Structure-related distribution of PCDD/Fs, PCBs and HCB in a river–sea system

Water concentrations of PCDD/Fs, HCB, and non-ortho, mono-ortho, and non-dioxin-like PCBs were measured four times during 1 year in a coastal area of the Baltic Sea, to investigate background levels and distribution behaviour. Sampling sites included two rivers, an estuary, and the sea. Particulate and apparently dissolved concentrations were determined using active sampling (filters + PUFs), while freely dissolved concentrations were determined using passive sampling (POM-samplers). The distribution between particulate + colloidal and freely dissolved phases, in the form of TOC-normalized distribution ratios (KTOC), was found to be near or at equilibrium. The observed KTOC were not significantly different between sampling sites or seasons. For PCDD/Fs, the concentrations were significantly correlated to suspended particulate matter (SPM), while no correlation to organic carbon (TOC) was observed. In the estuary and the sea, PCB concentrations were correlated to TOC. The sorption of various congeners to SPM and TOC appeared to be related to both hydrophobicity and 3D-structure. The PCDD/F concentration in the sea decreased to one third in May, likely connected to the increased vertical flux of particles during the spring bloom.

Research highlights
► PCDD/Fs, PCBs and HCB were measured in water in a background level area.
► Particulate, apparently dissolved and freely dissolved levels were determined.
► It appeared to be equilibrium between particle + colloid and freely dissolved phases.
► PCDD/F concentrations correlated to SPM, PCB7 concentrations to TOC.
► PCDD/F levels decreased markedly in the sea in May, probably due to spring bloom.