Abstract
Seawater samples off Southern California and various terrestrial waters of the United States were analyzed for four arsenic species: arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid. Generally, arsenate is dominant, but in the waters of the photic zone the other species are found in significant concentrations. A positive correlation is evident between the concentrations of arsenite and the methylated arsenicals and indicators of primary productivity, e.g. chlorophyll concentration and SUP-14 C-uptake. This indicates that the speciation of arsenic in natural waters is significantly influenced by biological activity. In the waters below the euphotic zone, arsenate concentrations increase with depth, suggesting regeneration from biological material. No evidence of anthropogenic contributions to the total arsenic concentrations was found in the water near a Los Angeles sewage outlet, but the high productivities in this area resulted in drastic changes in species distribution. Some marine macro-algae were analyzed for inorganic arsenic and methylated arsenicals. Large variations of inorganic arsenic concentrations and significant concentrations of the methylated species were found.