Blubber tissue samples from in total 40 juvenile ringed seals from the Baltic Sea collected between 1978 and 2014 were analyzed for "dioxins"; polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/PCDF) and dioxin-like PCBs (dl-PCB). Thirty-eight of the seals were bycaught in fishing gear and two were shot by mistake, taken for grey seals.

Concentrations of PCDDs, PCDFs and dl-PCBs have decreased over the study period in ringed seals with only a few exceptions. The decrease was primarily seen until year 2000 while the concentrations have been stable the last 15 years with a few exceptions. Two dioxins (1,2,3,4,6,7,8-HpCDD and OCDD) and one furan (1,2,3,7,8-PeCDF) demonstrate increased levels the last 15 year of the study period while one furan decreases (1,2,3,7,8,9-HxCDF). OCDD demonstrates the highest increase rate with 15 % yearly increase the last 15 years.

Concerning the dioxin-like PCBs, the four non-ortho, dl-PCBs demonstrate no trend the last 15 years. Four of the mono-ortho dl-PCBs continue to decrease until 2014 while the other four mono-ortho congeners show no statistically significant trends the last 15 years.

It should however be stated that a limited number of seals have been analyzed with an average of one seal/year and more analyses are demanded in order to achieve more significant time trend results.

Ringed seals show a low increase in population, approximately half of what is natural and reproductive impairment is still noted among ringed seals. If this has a connection to the concentrations of PCDD/F and dl-PCBs cannot be ruled out.