General characteristics of the frequency distributions of element concentrations and of interelemental correlations in aquatic organisms

Up to 27 elements were analyzed in each of 11 different types of biological tissue from unpolluted water using inductively coupled plasma mass spectrometry. The tissues included both marine and freshwater samples, bivalves and teleosts, as well as samples from the wild, the laboratory and aquaculture cages. Because individual organisms were analyzed, it was possible to construct a frequency distribution for each element in each particular type of tissue. Nearly all the distributions (except for potassium and selenium) were found to show some degree of positive skewness indicating a relatively large number of organisms with low concentrations of a particular element and a few organisms with disproportionately high concentrations. A correlation was found between the amount of variability in a distribution and the amount of skewness, indicating that the more variable distributions tended to show more skewness. The greatest levels of both skewness and variability were found for the heavy metals, rare earth elements and actinides. The lowest levels of both skewness and variability were found for the alkali metals, the non-metals and magnesium. There was a positive correlation between skewness, variability and the proportion of an element stored in an insoluble form. Two general types of interelemental correlation were noted. The first type was between elements with similar chemical properties (calcium/strontium,lanthanum/cerium/yttrium, copper/silver/manganese, arsenic/ selenium, lead/cadmium, rubidium/potassium, sodium/magnesium/lithium). The second type was a result of elements bound to sediment in the intestinal tracts of organisms (aluminum/iron/manganese/barium). All correlations observed were positive precluding the existence of competitive inhibition in these unpolluted samples.