Environ. Sci. Technol. 2002, 36, 3678-3682
Nonylphenol in Anaerobically Digested Sewage Sludge from New York State SCOTT W. PRYOR,† A N T H O N Y G . H A Y , * ,‡,§ A N D LARRY P. WALKER† Department of Biological and Environmental Engineering, Department of Microbiology, and the Institute for Comparative and Environmental Toxicology, Cornell University, Ithaca, New York 14853-5701
Nonylphenols (NPs) have been identified as xenoestrogens and have been found at high concentrations in Canadian and European biosolids. While nonylphenol polyethoxylates (NPEOs) are being phased out and regulated in several European countries, there is currently no regulation of these compounds in the United States, and little information is available concerning the presence of NPs in U.S. biosolids. Anaerobically digested sewage sludge from five wastewater treatment plants in central New York State was analyzed for the presence of NPs. Samples were taken from treatment plants in both small municipalities and larger metropolitan areas with a range of industrial inputs. Samples were extracted via Soxhlet apparatus and analyzed by GC/MS. The various isomers of NP were summed yielding total NP concentrations as high as 1840 mg/kg with a mean of 1500 mg/kg on a dry weight basis. These values are two to five times as high as previously reported concentrations for U.S. and Canadian biosolids from plants using similar treatment schemes.
Introduction Nonylphenols (NPs) are degradation products of a class of nonionic surfactants known as nonylphenol polyethoxylates (NPEOs). They form a complex mixture of isomers that have a branched nine-carbon alkyl chain attached to a phenolic ring. Isomers are distinguished by the branching pattern of the alkyl chain, but both NP and NPEOs are manufactured as mixtures of the various isomers. The parent compounds are found in many domestic and industrial products with national use in the United States estimated at 170 million kilograms annually (1). The polyethoxylate chain, initially comprised of from 1 to 20 ethoxy units, of NPEOs is shortened during aerobic and anaerobic wastewater treatment processes. Nonylphenol mono- and diethoxylates and the more hydrophobic metabolite nonylphenol preferentially adsorb to the organic matter in the waste stream and are removed with the sludge. The shortened ethoxylate chain is subsequently removed during anaerobic sludge digestion yielding NP and therefore higher NP concentrations in anaerobically digested sludge (ADS) (2). Resultant ADS concentrations are higher than found in other environmental matrices including sludge that has not been anaerobically digested (2, 3). * Corresponding author phone: (607)255-8471; fax: (607)255-3904; e-mail:
[email protected]. † Department of Biological and Environmental Engineering. ‡ Department of Microbiology. § Institute for Comparative and Environmental Toxicology. 3678
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An increasingly common disposal practice for municipal sludges is agricultural land application. Annually 180 000 dry tons of biosolids from New York State, 50% of total production, are land applied either directly or following additional stabilization processes (primarily composting or heat drying) (4). Currently there is no regulation regarding the concentration of NP in sludges applied to U.S. agricultural soils, and there is little information available on levels of NP in U.S. sludges or soils where sludge has been applied. In Denmark, a total concentration limit of 10 mg/kg (NPs together with nonylphenol mono- and diethoxylates) has been set for sludge to be spread on agricultural soils (5). Previous reports of NP concentrations in biosolids come primarily from Europe and Canada with reported values ranging between 22 and 4000 mg/kg (3). The most extensive and recent analysis of sludges and effluents from Canadian treatment plants showed a mean NP concentration of 330 mg/kg for the eight plants utilizing secondary treatment (activated sludge or rotating biological contactors) and anaerobic sludge digestion (6). The mean for all sludges analyzed (n ) 16) was 225 mg/kg. Little data is available on NP concentrations in U.S. sludges. Chalaux et al. reported a concentration of 370 mg/kg from an activated sludge plant with anaerobic sludge digestion in Los Angeles (7), while a more recent report showed a mean NP concentration of 754 mg/kg in five California ADS samples (8). Concentrations of NP in ADS from five upstate New York municipalities are reported here.
Experimental Section Anaerobically digested biosolids samples (1-10 kg) were collected from five wastewater treatment plants in New York State (see Table 1) between 02/00-07/00. Samples were stored in Ziploc freezer bags at -20 °C prior to analysis. Clean bags were extracted to test for the presence of contaminating background NP but none was detected. Nonhomogenized samples (20-30 g) were freeze-dried to approximately 5% moisture content (wet basis) before extraction. The surrogate and internal standards used in the analyses were 2,4,6-trimethylphenol (TMP) and phenyldodecane (PDD) (Aldrich Chemical), respectively (9). All standard solutions were prepared in ethyl acetate. Surrogate standard solution was added following freeze-drying, while the internal standard was added just prior to GC/MS analysis. Anhydrous magnesium sulfate was added at an approximate volumetric ratio of 1:2 (MgSO4:sample) before extraction. Triplicate samples (2-3 g, dry weight) were Soxhlet extracted for 16 h using ethyl acetate as the eluting solvent. Extracts were brought to 100 mL in a volumetric flask before the addition of PDD to 10 mg/L. Final extract samples were analyzed by GC/MS using an HP 6890 GC equipped with an HP-5MS column (5% phenyl methyl siloxane 30 m × 0.25 mm, 0.25 µm film thickness) using helium as the carrier gas. The oven temperature program used was as follows: 60 °C (hold for 1 min) to 160 °C (hold for 3 min) at 20 °C per min, 160 °C to 165 °C at 1 °C per min, 165 °C to 240 °C (hold for 10 min) at 20 °C per min, and 240 °C to 300 °C (hold for 2 min) at 60 °C per min. Samples of 1 µL were injected in splitless mode with an injector temperature of 250 °C. The detector used was an HP 5973 MSD with quadrapole and source settings of 150 °C and 230 °C, respectively. Concentrations were quantified against a four-point linear standard curve (R2 ) 0.998) of nonylphenol (Acros Organics, New Jersey) using the sum of peak areas for the ions (m/z+) 135 and 149 (9). A second NP standard (Schenectady 10.1021/es015546f CCC: $22.00
2002 American Chemical Society Published on Web 07/24/2002
TABLE 1. Operating Characteristics and Major Industries for Sampling Sites location and industry
plant flowa
treatment
biosolids production
Syracuse pharmaceuticals metal plating auto parts manufacturing Ithaca university gear/bearing manufacturer Cortland filter manufacturer power tool manufacturer monofilament manufacturer shampoo/soap product packaging Cayuga Heights auto parts manufacturer Monroe County NW Quadrant no industry, domestic waste only
80 mgd
activated sludge, anaerobic digestion
150 wet tons/day
chemically stabilized, land applied
10 mgd
activated sludge, anaerobic digestion
15 wet tons/day
landfill
7 mgd
activated sludge, anaerobic digestion
1.5 wet tons/day
landfill
2 mgd
trickling filter, anaerobic digestion activated sludge anaerobic digestion
4 wet tons/day
composted, land applied
1 dry ton/day
composted, land applied
a
18 mgd
sludge fate
Millions of gallons per day.
TABLE 2. NP Concentrations (Dry Weight Basis) in Municipal Biosolids location Syracusea Ithacab Cortlanda Cayuga Heightsb Monroe County NW Quadranta
mg/kgc 1840 1790 1480 1240 1130
TABLE 3. NP Concentrations (Dry Weight Basis) for Analytical Reference Check Samples
SD 61 68 38 161 188
a n ) 3. b n ) 6. c Concentrations corrected for extraction efficiency (91-105%).
International (SI)- Schenectady, NY) was checked for quantification and the standard curves of the different standards were compared. The two curves predicted each other to within 10% for the range of NP concentrations seen in the samples studied. It was therefore deemed unnecessary to quantify individual peaks using FID-normalized response factors as has been suggested by Isobe et al. (10). Surrogate and internal standards were quantified using the ions (m/z+) 121 and 136, and 92, respectively. All concentrations were corrected for TMP extraction efficiency (91-105%) and normalized with the internal standard, PDD.
Results Table 2 shows the concentrations of NP found in extracted ADS. Significant concentrations were detected in all samples with a mean concentration of 1500 mg/kg for all sites. Two sites (Ithaca and Cayuga Heights) were sampled during both winter and summer months. As there has been a temperature dependence noted for microbial degradation of NP in activated sludge treatment (11) and soil microcosms (12), lower concentrations were expected for the summer months. Average NP concentrations were found to be slightly lower for the summer samples, but differences were not significant at the 95% confidence level. Reported concentrations for these two sites are the mean of the triplicate extractions for both of the sampling periods (n ) 6). It was noted that the samples with a higher standard deviation (Cayuga Heights and Monroe County) appeared fibrous and did not have a uniform consistency after freeze-drying, while the other samples dried to a more homogeneous powder. As an analytical reference check, three ADS samples with previously determined NP concentrations were obtained from the Aquatic Ecosystem Protection Branch of the National Water Research Institute (NWRI) of Environment Canada. These samples were extracted concurrently with a NY ADS sample and quantified using the same procedure described
sampling location/date Toronto Main STP - 11/97 Toronto Main STP - 12/97 Guelph STP - 07/97 Syracuse, NY - 02/00 a
reported (13) mg/kg
measured mg/kg
96 220 390
312a
SD 23 33 40 242
333a 682b 1890a
n ) 3. b n ) 2.
above. The reference samples were originally extracted by NWRI using supercritical carbon dioxide fluid extraction (SFE) and in situ acetylation with samples of approximately 0.5 g. These extracts were passed through a silica gel column for cleanup and analyzed by GC/MS in SIM mode. Relative standard deviations for the previously determined concentrations were not given, although those for other samples tested with this method were typically (5% (13). Extraction efficiency for this method was determined to be 97% using samples spiked with up to 50 mg/kg NP (14). The previously determined NP concentrations of the reference check samples extracted with SFE were only 3066% (mean ) 51%) of those determined using Soxhlet extraction (Table 3). Discrepancies between values are likely due to differences in extraction methods. Optimized SFE has been shown to be superior to Soxhlet extraction in some cases (15, 16). However, supercritical carbon dioxide extraction requires additional cosolvents such as methanol in order to quantitatively extract polar compounds such as nonylphenol (15). The original analysis of the reference samples was completed using the method described by Lee and Peart (14). The method as described uses no cosolvent, and the operational parameters used were significantly different than the optimized parameters reported by Lin et al. (15). Spiked samples may show extraction efficiencies up to 10 times higher than heterogeneous environmental samples (17), explaining the high extraction efficiency reported for the method. SFE performed without using methanol as a cosolvent, however, recovered only 65% of the NP compared to the optimized extraction (15). The apparent discrepancy in the data between NP concentrations of reference samples is explained by the different extraction methods used. The extraction method used in this study has been reported to be more exhaustive than the SFE method originally used to analyze the reference samples (15). It is likely, therefore, that the reference NP concentrations were higher than reported by NWRI. Despite VOL. 36, NO. 17, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Representative chromatograms of a typical sludge extract and the Acros Chemical NP standard.
all peak heights with respect to the largest peak in the chromatogram (peak 11 using the Acros standard and peak 3 for the SI standard). Comparisons were made for peaks showing a higher degree of branching at the R-carbon (peaks 1-7) and those showing a lesser degree of branching at the R-carbon (peaks 8-12) (18). Paired t-tests were performed to examine the difference between the sludge extract and each standard. The Acros standard was shown to have a higher concentration of the peaks containing isomers with a lesser degree of branching (p ) 0.01). Similarly, those peaks containing the more branched isomers were less concentrated in the standard (p ) 0.023). Isomer distribution in the Schenectady International standard, however, was not significantly different from the sludge extract. In addition, no differences in isomer composition were seen between sludges taken from different locations or sampled during different times of year (data not shown). Decylphenols are a common contaminant in technical grade nonylphenol mixtures and elute from the GC column shortly after the nonylphenol isomers (Figure 1) (18). Comparison of the chromatograms shows that decylphenols were found in significantly (p < 0.001) greater proportion in sludge samples than in each of the NP standards.
Discussion
FIGURE 2. Representative chromatograms of a typical sludge extract and the Schenectady International NP standard. this discrepancy, the Syracuse sludge had a concentration of 200-500% higher than the reference sludges when all samples were concomitantly extracted using a Soxhlet apparatus. The mean concentration for all New York sludges tested was 250% higher than that of the Canadian reference samples. The chromatographic profile for ADS sample extracts appears to have different proportions than the NP standard chromatogram (Figure 1). Peaks eluting later from the GC column seem to be more concentrated in the NP standard, while those eluting earlier appear to be more concentrated in the sludge extract. Comparison with an NP standard from a different source (Schenectady International (SI)- Schenectady, NY), however, showed a more similar chromatographic profile (Figure 2). Further analysis was completed to explore this issue. Sludge extract chromatograms were compared with nonylphenol standards from both sources to examine the possibility of differential isomeric degradation in wastewater treatment processes. Assuming that the alkyl chain of the NPEOs in the influent waste stream has the same isomeric composition as commercially available NP and that all isomers are degraded and preferentially sorbed to biosolids equally well, the chromatographic profiles of the sludge extract and an NP standard should be identical. To gain a better perspective on the possibility of differential degradation, the mass spectra for the 12 peaks in the NP standard chromatogram were compared with mass spectra reported by Wheeler et al. (18), and the isomeric composition of each peak was assessed. Chromatograms for the NP standards and a sludge extract were compared by normalizing 3680
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Concentrations of NP in the New York anaerobically digested sludges examined ranged from approximately 1100-1800 mg/kg and were consistently higher than previously reported concentrations for U.S. and Canadian biosolids (3, 8). Reported values were in agreement with concentrations found in Swiss ADS prior to the ban on NPEOs in that country (19). One of the samples tested, Monroe County, came from a plant receiving only domestic inputs. NP concentrations in this sample were lower, though not statistically different, from plants treating more industrial waste, indicating that industrial inputs may not be the only significant source of NP in the region. Giger et al. quantified the significant contribution domestic inputs may have on NP levels in ADS by showing that NP concentrations dropped 75% within 2 years after a ban was enacted on NPEOs in fabric detergents (19). High concentrations of NP in municipal biosolids may indicate high concentrations in treatment plant effluents, thus increasing the risk to the aquatic environment. Data reported by Bennie et al. (6) was analyzed to determine the relationship between NP concentration in plant biosolids and effluent. The analysis shows a positive correlation between sludge and effluent NP concentrations from plants with secondary treatment and anaerobic sludge digestion (n ) 8, R2 ) 0.59, p ) 0.03). Effluent NP concentrations for U.S. treatment plants utilizing anaerobic digestion have not been widely reported; however, a recent study by the USGS found NP in more than 50% of the U.S. streams sampled (20). NP has been shown to exhibit toxic effects in fish, marine invertebrates (21-23), and mammals (24-26). It can also inhibit plant growth and be taken up in the roots and transported into shoots as a hydrophilic metabolite (27). As municipal biosolids are commonly applied to agricultural lands as a soil amendment, there is concern over the environmental and human toxicity of land applied sludge contaminants. Although acutely toxic to many marine organisms (21, 23, 28), its main mode of action in fish and other higher animals is as an endocrine disrupter (29, 30), competitively binding to estrogen receptors (31). The toxicity of NP to aquatic life has been fairly well documented, but little data is available showing what effect NP may have on the soil ecosystem. The limited data available concerning toxicity to terrestrial invertebrates shows EC50
(reproduction) values for the earthworm, Apporectodea calignosa, and the springtail, Folsomia fimentaria, of 14 and 66 mg/kg, respectively, and an EC10 of 3.4 mg/kg for the earthworm (32). Measured concentrations of NP in rivers generally fall well below the NOEC (no observable effects concentration) for aquatic species (3, 33). Soil concentrations, however, may be more significant as NP concentrations of approximately 2 mg/kg have been measured in sludge-amended soils in Switzerland and Canada (3). These concentrations are approaching the reported toxicity threshold for the earthworm and springtail. Average ADS NP concentrations reported here are 300-400% higher than the most recent and comprehensive study of Canadian sludges (6), suggesting the possibility of higher NP concentrations in U.S. agricultural soils receiving ADS. Assuming sludge with an NP concentration of 1500 mg/ kg was applied to a loam soil (bulk density 1.5 g/cm3) at a typical rate of 12 dry metric tons/ha (34) and tilled to 15 cm, the average NP concentration would be approximately 8 mg/ kg in a well-mixed soil. Such an application would theoretically result in soil NP concentrations approaching the EC50 values for the earthworm (32) and would be six times higher than the Estimated No Effects Value of 1.37 mg/kg established by Environment Canada (35). Incomplete mixing may cause localized concentrations to be much higher, possibly limiting degradability (36) and enhancing toxicity to terrestrial organisms. In addition, the issue of bioaccumulation in the terrestrial ecosystem has not been addressed. Although there have been studies demonstrating the degradation of NP in soil (12, 36, 37), the existence of a significant residual concentration seems likely. Marcomini et al. (37) showed that NP was degraded in soils that had been amended with an NP-spiked sludge, although a residual concentration of 0.5 mg/kg remained in the soil after 320 days. In a laboratory microcosm study, Topp et al. (12) showed that
