Submitted to: Journal of Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2010
Publication Date: 2/11/2010
Citation: Ryu, J., S. Gao, and K.K. Tanji. 2010. Speciation and behavior of arsenic in evaporation basins, California, USA. Environ Earth Sci. DOI 10.1007/s12665-010-0473-y. Available at: http://www.springerlink.com/content/k2m2r1346127604t/fulltext.pdf. Interpretive Summary: With the semi-arid climate and shallow ground water table, agricultural production in the Westside of San Joaquin Valley and the hydrologically closed Tulare Basin in California depends on both irrigation and subsurface drainage. Without the out-of-valley option, most drainage water has been disposed into constructed evaporation basins (or ponds). Selenium accumulation in pond waters has caused most attention because of its potential toxicity to water birds. Arsenic accumulation in the ponds has also raised concerns because of its properties. This research was conducted to investigate arsenic behavior after disposal into an evaporation basin facility by examining arsenic speciation in water and sediment samples along the water flow path as well as spatial changes. The data are essential for better understanding of arsenic fate in the system and for evaluation of future drainage disposal strategies.
Technical Abstract: Disposal of saline subsurface drainage waters from croplands into evaporation basins (or ponds) in the San Joaquin Valley of California causes excessive accumulation of salts and elevated concentrations of arsenic (As), a potentially high risk element with little information about its fate, in the agricultural evaporation ponds. We examined dissolved As concentration, speciation, and distribution in waters as well as As fractionation in sediments in the 10-cell South Evaporation Basin for better understanding of processes and conditions affecting As transformations and fate in a specific drainage disposal facility. The increase of total dissolved As concentrations were observed with higher Cl- and electric conductivity along flow path indicating that evaporation was an important factor regulating total dissolved As concentration. The increases of reduced As species such as arsenite [As(III)] and organic As (monomethylarsonic acid and dimethylarsinic acid) were found towards the terminal flow pathway. However, arsenate [As(V)], the oxidized species remained greater than 67% of total dissolved As in all cell waters. Sequential extractions of sediments indicated that reducing conditions may influence As behavior in sediments to be more soluble and exchangeable. Arsenic association with oxides was appreciable only under oxidizing condition. Carbonate minerals played an important role in immobilizing As into the sediments under alkaline condition and a broad range of redox conditions. However, these sink mechanisms did not significantly reduce As concentrations in the cell waters. The reducing condition facilitated by high concentration of organic matter might be a major factor for the increase in As mobility.