Occurrence and hazard screening of alkyl sulfates and alkyl ethoxysulfates in river sediments

Science of the Total Environment 367 (2006) 312 – 323 www.elsevier.com/locate/scitotenv

Occurrence and hazard screening of alkyl sulfates and alkyl ethoxysulfates in river sediments Hans Sanderson a,⁎, Bradford B. Price b , Scott D. Dyer b , Alvaro J. DeCarvalho a , David Robaugh c , Scott W. Waite d , Stephen W. Morrall b , Allen M. Nielsen e , Manuel L. Cano f , K. Alex Evans f a

The Soap and Detergent Association, 1500 K Street, NW, Suite 300, Washington, District of Columbia, 20005, United States b The Procter and Gamble Company, Cincinnati, OH 45253, United States c Midwest Research Institute, Kansas City, MO 64110, United States d Huntsman LLC, Austin, TX 78752, United States e Sasol North America, Inc., Westlake, LA 70669, United States f Shell Chemical LP, Houston, TX 77251, United States Received 27 June 2005; received in revised form 9 November 2005; accepted 15 November 2005 Available online 27 December 2005

Abstract Alkyl sulfates (AS) and alkyl ethoxysulfates (AES) are High Production Volume (HPV) ‘down-the-drain’ chemicals widely used globally in detergent and personal care products, resulting in low levels (ng to μg L− 1 range) ultimately released to the environment via wastewater. These surfactants have a strong affinity for sorption to sediments. However, data regarding the fate and effects following release into the environment has not been reported. Sediment samples from both normal exposed and presumably low exposed locations (background) were analyzed to determine the levels of AS/AES. The method used in this study shows broad applicability across various sediment types and the most common congeners of AS/AES. The combined levels of AS/ AES detected in the two presumed lower exposed sites ranged from 0.025 and 0.034 μg g− 1 on a dry weight (dw) basis while the presumed higher exposed site had combined levels of AS/AES of 0.117 μg g− 1 (dw) based on triplicate analyses. Results indicate that detectable levels of AS/AES can be found in sediments in the environment at these three sites that are below the concentrations expected to produce significant adverse ecological effects for individual homologues and the whole mixture, the hazard screening for these three sites had PECporewater/PNECtotal mixture ratios of 0.007–0.024. However, further investigation of potential effects and risk assessment is warranted. © 2005 Elsevier B.V. All rights reserved. Keywords: LC-MS; Exposure; Surfacewater; Wastewater; Mixture

1. Introduction Surfactants are the major cleaning ingredients found in household and personal care products. North Amer⁎ Corresponding author. E-mail address: [email protected] (H. Sanderson). 0048-9697/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2005.11.021

ican consumption volumes of alkyl sulfates (AS) and alkyl ethoxysulfates (AES) for 2003 were estimated to be 260 and 1083 million pounds, respectively (Modler et al., 2004). This amount exceeds the estimated volume for the major anionic surfactant linear alkylbenzene sulfonates (LAS) which remains at a comparatively stable annual usage rate of 700 million pounds for the

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past many years (Modler et al., 2004). Characteristics for AS and AES surfactants include a molecular structure containing a hydrophilic portion which provides high water solubility and a hydrophobic portion, usually from a long alkyl chain, that contributes to the surfactant properties needed for consumer detergents. These compounds are typically highly water soluble and surface active which may lead them to partition to suspended particles and become incorporated into sediments in the environment, where the highest exposure to substances such as AS/AES thus is expected (Marchesi et al., 1991). In addition, biodegradation rates and pathways of organic compounds, including some detergent ingredients, may be altered under anoxic conditions (Swisher, 1987; Schröder, 2001) that occur in sediments also increasing potential exposure. Surfactants commonly used in consumer products are effectively removed in conventional wastewater treatment systems (Schroder et al., 1999; Holt et al., 1995). Several studies report removal during wastewater treatment typically exceeding 99% in activated sludge operations and > 90% in less efficient trickling filter units (Schroder et al., 1999; Matthijs et al., 1997, 1999; McAvoy et al., 1998; Fendinger et al., 1992). Residual concentrations released to the environment via effluent are in the low ng to μg L− 1 range (Schwitzguebel et al., 2001). Once released into the environment, these compounds continue to degrade (Belanger et al., 1995a,b; Lee et al., 1995) and, therefore, are not expected to accumulate in oxic environments, under anoxic conditions degradation deposition in sediments may occur (Swisher, 1987; Schröder, 2001). Guckert et al. (1996) observed approximately a 20% loss over a 4.3-min residence time in stream surface water hence the half-life (DT50) of AS/AES in surface water is estimated to be less than half a day (Guckert et al., 1996). In some situations however, continuous inputs to the environment (e.g. via wastewater treatment plants effluent, other known and unknown point sources, and runoff) of compounds that biodegrade rapidly may replace dissipated material resulting in chronic low exposures. To assess the hazard of these situations, it is important to determine the environmental concentrations in the water and sediment compartments and apply this information to estimate the hazard to both aquatic and sediment dwelling organisms. Both AS and AES conform to the general structure: RO–ðCH2 CH2 OÞn –SO−3 Mþ where R is a saturated alkyl group with chain length of typically 12–15 carbons, n is the number of ethoxylates

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(typically ranging from 0 to 8), and M+ is the associated counter ion. A conventional shorthand notation for a material is “CxEOnS” where x is the alkyl chain-length and n is the degree of ethoxylation. Alkyl sulfates (AS) are the special case of the formula where n = 0 (AE0S). In most consumer product applications, the saturated alkyl group is essentially linear with a very small amount of branching. The alkyl chain is ethoxylated to a predetermined average number of moles and sulfated to provide a product with the desired properties (Biermann et al., 1986). The aquatic toxicity and effects of AS and AES has been studied extensively in stream mesocosm and in the laboratory (Belanger et al., 1995a,b; McCormick et al., 1997) and conclusions have been compiled by Van de Plassche et al. (1999) in the context of an aquatic effect assessment. This latter work considered both short-term toxicity data from eight aquatic taxonomic groups, as well as chronic No Observed Effect Concentration (NOEC) results from four different organisms covering three trophic levels (algae, rotifer, cladoceran and fish) to derive a Predicted No Effect Concentration (PNEC) for the aquatic compartment. Using an average composition of C12EO3.4S, the calculated aquatic PNEC was 400 μg L− 1, which is consistent with two stream mesocosm studies, which yielded a NOEC of 251 μg L− 1 for a higher alkyl chain-length C14–15EO2.2S material (Belanger et al., 1995b) and a NOEC of 106 μg L− 1 for non-ethoxylated mixtures of C14–15 EO0S alkyl sulfate (Belanger et al., 2004). Both of the materials studied in the mesocosm experiments would be expected to be more hydrophobic, hence potentially more toxic, than the material considered by Van de Plassche et al. (1999), which had a shorter alkyl chainlength and higher degree of ethoxylation. In all these studies, the toxicity was assessed based on an average alkyl and ethoxylate distribution for the complex mixture. This approach may be appropriate for a wellcharacterized Gaussian distribution of congeners but is not applicable for complex mixtures where congener distributions may not readily fit a normal or log normal distribution. Structure–Activity Relationships (SAR) for industrial surfactants have been evaluated for a number of years (Hall et al., 1989), so to aid in assessing the toxicity of complex congener mixtures, single homologue data has been used to construct a congener specific (SAR) model for the toxicity of AES to Ceriodaphnia dubia (Dyer et al., 2000). This SAR combined with measurements of individual homologues in river sediments can be used to assess potential impacts on sediment dependent organisms exposed to AS/AES. Assessment of the environmental exposure

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has been the limiting factor for reliable hazard assessment of AS/AES. While there is limited data on AS/AES levels, fate, and effects in the environment, the anionic surfactant LAS has been studied extensively in wastewater (Schroder et al., 1999; Matthijs et al., 1997; Holt et al., 1995; Rapaport and Eckhoff, 1990), receiving waters (Feijtel et al., 1999) and in both freshwater and marine sediments (León et al., 1995; Westall et al., 1999; Rapaport and Eckhoff, 1990). These data have been summarized in the OECD High Production Volume program report LAS SIAP (2005). The measured LAS surface water concentrations were generally below 50 μg L− 1, and total river sediment concentrations were generally less than 1–2 mg kg− 1 dry weight (LAS SIAP, 2003). Existing monitoring data on AS/AES is limited to studies of removal in wastewater treatment facilities where effluent concentrations of all combined AS/AES homologues were between 5.7 and 21 μg L− 1. Attempts have been made to generate reliable measurements of AS/AES in receiving surface waters, but these have been unsuccessful since levels have been at or below method detection limits (Pojana et al., 2004; Popenoe et al., 1994; Fendinger et al., 1992). Partitioning to sediments has only been reported under controlled laboratory conditions which demonstrated that AS/AES and LAS have a similar high tendency to partition to sediments. Distribution coefficients (Kd) for AS/AES range from 70 to 350 L kg−1, and increases with alkyl chain-length from C12 to C14 (LAS C12 = 330 L kg− 1) (Marchesi et al., 1991). Despite similar use volume and partitioning behavior to LAS, there have been no reported field measurements of either AS or AES in sediments to date. The paucity of field measurements and, in particular, field sediment measurements, may be partially attributed to: the general complex nature of commercial surfactant mixtures, the fact that commercially produced AES contain a mixture of as many as 36 homologues with the composition reflecting the aliphatic alcohol feedstock selection and the average degree of ethoxylation, and lack of suitable analytical methodology. The objective of the current work is four-fold. First, development of an appropriately sensitive, selective method for measuring AS/AES residues in sediments. This experimental work combines simple solvent extraction with the instrumental approach first described by Popenoe et al. (1994) and later refined by Cano et al. (1996) to measure homologue-specific distributions of AS/AES. Given the broad range of congeners within a commercial AS/AES mixture and the dependence of both the partition coefficient (Marchesi et al., 1991) and

toxicity (Dyer et al., 2000) on the homologue distribution, a feasible and suitable analytical method was required to provide homologue-specific data for AS/ AES surfactants in sediments. The method developed was designed to be simple, selective and accessible, utilizing LC/MS rather than the more expensive MS/MS approach. Due to the highly variable composition of sediments and the potential for interference, samples from three structurally different watersheds were examined, which included expected relative low, medium and high levels of AS/AES from consumer products via wastewater treatment effluent. Second, assessment of sample stability under different temperature conditions and formalin concentrations. Third, characterization and quantification of the distribution of AS/AES homologues from three sites. Fourth, preliminary assessment of the potential hazard to sediment dependent organisms where the highest potential for exposure to these surfactants is expected for each individual homologue, as well as to the entire mixture for each of these sites. 2. Materials and methods 2.1. Reagents and apparatus A reference commercial AS/AES mixture was characterized by electrospray mass spectrometry relative to a subset of custom synthesized single chain length pure ethoxymers each with purities of > 97% as determined by mass spectrometry and NMR. This mixture was subsequently used for all quantitation and spiking experiments and contained detectable levels of the entire homologue distribution of C12–C15 with 0–8 ethoxylate units. Individual homologue concentrations ranging from approximately 10% (w/w) for tridecyl sulfate to approximately 0.3% (w/w) for the tridecyl octaethoxysulfate ethoxymer. Deuterated sodium dodecyl sulfate (d25 SDS) was used as an internal standard and obtained from Cambridge Isotopes (Cambridge, MA, USA). All solvents, reagent water and ammonium acetate were HPLC grade. Formalin (37% formaldehyde solution) was used for all preservation experiments. Because of the ubiquitous use of AS/AES in the manufacturing and cleaning of many commonly used laboratory items, an extensive pre-cleaning procedure was applied to all critical lab-ware, including centrifuge tubes, laboratory vials and autosampler vials. The precleaning procedure for durable glassware included sequential rinses with hot (∼ 55 °C) water, 1 : 1 hydrochloric acid/water, Milli-Q water and high purity methanol with repeat rinses with the last two solvents.

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New disposable lab-ware was cleaned using only the sequential water/methanol rinses and discarded after use. Acrodisc® CR filter (Pall Corporation, East Hills, NY, USA), was found to be suitably clean and was used without pre-treatment. To the extent possible, products containing AS/AES were excluded from the laboratory. To assess laboratory contamination, a method reagent blank was carried through the entire process with each set of samples. Acceptable method blanks contained less than 4 ng of total AS/AES per sample (approximately 0.5 ng g− 1). 2.2. Sample description Approximately 1 liter samples of sediment were collected by surface drag-sampling of the top 2–5 cm of sediment. Drag samples from several square meters were combined to make the 1 L final sample from each river. Overlying water was decanted before compositing the separate drag samples, the composite was split into preserved (3% or 8% v/v formalin), preservation occurred in the field immediately after collection, typically within 2–3 min, and unpreserved portions and the sediments were transported cold (2–8 °C) to the laboratory for analysis. Samples were collected from three different locations during the autumn of 2000 which corresponded to three expected levels of AS/AES; low, medium, and high exposure. The first sample, representing low expected exposure, was obtained from a containment pond located at the University of Mississippi Biological Field Station (“Mississippi Pond”) in Abbeville, Mississippi, USA (without any known wastewater influent). A medium exposure sample was collected from the East Fork of the Little Miami River (“Little Miami River”), near Perrintown, Ohio, USA, approximately 5 km downstream from a municipal activated sludge wastewater treatment plant and the high exposure sample was collected from Town Creek in Glendale, OH (“Town Creek”) approximately 100 m downstream from the discharge of a small municipal trickling filter wastewater treatment plant which was studied previously (Belanger et al., 2004). Dilution of effluent into Town Creek was visually estimated as 1:2 or less. For sediment characteristics at these three sites see Table 1. 2.3. Sample preparation Some compaction of the sediment was observed during transport to the laboratory and prior to further handling the separated water was decanted. The solids

315

Table 1 Characteristics and classification of sediment samples from the three sites Parameter

Mississippi Pond

Little Miami River

Glendale Town Creek

Total water (%) Cation exchange capacity (meq 100 g− 1) Percent total organic carbon (solids) (foc) Sand (%) Silt (%) Clay (%) Classification

89.6 7.8

58.4 22

24.4 0.5

1.7

1.3

1.6

44 45 11 Loam

52 17 31 Sand clay loam

81 10 9 Loamy sand

were mixed under oxic conditions by hand and a 30–40 g sub-sample was transferred to a tared, pre-cleaned polypropylene centrifuge tube, excluding any large debris in the process. For spike recovery experiments, samples were fortified with an AS/AES stock solution at this point, mixed by hand and allowed to equilibrate for >2 h. Samples (30–40 g wet weight) were prepared for extraction by first centrifuging at ∼2200 G (3750 rpm) for 5 min. The separated interstitial water was decanted and reserved for analysis if needed. The remaining solids were freeze-dried to a free flowing powder and the dry material was transferred to 200 mL glass centrifuge bottles for extraction. Samples were extracted by covering the solids with 20–30 mL of methanol, automated shaking for 20 min and sonicating for ten additional minutes. The resulting mixture was centrifuged and the clarified methanol was decanted into a separate container. The methanol extraction was repeated a second time and the combined extracts were evaporated to dryness under nitrogen. The residue was re-dispersed with sonication into 1 mL of 1:1 methanol/water and internal standard (2.4 μg d25 SDS), vortexed and filtered through an Acrodisc CR filter into an autosampler vial for analysis. Due to the rapid biodegradability of AS/AES (Guckert et al., 1996; Popenoe et al., 1994; Fendinger et al., 1992), sample stability was a particular concern. To assess stability, samples of the Town Creek and the Little Miami River sediment were evaluated under various storage conditions. Samples were amended in the laboratory with 0.3–1.5 μg AS/AES per gram dry sediment and well mixed before subdividing. One fraction was held at room temperature (∼ 20 °C) without preservative, a second was preserved with 3% (v/v) formalin and maintained at 4 °C, while a third was

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preserved with 8% formalin and held at ∼ 20 °C, and again preservation occurred within minutes. Previous work in wastewater samples (Fendinger et al., 1992) has demonstrated that sample preservation is of critical concern for accurate assessment of AS/AES levels. In those and subsequent studies (Popenoe et al., 1994), 8% v/v formalin was used to minimize degradation of AS and AES. Based on those studies, 8% (v/v) formalin at room temperature (∼ 20 °C), 3% (v/v) formalin in refrigerated samples, and unpreserved samples (no formalin) at room temperature (∼ 20 °C) were evaluated. The lower level of formalin was desired to minimize potential interferences, lower worker exposure in the laboratory, and also to simplify shipping and transportation logistics. Samples from the Little Miami River (medium exposed) and Town Creek (high exposed) sites were used to assess different storage conditions for sediments. Individual sub-samples from the sites were spiked in the laboratory with the commercial mixture of AS/AES at approximately 2 μg g− 1 on a dry sediment basis and well mixed. The resulting spiked sediments preserved with either ‘3% formalin at 4 °C’ or ‘8% formalin at 20 °C’ were held for up to 14 days to assess storage stability. Duplicate samples were removed periodically, immediately lyophilized and extracted. The observed concentrations were normalized to the time zero (t0) = 1 concentration to provide a relative response measure. The suitability of the method was assessed through replicate analyses (n = 2–4) and spike recovery experiments performed on all three sediments. To determine appropriate spiking levels, samples were analyzed to assess the background signal and evaluate the homologue distribution of AS/ AES from the specific sites.

of AS/AES which may occur in the mobile phase and deposit on the head of the column during reequilibration. The mass spectrometer was operated as a single quadrupole analyzer in negative ion electrospray mode with a source temperature of 150 °C and a cone voltage of 25 V, scanning from m/z 258–700 Da over 2 s. By performing the analysis in this manner, the methodology can be directly transferred to less expensive, bench top mass selective detectors currently available. Studies to assess the benefit of an MS/MS approach found the LC/ MS to have comparable sensitivity with no significant loss of selectivity (Popenoe et al., 1994). In addition, previous studies of other anionic ethoxysulfate surfactants have found that MS/MS CID fragmentation gave poor reproducibility of daughter ions (Schröder, 2001) which may contribute to lower precision when operating in MS/MS mode. Minor improvements in sensitivity were achieved using selected ion recording mode due to the need to monitor 36 discrete masses, so all data was collected in scanning mode. Each homologue was quantified based on peak area using the internal standard approach, normalizing to the area of a 2 μg mL d25 SDS− 1 internal standard added to samples and standards alike. The use of the internal standard was critical for accurate quantitation as it minimized effects due to instrument drift. Periodic standard addition to a final sample extract was used to verify peak location and assess signal suppression. No significant peak suppression was observed in extracts from the various sediment matrices.

2.4. Instrumentation

Assessing organism exposure levels in sediment systems depends on the bioavailable fraction of a compound which can be predicted using an EqP approach (see Eq. (1)). The partition coefficient for each congener was estimated using partition coefficients (Koc) as described by Marchesi et al. (1991), and applying the coefficient for a given alkyl chain-length across the ethoxylate distribution. For sediment dwelling organisms, the predicted no effect concentration of AS/AES (PNECsediment) is related to the bioavailable fraction as described by DiToro (1991):

All analyses were performed on a VG Quattro Mass Spectrometer (Micromass, Beverly, MA, USA) equipped with an electrospray interface coupled to a Hewlett Packard Model 1090 liquid chromatograph (Agilent Technologies, Palo Alto, CA). Separations were performed using an acetonitrile/water/0.3mM ammonium acetate mobile phase on a 250 mm × 2.0 mm Prodigy™ C8 5 μ column (Phenomenex, Torrance, CA, USA) and gradient elution. A 30-min linear gradient of 40–65% acetonitrile was used to elute all the compounds of interest, followed by a 10-min 80% acetonitrile purge. These conditions were modified from the previous work (Popenoe et al., 1994) to help reduce interferences and carryover from the complex sediment extracts and minimize buildup of extremely low levels

2.5. Predicted no effect concentrations for sediment dependent organisms

* PNEC PNECsediment ¼ foc* Koc aquatic

ð1Þ

where foc is the fraction of organic carbon in the sediment (see Table 1), Koc is the partition coefficient to organic carbon and PNECaquatic is the predicted aqueous

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no effect concentration. This approach was verified with Hyalella azteca and the anionic surfactant LAS by Cano et al. (1996), where the EqP approach was more consistent with the experimental data than the anionic surfactant adsorption model developed by Westall et al. (1999). By applying an EqP approach, measured sediment concentrations of AS/AES can be used to assess the hazard of AS/AES to sediment dependent organisms. Using a series of acute and chronic exposures to 18 single chain-length homologues of AS and AES, Dyer et al. (2000) demonstrated that C. dubia toxicity increased with alkyl chain-length and decreased with degree of ethoxylation. For congener mixtures with higher alkyl chain lengths and low degrees of ethoxylation, limited water solubility appeared to limit toxicity. Seventy percent of the variance in the chronic data was addressed with a quadratic Eq. (2) (Dyer et al., 2000) relating toxicity to alkyl chain-length and EO units. In addition, a chronic toxicity test (7 days) with a mixture of four individual homologues indicated additivity of toxicity (Dyer et al., 2000):

317

3. Results 3.1. Sample characteristics Visually, the Mississippi containment pond sediment had a darker, silty appearance with significant amounts of plant matter. The Little Miami River sample was visually intermediate in composition with little debris and a silty character. The Glendale (Town Creek) sample was very heterogeneous with significant amounts of sand and gravel, mixed with silt and small shells. Sub-samples of unpreserved sediments were characterized by Soil Analytical Services, Inc. (College Station, TX) and are described in Table 1. The characterization was consistent with the visual assessment. Texture characteristics show a mixture of sand, clay and loam which provides a basis for evaluating method performance in a common variety of sample matrices. Characteristics of sediment from rivers may vary depending on sample technique, site, and season. 3.2. Storage stability

2

logendpoint ¼ ðalkyl chain lengthÞ þ ðalkyl chain lengthÞ þ ðEO unitsÞ þ intercept

ð2Þ

The hazard ratio for each congener was determined by comparing the predicted pore water concentrations to the predicted chronic no effect concentration per congener derived by Dyer et al. (2000). Further, Dyer et al. (2000) illustrated additive toxicity for AES congeners in a mixture. Several reviews for risk characterization of AS and AES have been conducted (Van De Plassche et al., 1999; HERA, 2002; HERA, 2004) and all have indicated that invertebrates are the most sensitive taxa in which to derive a PNEC. Further, ecosystem NOECs based on mesocosm experiments conducted with C12 AS and C14.5–2.17 AES (Belanger et al., 1995a,b; 2004) and C13.2–3AES (Lizotte et al., 2002) indicate that PNECs based on the Dyer et al. (2000) Quantitative Structure–Activity Relationship (QSAR) for AS/AES would be conservative. In the results we have not ascribed an assessment factor. The magnitude of assessment factors are dependent upon the regulatory jurisdictions and are context depended assessments, therefore we did not ascribe any assessment factor— rather we report the margin of safety from the predicted exposure to the predicted no effect concentrations in this preliminary hazard screening from three sites in the state of Ohio, USA.

Storage stability was evaluated sediment samples amended with approximately 2 μg/g of the commercial AS/AES mixture. For unpreserved samples (no formalin at ∼ 20 °C), the average relative response decreased to 0.91 after 3 days and to 0.43 after fourteen days, corresponding to a 57% loss over the 14-day period. Variation between sub-samples on a given day was significant with relative standard deviations of 42–77%. This rapid decrease in concentrations of unpreserved samples is consistent with previous studies of wastewater samples (Fendinger et al., 1992).

Table 2 Sample storage stability at 2 μg g− 1 level, under three different preparations over 14 days (n = 2–4) Preparation

Variable

Day 0

Day 3

Day 7

Day 14

Unpreserved at ∼ 20 °C

Recovery Crosshomologue RSD Recovery Crosshomologue RSD Recovery Crosshomologue RSD

1.00

0.91 (42%)

0.60 (52%)

0.43 (77%)

1.00

1.14 (8%)

1.32 (39%)

1.13 (21%)

1.00 (16%)

–

0.86 (12%)

0.79 (11%)

8% formalin at ∼ 20 °C

3% formalin at 4 °C

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The individual homologue data indicates that stability of non-ethoxylated homologues (AS) trended lower than for the ethoxylated materials and within the AS family the shorter alkyl chain materials were less stable than the longer chain materials. No other significant trends were noted for the various homologues with recoveries after seven days at 4 °C ranging from 71% to 112% and from 64% to 95% after 14 days. The total amount of AS/AES and distribution of the

The 8% formalin at room temperature (∼20 °C) option had no loss of surfactant material over the 14 days. In fact, the average recovery increased with time indicating anticipated analytical interference and subsequent potential analytical imprecision using this option. Moreover, the cross-homologue recovery standard deviations were relatively high after one week (21– 39%), indicating that measured recoveries were not consistent across the distribution of homologs (Table 2). 0.025 0.020

Mississippi Field Station Pond Total AS/AES = 0.034 µg·g-1

0.015 0.010 0.005

LOD = 0.0002

0.000 0.025

-1

µg·g (dry weight)

0.020 Little Miami River -1 Total AS/AES = 0.025 µg·g

0.015 0.010 0.005

LOD = 0.0002

0.000 0.025 0.020 Town Creek Total AS/AES = 0.117 µg·g-1

0.015 0.010

LOD = 0.0002

0.005

C15E7S

C15E5S

C15E3S

C15E1S

C14E8S

C14E6S

C14E4S

C14E2S

C14E0S

C13E7S

C13E5S

C13E3S

C13E1S

C12E8S

C12E6S

C12E4S

C12E2S

C12E0S

0.000

Fig. 1. Ambient levels of AS/AES homologues from a presumably less exposed site (Mississippi Pond), a slightly higher exposed site (East Fork Little Miami River) far downstream from a wastewater treatment plant discharge and a significantly exposed site (Town Creek) directly downstream from a trickling filter treatment plant.

H. Sanderson et al. / Science of the Total Environment 367 (2006) 312–323 Table 3 Spike recovery (n = 4)

319

1). The frequency of detected homologues where higher in the Little Miami River (36%) than in the Mississippi Pond (22%) of the total 36 AS/AES homologues (which were all detected in the Town Creek).

Nominal spike level

Spike recovery (%) Mississippi Pond

Little Miami River

Glendale Town Creek

0.2 μg g− 1 0.6 μg g− 1 2.0 μg g− 1

106 – 63

91, 106, [203] 72 , 89 57, 63

– – 35, 61, 68, 77

The overall mean recovery = 74% (±21% SD, n = 12). The number in brackets is an assumed outlier.

various homologues found is displayed in Fig. 1. Surprisingly, we found the highest observed level (0.021 μg g− 1), among all three sites, of AS (C12E0S) in the Mississippi pond, and the total amount of AS/AES in this presumed lowest exposed site had a slightly higher total AS/AES concentration than the assumed medium site at Little Miami River down stream from a sewage treatment plant with activated sludge processing (0.034 μg g− 1 and 0.025 μg g− 1, respectively, see Fig. Background

3.3. Analytical evaluation Method precision on un-spiked samples was evaluated (n = 4) using the Town Creek sample. Four replicate analyses gave an average value of 0.073 ± 0.039 μg g− 1 coefficient of variation CV = 54% on a dry weight basis. Based on the initial analyses, spike levels were established to be approximately 10–100 times the un-spiked signal. The spike addition was added to the preserved samples and allowed to equilibrate for 3–5 h before processing the samples. Results of the spike recovery experiments are summarized in Table 3. At the lowest spike level one analysis indicated anomalously high recovery (203%) indicating that this is an outlier. The anomaly is partially due to the Spiked

19.9

*

C15E0S

m/z 307.3

16.7 Linear 16.5

Relative Intensity

Branched

*

13.1

C14E0S

m/z 293.3

13.4

11.3

*

C13E0S

m/z 279.3 10.1

10.1

* 20.4

m/z 265.3 10

15

20

Retention Time (min)

25

7.9

C12E0S 10

15

20

25

Retention Time (min)

Fig. 2. C12–C15 Alkyl Sulfate ion chromatograms of Mississippi Pond sediment extract before and after fortification with AS/AES mixture at 0.2 μg g− 1. The expected position (or observed peak) for the homologue in the background sample is noted with an asterisk.

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proximity of the spike level to the detection limit, leading to high relative uncertainty for the less abundant homologues and also due to variability in the background levels found in the sample itself where replicate analyses gave values of 0.025 and 0.157 μg g− 1. The overall mean recovery = 74 ± 21% standard deviation SD, n = 12. Spike additions were performed prior to centrifugation and the AS/AES will likely partition between the interstitial water and residual solids. To estimate the losses associated with discarding the interstitial water, separated water from three spiked samples was decanted after centrifuging and analyzed by solid phase extraction followed by HPLC/MS, as described previously (Pope-

noe et al., 1994). In all three samples, less than 10% of the total AS/AES was in the interstitial water. An example of a spiked and background chromatogram for the C12–C15 alkyl sulfate homologues is shown in Fig. 2 demonstrating that minimal interferences were seen in the samples. The chromatographic separation is sufficient to discriminate between linear and branched components which may occur for each homologue and all quantitation included the sum of the linear and branched materials. To assess possible signal enhancement or suppression, a spike was also added to the final extract. No significant enhancement or suppression (< 20%) was observed, indicating that the LC/MS approach is suitable even for complex sediment extracts.

0.006

PECPorewater / PNECSediment

0.005

0.004

0.003

0.002

C15E8S

Alkyl-Ethoxylate Sulfate Chainlength

C15E0S C15E1S C15E2S C15E3S C15E4S C15E5S C15E6S C15E7S

C14E0S C14E1S C14E2S C14E3S C14E4S C14E5S C14E6S C14E7S C14E8S

C13E0S C13E1S C13E2S C13E3S C13E4S C13E5S C13E6S C13E7S C13E8S

C12E0S C12E1S C12E2S C12E3S C12E4S C12E5S C12E6S C12E7S C12E8S

0.001

Tow

Litt

Mis

nC reek ippi

le M

siss

iam

i

Fig. 3. AS/AES congeners PEC/PNEC for Ceriodaphnia dubia. The Mississippi Field Station was a low exposed AS/AES site, total mixture hazard ratio (PEC/PNEC) = 0.007. East Fork Little Miami River site is downstream a municipal activated sludge sewage treatment plant (medium exposed), total mixture hazard ratio = 0.008. Town Creek site directly below the outfall of the Glendale municipal trickling filter wastewater treatment plant (high exposure), total hazard ratio = 0.024.

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3.4. Hazard screening Fig. 3 illustrates the Predicted Environmental Concentration (porewater) divided by the Predicted No Effect Concentrations for sediment dependent organisms (PECporewater/PNECsediment) values for all the measured congeners of alkyl ethoxysulfate. The greatest hazard ratio are found immediately downstream from the trickling filter treatment plant discharge in Town Creek with ratios for C12E0S, C13E0S and C14E0S of approximately 0.004, 0.005 and 0.003, respectively. Samples from the other two sites also demonstrate that the non-ethoxylated congeners (AS) have the largest hazard ratios (0.003–0.005). Assuming concentrationaddition for AES mixture toxicity, as shown by Dyer et al. (2000), the summation of the hazard ratios over all congeners yields mixture hazard quotients of 0.024, 0.008 and 0.007 for Town Creek, East Fork of the Miami River, and the Mississippi Field Station Pond, respectively, indicating that the levels of alkyl ethoxysulfates measured will not pose a significant hazard to sediment dwelling organisms at these sites. The total mixture hazard ration was higher in the Little Miami River than the Mississippi Pond, despite lower total concentration due to higher frequency of detectable homologues in the Little Miami River. The margin of safety is 200–300 for the individual homologues, and 40–150 for the total mixture at these sites with this model, which has been found to be conservative relative to stream mesocosm studies (Belanger et al., 1995a,b, 2004; Lizotte et al., 2002), which usually carry an assessment factor of 1. 4. Discussion As anticipated, the Glendale sampling site at the Town Creek, located directly below a wastewater treatment plant discharge had readily detectable levels of a broad distribution of homologues representative of typical commercial blends of AS/AES. Selecting a lower level of formalin (3% v/v) and keeping samples cool (4 °C) appears to provide suitable preservation and provides the lowest cross-homologue variation, with a recovery after 14 days of 79% (± 11% RSD), see Table 2. The Glendale Town Creek site is immediately downstream from the discharge of a trickling filter wastewater treatment plant receiving primarily domestic inputs. This treatment facility was studied previously (McAvoy et al., 1998) and demonstrated removals of surfactants in the range of 78–96%, discharging with minimal dilution into Town Creek. For the Town Creek site, an average composition for the AS/AES found in

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the sediment corresponds to a C13.3E2.0S material. The distribution of AS/AES materials observed in the sample is consistent with those reported in wastewater (Popenoe et al., 1994) and is representative of a synthetic-sourced alcohol feedstock which includes both even (C12 and C14) and odd (C13 and C15) alkyl chain-lengths (Biermann et al., 1986). The dominance of alkyl sulfates and lower ethoxylates is also consistent with many commercial mixtures (Biermann et al., 1986) and the profiles observed in wastewater in both the United States (McAvoy et al., 1998; Popenoe et al., 1994) and Europe (Matthijs et al., 1999). The average AES distribution of C13.3E2.0S in this study is only slightly different from those observed in wastewater treatment plant effluents in Europe where an average distribution of C12.5EO3.4S was reported (Matthijs et al., 1999) and also consistent with the average AES distribution of C13.1EO1.6S observed in the effluent from wastewater treatment plants in the United States (McAvoy et al., 1998). In contrast with the high exposure site, both other sites lack the odd alkyl chain-length components and the observed pattern is not representative of profiles previously reported in wastewater effluent (Matthijs et al., 1999; McAvoy et al., 1998; Popenoe et al., 1994; Fendinger et al., 1992) which include significant portions of both C13 and C15 materials. The Mississippi pond was expected to be a low exposure site with no identifiable inputs which may contribute surfactants. Similarly, the Little Miami River site was several miles below any wastewater discharge and in a stream with relatively large dilution and would be expected to have low exposure and thus little or no measurable levels of AS/AES due to both dilution and in-stream biodegradation. The combined AS/AES level in the Mississippi pond was 0.034 μg g− 1 with an average composition of C12.3EO0.5S while the Little Miami River site contained 0.025 μg g − 1 with an average composition of C12.6EO0.7S. The subset of homologues observed in both these sites was more typical of an AS/AES blend commonly used in personal care products such as shampoo, soaps, etc., typically referred to as laureth sulfate (Biermann et al., 1986). It is not possible to determine the source of this unusual distribution in the samples presumed to have little or no sources of AS/ AES. Laboratory control samples show no similar patterns indicating that the measured levels are either due to a source other than typical wastewater discharge or potentially a low level contamination during sampling as previously observed (Popenoe et al., 1994). Non-point sources of surfactants to aquatic environments include; the use of biosolids containing

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surfactant residues as fertilizers on adjacent farmland leading to run-off, leaking septic tanks systems, stormrun-off, as well as, other products (pesticides, dyes, textile, etc.) that may contain AS/AES, and finally naturally produced sulphonated organic compounds (AS) (Schwitzgueble et al., 2001). Analyses of replicate sub-samples of sediment indicate that quantitation based on the summation of AS/AES homologues can lead to high variability in the calculated concentration. Four replicate sub-samples of Town Creek sediment show similar homologue distributions. However the cumulative concentration shows high variability with a relative standard deviation of 55%. Spike recoveries are consistent with reported values for other studies where anthropogenic activity marker compounds were being measured in river sediments (Kronimus et al., 2004). This variability is due to both the intrinsic heterogeneity of the sediment and the cumulative uncertainty introduced when a large number of congeners are measured near their detection limit. Individual congener detection limits were estimated to be approximately 0.001 μg g− 1 and several congeners are observed at or near this level. Improved precision is seen in spiked samples where levels of the various congeners are all significantly above the detection limit. 5. Conclusions A cost-effective, congener-specific method for measuring alkyl ethoxysulfate mixtures in sediments was developed and applied to sediment samples from low, medium, and high anticipated exposure. Low levels of alkyl ethoxysulfates were found in all samples, with the highest levels observed in the site immediately below the outfall of a trickling filter treatment plant. The observations and the congener fingerprints observed in the samples are consistent with the previously reported data from wastewater treatment plants in both the United States and Europe (Matthijs et al., 1999; McAvoy et al., 1998; Popenoe et al., 1994; Fendinger et al., 1992). Total AS/AES concentrations from presumably low exposure sites (Mississippi Pond and Little Miami River) were approximately a factor of four lower than the high exposure site (Town Creek) and composed of a significantly different congener fingerprint, indicating a different source of the AS/AES. Sample preservation conditions using 3% formalin and refrigeration were adequate for up to a week of storage before analysis. As the congener distributions vary between sites traditional averaging approaches are not amenable, however, combining congener-specific analytical meth-

ods with congener-specific SARs permits a more relevant assessment of the safety of complex mixtures of alkyl ethoxysulfates in receiving waters. While concentrations observed at all three sites were below levels (PECporewater/PNECtotal mixture = 0.007–0.024) expected to induce a chronic toxic effect toward sediment dwelling organisms, a more comprehensive assessment is required to evaluate a wider variety of exposure situations. Limited data on the partitioning of anionic surfactants to sediments exists and there is a need for additional field and structure–activity based approaches to assessing partitioning in sediments and toxicity across a more diverse set of sediment dwelling organisms and sites (Carignan and Villard, 2002). Additional work is warranted to evaluate different discharge and sediment exposure scenarios to broaden the understanding of the fate and effects in sediments of surface active compounds like alkyl ethoxysulfates used widely as consumer product ingredients. Acknowledgments The authors thank the members of the Soap and Detergent Association's Surfactant Sediments Task Force and Dennis Hooton of Midwest Research Institute for their assistance in planning and carrying out this work, and Barry Gillespie and Matt Moore for providing the sediment sample from the University of Mississippi Biological Field Station. References Belanger SE, Rupe KL, Bausch RG. Response of invertebrates and fish to alkyl sulfate and alkyl ethoxylate sulfate anionic surfactants during chronic exposure. Bull Environ Contam Toxicol 1995a;55:751–8. Belanger SE, Meiers EM, Bausch RG. Direct and indirect ecotoxicological effects of alkyl sulfate and alkyl ethoxysulfate on macroinvertebrates in stream mesocosms. Aquat Toxicol 1995b;33:65–87. Belanger SE, Lee DM, Bowling JW, LeBlanc EM. Responses of periphyton and invertebrates to a tetradecyl–pentadecyl sulfate mixture in stream mesocosms. Environ Toxicol Chem 2004;23:2202–13. Biermann M, Lange F, Piorr R, Ploog U, Rutzen H, Schindler J, et al. Synthesis of surfactants. In: Falbe J, editor. Surfactants in consumer products. Heidelberg, Germany: Springer-Verlag; 1986. Cano ML, Dyer SD, DeCarvalho AJ. Effect of sediment organic carbon on the toxicity of a surfactant to Hyalella azteca. Environ Toxicol Chem 1996;15:1411–7. Carignan V, Villard MA. Selecting indicator species to monitor ecological integrity: a review. Environ Monit Assess 2002;78:45–61. DiToro DM. Technical basis for establishing sediment quality criteria for nonionic organic chemicals using equilibrium partitioning. Environ Toxicol Chem 1991;10:1541–83.

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