Analysis of toxicological risks from local contamination by PCDDs and PCDFs: Importance of isomer distributions and toxic equivalents

The concentrations of 2,3,7,8-chlorinated dibenzo-p-dioxins and furans (PCDD/PCDFs) at Finnish contaminated sites associated with chlorophenolic (CP) wood preservatives were measured by isomer-specific GC/HRMS methods, and the implications of the spatial and structural distributions of the isomers and of toxic equivalent (TEF) systems for toxicological risks were investigated. High concentrations (maximum value of over 90 ppb and arithmetic mean value of 19 ppb I-TEQs in dry weight) of PCDD/Fs were found in soil samples from sites where wood presevative consisting of 2346-TeCP, PeCP and 246-TCP have been used. The PCDD/Fs were distributed heterogeneously between soil layers, the concentrations in topsoil samples being generally smaller (mean 9.1 ppb I-TEQ d.w.) than those in subsoil (mean 28 ppb I-TEQ d.w.). Concentrations of PCDD/Fs were unrelated to the CP contents in the soil samples. Hexa-, hepta- and octachlorinated dibenzofurans were the dominant congeners by concentration in these and in most other samples, also in the wood preservative. The isomer distribution differed considerably between study sites, and even between samples of soil and waste at the same site. The relative importance of the samples and isomers was affected by the selection of TEFs; the importance of some of the CP-related samples was increased when applying TEFs based on lethality to juvenile fish, due to the abundance of 123478-HxCDF. Low concentrations of PCDD/Fs (ca. 0.1 ppt I-TEQ in fresh weight, only slightly above those in a control lake) were measured in the muscle of roach from the recipient of a site where high concentrations (ca. 20 ppb I-TEQ d.w.) were quantitated in the surfical sediments of a leachate discharge ditch.