CLICK HERE TO SEE FIGURE 1Alkylphenol ethoxylates (APEs) are among the most widely used groups of surfactants. Worldwide, about 500,000 tons are produced annually for use in detergents, paints, pesticides, textile and petroleum recovery chemicals, metal working fluids, and personal care products (1). Nonylphenol ethoxylates are, by far, the most prevalent members of the "family."
It was discovered in 1984 that APE breakdown products are more toxic to aquatic organisms than their intact precursors are, and they were banned or restricted in Europe. In 1986, Germany instituted voluntary restrictions and Switzerland banned the use of surfactants in laundry detergents. Throughout northern Europe - England, France, Germany, and the Scandinavian countries - a voluntary ban on APE use in household cleaning products began in 1995, and restrictions on industrial cleaning applications are set to follow in 2000.
"The intrinsic properties of nonylphenol with respect to toxicity, persistence, and the liability to bioaccumulate have led to phase-outs," according to Håkan Björndal, a chemist responsible for APEs at the Swedish Environmental Protection Agency in Stockholm. "There is a general trend in Europe that the use of nonylphenol and nonylphenol ethoxylates is declining. In some countries, this is happening very fast." The Scandinavian countries, which currently consume about 5330 tons, have seen a 40% decline in APE use in the past five to six years, according to Nordic Council of Ministers estimates.
Recent evidence that some APE breakdown products are weakly estrogenic (see sidebar) has intensified concern over their environmental and human health effects and has spurred further regulatory concerns. Countries and organizations currently evaluating the human health or ecological risks of chemicals within the APE family include Canada, the United Kingdom, the European Union, the Organization for Economic Cooperation and Development (OECD), and the National Academy of Sciences (2).
Although the nascent endocrine disrupter issue may eventually eclipse concerns about the aquatic toxicity of APEs, scientists and regulators in Europe and the United States are concerned primarily about the latter. APE breakdown products, which are acknowledged to be highly toxic to aquatic organisms, pose environmental risks because of their occurrence, persistence, and concentration.
There has been no U.S. regulatory action to date. However, since 1987 EPA has been studying APEs in cooperation with CMA's panel, and this fall the agency will release draft water quality recommendations, some of which have taken two years to complete. Some industrial users and sewage treatment plant personnel will find these restrictions difficult to meet, according to state and federal regulators. An EPA draft risk assessment published last summer concluded that there is cause for concern in some U.S. rivers, and it recommends further evaluation (2) before making any decisions about possible regulations. The risk assessment will proceed to the final version after consideration of comments submitted by the CMA panel, according to Donald Rodier, a scientist responsible for the assessment at EPA's Office of Prevention, Pesticides, and Toxic Substances in Washington, D.C.
The EPA risk assessment, deliberations on the European ban, and a new European Union risk assessment expected in draft form this summer are the venues where these issues will be resolved.
APEs have been in use for more than 40 years as detergents, emulsifiers, wetting agents, and dispersing agents in household products and in agricultural and industrial applications. In the United States, industrial uses of APE encompass the largest category (55%); institutional cleaners comprise 30% of the total; and household cleaning and personal care products make up the rest (3). Most APEs enter the aquatic environment after disposal in wastewater.
The primary industrial uses of APEs are for emulsion polymerization and polymer stabilization in plastics and elastomers; cleaning, spinning, weaving, and finishing of textiles; wetting agents and emulsifiers in agricultural chemicals; and pulping and deinking in the paper industry. Institutional uses of APEs are confined to cleaning products, and most are found in commercial laundry detergents, janitorial products, and vehicle cleaners. In the household market, APEs are used mainly in laundry detergents and hard-surface cleaners (3).
Concerns about these surfactants arose in the early 1980s in Europe when a group of Swiss researchers discovered a twist in their environmental fate: the surfactants were inadvertently being transformed into more toxic compounds during the biodegradation that accompanies wastewater treatment. Particularly high APE levels were measured in digested sewage sludge. The metabolites were also shown to be more persistent and more lipophilic than the parent APEs, a finding that raised concerns about bioaccumulation. Research sponsored by the CMA panel challenges each of these conclusions.
The basic facts about APEs are undisputed. APEs are nonionic surfactants made up of a branched-chain alkylphenol that has been reacted with ethylene oxide to produce an ethoxylate chain (Figure 1). Commercial formulations are usually a complex mixture of homologues, oligomers, and isomers. The main alkylphenols used are nonylphenol (NP) and octylphenol (OP). Nonylphenol ethoxylates (NPEs) encompass about 80% of the world market, and octylphenol ethoxylates (OPEs) represent most of the rest (4).
CLICK HERE TO SEE FIGURE 1Biodegradation accomplished by stepwise shortening of the ethoxylate chain creates a complex soup of compounds that can be divided into three main groups: short-chain ethoxylates, alkylphenoxy carboxylic acids, and alkylphenols such as NP and OP (4). As the chain becomes shorter, the molecule becomes less soluble. The alkylphenoxy carboxylic acids and longer chain APEs are soluble in water; the shorter chain APEs, particularly NP and OP, have low water solubility and tend to adsorb onto suspended solids or sediments. Most studies and regulations focus on NPEs, because these ethoxylates are the most widely used. NP, one of the breakdown products, is also approximately 10 times more toxic than its ethoxylates.
However, when it comes to the environmental fate of APEs, the views of European academic scientists and regulators diverge strongly from those of U.S. industrial scientists and regulators. Europeans point to extensive research showing that APE metabolites persist and bioaccumulate. U.S. industrial scientists cite other research indicating that waste treatment effectively removes APEs and that any metabolites that do enter the environment do not persist.
The influential research by Walter Giger, Marijan Ahel, and co-workers at the Swiss Federal Institute for Environmental Science and Technology in Dubendorf followed APE transformation in 11 sewage treatment works in Switzerland (5). They reported that NPE removal averaged 59% (molar basis) or 70% (weight basis). Removal of dissolved organic carbon (DOC) was 57%, so NPE and DOC biodegradation rates were about the same; NPEs accounted for 4% of the DOC. They calculated an average mass balance for the NPEs and metabolites in the 11 works and found that <40% of the influent was subject to ultimate biodegradation. Twenty percent ended up adsorbed to the sludge, and 40-45% was in the water that left the plant.
The distribution of nonylphenolic compounds in the digested sludge was 95% NP and 5% short-chain ethoxylates, partly because of the hydrophobic nature of NP and partly because the anaerobic digestion of the sludge created NP. The more hydrophilic compounds were present in the secondary effluent of the Swiss sewage works. Other work by Giger and his colleagues (6) showed that NP concentrations in anaerobically digested sludge range from 0.45 to 2.53 grams per kilogram (g/kg) dry weight. In aerobically treated sludge, levels were lower: 0.08 and 0.5 g/kg dry weight. Giger and colleagues (7) also found that the concentration of NP in sewage sludge increased 15-fold during anaerobic digestion. Other European studies (8) have added to the region's perspective that, instead of safely degrading APEs, many sewage treatment works discharge substantial amounts of APE metabolites.
In the case of Switzerland's River Glatt, Ahel and co-workers in 1994 established that most of the nonylphenolic compounds that entered the river from 11 sewage treatment plants persisted in the environment (9).
The CMA panel began testing aquatic toxicity of NP in 1990 under a Toxic Substances Control Act Consent Order with EPA. A voluntary research program, instituted at the same time, included a study to determine levels of NP and its ethoxylates in U.S. rivers. The rivers included in the Thirty Rivers Study were effluent dominated. The CMA panel also monitored influent and effluent of 7 wastewater treatment plants, completed a monitoring study of the Fox River in Wisconsin, and sampled 6 of the original 30 rivers for carboxylates.
CMA panel-sponsored research, much of which has been presented at Society of Environmental Toxicology and Chemistry (SETAC) meetings during the past three years, indicates that U.S. sewage treatment works remove NPEs more efficiently than European studies have shown. In contrast to the 70-75% removal at European plants, panel-sponsored research indicates removal of 95-99% at U.S. treatment plants (10). These results may reflect differences in wastewater treatment, according to Rodier.
Although data on APE environmental concentrations are not abundant, the data available in 1995 led an OECD ad hoc expert group on APEs to conclude that NP concentrations are as much as 1 order of magnitude higher in the water of many rivers in Europe and the United Kingdom than in the United States (2). No one fully understands why environmental concentrations of APEs appear to be significantly lower in the United States, although U.S. rivers are larger and thus dilution factors are greater. Results of a round-robin analytical test organized by the OECD panel have ruled out analytical differences, according to Rodier. Therefore, the OECD panel will continue to study the issue of wastewater treatment plant efficiencies, possibly one of the causes for the differences in NP concentrations, according to the CMA panel.
In the United States, most municipal wastewater treatment involves aerobic decomposition and some form of activated sludge system (10). "As we see it, an APE problem is unlikely if wastewater treatment is adequate," according to Naylor. However, despite high removal rates, some state regulators note that effluent NP concentrations >10 micrograms per liter (µg/L) could result in detrimental environmental effects. Emerging U.S. and international regulatory standards are about 1 µg/L.
To further address the issue of biodegradation, the CMA panel has sponsored laboratory simulations of NPE biodegradation using radiocarbon-labeled NPEs in river water and activated sludge. According to results presented last November at the SETAC annual meeting in Washington, D.C., only a minor amount of NPEs and no detectable ether carboxylate breakdown products were found after 128 days, so it appeared that there were no persistent APE metabolites in the river water. But the research provoked skepticism among many European scientists. "Our field data show that the metabolites are persistent," said Geoff Brighty, research manager with the U.K. Environment Agency. "For the carboxylates, CMA wants to say that they are readily biodegradable on the basis of an OECD-approved test. On the basis of our field data, this is shocking. The test doesn't mimic what goes on in the environment."
For the Thirty Rivers Study, the panel used EPA's River Reach File database to randomly select 30 rivers likely to have been exposed to NPEs. Three or four water samples and two or three sediment samples at each site were collected and analyzed. Water and sediment analyses are necessary because the hydrophilic ethoxylates are likely to remain in the water column and the hydrophobic NP is likely to be absorbed onto sediments.
In the Thirty Rivers Study, NP and the parent ethoxylates were found in only 30% and 24% of the water samples, respectively. No water concentrations exceeded 1 µg/L. The highest concentration - 0.64 µg/L - was seen in the most contaminated river, the Grand Calumet in Indiana. The Grand Calumet's maximum sediment concentration of NP and short-chain ethoxylates was 3 parts per million (ppm), and its average concentration was 2 ppm. The next highest sediment concentration was in New York's Mohawk River, which had a maximum concentration of 1.7 ppm and an average of 0.3 ppm. The average for all sediments in all the rivers was 0.16 ppm NP and 0.02 ppm NPEs.
Concerns about the high concentrations of pulp and paper mills on Wisconsin's Fox River also prompted the CMA panel to fund comprehensive analyses of NP, short-chain ethoxylates, and carboxylates. Because there have been almost no investigations of carboxylate levels, the Fox River study provides comprehensive and rare data set (1, 11). Effluents from 15 paper mills and 6 publicly owned treatment works (POTWs) were sampled in the summer and winter of 1995. Concentrations were highest in the summer. Maximum NP in paper mill effluent was 28.6 µg/L, with total NPEs of 712 µg/L; 7 of the 15 mills discharged <1 µg/L. Of the six POTWs sampled, two released 1 µg/L, and the largest discharger released 15.9 µg/L of NP and 78.8 µg/L of NPEs. The separate study of carboxylates found the highest concentration of total carboxylates to be 1269.7 µg/L, and the highest POTW effluent concentration was 272.4 µg/L.
These results indicate that APEs are a problem on the Fox River, according to David Webb, a Wisconsin Department of Natural Resources aquatic chemist. "If you compare the toxicity data to the in-stream and effluent concentrations, it is likely that some effects are taking place. These may not be dramatic - there are no fish kills - but they are real."
In the United States and the United Kingdom, these water quality recommendations are unlikely to have major effects on most discharges because significant dilutions will be available for most effluents, and thus the standards for rivers will be met, according to Brighty. But Peter Howe, an EPA Region 5 toxicologist in Chicago, believes that in some areas the criterion could have a profound effect. "There are many places in the country where streams are dominated by effluent from POTWs. These waters may not meet the standard, and then the treatment plants will have the difficult task of trying to reduce inputs from countless sources."
In a separate effort, EPA's Office of Prevention, Pesticides, and Toxic Substances last summer completed a preliminary assessment of the aquatic environment's risk from NP (2). The assessment concluded that some APE metabolites are persistent in the environment but appear not to bioconcentrate to any significant extent. Overall, the assessment found that NP in general does not pose a significant risk to aquatic organisms throughout the country, but there are "hot spots" - rivers such as the Grand Calumet and the Fox. The agency is working on a more detailed assessment that will evaluate the additive effects of all APEs, determine risks from pesticides containing NP, and consider the results of a full life-cycle fish test aimed at assessing endocrine disruptive effects. According to Rodier, a decision on any possible regulatory action will not be made until after completion of the second risk assessment toward the end of this year.
U.S. and European regulatory efforts have been linked by the Oslo and Paris Commission and OECD initiatives. In Europe, the work on NP and NPEs started in 1989 with the Oslo and Paris Commission, the marine convention for the protection of the northeast Atlantic. Recommendations for voluntary phase-outs were set at a ministerial meeting in 1992. At about the same time, it was proposed that NP and NPEs be added to the OECD risk reduction program. EPA opposition to this measure led to the formation of an expert group, with Sweden and Germany as lead countries, involving EPA, CMA's panel, and academic researchers.
At a meeting in Berlin in 1993, the CMA panel agreed to conduct a research program aimed at resolving differences between Europe and the United States. The results of some of this research on biodegradation were presented at the SETAC meeting in 1996. In order to consider these new results, Sweden has agreed not to expedite a complete ban on APE this year, according to Björndal. Because the research has failed to reconcile the different perspectives on NP and NPE, researchers with both perspectives will participate in a workshop that is being planned for this summer or early fall.
Whether science can resolve these differences remains to be seen, because the crucial issues can be interpreted in two ways, observed Webb. On environmental degradation, CMA cites studies demonstrating that APEs readily biodegrade or can be efficiently treated. But field data indicate that metabolites are present in significant concentrations in effluent and river water. CMA studies show that removal is very efficient, but high concentrations of APE are still found in some effluents.
Although the Oslo and Paris Commission will reconsider its proposed APE ban in light of the panel's results, the European trend of phasing out APEs in favor of readily available substitutes such as alcohol ethoxylates appears likely to continue. In the United States, concerns about aquatic toxicity seem likely to lead to milder measures such as pollution prevention or source reduction efforts as opposed to APE bans.
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