Abstract
The silicone polymer polydimethysiloxane (PDMS) is a popular passive sampler for in situ and ex situ sampling of hydrophobic organic chemicals. Despite its limited sorptive capacity for polar and ionizable organic chemicals (IOC), IOCs have been found in PDMS when extracting sediment and suspended particulate matter. The pH-dependent partitioning of 190 organics and IOCs covering a range of octanol-water partition constants log K ow from -0.3 to 7.7 was evaluated with a 10-day shaking method using mixtures composed of all chemicals at varying ratios of mass of PDMS to volume of water. This method reproduced the PDMS-water partition constant K PDMS/w of neutral chemicals from the literature and extended the dataset by 93 neutral chemicals. The existing quantitative structure-activity relationship between the log K ow and K PDMS/w could be extended with the measured K PDMS/w linearly to a log K ow of -0.3. Fully charged organics were not taken up into PDMS. Thirty-eight monoprotic organic acids and 42 bases showed negligible uptake of the charged species, and the pH dependence of the apparent D PDMS/w(pH) could be explained by the fraction of neutral species multiplied by the K PDMS/w of the neutral species of these IOCs. Seventeen multiprotic chemicals with up to three acidity constants pK a also showed a pH dependence of D PDMS/w(pH) with the tendency that the neutral and zwitterionic forms showed the highest D PDMS/w(pH). D PDMS/w(pH) of charged species of more hydrophobic multiprotic chemicals such as tetrabromobisphenol A and telmisartan was smaller but not negligible. Since these chemicals show high bioactivity, their contribution to mixture effects has to be considered when testing passive sampling extracts with in vitro bioassays. This work has further implications for understanding the role of microplastic as a vector for organic micropollutants.
Highlights
Passive equilibrium sampling (PES) has been identified as a robust and promising method for monitoring the freely dissolved concentrations of chemicals in water and the bioavailable fractions in particles
Silicone is a popular absorbent phase that has been widely used in PES devices for in situ passive sampling in water[1,2] and sediment,[3] as well as for ex situ equilibrium partitioning in the laboratory.[4]
As both the log KPDMS/w and the logarithm of the sediment− water partition constant log Ksed/w are linearly correlated with the log Kow, the logarithms of the PDMS−sediment partition constants log KPDMS/sed are fairly independent of the log Kow.[7]
Summary
Passive equilibrium sampling (PES) has been identified as a robust and promising method for monitoring the freely dissolved concentrations of chemicals in water and the bioavailable fractions in particles. The partitioning of contaminants depends on the material of the passive samplers, the conditions of sampling/equilibration, as well as the physicochemical properties of target analytes.[5] PDMS has been recommended as a passive sampler for hydrophobic and nonionized chemicals because of its limited enrichment of hydrophilic chemicals with log Kow (octanol−water partition constant) lower than 3.6 As both the log KPDMS/w and the logarithm of the sediment− water partition constant log Ksed/w are linearly correlated with the log Kow, the logarithms of the PDMS−sediment partition constants log KPDMS/sed are fairly independent of the log Kow.[7] This feature has been exploited to apply PDMS extracts from sediments in in vitro bioassays because the mixture effect equivalents in PDMS can be directly translated into effect equivalents in sediments without the need to know the composition of the mixture.[8−11] This method has been applied for biota, such as fish tissue,[12−15] dugong blubber,[16] turtle blood,[17] and human tissue and blood[18] because the PDMS−lipid partition constants KPDMS/lipid are virtually independent of hydrophobicity
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