Evaluating bioaccumulation potential of cyclic and linear volatile methylsiloxanes in aquatic and terrestrial species: a comprehensive analysis using the Bioaccumulation Assessment Tool

A comprehensive analysis of the bioaccumulation of three cyclic (namely, D4, D5, and D6) and five linear (namely, L2, L3, L4, L5, and L6) volatile methylsiloxanes (VMS) in biota was conducted by reviewing 50 published articles and laboratory reports on aquatic (82%) and terrestrial species (18%). A total of 178 bioaccumulation values were evaluated employing a quantitative weight-of-evidence (qWoE) approach provided by the Bioaccumulation Assessment Tool. Considerable variability of bioconcentration factor (BCF) and bioaccumulation factor (BAF) values was observed for VMS in aquatic organisms, which ranged from below to above their respective regulatory threshold values. The frequency of evidence for non-bioaccumulation (ie, BCF or BAF <2000) was ≥50% for D6, L2, L5, and L6. Conversely, laboratory biomagnification factor (BMF) values were generally (≥71%) less than 1, indicating low bioaccumulation potential through dietary uptake. Field BMFs displayed more variability but still suggested a low bioaccumulation potential. Despite the majority (≥65%) of trophic magnification factors (TMFs) in aquatic food webs being below 1, the broad range of TMF values for all VMS examined indicates potential uncertainties introduced by environmental factors in the target environments (e.g., chemical exposure gradient) and sampling bias. Overall, lines of evidence (≥71%) suggest that cyclic and linear VMS generally do not bioaccumulate in aquatic species, with dietary uptake being the primary pathway. For terrestrial species, primarily rats, predicted and field BMFs were less than 1 at 37 °C, primarily via respiratory elimination. Field TMFs for terrestrial food webs, including invertebrates and various bird species with body temperatures of 18 and 40 °C, respectively, were sourced from a single study, where D4 demonstrated trophic dilution, while D5 and D6 generally did not biomagnify in this terrestrial food web.