Aging effects on molybdate lability in soils.

Jason K Kirby, Michael J McLaughlin, Yibing Ma, Babasola Ajiboye

CSIRO Land and Water, Water for a Health Country Flagship, Contaminant Chemistry and Ecotoxicology Program, Waite Campus, Waite Road, Urrbrae, SA 5064, Australia. jason.kirby@csiro.au

Chemosphere 2012 Oct

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Aging reactions in soils can influence the lability and hence bioavailability of added metals in soils through their removal from labile pools into pools from which desorption is slow (non-labile pools). The aims of this study were to examine the effect of aging reactions on the lability of soluble molybdate (MoO(4)(2-)) added into soils with varying physical and chemical properties and develop models to predict changes in the labile pool of MoO(4)(2-) in soils with incubation time. Soils were spiked with soluble MoO(4)(2-) at quantities sufficient to inhibit barley root growth by 10% (EC(10)) or 90% (EC(90)) and incubated for up to 18 months. The labile pool of MoO(4)(2-) (E value) was observed to decrease in soils with incubation time, particularly in soils with high clay content. A strong relationship was observed between measures of MoO(4)(2-) lability in soils determined using E and L value techniques (R(2)=0.98) suggesting E values provided a good measure of the potential plant available pool of MoO(4)(2-) in soils. A regression model was developed that indicates clay content and incubation time were the most important factors affecting the labile pool of MoO(4)(2-) in soils with time after addition (R(2)=0.70-0.75). The aging model developed suggests soluble MoO(4)(2-) will be removed into non-labile pools more rapidly with time in neutral to alkaline clay soils than in acidic sandy soils. Labile MoO(4)(2-) concentrations in molybdenum (Mo) contaminated soils was found to be <10% of the total Mo concentrations in soils. Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.