2
Acta Universitatis agriculturae Sueciae
2014:102
ISSN 1652-6880
ISBN (print version) 978-91-576-8152-2
ISBN (electronic version) 978-91-576-8153-9
© 2014 Maja A. Larsson, Uppsala
Print: SLU Service/Repro, Uppsala 2014
Vanadium in Soils, Chemistry and Ecotoxicity
Abstract
Vanadium is a redox-sensitive metal that is released to soils by weathering and
anthropogenic emissions. Swedish metallurgical slags are naturally high in vanadium
and used as soil amendments and in road materials. However, understanding of
vanadium chemistry and bioavailability in soils is limited. The aim of this thesis was to
provide knowledge of vanadium in soils in terms of sorption, toxicity and speciation, in
order to enable improved environmental risk assessments. Vanadium sorption to
ferrihydrite was evaluated in batch experiments. Toxicity assays using microorganisms
and plants were conducted to measure vanadium toxicity in different vanadium soil
treatments; freshly spiked, aged and blast furnace slag (800 mg V kg
-1
). Vanadium
speciation in a podzolic soil amended with converter lime (14.6 g V kg
-1
) 26 years
previously was assessed by using XANES spectroscopy and HPLC-ICP-MS.
Ferrihydrite adsorbed vanadium strongly, but adsorption was reduced by large
additions of phosphate. EXAFS spectroscopy revealed that a vanadate(V) edge-sharing
bidentate complex formed on the ferrihydrite surface. In the toxicity assays, increasing
vanadium sorption strength in the freshly spiked soils reduced the toxicity. Toxicity
was also reduced by soil ageing, possibly because of vanadium incorporation into metal
(hydr)oxides. No toxicity was observed when soils were amended with up to 29% blast
furnace slag, probably owing to the low solubility of vanadium in slag. The variation in
toxicity between soils and vanadium treatments was due to differences in
bioavailability of vanadium which was explained by the vanadium concentration in soil
solution. The vanadium added with converter lime was in pentavalent form, but the
main fraction of the vanadium recovered from the mor layer sorbed to organic matter as
vanadium(IV). In the mineral soil layers, the added vanadium sorbed to metal
(hydr)oxides as vanadium(V). The most toxic vanadium form, vanadium(V),
dominated in the soil solution but the concentrations were below toxic levels.
In conclusion, vanadium toxicity varies between soils and treatments and is most
accurately described by the vanadium concentration in the soil solution. Vanadium
speciation in soil is mainly controlled by soil properties, and not by the vanadium
species added to the soil.
Keywords: vanadium, soil, ferrihydrite, sorption, toxicity, bioavailability, speciation,
XANES spectroscopy, HPLC-ICP-MS.
Author’s address: Maja A. Larsson,
SLU
, Department of Soil and Environment,
P.O. Box 7014, 740 07 Uppsala, Sweden
E-mail:
Maja.Larsson@slu.se
.
Contents
List of Publications
7
Abbreviations
9
1
Introduction
11
2
Aim
13
3
Background
15
3.1
Vanadium in soils and waters
15
3.1.1
Sources
15
3.1.2
Redox chemistry
16
3.1.3
Retention in soils
17
3.1.4
Toxicity and bioavailability
19
3.2
Determining vanadium speciation in soils
20
3.2.1
Extraction and separation techniques
20
3.2.2
X-ray absorption spectroscopy
20
4
Materials and Methods
23
4.1
Vanadium sorption to 2-line ferrihydrite (Paper I)
24
4.2
Vanadium toxicity and bioavailability (Paper II-IV)
24
4.2.1
Soil treatments
26
4.2.2
Toxicity assays
27
4.2.3
Soil and plant vanadium
28
4.2.4
Statistical evaluation
29
4.2.5
Soil sorption properties
29
4.3
Long-term field study (Paper V)
30
4.4
Analytical methods
31
4.4.1
X-Ray Absorption Spectroscopy
31
4.4.2
HPLC-ICP-MS with EDTA complexation
33
5
Results and Discussion
35
5.1
Vanadium adsorption to ferrihydrite (Paper I)
35
5.2
Vanadium toxicity and bioavailability (Papers II-IV)
37
5.2.1
Threshold values
37
5.2.2
Bioavailability
39
5.3
Vanadium speciation - long-term field study (Paper V)
42