Determination of bioindicator mollusc species for Po-210

Among the radioactive pollutants 210Po is the most substantial one in terms of seafood safety due to its efficient accumulation in marine animals and high irradiation of its alpha emission. Approximately 70% of radiation dose to human beings due to the consumption of marine products is sourced from 210Po. To our knowledge neither 210Po levels nor potential 210Po indicator molluscs species has been determined in Gökçeada island, north-eastern Aegean Sea. In the current study the activity concentrations of 210Po were determined in soft tissue of twenty mollusc species, including 8 bivalves 7 gastropods and 5 cephalopods, collected at Gökçeada island. After collection soft tissue of molluscs was digested by using concentrated acids in a microwave digestion system. Afterwards 210Po was deposited spontaneously on a silver disc. The 210Po radioactivity of the samples were measured using silicon surface-barrier detectors connected to the multi-channel analyser of an ORTEC alpha spectrometer. Po-210 activities ranged between 11,7 and 1789 Bq kg-1 in the studied twenty mollusc species. A significant variation was noted among the 210Po activity in molluscs. The average and median 210Po concentrations were found to be 400 ± 448 Bq kg-1 and 223 Bq kg-1. The average 210Po concentrations in bivalves, cephalopods and gastropods were found to be 818 ± 434, 126 ± 178 and 117 ± 81 Bq kg-1. The 210Po activity median values were found to be 755, 17,9 and 108 Bq kg-1 in bivalves, cephalopods and gastropods, respectively. The 210Po activity in molluscs was, thus, ranked as bivalve >> gastropod > cephalopod. The gradual decrease in 210Po concentration through three trophic level (bivalve-gastropod-cephalopod) clearly showed biodilution of 210Po. Substantial bioaccumulation of 210Po in bivalves compared to gastropods and cephalopods is related to their disparate food preference. Apparently filter feeding as seen in bivalves increases 210Po bioaccumulation whereas predation as in gastropods and cephalopods does not support 210Po bioaccumulation. Among the cephalopod body parts, higher activity of 210Po was seen in viscera compared to mantle and arms. A higher 210Po activity was seen in all the body parts of small squid Illex coindetii compared to big individuals. Among the bivalves Anadara gibbosa displayed an exceptionally high 210Po activity. It could be considered as a sentinel organism for monitoring studies, addressing both 210Po. Cuttlefish Sepia orbignyana has also high 210Po concentration and can be used as a potential bioindicator of 210Po pollution. The annual effective ingestion dose levels of 210Po was calculated by using measured 210Po activities in molluscs. 7,0 kg (3,2-14,2) bivalve flesh intake is adequate due to 210Po ingestion in the studied region to reach 1 mSv which is the annual committed effective dose. Consumption of bivalve molluscs causes increased internal radiation dose in the studied region due to the alpha radiation of 210Po. However due to very low mollusc consumption in the region there is no risk of alpha radiation of 210Po above the limit values through mollusc consumption.