Determination of Polyparameter Linear Free Energy Relationship (pp-LFER) Substance Descriptors for Established and Alternative Flame Retardants

Abstract

Polyparameter linear free energy relationships (pp-LFERs) can predict partition coefficients for a multitude of environmental and biological phases with high accuracy. In this work, the pp-LFER substance descriptors of 40 established and alternative flame retardants (e.g., polybrominated diphenyl ethers, hexabromocyclododecane, bromobenzenes, trialkyl phosphates) were determined experimentally. In total, 251 data for gas-chromatographic (GC) retention times and liquid/liquid partition coefficients (K) were measured and used to calibrate the pp-LFER substance descriptors. Substance descriptors were validated through a comparison between predicted and experimental log K for the systems octanol/water (K(ow)), water/air (K(wa)), organic carbon/water (K(oc)) and liposome/water (K(lipw)), revealing a high reliability of pp-LFER predictions based on our descriptors. For instance, the difference between predicted and experimental log K(ow) was <0.3 log units for 17 out of 21 compounds for which experimental values were available. Moreover, we found an indication that the H-bond acceptor value (B) depends on the solvent for some compounds. Thus, for predicting environmentally relevant partition coefficients it is important to determine B values using measurements in aqueous systems. The pp-LFER descriptors calibrated in this study can be used to predict partition coefficients for which experimental data are unavailable, and the predicted values can serve as references for further experimental measurements.

Bioaccumulation kinetics of polybrominated diphenyl ethers and decabromodiphenyl ethane from field‐collected sediment in the oligochaete, Lumbriculus variegatus

“…Furthermore, hydrophobic chemicals tend to bind to sediment OC, leading to low C free and C s,bioavailable ( Table 1). As shown in Supplemental Data, Table S1, BCFs were estimated from C b,lipid and C free , and they were comparable to the values of less brominated PBDEs in the literature [26]. The relationship of log BCF (estimated) ¼ 0.95 Â log BCF (literature) (r 2 ¼ 0.81) suggested that C free was a good metric for the bioavailability of BFRs in sediment.…”

“…Polybrominated diphenyl ether (PBDE) and decabromodiphenyl ethane (DBDPE) in sediment collected from an electronic waste recycling site in South China [6], and the K OW value of DBDPE was from Kierkegaard et al [14]. The C free was calculated by dividing C fiber by the fiber-water partition coefficient (K fw ), which was calculated from log K OW using the equation of Stenzel et al [26]:…”

“…The C free values were calculated by dividing C fiber by the fiber-water partition coefficients (K fw ; Equation 6). The K fw values were calculated from log K OW values [6,14] using Equation 7, as proposed by Stenzel et al [26]. Using Equations 8 and 9, the readily bioavailable fractions of BFRs in sediment (C s, bioavailable ) and bioconcentration factors (BCFs) were attained, respectively.…”

Applications of Polyparameter Linear Free Energy Relationships in Environmental Chemistry

“…Partitioning systems that involve water as one of the phases are even a requirement for accurate determination of B. 47 However, experimental determination of solvent−water partition coefficients needs intensive laboratory work, and the results are typically less accurate and less precise compared to chromatographic retention times. We can thus generally conclude that a combination of methods is the most efficient way to obtain a robust set of descriptors.…”

“…2 A similar trend was found for B of aliphatic 43 The choice of B or B 0 has not become a major issue to date, at least in environmentally related studies, because the number of chemicals that need B 0 is small, and the reported differences between B and B 0 are also relatively small (<0.2). 14 Recently, Stenzel et al 47 found that different B values have to be used to characterize the partitioning into water and into trifluoroethanol for some flame retardants such as polybrominated diphenyl ethers and phosphate triesters 47 (Table S1 in the Supporting Information (SI)). B for the water phase are generally higher than B for the trifluoroethanol phase, and differences are up to 0.6, which can cause a difference of >2 log units in predicted solvent or sorbent−water partition coefficients.…”