Chlorinated paraffins are industrial chemicals that can be subdivided into short-chain (SCCP), medium-chain (MCCP), and long-chain (LCCP) chlorinated paraffins. The global production volumes of MCCPs are nowadays suspected to be much higher than those of S- and LCCPs, and the few available studies on the environmental occurrence of chlorinated paraffins report often higher MCCP concentrations than S- or LCCP concentrations in the environment. The present review focuses, therefore, on MCCPs specifically and provides a literature overview and a data analysis of the production volumes, PBT properties (persistence, bioaccumulation potential, and toxicity), and the worldwide measured concentrations of MCCP in environmental samples, biota, and humans. Furthermore, we include our own measurements of technical CP formulations from China, the major global producing country, to estimate the global production amounts of MCCPs. The key findings from this review are that (1) MCCPs are toxic to the aquatic environment, and the available data suggest that they are also persistent; (2) available time trends for MCCPs in soil, biota, and most of the sediment cores show increasing time trends over the last years to decades; and (3) MCCP concentrations in sediment close to local sources exceed toxicity thresholds (i.e., the PNEC). Our study shows that overall, MCCPs are of growing concern, and regulatory actions should be considered seriously.

Chlorinated paraffins (CPs) are high production volume chemicals and ubiquitous environmental contaminants. CPs are produced and used as complex mixtures of polychlorinated n-alkanes containing thousands of isomers, leading to demanding analytical challenges. Due to their high degree of chlorination, CPs have highly complex isotopic mass patterns that often overlap, even when applying high resolution mass spectrometry. This is further complicated in the presence of degradation products such as chlorinated alkenes (CP-enes). CP-enes are formed by dehydrochlorination of CPs and are expected thermal degradation products in some applications of CPs, for example, as metal working fluids. A mathematical method is presented that allows deconvolution of the strongly interfered measured isotope clusters into linear combinations of isotope clusters of CPs and CP-enes. The analytical method applied was direct liquid injection into an atmospheric pressure chemical ionization source, followed by quadrupole time-of-flight mass spectrometry (APCI-qTOF-MS), operated in full scan negative ion mode. The mathematical deconvolution method was successfully applied to a thermally aged polychlorinated tridecane formulation (Cl-Cl). Deconvolution of mass patterns allowed quantifying fractions of interfering CPs and CP-enes. After exposure to 220 °C for 2, 4, 8, and 24 h, fractions of CP-enes within the respective interfering clusters increased from 0-3% at 0 h up to 37-44% after 24 h. It was shown that thermolysis of CPs follows first-order kinetics. The presented deconvolution method allows CP degradation studies with mass resolution lower than 20000 and is therefore a good alternative when higher resolution is not available.

Chlorinated paraffins (CPs) are high production volume chemicals and ubiquitous environmental pollutants. In particular, data about the environmental fate of medium-chain (MCCPs, C14–C17) and long-chain (LCCPs, C≥18) CPs are urgently needed. Their analysis requires elaborate analytical methods and representative analytical standards. Complex mixtures that contain CPs of different carbon chain lengths and degrees of chlorination are currently used for quantification but are impractical when chain length distributions substantially differ between samples and standards. Single-chain CP mixtures of only one carbon chain length but varying degrees of chlorination are more suitable for accurate quantification but are not available for MCCPs and LCCPs. Such standards are useful for homologue pattern deconvolution and response factor calculations. Toxicity and transformation studies on MCCPs and LCCPs are scarce. Respective studies would also benefit from less complex CP standards, e.g., single-chain mixtures or even constitutionally defined CPs. Currently available analytical standards are inadequate for the demanding task of quantifying MCCPs and LCCPs. Improved standards are required. This review provides an overview of the available analytical CP materials, discusses their advantages and disadvantages for accurate CP analysis, and gives a recommendation for improvements. Recommendations for improved analytical standards include (A) complex CP mixtures that better resemble technical CP mixtures, (B) single-chain CP mixtures of different carbon chain lengths (C10–C30) and varying degrees of chlorination (40–70 wt%Cl), (C) constitutionally defined CPs with representative chlorination patterns, and (D) isotopically labeled CP isomers that represent a broad range of CPs.