Understanding of Cyclic Volatile Methyl Siloxane Fate in a High Latitude Lake Is Constrained by Uncertainty in Organic Carbon–Water Partitioning

Abstract

Cyclic volatile methyl siloxanes (cVMS) are emitted to aquatic environments with wastewater effluents. Here, we evaluate the environmental behavior of three cVMS compounds (octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6)) in a high latitude lake (Storvannet, 70°N 23°E), experiencing intermittent wastewater emissions and high latitude environmental conditions (low temperatures and seasonal ice cover). Measured cVMS concentrations in lake water were below detection limits in both March and June 2014. However, mean concentrations in sediments were 207 ± 30, 3775 ± 973 and 848 ± 211 ng g organic carbon for D4, D5 and D6, respectively. To rationalize measurements, a fugacity-based model for lakes (QWASI) was parametrized for Storvannet. The key removal process for cVMS from the lake was predicted to be advection due to the low hydraulic retention time of the lake, followed by volatilization. Predicted cVMS behavior was highly sensitive to the partition coefficient between organic carbon and water (K) and its temperature dependence. Predictions indicated lower overall persistence with decreasing temperature due to enhanced partitioning from sediments to water. Inverse modeling to predict steady-state emissions from cVMS concentrations in sediment provided unrealistically high emissions, when evaluated against measured concentrations in sewage. However, high concentrations of cVMS in sediment and low concentrations in water could be explained via a hypothetical dynamic emission scenario consistent with combined sewer overflows. The study illustrates the importance of considering compound-specific behavior of emerging contaminants that may differ from legacy organic contaminants.

A critical assessment of the environmental fate of linear and cyclic volatile methylsiloxanes using multimedia fugacity models

“…The parameters that were found to be most sensitive are DH OC , K OC , the fraction of organic carbon in the water (f OC ) and the deposition rate of sediment particles (Dep). This observation is also supported by the ndings of Krogseth et al 53 Out of all compartments, these parameters were found to be especially sensitive for the concentrations of VMS in the sediment. One could expect to see large differences in the concentrations of VMS in water too but the amount of siloxane in the water compartment is small under all scenarios and thus appears insensitive to changes in DH OC , K OC , f OC and Dep.…”

Ex Vivo Human Skin is not a Barrier for Cyclic Siloxanes (Cyclic Silicones): Evidence of Diffusion, Bioaccumulation, and Risk of Dermal Absorption Using a New Validated GC-FID Procedure

“…For many years, their use was considered safe for humans [ 3 , 7 ]; however, in recent years, it has been shown that they cause environmental pollution [ 1 , 2 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. In addition, these compounds can bioaccumulate in the living organisms [ 17 , 18 , 19 , 20 ], in the ecosystem with significant durability and the ability to transport to very remote areas, including the Arctic region [ 20 , 21 , 22 ]. This is mainly possible due to their physicochemical properties, such as high volatility (4.6–132 Pa at 25 °C), Henry’s law constant (1.210–4.945 kPa m 2 /mol at 25 °C), chemical stability [ 23 ], hydrophobicity (e.g., low water solubility: 5.3–56 mg/L), and high octanol-water partition coefficient (log Kow: 5.10–8.87 at 25 °C) [ 24 , 25 ].…”

Uncertainty and equifinality in environmental modelling of organic pollutants with specific focus on cyclic volatile methyl siloxanes

“…The uncertainty in the predicted steady state values of C W and C S arising from uncertainty in the model parameters was fairly modest, even for those parameters to which the model is relatively sensitive. For all three compounds, the uncertainty implied in C W is lower (CV of the order of 12-22%) than that in C S (CV of the order of 38-55%), reecting the propensity of cVMS compounds to sorb to sediment 20,56,57 and the sensitivity of the model to sediment deposition rate and K OC . 9,20,58 Predicted concentrations in sediment were more sensitive than predicted concentrations in water for the same simulations (the relative range of outputs was wider).…”

“…Models like QWASI have historically been shown to generate reasonable predictions of chemical exposure and the relative importance of competing loss processes in lake. 3,9,20,[28][29][30] The purpose here is not to undermine this successful approach. Rather, MCS provides a means of enhancing point estimates of exposure and persistence, with relatively modest additional computational effort (as long as the models are relatively simple).…”

“…18 Other combinations of parameters may yield similarly good predictions of the available data but better (and unknown) predictions of the unmeasured state variables. 19 MFTMs are oen used to investigate the implications of different physico-chemical properties for the environmental fate and transport of organic pollutants 20 and in risk assessment to estimate levels of exposure in different environmental compartments resulting from a given emission scenario. However, signicant uncertainties (and variability) exist in both chemical-specic parameters (such as partition coefficients and degradation rate constants) and in the parameters which are used to describe the characteristics of the receiving environment (such as inter-media mass transfer coefficients, advection rates, some system dimensions and organic carbon uxes).…”