Distinguishing between natural and anthropogenic sources for elements in the environment: regional geochemical surveys versus enrichment factors

Abstract

High element enrichment factors (EFs) are commonly used in the literature to support the hypothesis that a particular suite of elements is of anthropogenic origin. Real-world examples of regional geochemical surveys demonstrate that EFs can be high or low due to a multitude of reasons, of which contamination is but one. This applies to EFs calculated relative to either the crust or some local background (e.g., a deeper soil layer). Results from local studies near industrial centres showing high (and pollution-related) EFs cannot be generalised over large areas or for sample sites far removed (i.e., more than some tens of kilometers) from a likely pollution source. Regional-scale geochemical mapping, on the other hand, facilitates the reliable estimation of the influence of contamination on the measured element concentrations. EFs are strongly influenced by, among other factors, biogeochemical processes that redistribute chemical elements between environmental compartments at the Earth's surface. Using EFs to detect or ‘prove’ human influence on element cycles in remote areas should be avoided because, in most cases, high EFs cannot conclusively demonstrate, nor even suggest, such influence.