Alkylphenols in sewage sludge applied to land

Researchers at William & Mary’s Virginia Institute of Marine Science (VIMS) have found high levels of alkylphenols in biosolids derived from several wastewater treatment facilities across the United States. Despite their toxicity and ability to disrupt the endocrine system, alkylphenols were not examined by the U.S. EPA in 1993 when it developed regulations for applying sewage sludge onto agricultural fields. The presence of these and other toxic compounds recently found in sewage sludge, such as brominated flame retardants and pharmaceuticals, has some scientists saying it’s time for EPA to reexamine the issue.

Applying sewage sludge onto agricultural fields is an inexpensive way for wastewater treatment plants to dispose of their waste, and at the same time, recycle valuable nutrients. Sewage sludge, however, contains a myriad of toxic chemicals and microbial pathogens, and only a handful of them are regulated under current U.S. regulations. EPA has established limits for some heavy metals and pathogens in sludge applied to land, and it plans to set limits for the dioxin-like compounds. But in general, U.S. limits are less strict than those in Europe and cover far fewer compounds (Environ. Sci. Technol. 2000, 34, 430A–435A).

EPA’s 1993 legislation for managing sewage sludge is based on the National Sewage Sludge Survey conducted in 1988, which did not examine several contaminants in biosolids that are now of concern, says Mark La Guardia, who along with Robert Hale and colleagues at VIMS, reported nonylphenol levels as high as 887 mg/kg (dry weight) in U.S. biosolids destined for land application (Environ. Sci. Technol. 2001, es0109040, ASAP Nov. 15).

In the nonylphenol study, the VIMS researchers analyzed a total of 11 biosolids, including 3 distributed for home garden usage. The biosolids were all derived from U.S. wastewater treatment plants and had been stabilized by using either compost, lime (alkali), heat, or anaerobic digestion techniques. Nine of the samples exceeded the current Danish limit by 6–33 times. The European Union has established a limit of 50 mg/kg for total nonylphenol and its mono- and diethoxylates in biosolids, but Denmark has an even stricter limit of 30 mg/kg and intends to lower that limit to 10 mg/kg in 2002. Currently, there are no limits for nonylphenol and its ethoxylates in U.S. sludge.

Alkylphenol ethoxylates are used as surfactants in a wide variety of household products, including detergents, paints, pesticides, and personal care products. They are known to degrade to more toxic and estrogenic alkylphenols during wastewater treatment processes. Alkylphenols are more hydrophobic than their parent compounds and therefore tend to accumulate in sewage sludge. Of all the alkylphenolic compounds, nonylphenol and its ethoxylates have generated the most environmental health concerns because they are the most abundant. Octylphenol, however, is reportedly 10–20 times more estrogenic than nonylphenol.

Low levels of nonylphenol (8.3–85.6 µg/L) have been shown to cause endocrine-disrupting effects in rainbow trout in laboratory studies (Environ. Sci. Technol. 2001, 35, 2909–2916), but there have been no field studies showing that biosolids containing high levels of alkylphenols and their ethoxylates cause deleterious effects to health or the environment when applied to agricultural lands, says Ellen Harrison, director of the Cornell Waste Management Institute. Consequently, EPA has not shown much interest in setting limits for alkylphenols in sludge, she says.

Field studies have shown no adverse effects of alkylphenols in sludge applied to land on earthworms, insects, and birds, says Charles Staples, a private consultant with Assessment Technologies, who has worked closely with the Alkylphenols & Ethoxylates Research Council, an industry group composed of manufacturers, processors, users, and suppliers of alkylphenols and their ethoxylates. “Insects, in fact, thrived on sludge containing natural levels of nonylphenol and other toxic organic compounds. The nutrients in the sludge overwhelmed any kind of adverse effects on the insects that may have been seen,” he says.

Some believe there is no need to regulate alkylphenols in sludge applied to land because under aerobic conditions, the compounds tend to degrade in about a month. “But once conditions go anaerobic, alkylphenols become much more persistent,” says Andrew Johnson of the U.K.’s Centre for Ecology and Hydrology in Oxfordshire. Because of their hydrophobicity, however, alkylphenols will not be very mobile. “On the whole, alkylphenols stick well to soil,” says Johnson.

In laboratory experiments, the VIMS researchers subjected stabilized biosolids to EPA’s toxicity characteristic leaching procedure (EPA Method 1311) and saw about 2% of the alkylphenols in the leachate. If those biosolids had been applied to land, that 2% could have ended up in groundwater, they warn. “One of the ways wastewater treatment plants take care of their sludges is to put them in lagoons. There has been groundwater contamination of nonylphenols. There is a potential that these compounds can come out of the biosolids in the field and get into groundwater,” says La Guardia.

Recognizing that in the future it may need to look at additional chemicals and pathogens in sludge applied to land, EPA has asked a National Academy of Sciences committee to review the science behind its risk assessment. One of the committee’s charges is to examine EPA’s approach for identifying relevant chemical pollutants in sludge. The committee is expected to complete its review by summer 2002. —BRITT E. ERICKSON