210Po in the marine environment with emphasis on its behaviour within the biosphere

The distribution and behaviour of the natural-series alpha-emitter polonium-210 in the marine environment has been under study for many years primarily due to its enhanced bioaccumulation, its strong affinity for binding with certain internal tissues, and its importance as a contributor to the natural radiation dose received by marine biota as well as humans consuming seafoods. Results from studies spanning nearly 5 decades show that Po-210 concentrations in organisms vary widely among the different phylogenic groups as well as between the different tissues of a given species. Such variation results in Po-210 concentration factors ranging from approximately 10(3) to over 10(6) depending upon the organism or tissue considered. Po-210/Pb-210 ratios in marine species are generally greater than unity and tend to increase up the food chain indicating that Po-210 is preferentially taken up by organisms compared to its progenitor Pb-210. The effective transfer of Po-210 up the food chain is primarily due to the high degree of assimilation of the radionuclide from ingested food and its subsequent strong retention in the organisms. In some cases this mechanism may lead to an apparent biomagnification of Po-210 at the higher trophic level. Various pelagic species release Po-210 and Pb-210 packaged in organic biodetrital particles that sink and remove these radionuclides from the upper water column, a biogeochemical process which, coupled with scavenging rates of this radionuclide pair, is being examined as a possible proxy for estimating downward organic carbon fluxes in the sea. Data related to preferential bioaccumulation in various organisms, their tissues, resultant radiation doses to these species, and the processes by which Po-210 is transferred and recycled through the food web are discussed. In addition, the main gaps in our present knowledge and proposed areas for future studies on the biogeochemical behaviour of Po-210 and its use as a tracer of oceanographic processes are highlighted in this review. (C) 2010 Elsevier Ltd. All rights reserved.