Acidity and leaching of metals from acid sulphate soils (ASSs) impair the water quality of receiving surface waters.
The largest ASS areas in Europe are found in the coasts of the northern Baltic Sea. We used weight-ofevidence
(WoE) approach to assess potential risks in 14 estuary sites affected by ASS in the Gulf of Finland, northern
Baltic Sea. The assessment was based on exposure and effect profiles utilizing sediment and water metal
concentrations and concurrent pH variation, sediment toxicity tests using the luminescent bacterium Vibrio
fischeri and the midge Chironomus riparius, and the ecological status of benthic macroinvertebrate communities.
Sediment metal concentrationswere compared to national sediment quality criteria/guidelines, andwater metal
concentrations to environmental quality standards (EQSs). Hazard quotients (HQs) were established for maximumaluminium,
cadmiumand zinc concentrations at lowpH based on applicable US EPA toxicity database. Sediment
metal concentrationswere clearly elevated in most of the studied estuaries. The EQS of cadmium(0.1 μg/l)
was exceeded in 3 estuaries out of 14. The pH-minima were below the national threshold value (5.5) between
good and satisfactorywater quality in 10 estuaries. V. fischeri bioluminescence indicated toxicity of the sediments
but toxic response was not observed in the C. riparius emergence test. Benthic invertebrate communities were
deteriorated in 6 out of 14 sites based on the benthic invertebrate quality index. The overall ecotoxicological
risk was assessed as low in five, moderate in three and high in five of the estuary sites. The risk assessment utilizing
the WoE approach indicated that harmful effects of ASSs are likely to occur in the Baltic Sea river estuaries
located at the ASS hotspot area.