DISTRIBUTION OF ARSENITE AND TOTAL DISSOLVED ARSENIC IN MAJOR FRENCH ESTUARIES - DEPENDENCE ON BIOGEOCHEMICAL PROCESSES AND ANTHROPOGENIC INPUTS

The distribution of arsenite (As (III)), total dissolved arsenic and particulate arsenic was studied in major French rivers/estuaries: the Rhône, Gironde and Loire, which are representative of polluted, unpolluted, macrotidal and stratified systems. In these rivers, arsenite (1.3-2.1 nM) and total dissolved arsenic concentrations (8.8-20.5 nM) are comparable with mean concentrations in European and North American rivers. In the Rhône estuary (with flushing time of the order of 1 day) the maximum of dissolved arsenic (25-50 nM) occurring in the low-salinity zone is related to the variability of the river input. In the Gironde estuary (flushing time 20-86 days) arsenite and total dissolved As concentrations vs. chlorinity plots show a maximum (45 nm for dissolved arsenic) located in the low-salinity zone within the turbidity maximum. This maximum is interpreted as the result of remobilization processes which involve 'regeneration' of arsenic compounds from the degradation of organic matter, and perhaps of redox processes which occur in the anoxic 'fluid-mud layer' and/or sediments. In the Loire fluvio-estuarine system the maxima of arsenite (15 nM) and total dissolved arsenic (25 nM) are attributed to the anthropogenic inputs from land-based industries, and especially from the coal-power plant. The dissolved arsenic discharge has been estimated at 40 tons yr-1. © 1990.