This chapter discusses radionuclide concentrations measured in sediment samples collected on or in the vicinity of the Savannah River Site (SRS). We reviewed the history of sediment monitoring at the SRS and evaluated these data with regard to their potential usefulness for dose reconstruction. We compiled and examined sediment data to determine their potential value in source term verification, model validation, and direct exposure assessment. Uranium data collected from Steed’s Pond, which received liquid effluents from the M-Area via Tim’s Branch, may be useful for source term verification and model validation of uranium releases from the M-Area. However, the potential usefulness of the Steed’s Pond data, which are limited in number, is bounded by spatial resolution. Results of measurements of long-lived radionuclides (uranium, plutonium, and 137Cs) in streambeds do not appear useful because samples do not represent the entire streambed and demonstrate no spatial trends because of the complex sediment deposition processes involved. Appendix K further discusses potential uses for environmental monitoring data.

Phytoplankton was studied in the Loviisa archipelago (south coast of Finland) in 1971– 1994. Since 1977, thermal effluents from the Loviisa nuclear power plant have been dis­ charged into the sea there. A general increase of nutrients in the Gulf of Finland contributed to an increase in phytoplankton biomass and primary production in the Loviisa archipelago during the late 1970s and 1980s, though biomass seemed to decrease again in the 1990s. The rise in temperature was, however, a more important factor than nutrients stimulat­ ing the production and biomass in the area close to the cooling water outlet. The thermal discharges increased especially the biomass of Aphanizomenon spp., which is the most abundant cyanoprocaryote (blue-green alga) and one of the most common phytoplankton taxa in the study area. At the intake area, total amounts of phosphorus best explained the changes in total biomass. The results indicate that increased temperature can lengthen the growing season, advance eutrophication and somewhat change species dominances in the circumstances prevailing in the northern Baltic Sea.

The long-term behaviour of 137Cs was studied in two freshwater ecosystems in southern Finland in an area most loaded by the Chernobyl fallout in 1986. Samples were taken from water, sediments, aquatic plants and fish in the lakes and from soil, mushrooms and seed plants in the catchments. The activity concentrations of 137Cs in fish have remained at a relatively high level and decreased much more slowly in these two lakes than in other lakes studied by us. One reason for the continuously high concentrations in fish is evidently the prolonged stay of caesium at a relatively high level in the water of these lakes, which is associated with a slow sedimentation rate. The hydrographical properties of the lakes, i.e. the oligotrophic character associated with a deficiency of potassium in water and a low pH are other reasons for the effective uptake and long retention time of 137Cs in fish. The effect of humic substances on the uptake and delay of caesium in fish could not be proved clearly in this study. The swampy soil type of the catchment associated with a more oligotrophic status and lower pH of the water in Lake Siikajärvi explain at least partly the difference in activity concentrations and transfer of 137Cs between the two lakes studied. This refers to the higher transfer from the catchment to the lake and the higher uptake of 137Cs by fish and other biota in Lake Siikajärvi than in Lake Vehkajärvi. Perch and pike were more efficient accumulators of caesium than the best indicators among the aquatic plants. In the terrestrial environment, caesium was most effectively accumulated by mushrooms.

The process of assessing risk to the environment following a given release of radioactivity requires the quantification of activity concentrations in environmental media and reference organisms. The methodology adopted by the ERICA Integrated Approach involves the application of concentration ratios (CR values) and distribution coefficients (K(d) values) for aquatic systems. Within this paper the methodologies applied to derive default transfer parameters, collated within the ERICA Tool databases, are described to provide transparency and traceability in the documentation process. Detailed information is provided for the CR values used for marine and freshwater systems. Of the total 372 CR values derived for the marine ecosystem, 195 were identified by literature review. For the freshwater system, the number of values based on review was less, but still constituted 129 from a total of 372 values. In both types of aquatic systems, 70-80% of the data gaps have been filled by employing "preferable" approaches such as those based on substituting values from taxonomically similar organisms or biogeochemically similar elements.

The impact of the radioactive fallout caused by the accident at the Chernobyl NPP on the Baltic Sea is discussed in this paper. The fallout from Chernobyl was very unevenly distributed in the drainage area of the Baltic Sea; the Bothnian Sea and the eastern part of the Gulf of Finland received most of the deposition. This was reflected in the activity concentrations of the main fallout nuclides (especially Cs-137) that have been found in the marine environment of the Baltic Sea since then. The maximum concentrations that were detected soon after the fallout decreased significantly in a short time, and the distribution pattern of the Chernobyl-derived Cs-137 has changed over the course of time as a consequence of river discharges, mixing of water masses, sea currents and sedimentation processes. Sea currents have transported caesium from the Gulf of Finland and the Gulf of Bothnia into the Baltic Proper and further out of the Baltic Sea into the North Sea. In addition, a considerable amount of Cs-137 has been bound in the seabed of the Baltic Sea. In general, the concentrations of man-made radionuclides in the sediments have been at or below the concentrations of naturally-occurring radionuclides, and are not expected to cause harmful effects on the wildlife in the Baltic Sea. The exposure of the population to radiation caused by the ingestion of Baltic Sea fish after the Chernobyl accident was considered to be low compared with the mean annual exposure of Finns to radiation or to the dose caused by natural radionuclides in the sea.

Information included in this publication or extracts thereof are free for citation on the condition that the complete reference of the publication is given. Bottom sediments play an important role in radioecological studies of the marine environment because a large proportion of radioactive substances entering the sea is adsorbed over time onto suspended particulate matter and deposited in sediments. Generally, this is the fi nal sink for most of the organic material produced in the water phase, as well as for other particles transported by water currents from other sea areas and from adjacent terrestrial areas. During their slow settling , the particles tend to bind radionuclides from the water phase and carry them to the bottom. Under favourable conditions, the deposited particles form undisturbed laminae in a stratigraphic sequence on the seabed, and the bottom sediments create an archive from which the history of the area can be read. Various particle-bound substances can be identifi ed as markers of spe-cifi c historical events and, with the aid of marker horizons, the laminae can be dated. Modern dating methods provide reliable time scales in which time-dependent changes in the concentrations of radionuclides can be recorded. As an example, the radioactive fallout from atmospheric nuclear weapons tests in the 1950s and 1960s and the accident at the Chernobyl Nuclear Power Plant in April 1986 have created useful markers in the sediments of many sea areas, especially in the Baltic Sea. The Baltic Sea offers exceptionally good opportunities to conduct sedimentological studies because the average rate of sedimentation there is much higher than in the oceans and in most other coastal seas. The anoxic conditions in the near-bottom water of the Baltic Proper, and hence the lack of benthic animals over large bottom areas, result in the formation of an undisturbed sedimentary medium, which enables the sampling of sediment laminae in an undisturbed strati-graphic sequence. However, sediment sampling is extremely sensitive to errors, which can cause substantial differences in results. This fact should always be taken into account when considering sediment results. This report presents the results of a Sediment Baseline Study carried out by the HELCOM Project Group for Monitoring of Radioactive Substances in the Baltic Sea (HELCOM MORS-PRO) in 2000–2005. The goal of the study was to complement the knowledge and inventories of long-lived radionuclides in the seabed of the Baltic Sea by providing additional data from so-called " white …