Transcript Geochemical Mapping Methodologies and techniques

Determination of soluble salts in
soil samples from Cyprus
Dr Irene Christoforou
Outline
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Introduction
Sampling
Ion Chromatography
Ion Chromatography Method Development
Estimates of Reproducibility, Limits of Detection (LOD) and Limits of
Quantification (LOQ)
Distributions of Fluorides
Distributions of Chlorides
Distributions of Nitrates
Distributions of Sulfates
Conclusions
Introduction
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Soil comprises the loose top layer of our planet's crust and contains a
mixture of rock particles, organic matter, bacteria, air and water.
Minerals, nutrients
Ions in solution
Heat, cold, wind,
rain, hail, ice
Frost
Spontaneous
weathering
Mechanical
weathering
Oxides of iron & alumina
Silica
Clays
Parent material
Fine parent
material
Chemical
weathering
Acids, moisture
Carbonates
Introduction
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Plants and crops are dependent on soil for the supply of water, nutrients
and as a medium for growing. This dependence makes soil one of the most
fundamental components for supporting life on the planet.
The term soluble salts refers to the inorganic soil constituents (ions) that are
loosely bound to the matrix of soil and therefore can be dissolved in the
water with relative ease.
The levels of soluble salts in the soil are important since high concentrations
are considered an environmental stress and constitute a limiting factor for
agriculture.
Furthermore some of the most important soil threats, such as salinisation
and desertification are closely linked with increased concentrations of
soluble salts.
Therefore, the determination of soluble salts in soils is crucial for the
estimation of soil condition in relation to several soil threats and soil
contamination.
Introduction
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This study as a part of the compilation of the Geochemical Atlas of Cyprus
project, aims to provide a detailed geochemical “snap shot” of the
distribution and abundance of soluble salts in Cyprus soil.
For the purpose of this project an in-house method was developed for the
extraction of soluble salts, following an optimized procedure.
The dissolved anions (F-, Cl-, NO3-, SO42-) were determined by liquid
chromatography.
Introduction
Circum-Troodos Sedimentary Sequence (calcarenites, siltstones, carbonates)
Keryneia Terrane (allochthonous massive and recrystallised
limestones, dolomites and marbles)
Mamonia Terrane (igneous, sedimentary, metamorphic rocks)
Quaternary
Troodos Ophiolite Complex &
Arakapas Transform Sequence
pillow lavas
mafic units
ultramafic unit
Sampling Method
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5502 Top Soil Samples.
Sampling density - one site per 1 km2.
Troodos - reduced to one site per 2.2 km2.
Areas not under the effective control of the
Government of the Republic of Cyprus
Sampling Method
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Sample locations - determined by GPS.
The surface was cleared of recent organic debris.
Top soil samples (0–25 cm depth).
All samples were sieved to <2 mm.
Samples delivered and archived at the GSD.
400g Sample,
<2mm
300g
GSD archive
100g
UNSW
Steel Mill
5g
SS
2g
TC, TS, TOC
10g
XRF Majors
Ion Chromatography
Eluent
Data
Processing
Pump
Conductivity
Detector
Guard Separator Suppressor
Column Column
Trace
Instrument
Shimadzu
Eluent
1.8 mM of Na2CO3
1.7 mM of NaHCO3
Flow Rate
1 mL/min
Separator column
250 mmL x 4.0 mm Shim-pack IC-SA2
Guard column
Shim-pack IC-SA2(G)
Injection volume
50 μL
Detector
CDD-10Asp suppressed conductivity
Method Development
Concentration of calibration solutions
1.000 ± 0.002g/L
Low concentration range for F-, Cl-, NO3-, SO42-
0.05-10 mg/L
High concentration range for Cl-
20-75 mg/L
High concentration range for SO42-
10-50 mg/L
Squared correlation coefficient R2
> 0.99
140
100
F
80
Cl
60
NO3
40
SO4
20
0
5
10
20
5
10
20
5
10
20
conc. (mg/l)
conc. (mg/l)
120
200
180
160
140
120
100
80
60
40
20
0
F
Cl
NO3
SO4
5
5
5
100 100 100 100 100 100 100 100 100
100
200
300
30
120
120
120
30
30
60
60
60
120 120 120
m ass (gr) / volum e (m l) / tim e (m in)
m ass (gr) / volum e (m l) / tim e (m in)
Method Development
Sample Preparation:
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sieving < 2 mm mesh size
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milling
Experimental
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5g sample / 200ml DW
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120 minutes shaking
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filtration (ashless filter paper)
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conductivity measurement
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filtration (0.45 μm membrane filter)
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liquid chromatography
Samples of conductivity greater than 600μS/cm or with anion concentrations
exceeding the calibration range were diluted.
Control:
CYP-A , a calcareous sediment collected from an outcrop of Pakhna.
Method Development
F(ppm)
Cl(ppm)
NO3(ppm)
SO42(ppm)
12
12
12
12
Mean
0.163
1.722
0.454
2.938
SD
0.030
0.240
0.033
0.156
LOD
0.09
0.72
0.10
0.47
LOQ
0.27
2.16
0.30
1.40
F(ppm)
Cl(ppm)
NO3(ppm)
SO42(ppm)
151
151
151
151
MEAN
0.245
3.307
0.556
3.289
SD
0.080
1.242
0.104
0.408
RSD
0.327
0.376
0.186
0.124
%CVR
32.7
37.6
18.6
12.4
Anion
N
Anion
N
Distribution of Fluorides
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Fluorine is the most abundant halogen in the earth’s crust.
It is the most electronegative element and binds metals forming complexes,
which are adsorbed readily to the soil and plants.
Fluorine is phytotoxic, causing damage in vegetation, wildlife and humans.
Fluorine as an element in soil has a world average value of 200-300 mg/kg.
The main natural source of inorganic fluorides in soil is the parent rock.
During weathering, some fluoride minerals are rapidly broken down.
Fertilizer application is the main nongeogenic source of fluoride ions and
fluorapatite is an important calcium- and fluoride-containing mineral used as
a source of phosphates in the fertilizer industry.
Phosphate fertilizers are manufactured from rock phosphates, which
generally contain around 3.5% of fluorine.
Fluoride applied through fertilizer tends to have high residence time within
the soil matrix particularly in soils of high clay content, high organic carbon
content, high amorphous aluminium species or low pH.
Distribution of Fluorides
-
F
fluoride
34 E
Ion chromatography
LODreproducibility: 10 mg/kg
average value: 18.7 mg/kg
highest value: 3536 mg/kg
33 E
Top soil
Keryneia
Lefkosia
(0 – 25 cm)
Areas not under the effective
control of the Government
of the Republic of Cyprus
Ammochostos
Polis
35 N
Ayia Napa
Pafos
Lemesos
F(mg/kg)
500
25
22
20
19
18
16
14
12
11
8
Distribution of Chlorides
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The mantle, the crust and the oceans are the three main reservoirs of earth
chlorine with only the oceanic chlorine being readily mobile.
Since parent materials in general contain only minor amounts of chloride,
little of this nutrient arises from weathering.
Most of the chloride presents in soils arrives from rainfall, marine aerosols,
volcanic emissions, irrigation waters, and fertilizers.
Chloride accumulates primarily in soil under arid conditions where leaching
is minimal and where chloride moves upward in the soil profile in response
to evapotranspiration .
Near the ocean, soils have high levels of chloride.
High chloride ion concentrations in soil, above geogenic concentrations, are
often considered as a salinisation problem world wide and occur in warm
and dry locations where soluble salts precipitate from water and accumulate
in the soil.
Distribution of Chlorides
Clchloride
34 E
Ion chromatography
LODreproducibility: 149 mg/kg
average value: 809.3 mg/kg
highest value: 664778 mg/kg
33 E
Top soil
Keryneia
Lefkosia
(0 – 25 cm)
Areas not under the effective
control of the Government
of the Republic of Cyprus
Ammochostos
Polis
35 N
Ayia Napa
Pafos
Lemesos
Cl(mg/kg)
2,000
450
350
270
230
200
180
160
140
120
80
The Nitrogen Cycle
http://www.physicalgeography.net
Distribution of Nitrates
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Nitrate ions mainly originate from anthropogenic origins and constitute a
very clear descriptor for characterising agricultural land use.
The main source of nitrates is the application of synthetic fertilizers or
manure to fields.
Potential anthropogenic source of nitrates is the leakage from domestic
septic fields, municipal sewage systems and livestock facilities.
Excess nitrates in soil increases the risk of contamination of ground or
surface waters causing eutrophication (increasing algae growth, degrading
habitat for aquatic organisms) and adverse effects on human health.
Nitrate vulnerable zones (NVZ) have been designated by the Cyprus
government through studies (Geological Survey Department, 2000) in an
effort to comply with the Nitrate Directive (91/676/EEC).
The Directive has the objectives of reducing water pollution caused or
induced by nitrates from agricultural sources and preventing further
pollution.
Distribution of Nitrates
NO3nitrate
Ion chromatography
LODreproducibility: 12 g/kg
average value: 68.4 mg/kg
highest value: 3001 mg/kg
NO3-
34 E
(mg/kg)
33 E
Top soil
Keryneia
220
150
100
80
70
55
40
32
26
22
15
(0 – 25 cm)
Areas not under the effective
control of the Government
Lefkosia of the Republic of Cyprus
Ammochostos
Polis
35 N
Ayia Napa
Pafos
Lemesos
P
ICP-MS
Keryneia
P
Lefkosia
(%)
Ammochostos
Polis
Larnaca
Pafos
Lemesos
Ayia Napa
0.160
0.100
0.092
0.085
0.062
0.055
0.042
0.035
0.025
0.020
0.010
Distribution of Sulfates
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Sulfate ions are made available from dissolution of sulfate salts from
oxidation of sulfur-bearing minerals in soils all around the world.
Among the sulfur-bearing minerals identified in sedimentary rocks, iron
sulfide polymorphs, pyrite and marcasite, are the more common forms, of
which pyrite is the most common. Oxidation of these sulfide groups releases
sulfate phases into soils.
The soils that contain iron sulfide minerals or their oxidation products are
known as Acid Sulfate Soils (ASS).
If the ASS are drained and exposed to air, the sulfides react with oxygen to
form sulfuric acid which can create a variety of adverse impacts: killing
vegetation and aquatic organisms, acidifying groundwater and water bodies,
degrading concrete and steel structures to the point of failure.
Distribution of Sulfates
SO42sulfate
34 E
Ion chromatography
LODreproducibility: 49 mg/kg
average value: 160.3 mg/kg
highest value: 231701 mg/kg
33 E
Top soil
Keryneia
Lefkosia
(0 – 25 cm)
SO42(mg/kg)
750
300
180
140
120
100
80
65
55
45
30
Areas not under the effective
control of the Government
of the Republic of Cyprus
Ammochostos
Polis
35 N
Ayia Napa
Pafos
Lemesos
100,000
S
XRF
Keryneia
S
Lefkosia
(mg/kg)
Ammochostos
Polis
10,000
S
XRF 1,000
(mg/kg)
100
10
Larnaca
10
100
SO42ion chrom
1,000 10,000 100,000 (mg/kg)
Pafos
Lemesos
Ayia Napa
6000
1500
1200
1000
900
800
700
500
400
300
200
Distribution of Soluble Salts
-
F
fluoride
-
Cl
chloride
34 E
33 E
Top soil
Keryneia
34 E
33 E
Top soil
Keryneia
(0 – 25 cm)
(0 – 25 cm)
Lefkosia
Lefkosia
Ammochostos
Polis
Ammochostos
Polis
35 N
Ayia Napa
Pafos
35 N
Ayia Napa
Pafos
Lemesos
Lemesos
-
NO3
nitrate
-
SO42
sulfate
34 E
33 E
Keryneia
Top soil
34 E
33 E
Keryneia
(0 – 25 cm)
(0 – 25 cm)
Lefkosia
Lefkosia
Ammochostos
Polis
Ammochostos
Polis
35 N
Ayia Napa
Pafos
35 N
Ayia Napa
Pafos
Lemesos
Top soil
Lemesos
Conclusions
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The soluble salt distribution maps provide the baseline values for every
geological formation of the island of Cyprus and give sufficient information
of soil contamination sides.
The two salt lakes of the island are considered to be the main nonanthropogenic contamination sources resulting to enhance values of all the
measured soluble salts and particularly those of the chlorides and sulfates.
The soluble salt distribution maps confirms also the anthropogenic soil
contamination with nitrates and sulfates due to fertilizers application and
mining activity respectively.
This study provides a basis for a number of future projects dealing with
environmental monitoring and management.
The observed soil contamination caused by mining activity gives also the
opportunity to run several mine rehabilitation projects in Cyprus.