Comparison of Se and As concentrations in soils of the western San Joaquin valley, California: 1946–1985

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Abstract
Accumulation of Se in drainage waters from irrigated soils has resulted in a serious environmental problem in the San Joaquin Valley of California. Although As is not known to have reached toxic levels in drainage waters, it is known to be potentially hazardous. Comparisons of Se and As concentrations in soils collected more than 40 years ago (archive soils) to soils recently collected (contemporary soils) at the same sites were made to determine trends in concentration changes. Extractable (phosphate) and total Se and extractable (phosphate) As concentrations were determined in eight different types of soils sampled at various depths. Soils formed from marine sedimentary alluvial deposits had higher amounts of total Se than soils formed from granitic alluvium. Contemporary soils had less extractable Se, in general, than archive soils probably as a result of irrigation and drainage. Nonextractable Se concentrations in the soils were usually much greater than extractable Se concentrations. Extractable Se was related to soil solution electrical conductivity, although other factors, such as oxidation state of Se, might influence the relationship. Contemporary soils generally had higher concentrations of extractable As than archive soils. This may be the result of herbicide applications, although As enrichment was not found in surface soil samples.