Determination of soluble salts in soil samples from Cyprus

1
Determination of soluble salts in soil samples
from Cyprus

• Dr Irene Christoforou

2
Outline

• 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

3
Introduction

• Soil comprises the loose top layer of our
  planet's crust and contains a mixture of rock
  particles, organic matter, bacteria, air and
  water.

4
Introduction

• 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.

5
Introduction

• 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.

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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
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Sampling Method

• 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
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Sampling Method

• Sample locations - determined by GPS.
• The surface was cleared of recent organic debris.
• Top soil samples (025 cm depth).
• All samples were sieved to lt2 mm.
• Samples delivered and archived at the GSD.

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Ion Chromatography
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
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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 gt 0.99
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Method Development

• Sample Preparation
• sieving lt 2 mm mesh size
• milling
• Experimental
• 5g sample / 200ml DW
• 120 minutes shaking
• filtration (ashless filter paper)
• conductivity measurement
• filtration (0.45 µm membrane filter)
• 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.

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Method Development
Anion F- (ppm) Cl- (ppm) NO3- (ppm) SO42- (ppm)
N 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
Anion F- (ppm) Cl- (ppm) NO3- (ppm) SO42- (ppm)
N 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
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Distribution of Fluorides

• Fluorine is the most abundant halogen in the
  earths 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.

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Distribution of Fluorides
LODreproducibility 10 mg/kg average value 18.7
mg/kg highest value 3536 mg/kg
15
Distribution of Chlorides

• 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.

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Distribution of Chlorides
LODreproducibility 149 mg/kg average value
809.3 mg/kg highest value 664778 mg/kg
17
The Nitrogen Cycle
http//www.physicalgeography.net
18
Distribution of Nitrates

• 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.

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Distribution of Nitrates
NO3- nitrate Ion chromatography
34 ?E
33 ?E
Top soil (0 25 cm)
Keryneia
LODreproducibility 12 g/kg average value 68.4
mg/kg highest value 3001 mg/kg
Areas not under the effective control of the
Government of the Republic of Cyprus
Lefkosia
Ammochostos
Polis
35 ?N
Ayia Napa
Pafos
Lemesos
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Distribution of Sulfates

• 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.

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Distribution of Sulfates
LODreproducibility 49 mg/kg average value 160.3
mg/kg highest value 231701 mg/kg
S (mg/kg)
100,000
10,000
S XRF (mg/kg)
1,000
100
SO42- ion chrom (mg/kg)
10
1,000
100,000
100
10
10,000
22
Distribution of Soluble Salts
23
Conclusions

• 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 non-anthropogenic 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.