Environmental Impact of Cadmium in a Volcanic Archipelago: Research Challenges Related to a Natural Pollution Source

Cadmium (Cd) is a highly toxic heavy metal particularly susceptible to mobilization by anthropogenic and natural processes. The volcanic nature of oceanic islands in the Macaronesia geographical region such as the Azores archipelago, located near the Mid-Atlantic Ridge, is reflected in deep-sea and shallow-water hydrothermal activities that release heavy metals such as Cd to seawater, affecting marine organisms and integrating food webs. In this paper, a thorough systematic review of all studies performed on coastal marine species in Macaronesia focusing on Cd was conducted, specifically considering the Azorean geological setting and socioeconomic context. Present results are compared and discussed with data from the Mediterranean, a region with apparent strong anthropogenic pollution. The Azorean marine species seem to be particularly strong Cd accumulators, displaying high levels that should be closely monitored, reflecting an important local natural source that should not be underestimated; especially considering the high consumption rates of some of these organisms, which may lead to a potential seafood safety issue. In light of these findings, the potential effects, impacts, and future research challenges are discussed, from an ecological and public health perspective.