardized sediment toxicity tests, the applied water exchange methods range from static to flow-through conditions and vary between protocols and laboratories even for the same test species. This variation potentially results in variable chemical exposure, hampering the interpretation of toxicity and bioaccumulation. To address these issues, we performed sediment toxicity tests with a mixture of three polycyclic aromatic hydrocarbons (PAHs) and the freshwater epibenthic amphipod Hyalella azteca as model chemicals and organism, respectively. Five standardized water exchange methods were applied: static, semi-static, or flow-through conditions. By measuring total (Cdiss) and freely dissolved concentrations (Cfree) of PAHs with water sampling and direct immersion solid-phase microextraction methods, respectively, we found that Cdiss in overlying water differed by a factor of up to 107 among water exchange conditions, whereas both Cdiss and Cfree in pore water did not differ by more than a factor of 2.6. Similar survival rates, growth rates, and bioaccumulation of PAHs between water exchange methods suggest that H. azteca was predominantly exposed to pore water rather than overlying water. By applying mechanistic kinetic modeling to simulate spatiotemporal concentration profiles in sediment toxicity tests, we discuss the importance of the water exchange rates and resulting temporal and spatial exposure variability for the extrapolation of laboratory sediment toxicity to field conditions, particularly for chemicals with relatively low hydrophobicity and sediments with low organic carbon content.
Collapse
Affiliation(s)
- Kyoshiro Hiki
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| | - Fabian Christoph Fischer
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| | - Takahiro Nishimori
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| | - Satoshi Endo
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| | - Haruna Watanabe
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| | - Hiroshi Yamamoto
- Health and Environmental Risk Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
| |
Collapse
|
2
|
Silva PV, Santos CSA, Papadiamantis AG, Gonçalves SF, Prodana M, Verweij RA, Lynch I, van Gestel CAM, Loureiro S. Toxicokinetics of silver and silver sulfide nanoparticles in Chironomus riparius under different exposure routes. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 865:161087. [PMID: 36566851 DOI: 10.1016/j.scitotenv.2022.161087] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 12/15/2022] [Accepted: 12/16/2022] [Indexed: 06/17/2023]
Abstract
Engineered nanoparticles released into surface water may accumulate in sediments, potentially threatening benthic organisms. This study determined the toxicokinetics in Chironomus riparius of Ag from pristine silver nanoparticles (Ag NPs), a simulating aged Ag NP form (Ag2S NPs), and AgNO3 as an ionic control. Chironomid larvae were exposed to these Ag forms through water, sediment, or food. The potential transfer of Ag from larvae to adult midges was also evaluated. Results revealed higher Ag uptake by C. riparius upon exposure to Ag2S NPs, while larvae exposed to pristine Ag NPs and AgNO3 generally presented similar uptake kinetics. Uptake patterns of the different Ag forms were generally similar in the tests with water or sediment exposures, suggesting that uptake from water was the most important route of Ag uptake in both experiments. For the sediment bioaccumulation test, uptake was likely a combination of water uptake and sediment particles ingestion. Ag uptake via food exposure was only significant for Ag2S NPs. Ag transfer to the terrestrial compartment was low. In our environmentally relevant exposure scenario, chironomid larvae accumulated relatively high Ag concentrations and elimination was extremely low in some cases. These results suggest that bioaccumulation of Ag in its nanoparticulate and/or ionic form may occur in the environment, raising concerns regarding chronic exposure and trophic transfer. This is the first study determining the toxicokinetics of NPs in Chironomus, providing important information for understanding chironomid exposure to NPs and their potential interactions in the environment.
Collapse
Affiliation(s)
- Patrícia V Silva
- CESAM-Centre for Environmental and Marine Studies & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
| | - Cátia S A Santos
- CESAM-Centre for Environmental and Marine Studies & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| | - Anastasios G Papadiamantis
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK; NovaMechanics Ltd., 1065 Nicosia, Cyprus
| | - Sandra F Gonçalves
- CESAM-Centre for Environmental and Marine Studies & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| | - Marija Prodana
- CESAM-Centre for Environmental and Marine Studies & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| | - Rudo A Verweij
- Amsterdam Institute for Life and Environment (A-LIFE), Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
| | - Iseult Lynch
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT, Birmingham, UK
| | - Cornelis A M van Gestel
- Amsterdam Institute for Life and Environment (A-LIFE), Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
| | - Susana Loureiro
- CESAM-Centre for Environmental and Marine Studies & Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
| |
Collapse
|
3
|
Nishimori T, Hiki K, Fischer FC, Endo S, Yamamoto H, Watanabe H. Comparing 10- and 28-Day Sediment Toxicity and Bioaccumulation of Fluoranthene in Hyalella azteca Using Passive Sampling Techniques. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2022; 41:2679-2687. [PMID: 35959891 DOI: 10.1002/etc.5460] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 06/23/2022] [Accepted: 08/05/2022] [Indexed: 06/15/2023]
Abstract
Understanding the changes in the temporal and spatial concentrations of chemical substances in sediment toxicity tests facilitates interpretation of their toxicity and accumulation in benthic organisms because benthic organisms are affected by chemicals via multiple exposure pathways. However, such investigations using chronic sediment toxicity tests have rarely been performed. To examine the concentration profiles of a hydrophobic organic chemical using chronic spiked-sediment toxicity tests, we performed 28-day sediment toxicity tests of fluoranthene with a freshwater amphipod, Hyalella azteca, using a semi-flow-through system and compared the results with those of 10-day tests. In these experiments, we measured various types of fluoranthene concentrations over the test periods: total dissolved (Cdiss ) and freely dissolved (Cfree ) concentrations in overlying water and porewater as well as sediment concentrations. We also examined which concentration correlated with the amphipod bioconcentration factor (BCF). We found that both overlying water and porewater Cfree did not differ significantly on days 10 and 28. Sediment concentrations remained almost stable for 28 days, whereas Cdiss in overlying water varied temporally. These results suggest that the 28-day test provides almost constant concentrations of fluoranthene, particularly in porewater, even in a semi-flow-through system. In addition, the comparison of BCF of fluoranthene on day 10 in the present study with that obtained from water-only tests reported in the literature suggested that Cfree in pore water was the most representative indicator of bioaccumulation in H. azteca. Our findings support the possible use of a water-exchange system in chronic spiked-sediment toxicity tests of hydrophobic organic chemicals. However, further studies using sediments and chemicals with different properties are warranted to generalize the findings of the present study. Environ Toxicol Chem 2022;41:2679-2687. © 2022 SETAC.
Collapse
Affiliation(s)
- Takahiro Nishimori
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| | - Kyoshiro Hiki
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| | - Fabian Christoph Fischer
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| | - Satoshi Endo
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| | - Hiroshi Yamamoto
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| | - Haruna Watanabe
- Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
| |
Collapse
|
4
|
Lauper B, Anthamatten E, Raths J, Arlos M, Hollender J. Systematic Underestimation of Pesticide Burden for Invertebrates under Field Conditions: Comparing the Influence of Dietary Uptake and Aquatic Exposure Dynamics. ACS ENVIRONMENTAL AU 2022; 2:166-175. [PMID: 37101586 PMCID: PMC10114668 DOI: 10.1021/acsenvironau.1c00023] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/28/2023]
Abstract
Pesticides used in agriculture can end up in nearby streams and can have a negative impact on nontarget organisms such as aquatic invertebrates. During registration, bioaccumulation potential is often investigated using laboratory tests only. Recent studies showed that the magnitude of bioaccumulation in the field substantially differs from laboratory conditions. To investigate this discrepancy, we conducted a field bioaccumulation study in a stream known to receive pollutant loadings from agriculture. Our work incorporates measurements of stream pesticide concentrations at high temporal resolution (every 20 min), as well as sediment, leaves, and caged gammarid analyses (every 2-24 h) over several weeks. Of 49 investigated pesticides, 14 were detected in gammarids with highly variable concentrations of up to 140 ± 28 ng/gww. Toxicokinetic modeling using laboratory-derived uptake and depuration rate constants for azoxystrobin, cyprodinil, and fluopyram showed that despite the highly resolved water concentrations measured, the pesticide burden on gammarids remains underestimated by a factor of 1.9 ± 0.1 to 31 ± 3.0, with the highest underestimations occurring after rain events. Including dietary uptake from polluted detritus leaves and sediment in the model explained this underestimation only to a minor proportion. However, suspended solids analyzed during rain events had high pesticide concentrations, and uptake from them could partially explain the underestimation after rain events. Additional comparison between the measured and modeled data showed that the pesticide depuration in gammarids is slower in the field. This observation suggests that several unknown mechanisms may play a role, including lowered enzyme expression and mixture effects. Thus, it is important to conduct such retrospective risk assessments based on field investigations and adapt the registration accordingly.
Collapse
Affiliation(s)
- Benedikt
B. Lauper
- Department
of Environmental Chemistry, Eawag, 8600 Dübendorf, Switzerland
- Institute
of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland
| | - Eva Anthamatten
- Department
of Environmental Chemistry, Eawag, 8600 Dübendorf, Switzerland
- Institute
of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland
| | - Johannes Raths
- Department
of Environmental Chemistry, Eawag, 8600 Dübendorf, Switzerland
- Institute
of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland
| | - Maricor Arlos
- Department
of Environmental Chemistry, Eawag, 8600 Dübendorf, Switzerland
- Department
of Civil and Environmental Engineering, University of Alberta, 9211-116 St. NW, Edmonton, T6G 1H9 AB, Canada
| | - Juliane Hollender
- Department
of Environmental Chemistry, Eawag, 8600 Dübendorf, Switzerland
- Institute
of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092 Zürich, Switzerland
| |
Collapse
|
5
|
Dorn A, Kaiser C, Hammel K, Dalkmann P, Faber D, Trisna A, Hellpointner E, Telscher M, Lamshoeft M, Bruns E, Seidel E, Hollert H. What is the spatial-temporal behavior of a low, medium and high adsorptive compound in two contrasting natural sediments in OECD 218/219 test systems? THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 809:151096. [PMID: 34743820 DOI: 10.1016/j.scitotenv.2021.151096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 10/05/2021] [Accepted: 10/16/2021] [Indexed: 06/13/2023]
Abstract
Artificial sediment used in studies according to OECD 218/219 (Sediment Water Chironomid Toxicity Test Using Spiked Sediment/Water) does not necessarily mirror the characteristics of natural sediments. To investigate the influence of sediment characteristics on the spatial-temporal behaviors of bixafen (KfOM = 2244 mL/g), fluopyram (KfOM = 162 mL/g) and N,N-dimethylsulfamide (KfOM ≈ 0 mL/g), experiments according to OECD 218/219 with two contrasting natural sediments were conducted. The silt loam sediment provided a high content of organic matter (OM) (13.1%), while the OM (0.45%) of the sandy sediment was low. Diffusion into (OECD 219) or out (OECD 218) of the sediment was dependent on the extent of adsorption, which is linked to the model compounds ́ adsorption affinities and the sediments ́ OM. Consequently, N,N-dimethylsulfamide showed unhindered mobility in each experimental set up, while the high adsorption affinities of fluopyram and bixafen limited the diffusion in the respective sediments. Therefore, in experiments with the silt loam sediment, both compounds revealed a limited mobility and either accumulated in the top 5 mm of the sediment (OECD 219) or remained homogenously distributed over the sediment depth (OECD 218). A greater mobility was observed within the sandy sediment.The influence of OM as found in a study using artificial sediment could be confirmed. Moreover, the applicability of a TOXSWA model was reassured to predict the measured concentrations at different sediment depths. TOXSWA is used in the regulatory exposure assessment to simulate the behavior of pesticides in surface waters. Calibration of three driving input parameters by inverse modelling (diffusion-, adsorption coefficient and OM) revealed no potential for improvement. The core sampling technique used and the model may contribute to a more realistic determination of concentration to which the Chironomid larvae are exposed to. This applies to water sediment test systems where the test organisms do not evenly inhabit the sediment.
Collapse
Affiliation(s)
- Alexander Dorn
- Institute of Environmental Research, RWTH Aachen University, 52074 Aachen, Germany.
| | - Christina Kaiser
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Klaus Hammel
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Philipp Dalkmann
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Daniel Faber
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Audrey Trisna
- Department of Chemical Engineering, CPE Lyon, 69616 Villeurbanne Cedex, France
| | - Eduard Hellpointner
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Markus Telscher
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Marc Lamshoeft
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Eric Bruns
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Erika Seidel
- Environmental Safety, Crop Science Division, Bayer AG, 40789 Monheim, Germany
| | - Henner Hollert
- Institute of Ecology, Evolution & Diversity, Goethe Universität, 60438 Frankfurt am Main, Germany
| |
Collapse
|
6
|
Hiki K, Iwasaki Y, Watanabe H, Yamamoto H. Comparison of Species Sensitivity Distributions for Sediment-Associated Nonionic Organic Chemicals Through Equilibrium Partitioning Theory and Spiked-Sediment Toxicity Tests with Invertebrates. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2022; 41:462-473. [PMID: 34913527 PMCID: PMC9303217 DOI: 10.1002/etc.5270] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2021] [Revised: 10/29/2021] [Accepted: 12/09/2021] [Indexed: 06/12/2023]
Abstract
Equilibrium partitioning (EqP) theory and spiked-sediment toxicity tests are useful methods to develop sediment quality benchmarks. However, neither approach has been directly compared based on species sensitivity distributions (SSDs) to date. In the present study, we compared SSDs for 10 nonionic hydrophobic chemicals (e.g., pyrethroid insecticides, other insecticides, and polycyclic aromatic hydrocarbons) based on 10-14-day spiked-sediment toxicity test data with those based on EqP theory using acute water-only tests. Because the exposure periods were different between the two tests, effective concentrations (i.e., median effective/lethal concentration) were corrected to compare SSDs. Accordingly, we found that hazardous concentrations for 50% and 5% of species (HC50 and HC5, respectively) differed by up to a factor of 100 and 129 between the two approaches, respectively. However, when five or more species were used for SSD estimation, their differences were reduced to a factor of 1.7 and 5.1 for HC50 and HC5, respectively, and the 95% confidence intervals of HC50 values overlapped considerably between the two approaches. These results suggest that when the number of test species is adequate, SSDs based on EqP theory and spiked-sediment tests are comparable in sediment risk assessments. Environ Toxicol Chem 2022;41:462-473. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Collapse
Affiliation(s)
- Kyoshiro Hiki
- Health and Environmental Risk Research DivisionNational Institute for Environmental StudiesTsukubaIbarakiJapan
| | - Yuichi Iwasaki
- Research Institute of Science for Safety and SustainabilityNational Institute of Advanced Industrial Science and TechnologyTsukubaIbarakiJapan
| | - Haruna Watanabe
- Health and Environmental Risk Research DivisionNational Institute for Environmental StudiesTsukubaIbarakiJapan
| | - Hiroshi Yamamoto
- Health and Environmental Risk Research DivisionNational Institute for Environmental StudiesTsukubaIbarakiJapan
| |
Collapse
|
7
|
Hiki K, Fischer FC, Nishimori T, Watanabe H, Yamamoto H, Endo S. Spatiotemporal Distribution of Hydrophobic Organic Contaminants in Spiked-Sediment Toxicity Tests: Measuring Total and Freely Dissolved Concentrations in Porewater and Overlying Water. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2021; 40:3148-3158. [PMID: 34432908 PMCID: PMC9293400 DOI: 10.1002/etc.5199] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 07/27/2021] [Accepted: 08/23/2021] [Indexed: 06/12/2023]
Abstract
The sediment-water interface of spiked-sediment toxicity tests is a complex exposure system, where multiple uptake pathways exist for benthic organisms. The freely dissolved concentration (Cfree ) in sediment porewater has been proposed as a relevant exposure metric to hydrophobic organic contaminants (HOCs) in this system. However, Cfree has rarely been measured in spiked-sediment toxicity tests. We first developed a direct immersion solid-phase microextraction method for measuring Cfree in overlying water and porewater in a sediment test using polydimethylsiloxane-coated glass fibers, resulting in sensitive and repeatable in situ measurements of HOCs. Then, we measured Cfree and total dissolved concentrations (Cdiss ) in the sediment test systems with the freshwater amphipod Hyalella azteca and thoroughly evaluated the temporal and spatial profiles of four HOCs (phenanthrene, pyrene, benzo[a]pyrene, and chlorpyrifos). Furthermore, we examined the relationship between the measured concentrations and the lethality of H. azteca. We found that the test system was far from an equilibrium state for all four chemicals tested, where Cdiss in overlying water changed over the test duration and a vertical Cfree gradient existed at the sediment-water interface. In porewater Cdiss was larger than Cfree by a factor of 170 to 220 for benzo[a]pyrene because of the strong binding to dissolved organic carbon. Comparison of the median lethal concentrations of chlorpyrifos in the sediment test and those in water-only tests indicates that Cfree in porewater was the most representative indicator for toxicity of this chemical. The method and findings presented in the present study warrant further research on the chemical transport mechanisms and the actual exposure in sediment tests using different chemicals, sediments, and test species. Environ Toxicol Chem 2021;40:3148-3158. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Collapse
Affiliation(s)
- Kyoshiro Hiki
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| | - Fabian Christoph Fischer
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| | - Takahiro Nishimori
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| | - Haruna Watanabe
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| | - Hiroshi Yamamoto
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| | - Satoshi Endo
- Health and Environmental Risk DivisionNational Institute for Environmental Studies, TsukubaIbarakiJapan
| |
Collapse
|
8
|
Fischer FC, Hiki K, Soetaert K, Endo S. Mind the Exposure Gaps-Modeling Chemical Transport in Sediment Toxicity Tests. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:11885-11893. [PMID: 34488347 DOI: 10.1021/acs.est.1c03201] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Chemical exposure in flow-through sediment toxicity tests can vary in time, between pore and overlying water, and amid free and bound states, complicating the link between toxicity and observable concentrations such as free pore (Cfree,pore), free overlying (Cfree,over), or the corresponding dissolved concentrations (Cdiss, free + bound to dissolved organic carbon, DOC). We introduce a numerical model that describes the desorption from sediments to pore water, diffusion through pores and the sediment-water boundary, DOC-mediated transport, and mixing in and outflow from overlying water. The model explained both the experimentally measured gap between Cfree,over and Cfree,pore and the continuous decrease in overlying Cdiss. Spatially resolved modeling suggested a steep concentration gradient present in the upper millimeter of the sediment due to slow chemical diffusion in sediment pores and fast outflux from the overlying water. In contrast to continuous decrease in overlying Cdiss expected for any chemical, Cfree,over of highly hydrophobic chemicals was kept relatively constant following desorption from DOC, a mechanism comparable to passive dosing. Our mechanistic analyses emphasize that exposure will depend on the chemical's hydrophobicity, the test organism habitat and uptake of bound chemicals, and the properties of sediment components, including DOC. The model can help to re-evaluate existing toxicity data, optimize experimental setups, and extrapolate laboratory toxicity data to field exposure.
Collapse
Affiliation(s)
- Fabian Christoph Fischer
- Health and Environmental Risk Division, National Institute for Environmental Studies (NIES), Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan
| | - Kyoshiro Hiki
- Health and Environmental Risk Division, National Institute for Environmental Studies (NIES), Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan
| | - Karline Soetaert
- Department of Estuarine and Delta Systems, NIOZ Royal Netherlands Institute for Sea Research, Korringaweg 7, 4401 NT Yerseke, The Netherlands
| | - Satoshi Endo
- Health and Environmental Risk Division, National Institute for Environmental Studies (NIES), Onogawa 16-2, 305-8506 Tsukuba, Ibaraki, Japan
| |
Collapse
|