A Critical Review of the Formation of Mono- and Dicarboxylated Metabolic Intermediates of Alkylphenol Polyethoxylates during Wastewater Treatment and Their Environmental Significance

Abstract

Alkylphenoxyacetic acids, the metabolic biodegradation products of alkylphenol ethoxylates, are commonly found in wastewaters and sewage effluents. These persistent hydrophilic derivatives possess intrinsic estrogenic activity, which can mimic natural hormones. Their concentrations increase through the sewage treatment works as a result of biodegradation and biotransformation, and when discharged can disrupt endocrine function in fish. These acidic metabolites represent the dominant alkylphenolic compounds found in wastewater effluent and their presence is cause for concern as, potentially, through further biotransformation and biodegradation, they can act as sources of nonylphenol, which is toxic and estrogenic. The authors aim to assess the mechanisms of formation as well as elimination of alkylphenoxyacetic acids within conventional sewage treatment works with the emphasis on the activated sludge process. In addition, they evaluate the various factors influencing their degradation and formation in laboratory scale and full-scale systems. The environmental implications of these compounds are considered, as is the need for tertiary treatment processes for their removal.

Influence of Operating Parameters on the Biodegradation of Steroid Estrogens and Nonylphenolic Compounds during Biological Wastewater Treatment Processes

“…The 41 effluents discharged from sewage treatment works (STWs) are major sources of these 42 anthropogenic chemicals to the aquatic environment (3). In addition, APEOs biodegrade 43 during wastewater treatment to generate the parent alkylphenols (AP), octylphenol (OP) 44 and nonylphenol (NP), the shorter chain mono to triethoxylates (NP 1 EO, NP 2 EO and 45 NP 3 EO) and a range of carboxylated intermediate by-products (4,5) which are more 46 estrogenic than their parent substances (5)(6)(7)(8). In the aquatic environment these 47 compounds are amenable to further biotransformation and bioconcentration (9) and may 48 potentially bioaccumulate (10); as a consequence of this behaviour complex issues for 49 environmental health arise (2).…”

The effectiveness of anaerobic digestion in removing estrogens and nonylphenol ethoxylates

“…However, the breakdown products produced during biological treatment are more hydrophobic and are therefore much better removed than the parent compounds leading to higher concentrations in the biomass and hence in the mixed sludge [2,24].…”

“…In anaerobic, as well as aerobic conditions, the ethoxylate chain of higher ethoxylate NPEOs is shortened until persistent short-chained NP1-2EOs and NP are formed. This breakdown proceeds by the stepwise removal mechanism of one ethylene glycol unit [2,17]. It appears that NP, a major product of degradation, is frequently reported as not undergoing further transformation [18,19].…”

“…Recently those organic micropollutants with endocrine disrupting ability have been the subject of major research investigations [2][3][4][5]. Endocrine disruption in fish has been predominantly attributed to the presences of free natural estrogens such as estrone (E1) and 17β-estradiol (E2) together with the synthetic estrogen 17α-ethinylestradiol (EE2) as well as nonylphenols (NP) and nonylphenol ethoxylates (NPEOs).…”

“…Those compounds which have not biodegraded or have only partially biodegraded during wastewater treatment may be adsorbed to the sewage solids [2,3] and will be subject to further treatment prior to reuse. A common form of sewage sludge treatment is anaerobic digestion (AD).…”