Chromium(VI) generation in vadose zone soils and alluvial sediments of the southwestern Sacramento Valley, California: A potential source of geogenic Cr(VI) to groundwater

Weathering and transport of chromium and nickel from serpentinite in the Coast Range ophiolite to the Sacramento Valley, California, USA

“…Most of these samples were one depth in a core and were interlayered with higher Cr T samples. Large fluctuations in Cr T concentrations with depth were also observed for cores farther downstream of Putah Creek and were also observed for much deeper cores (up to 32 m) analyzed by Mills et al (2011). That Cr T fluctuates more than Cr 4a or Ni in these Putah Creek soils and sediments suggests dense, larger grained chromite grains are being transported independently of the finer grained material during high-energy storm events.…”

“…Chromium was not speciated as part of this study, but Mills et al (2011) showed that, when present, Cr(VI) is a minute fraction of the total Cr in valley soils and sediments. This is likely because Cr(VI) is an end product of Cr weathering in valley soils.…”

“…The NIOSH 10 hour time weighted average REL for Cr(VI) is 0.001 mg m -3 . Mills et al (2011) found that leachable Cr(VI) was below detection (<2 µg kg -1 ) in surface and shallow soils.…”

“…The residence of the Cr(III) in the soil is likely an important determinant of the rate of Cr(VI) generation. Although it has been shown that Cr(VI) can be generated from chromite at circumneutral pH (Oze et al, 2007), it is likely that Cr(III) associated with clays and oxides is more mobile and oxidizable (Mills et al, 2011;2012).…”

Origin and concentration profile of chromium in a Greek aquifer

“…Two main factors that affect pH are the presence of organic matter and weathering/leaching processes, which result in decreasing pH [24,45,46]. Particularly topsoils are influenced by organic matter and in agricultural areas, by acidification through the use of ammonium fertilizers [47]. Both factors are likely at play for the surficial soils in Vergina, an area with intense agricultural activity.…”