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Aging Effects on Cobalt Availability in Soils
Author(s) -
Wendling Laura A.,
Kirby Jason K.,
McLaughlin Michael J.
Publication year - 2009
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/08-544.1
Subject(s) - soil water , chemistry , lability , cobalt , environmental chemistry , manganese , ammonium , clay minerals , metal , inorganic chemistry , mineralogy , soil science , geology , biochemistry , organic chemistry
Abstract Aging processes in soils can significantly affect the potential biological availability of introduced metals via incorporation into crystal lattices, diffusion into micropores, or formation of metal precipitates on the surfaces of soil minerals. Over time, metals in contact with the soil solid phase are less freely exchangeable with the soil solution and, hence, less available to soil biota. In the present study, the effects of aging on the fate and behavior of added divalent cobalt (Co 2+ ) in a range of soils with varying physicochemical characteristics was assessed using isotope‐exchange techniques, chemical extraction, and plant growth. Following addition to soil, the Co 2+ salt rapidly partitioned to the soil solid phase. Particularly in soils with neutral to alkaline pH, a large percentage of the surface‐bound Co was fixed in forms no longer in equilibrium with soil solution cobalt through aging reactions. Using techniques commonly applied to estimate metal bioavailability in soil, the lability (E values), plant availability (L values), and extractability of added Co 2+ salts with the mild chemical extractants calcium chloride (CaCl 2 ) and ammonium nitrate (NH 4 NO 3 ) were observed to markedly decrease with time, particularly in soils with high pH or those containing appreciable quantities of iron/ manganese oxyhydroxide minerals. Results indicated rapid partitioning of added Co 2+ into isotopically nonexchangeable pools, with more than 60% of the aging occurring within 15 d in most soils. Soil pH was the primary factor controlling the rate of cobalt aging and extent of exchangeability in the soils examined. Understanding the influence of long‐term aging on cobalt availability in soils is necessary to accurately assess the potential risk associated with cobalt contamination of soil environments.