Environ. Sci. Technol. 2000, 34, 304-310
LAS Bioconcentration: Tissue Distribution and Effect of Hardness-Implications for Processes JOHANNES TOLLS,* MANUELA HALLER, WILLEM SEINEN, AND DICK T. H. M. SIJM† Environmental Toxicology and Chemistry, RITOX-Research Institute of Toxicology, P.O. Box 80058, NL-3508 TB Utrecht, The Netherlands
Linear alkylbenzene sulfonate (LAS) is the most important synthetic surfactant in household detergents. Nevertheless, little parent compound-specific information is available about the processes involved in LAS bioconcentration. Here, we employ reversed-phase HPLC to quantify the selected LAS model compounds. The time-dependent tissue distribution and the effect of water hardness on LAS uptake is investigated in order to deepen the understanding of LAS bioconcentration. The concentrations of the selected LAS constituents (C10-2- to C13-2-LAS) in the liver and the internal organs of juvenile rainbow trout increased rapidly demonstrating fast uptake into systemic circulation. The relatively slow increase of LAS concentrations in the less well perfused tissues pointed to internal redistribution being controlled by perfusion. Uptake occurred via the gills rather than the skin. The bioconcentration factors (BCFs) ranged between 1.4 and 372 L kg-1 and increased with hydrophobicity in a manner similar to that in fathead minnows. In the latter species the BCFs were higher (6990 L kg-1) and apparently not related to the fish lipid content. The hydrophobicity dependence of LAS uptake rate constants was affected by water hardness, indicating that hydrophobic and electrostatic interactions played a role in the velocity of LAS uptake. Water hardness was found to reduce electrostatic repulsion to such an extent that hydrophobic interactions became determining for the rate of uptake.
Introduction Linear alkylbenzene sulfonate (LAS) is the most important synthetic household detergent with an annual production rate of about 4 million tons per year (1), and a substantial amount of data exists on LAS toxicity (2). In contrast, the processes and factors involved in the uptake of LAS into organisms have received less attention in the past (3). Moreover, almost all of this information is difficult to interpret because the data were obtained using radiolabeled compounds without separation of the parent surfactant from its biotransformation products (3). Since LAS has to be taken up into an organism before it can elicit an effect, the processes and factors influencing uptake are relevant when assessing the environmental risk. * Corresponding author: telephone: 31-30-253 2578; fax: 3130-253 2837; e-mail:
[email protected]. † Present address: RIVM-CSR, P.O. Box 1, 3720 BA Bilthoven, The Netherlands. 304
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There is strong evidence that LAS is taken up via the gills (3, 4) and biotransformed (5, 6). In contrast, information about the influence of the exposure concentration (7, 8), and the concentrations of the divalent cations Ca2+ and Mg2+ (water hardness) on LAS bioconcentration is inconclusive (9). Water hardness influences the aqueous phase behavior of LAS (1, 10) and increases the surface potential at negatively charged surfaces such as biological membranes (11). According to the theory of the electrical double layer, this results in increased concentrations of anions at the water-membrane interface (Cw,if) (12, 13). As a consequence, increased water hardness can be expected to bring about higher LAS concentration gradients across the gill membrane and, consequently, higher fluxes of LAS from water into fish, in agreement with the observed hardness dependency of toxicity (9). In this paper, we present new experimental information on LAS bioconcentration obtained using parent compoundspecific analysis. The time course of LAS concentrations in different tissues of juvenile rainbow trout (Oncorhynchus mykiss) is studied. The velocity of uptake of LAS from water into fathead minnows (Pimephales promelas) is determined under varying conditions of water hardness. Previously determined parent compound-specific BCFss data (14) are analyzed statistically in order to identify factors influencing LAS bioconcentration. Finally, the environmental risk of LAS is discussed in the light of the outcome of the present research.
Experimental Section Fish, Chemicals, and Chemical Analysis. Fathead minnows originating from the U.S. EPA Midcontinent Ecology Laboratory (Duluth, MI) were reared at Utrecht University. Rainbow trout fry were purchased from the Vijge Hatchery (Vaassen, The Netherlands). Fish of both species were kept at 25 °C (fathead minnows) and 14 °C (rainbow trout). Prior to experiments, the fish were acclimated to the specific water conditions of the experiment for at least 1 week. They were fed dryfeed at 1% of their body weight per day (fathead minnows: Lapis dryfeed, Lapis, The Netherlands; rainbow trout: Trouvit dryfeed). The individual LAS constituents used in this study are referred to by the shorthand formula Cn-m-LAS, with n specifying the length of the alkyl chain and m specifying the substitution position of the p-sulfophenyl moiety. C10-2-LAS is thus the abbreviation of 2-n-(p-sulfophenyl)decane. All test compounds (C10-2-, C11-2-, C11-5-, C12-2-, C12-3-, C12-6-, C13-2-LAS) and internal standards (C12-1- and C13-1-LAS) were synthesized as sodium salts in our laboratory (1) and were more than 97% pure. The number of C atoms in the alkyl chain is a measure of hydrophobicity in the homologous series of the 2-sulfophenylalkanes. Alternatively, the n-octanol-water partition coefficient (log KOW,Rob) estimated according to Roberts’s algorithm (15) can be used as a hydrophobicity scale for LAS. Solvents (CH3CN, CH3OH, ethyl acetate (EtOAc) and CH2Cl2) were of HPLC gradient grade (Mallinckrodt-Baker, Deventer, The Netherlands, or Merck, Amsterdam, The Netherlands). Technical grade hexane (Mallinckrodt-Baker, Deventer, The Netherlands) was redistilled prior to use. Octadecylsilica solid-phase extraction cartridges were supplied by Bester (Amstelveen, The Netherlands), and bulk octadecylsilica (ODS) was obtained from Mallinckrodt-Baker (Deventer, The Netherlands). Water for HPLC analyses was purified using an ELGASTAT (Elga, Buchs, Switzerland) purification system. NaOH and tetrabutylammonium hydroxide were purchased from Fluka (Zwijndrecht, The Netherlands). 10.1021/es990296c CCC: $19.00
2000 American Chemical Society Published on Web 12/10/1999
TABLE 1. Summary of the Results of Bioconcentration Experiments with Fathead Minnows (Pimephales promelas) (14) Using Compound-Specific Analysisa n
BCFss, L kg-1
BBLAS, µmol kg-1
Cw,C12-2, µM
CTOC, mg L-1
t, h
compd testedb
food
A B C D
6 20 19 20
41 (33) 97 (20) 168 (38) 211 (27)
100 (28) 111 (27) 81 (39) 76 (26)
0.47 (16) 0.68 (8) 0.21 (6) 0.02 (11)
3.0 (30) 3.1 (62) 3.7 (11) 1.6 (30)
30-55 96-194 72-120 94-193
no yes yes yes
E
20
138 (27)
25 (42)
0.18 (27)
2.0 (8)
95-166
C10-2, C11-2, C13-2 C11-5, C12-5, C13-5 C11-5, C12-6, C12-3 C10-2, C11-2, C13-2, C10-i, C11-i, C12-i, C13-ic none
exp
yes
a
Average values of the steady-state bioconcentration factor (BCFss), the number of fish tested (n), the concentration of all test compounds in fish (BBLAS), the C12-2-LAS exposure concentration (CW,C12-2), the concentration of total organic carbon (CTOC), the O2 concentration (CO2), the period of sampling of fish (t), the test compounds other than C12-2-LAS, and whether fish were fed or not. The values in parentheses specify the CV in %. b Other than the reference compound C12-2-LAS. c The letter i denotes the sum of the 3-, 4-, 5-, 6-, and 7-isomers that cannot be resolved by RP-HPLC.
Water samples and fish were extracted by solid-phase extraction (16) and matrix solid-phase dispersion extraction, respectively. In short, a whole fathead minnow specimen or a tissue sample was extracted by mixing the sample with bulk ODS powder and subsequent homogenization in a mortar until a paste was obtained. Upon drying, the paste turned to a powder that was filled into a column. First, the column was washed with hexane and EtOAc. Then the test compounds were eluted by EtOAc:CH3OH (1:1, v:v) and subsequently isolated from the sample matrix by ion-pair liquid-liquid extraction. Parent compound-specific determination of the individual LAS constituents in water and fish was performed by reversed-phase HPLC with fluorescence detection. A detailed description of the analytical procedures was given elsewhere (17). Neutral lipids are commonly believed to be the storage site of hydrophobic compounds and were determined as the dry weight of the hexane fraction (18). The lipid contents agreed favorably with literature values for Fathead minnows (19, 20). Exposure Conditions. Fish were exposed in flow-through exposure aquaria with specific water renewal rates higher than 1 L d-1 g-1 fish (14). Exposure water was prepared by reconstituting distilled water with 0.75 mM CaCl2‚2H2O, 0.46 mM MgSO4‚7H2O, 1.51 mM NaHCO3, 0.04 mM KH2PO4, 1.01 mM NaNO3, and 0.10 mM Na2SiO3. The pH in the aquaria was 7.2. The water hardness was abbreviated as [Me2+] and adjusted to 1.21 mM in the tissue distribution experiment and the uptake experiments at intermediate [Me2+]. The uptake experiments at low and high [Me2+] were performed at 0.4 and 3.63 mM, respectively. Time-Dependent Tissue Distribution and Bioconcentration of LAS in Rainbow Trout. Thirty juvenile (5 months old) rainbow trout (Oncorhynchus mykiss) weighing on the average 2.25 ((0.50) g were employed. The surface areas of their gills (16.3 cm2) and skin (17.2 cm2) were estimated by means of allometric relationships (21). The fish were exposed at 14 °C to a mixture of test compounds containing 1.32 ( 0.11 µM C10-2-, 0.62 ( 0.12 µM C11-2-, 0.20 ( 0.05 µM C12-2-, and 0.08 ( 0.03 µM C13-2-LAS for 120 h. Thereafter, six fish were transferred to clean water and allowed to depurate for 3 h. Duplicate water samples were taken each day. Fish (n ) 6) were sampled after 3, 8, 78, and 120 h of exposure and after 3 h in clean water, killed by cervical dislocation, and dissected into skin, gills, head, fillet, liver, and internal organs (IO). Given the difficulty of dissecting the small fish, the muscle was not separated from the bones, and the liver was the only individual internal organ isolated because of its importance in xenobiotic metabolism. The remaining internal organs (intestine, kidney, spleen, stomach, pyloric caeca, heart, gall bladder, and gonads) were combined to IO. All samples were stored at -20 °C until analysis. The livers of all six fish sampled at one time point were pooled in order to obtain one sample of sufficient size. Likewise, the IO, skin,
gills, and heads of a pair of two specimens were pooled into one sample. Muscles of individual fish were analyzed. The tissue specific concentrations were referred to as Ctis with the subscript ‘tis’ standing for any of the above tissues. The average test compound concentration in two pooled fish samples (Cf) was calculated by summing up the amounts of the test compound in the individual tissues and dividing by the sum of the body weights of two paired fish pooled. The time course of Ctis was evaluated after normalizing Ctis to the concentration in the water (Cw) because the concentration of the test compound in the exposure solution decreased by about a factor of 2 during the 120-h exposure period. Perfusion intensity was quantified as the ratio of the cardiac output received by a tissue and the weight of the respective tissue (22). Hardness Dependence of LAS Uptake in Fathead Minnows. Uptake experiments at low [Me2+] were performed at 0.4 mM hardness established by substituting CaCl2 with NaCl to maintain ionic strength. In high water hardness experiments, [Me2+] was adjusted to 3.63 mM by addition of CaCl2. Fathead minnows (8-12 months, 0.5-1 g) were exposed for 3 h to mixtures of individual LAS constituents (C10-2-, C11-2-, C11-5-, C12-2-, C12-3-, C12-6-, and C13-2-LAS) in water of low, intermediate, and high [Me2+] at an average temperature of 21.4 ((0.6) °C. The time course of the concentrations of the individual test compounds in water (Cw) and fish (Cf) was followed by hourly sampling of water (in duplicate) and fish (in triplicate or quadruplicate). To that end, whole fathead minnows were analyzed. The uptake rate constant k1 was determined as the slope of the regression line of CfCw-1 vs time. Values of Cw ranged between 0.04 and 1.3 µM and were chosen such that the individual LAS constituents were measurable in the fish. The effect of [Me2+] was quantified as the ratio of the values of k1 between intermediate and low (∆inter/low) and between high and intermediate water hardness (∆high/inter). Fathead Minnow Bioconcentration Data and Data Analysis. Table 1 summarizes parent compound-specific steady-state bioconcentration factor (BCFss) data for C12-2LAS that were obtained earlier (14, 23). The concentrations of C12-2-LAS (Cw,C12-2), total organic carbon (CTOC) in the exposure solution, and the LAS body burden (BBLAS, the sum of the concentration of all LAS test compounds in fish in mol kg-1) in the respective experiments are also specified. Relationships between a given response variable (BCFss, log k1) and independent variables (Cw,C12-2, CTOC, BBLAS, lipid content, and hydrophobicity) were explored using linear regression.
Results and Discussion LAS Bioconcentration in Rainbow Trout: Steady State. In an earlier investigation of LAS bioconcentration in fathead VOL. 34, NO. 2, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Results of the Tissue Distribution Experiment in Rainbow Trout (Oncorhynchus mykiss) Ctis/Cw,ss organ
% BW
% Cardb
% Card/% BW
C10-2
C11-2
C12-2
C13-2
gill IOe head skin muscle liver BCFssc BCFssd Cw,ss (nM)
7.1 (0.2) 9.7 ( 0.2 17.3( 0.2 15.9 ( 0.2 48.6 ( 0.1 1.4 ( 0.1 rainbow trout fathead minnow
0.01 28 *f * 69 3
gills > liver > head > IO > muscle for C11-2-, C12-2-, and C13-2-LAS (Table 2) while C10-2-LAS deviated slightly from this pattern. Notwithstanding the high metabolic activity in the liver, Cliver Cw-1 was high relative to IO, head, and muscle implying that LAS loss by biotransformation was compensated for by rapid uptake from the water and transport to the liver. Tissue Distribution of LAS: Time Course. All test compounds displayed a similar pattern in the time course of the tissue distribution data. Therefore, the ratio CtisCw-1 in all individual tissues will be discussed for C12-2-LAS as the reference compound. The gills attained 40% of their steady306
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state concentration after 3 h, while all other tissues reached 13 and 20%. After 8 h, the value of CtisCw-1 exceeded 80% of the values observed after 78 and 120 h in gills, IO and liver. In contrast, CtisCw-1 ratios of C12-2-LAS in the head, muscle, and skin ranged around 60%. This pointed to C12-2-LAS being rapidly taken up, transported into systemic circulation, and delivered to the liver and IO. The more peripheral tissues (head, muscle, and skin) are apparently slower in approaching steady state with the surrounding water. An elimination period of 3 h did not result in a pronounced change of CtisCw-1 for C12-2-LAS. Exceptions were the gills (-33%) and the liver (-24%). Given that the liver is the most active organ in xenobiotic transformation and that biotransformation of C122-LAS contributes significantly to elimination of the parent LAS (5, 6, 23), the reduction of the LAS concentration in the liver was most likely brought about by biotransformation. LAS transfer from the gills to the water explains the rapid drop of CgillCw-1. The large surface areas of gills and skin were in intimate contact with the exposure solution because swimming movements and respiration continuously renewed the water layer adjacent to these tissues. Due to its interfacial activity, LAS can adsorb to the tissue surfaces and establish high local concentrations at these water-fish interfaces. Hence, both tissues were possible ports of LAS entry from water into the systemic circulation of the fish. Figure 3 compares the time courses of CgillCw-1 and CskinCw-1. During the first 3 h of exposure, CgillCw-1 increased more rapidly than CskinCw-1 for all compounds tested. Moreover, CgillCw-1 reached more than 70% of its respective steady-state level after 8 h, while the skin had attained approximately 50%. Three hours of elimination resulted in a rapid reduction of CgillCw-1 (30100%) for all LAS constituents (Figure 3) in comparison to a decrease of 3-70% of CskinCw-1. The uptake and the elimination data suggest that the kinetics of LAS exchange between water and skin were slower than between water and the gills. The present data and evidence from the literature (5, 24, 25) indicate that the gills are the primary site of LAS exchange between water and juvenile rainbow trout. Perfusion Limitation. The rate of the initial increase (0-3 h) of the concentration of C12-2-LAS in tissues displayed the following order: gills > (liver, IO) > head ≈ muscle ≈ skin. While the liver and IO approach their respective steady-state values within 8 h, the concentrations in muscle and skin continue to increase until 78 h. This can be explained by looking at the numeric values of the perfusion intensity
FIGURE 2. Average of the tissue-water concentration ratio (CtisCw-1) of C12-2-LAS in all tissues of rainbow trout as a function of time during uptake (3, 8, 78, and 120 h) and after 3 h of elimination (Eli-3h). The error bars represent the standard deviation of the average with the number of replicates being six for the muscle and three for gills, IO, skin, and head. (Table 2). Unfortunately, no such values could be calculated for the skin and the head. Since the skin receives its blood supply by capillaries exclusively, it is the most slowly perfused tissue. The head comprises the brain, the eyes, and the skull. It should therefore be relatively well perfused, so that the ranking of the perfusion intensities is as follows: IO > liver > head ≈ muscle > skin (22). This ranking allows for grouping the tissues into the intensely perfused internal organs (liver and IO), the less well perfused tissue groups (head and muscle), and the skin. This grouping corresponds to the velocity of attainment of steady state and suggests that the tissue-specific perfusion intensity controlled the rate of redistribution of LAS throughout the body. The stable values of CtisCw-1 in most tissues and the rapid decrease of Cgill during 3 h of elimination indicated that LAS transport from peripheral tissues to the gills was too slow to compensate for the rapid loss from the gills to the water. The elimination data thereby confirmed that perfusion limited the transport of LAS within fish. Hardness Dependence of LAS Uptake. The hardness dependent values of k1 (standard errors in parentheses) are presented in Table 3. The data for C12-2-LAS at intermediate hardness demonstrate that the variability between experiments [expressed as the coefficient of variation (CV)] of k1 of C12-2-LAS is approximately 25% (n ) 4). When going from low ([Me2+] ) 0.46 mM) to intermediate hardness ([Me2+] ) 1.21 mM), the values of k1 increased for all LAS constituents, and the average of ∆inter/low for all compounds was 3.5 indicating a pronounced increase of k1. Upon increasing [Me2+] to 3.63 mM, the results were less consistent. For some compounds an increase and for others a decrease was observed, and the resulting average (∆high/inter) was 1. The data thus pointed to an asymptotic increase of k1 with [Me2+]. The Guoy-Chapman theory of the electrical double layer can be employed to model ionic interactions at biological membranes (26). It predicts an almost linear increase of the concentration of anions at the interface (Cw,if) in the [Me2+] range from 0.15 to 6 mM, irrespective of the surface charge density (σ) (range tested: one negative charge per 75-600 Å2). The contradiction between the experimental findings
and the behavior expected based upon electrostatic effects suggests factors in addition to electrostatic repulsion to be controlling LAS uptake. Plotting the values of k1 of all LAS constituents tested against hydrophobicity revealed a steep increase of k1 with increasing log KOW,Rob at low [Me2+] (Figure 4). The slope of the respective regression line was 1.35 ( 0.12 (r 2 ) 0.97), while those obtained at intermediate [Me2+] (0.97 ( 0.08, r 2 ) 0.97) and high [Me2+] (0.98 ( 0.13, r 2 ) 0.92) were almost identical to each other but shallower than the low hardness slope. Thus, the hydrophobicity dependence of k1 was altered by water hardness, suggesting that an interplay of electrostatic and hydrophobic interactions determined the uptake velocity. LAS concentrations increased within hours in the internal organs of rainbow trout (Figure 2), suggesting that the transfer of LAS anions from the bulk solution into the gill membrane rather than transport across the gills limited the velocity of LAS uptake into the fish. Consequently, k1 can be assumed to be proportional to the free energy of LAS transfer from the bulk water to the membrane (∆Gtrans). Theoretically, ∆Gtrans can be conceived as the sum of an electrostatic (∆GCoulomb) and a hydrophobic contribution (∆Gh-phob) (27). ∆Gh-phob is proportional to hydrophobicity and independent of [Me2+]. The difference in the log KOW,Rob-log k1 relationship between low and intermediate hardness (Figure 4) thus reflects differences in ∆GCoulomb because [Me2+] reduces electrostatic repulsion. Apparently, the differences in ∆GCoulomb become smaller as log KOW,Rob increases, suggesting that the contribution of ∆Gh-phob to ∆Gtrans increases with hydrophobicity. The value of log KOW,Rob (4.2-4.3) at which the log KOW,Roblog k1 relationships intersect can then be interpreted as the hydrophobicity above which no influence of [Me2+] on k1 can be discerned. Moreover, the almost identical log KOW,Roblog k1 relationships at intermediate and high [Me2+] indicate that increased [Me2+] did not reduce ∆GCoulomb any further. Hydrophobic interactions therefore dominated uptake behavior of all LAS constituents at high and intermediate [Me2+]. LAS anions apparently fall into a hydrophobicity range in which we can distinguish between the contributions of hydrophobic and electrostatic interactions to the forces VOL. 34, NO. 2, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Average of the tissue-water concentration ratio (CtisCw-1) in gills and skin for all LAS constituents tested (A, C10-2-LAS; B, C11-2-LAS; C, C12-2-LAS; D, C13-2-LAS) in rainbow trout as a function of time during uptake (3, 8, 78, 120 h) and after 3 h of elimination (Eli-3h). The error bars represent the standard deviation of three replicates.
TABLE 3. Dependence of the Uptake Rate Constants k1 (L kg-1 d-1) of Water Hardness in Fathead Minnows (Pimephales promelas)a compd hardness (mM) C13-2 C12-2
C11-2 C10-2 C12-3 C12-6 C11-5 average
log KOW,Rob
k1 (L kg-1 d-1)
k1 (L k1 (L ∆inter/low kg-1 d-1) ∆high/inter kg-1 d-1)
0.4
1.2
4.08 3.54
458 (61) 120 (14) 52 (11)
1.20 1.54
3.00 2.46 3.28 2.85 2.42
29 (4) 5 (1) 34 (3) 7 (1) 2 (0)
2.96 3.95 3.58 5.86 5.33 3.48
551 (95) 271 (41) 156 (9) 260 (17) 160 (10) 86 (24) 20 (5) 123 (9) 40 (7) 12 (1) (1.75)
3.6 0.81 1.13
445 (48) 328 (61) 150 (8)
0.36 0.48 1.22 1.11 1.62 0.96
31 (3) 10 (1) 150 (22) 45 (17) 19 (5) (0.44)
a The values in parentheses represent the standard error of the estimate of k1. ∆inter/low and ∆high/inter specifies the relative increase of k1 with increasing water hardness for low to intermediate and from intermediate to high hardness. Average is the arithmetic mean of the values of ∆inter/low and ∆high/inter of all compounds. Log KOW,Rob is an estimate of hydrophobicity calculated according to Roberts’s algorithm (15).
determining the uptake rates. For more hydrophobic anions, ∆Gh-phob is the dominating contribution to ∆Gtrans. Consequently, [Me2+] does not affect the uptake rate constants. Conversely, [Me2+] can be expected to be the factor controlling the rate of uptake of organic anions that are less hydrophobic (small ∆Gh-phob) than LAS. 308
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Besides the effect on the electrostatic properties, changes in [Me2+] are likely to influence the physical properties of membranes (26) and the electrophysiological behavior of cells (28). Moreover, increased [Me2+] induces osmoregulatory changes. While these physiological alterations might contribute to the hardness dependence of LAS uptake, they are not amenable to experimental verification. In contrast, determination of partition coefficients between membrane vesicles and water at varying [Me2+] could provide a quantitative basis for the above explanation of the observed hardness dependence of LAS uptake. Such measurements could be fundamental to understanding the behavior of organic anions at the membrane-water interface. Implications for LAS Risk in the Environment. C12-2LAS was used as a reference compound in recent experiments (14), and a large number of parent compound-specific bioconcentration data were obtained for this compound. From 79 observations, we calculated an average BCFss of C12-2-LAS of 153 L kg-1 (CV: 9%). We suggest the use of this value in combination with the relative bioconcentration factors reported by Tolls et al. (14) for assessment of the bioaccumulation potential of LAS mixtures in the environment. The results of exp A were excluded from this calculation since in that experiment fish were starved and BCFss was based on merely six individual CfCw-1 measurements. For the two most hydrophobic LAS constituents tested in exp D (14), C12-2- and C13-2-LAS, the variation of CfCw-1 amounted to factors 4 and 2 in a population of 20 observations, respectively (Figure 5) while the inter-individual variation of the lipid content ranged between 5 mg L-1; 32) than those usually encountered in surface waters. The bioconcentration potential of environmental mixtures of LAS in fathead minnows is 22 L kg-1 (14). Considering the 90th percentile of the environmental LAS concentrations of ca. 0.03 µM (33), maximum concentrations in fathead minnows of less than 0.7 µmol kg-1 can be expected in feral fish unless LAS concentrations are exceptionally high. Experimentally determined critical body burdens, i.e., the LAS concentrations in fish killed by exposure to LAS, range between 0.1 and 1.7 mmol kg-1 (34). The most frequently occurring LAS concentrations are therefore not likely to result in LAS body burdens that are critical to survival of fish. The fillet (muscle) is the most relevant tissue for human consumption. Since the values of CmuscleCw-1 are relatively small, VOL. 34, NO. 2, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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and given the low bioconcentration potential of LAS in relation to persistent hydrophobic chemicals, it appears that consumption of fish is not an important pathway of LAS exposure to humans.
Acknowledgments We thank Dr. H. Verhaar for his valuable advice in analysis of the differences between bioconcentration factors, the members of the AISE/CESIO steering committee for the valuable contributions in numerous discussions, AISE/CESIO for financial support, and the anonymous reviewers, who helped to improve the manuscript.
Literature Cited (1) Zhu, Y.-P.; Rosen, M. J.; Morall, S. W.; Tolls, J. J. Surf. Deterg. 1998, 1, 187-193. (2) Little, A. D. Environmental and Human Safety of Major Surfactants; Final Report to The Soap and Detergent Association; Arthur D. Little: Cambridge, MA, 1991. (3) Tolls, J.; Kloepper-Sams, P.; Sijm, D. T. H. M. Chemosphere 1994, 29, 693-717. (4) Kikuchi, M.; Wakabayashi, M.; Kojima, H.; Yoshida, T. Water Res. 1980, 14, 1541-1548. (5) Comotto, R. M.; Kimerle, R. A.; Swisher, R. D. In Aquatic Toxicology; Marking, L. L., Kimerle, R. A., Eds.; ASTM STP 667; American Society of Testing Materials: Philadelphia, 1979; pp 232-250. (6) Newsome, C. S.; Howes, D.; Marshall, S. J.; Van Egmond, R. A. Tenside Surf. Deterg. 1995, 32, 498-503. (7) Wakabayashi, M.; Kikuchi, M.; Sato, A.; Yoshida, T. Bull. J. Soc. Fish. 1981, 47, 1383-1387. (8) Bishop, W. E.; Maki, A. W. A critical comparison of bioconcentration test methods; American Society of Testing Materials: Washington, DC, 1980. (9) Wakabayashi, M.; Kikuchi, M.; Kojima, H.; Yoshida, T. Chemosphere 1978, 11, 917-924. (10) Matheson, K. L.; Cox, M. F.; Smith, D. L. J. Am. Oil. Chem. Soc. 1985, 62, 1391-1395. (11) Israelachvili, J. Intermolecular and surface forces, 2nd ed.; Academic Press: London, 1991. (12) McLaughlin, S.; Harary, H. Biochemistry 1976, 15, 1941-1948. (13) Escher, B. I.; Schwarzenbach, R. P. Environ. Sci. Technol. 1996, 30, 260-270. (14) Tolls, J.; de Graaf, I.; Thijssen, M. A. T. C.; Haller, M.; Sijm, D. T. H. M. Environ. Sci. Technol. 1997, 31, 3426-3431. (15) Roberts, D. W. Commun. J. Comite Espanol Deterg. 1989, 20, 35-43.
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(16) Matthijs, E.; De Henau, H. Tenside Surf. Deterg. 1987, 24, 193199. (17) Tolls, J.; Haller, M.; Sijm, D. T. H. M. Anal. Chem. 1999, 71, 5242-5247. (18) Barker, S. A.; Long, A. R.; Hines, M. E., II J. Chromatogr. A 1993, 629, 23-24. (19) de Maagd, P. G. J.; van den Klundert, I. C. M.; Opperhuizen, A.; Wezel, A. P.; Sijm, D. T. H. M. Ecotoxicol. Environ. Saf. 1997, 38, 232-237. (20) Sijm, D. T. H. M.; Verberne, M. E.; de Jonge, W. J.; Pa¨rt, P.; Opperhuizen, A. Toxicol. Appl. Pharmacol. 1995, 131, 130-135. (21) Lien, G. J.; McKim, J. M. Aquat. Toxicol. 1993, 27, 15-32. (22) Barron, M. G.; Tarr, B. D.; Hayton, W. L. J. Fish Biol. 1987, 31, 735-744. (23) Tolls, J.; Lehmann, M.; Sijm, D. T. H. M. Submitted for publication in Environ. Sci. Technol. (24) Kikuchi, M.; Wakabayashi, M.; Kojima, H.; Yoshida, T. Ecotoxicol. Environ. Saf. 1978, 2, 115-127. (25) Kimerle, R. A.; Swisher, R. D.; Schroeder-Comotto, R. M. Surfactant structure and aquatic toxicity. Presented at the Symposium on Structure-Activity Correlations in Studies on Toxicity and Bioconcentration with Aquatic Organisms, Burlington, ON, Canada, March 11-13, 1975. (26) Gennis, R. B. Biomembranes; Springer: New York, 1989. (27) Stumm, W. Chemistry of the Solid Water Interface; Wiley: New York, 1992. (28) Hille, B. Ionic Channels of Excitable Membranes, 2nd ed.; Sinauer: Sunderland, MA, 1992. (29) Hebert, C. E.; Keenleyside, K. A. Environ. Toxicol. Chem. 1995, 14, 801-807. (30) Stow, C. A.; Jackson, L. J.; Amrhein, J. F. Can. J. Fish. Aquat. Sci. 1997, 54, 1031-1038. (31) Geyer, H.; Scheunert, I.; Korte, F. Chemosphere 1985, 14, 545555. (32) Traina, S. J.; McAvoy, D. C.; Versteeg, D. J. Environ. Sci. Technol. 1996, 30, 1300-1309. (33) Feijtel, T. C. J.; Van de Plassche, E. J. Environmental Risk Characterization of 4 Major Surfactants Used in The Netherlands; 679101 025 National Institute of Public Health and the Environment: 1995. (34) Rawlings, J. M.; Versteeg, D. J. Critical body burdens of the anionic surfactant dodecyl linear alkyl benzene sulfonate, C12LAS, in aquatic organisms. Presented at the SETAC 19th Annual Meeting, Charlotte, NC, November 15-19, 1998.
Received for review March 16, 1999. Revised manuscript received October 19, 1999. Accepted October 26, 1999. ES990296C
