Intrinsic flaws of element enrichment factors (EFs) in environmental geochemistry

The popular concept of enrichment factors (EFs) as a means of identifying a nd quantifying human interference with global element cycles is evaluated. It is demonstrated that the concept of normalizing element concentrations t o an average total crust value is of doubtful merit, for theoretical consid erations alone. Serious flaws with EFs include the variable composition of the Earth's crust at a ny given point compared to the global average, the n atural fractionation of elements during their transfer from the crust to th e atmosphere through processes such as weathering and winnowing of fines, a nd the differential solubility of minerals in the weak chemical digestions generally used in environmental studies. Furthermore the impact of biogeoch emical processes is neglected. A biomonitoring survey of atmospheric chemis try over a 1.5 million km(2) area in northern Europe is used to show that E Fs are governed here by completely different processes than anthropogenic a ctivities. As a simple means to assess the maximum possible interference of human activities with global element reservoirs, the mining interference f actor (MIF = (total tonnage mined annually/total tonnage in upper 2 km of c rust) x 100%) is introduced. The elements C >> Br > Cu > Sb >> Ag > Cd > Pb show the highest MIFs, while Ga, Cs, Ge, K, In, I, and Rh show very low MI Fs. We recommend indiscriminate usage of EFs in the scientific literature b e abandoned and more large-scale surveys be supported internationally to co llect quality, statistically significant environmental data. Only thus can human interference with natural biogeochemical cycles be properly documente d.