An index for estimating the potential impact on the environment of the pollutant content in aquatic populations

The so-called "Concentration factor" (C.F.) should express a direct positive relationship between the concentration of a pollutant (e.g. metals, radioisotopes) in an organism and the concentration of the same pollutant in the water. While this index is very useful in some cases, it cannot give any information on the influence of the biota on its environment, an important topic in research on biogeochemical cycles. A new index (the Influence index) has consequently been developed to quantify the potential influence of the pollutant content in the population biomass on the habitat in which the population lives. The value of this index is calculated as the ratio between the pollutant content in the population biomass per sediment surface unit (e.g. m2) and the concentration of the same pollutant in the water, and is expressed as water volume with the same pollutant concentration as in the water of the population habitat. The value increases with the increase of the pollutant content in the population biomass and the decrease of the pollutant concentration in the water. As an example, some applications of the index to heavy metal contaminations of a freshwater mussel (Unio pictorum mancus) population are described.