High concentrations of arsenic (>50μg L(-1)) have been detected for the first time
in groundwater of the wave-dominated Paraiba do Sul delta, Brazil. The deltaic shallow
groundwater aquifer is enriched in arsenic fixed by authigenic sulfides. A study of
palynomorphs confirmed that aquifer sediments were formed in inter-dune lakes/swamps
lately covered by eolian sands. The organic sediments of contemporaneous inter-dune
lake/swamp contain very high concentration of As: up to 180mg kg(-1) and 163μg L(-1)
in dry gyttja material and interstitial water, respectively. The As in recent lake/swamp
sediments is retained by iron hydroxides in upper and probably by sulfides in lower
layers. In the absence of connection of inter-dune lakes/swamps with fluvial currents,
the atmospheric input of As could be considered as the principal source in sediments.
The calculation demonstrates the possibility of high concentrations of As accumulation
in sediments of inter-dune lakes/swamps from atmospheric precipitations within several
centuries before they will be covered by eolian sands and turned into shallow aquifer.
Considering the commonalities of wave-dominated delta formations, we can predict more
prevalent As accumulation in delta plain groundwater.