J. Cosmet. Sci., 72, 91–98 (January/February 2021) 91 Fate of Alkyl Polyglucosides in the Environment RACHNA RASTOGI , Research and Development, Bregma Science LLP, Bangalore 560098, India (R.R.) Accepted for publication August 17, 2020. Synopsis Alkyl polyglucosides (APGs) belong to the class of green or natural surfactants synthesized from fatty acids and sugars. Growing concerns on toxicity of sulfates and ethoxylates has led to their popularity in personal and home care products. Increasing usage has resulted in higher concentrations in discharge sites or wastewater treatment plants. Studies show that APGs are readily biodegradable in laboratory settings however, limited data are available on their effects on the environment. In this focused review, we discuss their biodegradation profi le and toxicity of the parent compounds and metabolites in aquatic systems. INTRODUCTION With the increasing demand for natural and organic formulations, use of green surfactants is also on the rise. One such class of compounds, alkyl polyglucosides (APGs), derived from sugars (glucose) and long-chain fatty acids (coconut/palm), is now gaining traction because of easy availability, improved production methods, lower cost, and excellent skin compatibility as a replacement to conventional surfactants. APGs are also approved for use by ECOCERT, France, International Organic and Natural Cosmetics Corporation GmbH, BDIH, Germany, and COSMOS, Europe (1–4). Recently, APGs have also found applications in home care and institutional products because of their good cleaning abil- ities, a category dominated by ethoxylated and sulfated surfactants. Apart from their use in cleansing applications, APGs are also being used as emulsifi ers in skin care products and stabilizers in drug delivery (3). Thus, as their usage increases, there is a renewed in- terest in understanding their impact on the environment. Personal care and cleaning products post-use end up in wastewater treatment plants or directly let out into aquatic zones where decontamination facilities are not available. Because of their higher consumption, surfactants and their degradation products have been detected at various concentrations in surface waters, sediments, and sludge-amended soils (5). Because of their dissolution capability, surfactants tend to accumulate at the interfaces and can be toxic to the microbiota. If tolerated or after an acclimatization period, surfactants undergo biotransformation leading to loss of their surface activity. Address all correspondence to bregmascience@gmail.com.
JOURNAL OF COSMETIC SCIENCE 92 Depending on the by-products, the toxicity profi le of the surfactants may change. This mineralization process beginning from the infl uent to fi nal discharge into aquatic systems can last for days to months depending on environmental factors, microbiome distribu- tion, and nutrient levels (1,5). Environmental compatibility of surfactants and chemicals is determined by guidelines laid down by the Organisation for Economic Cooperation and Development (OECD). Environmental hazard assessment includes determination of potential effects on the aquatic (including sediment), terrestrial, and atmospheric zones along with accumulation in food chain and microbiological activity in sewage treatment systems (6,7). APGs have been classifi ed as readily biodegradable and nontoxic in early research (8). Growing use of these surfactants as sulfated surfactant replacements and demand for natural and organic formulations warrants re-scanning of the available ecotoxicity data (9). This review aims at the general chemistry, degradation mechanisms, and toxicity of APGs and their metabolites in aquatic environment. CHEMISTRY AND BIODEGRADATION PATHWAY Surfactants are made of a hydrophobic tail and a hydrophilic headgroup. In case of APGs, the hydrophobic tail is derived from fatty alcohols of coconut and/or palm origin and a hydrophilic sugar, usually D-glucose from corn (Figure 1). These are linked together through glycosidic linkages at the anomeric carbon (carbon linked to two oxygen atoms) using strong acids as catalysts. The alkyl residues range from 6 to 18 carbon atoms, pre- dominantly linear with the degree of polymerization (DP) of 1–3. Commercial grades of APGs usually are monoglucosides with a DP of 1.3–1.7 (1,3). Figure 2 illustrates the two most common biodegradation mechanisms for APGs. One possible mechanism is APG hydrolysis to form glucose or saccharide units and Figure 1. Emp i rical and structural formula of APGs, where n = average number of glucose units and x = number of carbon atoms in the alkyl chain. Example of lauryl glucoside or dodecyl—α-D-glucopyranoside, where n = 1 and x = 12 R = alkyl group.
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