Ethoxylated alcohols, biodegradability

Branched Primary Alcohol Ethoxylates (BPAE). The hydrophobes of BPAE are produced by oligomerization of propylene or butene followed by catalytic addition of CO and H2 to yield highly branched alcohols. The ethoxylates of these alcohols biodegrade more slowly and less extensively than the linear alcohol ethoxylates (11.12). 

Important classes of nonionic surfactants are aliphatic poly-ethoxylate alcohols (AEO), and octyl or nonyl phenol polyethoxylates (OPEO and NPEO). The alkylphenol ethoxylates (APEO) attracted special attention due to their supposedly endocrine disrupting properties (Ch. 8.3). LC-MS analysis may also involve nonylphenolethoxycarboxylates (NPEC), biodegradation products of NPEO, and halogenated analogues, generated in chlorine disinfection treatments in drinking water production plants. 

In contrast to alkyl phenol ethoxylates the class of fatty alcohol ethoxylates is biodegradable and eco-friendly. Efficient technical surfactants found in this class are Lutensol XL 700, Lutensol T08, Lutensol A07, Lutensol AO8 and Eusapon OD. The phase behaviour was characterised in systems of type H20/NaCl-suet-technical non-ionic surfactant. The salt mass fraction was kept constant at = 0.10 and the oil volume fraction at = 0.50. In view of the degreasing process, which is conducted at 30°C, the X-point of the optimal system should be located around 30°C and the formation of the highly viscous La-phase should be suppressed. Figure 10.5 presents the T-y cuts for the respective systems. 

Steinle et al. [426] studied the primary biodegradation of different surfactants containing ethylene oxide, such as sulfates of linear primary alcohols, primary oxoalcohols, secondary alcohols, and primary and secondary alkyl-phenols, as well as sulfates of all these alcohols and alkylphenols with different degrees of ethoxylation. Their results confirm that primary linear alcohol sulfates are slightly more readily biodegradable than primary oxoalcohol sulfates and that secondary alcohol sulfates are also somewhat worse than the corresponding linear primary. 

Alkylphenol ether sulfates are slightly more resistant to biodegradation than alkylbenzenesulfonates. Similarly to alcohol ether sulfates, this resistance increases with the degree of ethoxylation. Again there are some differences in favor of primary alkylphenol ether sulfates with respect to secondary alkylphenol ether sulfates [426]. 

Di Corcia A, C Crescenzi, A Marcomini, R Samperi (1998) Liquid-chromatography-electrospray-mass spectrometry as a valuable tool for characterizing biodegradation intermediates of branched alcohol ethoxyl-ate surfactants. Environ Sci Technol 32 711-718. 

The only study available on metabolites of AE was performed by Crescenzi et al. [17]. The initial biodegradation of AE occurs by cleavage at the ether bridge between the alkyl and ethoxylate chain, resulting in polyethylene glycols (PEG) and alcohols. In consecutive oxidation steps, the PEG chains are shortened and mono- and dicarboxylated metabolites (MCPEG and DCPEG, respectively) are formed. 

Nonionic surfactants contain (Fig. 23) no ionic functionalities, as their name implies, and include ethylene oxide adducts (EOA) of alkylphenols and fatty alcohols. Production of detergent chain-length fatty alcohols from both natural and petrochemical precursors has now increased with the usage of alkylphenol ethoxylates (APEO) for some applications. This is environmentally less acceptable because of the slower rate of biodegradation and concern regarding the toxicity of phenolic residues [342]. 

This paper will review the biodegradation of nonionic surfactants. The major focus will be on alcohol ethoxylates and alkylphenol ethoxylates—the two largest volume nonionics. In this paper the effect of hydrophobe structure will be discussed, since hydrophobe structure is considered more critical than that of the hydrophile in biodegradability of the largest volume nonionics. The influence of the hydrophobe on the biodegradation pathway will be examined with an emphasis on the use of radiolabeled nonionics. 

Ethoxylates derived from essentially linear alcohols produced by the above processes have been shown in many extensive studies (3-10) to biodegrade rapidly to products which do not foam or show toxicity to aquatic life. 

Linear Secondary Alcohol Ethoxylates (LSAE). The hydrophobes of LSAE are made via borate-modified oxidation of n-parafiins to form inorganic esters followed by hydrolysis. The resulting alcohols contain secondary hydroxyl groups randomly located along the linear alkyl chain. LSAE biodegrade slightly slower than LPAE (13.14). 

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