Biotransformation of short-chain chlorinated paraffins (SCCPs) with LinA2: A HCH and HBCD converting bacterial dehydrohalogenase

Abstract

Short-chain chlorinated paraffins (SCCPs) are polyhalogenated hydrocarbons as are hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). They all have been classified as persistent organic pollutants (POPs) under the UN Stockholm Convention. Per se such compounds are transformed slowly in the environment, transported over long distances and accumulate in biota. Several Sphingomonadacea strains isolated from HCH dump sites have evolved to express enzymes that can transform HCHs and HBCDs. We hypothesized that LinA2, a dehydrohalogenase expressed in such bacteria, may also transform CPs to chlorinated olefins (COs). Three mixtures of penta- to deca-chlorinated undecanes (C11), dodecanes (C12) and tridecanes (C13) were exposed to LinA2. High-resolution full-scan mass spectra (R∼8′000) of CPs and COs were obtained applying a soft ionization method, enhancing chloride-adduct [M+Cl]- formation. A mathematical deconvolution procedure was used to separate interfering spectra to verify that LinA2 indeed catalyzed the conversion of CPs to COs. About 20–40% of the material was transformed in 24 h, about 50–70% was converted in 200 h. A bimodal first-order kinetic model could describe transformations of reactive and persistent CPs. Under the given conditions reactive CPs (τ1/2 = 1.4–6.9 h) were converted 30 to 190-times faster than the persistent ones (τ1/2 = 150–260 h). Proportions of persistent isomers (pp) varied from 60 to 80%. Lower chlorinated homologues contained higher proportions of persistent isomers. In conclusion, SCCP mixtures contain both, material that is readily converted by LinA2, and persistent material that is not or only slowly transformed.