Cadmium in groundwater − A synopsis based on a large hydrogeochemical data set

Elevated cadmium (Cd) concentrations in groundwater have widespread implications for water supply and agriculture. The aqueous chemistry of Cd is considered not complex; however, aside from intense industrial pollution, multi-faceted hydrogeochemical interactions control Cd mobility. Therefore, the behavior of Cd in groundwater was investigated through statistical analyses of a large hydrogeochemical data set, which contained analyses from 6300 sampling locations in Northern Germany. Cadmium concentrations of above 0.5 μg/L were linked to groundwater conditions caused (1) by woodlands in connection with acidification or (2) elevated nitrate concentrations beneath farmland due to fertilization. Comparably, both geogenic and anthropogenic Cd input were less important. The main hydrogeochemical parameters affecting Cd mobility were pH and redox potential, which are probably linked to Cd sorption to mineral surfaces and Cd release from carbonates and sulfides, such as pyrite. Thus, Cd concentrations were primarily elevated when groundwater conditions were oxic and autotrophic nitrate reducing. In addition, enhanced groundwater recharge and limited Cd retention capacity by the aquifer matrix were responsible for elevated Cd concentrations in groundwater, potentially breaching legal regulations.