Estimating divalent cadmium activities measured in arid-zone soils using competitive chelation

Journal Article · · Soil Science Society of America Journal; (United States)

DOI:https://doi.org/10.2136/sssaj1990.03615995005400040009x· OSTI ID:5535292

Workman, S M ^[1]; Lindsay, W L ^[2]

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1. Analytical Technologies, Inc., Fort Collins, CO (United States)
2. Colorado State Univ., Fort Collins (United States)

Competitive chelation was explored as a method of measuring divalent Cd activity in neutral to alkaline soils. The most successful combination of chelating agents and competing metals comprised DTPA (diethylenetriaminepentaacetic acid) and Pb{sup 2+} in equilibrium with added PbCO{sub 3}(c). A series of 10{sup {minus}5} M DTPA solutions containing varying initial mole fractions of Cd and Pb were reacted with soils for 140 hours. Some solutions lost Cd and gained Pb, while others gained Cd and lost Pb. From these results it was possible to estimate the composition of a unique solution that does not change upon reaction with a given soil. The composition of this unique solution reflects equilibrium conditions and was used to calculate Cd{sup 2+} activity. Eight soils ranging in pH from 7.15 to 8.25 showed Cd{sup 2+} activities ranging from 10{sup {minus}6.6} to 10{sup {minus}9.4} M. This solubility of Cd{sup 2+} in soils is approximately two orders of magnitude lower than the activity of Cd{sup 2+} in equilibrium with CdCO{sub 3}(c) and atmospheric CO{sub 2}. No known Cd mineral has yet been identified whose solubility reflects this low activity of Cd{sup 2+}. The competitive chelation method used here avoids many of the pitfalls encountered in measuring extremely low levels of Cd in neutral and alkaline soils where Cd-organic complexes may be present.

• OSTI ID: 5535292
• Journal Information: Soil Science Society of America Journal; (United States), Journal Name: Soil Science Society of America Journal; (United States) Vol. 41:4; ISSN SSSJD; ISSN 0361-5995
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
AMINO ACIDS
ARID LANDS
CADMIUM
CADMIUM COMPOUNDS
CARBOXYLIC ACIDS
CATIONS
CHARGED PARTICLES
CHELATING AGENTS
CHEMISTRY
DRUGS
DTPA
ELEMENTS
IONS
LEAD
LEAD COMPOUNDS
MEASURING METHODS
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
RADIOPROTECTIVE SUBSTANCES
SOIL CHEMISTRY
SOILS
SOLUBILITY