Polonium-210 and Lead-210 in Marine Organisms: Allometric Relationships and Their Significance

Abstract

Allometric relationships which indicate that Po-210 concentrations in marine organisms decrease with increasing organism mass have been reported previously in a few taxa. We report here the results of a study of nearly 400 data covering nine taxa of marine organisms. The data for each taxon are fitted to the allometric equation log Q = log a + b log M, where Q is the Po-210 concentration (mBq/g dry mass) and M is the dry mass per individual (g). For eight of the nine taxa the slope is negative, and for six the correlation is statistically significant. Data for Pb-210, the Po-210 grandparent, are available for some sixty per cent of the samples, covering eight taxa. For seven of these taxa b is again negative, and for four the correlation is statistically significant. The weighted mean of the nine Po-210 slopes is -0.24 ±0.05, and of the eight Pb-210 slopes is -0.22 ±0.05. These values are close to the slope of -0.25 frequently found in mass-specific allometric relationships in biology; an association between radionuclide concentration and food ingestion rate is indicated. The intertaxon variations in the intercept log a are large, nearly two orders of magnitude for Po-210, a fact which almost certainly reflects intertaxon differences in diet and/or assimilation. Within taxa, sub-groupings of the Po-210 data are found; these are discussed and an attempt is made to classify them statistically for the data as a whole.