Bioaccumulation of decamethylpentacyclosiloxane (D5): A review

Abstract

Decamethylpentacyclosiloxane (D5) is a widely used, high-production volume personal care product with an octanol-water partition coefficient (log K OW ) of 8.09. Because of D5's high K OW and widespread use, it is subject to bioaccumulation assessments in many countries. The present study provides a compilation and an in-depth, independent review of bioaccumulation studies involving D5. The findings indicate that D5 exhibits depuration rates in fish and mammals that exceed those of extremely hydrophobic, nonbiotransformable substances; that D5 is subject to biotransformation in mammals and fish; that observed bioconcentration factors in fish range between 1040 L/kg and 4920 L/kg wet weight in laboratory studies using non-radiolabeled D5 and between 5900 L/kg and 13 700 L/kg wet weight in an experiment using C 14 radiolabeled D5; and that D5 was not observed to biomagnify in most laboratory experiments and field studies. Review of the available studies shows a high degree of internal consistency among findings from different studies and supports a broad comprehensive approach in bioaccumulation assessments that includes information from studies with a variety of designs and incorporates multiple bioaccumulation measures in addition to the K OW and bioconcentration factor. Environ

Fugacity and activity analysis of the bioaccumulation and environmental risks of decamethylcyclopentasiloxane (D5)

“…We therefore conclude that fugacity and activity ratios of D5 are likely below 1, suggesting that D5 does not have a propensity to biomagnify in food webs. This observation is in agreement with several food web bioaccumulation field studies, which report trophic dilution of D5 in aquatic food webs and trophic magnification factors for D5 of less than 1 . Only studies in Lake Mjøsa, Norway have indicated biomagnification, as discussed in more detail in Gobas et al .…”

Bioconcentration and Aquatic Toxicity of Superhydrophobic Chemicals: A Modeling Case Study of Cyclic Volatile Methyl Siloxanes

“…Table S1 is a compilation of acute and chronic toxicity data of cVMS to aquatic organisms, showing a general lack of measurable toxicity up to the water solubility or sorptive capacity in sediment. 4,29,30,38 No effects have been observed with cVMS in standard 48-or 96-h acute toxicity tests. Effects were observed for D4 (reviewed by Hobson et al 59 ) in 14-and 18-d prolonged acute toxicity studies with rainbow trout (Oncorhynchus mykiss) but not sheepshead minnow (Cyprinodon variegatus), whereas no effects were observed for D5 (D6 was not tested) in any of the prolonged acute toxicity studies.…”

“…Activities are simply the ratio of concentration to solubility or fugacity to vapor pressure, i.e., the fraction of saturation. 29,56,57 For narcotic chemicals, acute lethality generally occurs in a range of chemical activities of 0.01−0.1; therefore, the proximity to potentially toxic conditions is readily evaluated by examining the absolute and relative activities in food web samples, as has been done for D5 by Gobas et al 29 For regulatory purposes, chemical toxicities are generally expressed either as external exposure concentrations (e.g., LC 50 values) or internal concentrations in the organism (CBR values) that cause an adverse effect. For superhydrophobic chemicals, measuring and using LC 50 values is challenging, and extrapolating them to environmental conditions is difficult because of the necessarily low exposure concentrations in water and the likely low bioavailability because of sorption to organic surfaces.…”

Decamethylcyclopentasiloxane (D5) environmental sources, fate, transport, and routes of exposure

“…Similarly to K OC , K LW is lower than would be expected based on the conventional correlation assumption that K LW equals K OW (Table ) . This assumption is not valid for D5 and possibly for other classes of lipophilic substances, as discussed by Gobas et al and Seston et al . Again, it is plausible that the behavior of D5 compared with nonpolar organics having similar K OW values relates to the differing capacities of these chemicals for the various types of molecular interactions controlling their absorption by octanol and lipids .…”

“…The present review specifically addresses steps 1 to 4 and step 7. Gobas et al address bioaccumulation (step 5), Fairbrother et al address toxicity and risk evaluation (steps 6 and 8), and Xu et al provide a more comprehensive treatment of physical and chemical properties (step 2).…”