Environ. Sci. Technol. 2010, 44, 5546–5552
Bioaccumulation of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans in E. fetida from Floodplain Soils and the Effect of Activated Carbon Amendment S O N J A K . F A G E R V O L D , †,⊥ YUNZHOU CHAI,‡ JOHN W. DAVIS,‡ MICHAEL WILKEN,§ GERARD CORNELISSEN,| AND U P A L G H O S H * ,† Department of Civil and Environmental Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, Toxicology and Environmental Research and Consulting, The Dow Chemical Company, 1803 Building, Midland, Michigan 48674, Environmental Analytical Support, The Dow Chemical Company, 1602 Building, Midland, Michigan 48674, and Norwegian Geotechnical Institute (NGI), Sognsveien 72, 0855 Oslo, Norway
Received September 8, 2009. Revised manuscript received May 24, 2010. Accepted June 4, 2010.
Laboratory studies were conducted to evaluate the bioaccumulation of aged polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in soil near the base of the terrestrial food chain using earthworms (E. fetida) as a model organism. This research also assessed the effect of activated carbon (AC) addition to soil on PCDD/F bioaccumulation in earthworms and passive uptake in polyoxymethylene (POM) samplers. Two soils taken from a wetland and a levee along the Tittabawassee River floodplain downstream of Midland, MI were used in this study. In the untreated soils, biota sediment accumulation factors (BSAFs) ranged from 0.17 for 2,3,7,8-TCDD to 0.02 for some of the higher chlorinated congeners, which were substantially lower than would be predicted using a conventional equilibrium partitioning model. The addition of AC to the floodplain soils generally reduced the BSAF values to lower than 0.02. Amendment of the wetland soil (having a high organic content) with 2% and 5% AC resulted in a 78 and 91% reduction of toxicity equivalent (TEQ) in earthworms, respectively. More strikingly, amendment of the natural levee soil (having a low organic content) with 2% and 5% AC showed >99% reduction of TEQ in earthworms. Also, freely dissolved aqueous concentrations of PCDD/Fs in soil slurries, as measured by equilibrium passive samplers, decreased up to 99% with AC treatment. Results of this study indicate that bioaccumulation of PCDD/Fs in earthworms from historically impacted floodplain soils is low and can be further reduced by amending with a strong sorbent. * Corresponding author phone: 410-455-8665; fax: 410-455-6500; e-mail:
[email protected]. † University of Maryland Baltimore County. ‡ Toxicology and Environmental Research and Consulting, The Dow Chemical Company. § Environmental Analytical Support, The Dow Chemical Company. | Norwegian Geotechnical Institute (NGI). ⊥ Current address: Observatoire Oce´anologique, Banyuls-sur-mer, 66651, France. 5546
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Introduction Low levels of anthropogenic chemicals in terrestrial soils over large areas from past industrial activities pose serious challenges in risk assessment and the development of appropriate and protective remedies. Some of these legacy contaminants such as polychlorinated dibenzo-p-dioxins/ dibenzofurans (PCDD/Fs) are chemically very stable and are highly hydrophobic compounds with logarithm of octanolwater partitioning coefficients above 5 (1). PCDD/Fs have a high affinity to organic matter and have limited mobility unless transported in association with particulate organic matter. However, these compounds are bioaccumulative, can be found in the terrestrial food chain, and have been reported to cause observable impact to the biota at the higher trophic levels. Effective in situ containment can be a reasonable alternative to excavation and incineration of large areas of contaminated soils with low concentrations of PCDD/Fs which are often associated with high costs as well as adverse impacts to existing ecosystems. One possible way of containing PCDD/Fs and reducing bioaccumulation potential is the addition of strong sorbents such as activated carbon (AC) to soil. The addition of AC has been shown to decrease bioaccumulation of hydrophobic contaminants in aquatic sediments (2, 3). This decrease in bioaccumulation is generally through decreased aqueous phase concentration (4) and a reduction of the fraction that is bioavailable (2, 3). Recently Bra¨ndli et al. (5) found that the addition of AC to soil slurries reduced the freely dissolved aqueous concentration of the native PAHs up to 99%. Cornelissen et al. (6) examined the available fraction of PCDD/Fs in soils from a former wood impregnation site in Sweden and found that although the concentrations were relatively high, the available fraction was considerably less than predicted due to strong sorption of the contaminants to the native black carbon. Recent studies (5, 6) used passive samplers such as polyoxymethylene (POM, 55 µm thin) to measure the freely dissolved concentration of contaminants in sediment porewater. Passive sampling techniques have been used to successfully predict the bioaccumulation potential of hydrophobic contaminants in soil (7-10). Although ingestion might play a dominant role for the uptake of more hydrophobic chemicals like PCBs and PCDD/Fs (11) in soil invertebrates, the porewater concentration is a good indicator of the activity or bioavailability of the chemical in soil (7). Earthworms are commonly used for bioaccumulation tests in soil. Earthworms live in close contact with soil particles, are near the base of the food chain, and are therefore an important link in the transport of environmental contaminants in the soil to the terrestrial food web. Typical biota to soil accumulation factor (BSAF) values of PCDD/Fs in terrestrial earthworms are 0.09 to 1.1 (12). A lower range (0.09-0.28) was found in 28-day bioaccumulation tests with N. virens in dredged sediments (13) while higher BSAF values for dioxins have been reported for several aquatic species (http://el.erdc.usace.army.mil/bsaf/). BSAF values for other hydrophobic compounds in terrestrial earthworms are generally higher. For example Blankenship et al. (14) found BSAF values for PCBs in earthworms of 0.48 and 2.4, depending on the level of contamination and soil type in aged soil. The soil from the floodplain of Tittabawassee River and sediment in the river have been found to contain elevated levels of PCDD/Fs due to historic discharge from The Dow Chemical Company facilities located in Midland, MI that 10.1021/es9027138
2010 American Chemical Society
Published on Web 06/18/2010
have been in operation since 1897. The PCDD/F contamination is likely associated with past chloralkali production process occurring in the early 20th century and chlorophenols production which took place from late 1930s until 1980. Prior to the installation of the site’s wastewater treatment plant in the mid 1930s, wastes from the manufacturing operations were incinerated, discharged to waste management ponds that were occasionally breached during flooding events, or discharged directly to the Tittabawassee River. In order to develop a sound management strategy for the soil in the floodplain, studies are being performed to understand the fate, transport, and biouptake processes that determine the exposure risk of the PCDD/Fs to ecological systems and the risk to human health (15, 16). This paper presents one element of the effort by investigating the bioaccumulation of PCDD/ Fs to the terrestrial worm, E. fetida, and the effect of activated carbon amendment. The objectives of this study were to (i) evaluate the bioaccumulation of the aged PCDD/Fs near the base of the food chain, (ii) investigate the effect of AC addition to soil on bioaccumulation, and (iii) assess whether passive samplers can be used to predict the bioaccumulation potential of PCDD/Fs in soil. The bioaccumulation studies were conducted using two distinct Tittabawassee River soils with different soil textures and PCDD/F congener profiles.
Materials and Methods Site Description and Soil Samples. Soil samples were collected from the Tittabawassee River floodplain at several depths from two locations with different geomorphic settings. Soil samples were taken using a hand auger after the removal of the overlying grass and leaves. Soil SW-20 was collected on a natural levee/intermediate terrace at 5-6 ft below ground surface. Soil SW-265 was collected in a wetland area at 0-0.8 ft below ground surface. Soils were passed through a 2 mm sieve to remove large objects such as gravel, leaves and grass roots, homogenized, and stored at 4 °C in sealed containers until further use. An artificial soil (AS) was used as a control for weight loss of the worms during the 28-day incubation, as well as a background control for PCDD/F analysis. The AS comprised of (by dry weight) 10% sphagnum peat, 20% kaolin clay, and 70% silica sand and pH was adjusted with calcium carbonate to pH 7 (17). Water holding capacity of the soils was determined (18), to be 30.2 ((0.6)%, 21.8 ((0.3)%, and 36.8 ((0.1)% for soils AS, SW-20, and SW265, respectively. Total Organic Carbon Content of Soil. Three aliquots (∼2 g dry wt for each) were taken from each soil, dried in an oven at 105 °C, pulverized and pooled, then acidified with 6N HCl to remove the inorganic carbon. The weight percentage of carbon, hydrogen and nitrogen (CHN) in each soil were determined using a Perkin-Elmer 2400 CHN Analyzer. The organic carbon content (foc) values were 5.6% for SW-265, 0.38% for SW-20, and 3.1% for AS. Earthworms. Mixed age adult (>90 days) worms, Eisenia fetida, were obtained from Aquatic Research Organisms (Hampton, NH) and cultured in an aquarium according to culture conditions described in ASTM method E1676 (17). At the start of this study, adult worms with well-developed clitella were transferred from the culturing media, washed, and allowed to depurate on wet tissue paper for 24 h. They were then washed, dried by blotting with a tissue, and weighed before being transferred to test beakers for the bioaccumulation tests. Activated Carbon Amendment. Granular activated carbon (type TOG LF 80 × 325 mesh or 44-177 µm, Calgon Corp. Pittsburgh, PA) was added to the three soils (AS, SW20, and SW-265) at two doses of 2% (2% AC) and 5% (5% AC) by dry weight, and then rolled on a cell production roller (Bellco, Vineland, NJ) at 3.25 rpm for 14 days before the start
of the bioaccumulation study. The soil without AC amendment was denoted as NT. A 5% dose of AC was chosen as a practical upper limit of a feasible dose for large-scale soil amendment and the smaller 2% dose was chosen to observe a dose-response effect. Bioaccumulation Test. The earthworm bioaccumulation test was performed in 400 mL glass beakers, each containing equivalent to 200 g dry soil. The soil was moistened to 75% of the water holding capacity 24 h before the initiation of the study. Three treatments (NT, 2% AC, and 5% AC) were designed for each of the three soils (AS, SW-20, and SW-265). Four replicate beakers were incubated with earthworms for each soil per treatment. In total, 36 beakers were set up for worm exposure. Six worms were added to each beaker, which was covered with nylon mesh to prevent worms from escaping. No food was added during the 28-day incubation. Thus, the exposure times had to be limited to this time frame but is in agreement with many earlier tests (7-10). The beakers were weighed every 3-4 days to ensure proper moisture content. At the end of incubation, the worms were washed and allowed to depurate in clean AS for 24 h to ensure the clearing of the gut of particles containing PCCD/Fs. After another 24 h depuration on wet tissue paper, the worms were cleaned, dried by blotting, weighed, and immediately frozen. Worms were then freeze-dried overnight in a Freeze Mobile 6 (Virtis, Gardiner, NY) before chemical analysis. Replicate samples (n ) 4) of earthworms were subjected to PCDD/F analysis separately, whereas the four replicate soil samples were pooled after extraction for PCDD/F analysis. Lipid Content of Worms. Total lipids were extracted by crushing one freeze-dried worm from each beaker in a mortar and pestle with 5 mL 1:1 chloroform/methanol and 0.5 g anhydrous sodium sulfate. The lipid concentration in the supernatant was determined as described in van Handel (19) using soybean oil as the standard. Spectrophotometric analysis was performed on a Genesys 10 spectrophotometer (Thermo Electron Corp. Waltham, MA) at 525 nm. Biota-soil Accumulation Factor (BSAF) Calculations. Biota-soil accumulation factors of PCDD/Fs were calculated by dividing the lipid-normalized concentrations in earthworms by the concentration in soil normalized to organic carbon. Cworm
BSAF )
Csoil
/flipid
/foc
where Cworm is the concentration of individual PCDD/F congener in dry worms, Csoil is the concentration of individual PCDD/F congener in soils, foc is the fraction of organic carbon in soil and flipid is the fraction of lipid in dry worm. The concentration of worm PCDD/F and lipids were based upon replicate samples (n ) 4) for each soil per treatment, while the concentration of PCDD/F in soil was based upon one pooled sample for each soil per treatment. Aqueous Concentration Using Polyoxymethylene (POM) Passive Sampler. Polyoxymethylene strips (55 µm thick) were cleaned by Soxhlet extraction for 12 h with hexane before use. Ten grams (dry wt.) of soils SW-20 and SW-265, as well as 2% AC and 5% AC amended soils were added to 300 mL amber glass bottles. Water containing 25 mg/L sodium azide and 0.01 M calcium chloride (20) was added to these bottles in addition to 200 mg POM per bottle. The bottles were shaken horizontally on an orbital shaker (Bellco, Vineland, NJ) at 3.2 rpm for 120 days to enhance mass transfer from soil. After contact, the POM strips were removed, cleaned with a moist tissue and extracted according to the method described below. Freely dissolved PCDD/Fs were determined based upon the following equation: VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Cw )
CPOM KPOM
where CPOM is the concentration of individual PCDD/F congener in POM, Cw is the porewater concentration of the corresponding congener and KPOM is the POM-water distribution ratio. We acknowledge that KPOM values for some of the higher molecular weight compounds may not represent true long-term equilibrium. Values of KPOM from Cornelissen et al. (6) were used which were 100-1000 times lower than KOC for PCDD/Fs in soil (6). This implies that 200 mg POM would sorb as much as around 0.2-2 mg of TOC, very little compared to the 38-560 mg of TOC presented in our experiments. PCDD/F Analysis. Sample extraction and purification were based on U.S. Environmental Protection Agency (U.S. EPA) method 1613B (21). Briefly, freeze-dried worm samples (100-200 mg) were digested using 75 mL concentrated HCl at ambient temperature for approximately 18 h. The digested worm samples and soil samples (10-30 g) were extracted in a Soxhlet apparatus with toluene (∼250 mL) as a solvent for 20 h. Seventeen 13C-labeled 2,3,7,8-substituted PCDD/F standards were added to the worm samples before digestion and to the soil samples before extraction. An aliquot of the extract was purified using a multistep cleanup with a mixed silica gel/acid/base column, silica gel/silver nitrate column and activated aluminum oxide. The solvent in the purified extract was exchanged to nonane after blow-down using high purity nitrogen. Polyoxymethylene (POM) samples were dissolved in half-concentrated sulfuric acid. After the addition of internal standards, the POM solution was extracted with a benzene/hexane mixture (5% benzene by volume) followed by the cleanup and solvent exchange described above. The seventeen 2,3,7,8-substituted PCDD/F congeners (TM17) and total homologues were quantified using high resolution gas chromatography/high resolution mass spectroscopy (HRGC/ HRMS) (21). The seventeen 2,3,7,8-substituted PCDD/Fs are considered to be of toxicological significance and their relative potencies are estimated using the toxic equivalent factor (TEF). The toxic equivalent (TEQ) is the concentration of individual congener multiplied by its TEF (22). In the present paper, tetra-, penta-, hexa-, hepta-, and octa- chlorinated dibenzo-p-dioxins/dibenzofurans are denoted as TCDD/F, PeCDD/F, HxCDD/F, HpCDD/F, and OCDD/F.
Results and Discussion PCDD/Fs in Soils. The two floodplain soils evaluated in this study exhibited varied soil textures and different PCDD/F profiles. Soil SW-20, which is typical of the soil type along the Tittabawassee River floodplain, was a loamy sand (sand 83%, silt 12%, and clay 5%) with a very low organic carbon content (foc of 0.38%). Conversely, soil SW-265, a loam sampled from a wetland area along the river, had a much lower sand content (sand 33%, silt 46%, and clay 21%) and an approximate 15-fold higher organic carbon content (foc of 5.6%). The concentrations of the PCDD/Fs in SW-20 and SW-265 soils were 363 and 57 µg/kg, while the level of the TM17 were 196 and 43 µg/kg respectively. Larger differences were noted in the WHO-TEQs between soils which were 23.9 (SW 20) and 1.16 (SW 265). The concentration of each homologue group of PCDD/F in these two soils are presented in Supporting Information (SI) Figure S1, and the concentrations of each of the 17 2,3,7,8-substituted congeners are presented in SI Table S1. Soil SW-20 was primarily impacted by tetra-, penta-, and hexa-chlorinated furans, with the 2,3,7,8-TCDF, 2,3,4,7,8PeCDF, and 1,2,3,4,7,8-HxCDF congeners comprising nearly 90% of the TEQ profile. In contrast, the dioxin congeners were either near or below the detection limit and did not contribute significantly to TEQ for this soil. These data are 5548
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consistent with the observation of Wilken et al. (23), who reported that these three congeners were the dominant contributor to the TEQ profile along the banks of the Tittabawassee River and likely originated from chloralkali production that began in the late 19th century. In contrast, soil SW-265 was somewhat impacted by hepta- and octachlorinated PCDD/Fs in addition to tetra, penta, and hexachlorinated furans (SI Figure S1), which indicates sources from chlorophenol production processes in addition to the chloralkali production (23). Three furan congeners 2,3,7,8TCDF, 2,3,4,7,8-PeCDF, and 1,2,3,4,7,8-HxCDF contributed approximately 75% of the TEQ for soil SW-265 while the dioxin congeners 2,3,7,8 TCDD and 1,2,3,7,8 PeCDD contributed approximately 13% of the TEQ for this soil. Laboratory prepared AS used in bioaccumulation experiments had a low total concentration of PCDD/F (0.2 µg/kg) as shown in SI Figure S1 and Table S1. Earthworm Bioaccumulation. The total homologue concentrations of PCDD/Fs in worms after 28 days exposure in AS, SW-20, and SW-265 are shown in SI Figure S2 with the individual congener concentrations presented in SI Table S3. Overall, bioaccumulation was 2 orders of magnitude higher in soil SW-20 compared to soil SW-265, which is likely attributable to an order of magnitude higher total concentration of PCDD/Fs in soil and an order of magnitude lower fraction organic carbon content in SW-20 compared to SW265. The PCDD/F concentrations in worms exposed to AS were 4 orders of magnitude lower compared to soil SW-20 and 3 orders of magnitude lower than soil SW-265. As shown in Figure 1, the measured BSAF values for the two untreated soils were similar and ranged from 0.17 for 2,3,7,8-TCDD to 0.02 for some of the higher chlorinated congeners. The BSAF values presented here are based on standard 28-day laboratory exposures and may not necessarily reflect long-term equilibrium conditions. The BSAF values are substantially lower than would be predicted using conventional equilibrium partitioning model for organism lipids and soil organic matter. A similar range of BSAF values (0.09 to 0.28) have been reported in 28-day bioaccumulation tests with N. virens exposed to dredged sediments (13). In contrast, higher values were reported in indigenous worms from agricultural soils in Sweden where BSAF values ranged from 0.09 to 1.1 (12). The BSAF values for the native PCDD/Fs in soils that have presumably aged in the field for several decades are generally lower compared to reported values for other hydrophobic organics such as PCBs. Sun and Ghosh (3) found that BSAFs for PCBs initially increased with increasing log Kow and then began decreasing for log Kow values higher than 6.7. Thus, for PCDD/Fs that have log Kow values in the range of 6.5-8.5, the BSAF values are expected to be in the lower range compared to PCBs and decrease with increasing hydrophobicity. As shown in SI Figure S3 for both soil samples, BSAF values showed a decreasing trend with increasing congener Kow value. Effect of Activated Carbon Amendment on Bioaccumulation. Addition of activated carbon to soils greatly reduced the biouptake of PCDD/Fs in the earthworms as illustrated in Figure 1. For example, the addition of 2% AC to soil SW-20 reduced bioaccumulation of total TCDFs from 210 to 1 µg/kg, a 99% decrease (SI Table S2). AC addition to both soils resulted in a decrease in the concentration of PCDD/Fs in all worm samples, with a more pronounced decrease for soil SW-20. The reduction in soil SW-20 could be attributed to its higher initial PCDD/F concentration and lower organic carbon content than soil SW-265. For both soils, after amendment with 5% AC, the uptake of total PCDD/ Fs in earthworms was similar to that measured in the laboratory AS exposures (i.e., controls). Note that the elevated PCDD/F concentrations in worms exposed to AS amended with 5% AC was primarily driven by one replicate which was
FIGURE 1. Biota-soil accumulation factors (BSAF) for individual dioxin and furan congener in soils SW-20 and SW-265 with different activated carbon amendments. Solid, open, and hatched bars represent BSAF values for worms exposed to untreated soil, soil amended with 2% activated carbon, and soil with 5% activated carbon, respectively. Error bars show (1 standard error. 3.6 µg/kg and the average ( standard deviation for the rest three replicates was 0.44 ( 0.06 µg/kg. It is possible that the worms in the anomalous replicate accumulated some background PCDD/Fs from food and culture media before they were exposed to the AS. This anomalous sample in one of the treated AS exposures does not impact the interpretation of the bioaccumulation results for soil SW-20 and SW-265. For the soil SW-20, TCDFs and PeCDFs were the dominant homologues and the decrease of these compounds in the worms after AC amendment of the soil SW-20 was approximately 99%. In contrast, OCDD was the most abundant homologue in soil SW-265 and the decrease in worm concentrations following AC amendment was approximately 60%. Generally, percent reductions in biouptake with AC amendment were higher for the lower chlorinated congeners (tetra- to hexa-furans) compared to the highly chlorinated OCDD/F for each soil. The tetra- to hexa-furans are the major contributors to TEQ, thus reduction of these congeners is important to have a net impact on toxicity. Previous work with PCBs in sediments also demonstrated a similar phenomenon of greater effectiveness for the lower chlorinated congeners after short periods of sediment/AC contact (2, 3). This phenomenon might be attributed to the lower aqueous solubility and slower mass transfer rates of the higher chlorinated congeners between soil/sediment and AC particles. The addition of AC to the two soils substantially reduced the BSAF values to generally lower than 0.02 (Figure 1). Higher reductions in BSAF values were observed at the 5% AC doses. Based on the large reductions of measured BSAF values, especially for the soil SW-20, it appears that a much smaller
TABLE 1. Toxic Equivalent (TEQ) Values for Soils and Worms
a TEQ (ng/kg) was determined by WHO 2005 TEF values, nondetect ) 0. b NT denotes no treatment with AC. c Worm data was average ( standard error (n ) 4), soil data was pooled from 4 replicates. d This elevated level was primarily driven by one replicate which was 252 ng/kg, the average ( standard error for the rest 3 replicates was 1.7 ( 1.2 ng/kg.
dose of AC to soil in the range of 1% by weight may be effective in sequestering and reducing the uptake of the available fraction of the PCDD/Fs in sandy soils with low native organic carbon (and black carbon) content. TEQ Reduction. The addition of activated carbon to the soils resulted in a large decrease in the TEQ levels in the earthworms (Table 1). The amendment of soil SW-265 with 2% and 5% AC exhibited 78 and 91% reduction of the TEQ concentration in earthworms, respectively. More strikingly, the amendment of soil SW-20 with 2% and 5% AC showed VOL. 44, NO. 14, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. Dioxin and furan aqueous concentrations estimated from POM passive samplers in soil slurries of untreated and activated carbon treated soils. Solid, open, and hatched bars represent aqueous concentrations corresponding to untreated soil, soil amended with 2% activated carbon, and soil with 5% activated carbon, respectively. Note the difference in concentration scales for dioxins and furans in soil SW-20. Error bars show (1 standard error. greater than 99% reduction of TEQ levels in earthworms. The effectiveness of the AC amendment was more pronounced in the lower organic carbon soil SW-20 which could be attributed to the larger increase in sorptive capacity for the PCDD/Fs as compared to the higher organic carbon soil SW-265. Possible Effect of AC on Earthworms. No additional food was provided to the earthworms during the 28 day exposure period resulting in weight loss for all worms, except those in contact with soil SW-265 with no AC amendment (SI Figure S4). Weight loss averages were approximately 2% for worms incubated with untreated AS to about 30% for worms incubated with soil SW-20 amended with 5% AC. Worms incubated with SW-265 exhibited a small increase in weight after the 28-day incubation. This may be attributed to the higher organic carbon content of this soil (5.6%) compared to soil SW-20 (foc ) 0.38%). The poor nutritional quality of the soils, especially after amendment with AC and the lack of additional food during the test, may be responsible for the weight loss observed in the worms. The worms may also have released egg cocoons during the exposure period which would also contribute to weight loss in the organisms. However, we did not find a correlation between the weight loss and the lipid % for the different AC treatments (SI Figure S4), indicating that the loss of storage lipids might not be the main weight loss mechanism. Millward et al. (2) also observed a reduced growth of the polychaete Neanthes arenaceodentata after 28 days of incubation with sediment amended with 3.4% AC with no change in the lipid content. Jonker et al. (24) observed reduced lipid contents of aquatic worms (Limnodrilus sp.) in the presence of a charcoal and later Jonker et al. (25) reported reduced lipid contents of Lum5550
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briculus variegatus in sediments with AC. In contrast, Cornelissen et al. (26) reported no significant changes in lipid content of a snail and a ragworm in three sediments amended with 2% AC. Thus, the effect of AC addition seems to vary between species and environments. Earthworms feed on organic debris and one can speculate on whether the AC sequesters the organic compounds that the earthworms would otherwise use for nutrition (24). Another possible mechanism contributing to weight loss is avoidance of the AC treated soil which could result in a reduction of the ingested soil needed for weight maintenance. However, we would expect loss of storage lipids if the worms were starving for 28 days. Also, if reduction in feeding rate could explain the decline in PCDD/F biouptake in the worms after AC amendment, we would expect a much more drastic reduction in the biouptake of the hepta- and octa-congeners that are less soluble and are primarily taken up by ingestion. Rather, the reduction for the TCDF homologues were were approximately 2-fold higher (80 vs 40%) than noted for the HpCDF homologues in soil SW-265 with 2% AC amendment. In addition, weight losses were small (
