FATE OF ALKYL POLYGLUCOSIDES IN THE ENVIRONMENT 93 fatty alcohol. Glucose can then be metabolized via pyruvate cycle into carbon dioxide and water, whereas fatty alcohols undergo β-oxidation into fatty acids and metabo- lized intracellularly. This mechanism has been proven by using High Performance Liquid Chromatography (HPLC) and anthrone assay (10–13). Another proposed mechanism by Eichhorn and Knepper (11) is based on degradation of linear alkylbenzene sulfo- nates or alcohol ethoxylates, and involves ω-oxidation of the glucosides into corre- sponding alcohols, followed by breakdown into glucose and other by-products. However, in the Liquid Chromatography - Mass Spectroscopy (LC-MS) analysis of degraded samples, scientists failed to identify the corresponding alkanoic acid ions or adducts (11–13). Zhang et al. (14) report the ω-oxidation pathway such as sugar esters, based on degradation rates of linear and oxo-alcohol–derived APGs. The authors report that the longest and highly branched oxo C14–15 APG had the slowest degradation Figure 2. Biodeg r adation pathways for APGs. Based on chemical and spectroscopic analyses, the glucosidic bond cleavage is the predominant mechanism. Redrawn from Zgola-Grześkowiak et al. (10) Eichorn and Knepper (11) Jurado et al. (13).

JOURNAL OF COSMETIC SCIENCE 94 rate of ~80% compared with its linear counterpart which was more than 90% degraded in the same duration. The presence of highly complex and branched structure increased the time taken for the alkyl chain oxidation supporting the alkyl chain oxidation. ARE APGS READILY BIODEGRADABLE? Biot ransformation or primary biodegradation is defi ned as a structural breakdown of a material such that it loses its inherent properties (9). Biodegradation profi le under both aerobic and anaerobic conditions is important to establish the ultimate behavior of molecules in natural and wastewater environment. Low degradation rate in anaerobic conditions can potentially lead to surfactant accumulation in wastewater treatment plants and eventual soil contamination if used as a fertilizer. Ultimate biodegradation or miner- alization is the conversion of the parent compound and its metabolites to carbon (9). In initial studies, Madsen et al. (15). have shown biotransformation of three APGs, namely, a linear, a branched and a monoester, and an alkyl ethoxylate in laboratory conditions. Ethyl glucoside esters, C10 and C12 ethyl glucoside esters, showed complete degradation in anaerobic conditions when exposed to three different innocula, freshwater sediment, marine, and digested sludge after typical lag periods of 3–4 weeks. Gas production was transiently inhibited in the early phase, but more than 75% of theoretical volume was achieved after 6 weeks (16). In another study, Jurado et al. (13) reported primary biodeg- radation pathways for C8–16 glucoside, commonly known as coco glucoside from days 1 to 12 as hydrolysis of the APG into alcohol and polysaccharide. Fact ors affecting the biodegradation rate: In isolated studies, various factors have been reported to affect the degradation rate. i. Init ial concentration: Usi ng the anthrone method analysis, the effect of concentration has been demonstrated (13). Signifi cant differences in degradation rates were noted as a function of initial concentration in aerobic conditions. Lower concentrations of 15 and 25 mg/L showed rapid degradation, whereas higher concentrations of 75 and 100 mg/L had an exponential decay curve with considerably lower degradation rates. Only 0.04% biotransformation in 50 h was noted for 100 mg/L compared with 62.09% for 15 mg/L (13). Starting concentration affected degradation rates 100 mg/L APG dose in anaerobic testing conditions did not show complete degradation. Only 40.05% mineralization reached after 60 d for C8–10, whereas longer chains showed less than 30% degradation in anaerobic conditions because of limited solubility (17). Thus, although APGs may be classifi ed as readily biodegradable under aerobic conditions, their slower metabolism in the absence of oxygen can lead to eventual accumulation of parent molecules and their metabolites in anaerobic environments. ii. S ize of the hydrophobic residue: Biot ransformation studies on linear and oxo derivatives of glucosides also confi rm the effect of chain length on the degradation rate. Latency time of 0.5 d was noted for C8 versus 2 d for C10 and above. After the primary degradation phase, the overall degradation rate was found to be similar for all chain lengths. The degradation rate was found to follow the following order: C8 C10 ~ C12 C14 (10,12). Similar observation had been previously reported for linear and branched glucosides and a monoester. The molecules showed higher degradation rates for lower alkyl chain length branching may lead to increase in degradation time (12,13).