Non-ionic POEA surfactants are synthesized from fatty acids with 12-18 carbons derived from animal fat, among them oleic acid, palmitic acid, stearic acid, palmitoleic acid, and myristic acid. The fatty acids are ethoxylated into tallow amines by adding ethylene oxide. One alkyl chain (R) and two repeating ethoxylate (EO) units make up the resulting tertiary amine (Fig. ). The tallow amine R chain is primarily composed of C16H33, C18H35, or C18H37 moieties. The two EO units (m and n) add up to 2 to 15 moles of ethylene oxide, but some GBHs contain POEA with higher amounts of polyethoxylation. There is a great deal of uncertainty regarding the structures and quantities of co-formulants because their composition is often proprietary. Yet this complexity creates several problems for quantification and biomonitoring. Minor compositional changes can have a significant impact on properties of POEAs. Toxicity and environmental persistence can vary with length of the alkyl and ethoxylated chains. Therefore, a biomonitoring method must overcome obstacles in the type of biospecimen, cleanup, and analytical sensitivity for detection at biologically relevant concentrations.