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Comparisons of coarse and fine versions of two carbons for reducing the bioavailabilities of sediment-bound hydrophobic organic contaminants
Chemosphere 50 (2003) 1309–1317 www.elsevier.com/locate/chemosphere
Comparisons of coarse and fine versions of two carbons for reducing the bioavailabilities of sediment-bound hydrophobic organic contaminants J.A. Lebo
a,*
, J.N. Huckins a, J.D. Petty a, W.L. Cranor a, K.T. Ho
b
a
b
US Geological Survey, Columbia Environmental Research Center (CERC), 4200 New Haven Road, Columbia, MO 65201, USA Atlantic Ecology Division, US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory (NHEERL), 27 Tarzwell Drive, Narragansett, RI 02882, USA Received 19 March 2002; received in revised form 7 November 2002; accepted 27 November 2002
Abstract Coarse (whole) and finely ground Ambersorb 1500 and coarse and fine coconut charcoal were compared as to their efficiencies in scavenging organic contaminants desorbed from sediment. Aqueous slurries of a test sediment spiked (1 ppm) with p; p0 -DDE (DDE), 2,20 ,5,50 -tetrachlorobiphenyl (TCB), naphthalene (NAP), or phenanthrene (PHEN), and containing 1% levels of the test carbons were treated by shaking at 35 °C while exposed to clusters of low-density polyethylene membrane (detox spiders). Controls consisted of spiked sediments and detox spiders but no added carbon of any kind and thus represented unimpeded bioavailabilities (to the spiders). After the treatments––agitation periods from 2.5 to 60 h, depending on contaminant hydrophobicity––the exposed detox spiders were analyzed. The fine carbon of either type was more effective than its coarser variant in obstructing contaminant bioavailabilities. The finer variants of both carbons obstructed the bioavailabilities of NAP and PHEN equally well as did the coarser variants of both. Whole Ambersorb 1500 and coarse coconut charcoal were similarly ineffective in intercepting TCB and DDE. Ground Ambersorb 1500 obstructed virtually all bioavailability of all four contaminants and was far more effective than fine coconut charcoal in intercepting DDE and TCB. An additional experiment compared the effectiveness of ground Ambersorb 1500 and fine coconut charcoal in obstructing the bioavailabilities from sediment of a broad array of spiked organochlorine pesticides. The performance of ground Ambersorb 1500 was again found to be superior; the bioavailable levels of each of the 27 pesticides were markedly lower in the presence of ground Ambersorb 1500 than in the presence of fine coconut charcoal. Published by Elsevier Science Ltd. Keywords: Sediment; Organic contaminants; Bioavailability; Charcoal; Adsorption; TIE
1. Introduction Carbonaceous adsorbents have been proposed as media for ameliorating the toxicities of sediments that
*
Corresponding author. Tel.: +1-573-876-1837; fax: +1-573876-1896. E-mail address: [email protected] (J.A. Lebo). 0045-6535/03/$ - see front matter Published by Elsevier Science Ltd. doi:10.1016/S0045-6535(02)00817-2
have been contaminated with organic pollutants. Toxicity identification evaluation (TIE) researchers have found that mixing Ambersorb carbonaceous adsorbents (Ankley et al., 1996; Kosian et al., 1999; West et al., 2001) and coconut charcoal (Ho et al., 1999) with sediments are, to varying degrees, effective techniques for reducing the bioavailabilities of sediment-bound organic contaminants. In such TIE situations (and potentially in remediation scenarios) where the inextricable mixing of
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carbons with the sediment is judged to be permissible, the potentially intimate contact between the sediment and carbon particles is greatly advantageous. As contaminant molecules desorb from sediment particles, nearby carbonaceous particles are likely to intercept the molecules from the pore water before they can be ingested or bioconcentrated by aquatic organisms. This encounter probability is believed to be enhanced when the particle sizes of the carbons are very small because of the potential for greater contact between sediment and carbon particles and because of the greater carbon surface areas per unit masses of carbon. Lebo et al. (1999, 2000) demonstrated the use of lipidcontaining semipermeable membrane devices (SPMDs) and clusters of low-density polyethylene (LDPE) film (the so-called detox spiders) for removing organic contaminants from sediments. These media offer two advantages over carbonaceous adsorbents for this use: (1) In contrast to inextricably mixed carbonaceous materials, SPMDs or detox spiders can be easily removed from the sediment slurries after the treatments are complete. (2) The organic contaminants are readily recoverable (i.e., analyzable) from the SPMDs or detox spiders. In the present work, Ambersorb 1500 (a spherical carbonaceous adsorbent no longer commercially available) and a relatively coarse (large-particle-size) coconut charcoal were compared as to their efficacies in obstructing the bioavailabilities of organic contaminants desorbed from sediment. Also compared were the performances of finely ground Ambersorb 1500 and a small-particle-size coconut charcoal. Thus, performance comparisons of coarse versus fine particle size ranges within each adsorbent type were also achieved. These performance comparisons were accomplished through use of detox spiders. Each sediment slurry contained an admixed carbon during treatment (agitation at 35 °C), and it also contained a spider destined to be removed and analyzed after treatment. When used in the manner described here, detox spiders mimic organisms capable of organic contaminant uptake via bioconcentration but incapable of uptake via ingestion. The specific information being sought was the following: Which carbon type or variant would intercept the most contaminant molecules as they desorbed from the sediment, thereby most effectively reducing the levels bioavailable to the detox spiders? The performances of the carbons were compared to each other and relative to control conditions in which no added carbons were present to compete with the spiders. Although no organisms were used in this work, the term bioavailability is used freely throughout the paper. Huckins et al. (1996) showed that the lipid-containing SPMD, owing to the permeant size limitation of its LDPE membrane (similar to the limitation of biomembranes), samples only dissolved organic contaminants; that is, it samples only contaminants available to bioconcentration
processes and does not sample contaminants associated with particles or dissolved organic carbon. Because the detox spiders used here consisted solely of LDPE (i.e., were simply SPMDs minus the enclosed lipid), the same assumption can be made about them. Also, the term bioavailable is used more broadly here than to refer merely to the quantities of dissolved contaminants that are instantaneously bioavailable (which would be predictable through such parameters as the percent organic carbon of the sediments and the organic carbon [sediment]–water partition coefficients [Koc s] of the contaminants). The sediment treatments described herein include elevated temperature and mechanical agitation. Lebo et al. (2000) used this approach (i.e., energy inputs) to effect temporally compressed contaminant uptake curves for SPMDs and detox spiders. That study demonstrated that the bioavailable portion of a contaminant in a system is more than a tiny, static proportion of the total contaminant present, but in a holistic sense, it is most or even all of the contaminant present. As stated above, the goal of this work was to find which type and particle size range of the candidate carbonaceous adsorbents were generally most effective in obstructing the bioavailabilities of organic contaminants in sediment slurries. The test conditions, consisting of vigorous agitation at 35 °C, should not be regarded as a recommendation of conditions under which future sediment decontamination or remediation work should be performed. It remains an unproven assumption that the carbonaceous adsorbent that performed best as tested here would also perform best at ambient temperature and under quiescent conditions.
2. Experimental 2.1. Reagents, apparatus, and materials 0(1) Test sediment: Obtained from a pond at CERC (Lebo et al., 2000). The homogenized, powdery sediment contains only trace levels of a few organic contaminants and is 5.7% organic matter and 3.8% organic carbon by weight. Particle size distribution is 20% sand, 12% silt/loam, and 68% clay. 0(2) Standard reference material (SRM) sediment HS-2: National Research Council of Canada, Halifax, Nova Scotia, Canada. This marine sediment contains environmentally incorporated polychlorinated biphenyls (PCBs). 0(3) LDPE layflat tubing: Brentwood Plastics, St. Louis, MO. The LDPE tubing was 5.1-cm wide, of 38-lm wall thickness, and contained no additives. Segments of tubing 54- and 270-cm long (weighing 2.0 and 10.0 g, respectively) were used as previously described (Lebo et al., 2000) to make contaminantabsorbing clusters (detox spiders) for immersion in
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0(4)
0(5)
0(6)
0(7) 0(8)
0(9)
(10)
(11)
sediment slurries. The 2.0- and 10.0-g detox spiders had 1100 and 5500 cm2 surface areas, respectively. Coconut charcoals: Calgon Carbon Corporation, Pittsburgh, PA, USA. Two coconut charcoals were used in this work: PCB carbon 30 140 (the coarser) and PCB carbon G (the finer of the two). (PCB is CalgonÕs designation for the charcoals and has no connection with PCBs.) Table 1 gives information about the particle size distribution of these charcoals. Ambersorb 1500 synthetic carbonaceous adsorbent: Rohm and Haas Co., Spring House, PA, USA. See Table 1. Shatterbox: Cat. no. 8510, SPEX Industries, Inc., Metuchen, NJ, USA. Ambersorb 1500 was finely ground with this shatterbox. Mason jars: 480 ml, polypropylene, Cole-Parmer Instrument Company, Vernon Hills, IL, USA. Incubator shaker: Series 25, New Brunswick Scientific Co., Inc., Edison, NJ, USA. This instrument shakes with an orbital motion (2.5-cm-orbit diameter) and was operated at 200 rpm and 35 °C. Radiolabeled contaminants: Sigma Chemical Co., St. Louis, MO, USA. The following 14 C-labeled compounds were used: p; p0 -DDE (DDE), 2,20 ,5,50 tetrachlorobiphenyl (TCB), naphthalene (NAP), and phenanthrene (PHEN). Multipesticide stock solution: AccuStandard, New Haven, CT, USA. This custom-made solution contains 27 ‘‘cold’’ (not radiolabeled) pesticides in equal concentrations. The identities of these pesticides are given in a table below. Liquid scintillation counting (LSC) cocktail: Ready Organic Cocktail, Beckman Instruments, Inc., Fullerton, CA, USA.
2.2. Spiking and aging of sediment for Experiment 1 Each of four large (about 2.4-kg) batches of the test sediment was spiked as previously described (Lebo et al., 2000) to 1.0-lg/g (dry-weight basis) concentrations with
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one of the four 14 C-labeled contaminants. After the spiked sediments had been air-dried (i.e., after the spike solvent had evaporated) and homogenized, three 10.0-g subsamples of each were radiometrically analyzed. Then 150-g portions of each spiked sediment were weighed into 15 Mason jars. Each jar also received 225 ml of deionized (DI) water. The jars were capped and swirled vigorously until the sediments were completely wetted; the sediments were then allowed 7 d to quiescently age at ambient temperature. 2.3. Radiometric analyses of subsamples of spiked sediments (Experiment 1) The four triplicate 10.0-g subsamples of spiked, homogenized (but not wetted or aged) sediments were analyzed as follows. The sediments were blended with 50-g portions of anhydrous Na2 SO4 then were extracted with 150 ml of CH2 Cl2 . Because the extracts were translucent yellow–green and would otherwise have color-quenched when evaluated by LSC, the extract solutions were subjected to a chromatographic cleanup as follows. After condensation to 3-ml volumes, the extracts were applied to Pasteur pipette columns containing potassium silicate (Lebo et al., 1989) and the contaminants were recovered with 5 ml of 98:2; hexane/ toluene. The purified sediment extracts were evaluated with a Beckman LS 6500 LSC. The mean percent recoveries (n ¼ 3; standard deviations in parentheses) of DDE, TCB, NAP, and PHEN were 93.6 (0.2), 88.2 (0.3), 41.6 (1.5), and 77.8 (2.1), respectively. 2.4. Introductions of carbons to spiked sediments (Experiment 1) The four carbons––coarse (whole) and finely ground Ambersorb 1500 and coarse and fine coconut charcoal (hereafter denoted by CA, FA, CC, and FC)––were weighed into 15-ml centrifuge tubes, 1.50 g per tube. To facilitate complete wetting of the carbons, the 1.50-g portions were conditioned with methanol then were
Table 1 Particle size and surface area information on whole and finely ground Ambersorb 1500, PCB carbon 30 140, and PCB carbon G Adsorbent type
Total surface area (m2 /g)
Estimated particle size range and mean particle size (lm)
External surface area (m2 /g)
Ambersorb 1500 (CA) Ground Ambersorb 1500 (FA) Calgon PCB 30 140 (CC) Calgon PCB carbon G (FC)
1200 1200 1100 1100
150–300, mean 225 2–30a , mean 10 75–800, mean 350 10–50b , mean 20
0.07 1.4 0.04 0.7
Most of the information displayed here was supplied by the manufacturers. A footnote indicates which information on mean particle particle size was obtained through use of scanning electron microscopy. External surface areas were calculated from estimated mean particle sizes. a Particle size information about the finely ground Ambersorb (FA) came entirely from SEM. b Manufacturer-supplied information about the particle size range of PCB carbon G was supplemented by SEM.
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washed several times with DI water. These washings entailed alternate centrifugations of the tubes and decantations of supernatants. The aqueous carbon slurries were added to the Mason jars containing the 150-g portions of wetted, aged sediments. The incubator shaker was used to shake the jars until the carbons were uniformly mixed into the sediment slurries. Each test (e.g., DDE-spiked sediment with coarse coconut charcoal [DDE-CC], PHEN-spiked sediment with finely ground Ambersorb 1500 [PHEN-FA], etc.) was performed in triplicate. Also, for each contaminant, there were three jars of spiked sediments to which no carbons were added (e.g., NAP-spiked sediment with no [zero] added carbon [NAP-ZC]). These latter constituted the control groups.
2.5. Treatment of spiked sediment with detox spiders (Experiment 1) Before treatments of the sediments were begun, the spiked, aged sediments were allowed to interact quiescently and at ambient temperature with their added carbons. These interactive intervals were 24 h for sediments spiked with DDE or TCB but only 1 h for sediments spiked with NAP or PHEN (because of their lesser hydrophobicities). Afterward, a 2.0-g detox spider was placed in each jar; treatments consisting of shaking of the jars at 200 rpm and at 35 °C were begun. Sediments spiked with DDE or TCB were subjected to two successive treatment intervals: 0–24 h then 24–60 h. Fresh spiders were substituted for the exposed ones after the 0–24 h intervals. For sediments spiked with NAP or PHEN, only one treatment interval (0–2.5 or 0–3.0 h, respectively) and only one detox spider per jar was used. As the exposed detox spiders were removed from the jars, the sediment that adhered to them was rinsed back into the jars with DI water.
2.6. Radiometric analyses of detox spiders (Experiment 1) The staple was removed from a spider, and the resulting eight pieces of single-ply LDPE were placed in a 1-l screw-cap Erlenmeyer flask with about 700 ml of DI water. The flask was capped, thoroughly shaken, and the water was discarded. This wash step was performed three times for each spider. The washed LDPE pieces were blotted dry with paper towels. Each piece of LDPE was cut in two with scissors; the 16 pieces were distributed about equally among three LSC vials. To each LSC vial were added 0.5 ml of isopropanol (dispersed residual water, if present), 10 ml of LSC cocktail, and 7 ml of 50:50; hexane/toluene (provided volume to ensure that the LDPE fragments were submerged). At least 18 h was allowed for the LDPE to interact with the cocktail and
solvents before the radiometric analyses were performed. 2.7. Experiment 2––further comparison of the scavenging efficiencies of FA and FC A sediment containing 27 nonradiolabeled pesticides, each at a 4.0 ng/g (dry-weight basis) concentration, was produced from the test sediment according to the spiking procedure described for Experiment 1. Fifty-gram portions of this spiked sediment were weighed into each of three jars, 75 ml of DI water was added, and the sediment samples were aged for 7 d as previously described. (Glass jars with aluminum foil-lined lids were used for this experiment.) A fourth sediment sample that was aged in parallel with the three pesticide-spiked samples consisted of 150 g of unspiked test sediment wetted with 225 ml of DI water. After the aging period, 20 g of HS-2 SRM sediment, 80 g of unspiked test sediment, and 150 ml of DI water were added to Jars 1, 2, and 3. Jars 1, 2, and 3 thereby contained 150 g of sediment with 27 pesticides (spiked and aged) at 1.3-ng/g concentrations, PCB congeners (environmentally incorporated) at a 7.5-fold dilution of their certified (HS-2) concentrations, and 225 g of DI water. Jar 4 was a control for this experiment. To Jars 1 and 2 were added 1.50 g of FA and FC, respectively, which had been wetted as described above. No carbons were added to Jars 3 or 4. The carbons were uniformly mixed throughout the sediment slurries, and the sediments and carbons were allowed 24 h to interact. A 10.0-g detox spider was placed in each of the four jars and treatments, performed as previously described, were begun. For this experiment, the treatment interval was 36 h, throughout which the single spider remained in each jar. Because ‘‘cold’’ contaminants were used in Experiment 2, the exposed spiders were analyzed by gas chromatography (GC) by the following sequence of steps. First, the detox spiders were extracted as described in Lebo et al. (2000) and as briefly summarized below. The spiders were washed with DI water and separated into small pieces of LDPE, which were blotted dry with paper towels. Then the LDPE pieces were briefly dipped in methanol and were extracted by being soaked in hexane. Hexane was used to partition the methanol into which the LDPE had been dipped. The methanol–water phases were discarded, and the upper, hexane phases were combined with the main hexane extracts. The spider extracts were subjected to cleanup and fractionation according to a scheme described by Petty et al. (2000) and summarized below. Size exclusion chromatography was used to remove pigments, polyethylene waxes, and elemental sulfur from the extracts. Three 1.0-ml injections were used to introduce each sample onto the described size exclusion column (Petty et al., 2000); the three collected fractions corresponding with each sample
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were combined afterward. Next, the solutions were subjected to cleanup on Florisil followed by fractionation on silica gel. The nonpolar, first fractions collected from silica gel contained the PCBs and four or five of the least polar pesticides. The more polar, second fractions from silica gel contained the remainder of the pesticides. Both fractions from each sample were concentrated to 5.0-ml volumes and were analyzed by GC and electron capture detection. The GC was equipped with a 30-m DB-35 ms capillary column (J&W Scientific, Folsom. CA, USA). Chromatographic conditions were as described by Petty et al. (2000).
3. Results 3.1. Experiment 1––effects of the carbons on bioavailabilities of DDE, TCB, NAP, and PHEN Displayed in Table 2 are the results of Experiment 1 that compared the effects of CA, FA, CC, and FC on the bioavailabilities from sediment of DDE, TCB, NAP, and PHEN. The tabulated numbers express the recoveries of
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contaminants from the detox spiders as percentages of the total quantities of the contaminants that had been spiked into the 150-g portions of sediment. Test conditions denoted as ZC signify that the Mason jars contained none of the carbons to impede contaminant bioavailabilities to the spiders. The mean percentages of DDE and TCB removed from the ZC jars by their spiders after 60 h of treatment were 39.6% and 40.5%, respectively, of the totals contained by the 150-g sediment portions. These values are shown in the right-hand column of Table 2 adjusted to 100% (for normalization purposes). The mean total (0–60 h) percentages of DDE and TCB removed by the spiders from the carbon-containing jars have been normalized to the DDE-ZC or TCB-ZC values and are also shown in the right-hand column. Although there was only one short (2.5- or 3.0-h) treatment interval for sediments spiked with NAP and PHEN, the contaminant removal data for these compounds are treated similarly in the table. Fig. 1 is a graphic presentation of the normalized data from the right-hand column of Table 2. The data from the four triplicate ZC jars have been omitted from and are only implicit in Fig. 1.
Table 2 Percent removal by detox spiders of DDE, TCB, NAP, and PHEN from spiked sediments mixed with coarse and fine carbonaceous adsorbents Test conditions
0–2.5 h total
0–3.0 h total
First spider 0–24 h
Second spider 24–60 h
0–60 h total
Normalizeda total
DDE-ZCb DDE-CA DDE-FA DDE-CC DDE-FC
– – – – –
– – – – –
24.1 22.9 0.3 23.2 15.1
(0.3) (1.5) (0.1) (0.4) (0.8)
15.6 (0.4) 14.0 (0.3) 0.2 (0.1) 15.0 (0.2) 9.3 (0.9)
39.6 36.9 0.5 38.2 24.3
(0.7) (1.8) (0.1) (0.3) (1.6)
100 93 1.3 96 61
TCB-ZC TCB-CA TCB-FA TCB-CC TCB-FC
– – – – –
– – – – –
24.8 20.3 0.1 21.0 10.7
(0.4) (0.3) (0) (0.2) (0.2)
15.7 (0.2) 11.3 (0.3) 0 (0) 12.8 (0.9) 5.3 (0.3)
40.5 31.6 0.1 33.8 16.0
(0.6) (0.5) (0) (0.8) (0.5)
100 78 0 83 40
NAP-ZC NAP-CA NAP-FA NAP-CC NAP-FC
5.7 (1.1) 1.2 (0.1) 0 (0) 2.6 (0) 0 (0)
– – – – –
– – – – –
– – – – –
– – – – –
100 21 0 46 0
PHEN-ZC PHEN-CA PHEN-FA PHEN-CC PHEN-FC
– – – – –
17.4 (1.9) 12.6 (1.4) 0 (0) 14.0 (0.4) 0.6 (0.2)
– – – – –
– – – – –
– – – – –
100 72 0 80 3
The values displayed in the five central columns are the mean (n ¼ 3) percentages of the contaminants that were removed by the spiders during the individual treatment intervals or during the total treatments. Standard deviations are given in parentheses. The right-hand column gives the total percentages normalized to ZC (unimpeded bioavailability) test conditions. a The average, total percentages given in this column are normalized to those of the ZC (zero carbon) replicates, which represent unobstructed bioavailabilities. b Compounds and adsorbents are denoted by the same abbreviations as are used in the text.
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data was the same as for the pesticides, that is, FA obstructed the bioavailabilities of the PCBs better than did FC. Unfortunately, the detox spider from Jar 4 inexplicably contained PCBs at levels higher than those from Jars 1, 2, and 3, although the congener distribution pattern was markedly different than that of the PCBs from the SRM sediment. Because this phenomenon could not be explained, the data concerning the relative uptake efficiencies of FA and FC for PCBs are not reported in this paper.
4. Discussion and conclusions
Fig. 1. Relative bioavailabilities of sediment-bound contaminants in the presence of coarse and fine versions of two carbons. These data are from Experiment 1. Denotations for sorbent types and contaminants are the same as in the text. Error bars are not shown.
3.2. Experiment 2––uptake efficiency of FA versus FC for pesticides Table 3 show the results of the second experiment in which FA and FC were compared as to their efficiencies in obstructing the bioavailabilties from sediment of spiked organochlorine pesticides and environmentally incorporated PCBs. As stated above, Jar 4 (150 g of unspiked test sediment; no added carbon) constituted a control for this experiment. After treatment, its spider should theoretically have contained no PCB congeners or pesticides. Jar 3, which had contained sediments and contaminants equivalent to those in Jars 1 and 2, but had no added carbon, should be regarded as another control. After treatment, Jar 3Õs spider should theoretically have contained masses of the contaminants representative of unimpeded bioavailability. Jars 1, 2, and 3 each had contained 150 g of composited sediment that had effectively been spiked at a 1.33-ng/g concentration with each of the 27 pesticides, that is, 200 ng of each pesticide per jar. The numbers in Table 3 are the percentages of the 200 ng that were taken up by the detox spiders. Not given in Table 3 are data showing the relative scavenging efficiencies of FA and FC for PCB congeners originating in the HS-2 SRM sediment. This SRM had been included in the sediment composites with the intention of comparing the effectiveness of FA and FC for scavenging environmentally incurred (as opposed to spiked) hydrophobic contaminants. The trend for these
Section 2.3 gives the average recoveries of the 14 Ccontaminants that were extracted with CH2 Cl2 from triplicate subsamples of sediments. These analyses were of spiked, air-dried (to evaporate spiking solvent), and homogenized (but not wetted or aged) sediment. The degrees of precision apparent in the average recoveries demonstrate that the spiked contaminants had been homogeneously distributed throughout the batches of sediment. The volatility of NAP likely caused losses (mean recovery 41.6%) during the air-drying of the spiked sediment and during the evaporative concentration of extracts of the NAP-spiked sediment. Losses probably also occurred during the 7 d of aging to which the remaining bulk of the NAP-spiked sediment was subjected, as evidenced by the extremely low total uptake of NAP by the NAP-ZC detox spiders (Table 2). The lids of the Mason jars did not form airtight seals; furthermore, the gaskets in these lids consisted of a silicone-like substance probably capable of absorbing airborne organic contaminants. Losses during these procedural steps seem to have occurred to a lesser extent with PHEN. Although these losses of NAP and PHEN did not adversely affect Experiment 1, improved (airtight and inert) sample containers were used in Experiment 2. In studying the present work, the detox spiders and carbons should be thought of as competing scavengers. Lebo et al. (2000) demonstrated the primacy of the external surface area of a scavenging media over its mass (assuming equilibrium is not approached) for high contaminant uptake rates. They used detox spiders and SPMDs (with no added carbons to compete) to remove contaminants from sediments. The masses and surface areas of the detox spiders used in Experiment 1 of the present work remained constant (2.0-g spiders with 1100 cm2 surface areas) but the external surface areas of the added carbons were varied. (The 1.5-g portions of CA and CC had less external surface areas than did the 1.5-g portions of FA and FC, respectively.) It intuitively had seemed likely that the same primacy-of-surface-areaover-mass relationship that had previously applied to the spiders (Lebo et al., 2000) would apply here to the carbons, the competing scavengers. This prediction was
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Table 3 Data from Experiment 2; uptake by detox spiders of organochlorine pesticides from sediments admixed with 1% levels of finely ground Ambersorb 1500 (FA) or PCB carbon G (FC) Contaminant
Jar 4 (no carbon; control sediment)
Jar 1 (FA carbon; spiked and HS-2 sediment)
Jar 2 (FC carbon; spiked and HS-2 sediment)
Jar 3 (no carbon; spiked and HS-2 sediment)
Hexachlorobenzene Pentachloroanisole a-BHC c-BHC (lindane)
0 0 0 0
0 0 0 0
15 2 0 0
57 31 19 7
b-BHC Heptachlor d-BHC Dacthal (DCPA)
0 0 2 8
0 0 0 0
0 0 0 10
7 2 6 18
Oxychlordane Heptachlor epoxide trans-Chlordane trans-Nonachlor
0 0 1 0
11 0 12 21
45 25 32 37
43 28 34 42
o; p0 -DDEa cis-Chlordane Endosulfan DDEa
2 2 0 11
3 15 0 17
26 42 22 170
37 46 31 231
Dieldrin o; p0 -DDDa Endrin cis-Nonachlor
2 0 0 0
2 0 0 10
30 29 24 24
37 39 31 26
o; p0 -DDTa p; p0 -DDDa Endosulfan II p; p0 -DDTa
0 0 4 8
0 0 6 12
0 43 34 19
0 60 47 35
Endosulfan sulfate Methoxychlor Mirex
0 0 0
0 0 40
0 0 48
8 11 55
The tabulated values are expressed as percentages of the 200-ng totals of each pesticide that each jar had contained. (Jar 4 had theoretically been devoid of contaminants.) a These data were possibly affected by DDE contributions from the HS-2 SRM sediment and from the nearly pristine test sediment. Breakdown of p; p0 -DDT and o; p0 -DDT may also have affected the data.
correct. Table 2 and Fig. 1 show that FA and FC obstructed bioavailability better than did their respective coarser variants. An integral objective of this work was to compare the scavenging efficiencies of Ambersorb 1500 and coconut charcoal of roughly similar size ranges (i.e., CA versus CC and FA versus FC). Fig. 1 most concisely facilitates these comparisons. CA was slightly better at obstructing bioavailabilities of all four contaminants than was CC. FA and FC seem to have performed similarly well in scavenging NAP and PHEN. The most striking result of the experiment was that FAÕs uptake of the bioavailable (to the spider) DDE and TCB was virtually complete whereas FC intercepted only 39% and 60%, respectively, of the bioavailable DDE and TCB. Experiment 2 focused solely on comparing the scavenging capabilities of
FA and FC for chlorinated contaminants. The trend seen in Experiment 1 was repeated; FAÕs performance was clearly superior to FCÕs, as can be seen in Table 3. Two noteworthy phenomena are evident upon studying Table 3. First, Jar 3Õs spider (in the absence of added carbon) took up lower percentages of the BHCs, heptachlor and endosulfan sulfate than of the other pesticides. Note that the detox spiders from Jars 1 and 2 were virtually devoid of these pesticides. Explanation of the relatively low uptake efficiency of the LDPE spider for these compounds is not within the scope of this paper. Second, the detox spiders from Jar 3 (in the absence of added carbon) took up elevated levels of DDE (more than the 200 ng total that was spiked). This elevated DDE level would seem to have arisen from three sources. The HS-2 sediment contained residues of p; p0 -DDT
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and its degradation products (i.e., p; p0 -DDD and DDE) for which the sediment was not certified. The test sediment (from a CERC pond) contributed a small portion of this bias (note that Jar 4Õs detox spider took up DDE). Matrix-enhanced DDT and DDD breakdown (Foreman and Gates, 1997) undoubtedly also contributed to this positive bias to DDE levels in Jar 3Õs spider. This degradation seems to have been more pronounced with o; p0 -DDT than with p; p0 -DDT and may have taken place in the jars as well as during GC analysis. Whatever the sources of the excess DDE, the ground Ambersorb 1500 in Jar 1 seems to have intercepted it more effectively than did Jar 2Õs fine coconut charcoal. It is natural to wonder why FAÕs performance (obstruction of bioavailabilities) in both experiments was either equal to or vastly superior to FCÕs, depending on the compound, and why CAÕs performance for all four radiolabeled compounds was a little better than CCÕs. Were these differences in performance due to chemical or physicochemical differences between Ambersorb 1500 and coconut charcoal, or were they attributable to differences in surface area-to-mass ratios of CA and FA vis-a-vis CC and FA, respectively? Any suggestions given thus far that CA and CC (and FA and FC) were of similar particle size ranges have been made only to simplify discussions of these performance comparisons. Table 1 contains information about the particle size distribution of CA, CC, and FC that was supplied by the manufacturers (Calgon Carbon Corporation, 1986; Rohm and Haas Co., 1992). The estimate of FAÕs particle size range in Table 1 came entirely from examination of scanning electron micrographs (SEM), and the manufacturerÕs information about FC in the table was supplemented by SEM. Note that the surface area of a carbon particle is not simply a function of its diameter. Particles (having the same diameter) of two different carbons can have greatly disparate total surface areas because oneÕs pore structure can contribute more surface area to its total than the otherÕs. Some information about the surface characteristics of Ambersorb 1500 is proprietary (Rohm and Haas Co., 1992). Ambersorb 1500 was (and the other Ambersorb synthetic carbonaceous adsorbents are) made by pyrolysis of highly sulfonated styrene/divinylbenzene resin having a mac) structure. As can be seen in roporous (i.e., >550 A Table 1, the total surface area of this Ambersorb is 1100 m2 /g. Coconut charcoal is made from coconut shells and has an almost identical total surface area of 1200 m2 /g (Calgon Carbon Corporation, 1986). The coconut char coal has pores that are predominately in the 18–20 A range. In contrast to the Ambersorb 1500, the coconut charcoal lacks macroporosity; however, the pores of the coconut charcoal are amply large for the test contaminants to enter and become adsorbed. Table 1 shows that the total surface areas of the carbons include both external surface areas (calculated from the estimated mean
particle sizes) and internal surface areas, and that the external surface areas contribute negligibly to the total surface areas. Although the external surface areas per gram are dependent on particle size ranges, even for FA and FC the internal surface areas are 1000-fold greater than the external. Any performance differences for the four carbons that are related to differences in their surface areas must be attributed to differences in their external surface areas, because these external surface areas are where the only differences lie. The combined data (i.e., experimental results interpreted in light of estimates of surface areas) are insufficient to explain with absolute certainty why FA and CA obstructed contaminant bioavailabilities more efficiently than did FC and CC, respectively. However, setting aside any possible chemical or physicochemical differences between coconut charcoal and Ambersorb 1500, the following suggestions can be made. The magnitude of the particle size differences between CA and CC is probably enough to explain CAÕs slight performance advantage over CC. The cause of FAÕs great outperformance of FC in scavenging DDE and TCB probably cannot be completely attributed to its smaller particles. Additional (i.e., possibly physicochemical) factors may have been involved. When the beads of Ambersorb 1500 were crushed, previously sheltered sites or functional groups with high affinities for these chlorinated contaminants may have become exposed. In other words, the insides of the beads of Ambersorb 1500 (CA) may differ physically or chemically from the exteriors. However, this is only conjecture, and no conclusions explaining FAÕs superiority over FC can be drawn with certainty from the data presented here. Unbeknownst to the authors, Rohm and Haas Co. had discontinued manufacture of Ambersorb 1500 before this work was begun. Using one of the similar, stillavailable Ambersorbs in its place might have given similar results. References Ankley, G.T., West, C.W., Kosian, P.A., Makynen, E.A., 1996. Use of non-polar resin for in situ control of organic contaminant bioavailability in sediments. Presentation at the 17th Annual SETAC Meeting, Washington, DC. Calgon Carbon Corporation, 1986. Type PCB Granular Carbon––PCB-G Sales Specification Sheet, 3pp. Foreman, W.T., Gates, P.M., 1997. Matrix-enhanced degradation of p; p0 -DDT during gas chromatographic analysis: a consideration. Environ. Sci. Technol. 31, 905–910. Ho, K.T., Cook, H., Tien, R., Kiddon, J., Burgess, R.M., Kuhn, A., Lebo, J.A., Huckins, J.N., Petty, J.D., 1999. Characterization and isolation of organic toxicants in whole-sediment toxicity identification evaluations (TIEs). Presentation at 20th Annual SETAC Meeting, Philadelphia, PA. Huckins, J.N., Petty, J.D., Lebo, J.A., Orazio, C.E., Prest, H.F., Tillitt, D.E., Ellis, G.S., Johnson, B.T., Manuweera, G.K.,
J.A. Lebo et al. / Chemosphere 50 (2003) 1309–1317 1996. Semipermeable membrane devices (SPMDs) for the concentration and assessment of bioavailable organic contaminants in aquatic environments. In: Ostrander, G.K. (Ed.), Techniques in Aquatic Toxicology. CRC-Lewis Publishers, Boca Raton, FL, pp. 625–655. Kosian, P.A., West, C.W., Pasha, M.S., Cox, J.S., Mount, D.R., Huggett, R.J., Ankley, G.T., 1999. Use of nonpolar resin for reduction of fluoranthene bioavailability in sediment. Environ. Toxicol. Chem. 18, 201–206. Lebo, J.A., Zajicek, J.L., May, T.W., Smith, L.M., 1989. Largescale preparation of potassium hydroxide-modified silica gel adsorbent. J. Assoc. Off. Anal. Chem. 72, 371–373. Lebo, J.A., Huckins, J.N., Petty, J.D., Ho, K.T., 1999. Removal of organic contaminant toxicity from sediments––early work toward development of a toxicity identification evaluation (TIE) method. Chemosphere 39, 389–406.
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Lebo, J.A., Huckins, J.N., Petty, J.D., Ho, K.T., Stern, E.A., 2000. Selective removal of organic contaminants from sediments: a methodology for toxicity identification evaluations (TIEs). Chemosphere 40, 811–819. Petty, J.D., Orazio, C.E., Huckins, J.N., Gale, R.W., Lebo, J.A., Meadows, J.C., Echols, K.R., Cranor, W.L., 2000. Considerations involved with the use of semipermeable membrane devices for monitoring environmental contaminants. J. Chromatogr. A 879, 83–95. Rohm and Haas Co., 1992. Technical Notes: Ambersorb Carbonaceous Adsorbents, 14pp. West, C.W., Kosian, P.A., Mount, D.R., Makynen, E.A., Pasha, M.S., Sibley, P.K., Ankley, G.T., 2001. Amendment of sediments with a carbonaceous resin reduces bioavailabilty of polycyclic aromatic hydrocarbons. Environ. Toxicol. Chem. 20, 1104–1111.
Comparisons of coarse and fine versions of two carbons for reducing the bioavailabilities of sediment-bound hydrophobic organic contaminants J.A. Lebo
a,*
, J.N. Huckins a, J.D. Petty a, W.L. Cranor a, K.T. Ho
b
a
b
US Geological Survey, Columbia Environmental Research Center (CERC), 4200 New Haven Road, Columbia, MO 65201, USA Atlantic Ecology Division, US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory (NHEERL), 27 Tarzwell Drive, Narragansett, RI 02882, USA Received 19 March 2002; received in revised form 7 November 2002; accepted 27 November 2002
Abstract Coarse (whole) and finely ground Ambersorb 1500 and coarse and fine coconut charcoal were compared as to their efficiencies in scavenging organic contaminants desorbed from sediment. Aqueous slurries of a test sediment spiked (1 ppm) with p; p0 -DDE (DDE), 2,20 ,5,50 -tetrachlorobiphenyl (TCB), naphthalene (NAP), or phenanthrene (PHEN), and containing 1% levels of the test carbons were treated by shaking at 35 °C while exposed to clusters of low-density polyethylene membrane (detox spiders). Controls consisted of spiked sediments and detox spiders but no added carbon of any kind and thus represented unimpeded bioavailabilities (to the spiders). After the treatments––agitation periods from 2.5 to 60 h, depending on contaminant hydrophobicity––the exposed detox spiders were analyzed. The fine carbon of either type was more effective than its coarser variant in obstructing contaminant bioavailabilities. The finer variants of both carbons obstructed the bioavailabilities of NAP and PHEN equally well as did the coarser variants of both. Whole Ambersorb 1500 and coarse coconut charcoal were similarly ineffective in intercepting TCB and DDE. Ground Ambersorb 1500 obstructed virtually all bioavailability of all four contaminants and was far more effective than fine coconut charcoal in intercepting DDE and TCB. An additional experiment compared the effectiveness of ground Ambersorb 1500 and fine coconut charcoal in obstructing the bioavailabilities from sediment of a broad array of spiked organochlorine pesticides. The performance of ground Ambersorb 1500 was again found to be superior; the bioavailable levels of each of the 27 pesticides were markedly lower in the presence of ground Ambersorb 1500 than in the presence of fine coconut charcoal. Published by Elsevier Science Ltd. Keywords: Sediment; Organic contaminants; Bioavailability; Charcoal; Adsorption; TIE
1. Introduction Carbonaceous adsorbents have been proposed as media for ameliorating the toxicities of sediments that
*
Corresponding author. Tel.: +1-573-876-1837; fax: +1-573876-1896. E-mail address: [email protected] (J.A. Lebo). 0045-6535/03/$ - see front matter Published by Elsevier Science Ltd. doi:10.1016/S0045-6535(02)00817-2
have been contaminated with organic pollutants. Toxicity identification evaluation (TIE) researchers have found that mixing Ambersorb carbonaceous adsorbents (Ankley et al., 1996; Kosian et al., 1999; West et al., 2001) and coconut charcoal (Ho et al., 1999) with sediments are, to varying degrees, effective techniques for reducing the bioavailabilities of sediment-bound organic contaminants. In such TIE situations (and potentially in remediation scenarios) where the inextricable mixing of
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carbons with the sediment is judged to be permissible, the potentially intimate contact between the sediment and carbon particles is greatly advantageous. As contaminant molecules desorb from sediment particles, nearby carbonaceous particles are likely to intercept the molecules from the pore water before they can be ingested or bioconcentrated by aquatic organisms. This encounter probability is believed to be enhanced when the particle sizes of the carbons are very small because of the potential for greater contact between sediment and carbon particles and because of the greater carbon surface areas per unit masses of carbon. Lebo et al. (1999, 2000) demonstrated the use of lipidcontaining semipermeable membrane devices (SPMDs) and clusters of low-density polyethylene (LDPE) film (the so-called detox spiders) for removing organic contaminants from sediments. These media offer two advantages over carbonaceous adsorbents for this use: (1) In contrast to inextricably mixed carbonaceous materials, SPMDs or detox spiders can be easily removed from the sediment slurries after the treatments are complete. (2) The organic contaminants are readily recoverable (i.e., analyzable) from the SPMDs or detox spiders. In the present work, Ambersorb 1500 (a spherical carbonaceous adsorbent no longer commercially available) and a relatively coarse (large-particle-size) coconut charcoal were compared as to their efficacies in obstructing the bioavailabilities of organic contaminants desorbed from sediment. Also compared were the performances of finely ground Ambersorb 1500 and a small-particle-size coconut charcoal. Thus, performance comparisons of coarse versus fine particle size ranges within each adsorbent type were also achieved. These performance comparisons were accomplished through use of detox spiders. Each sediment slurry contained an admixed carbon during treatment (agitation at 35 °C), and it also contained a spider destined to be removed and analyzed after treatment. When used in the manner described here, detox spiders mimic organisms capable of organic contaminant uptake via bioconcentration but incapable of uptake via ingestion. The specific information being sought was the following: Which carbon type or variant would intercept the most contaminant molecules as they desorbed from the sediment, thereby most effectively reducing the levels bioavailable to the detox spiders? The performances of the carbons were compared to each other and relative to control conditions in which no added carbons were present to compete with the spiders. Although no organisms were used in this work, the term bioavailability is used freely throughout the paper. Huckins et al. (1996) showed that the lipid-containing SPMD, owing to the permeant size limitation of its LDPE membrane (similar to the limitation of biomembranes), samples only dissolved organic contaminants; that is, it samples only contaminants available to bioconcentration
processes and does not sample contaminants associated with particles or dissolved organic carbon. Because the detox spiders used here consisted solely of LDPE (i.e., were simply SPMDs minus the enclosed lipid), the same assumption can be made about them. Also, the term bioavailable is used more broadly here than to refer merely to the quantities of dissolved contaminants that are instantaneously bioavailable (which would be predictable through such parameters as the percent organic carbon of the sediments and the organic carbon [sediment]–water partition coefficients [Koc s] of the contaminants). The sediment treatments described herein include elevated temperature and mechanical agitation. Lebo et al. (2000) used this approach (i.e., energy inputs) to effect temporally compressed contaminant uptake curves for SPMDs and detox spiders. That study demonstrated that the bioavailable portion of a contaminant in a system is more than a tiny, static proportion of the total contaminant present, but in a holistic sense, it is most or even all of the contaminant present. As stated above, the goal of this work was to find which type and particle size range of the candidate carbonaceous adsorbents were generally most effective in obstructing the bioavailabilities of organic contaminants in sediment slurries. The test conditions, consisting of vigorous agitation at 35 °C, should not be regarded as a recommendation of conditions under which future sediment decontamination or remediation work should be performed. It remains an unproven assumption that the carbonaceous adsorbent that performed best as tested here would also perform best at ambient temperature and under quiescent conditions.
2. Experimental 2.1. Reagents, apparatus, and materials 0(1) Test sediment: Obtained from a pond at CERC (Lebo et al., 2000). The homogenized, powdery sediment contains only trace levels of a few organic contaminants and is 5.7% organic matter and 3.8% organic carbon by weight. Particle size distribution is 20% sand, 12% silt/loam, and 68% clay. 0(2) Standard reference material (SRM) sediment HS-2: National Research Council of Canada, Halifax, Nova Scotia, Canada. This marine sediment contains environmentally incorporated polychlorinated biphenyls (PCBs). 0(3) LDPE layflat tubing: Brentwood Plastics, St. Louis, MO. The LDPE tubing was 5.1-cm wide, of 38-lm wall thickness, and contained no additives. Segments of tubing 54- and 270-cm long (weighing 2.0 and 10.0 g, respectively) were used as previously described (Lebo et al., 2000) to make contaminantabsorbing clusters (detox spiders) for immersion in
J.A. Lebo et al. / Chemosphere 50 (2003) 1309–1317
0(4)
0(5)
0(6)
0(7) 0(8)
0(9)
(10)
(11)
sediment slurries. The 2.0- and 10.0-g detox spiders had 1100 and 5500 cm2 surface areas, respectively. Coconut charcoals: Calgon Carbon Corporation, Pittsburgh, PA, USA. Two coconut charcoals were used in this work: PCB carbon 30 140 (the coarser) and PCB carbon G (the finer of the two). (PCB is CalgonÕs designation for the charcoals and has no connection with PCBs.) Table 1 gives information about the particle size distribution of these charcoals. Ambersorb 1500 synthetic carbonaceous adsorbent: Rohm and Haas Co., Spring House, PA, USA. See Table 1. Shatterbox: Cat. no. 8510, SPEX Industries, Inc., Metuchen, NJ, USA. Ambersorb 1500 was finely ground with this shatterbox. Mason jars: 480 ml, polypropylene, Cole-Parmer Instrument Company, Vernon Hills, IL, USA. Incubator shaker: Series 25, New Brunswick Scientific Co., Inc., Edison, NJ, USA. This instrument shakes with an orbital motion (2.5-cm-orbit diameter) and was operated at 200 rpm and 35 °C. Radiolabeled contaminants: Sigma Chemical Co., St. Louis, MO, USA. The following 14 C-labeled compounds were used: p; p0 -DDE (DDE), 2,20 ,5,50 tetrachlorobiphenyl (TCB), naphthalene (NAP), and phenanthrene (PHEN). Multipesticide stock solution: AccuStandard, New Haven, CT, USA. This custom-made solution contains 27 ‘‘cold’’ (not radiolabeled) pesticides in equal concentrations. The identities of these pesticides are given in a table below. Liquid scintillation counting (LSC) cocktail: Ready Organic Cocktail, Beckman Instruments, Inc., Fullerton, CA, USA.
2.2. Spiking and aging of sediment for Experiment 1 Each of four large (about 2.4-kg) batches of the test sediment was spiked as previously described (Lebo et al., 2000) to 1.0-lg/g (dry-weight basis) concentrations with
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one of the four 14 C-labeled contaminants. After the spiked sediments had been air-dried (i.e., after the spike solvent had evaporated) and homogenized, three 10.0-g subsamples of each were radiometrically analyzed. Then 150-g portions of each spiked sediment were weighed into 15 Mason jars. Each jar also received 225 ml of deionized (DI) water. The jars were capped and swirled vigorously until the sediments were completely wetted; the sediments were then allowed 7 d to quiescently age at ambient temperature. 2.3. Radiometric analyses of subsamples of spiked sediments (Experiment 1) The four triplicate 10.0-g subsamples of spiked, homogenized (but not wetted or aged) sediments were analyzed as follows. The sediments were blended with 50-g portions of anhydrous Na2 SO4 then were extracted with 150 ml of CH2 Cl2 . Because the extracts were translucent yellow–green and would otherwise have color-quenched when evaluated by LSC, the extract solutions were subjected to a chromatographic cleanup as follows. After condensation to 3-ml volumes, the extracts were applied to Pasteur pipette columns containing potassium silicate (Lebo et al., 1989) and the contaminants were recovered with 5 ml of 98:2; hexane/ toluene. The purified sediment extracts were evaluated with a Beckman LS 6500 LSC. The mean percent recoveries (n ¼ 3; standard deviations in parentheses) of DDE, TCB, NAP, and PHEN were 93.6 (0.2), 88.2 (0.3), 41.6 (1.5), and 77.8 (2.1), respectively. 2.4. Introductions of carbons to spiked sediments (Experiment 1) The four carbons––coarse (whole) and finely ground Ambersorb 1500 and coarse and fine coconut charcoal (hereafter denoted by CA, FA, CC, and FC)––were weighed into 15-ml centrifuge tubes, 1.50 g per tube. To facilitate complete wetting of the carbons, the 1.50-g portions were conditioned with methanol then were
Table 1 Particle size and surface area information on whole and finely ground Ambersorb 1500, PCB carbon 30 140, and PCB carbon G Adsorbent type
Total surface area (m2 /g)
Estimated particle size range and mean particle size (lm)
External surface area (m2 /g)
Ambersorb 1500 (CA) Ground Ambersorb 1500 (FA) Calgon PCB 30 140 (CC) Calgon PCB carbon G (FC)
1200 1200 1100 1100
150–300, mean 225 2–30a , mean 10 75–800, mean 350 10–50b , mean 20
0.07 1.4 0.04 0.7
Most of the information displayed here was supplied by the manufacturers. A footnote indicates which information on mean particle particle size was obtained through use of scanning electron microscopy. External surface areas were calculated from estimated mean particle sizes. a Particle size information about the finely ground Ambersorb (FA) came entirely from SEM. b Manufacturer-supplied information about the particle size range of PCB carbon G was supplemented by SEM.
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washed several times with DI water. These washings entailed alternate centrifugations of the tubes and decantations of supernatants. The aqueous carbon slurries were added to the Mason jars containing the 150-g portions of wetted, aged sediments. The incubator shaker was used to shake the jars until the carbons were uniformly mixed into the sediment slurries. Each test (e.g., DDE-spiked sediment with coarse coconut charcoal [DDE-CC], PHEN-spiked sediment with finely ground Ambersorb 1500 [PHEN-FA], etc.) was performed in triplicate. Also, for each contaminant, there were three jars of spiked sediments to which no carbons were added (e.g., NAP-spiked sediment with no [zero] added carbon [NAP-ZC]). These latter constituted the control groups.
2.5. Treatment of spiked sediment with detox spiders (Experiment 1) Before treatments of the sediments were begun, the spiked, aged sediments were allowed to interact quiescently and at ambient temperature with their added carbons. These interactive intervals were 24 h for sediments spiked with DDE or TCB but only 1 h for sediments spiked with NAP or PHEN (because of their lesser hydrophobicities). Afterward, a 2.0-g detox spider was placed in each jar; treatments consisting of shaking of the jars at 200 rpm and at 35 °C were begun. Sediments spiked with DDE or TCB were subjected to two successive treatment intervals: 0–24 h then 24–60 h. Fresh spiders were substituted for the exposed ones after the 0–24 h intervals. For sediments spiked with NAP or PHEN, only one treatment interval (0–2.5 or 0–3.0 h, respectively) and only one detox spider per jar was used. As the exposed detox spiders were removed from the jars, the sediment that adhered to them was rinsed back into the jars with DI water.
2.6. Radiometric analyses of detox spiders (Experiment 1) The staple was removed from a spider, and the resulting eight pieces of single-ply LDPE were placed in a 1-l screw-cap Erlenmeyer flask with about 700 ml of DI water. The flask was capped, thoroughly shaken, and the water was discarded. This wash step was performed three times for each spider. The washed LDPE pieces were blotted dry with paper towels. Each piece of LDPE was cut in two with scissors; the 16 pieces were distributed about equally among three LSC vials. To each LSC vial were added 0.5 ml of isopropanol (dispersed residual water, if present), 10 ml of LSC cocktail, and 7 ml of 50:50; hexane/toluene (provided volume to ensure that the LDPE fragments were submerged). At least 18 h was allowed for the LDPE to interact with the cocktail and
solvents before the radiometric analyses were performed. 2.7. Experiment 2––further comparison of the scavenging efficiencies of FA and FC A sediment containing 27 nonradiolabeled pesticides, each at a 4.0 ng/g (dry-weight basis) concentration, was produced from the test sediment according to the spiking procedure described for Experiment 1. Fifty-gram portions of this spiked sediment were weighed into each of three jars, 75 ml of DI water was added, and the sediment samples were aged for 7 d as previously described. (Glass jars with aluminum foil-lined lids were used for this experiment.) A fourth sediment sample that was aged in parallel with the three pesticide-spiked samples consisted of 150 g of unspiked test sediment wetted with 225 ml of DI water. After the aging period, 20 g of HS-2 SRM sediment, 80 g of unspiked test sediment, and 150 ml of DI water were added to Jars 1, 2, and 3. Jars 1, 2, and 3 thereby contained 150 g of sediment with 27 pesticides (spiked and aged) at 1.3-ng/g concentrations, PCB congeners (environmentally incorporated) at a 7.5-fold dilution of their certified (HS-2) concentrations, and 225 g of DI water. Jar 4 was a control for this experiment. To Jars 1 and 2 were added 1.50 g of FA and FC, respectively, which had been wetted as described above. No carbons were added to Jars 3 or 4. The carbons were uniformly mixed throughout the sediment slurries, and the sediments and carbons were allowed 24 h to interact. A 10.0-g detox spider was placed in each of the four jars and treatments, performed as previously described, were begun. For this experiment, the treatment interval was 36 h, throughout which the single spider remained in each jar. Because ‘‘cold’’ contaminants were used in Experiment 2, the exposed spiders were analyzed by gas chromatography (GC) by the following sequence of steps. First, the detox spiders were extracted as described in Lebo et al. (2000) and as briefly summarized below. The spiders were washed with DI water and separated into small pieces of LDPE, which were blotted dry with paper towels. Then the LDPE pieces were briefly dipped in methanol and were extracted by being soaked in hexane. Hexane was used to partition the methanol into which the LDPE had been dipped. The methanol–water phases were discarded, and the upper, hexane phases were combined with the main hexane extracts. The spider extracts were subjected to cleanup and fractionation according to a scheme described by Petty et al. (2000) and summarized below. Size exclusion chromatography was used to remove pigments, polyethylene waxes, and elemental sulfur from the extracts. Three 1.0-ml injections were used to introduce each sample onto the described size exclusion column (Petty et al., 2000); the three collected fractions corresponding with each sample
J.A. Lebo et al. / Chemosphere 50 (2003) 1309–1317
were combined afterward. Next, the solutions were subjected to cleanup on Florisil followed by fractionation on silica gel. The nonpolar, first fractions collected from silica gel contained the PCBs and four or five of the least polar pesticides. The more polar, second fractions from silica gel contained the remainder of the pesticides. Both fractions from each sample were concentrated to 5.0-ml volumes and were analyzed by GC and electron capture detection. The GC was equipped with a 30-m DB-35 ms capillary column (J&W Scientific, Folsom. CA, USA). Chromatographic conditions were as described by Petty et al. (2000).
3. Results 3.1. Experiment 1––effects of the carbons on bioavailabilities of DDE, TCB, NAP, and PHEN Displayed in Table 2 are the results of Experiment 1 that compared the effects of CA, FA, CC, and FC on the bioavailabilities from sediment of DDE, TCB, NAP, and PHEN. The tabulated numbers express the recoveries of
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contaminants from the detox spiders as percentages of the total quantities of the contaminants that had been spiked into the 150-g portions of sediment. Test conditions denoted as ZC signify that the Mason jars contained none of the carbons to impede contaminant bioavailabilities to the spiders. The mean percentages of DDE and TCB removed from the ZC jars by their spiders after 60 h of treatment were 39.6% and 40.5%, respectively, of the totals contained by the 150-g sediment portions. These values are shown in the right-hand column of Table 2 adjusted to 100% (for normalization purposes). The mean total (0–60 h) percentages of DDE and TCB removed by the spiders from the carbon-containing jars have been normalized to the DDE-ZC or TCB-ZC values and are also shown in the right-hand column. Although there was only one short (2.5- or 3.0-h) treatment interval for sediments spiked with NAP and PHEN, the contaminant removal data for these compounds are treated similarly in the table. Fig. 1 is a graphic presentation of the normalized data from the right-hand column of Table 2. The data from the four triplicate ZC jars have been omitted from and are only implicit in Fig. 1.
Table 2 Percent removal by detox spiders of DDE, TCB, NAP, and PHEN from spiked sediments mixed with coarse and fine carbonaceous adsorbents Test conditions
0–2.5 h total
0–3.0 h total
First spider 0–24 h
Second spider 24–60 h
0–60 h total
Normalizeda total
DDE-ZCb DDE-CA DDE-FA DDE-CC DDE-FC
– – – – –
– – – – –
24.1 22.9 0.3 23.2 15.1
(0.3) (1.5) (0.1) (0.4) (0.8)
15.6 (0.4) 14.0 (0.3) 0.2 (0.1) 15.0 (0.2) 9.3 (0.9)
39.6 36.9 0.5 38.2 24.3
(0.7) (1.8) (0.1) (0.3) (1.6)
100 93 1.3 96 61
TCB-ZC TCB-CA TCB-FA TCB-CC TCB-FC
– – – – –
– – – – –
24.8 20.3 0.1 21.0 10.7
(0.4) (0.3) (0) (0.2) (0.2)
15.7 (0.2) 11.3 (0.3) 0 (0) 12.8 (0.9) 5.3 (0.3)
40.5 31.6 0.1 33.8 16.0
(0.6) (0.5) (0) (0.8) (0.5)
100 78 0 83 40
NAP-ZC NAP-CA NAP-FA NAP-CC NAP-FC
5.7 (1.1) 1.2 (0.1) 0 (0) 2.6 (0) 0 (0)
– – – – –
– – – – –
– – – – –
– – – – –
100 21 0 46 0
PHEN-ZC PHEN-CA PHEN-FA PHEN-CC PHEN-FC
– – – – –
17.4 (1.9) 12.6 (1.4) 0 (0) 14.0 (0.4) 0.6 (0.2)
– – – – –
– – – – –
– – – – –
100 72 0 80 3
The values displayed in the five central columns are the mean (n ¼ 3) percentages of the contaminants that were removed by the spiders during the individual treatment intervals or during the total treatments. Standard deviations are given in parentheses. The right-hand column gives the total percentages normalized to ZC (unimpeded bioavailability) test conditions. a The average, total percentages given in this column are normalized to those of the ZC (zero carbon) replicates, which represent unobstructed bioavailabilities. b Compounds and adsorbents are denoted by the same abbreviations as are used in the text.
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data was the same as for the pesticides, that is, FA obstructed the bioavailabilities of the PCBs better than did FC. Unfortunately, the detox spider from Jar 4 inexplicably contained PCBs at levels higher than those from Jars 1, 2, and 3, although the congener distribution pattern was markedly different than that of the PCBs from the SRM sediment. Because this phenomenon could not be explained, the data concerning the relative uptake efficiencies of FA and FC for PCBs are not reported in this paper.
4. Discussion and conclusions
Fig. 1. Relative bioavailabilities of sediment-bound contaminants in the presence of coarse and fine versions of two carbons. These data are from Experiment 1. Denotations for sorbent types and contaminants are the same as in the text. Error bars are not shown.
3.2. Experiment 2––uptake efficiency of FA versus FC for pesticides Table 3 show the results of the second experiment in which FA and FC were compared as to their efficiencies in obstructing the bioavailabilties from sediment of spiked organochlorine pesticides and environmentally incorporated PCBs. As stated above, Jar 4 (150 g of unspiked test sediment; no added carbon) constituted a control for this experiment. After treatment, its spider should theoretically have contained no PCB congeners or pesticides. Jar 3, which had contained sediments and contaminants equivalent to those in Jars 1 and 2, but had no added carbon, should be regarded as another control. After treatment, Jar 3Õs spider should theoretically have contained masses of the contaminants representative of unimpeded bioavailability. Jars 1, 2, and 3 each had contained 150 g of composited sediment that had effectively been spiked at a 1.33-ng/g concentration with each of the 27 pesticides, that is, 200 ng of each pesticide per jar. The numbers in Table 3 are the percentages of the 200 ng that were taken up by the detox spiders. Not given in Table 3 are data showing the relative scavenging efficiencies of FA and FC for PCB congeners originating in the HS-2 SRM sediment. This SRM had been included in the sediment composites with the intention of comparing the effectiveness of FA and FC for scavenging environmentally incurred (as opposed to spiked) hydrophobic contaminants. The trend for these
Section 2.3 gives the average recoveries of the 14 Ccontaminants that were extracted with CH2 Cl2 from triplicate subsamples of sediments. These analyses were of spiked, air-dried (to evaporate spiking solvent), and homogenized (but not wetted or aged) sediment. The degrees of precision apparent in the average recoveries demonstrate that the spiked contaminants had been homogeneously distributed throughout the batches of sediment. The volatility of NAP likely caused losses (mean recovery 41.6%) during the air-drying of the spiked sediment and during the evaporative concentration of extracts of the NAP-spiked sediment. Losses probably also occurred during the 7 d of aging to which the remaining bulk of the NAP-spiked sediment was subjected, as evidenced by the extremely low total uptake of NAP by the NAP-ZC detox spiders (Table 2). The lids of the Mason jars did not form airtight seals; furthermore, the gaskets in these lids consisted of a silicone-like substance probably capable of absorbing airborne organic contaminants. Losses during these procedural steps seem to have occurred to a lesser extent with PHEN. Although these losses of NAP and PHEN did not adversely affect Experiment 1, improved (airtight and inert) sample containers were used in Experiment 2. In studying the present work, the detox spiders and carbons should be thought of as competing scavengers. Lebo et al. (2000) demonstrated the primacy of the external surface area of a scavenging media over its mass (assuming equilibrium is not approached) for high contaminant uptake rates. They used detox spiders and SPMDs (with no added carbons to compete) to remove contaminants from sediments. The masses and surface areas of the detox spiders used in Experiment 1 of the present work remained constant (2.0-g spiders with 1100 cm2 surface areas) but the external surface areas of the added carbons were varied. (The 1.5-g portions of CA and CC had less external surface areas than did the 1.5-g portions of FA and FC, respectively.) It intuitively had seemed likely that the same primacy-of-surface-areaover-mass relationship that had previously applied to the spiders (Lebo et al., 2000) would apply here to the carbons, the competing scavengers. This prediction was
J.A. Lebo et al. / Chemosphere 50 (2003) 1309–1317
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Table 3 Data from Experiment 2; uptake by detox spiders of organochlorine pesticides from sediments admixed with 1% levels of finely ground Ambersorb 1500 (FA) or PCB carbon G (FC) Contaminant
Jar 4 (no carbon; control sediment)
Jar 1 (FA carbon; spiked and HS-2 sediment)
Jar 2 (FC carbon; spiked and HS-2 sediment)
Jar 3 (no carbon; spiked and HS-2 sediment)
Hexachlorobenzene Pentachloroanisole a-BHC c-BHC (lindane)
0 0 0 0
0 0 0 0
15 2 0 0
57 31 19 7
b-BHC Heptachlor d-BHC Dacthal (DCPA)
0 0 2 8
0 0 0 0
0 0 0 10
7 2 6 18
Oxychlordane Heptachlor epoxide trans-Chlordane trans-Nonachlor
0 0 1 0
11 0 12 21
45 25 32 37
43 28 34 42
o; p0 -DDEa cis-Chlordane Endosulfan DDEa
2 2 0 11
3 15 0 17
26 42 22 170
37 46 31 231
Dieldrin o; p0 -DDDa Endrin cis-Nonachlor
2 0 0 0
2 0 0 10
30 29 24 24
37 39 31 26
o; p0 -DDTa p; p0 -DDDa Endosulfan II p; p0 -DDTa
0 0 4 8
0 0 6 12
0 43 34 19
0 60 47 35
Endosulfan sulfate Methoxychlor Mirex
0 0 0
0 0 40
0 0 48
8 11 55
The tabulated values are expressed as percentages of the 200-ng totals of each pesticide that each jar had contained. (Jar 4 had theoretically been devoid of contaminants.) a These data were possibly affected by DDE contributions from the HS-2 SRM sediment and from the nearly pristine test sediment. Breakdown of p; p0 -DDT and o; p0 -DDT may also have affected the data.
correct. Table 2 and Fig. 1 show that FA and FC obstructed bioavailability better than did their respective coarser variants. An integral objective of this work was to compare the scavenging efficiencies of Ambersorb 1500 and coconut charcoal of roughly similar size ranges (i.e., CA versus CC and FA versus FC). Fig. 1 most concisely facilitates these comparisons. CA was slightly better at obstructing bioavailabilities of all four contaminants than was CC. FA and FC seem to have performed similarly well in scavenging NAP and PHEN. The most striking result of the experiment was that FAÕs uptake of the bioavailable (to the spider) DDE and TCB was virtually complete whereas FC intercepted only 39% and 60%, respectively, of the bioavailable DDE and TCB. Experiment 2 focused solely on comparing the scavenging capabilities of
FA and FC for chlorinated contaminants. The trend seen in Experiment 1 was repeated; FAÕs performance was clearly superior to FCÕs, as can be seen in Table 3. Two noteworthy phenomena are evident upon studying Table 3. First, Jar 3Õs spider (in the absence of added carbon) took up lower percentages of the BHCs, heptachlor and endosulfan sulfate than of the other pesticides. Note that the detox spiders from Jars 1 and 2 were virtually devoid of these pesticides. Explanation of the relatively low uptake efficiency of the LDPE spider for these compounds is not within the scope of this paper. Second, the detox spiders from Jar 3 (in the absence of added carbon) took up elevated levels of DDE (more than the 200 ng total that was spiked). This elevated DDE level would seem to have arisen from three sources. The HS-2 sediment contained residues of p; p0 -DDT
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and its degradation products (i.e., p; p0 -DDD and DDE) for which the sediment was not certified. The test sediment (from a CERC pond) contributed a small portion of this bias (note that Jar 4Õs detox spider took up DDE). Matrix-enhanced DDT and DDD breakdown (Foreman and Gates, 1997) undoubtedly also contributed to this positive bias to DDE levels in Jar 3Õs spider. This degradation seems to have been more pronounced with o; p0 -DDT than with p; p0 -DDT and may have taken place in the jars as well as during GC analysis. Whatever the sources of the excess DDE, the ground Ambersorb 1500 in Jar 1 seems to have intercepted it more effectively than did Jar 2Õs fine coconut charcoal. It is natural to wonder why FAÕs performance (obstruction of bioavailabilities) in both experiments was either equal to or vastly superior to FCÕs, depending on the compound, and why CAÕs performance for all four radiolabeled compounds was a little better than CCÕs. Were these differences in performance due to chemical or physicochemical differences between Ambersorb 1500 and coconut charcoal, or were they attributable to differences in surface area-to-mass ratios of CA and FA vis-a-vis CC and FA, respectively? Any suggestions given thus far that CA and CC (and FA and FC) were of similar particle size ranges have been made only to simplify discussions of these performance comparisons. Table 1 contains information about the particle size distribution of CA, CC, and FC that was supplied by the manufacturers (Calgon Carbon Corporation, 1986; Rohm and Haas Co., 1992). The estimate of FAÕs particle size range in Table 1 came entirely from examination of scanning electron micrographs (SEM), and the manufacturerÕs information about FC in the table was supplemented by SEM. Note that the surface area of a carbon particle is not simply a function of its diameter. Particles (having the same diameter) of two different carbons can have greatly disparate total surface areas because oneÕs pore structure can contribute more surface area to its total than the otherÕs. Some information about the surface characteristics of Ambersorb 1500 is proprietary (Rohm and Haas Co., 1992). Ambersorb 1500 was (and the other Ambersorb synthetic carbonaceous adsorbents are) made by pyrolysis of highly sulfonated styrene/divinylbenzene resin having a mac) structure. As can be seen in roporous (i.e., >550 A Table 1, the total surface area of this Ambersorb is 1100 m2 /g. Coconut charcoal is made from coconut shells and has an almost identical total surface area of 1200 m2 /g (Calgon Carbon Corporation, 1986). The coconut char coal has pores that are predominately in the 18–20 A range. In contrast to the Ambersorb 1500, the coconut charcoal lacks macroporosity; however, the pores of the coconut charcoal are amply large for the test contaminants to enter and become adsorbed. Table 1 shows that the total surface areas of the carbons include both external surface areas (calculated from the estimated mean
particle sizes) and internal surface areas, and that the external surface areas contribute negligibly to the total surface areas. Although the external surface areas per gram are dependent on particle size ranges, even for FA and FC the internal surface areas are 1000-fold greater than the external. Any performance differences for the four carbons that are related to differences in their surface areas must be attributed to differences in their external surface areas, because these external surface areas are where the only differences lie. The combined data (i.e., experimental results interpreted in light of estimates of surface areas) are insufficient to explain with absolute certainty why FA and CA obstructed contaminant bioavailabilities more efficiently than did FC and CC, respectively. However, setting aside any possible chemical or physicochemical differences between coconut charcoal and Ambersorb 1500, the following suggestions can be made. The magnitude of the particle size differences between CA and CC is probably enough to explain CAÕs slight performance advantage over CC. The cause of FAÕs great outperformance of FC in scavenging DDE and TCB probably cannot be completely attributed to its smaller particles. Additional (i.e., possibly physicochemical) factors may have been involved. When the beads of Ambersorb 1500 were crushed, previously sheltered sites or functional groups with high affinities for these chlorinated contaminants may have become exposed. In other words, the insides of the beads of Ambersorb 1500 (CA) may differ physically or chemically from the exteriors. However, this is only conjecture, and no conclusions explaining FAÕs superiority over FC can be drawn with certainty from the data presented here. Unbeknownst to the authors, Rohm and Haas Co. had discontinued manufacture of Ambersorb 1500 before this work was begun. Using one of the similar, stillavailable Ambersorbs in its place might have given similar results. References Ankley, G.T., West, C.W., Kosian, P.A., Makynen, E.A., 1996. Use of non-polar resin for in situ control of organic contaminant bioavailability in sediments. Presentation at the 17th Annual SETAC Meeting, Washington, DC. Calgon Carbon Corporation, 1986. Type PCB Granular Carbon––PCB-G Sales Specification Sheet, 3pp. Foreman, W.T., Gates, P.M., 1997. Matrix-enhanced degradation of p; p0 -DDT during gas chromatographic analysis: a consideration. Environ. Sci. Technol. 31, 905–910. Ho, K.T., Cook, H., Tien, R., Kiddon, J., Burgess, R.M., Kuhn, A., Lebo, J.A., Huckins, J.N., Petty, J.D., 1999. Characterization and isolation of organic toxicants in whole-sediment toxicity identification evaluations (TIEs). Presentation at 20th Annual SETAC Meeting, Philadelphia, PA. Huckins, J.N., Petty, J.D., Lebo, J.A., Orazio, C.E., Prest, H.F., Tillitt, D.E., Ellis, G.S., Johnson, B.T., Manuweera, G.K.,
J.A. Lebo et al. / Chemosphere 50 (2003) 1309–1317 1996. Semipermeable membrane devices (SPMDs) for the concentration and assessment of bioavailable organic contaminants in aquatic environments. In: Ostrander, G.K. (Ed.), Techniques in Aquatic Toxicology. CRC-Lewis Publishers, Boca Raton, FL, pp. 625–655. Kosian, P.A., West, C.W., Pasha, M.S., Cox, J.S., Mount, D.R., Huggett, R.J., Ankley, G.T., 1999. Use of nonpolar resin for reduction of fluoranthene bioavailability in sediment. Environ. Toxicol. Chem. 18, 201–206. Lebo, J.A., Zajicek, J.L., May, T.W., Smith, L.M., 1989. Largescale preparation of potassium hydroxide-modified silica gel adsorbent. J. Assoc. Off. Anal. Chem. 72, 371–373. Lebo, J.A., Huckins, J.N., Petty, J.D., Ho, K.T., 1999. Removal of organic contaminant toxicity from sediments––early work toward development of a toxicity identification evaluation (TIE) method. Chemosphere 39, 389–406.
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Lebo, J.A., Huckins, J.N., Petty, J.D., Ho, K.T., Stern, E.A., 2000. Selective removal of organic contaminants from sediments: a methodology for toxicity identification evaluations (TIEs). Chemosphere 40, 811–819. Petty, J.D., Orazio, C.E., Huckins, J.N., Gale, R.W., Lebo, J.A., Meadows, J.C., Echols, K.R., Cranor, W.L., 2000. Considerations involved with the use of semipermeable membrane devices for monitoring environmental contaminants. J. Chromatogr. A 879, 83–95. Rohm and Haas Co., 1992. Technical Notes: Ambersorb Carbonaceous Adsorbents, 14pp. West, C.W., Kosian, P.A., Mount, D.R., Makynen, E.A., Pasha, M.S., Sibley, P.K., Ankley, G.T., 2001. Amendment of sediments with a carbonaceous resin reduces bioavailabilty of polycyclic aromatic hydrocarbons. Environ. Toxicol. Chem. 20, 1104–1111.