Abstract
Transformation studies of chlorinated paraffins (CPs) and the effects of CP transformation products on humans, biota and environment are rare. The focus here is on hydroxylation reactions. As for polyhalogenated persistent organic pollutants (POPs) in general, hydroxylation reactions convert lipophilic material to more polar compounds with increased mobility. We investigated the in-vitro transformation of single-chain CP-mixtures to hydroxylated products with the dehalogenase LinB from Sphingobium indicum. C11-, C12- and C13-single-chain CP-homologues were exposed to LinB and mono-hydroxylated (CP-ols) and di-hydroxylated (CP-diols) transformation products were formed. Liquid-chromatography coupled to mass-spectrometry (LC-MS) was used to detect hydroxylated products and to separate them from the starting material. The presented data can be used to identify these CP-ol and CP-diol homologues in other samples. Hydroxylated products had lower chlorination degrees (nCl) than respective CP-starting-materials. Reactive and persistent CP-material was found in each homologue group. Reactive material is converted within hours by LinB, while more persistent CPs are transformed within days. Homologue-specific kinetic models were established to simulate the stepwise hydroxylation of persistent CPs to mono- and di-hydroxylated products. First-order rate constants for the formation of CP-ols (k1) and CP-diols (k2) were deduced for different homologues. Lower-chlorinated CP-ols did not accumulate to large extent and were transformed quickly to CP-diols, while higher-chlorinated CP-ols and -diols both accumulated. By enzymatic transformation of single-chain CPs with LinB, we synthesized unique sets of mono- and di-hydroxylated materials, which can be used as analytical standards and as starting materials for metabolic, toxicity and environmental fate studies.
Highlights
Chlorinated paraffins (CPs) are widely used as plastic additives e.g. as plasticizers and flame retardants (Fiedler, 2010; UNEP, 2016)
We showed that the bacterial dehydrohalogenase LinA2 from Sphingobium indicum catalyzes a step-wise elimination of hydrochloric acid (HCl) converting CPs to chloro-olefins (COs) and –diolefins (CdiOs) as shown in Fig. 1B (Heeb et al, 2019)
extracted ion chromatograms (EICs) of CPhomologues were exposed to LinB and mono-hydroxylated (CP-ols) and CP-diols show interferences from olefinic ho mologues because the LC-APCI-QTOF-MS used for measurements cannot resolve these signals as described in chapter 1, but mathematical deconvolution can
Summary
Chlorinated paraffins (CPs) are widely used as plastic additives e.g. as plasticizers and flame retardants (Fiedler, 2010; UNEP, 2016). Mass spectra of saturated hydroxylated CPs (0 DBE) and unsatu rated hydroxylated COs, ethers, epoxides and carbonyls (>0 DBE) are interfered as well (Fig. 1). To resolve such interferences, a mass reso lution >68′000 is needed. We showed that the bacterial dehydrohalogenase LinA2 from Sphingobium indicum catalyzes a step-wise elimination of HCl converting CPs to chloro-olefins (COs) and –diolefins (CdiOs) as shown in Fig. 1B (Heeb et al, 2019). We used LinB to produce sets of C11-, C12- and C13-CP-ols and -diols from respective single-chain CP-materials These new hydroxylated materials can be used as analytical standards for metabolomic, toxicological and environmental fate studies. These models included first-order rate con stants which were deduced from time-dependent data, describing the step-wise formation of CP-ols and CP–diols and the accumulation of mono- and di-hydroxylated CPs with time
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