Unique Physicochemical Properties of Perfluorinated Compounds and Their Bioconcentration in Common Carp Cyprinus carpio L.

  • Yoshiyuki Inoue
  • Naoki Hashizume
  • Naoaki Yakata
  • Hidekazu Murakami
  • Yasuyuki Suzuki
  • Erina Kikushima
  • Masanori Otsuka
Article

Abstract

Carp (Cyprinus carpio L.) was exposed to perfluorinated compounds (PFCs)—perfluoroalkyl carboxylic acids (number of carbon atoms, C = 8, 11, 12, 14, 16, and 18) and perfluorooctane sulfonate (PFOS)—in bioconcentration tests to compare the bioconcentration factors (BCFs) and physicochemical properties of each specific compound. Despite having the same number of carbon atoms (C = 8), the BCFs of perfulorooctanoic acid (PFOA) and PFOS differed by more than two orders of magnitude (PFOA BCF = < 5.1 to 9.4; PFOS BCF = 720 to 1300). The highest BCFs were obtained from perfluorododecanoic acid (BCF = 10,000 to 16,000) and perfluorotetradecanoic acid (BCF = 16,000 to 17,000). The longest observed depuration half-lives were for perfluorohexadecanoic acid (48 to 54 days) and PFOS (45 to 52 days). The concentrations of PFCs were highest in the viscera, followed by the head, integument, and remaining parts of the test fish. PFCs concentrations in the integument, which was in direct contact with the test substances, were relatively greater than that of other lipophilic substance (hexachlorobenzene). It is likely that Clog P would be a better parameter than log Kow for the prediction of BCFs for PFCs. Threshold values for PFCs bioaccumulation potential (molecular weight = 700, maximum diameter = 2 nm) seemed to deviate from those generally reported because of the specific steric bulk effect of molecule size.

Since the 1970s, there has been a steady increase in the commercial use of perfluorinated compounds (PFCs) as surfactants (Giesy and Kannan 2001). The perfluoroalkyl acids are a family of anionic fluorinated surfactants that consist of a carbon chain, typically 4 to 14 carbon atoms in length, and a charged functional moiety (primarily carboxylate, sulfonate, or phosphonate) (Lau et al. 2007). The most useful fluorinated surfactants are eight-carbon chemicals: perfulorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). PFOS precursors have been used as water, oil, soil, and grease repellents for packaging, rugs and carpets, and leather; as surfactant detergents, emulsifiers, wetting agents, and dispersants; and in firefighting foam and other applications (Organisation for Economic Cooperation and Development [OECD] 2005). However, these chemicals, which do not exist naturally, are only slightly biodegradable and persist in the environment (Yakata et al. 2003). Some overviews of the monitoring and toxicological findings for PFCs (Lau et al. 2007; Buck et al. 2011; Kannan 2011) include studies of human blood (whole blood, plasma, and serum) (Olsen et al. 2003; Kannan et al. 2004; Calafat et al. 2007) and that of wildlife, including fish, birds, and marine mammals (Tolls et al. 1994; Giesy and Kannan 2001; Taniyasu et al. 2003; Lehmler 2005; Sinclair et al. 2006) as well as of their hepatotoxicity (Klaunig et al. 2003; Shipley et al. 2004), immunotoxicity (Yang et al. 2000; Wan and Badr 2006), hormonal effects (Langley and Pilcher 1985; Maras et al. 2006), reproductive toxicity (Peng et al. 2010; Stump et al. 2008), and developmental toxicity (Olsen et al. 2009).

There are many pathways for human exposure to PFCs, e.g., the atmosphere, drinking water, food, plants, soils, and fish (So et al. 2006; Stahl et al. 2009; Lau 2010; Murakami et al. 2011; Xiao et al. 2011). Fish is a primary source of protein for human consumption and would seem to be an important source of human exposure, considering PFCs pollution in the aquatic environment (Jin et al. 2009; Yoo et al. 2009; Tsuda et al. 2010).

On May 9, 2009, at the fourth meeting of the Conference of the Parties to the Stockholm Convention in Geneva (http://chm.pops.int/Convention/Pressrelease/COP4Geneva9May2009/tabid/542/language/en-US/Default.aspx), PFOS, and perfluorooctane sulfonyl fluoride were placed in Annex B of the convention. Despite worldwide interest, as evidenced by similar nominations of persistent organic pollutants (POPs), there are only a few experimental data for these chemicals using fish as test subjects, and there is a need for reliable hazard information about PFCs with longer (>7) fluorinated carbon chains (Conder et al. 2008). The development of quantitative structure–activity relationships (QSARs) has allowed the prediction of bioconcentration factors (BCFs) from the physicochemical properties of chemical substances, but these relationships are not well known for PFCs.

Our goal in this study was to clarify unique BCFs of PFCs using common carp (Cyprinus carpio L.) as a test organism and to discuss the bioaccumulation potential of PFCs based on their physicochemical properties.

Materials and Methods

Test Substances

Perfulorooctanoic acid (PFOA [98%]) was purchased from Daikin Industries, Ltd. (Osaka, Japan). Perfluoroundecanoic acid (PFUnA [99.0%]), perfluorotetradecanoic acid (PFTA [97.3%]), and perfluorooctadecanoic acid (PFODA [98.7%]) were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Perfluorododecanoic acid (PFDoA [98.5%]) was purchased from Wako Chemical, Ltd. (Kanagawa, Japan). Perfluorohexadecanoic acid (PFHxDA [100.67%]) was purchased from Lancaster Synthesis Ltd. (Lancashire, UK). PFOS (potassium salt [100.3%]) was purchased from Kishida Chemical Co., Ltd. (Osaka, Japan).

Measurement of BCFs

Test Fish and Feeding

Test fish were yearling carp Cyprinus carpio L. either purchased from a commercial fish farm or produced in our laboratory and were acclimatized according to the OECD (1996) test guideline (TG) 305. The lipid content of the test fish was measured as described by Bligh and Dyer (1959). The body weights, lengths, and lipid contents of the test fish at the beginning of the exposure phase were 3.15 to 7.77 g, 6.1 to 8.8 cm, and 3.10 to 3.87%, respectively. The fish were fed pellets for carp (Nippon Formula Feed Manufacturing, Kanagawa, Japan) twice a day (2% of the total body weight). Feeding was stopped 1 day before the fish were removed for analysis.

Preparation of Test Substance Stock Solution

Flow-through exposure tests require a system that continuously dispenses and dilutes a stock solution of the test substance to deliver the test concentrations to the test tanks (OECD 1996). The stock solution for the PFOS test was prepared by simply dissolving the test substance in deionized water. Stock solutions of other test substances were prepared using polyoxyethylene hydrogenated castor oil (HCO-40 or HCO-60; Nikko Chemicals Tokyo, Japan) as a dispersant at 1–50 times the amount of the test substance and then dissolving in 2-methoxyethanol (Wako Pure Chemical Industries) or N,N-dimethylformamide (Nacalai Tesque, Kyoto, Japan). For each test, a stock solution (at a flow rate of 0.02 to 2 ml min−1) was diluted by groundwater (800 to 1600 ml min−1) from the premises of the investigators’ laboratory. The solubilizing agents in the test water were within the range prescribed in OECD TG 305 (<0.1 ml l−1).

Test and Environmental Conditions

The bioconcentration tests were performed according to OECD procedures for a flow-through fish test (OECD 1996). The test tank was either a 70- or 100-l glass tank. Tests were performed with a photoperiod of 16 h and test water kept at 25 ± 2°C. Dissolved oxygen concentrations in the test water were maintained >6 mg l−1. The number of test fish at the beginning of the exposure phase ranged from 28 to 56. Tests were conducted at two concentration levels. Which were selected based on the water solubility of each test substance. After a 28- to 60-day exposure phase, the depuration phase lasted for 29 to 77 days, except for the PFOA test, which had no depuration phase because of a low BCF. The details of the test conditions are listed in Table 1.
Table 1

Bioconcentration test conditions

Test substance (acronym)

Chemical structure

Nominal test concentrationa

Measured test concentrationa,b

Exposure period (d)

Depuration period (d)

High

Low

High

Low

PFOA

CF3(CF2)6COOH

50

5

47.6 (1.5)

4.71 (0.10)

28

c

PFUnA

CF3(CF2)9COOH

1

0.1

0.946 (0.030)

0.0911 (0.0034)

60

66 or 23d

PFDoA

CF3(CF2)10COOH

1

0.1

0.978 (0.031)

0.0978 (0.0043)

60

28 or 47e

PFTA

CF3(CF2)12COOH

1

0.1

0.890 (0.068)

0.0893 (0.0083)

60

29

PFHxDA

CF3(CF2)14COOH

1

0.1

0.998 (0.020)

0.100 (0.002)

60

77

PFODA

CF3(CF2)16COOH

1

0.1

0.967 (0.020)

0.0974 (0.0032)

60

24

PFOS

CF3(CF2)7SO3K

20

2

16.0 (1.1)

1.88 (0.09)

58

37

aTest concentrations are in μg l−1

bValue in parentheses is the SD of the measured test concentration

cThere was no depuration phase for the PFOA test

dDepuration period: 66 days for high and 23 days for low level

eDepuration period: 28 days for high and 47 days for low level

Analysis for Test Substances

Concentrations of test substances in the test water were measured six times, and test substances in the fish were measured five times (in duplicate) during the exposure phase. At the end of the exposure phase, the distribution of test substances in tissues was determined, except for PFOA and PFODA, by measuring the concentrations in the integument (including alimentary canal and gills), head, viscera (internal organs except the alimentary canal), and remaining parts. During the depuration phase, concentrations of test substances in the test fish were measured at 4 to 5 time points (in duplicate) until the test duration was clearly past the depuration half-life of the test substances.

Test substances were analyzed by liquid chromatography-mass spectrometry (LC-MS) with a Micromass ZMD LC/MS (Micromass, Manchester, UK) and a Waters 2690 separations module (Waters, Milford, MA) or by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with a Micromass Quattro-LC (Micromass) and liquid chromatograph type 1100 Series (Agilent, Waldbronn, Germany) in electrospray negative ionization mode; m/z = 413 (PFOA), 563 (PFUnA), 613 > 569 (PFDoA), 713 (PFTA), 813 > 769 (PFHxDA), 913 > 869 (PFODA), and 499 (PFOS). An L-column octadecyl-silane (ODS) (150 × 2.1 mm ID; particle size 5 μm [Chemicals Evaluation and Research Institute, Japan]) was used for all analyses. Mobile phase was mixture of acetonitrile/water or methanol/water containing 5 mmol l−1 ammonium acetate for PFUnA or 5 mmol l−1 di-n-butylammonium acetate for the other test substances.

For analysis of PFOA and PFOS in test water, the test water was directly analyzed by LC-MS after sampling from the test tank. For the other test substances, acetic acid (Kanto Chemical Tokyo, Japan) or formic acid (Wako Pure Chemical Industries) was added to the test water to create acidic conditions (pH 2 to 3), and then test substances were extracted by solid-phase extraction using a Sep-Pak C8 (Nihon Waters K.K., Tokyo, Japan) for PFUnA, PFDoA, and PFHxDA or Sep-Pak C18 (Nihon Waters K.K.) for PFTA and PFODA.

For analysis of test substances in test fish, whole fish were shredded using a polytron (Kinematica, Bohemia, NY), and a 3- to 5-g sample of each test fish was analyzed. The fish samples for PFOS analysis were homogenized in 15 ml of methanol (Wako Pure Chemical Industries) to extract the test substances from the fish sample. For the fish samples for PFOA analysis, acetonitrile (Wako Pure Chemical Industries) was used instead of methanol, and for the other test substances, acetonitrile with acetic acid or formic acid (0.5 to 2 ml) was used. The supernatant obtained by centrifugation of the homogenized sample (7000×g, 5 min) was brought to a volume of 25 ml with extracting solvent. These samples were analyzed by LC-MS or LC-MS/MS after diluting with water or methanol/water to the appropriate concentrations for analysis.

Calculation of BCFs

BCFs were calculated using the following equation (Eq. 1):
$$ {\text{BCF}}_{n} = {\text{Cf}}_{n} /{\text{Cw}}_{n} , $$
(1)
where BCFn is the BCF after n days; Cfn is the concentration of the test substance in fish after n days; and Cwn is the mean concentration of the test substance in the test water by the nth day. The steady-state BCF (BCFss) was defined as when the variation of BCFs in three successive analyses at intervals of >48 h was within ±20%.

Depuration rate constants (k2) were determined by fitting the data to a first-order decay curve (ln concentration in fish = a + b × time [day], where a is a constant and b is k2). The depuration half-life (t1/2) was then calculated as: t1/2 = 0.693/k2.

Measurement of Physicochemical Properties

The solubility of each test substance in water was measured according to OECD TG 105 (OECD 1995); the flask method was used for PFOA and PFOS, and the column elution method was used for the other test substances. The n-octanol-water partition coefficient (log Pow) was calculated by two software programs: Kowwin v. 1.67 (United States Environmental Protection Agency [USEPA]) for log Kow and Clog P v. 4.0 (Biobyte, Claremont, CA) for Clog P, respectively. Clog P is a model for calculating the log P from chemical structure based on fragmental method, which represents log P as sum of fragment constants and correction factors (Hansch and Leo 1995). Detailed information about Clog P is available at: http://www.biobyte.com/index.html.

The log Pow values for PFOA, PFUnA, and PFTA were measured according to OECD TG 117 (OECD 2004) using the high-performance liquid chromatography method with acidic buffer for the eluent (pH 1 to 2) to measure the undissociated (free acid) form of the test substances. To estimate the molecular size of test substances, we used OASIS Software–Database Manager v. 1.4 (Laboratory of Mathematical Chemistry, Bourgas, Bulgaria) to calculate molecular weight (MW), effective cross-sectional diameter (Deff), and maximum diameter (Dmax) with the following program settings: converter mode, automated precise; conformer generation, accurate; and calculation method, AM1.

Results and Discussion

BCFs

The concentrations of test substances in test water are listed in Table 1. For all test substances, the concentration in test water was maintained at >80% of each nominal concentration, and the variation was within ±11% of the averaged measured concentrations. The water solubility of PFOA and PFOS was 3,300 and 910 mg l−1, respectively; however, the solubilities of the longer perfluoroalkyl chains were <1 mg l−1 (Table 2). This suggests that PFOA and PFOS have greater surface activity than the other test substances.
Table 2

BCFss and physicochemical properties of test substances

Test substance

BCFss

Depuration half-life (d)

Water solubilitya (mg l−1)

log Powb

log Kowc

Clog Pd

MWe

Deffe(nm)

Dmaxe(nm)

High

Low

High

Low

PFOA

3.1

<5.1–9.4

f

3300

2.8

6.30

3.23

414.1

0.61

1.36

PFUnA

2300

3700

29

15

0.597

4.0

9.20

3.94

564.1

0.79

1.55

PFDoA

16,000

10,000

9

8

0.520

10.2

4.17

614.1

0.82

1.72

PFTA

16,000

17,000

13

18

0.296

5.1

12.1

4.64

714.1

0.63

2.18

PFHxDA

4800

4700

48

54

0.153

14.0

5.11

814.1

0.96

2.16

PFODA

430

320

12

11

0.00470

16.0

5.58

914.1

0.92

2.48

PFOS

720

1300g

45

52

910

4.13

3.09

538.2

0.63

1.55

MW molecular weight, Deff effective cross-sectional diameter, Dmax maximum diameter

aMeasured according to OECD TG 105 (OECD 1995)

bMeasured by according to OECD TG 117 (OECD 2004)

cCalculated using Kowwin v. 1.67 (USEPA)

dCalculated using Clog P v. 4.0 (Biobyte)

eCalculated using OASIS Software–Database Manager v. 1.4 (Laboratory of Mathematical Chemistry)

fNot measured

gAverage BCF value on the final day of exposure phase

The BCFs and associated parameters of test substances are listed in Table 2. There was no mortality or abnormal behavior in any treated or control fish. The BCFs of test substances did not differ substantially between the 2 test concentrations, which differed by a factor of 10. The BCF of PFOA was low (<5.1 to 9.4), whereas the BCF of PFOS (720 to 1300), which has the same number of carbon atoms (C = 8), was greater by 2 orders of magnitude. Monitoring data showing a similar trend are reviewed by Lau et al. (2007); concentrations of PFOS in serum or plasma of humans and wildlife were approximately the same or one order of magnitude greater than those of PFOA. The reason for the different BCFs for PFOS and PFOA is not clear but may be due to the different surfactant properties of the molecules. Additional study will be required to resolve this issue.

The curvilinear relationship between the BCFs of PFCs and the number of carbon atoms (Fig. 1) can be expressed as Eq. 2 (r2 = 0.984):
$$ \begin{gathered} {\text{log BCF }} = \, -0. 10 4\left( {\text{number of carbons}} \right)^{ 2} + { 2}. 8 7\left( {\text{number of carbons}} \right) \, -{ 15}. 5 \end{gathered} $$
(2)
with the highest BCFs for PFDoA (C = 12; BCF = 10,000 to 16,000) and PFTA (C = 14; BCF = 16,000 to 17,000). Martin et al. (2003) reported similar BCFs of PFCs (C = 5 to 14) using rainbow trout; for example, PFDoA (BCF = 18,000), PFTA (BCF = 23,000), and PFOS (BCF = 1100). One possible source of the observed variability in BCFs between fish species is the metabolism and biotransformation of the chemicals in the fish (Arnot and Gobas 2006). The same bioconcentration potential of PFCs in different fish species may due to the properties of PFCs; for example, they are not metabolized or they are highly bound to proteins (Lau et al. 2007).
Fig. 1

Relationship between log BCF and the number of carbon atoms in PFCs. Solid line (log BCF = –0.104[number of carbons]2 + 2.87[number of carbons] − 15.5; r2 = 0.984) shows the curvilinear regression from PFCs data for the relationship between log BCF and the number of carbons. Filled symbols show high level, and open symbols show low level. PFOS data are not included in the regression line

There was no apparent relationship between the number of carbon atoms in the test substances and the depuration half-life. The depuration half-lives of PFCs were between 8 and 29 days, but they were much longer for PFHxDA (48 to 54 days) and PFOS (45 to 52 days), with values similar to those for POPs, such as polychlorinated biphenyls (24 to 224 days) and hexachlorobenzene (HCB; 42 to 43 days) (Fisk et al. 1998). This result reflects the persistence of PFCs as pollutants in aquatic organisms; more laboratory and field research is necessary to fully characterize the hazards of PFCs with longer perfluoroalkyl chains as well as those of PFOS.

Tissue Distribution

Concentrations of test substances and other type of chemicals as well as lipid content in each part of the fish are listed in Table 3. The PFCs concentrations in carp were highest in the viscera, followed by the head, integument, and remaining parts. In addition, a similar trend is observed in polyfluorinated compounds with other structure types (fluorinated ethers and fluorinated alcohols) and a persistent lipophilic chemical (HCB). In contrast, PFCs concentrations in the integument, which was in direct contact with the test substances, were relatively high compared with HCB concentrations. In general, there is strong evidence that hydrophobic substances reach equilibrium in the lipid fraction of different tissues of an organism (Bertelsen et al. 1998; Tietge et al. 1998; Gobas et al. 1999 as cited in Arnot and Gobas (2006); Inoue et al. 2011). This result may be partially attributable to the particular properties of PFCs as surfactants with a unique hydrophobic and oleophobic nature, resulting in extremely low surface tension and high surface activity (Lehmler 2005; Lau et al. 2007).
Table 3

Concentrations of test substances and other type of chemicals as well as lipid content in each fish tissue and ratio of the concentrations to that in the head

Test substance

Test concentration

Integumenta

Head

Viscera

Remaining parts

μg l−1

ng g−1 (ratio)

FPUnA

0.1

229 (0.80)

287 (1)

402 (1.40)

73.2 (0.26)

PFDoA

0.1

1110 (0.89)

1240 (1)

1500 (1.21)

386 (0.31)

PFTA

0.1

3020 (1.19)

2540 (1)

3460 (1.36)

724 (0.29)

PFHxDA

0.1

464 (0.97)

480 (1)

1030 (2.12)

229 (0.48)

PFOS

2

5120 (0.99)

5170 (1)

8550 (1.66)

1600 (0.31)

Fluorinated etherb

0.1

680 (0.65)

1040 (1)

1260 (1.21)

410 (0.39)

Fluorinated alcoholc

1

2830 (0.79)

3560 (1)

6750 (1.90)

1560 (0.44)

HCBd

0.005

86.8 (0.65)

134 (1)

190 (1.41)

56.1 (0.42)

Lipid content (μg g−1)e

88.4 (0.97)

91.0 (1)

198 (2.18)

50.9 (0.56)

aIncluding alimentary canal and gills

b2,2-Bis[p-(1,1,2,2-tetrafluoroethoxy)phenyl]-4-methylpentane (Yakata et al. 2003)

c1H,1H,11H-Eicosafluoro-1-undecanol [National Institute of Technology and Evaluation, Japan. CHEmical Collaboration Knowledge database (J-CHECK) (1994)]

dHexachlorobenzene (Ministry of Economy, Trade and Industry unpublished data)

eData form Inoue et al. (2011)

Relationship Between BCFs and Physicochemical Properties

The physicochemical properties of the test substances are listed in Table 2. The curvilinear relationship between BCFs of PFCs and their log Kow (Fig. 2) can be expressed as Eq. 3 (r2 = 0.984):
$$ {\text{log BCF}} = -0. 1 1 1\left( {{ \log }\,K_{\text{ow}} } \right)^{ 2} + 2. 6 5\left( {{ \log }\,K_{\text{ow}} } \right)- 1 1. 5. $$
(3)
Fig. 2

Relationship between log BCF and log Kow. Solid line (log BCF = −0.111[log Kow]2 + 2.65[log Kow] − 11.5; r2 = 0.984) shows the curvilinear regression derived from log BCF and log Kow data for PFCs. PFOS data are not included in the regression line. Circles show the measured log Pow of PFOA, PFUnA, and PFTA under high- and low-exposure conditions, respectively. These data were not included in the regression analysis

The curvilinear relationship between BCFs of PFCs and their Clog P (Fig. 3) can be expressed as Eq. 4 (r2 = 0.984):
$$ {\text{log BCF}} = - 1. 8 8\left( {{\text{Clog }}P} \right)^{ 2} + { 17}. 3\left( {{\text{Clog }}P} \right)- 3 5. 4. $$
(4)
Fig. 3

Relationship between log BCF and Clog P. Solid line (log BCF = −1.88[Clog P]2 + 17.3[Clog P] − 35.4; r2 = 0.984) shows the curvilinear regression derived from log BCF and Clog P data for PFCs. PFOS data are not included in the regression line. Filled and hollowsymbols show measured log Pow of PFOA, PFUnA, and PFTA under high- and low-exposure conditions, respectively. These data were not included in the regression analysis

There are large differences between the curvilinear relationships for BCFs and log Kow or Clog P. The measured log Pow of PFOA (log Pow = 2.8), PFUnA (log Pow = 4.0), and PFTA (log Pow = 5.1) was a good fit to the curvilinear relationship between BCFs and Clog P. Thus, it is likely that Clog P would be a better parameter than log Kow for the prediction of BCFs for PFCs.

The relationships between BCFs of PFCs and their MW or Dmax are shown in Figs. 4 and 5, respectively. The threshold MW and Dmax values for PFCs bioaccumulation potential were approximately 700 and 2 nm, respectively (PFDoA: MW = 614, Dmax = 1.72 nm; PFTA: MW = 714, Dmax = 2.18 nm). Our results seem to be much different than the threshold values reviewed by Arnot et al. (2010); for example, Deff > 0.95 nm results in loss of membrane permeation (Opperhuizen et al. 1985); Dmax > 1.47 nm yields BCFs < 5000 (Dimitrov et al. 2003); molecules with MW > 700 are less likely to bioaccumulate (EC 2003); and MW < 550, Dmax < 2.9 nm, and Deff < 1.4 nm yield BCFs > 1000 (Sakuratani et al. 2008). Moreover, when there is a threshold Dmax value for the uptake of a chemical into an aquatic organism, the BCF may be drastically decreased when Dmax exceeds the threshold value. We found that the BCFs of PFCs decreased when Dmax exceeded 2 nm, but the slope of the decrease was moderate. Therefore, it does not appear that the Dmax of PFCs alone is applicable as a cutoff criterion for bioaccumulation potential.
Fig. 4

Relationship between log BCF and MW. Solid line (log BCF = −4.15 × 10−05[MW]2 + 0.0585[MW] − 16.3; r2 = 0.984) shows the curvilinear regression derived from log BCF and MW data for PFCs. PFOS data are not included in the regression line. Dashed line shows the threshold MW cutoff criteria for bioaccumulation potential (EC 2003)

Fig. 5

Relationship between log BCF and Dmax. Solid line (log BCF = −8.80[Dmax]2 + 34.8[Dmax] − 29.9; r2 = 0.887) shows the curvilinear regression derived from log BCF and Dmax data for PFCs. PFOS data are not included in the regression line. Dashed line shows the threshold Dmax cutoff criteria for bioaccumulation potential (Dimitrov et al. 2003)

The relationship between Dmax and MW of PFCs and fatty acids (FAs) are shown in Fig. 6. The slope of the relationship for PFCs (0.0023) was approximately one fourth as steep as that for FAs (0.0092). This can be attributed to the characteristic properties of fluorine atoms (F, atomic weight 19), which are the smallest after hydrogen atoms (H, atomic weight 1) in three dimensions (H = 0.120 nm and F = 0.135 nm [on the basis of the van der Waals radius]). In addition, the ability of a fluorine atom to bind to a carbon atom (C–F bond, 116 kcal mol−1) is stronger than that of a hydrogen atom (C–H, 99.5 kcal mol−1) or the other halogen atoms (e.g., C–Cl, 78 kcal mol−1). The rigid molecular structure of compounds such as PFCs, which have linear perfluoroalkyl chains (Deff = 0.61–0.96 nm in C = 8 to 18 PFCs), may enable them to pass through biological membranes more easily (Anliker et al. 1988), thus leading to greater bioaccumulation (Dimitrov et al. 2002). These specific physicochemical properties of PFCs would result in an underestimation of the steric bulk effect of molecule size (e.g., Dmax) when evaluated on the basis of MW and the greater bioaccumulation potential of PFCs even with their relatively large MWs.
Fig. 6

Relationship between Dmax and MW of PFCs (C = 8 to 18) and FAs (C = 8 to 18). octanoic acid (Dmax 1.30, MW 144.2), undecanoic acid (Dmax 1.70, MW 186.3), dodecanoic acid (Dmax 1.85, MW 200.3), tetradecanoic acid (Dmax 2.07, MW 228.4), hexadecanoic acid (Dmax 2.33, MW 256.4), and octadecanoic acid (Dmax 2.61, MW 284.5). Solid line (Dmax-PFCs = 0.00233[MWPFCs] + 0.338; r2 = 0.943) shows the linear regression derived from Dmax and MW data for PFCs. Dashed line shows the linear regression (Dmax-FA = 0.00919[MWFA] − 0.0134; r2 = 0.999) derived from Dmax and MW data (×) for FAs

Conclusion

In this study, we emphasized that the physicochemical properties of PFCs lead to unique bioconcentration potentials in carp, and threshold values for PFCs bioaccumulation potential seemed to deviate from those generally reported because of the specific steric bulk effect of molecule size. Care should be taken when estimating the bioaccumulation potential of PFCs using existing regulatory criteria or QSARs. Our results also provide evidence to explain the persistent residual of PFCs with long perfluoroalkyl chains (e.g., PFTA and PFUnA) in aquatic organism; more reliable hazard information for PFCs is required in the future.

Notes

Acknowledgments

This work was supported by the Ministry of Economy, Trade and Industry and the New Energy and Industrial Technology Development Organization. We especially thank Y. Sakuratani (Chemical Management Center, National Institute of Technology and Evaluation) for the estimation of molecular size and for technical support.

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Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • Yoshiyuki Inoue
    • 1
  • Naoki Hashizume
    • 1
  • Naoaki Yakata
    • 2
  • Hidekazu Murakami
    • 1
  • Yasuyuki Suzuki
    • 1
  • Erina Kikushima
    • 1
  • Masanori Otsuka
    • 1
  1. 1.Chemicals Evaluation and Research Institute, CERI KurumeFukuokaJapan
  2. 2.Chemicals Assessment and Research Center, Chemicals Evaluation and Research InstituteSaitamaJapan

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