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Keywords:

  • Biotransformation;
  • Body residue;
  • Chironomus dilutus;
  • Hyalella azteca;
  • SPME fiber;
  • Toxicity

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

In the companion paper, solid phase microextraction (SPME) fiber concentrations were used as a dose metric to evaluate the toxicity of hydrophobic pesticides, and concentration–response relationships were found for the hydrophobic pesticides tested in the two test species. The present study extends the use of fiber concentrations to organism body residues to specifically address biotransformation and provide the link to toxic response. Test compounds included the organochlorines p,p′-dichlorodiphenyltrichloroethane (p,p′-DDT), p,p′-dichlorodiphenyldichloroethane (p,p′-DDD), and p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE); two pyrethroids, permethrin and bifenthrin; and an organophosphate, chlorpyrifos. Toxicity, body residues, and biotransformation of the target compounds were determined for the midge Chironomus dilutus and the amphipod Hyalella azteca. Significant regression relationships were found without regard to chemical, extent of biotransformation, or whether the chemical reached steady state in the organisms. The equilibrium SPME fiber concentrations correlated with the parent compound concentration in the biota; however, the regressions were duration specific. Furthermore, the SPME fiber-based toxicity values yielded species-specific regressions with the parent compound–based toxicity values linking the use of SPME fiber as a dose metric with tissue residues to estimate toxic response. Environ. Toxicol. Chem. 2012; 31: 2168–2174. © 2012 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

Solid phase microextraction (SPME) is a passive sampling technique used to assess organism exposure and make body residue estimates 1–3. The SPME fiber concentration, through the fiber water partition coefficient (Kfw), represents the apparent chemical activity of the contaminant usually expressed as the concentration of the chemical that is freely dissolved in the aqueous phase and available for biological uptake. The measured SPME fiber concentration can be used to effectively estimate body burdens for a variety of hydrophobic compounds 3–10. In most of these studies, bioaccumulation was measured at sublethal levels. For example, accumulation by the oligochaete Lumbriculus variegatus correlated well with matrix-SPME fiber concentrations across chemical classes 7. Fewer studies have linked SPME fiber concentrations to body residues at lethal levels or linked SPME fibers to the subsequent toxic effects 1, 11–13. Additionally, most studies were conducted on compounds in which biotransformation was expected to be minimal. However, many important environmental contaminants (such as pyrethroid insecticides) can be extensively biotransformed. Our companion paper demonstrated relationships between parent compound concentrations at equilibrium in the SPME fibers and the toxic responses to Hyalella azteca and Chironomus dilutus from exposure to various hydrophobic pesticides after specific exposure durations. Whereas a conceptual model supported the theory that a relationship would be expected between SPME concentrations at equilibrium and toxic responses 13, a more complete explanation linking SPME fibers concentrations and toxicity response was important for future reliance on this approach. Furthermore, if SPME fibers are to serve as a dose metric at other than steady-state conditions reflecting other toxicokinetic states and can be shown to reflect the associated absorbed dose driving the toxic response, then the SPME fiber concentration and toxicity relationship would be more defensible and have a wider range of application (Fig. 1).

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Figure 1. Conceptual model using solid phase microextraction (SPME) fiber to relate to organism absorbed dose and to estimate toxicity of hydrophobic pesticides. Kfw = partition coefficient between fiber and water; Cf = equilibrium-equivalent fiber concentration; Cb = body residue based on parent compound concentration. The dashed line between the SPME concentration and the absorbed dose represents an expected proportionality that will vary depending on exposure time to reflect the toxicokinetic state of the organisms. Thus, the proportionality between absorbed dose (parent compound) and the SPME should also yield a proportional relationship to toxic response.

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The objective of the present study was to investigate the relationships between equilibrium SPME fiber concentrations and body residues of hydrophobic pesticides at toxic concentrations, not necessarily at steady state, to two freshwater invertebrates, C. dilutus and H. azteca. Test compounds included an organochlorine pesticide p,p′-dichlorodiphenyltrichloroethane (p,p′-DDT), and its major degradation products, p,p′-dichlorodiphenyldichloroethane (p,p′-DDD) and p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE); two pyrethroid pesticides, permethrin and bifenthrin; and an organophosphate pesticide, chlorpyrifos. These pesticides were selected because they represent different classes of pesticides, some of them are readily biotransformed in freshwater organisms and have been widely detected in both urban and agricultural sediments throughout the United States 14–16.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

Chemicals

Radiolabeled 14C-permethrin (260 mCi/mmol) was purchased from Moravek Biochemicals, 14C-bifenthrin (41.97 mCi/mmol) was purchased from Institute of Isotope, Germany, and 14C-p,p′-DDT (18.7 mCi/mmol), 14C-p,p′-DDD (2.6 mCi/mmol), and 14C-p,p′-DDE solutions (13 mCi/mmol) were obtained from Sigma-Aldrich. Purity of the compounds was checked using high-performance liquid chromatography (HPLC) (Agilent Technologies) separation followed by liquid scintillation counting (LSC) with a Packard TriCarb 2900 Liquid Scintillation Analyzer (Packard Instruments). Sample counts were corrected for background and quench using the external standards ratio method. All stocks were greater than 97% pure, with the exception of p,p′-DDT, which had a purity of 94% (DDE 3.7%, DDD 1.7%, and 0.6% other polar metabolites). Nonradiolabeled bifenthrin, permethrin, and chlorpyrifos were purchased from ChemService, p,p′-DDT, p,p′-DDE, and p,p′-DDD were purchased from Supelco. The surrogates, 4, 4′-dibromooctafluorobiphenyl and decachlorobiphenyl, were obtained from Supelco. The purity of all the nonradiolabeled standard chemicals was greater than 98% as indicated by the manufacturer. Stock solutions for the bioassays were prepared by mixing known quantities of radiolabeled and nonradiolabeled compounds using acetone as the carrier. Stock concentrations were verified using LSC, and the specific activity was recalculated by adjusting for the isotopic dilution. Chlorpyrifos solutions were directly prepared with nonradiolabeled compounds using acetone as a carrier.

Organisms and toxicity testing

The benthic invertebrates were cultured in accordance with standard protocols 17 at Southern Illinois University. Third instar C. dilutus larvae and H. azteca (7- to 14-d old) were used for testing. Lipid content of the organisms was measured using a phosphovanillin spectrometric method after Folch purification with 0.9% NaCl and sulfuric acid digestion 18, 19.

Toxicity of the selected pesticides was examined in 4- and 10-d standard water toxicity bioassays in reconstituted water following U.S. Environmental Protection Agency (U.S. EPA) standard protocols 17, and the details of these methods are provided in Supplemental Data. Water concentrations were monitored at the beginning and end of the experiment. For 14C-spiked water, concentrations were directly measured using LSC, and for chlorpyrifos, water samples were extracted using liquid-liquid extraction with methylene chloride and analyzed using gas chromatography with an electron capture detector (Wang et al. 20 method detailed in the supplemental information). At 4 and 10 d, organism survival and affected C. dilutus, which were unable to perform a normal swimming motion (immobilization) when pinched with a pair of forceps 21, were enumerated. Live organisms were rinsed, blotted dry, and weighed to the nearest 0.01 mg using a Mettler analytical balance. Organisms, for total absorbed compound, exposed to radiolabeled chemicals were analyzed by placing them directly into scintillation cocktail and sonicated for 60 s using a Tekmar High-Intensity Ultrasonic Processor (Tekmar). The radioactivity was measured using LSC. Sample blanks were included to track any potential contamination. For chlorpyrifos, the organisms were extracted using a matrix solid-phase dispersion method and analyzed using gas chromatography with an electron capture detector 22, and the extraction efficiency of this method was 83 ± 10%, and only parent chlorpyrifos was measured.

Biotransformation

In the biotransformation experiments, C. dilutus and H. azteca were exposed to 14C chemical in 1 L of spiked reconstituted water. Each species was exposed at two concentrations (low and high; Table 1), two replicates per concentration, and 20 individuals per replicate. Organisms were exposed under the same conditions as described for the toxicity tests (4- and 10-d static tests at 23°C). At the end of the exposure, live organisms were retrieved and stored at −20°C before analysis for parent compound and biotransformation products. Frozen organisms were thawed at room temperature and blotted dry with a paper towel. Organisms were weighed and homogenized in a tissue homogenizer with 2 ml acetone and washed three additional times with 1 ml acetone. The combined extracts were centrifuged, decanted, evaporated to near dryness, solvent exchanged to 0.1 ml of acetonitrile, and the extract was analyzed by LSC after HPLC separation. Because of the difficulty in separating and detecting the metabolites, no testing was conducted to assess biotransformation of chlorpyrifos, the only nonradiolabeled compound studied.

Table 1. Percentage of parent compound in Chironomus dilutus and Hyalella azteca after 4- and 10-d biotransformation tests at two exposure concentrationsa
OrganismCompoundDurationConcentration (µg/L)% Mortality% ParentConcentration (µg/L)% Mortality% Parent
  • a

    Percentage of parent bifenthrin was only determined at 4 d in the high concentration exposure in the C. dilutus test due to the relatively low measured radioactivity in other treatments, and 4-d parent bifenthrin was used for all body residue calculations. Biotransformation of dichlorodiphenyldichloroethylene (DDE) in C. dilutus, and dichlorodiphenyldichloroethane (DDD) and DDE in H. azteca were not measured, because previous studies showed that C. dilutus had a limited ability to biotransform DDE 28, and H. azteca had a limited ability to biotransform DDD and DDE 29.

    p,p-DDT = p,p′-dichlorodiphenyltrichloroethane; p,p-DDD = p,p′-dichlorodiphenyldichloroethane; ND = not determined.

C. dilutusp,p′-DDT4 d1031.446333.4
10 d0.3103.42654.2
p,p′-DDD4 d0.1097.00.54097.0
10 d0.11795.70.54096.0
Permethrin4 d0.0251529.90.24524.7
10 d0.0251317.70.28527.4
Bifenthrin4 d0.0110nd0.13846.7
H. aztecap,p′-DDT4 d0.151538.10.65534.5
10 d0.0751025.00.37027.1
Permethrin4 d0.011018.20.035019.1
10 d0.011513.50.037310.0

Solid phase microextraction and fiber-based median lethal concentration (LC50) values

Both the equilibrium fiber concentrations (Cf) and the LC50 and median effective concentration (EC50) values on a fiber concentration basis were determined in our companion paper 13.

Data analysis

Tissue residues based on the parent compound were determined by multiplying the total body residue by the average percentage of parent compound determined from each concentration in the biotransformation study. Because no significant effect of concentration on biotransformation rate was seen, the proportion parent compound was assumed to be constant across exposure concentrations. Therefore, the average of the two values (low and high) was used to represent the average proportion parent among concentrations. The median lethal (LR50) and effect (ER50) parent tissue residues were estimated by using either standard probit analysis (SAS version 8.02, SAS Institute) or trimmed Spearman-Karber analyses.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

Water quality was maintained within U.S. EPA 17 acceptable limits during the bioassays (temperature 23 ± 1°C, conductivity 321–362 µS/cm, dissolved oxygen 6.23–7.50 mg/L, pH 7.6–7.8, ammonia 0.3–0.6 mg/L). The average percentage of lipids, on a wet-weight basis, were 1.18 ± 0.096% and 3.25 ± 0.59% (n = 8) for C. dilutus and H. azteca, respectively.

The extent of biotransformation varied among the compounds, with no biotransformation for DDE, and very little for DDD, and extensive biotransformation was noted for the pyrethroids and DDT (Table 1). Of particular interest was that the extent of biotransformation was not equal between exposure periods. The longer the exposure, the lower the fraction of parent compound of the total absorbed dose, indicating a greater degree of biotransformation. What was more unexpected was the similarity of the extent of biotransformation among the two exposure concentrations. Despite the fact that the organisms were stressed to the point of mortality, the biotransformation was consistent between concentrations. Biotransformation was not generally examined in toxicity testing, but it was important for applying the fiber concentration as a representation of the amount of the toxicant in the organism at different exposure durations and across treatments.

The ability of body residues to access toxicity 23 and the SPME fiber concentrations to predict absorbed dose at steady state has been established in the literature 1, 24. However, the connection among the fiber concentration, absorbed dose, and toxicity, acknowledging the rationale for the ability of the SPME fiber to serve as the dose metric for toxicity studies, although present in the literature, was less well established 2, 11–13. Because both the absorbed dose and the SPME fiber concentration are driven by the chemical activity in the exposure medium—often expressed as the freely dissolved compound—logically the absorbed dose should remain proportional to the equilibrium fiber concentration in relation to the organism toxicokinetics, just as the water was proportional to the absorbed dose for any toxicokinetic state. Therefore, the response of the organism, based on the absorbed dose and the toxicodynamics, should also be reflected by the equilibrium fiber concentration, however, the relationship will be exposure duration dependent to reflect the toxicokinetic state of the organism (Fig. 1) 13.

When the equilibrium fiber concentrations for each exposure were plotted against the measured body residues based on lipid-normalized parent compound, for each species and exposure duration, significant log-log linear relationships (p ≤ 0.05) were obtained for DDD and DDE that were not biotransformed, as well as for DDT, permethrin, and bifenthrin that were extensively biotransformed in the organisms (Fig. 2 and Table 2). The C. dilutus 10-d DDE regression was not significant (p = 0.11), which was likely attributable, in part, to the limited number of data points (n = 3). The low number of data points results from the fact that for some treatments, high percentage of mortalities were observed; thus, body residues were not available for developing the relationship. Among these regressions, the slopes were only significantly different between the 4- and 10-d exposures for C. dilutus for DDE, likely reflecting the difficulty of the low number of data points for the 10-d exposure and for permethrin. The intercepts were also different for these two conditions with C. dilutus and also for DDT with H. azteca. However, for the most part, the data from the different exposures tended to be very similar between exposure durations and tended to follow the same trend between tissue and fiber concentrations even between organisms (Fig. 2). This suggested that the organisms may well have been at steady state or nearly so by the end of 4 d.

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Figure 2. The log–log relationship between equilibrium-equivalent fiber concentrations and lipid-normalized body residues. Cd = Chironomus dilutus; Ha = Hyalella azteca; DDT = dichlorodiphenyltrichloroethane; DDD = dichlorodiphenyldichloroethane; DDE = dichlorodiphenyldichloroethylene.

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Table 2. Regression models predicting log (lipid normalized parent tissue concentration, y, nmol/g lipid) in Chironomus dilutus (Cd) and Hyalella azteca (Ha) using log (solid phase microextraction fiber concentration, x, nmol/mlPDMS)
CompoundTestRegressionr2p
  1. p,p-DDT = p,p′-dichlorodiphenyltrichloroethane; p,p-DDD = p,p′-dichlorodiphenyldichloroethane; p,p-DDE = p,p′-dichlorodiphenyldichloroethylene.

p′-DDTCd 4 dy = (0.93 ± 0.12) x + (0.41 ± 0.39)0.950.005
Cd 10 dy = (1.06 ± 0.06) x − (0.37 ± 0.14)0.990.0003
Ha 4 dy = (0.59 ± 0.32) x + (0.59 ± 0.14)0.900.05
Ha 10 dy = (0.93 ± 0.18) x − (0.03 ± 0.31)0.930.03
p′-DDDCd 4 dy = (1.44 ± 0.11) x − (0.63 ± 0.24)0.980.0009
Cd 10 dy = (1.27 ± 0.12) x − (0.46 ± 0.21)0.980.009
Ha 4 dy = (1.04 ± 0.07) x + (0.12 ± 0.16)0.990.04
Ha 10 dy = (1.32 ± 0.42) x − (0.19 ± 0.91)0.770.05
p′-DDECd 4 dy = (0.92 ± 0.12) x − (0.53 ± 0.57)0.970.02
Cd 10 dy = (0.65 ± 0.12) x + (0.91 ± 0.52)0.970.11
Ha 4 dy = (0.79 ± 0.19) x − (0.21 ± 0.67)0.900.05
Ha 10 dy = (1.05 ± 0.21) x − (1.06 ± 0.75)0.920.04
PermethrinCd 4 dy = (1.07 ± 0.01) x − (1.25 ± 0.01)0.99<0.0001
Cd 10 dy = (1.27 ± 0.08) x − (1.83 ± 0.10)0.990.0005
Ha 10 dy = (1.08 ± 0.12) x − (1.12 ± 0.07)0.980.01
BifenthrinCd 4 dy = (0.94 ± 0.10) x − (0.58 ± 0.10)0.970.003
Cd 10 dy = (0.88 ± 0.10) x − (0.74 ± 0.09)0.960.003

Because body residues were directly related to the toxic responses noted in the bioassays, expressed as LR50s (Tables 3 and 4), the relationship between the SPME concentration and body residue for each compound provides the support for SPME to serve as a surrogate dose metric despite the influence of biotransformation and toxicokinetic state. This linkage was further supported by the relationship between the LC50 and EC50 on a fiber basis to that of the LR50 and ER50 for each species (Fig. 3). Thus, for these two species, the fiber-based LC50 appeared to be proportional to the tissue residue–based LC50 for each species, which specifically supports the hypothesis that the fiber concentration was a reasonable surrogate to represent exposure and toxicity. However, some variability in the relationship needs to be examined and explained. Identifying the compounds falling into a particular cluster of points was possible, for example, the permethrin data for C. dilutus fell below the line but was parallel to it. The cause of this variation cannot be identified from the limited work performed in the two papers, the present study and Ding et al. 13. Some of this may be attributable to measurement variability and some to organism-specific variation, such as differences in biotransformation and some variation in response. This will require additional investigation to improve our understanding of the factors influencing the relationship.

Table 3. Median lethal (LR50) and effect residue (ER50) values calculated for Chironomus dilutus in the toxicity bioassaysa,b
Compound4-d LR50 (nmol/g lipid)4-d ER50 (nmol/g lipid)10-d LR50 (nmol/g lipid)10-d ER50 (nmol/g lipid)
  • a

    Body residues were not determined at 10 d for chlorpyrifos because concentrations were below reporting limits even after combining all of the replicates. The dichlorodiphenyldichloroethylene (DDE) 4-d LR50 value was not determined because of limited mortality in that test.

  • b

    Toxicity values were based on lipid-normalized parent body residues. Confidence intervals (95%) are shown in parentheses.

    p,p-DDT = p,p′-dichlorodiphenyltrichloroethane; p,p-DDD = p,p′-dichlorodiphenyldichloroethane; p,p-DDE = p,p′-dichlorodiphenyldichloroethylene; ND = not determined.

p′-DDT825 (674–1,009)787 (657–941)320 (282–362)223 (201–248)
p′-DDD198 (168–231)139 (78.8–225)236 (109–1,534)104 (74.6–150)
p′-DDEND9,492 (9,068–10,000)6,737 (6,398–7,093)6,254 (5,992–6,534)
Permethrin2.80 (2.12–3.47)0.85 (0.34–1.69)0.76 (0.68–0.93)0.68 (0.59–0.76)
Bifenthrin3.90 (3.22–4.75)2.54 (2.29–3.05)1.19 (0.76–1.86)1.19 (0.76–1.86)
Chlorpyrifos4.41 (2.80–7.03)2.54 (0.85–5.93)NDND
Table 4. Median lethal residue (LR50) values calculated for Hyalella azteca in the toxicity experimentsa,b,c
Compound4-d LR50 (nmol/g lipid)10-d LR50 (nmol/g lipid)
  • a

    LR50s were based on lipid-normalized parent body residue. Confidence intervals (95%) are shown in parentheses.

  • b

    Body residues could not be quantified for bifenthrin and chlorpyrifos because of the low concentrations.

  • c

    The dichlorodiphenyldichloroethylene (DDE) LR50s were not determined because 100% mortality occurred at the highest concentration and less than 50% mortality occurred at the second highest concentration.

    p,p-DDT = p,p′-dichlorodiphenyltrichloroethane; p,p-DDD = p,p′-dichlorodiphenyldichloroethane.

p′-DDT209 (184–237)45.9 (41.5–50.5)
p′-DDD588 (440–763)548 (462–649)
Permethrin2.15 (1.85–3.08)0.62 (0.49–0.92)
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Figure 3. The log–log relationship between the median lethal concentration (LC50) and median effective concentration (EC50) values on a fiber concentration basis and the median lethal (LR50) and effect (ER50) parent tissue residues for the midge Chironomus dilutus (A) log (ER50 or LR50) = 1.1 ± 0.11 log (LC50 or EC50) – 0.72 ± 0.27, r2 = 0.82, n = 21, and amphipod Hyalella azteca (B) log (LR50) = 1.49 ± 0.21 log (LC50) – 0.98 ± 0.41, r2 = 0.92, n = 6 linking solid phase microextraction to tissue residue effects metrics.

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Previous studies have hypothesized that for extensively biotransformed compounds, making assessments based on either tissue residues or SPME fibers, which only measure parent compound, would be more difficult 25, 26. In part, the biotransformation products are expected to have varying effects on toxicity and would thus contribute differentially to the residue responsible for response. In the current study, several of the compounds were extensively biotransformed by both species, and the biotransformation products were expected to contribute little to the toxic response for DDT and the pyrethroids, but should be the actual toxicant for chlorpyrifos 27. The C. dilutus extensively biotransformed DDT, bifenthrin, and permethrin, but not DDD and DDE, whereas DDT and permethrin were biotransformed by H. azteca. The degree of organism mortality found in the biotransformation tests was comparable to that found in the toxicity tests (Table 1). Although biotransformation varied among species and compounds, as long as the biotransformation was addressed, the parent body residue was proportional to the equilibrium fiber concentration (in the present study and Harwood et al. 26). Despite the variations in biotransformation among species and compounds, the SPME fiber concentrations correlated well with the organism's body residues, but the regressions varied somewhat with chemical and species (Fig. 2). These regressions demonstrate that SPME fibers can access bioaccumulation for both nonbiotransformed and biotransformed compounds. However, the correlations between fiber and tissue concentrations had a large range of slopes (0.59–1.44) and intercepts (−1.83–0.91) among compounds and species (Table 2). In a previous study 26 using pyrethroids (permethrin and bifenthrin), the relationship between equilibrium fiber concentrations and lipid-normalized parent concentrations were also significantly different between compounds. Therefore, the best SPME fiber to absorbed dose or toxicity relationship may be compound and species specific, reflecting differences in biotransformation capability and toxicity of metabolites. More studies with biotransformed compounds will be needed to sort out how much specificity will be required to develop solid relationships for management applications.

Generally, the time required for hydrophobic chemicals to reach steady state in an organism is chemical, species, and exposure condition dependent. When the concentration of the chemical in the organism is at nonsteady-state conditions, biotransformation should theoretically change the relationship between the SPME fiber and the tissue concentrations compared with steady-state conditions. If animals reach a steady-state parent tissue concentration, then the SPME fiber measured concentration for biotransformed compounds should correlate to parent tissue concentrations equally well as nonbiotransformed compounds 26. However, the absorbed concentration in the organism at any point in time during the exposure is also proportional to the chemical activity in the matrix dependent on the toxicokinetics. Therefore, separate relationships between the equilibrium fiber concentration and organism concentration for each specific exposure duration may be required to make comparisons to bioaccumulation or response when it is clear that the organisms are not at steady state. The fiber-absorbed dose response relationships from the current study (Fig. 2) support the notion that these small organisms were likely at or near steady state by the end of 4 d as discussed. For example, the regression lines between 4- and 10-d exposure durations were not significantly different for DDT, DDD, and bifenthrin in the C. dilutus tests, and for DDD and DDE in the H. azteca tests. Thus, strong correlations between the fiber concentration and the parent compound body residues, which led to the good correlation between the response values expressed either on a body residue or fiber concentration basis, were not surprising.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

In the companion paper, equilibrium SPME fiber concentrations exhibited concentration–response relationships for the hydrophobic pesticides in the two test species. Conceptually, this was equivalent to expressing the toxicity on a bioavailable external concentration basis, because chemical activity drives both the absorbed dose and equilibrium fiber concentrations. In the present study, the relationship between the equilibrium fiber concentration and organism absorbed dose was demonstrated. Thus, the basis for the use of SPME as a dose metric to determine toxic effects for hydrophobic pesticides was linked. This was supported by the good correlation between toxicity response values based on equilibrium fiber concentration and body residues. Finding that SPME can serve as a clearly linked surrogate to absorbed dose that reflects the toxic response provides a bioavailable link between exposure and toxicity. Continued development of the use of SPME as a dose metric should improve environmental risk assessments by making better use of the bioavailability measurements as part of a regulatory decision.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

Y. Ding was supported by an SIUC 2010–2011 Dissertation Research Assistantship Award. A.D. Harwood was supported by an SIUC 2011–2012 Dissertation Research Assistantship Award. J. You was financially supported by “the Hundred Talents Program” of the Chinese Academy of Sciences (kzcx2-yw-BR-05). We thank E. Tripp-Mackenbach for her work culturing Chironomus dilutus and Hyalella azteca.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information

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