Arsenic Environmental Biogeochemistry

Arsenic represents a ubiquitous element in the environment, characterized by high mobility, complex chemical speciation and a strong sensitivity to redox conditions and biological activity. The present review provides an integrated synthesis of arsenic biogeochemical cycling across terrestrial, freshwater and marine ecosystems, emphasizing the central role of chemical speciation in controlling the arsenic levels, mobility and bioavailability. Natural processes regulating arsenic distribution are examined from mineralogical sources and soil–water interactions to biologically mediated transformations in aquatic and marine biotic compartments, highlighting the contrast between inorganic arsenic dominance in abiotic reservoirs and the prevalence of organoarsenicals in tissues of living organisms. The review further explores arsenic behaviour under natural environmental alterations and in extreme or unconventional ecosystems, where redox constraints, sulphide chemistry or intense fluid–sediment exchanges lead to deviations from the baseline speciation patterns. Against this framework, anthropogenic perturbations are discussed through several documented case studies, illustrating how industrial releases, the long‑term effects of mining activities, agricultural practices and the use of synthetic arsenical compounds may change the arsenic pathways primarily by altering geochemical and biological controls rather than the generalized increase of the total arsenic content. Overall, the topics covered provide an integrated framework for interpreting arsenic dynamics across environmental systems, emphasizing the complex biogeochemical processes governing arsenic cycling.