Department of Environmental Science and Technology, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UK.
Chemosphere. 2013 Jun;91(11):1566-76. doi: 10.1016/j.chemosphere.2012.12.048. Epub 2013 Jan 18.
The behaviour of cyclic volatile methyl siloxanes (cVMS) in lakes was explored using a fugacity-based steady-state non-equilibrium multimedia fate and transport model (a modified version of QWASI). Three substances were investigated: Octamethylcyclotetrasiloxane (D4), Decamethylcyclopentasiloxane (D5) and Dodecamethylcyclohexasiloxane (D6) in two contrasting North American lakes: Lake Ontario and Lake Pepin (a natural shallow lake on the Mississippi river between Minnesota and Wisconsin). Values for the principal partition coefficients and the hydrolysis rate constant were adjusted for the mean annual temperatures of each lake. Hydrolysis rate constants were also adjusted for the fraction of chemical calculated to be in the freely dissolved phase. Half-lives in sediment were calculated from partitioning theory, assuming hydrolysis can occur only in the dissolved phase. Best estimates of substance-specific emissions were obtained by combining current per capita approximations of usage and fraction lost to domestic waste water, the population of the lake catchment and cVMS removal in waste water treatment. Concentrations were generally lower and chemical residence times longer in Lake Ontario than in Lake Pepin, owing to greater depth, a higher hydraulic retention time and a higher degree of dilution. Overall persistence in Lake Pepin is significantly influenced by the high rate of sediment burial assumed in the model, as well as by a relatively high rate of water discharge. Despite the many similarities of the compounds considered, the dominant loss mechanisms vary significantly and are not the same in each lake system. This highlights the pitfalls of subjective evaluation of chemical fate and illustrates the important role which models have to play in providing a quantitative framework for assessing chemical behaviour objectively under the influence of a complex and interacting set of factors.
采用基于逸度的稳态非平衡多介质物质输运模型（QWASI 的一个改良版本）研究了环状挥发性甲基硅氧烷（cVMS）在湖泊中的行为。研究了三种物质：八甲基环四硅氧烷（D4）、十甲基环五硅氧烷（D5）和十二甲基环六硅氧烷（D6），这三种物质存在于两个具有鲜明对比的北美湖泊中：安大略湖和皮平湖（密西西比河上明尼苏达州和威斯康星州之间的一个天然浅湖）。对主要分配系数和水解速率常数的值进行了调整，以适用于每个湖泊的年均温度。还针对计算得出的处于自由溶解相的化学物质的分数，对水解速率常数进行了调整。根据分配理论，从半衰期在沉积物中计算，假设水解只能在溶解相中发生。通过将目前人均使用量和损失到生活污水中的分数、湖泊流域的人口以及生活污水处理中 cVMS 的去除率进行结合，获得了特定物质排放量的最佳估计值。由于深度较大、水力停留时间较长且稀释程度较高，安大略湖中的浓度通常低于皮平湖，化学物质的停留时间也较长。在皮平湖中，整体持久性受到模型中假设的高沉积速率以及相对较高的水排放量的显著影响。尽管所考虑的化合物具有许多相似之处，但主要的损失机制差异很大，并且在每个湖泊系统中并不相同。这突显了主观评估化学物质命运的缺陷，并说明了模型在提供客观评估化学物质行为的定量框架方面所扮演的重要角色，因为化学物质受到一组复杂且相互作用的因素的影响。
