Whelan M J, Sanders D, van Egmond R
Department of Natural Resources, School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UK.
Chemosphere. 2009 Feb;74(8):1111-6. doi: 10.1016/j.chemosphere.2008.10.037. Epub 2008 Nov 29.
The behaviour of the cyclic volatile methyl siloxane (cVMS) decamethylcyclopentasiloxane (D5) in surface waters is explored using a combination of laboratory experimentation and mathematical modelling. In the laboratory experiment, changes were observed in the concentration of radiolabelled D5 in open stirred beakers containing mineral medium with different concentrations of added Aldrich humic acid over 120 h. Although D5 is very volatile, its strong affinity for dissolved organic carbon (DOC) reduced the rate of water to air transfer significantly. The data were well described using a simple partitioning model which accounted for hydrolysis and for depth and DOC changes resulting from sampling and evaporation, although there was some evidence for the formation of a hypothetical bound residue with increasing time. The model was used to derive effective values for the partition coefficient between DOC and water [log(K(DOC))]. These values were relatively consistent across five treatments and varied between 5.04 and 5.40 log(L kg(-1)), with no systematic treatment bias. These values are significantly higher than previously published experimental estimates of K(OC) for D5 but more than two orders of magnitude lower than some K(OC) estimates based on the octanol:water partition coefficient (K(OW)). The data confirm that volatilisation will be an important loss mechanism from surface waters for D5, although the rate of loss will decrease with increasing DOC concentration.
采用实验室实验与数学建模相结合的方法，探究了环状挥发性甲基硅氧烷（cVMS）十甲基环五硅氧烷（D5）在地表水中的行为。在实验室实验中，观察了在含有不同浓度添加的奥尔德里奇腐殖酸的矿物培养基的开放式搅拌烧杯中，放射性标记的D5浓度在120小时内的变化。尽管D5挥发性很强，但其对溶解有机碳（DOC）的强亲和力显著降低了水向空气的转移速率。使用一个简单的分配模型对数据进行了很好的描述，该模型考虑了水解以及采样和蒸发导致的深度和DOC变化，尽管有证据表明随着时间的推移会形成一种假设的结合残留物。该模型用于推导DOC与水之间分配系数的有效值[log(K(DOC))]。这些值在五种处理中相对一致，在5.04至5.40 log(L kg(-1))之间变化，没有系统的处理偏差。这些值显著高于先前发表的D5的K(OC)实验估计值，但比一些基于正辛醇：水分配系数（K(OW)）的K(OC)估计值低两个多数量级。数据证实，挥发将是D5从地表水损失的一个重要机制，尽管损失速率会随着DOC浓度的增加而降低。
