Environ. Sci. Technol. 1999, 33, 113-118
Static Die-away of a Nonylphenol Ethoxylate Surfactant in Estuarine Water Samples T H O M A S L . P O T T E R , * ,† KATHLEEN SIMMONS,‡ JUNNAN WU,‡ MAURICIO SANCHEZ-OLVERA,‡ PAUL KOSTECKI,§ AND EDWARD CALABRESE§ USDA-ARS, Southeast Watershed Research Laboratory, Tifton, GA 31793, and Department of Food Science and School of Public Health, University of Massachusetts, Amherst, Massachusetts
The static die-away of the nonylphenol ethoxylate (NPE) surfactant used to stabilize the bitumen-water emulsion in the fuel Orimulsion was studied using estuarine water samples collected at four stations in Tampa Bay, FL. Incubations were in the dark at 28 °C for 183 days. Primary degradation was complete in 4-24 days with lag periods between 0 and 12 days. The concentration of five NPE intermediate degradation products and total surfactant were monitored at 4-8-day intervals for the first 89 days and at 30-day intervals thereafter. The intermediates detected included nonylphenol diethoxylate (NP2EO) and nonylphenoxy ethoxy acetic acid (NP2EC). Much smaller amounts of nonylphenoxy acetic acid (NP1EC) and nonylphenol monoethoxylate (NP1EO) were detected. The completely deethoxylated metabolite nonylphenol (NP) was not detected. On a molar basis, NP2EC accounted for 66.0-93.3% of degradation products and for 22.7-75.6% of the starting material at the termination of the experiment. The sequence of degradation and intermediate accumulation and decay indicated the initial formation of NP2EO from higher NPE homologues followed by oxidation to NP2EC. A second phase of the experiment was initiated on day 296. The remaining water in two sample incubation containers was combined with equal volumes of freshly collected Tampa Bay water. In three of five replicates from one sample, dieaway of the residual NP2EC began at day 20 and declined to approximately 50% of the initial concentration on day 32. In other replicates of this sample and in a second sample, no change in NP2EC or NP1EC concentrations was observed. The data have confirmed relatively rapid primary degradation of the parent NPE and the formation in sequence of two degradation products, NP2EO and NP2EC. The later compound appears to be relatively resistant to further degradation However, data did indicate that microorganisms were present in the Bay that are capable of transformation and degradation of the compound.
* Corresponding author e-mail:
[email protected]; phone: (912)386-7073; fax: (413)386-7294. † USDA-ARS. ‡ Department of Food Science. § School of Public Health. 10.1021/es9804464 CCC: $18.00 Published on Web 11/14/1998
1998 American Chemical Society
Introduction Orimulsion is a bitumen-based fuel that was developed and is produced exclusively in Venezuela. It was introduced on the world market in 1993 and has the potential to be a significant component of the fuel mix used for electrical power generation in the next century (1). It is currently being used in power plants in Canada, Japan, Denmark, Italy, Lithuania, and China. To facilitate its transport and handling, the product is formulated as a oil-in-water emulsion comprised of 70% Cerro Negro bitumen and 30% water (1, 2). The emulsion is stabilized with a nonylphenol ethoxylate (NPE) surfactant known commercially as Intan-100. Fuel specifications require the surfactant concentration to be between 0.15 and 0.22% (2). NPE surfactants such as Intan-100 are homologous series whose homologues (ethoxymers) differ depending on the length of the ethoxylate (EO) chain. Intan-100 is an NPEO18, i.e., an NPE whose ethoxymer distribution is centered on molecules having ethoxylate (EO) chain lengths of 18 units. Each ethoxymer is a mixture of isomers that differ depending on the C9 alkyl side-chain branching pattern and its position of substitution on the aromatic ring. Bhatt et al. (3) separated 31 peaks in the GC/MS/FTIR analysis of technical nonylphenol. They reported that that the 10 major peaks were branched-chain nonyl isomers with the nonyl group positioned para to the phenolic hydroxyl. In the event of a transportation-related Orimulsion spill, Intan-100 will be released into the environment. Concerns have been expressed about the ecotoxicological consequences of such a release. This is primarily due to reports that certain NPE environmental degradation products, in particular nonylphenol (NP), are persistent in the environment (4-6), are acutely toxic (7-9), may accumulate in aquatic organisms (10), and may behave as environmental “estrogens” (11-13). NP and other products of NPE degradation are widely distributed in wastewater (4, 13-19) and surface water receiving waste discharges (5, 6, 15, 19-22) and sediments (5). NPE degradation under conventional sewage treatment and environmental conditions has been reviewed (8, 9, 23). It was noted that degradation initially involves shortening of ethoxylate chains by enzymatic hydrolysis. The three most common groups of intermediates reported were as follows: (a) NP (i.e., completely de-ethoxylated NPE); (b) short-chain nonylphenol ethoxylates having 1-4 ethoxylate units, with NP2EO predominating; and (c) a series of ether carboxylates including nonylphenoxy acetic acid (NP1EC) and nonylphenoxy ethoxy acetic acid (NP2EC). Metabolism of the aromatic ring and alkyl side chain have also been reported, although the mechanisms remain unclear (8, 9, 23). Reviewers have also noted that studies on the fate of NPEs and their degradation products in aquatic environments are limited. The literature review conducted for this investigation identified only four related studies in marine and estuarine waters (5, 20, 24, 25). In one study, the die-away of a commercial NPE surfactant was monitored (24). It was reported that the time required for 50% degradation of an NPEO10 was 23-69 days at 13 °C and 2.5-35 days at 22.5 °C. The principal intermediate product detected was NP2EO. At 22.5 °C, this compound reached its maximum concentration in 15 days, decaying to near zero in 30 days. The authors also reported that NP was not detected. This was explained by the fact that the conditions of the die-away study were aerobic. Another significant feature of the study was that there was no discussion of the ether-carboxylate degradation VOL. 33, NO. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
113
TABLE 1. Water Quality at Sample Collection Sites site 1 date collected depth (m) salinity (ppt) 30 cm below surface mid-water 30 cm above bottom temperature (°C) 30 cm below surface mid-water 30 cm above bottom dissolved oxygen (mg L-1) 30 cm below surface mid-water 30 cm above bottom
site 2
site 3
site 4
July 1 July 1 July 1 July 10 0.6 5.7 8.8 10.6 18.5
30.0 29.5 30.0
32.5 32.5 33.0
22.0 25.5 29.0
30.7
31.0 29.2 29.4
30.8 29.6 29.8
28.5 27.5 28.0
5.1
6.6 8.4 8.0
6.3 7.3 8.2
6.7 4.9 4.9
TABLE 2. Relative Concentration (Molar Basis) of NPE Metabolites to the Initial NPE Concentration on Experiment Day 183a treatment A
FIGURE 1. Location of sites in Tampa Bay, FL, where samples were collected for the static die-away experiment. products. Several studies have reported that these compounds, in particular NP2EC, are the principal NPE degradation products in sewage treatment effluents (18, 19). Investigations published to date have indicated that NPE released in marine or estuarine environments would be subject to primary and ultimate biodegradation. However, the limited database makes generalization of results uncertain. There are no studies in which the accumulation and decay of the ether-carboxylate metabolites was monitored. To advance the state of knowledge regarding the potential human and ecological risks of an Orimulsion spill in marine and coastal environments, data of this type are needed. The study reported here involved monitoring the static-die of the surfactant used to formulate Orimulsion in water samples collected in Tampa Bay, FL. Data are provided on surfactant primary degradation and the accumulation and decay of five intermediate degradation products.
Materials and Methods Study Area. Forty-liter water samples were collected at four stations in Tampa Bay in July 1996. These samples were used in part I of the die-away experiments. Sampling locations are shown in Figure 1. Two samples were collected near the middle of the Bay (sites 2 and 3), a third was in a port area (site 4), and the forth was in a tidal river (site 1) that discharges into the Bay. Samples were also collected at sites 3 and 4 in April 1997. They were used in part II of the die-away study. General water quality parameters measured at the time of sampling are compiled in Table 1. As indicated, there was little variation with depth. The Bay is well mixed vertically. Between sampling locations, salinity ranged from 18.5 to 33, dissolved oxygen ranged from 5.1 to 8.4 mg L-1, and temperature ranged from 27.5 to 31.0 °C. Salinity near the middle of the Bay approached that of the adjoining Gulf of Mexico. Freshwater discharge into the Bay is less than 1% of the total water volume exchanged with the diurnal tide (1). Decreasing transparency of the samples was indicative of the following water quality gradient: site 3 ) site 2 > site 4 > site 1. 114
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 1, 1999
Site 1 Site 2 Site 3 Site 4
B
NP2EC
sum metabolites
NP2EC
sum metabolites
39.0 (57.3) 22.7 (33.4) 49.9 (73.4) 30.6 (45.0)
42.6 (61.5) 37.4 (50.5) 68.9 (95.4) 42.6 (58.8)
35.9 (52.7) 51.5 (75.6) 38.8 (57.10 39.9 (58.6)
35.9 (52.7) 51.5 (75.6) 38.9 (57.1) 39.9 (58.6)
a Site 3, treatment A, received double the initial concentration of Intan-100; the final day on which samples were analyzed for site 4 was experiment day 174.
Sample Collection. Water samples were collected at each site at 30 cm below the surface, mid-water, and 30 cm above the bottom using a 4.2-L Alpha-Bottle (Wildlife Supply). The depth at site was NP7EO and 95%. The reference sample of NP1EO was donated by Huntsman Chemical Company (Austin, TX). The NP2EC was donated by Union Carbide (Charleston, WV). The Intan-100 used for spiking water samples was used as the reference standard for total Intan100. The analytical limit of detection in the HPLC analysis was 0.050 mg L-1. More specific analytical data for the degradation products were obtained by GC/MS. Prior to GC/MS analysis, NP1EC and NP2EC were methylated by combining a 3-mL aliquot of the sample extracts with 1 mL of 12 N HCl and heating at 90 °C for 1 h. After dilution in distilled-deionized water and extraction of analytes into methylene chloride by liquidliquid extraction in a separatory funnel, NP, NP1EO, and NP2EO were acylated by reaction with acetic anhydride in the presence of aqueous 2% K2CO3. The reagents were obtained from Fisher Scientific (Medford, MA). The surrogate standards used in this analysis were benzoic acid-d5 and phenol-d6 (Aldrich, Milwaukee, WI). Samples were analyzed by GC/MS using a Hewlett-Packard model 5989 GC/MS system. The GC oven was fitted with a DB5MS fused-silica capillary column, 30 m × 0.25 mm (i.d.) × 0.25 µm film (J&W Scientific, Rancho Cordovo, CA). The oven temperature was set initially at 60 °C and held for 1 min. The temperature was then increased at the rate of 4 °C/min to 290 °C and held for 1 min. Helium carrier head pressure was fixed at 100 kPa with automated injection in the splittless mode at 280 °C. The column was directly coupled to the ion source through a heated transfer line maintained at 280 °C. Prior to analysis, samples were fortified with naphthalene-d8 (Aldrich, Milwaukee, WI) at 1.3 µg mL-1. Data acquisition was in the selected ion-monitoring mode with dwell times of 100 ms per ion. Pairs of ions monitored for each analyte were phenold6 acetate (99, 141), methylbenzoate-d5 (110, 141), naphthalene-d8 (108, 136), NP acetate (135, 262), NP1EO acetate (87, 306), NP2EO acetate (87, 350), NP1EC methyl ester (207, 292), and NP2EC methyl ester (117, 336). The source of the analytical standards was described above. An extracted ion current chromatogram of a standard mixture of NP, NP1EO, NP1EC, and NP2EC at 20 µg mL-1 is shown in Figure 3. For quantitation, peak areas were summed for the degradation products over retention time windows determined by analysis of standards. Retention time data for NP2EO and relative response factors to the internal standard were obtained through analysis of a mixture of NP1EO and NP2EO sold commercially as POE 1-2 (Chem-Serv, Chester, PA). Its relative composition was 79% NP1EO and 17% NP2EO by GC/FID analysis. The lowest concentration standard, which was analyzed in the calibration of the GC/MS prior to analysis each set of samples, was 1.5 µg mL-1. This corresponded to an analytical detection limit of 0.010 mg L-1 per degradation product. Percent recoveries of surrogate standards were between 71 and 130% for the more than 300 samples analyzed. In the VOL. 33, NO. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
115
FIGURE 3. Extracted ion current chromatograms obtained in the GC/MS analysis of the derivatized mixture of NP, NP1EO, NP1EC, and NP2EC.
FIGURE 4. Intan-100 die-away and the accumulation and die-away of NP, NP1EO, NP2EO, NP1EC, and NP2EC in Tampa Bay water collected at site 2 and fortified with the water-soluble fraction of an Orimulsion sample (treatment A). analysis of a series of matrix spikes prepared by fortifying Tampa Bay water, the percent recovery of Intan-100 averaged 93% with 2.3% RSD. Mean degradation products recoveries ranged from 61 to 80% with % RSD in the 4.1-11.8% range.
Results and Discussion Results for a mid-Bay water sample (site 2) fortified with an Orimulsion extract (treatment A) is summarized in Figure 4. It shows relatively rapid primary surfactant degradation 116
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 1, 1999
flowed by accumulation and decay of NP2EO and accumulation of NP2EC in sequence. Data obtained with all other water samples exhibited the same trends. Primary degradation was essentially complete within
