Determination of soluble Determination of soluble salts in soil samples salts in soil samples

from Cyprusfrom Cyprus

Dr Irene Christoforou

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

Frost

Heat, cold, wind, rain, hail, ice

Mechanicalweathering

Fine parent material

Parent material

Minerals, nutrientsIons in solution

Oxides of iron & alumina

Silica

Clays

Carbonates

Spontaneousweathering

Acids, moisture

Chemicalweathering

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.

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.

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-, SO4

2-) were determined by liquid chromatography.

Introduction

Mamonia Terrane (igneous, sedimentary, metamorphic rocks)

Troodos Ophiolite Complex &Arakapas Transform Sequence

Quaternary

Keryneia Terrane (allochthonous massive and recrystallisedlimestones, dolomites and marbles)

Circum-Troodos Sedimentary Sequence (calcarenites, siltstones, carbonates)

ultramafic unitmafic unitspillow lavas

5502 Top Soil Samples. Sampling density - one site per 1 km2. Troodos - reduced to one site per 2.2 km2.

Sampling Method

Areas not under the effective control of the Government of the Republic of Cyprus

Sampling Method 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.

Instrument Shimadzu

Eluent1.8 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

Eluent

Pump

Guard Column

Separator Column

Suppressor

Conductivity Detector

Trace

Data Processing

Ion Chromatography

Concentration of calibration solutions 1.000 ± 0.002g/L

Low concentration range for F-, Cl-, NO3-, SO4

2- 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

0

20

40

60

80

100

120

140

5 10 20 5 10 20 5 10 20

100 100 100 100 100 100 100 100 100

30 30 30 60 60 60 120 120 120

mass (gr) / volume (ml) / time (min)

con

c. (

mg

/l) F

Cl

NO3

SO4

020406080

100120140160180200

5 5 5

100 200 300

120 120 120

mass (gr) / volume (ml) / time (min)

con

c. (

mg

/l) F

Cl

NO3

SO4

Method Development

Method Development Sample Preparation: sieving < 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.

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

AnionF-

(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

Method Development

Distribution of Fluorides 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.

F-

fluorideIon chromatography

Top soil (0 – 25 cm)

50025

22

2019

181614

1211

8

F- (mg/kg)

33 EKeryneia

34 E

Polis

Ayia Napa

35 N

Ammochostos

Pafos

Lemesos

Lefkosia

Areas not under the effective control of the Government of the Republic of Cyprus

Distribution of Fluorides

LODreproducibility: 10 mg/kgaverage value: 18.7 mg/kg highest value: 3536 mg/kg

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.

Distribution of ChloridesCl-

chlorideIon chromatography

Top soil (0 – 25 cm)

2,000450

350

270230

200180160

140120

80

Cl- (mg/kg)

33 EKeryneia

34 E

Polis

Ayia Napa

35 N

Ammochostos

Pafos

Lemesos

Lefkosia

Areas not under the effective control of the Government of the Republic of Cyprus

LODreproducibility: 149 mg/kgaverage value: 809.3 mg/kg highest value: 664778 mg/kg

The Nitrogen Cycle

http://www.physicalgeography.net

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.

Distribution of NitratesNO3

-

nitrateIon chromatography Top soil

(0 – 25 cm)2201501008070554032262215

NO3-

(mg/kg)33 E

Keryneia

34 E

Polis

Ayia Napa

35 N

Ammochostos

Pafos

Lemesos

Lefkosia

Areas not under the effective control of the Government of the Republic of Cyprus

LODreproducibility: 12 g/kgaverage value: 68.4 mg/kg highest value: 3001 mg/kg

Polis

Lefkosia

Ayia Napa

Keryneia

Ammochostos

Larnaca

PafosLemesos

PICP-MS

0.1600.1000.0920.0850.0620.0550.0420.0350.0250.0200.010

P(%)

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.

SO42-

sulfateIon chromatography Top soil

(0 – 25 cm)

33 EKeryneia

34 E

Polis

Ayia Napa

35 N

Ammochostos

Pafos

Lemesos

Lefkosia

Areas not under the effective control of the Government of the Republic of Cyprus

Distribution of Sulfates

6000150012001000

900800700500400300200

S(mg/kg)

7503001801401201008065554530

SO42-

(mg/kg)

Polis

Lefkosia

Ayia Napa

Keryneia

Ammochostos

Larnaca

PafosLemesos

SXRF

LODreproducibility: 49 mg/kgaverage value: 160.3 mg/kg highest value: 231701 mg/kg

SO42-

ion chrom(mg/kg)1,000 100,00010010

1,000

100,000

100

10

SXRF

(mg/kg)

10,000

10,000

Distribution of Soluble SaltsF-

fluorideTop soil (0 – 25 cm)

33 EKeryneia

34 E

Polis

Ayia Napa35 N

Ammochostos

Pafos

Lemesos

Lefkosia

Cl-

chlorideTop soil (0 – 25 cm)

33 EKeryneia

34 E

Polis

Ayia Napa35 N

Ammochostos

Pafos

Lemesos

Lefkosia

NO3-

nitrateTop soil (0 – 25 cm)

33 EKeryneia

34 E

Polis

Ayia Napa35 N

Ammochostos

Pafos

Lemesos

Lefkosia

SO42-

sulfateTop soil (0 – 25 cm)

33 EKeryneia

34 E

Polis

Ayia Napa35 N

Ammochostos

Pafos

Lemesos

Lefkosia

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.