Environmental Sampling And Analysis Of Trace Organics Biology Essay

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The anthropogenic activities of man has led to the production of an array of chemical compounds for several beneficial uses; but unknown to him that some would have adverse environmental impact. The realisation of their adverse impact led to the introduction of measures to reduce and eliminate their production, and emission in to the environment. Chemicals found in this category include the persistent organic pollutants (POPs). The objective of this study is to determine the presence and analytically measure the ambient concentrations of the trace persistent organic pollutants. In this study, soil and vegetation samples were collected from LEC court yard and Lancaster university woodland. Samples were homogenized, spiked and soxhlet extracted. Extracts were cleaned through chromatographic processes and measured using gas chromatography-mass spectrometry. These processes were carried out with the incorporation of quality control measures so as to assure a sound analytical process and robust data. Results obtained reveal the presence of POPs (HCB, DDT and PCBs) in the ambient environment and consequently buttresses their characteristic of persistence and potential for long range atmospheric transport. Some significant results observed are the comparatively higher concentrations of PCB 153 and p.p DDT in LEC and woodland soils and organic matter respectively.

COURSE LECTURER: DR. ANDY SWEETMAN

ABSTRACT

INTRODUCTION

Pollution from persistent organic pollutants (POPs) is of global concern because of its environmental impact and toxic legacy (Stockholm Convention, 2001). Two categories of policies have been put forward to address POPs in the environment. These are air quality and chemical safety policies. These categories served as basis for the formulation of the Stockholm convention on POPs with the enlistment of twelve chemicals as causing adverse effects for humans and the ecosystem. Amongst these are Hexachlorbenzene (HCB) and Polychlorinated biphenyls (PCBs) which fell under Annex A and Annex C and Dichlorodiphenyltrichloroethane (DDT) which is enlisted under Annex B (Stockholm Convention, 2001).

HCB, DDT and PCBs are classical POPs. POPs are very persistent in the soil, they bioaccumulate within biota, have intrinsic potential for long-range transport and they elicit toxicity to human, animal and aquatic health. (EPA, 2011). HCB was first used in 1945 as fungicide for seed treatments of grain crops, and also used in making fireworks, ammunition, and synthetic rubber (UNEP, 2002). At present, the main sources are by-product in the production of a large number of chlorinated compounds, particularly lower chlorinated benzenes and solvents.

PCBs were introduced in 1929 and were produced in different countries under different trade names e.g., Aroclor, Clophen, Phenoclor (UNEP, 2002). They are chemically stable and heat resistant, and were used globally as transformer and capacitor oils, hydraulic and heat exchange fluids, and lubricating and cutting oils. There are theoretically, about 209 possible chlorinated biphenyl congeners, but only about 130 of these are likely to be found in commercial products (UNEP, 2002).

DDT was extensively used during World War II to control vector insects responsible for spreading diseases like malaria and typhus in order to protect soldiers and civilians (UNEP, 2002). It has been used for agricultural purposes and also applied on mosquitoes for control of malaria.

Production of these chemicals has been banned for about 30 years in most countries, but they are still observed all over the world in air, soil, water, sediment, biota and human tissues (Wang et al., 2010). Soils constitute a sink or reservoir for many chemicals including POPs. Soils and vegetation can receive input of POPs from distant sources because of the intrinsic long-range atmospheric transport characteristic of POPs. POP's are capable of partitioning within soil, transferring to lower depths where degradation occurs. They can also remain on the top soil or vegetation where remobilisation can occur resulting in inter-media exchanges with temperature or seasonal changes (Dalla Valle et al, 2004).

It is been demonstrated by Wang et al. (2010) that the atmospheric concentrations of these POPs are now on the decline and are currently fairly uniform, however there is a variation at background sites. Despite the decline, highest PCBs and HCB air concentrations are still found in historical source regions, signifying that there are some on-going primary or secondary emissions (Jaward et al., 2005).

This study is aimed at using an established sampling and analytical protocol or design to measure the environmental concentration of persistent organic pollutants which is expected to be present at trace concentrations. The concentration measured would be used in making deduction on its fate and global distribution since the production and usage of most of these chemicals have been stopped for about two to three decades.

EXPERIMENTAL SET UP AND PROCEDURE

Sampling Materials: Bulb planters, zip lock bag, wash bottle with de-ionized water, permanent markers, and tissues.

Analytical Materials: Glass jars, wash bottles with acetone, baked NaSO4, pre-extracted cellulose thimbles, baked glass-fibre filter papers, spatulas, recovery standard, 25ul pipettes with pipette tips, Soxhlet apparatus (baked), baked round bottom flask, acetone, dichloromethane, 400ml beakers, anti-bumping granules (baked), rotary evaporator, filter paper, glass columns (2.5cm internal diameter), glass reservoirs/funnels, 250ml round bottom flasks and stoppers (baked at 450oC), conical flask (250ml), waste jars, hexane, silica (activated), silica (acidified), vial marked for 8g for activated silica, vial marked for 8g for acidified silica, glass Pasteur pipette (baked at 450oC), small conical flask (for hexane), amber vials (7.5ml and caps), small squares of aluminium foil (baked at 450oC), Iso-octane,1ml pipette and pipette tips, GPC columns with Bio-Beads, Hexane/DCM (1:1), 35ml amber vials marked at 30ml (baked at 450oC), glass Pasteur pipette (baked at 450oC), Dodecane (contains the internal standard), GC-vials, GC-MS.

PROCEDURE

Soil sample was collected using a bulb planter from a depth of 5cm, transferred to a zip-lock bag and labelled LEC soil 1.

Another core sample was collected immediately from a point close to the first sample.

This was also transferred to zip-lock bag and labelled.

The bulb planter was rinsed with de-ionized water and kept in equipment rack.

For trace organics analyses, 29.32g of LEC soil was transferred in to cellulose thimble.

15g of Na2SO4 was added to remove water from the sample and have the sample homogenized.

The homogenized mixture was spiked with 25 μl of recovery standards containing 25 pg/μl 13C12-labeled polychlorinated biphenyl (PCB) congeners101, 153, and 180 in iso-octane.

The spiking with a recovery standard was a quality control measure taken to check for error that may arise in the analytical process (amount of analyte of interest that may be lost in preparation through analysis).

EXTRACTION

Figure 1: SOXHLET EXTRACTOR

C:\Users\owner\Pictures\2013-02-11 001\IMG-20130211-00363.jpg http://buymarijuanaseeds.com/community/attachments/soxhletextractor-gif.164247/

Soxhlet Extracting Unit

Adapted from buymarijuanaseeds.com

The soxhlet extractor and round bottom flask were both rinsed with acetone.

The round bottom flask was filled with 300ml of dichloromethane (DCM) and anti-bumping granules added.

The soxhlet extractor was labelled.

The cellulose thimble with the sample was transferred to the soxhlet body.

The cellulose thimble with the sample was assembled to the soxhlet extraction unit and the set up was switched on.

The soxhlet extraction in dichloromethane (DCM) was carried out for 16 hours (hrs)

As the soxhlet is switched on, the extraction solvent (DCM) becomes heated up and starts boiling. This is a reflux system in which the vapour arises and moves through the distillation arm in to the condenser then condenses and drips down on the extracting sample. The condenser serves to ensure that any vapour from solvent cools, and trickles back into the compartment housing the solid material (sample). The chamber containing the solid material is gradually filled with the warm solvent. Some of the semi volatile organic compounds then dissolve in the warm solvent. Once the Soxhlet chamber is getting full, the chamber is emptied automatically by a siphon arm in to the distillation flask. This cycle is allowed to run for about 16hrs after which the compounds are concentrated in the distillation flask. This is usually when the colour in the soxhlet chamber is the same as the pure solvent (Zhang, 2007).

After the soxhlet extraction was completed, the flask containing the extracted sample was removed and taken to the rotary extractor.

Figure 2: ROTARY EVAPORATOR

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Isooctane was added to ensure the analyte does not dry up in the process of evaporation.

The flask containing the analyte and DCM solvent was fixed to the rotary evaporator.

The process was operated at low temperature of about 40oC because of the low boiling point of DCM.

It was operated at reduced pressure about 800-900 milli bar (mb) for a start.

The solvent boils and condenses at the condenser and drips down to the recovery flask.

The process was observed until the sample extract remains about 4-5ml.

This was removed and further reduced to about (≈1 ml) under a stream of Nitrogen (N2).

Figure 3: NITROGEN BLOWER.

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CLEAN UP

This involves the process of removing interfering chemicals from the sample while keeping the target analytes from decomposing or getting lost in the sample matrices before instrumental analysis (Zhang, 2007).

Alumina/Silica Column Chromatography

Clean-up was performed using chromatography glass columns of internal diameter 2.5cm.

Waste jar was placed under the glass column.

The apparatus for the clean-up process was rinsed with acetone and hexane and washed in to the waste jar.

150ml of hexane was poured into a 250ml conical flask.

About 1cm of anhydrous sodium sulphate (NaSO4) was added to the column.

About 8g of acid silica was added using a marked vial.

Also added 8g of activated silica using a marked vial.

It was completed with anhydrous sodium sulphate (NaSO4) of 1cm on the column.

Reservoir jar was placed under the column.

It was topped up with hexane (1-2 columns) to wash through.

The reservoir jar was replaced with a round bottom flask.

The sample extract was introduced with a glass Pasteur pipette in to the column.

The sample vial was rinsed with 1ml of hexane 3 times and introduced using a different pipette to avoid contamination.

The extracts were eluted (washed) with 150 ml of hexane initially poured into the 250ml conical flask.

After washing was complete the round bottom flask was removed and the stopper replaced.

Iso-octane of about I ml was added to the sample.

It was taken to the rotary evaporator and rotary evaporated to 5 ml at a temperature of 40oC and pressure of about 340mb.

The sample was transferred to 7.5ml vial that has been rinsed 3 times with hexane.

The vial was covered with aluminium foil that has been baked and rinsed with hexane.

This was finally reduced to 0.5 ml under a stream of nitrogen.

The principle of this separation technique is based on the interaction of the components in the mixture between a mobile phase and the stationary phase. The eluent (hexane) flows down through the stationary silica gel and the constituents are separated in this process. The sample is introduced around the side of the glass as to have a uniform distribution during separation and the process is closely observed so that the silica does not dry up before topping up with hexane (Zhang, 2007).

Figure 4: ALUMINA/SILICA COLUMN CHROMATOGRAPHY

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Gel Permeation Column (GPC)

The second clean up step involves the use of a gel permeation column (GPC). The basic principle of the GPC separation technique is based on a hydrophobic stationary phase and mobile phase provided by an organic solvent (eluent). It separates constituents on the basis of their size by pumping them through the gel pores (Zhang, 2007). The organic solvent such as hexane-dichloromethane mixture selectively passes large macromolecules through the pore while the target analytes such as the SVOCs are trapped within the gel pore.

The gel permeation chromatography columns (GPC) packed with 6 g Biobeads SX3 and eluted with hexane and DCM (1:1 v:v) in to a waste jar.

The waste jar was exchanged for a waste vial.

Sample was introduced in to the column with a glass pipette and this was done with caution in order not to disturb the bio-beads.

The glass was washed 3 times using hexane and DCM with an intermittent closing and opening of the tap during the washing process.

The column was carefully topped up with Hexane-DCM so the Bio-beads were not disturbed.

The first 16ml was collected in the waste vial and discarded.

Sample vial was kept under the column and the tap opened.

About 30ml of eluted sample was collected with the sample vial.

This was covered with baked and acetone rinsed aluminium foil.

The sample was reduced and concentrated under a gentle stream of N2 to about 0.5-1ml.

MEASURMENT

Preparation for GC-MS Injection

The sample was transferred into gas chromatography (GC) vial baked at 450oC with a keeper such as dodecane (25 μl) containing 13C12-labeled PCB congeners 141 which serves as an internal standard.

The sample was washed 3 times with a small volume of hexane.

It was further reduced to 25 μl under a stream of hydrogen and the vial was closed with a cap

Figure 5: GAS CHROMATOGRAPHY-MASS SPECTROMETRY

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Analysis was carried out using gas chromatography-mass spectrometry (GC-MS) operated in selected ion monitoring mode.

The basic components of the GC-MS are the carrier gas supply, temperature control zone, flow control, sample introduction and splitter, separation column, detector and data-output system (Zhang, 2007).

As a quality control step, calibration curves were generated based on a set of seven standards with concentrations between 2pg/ μl and 200 pg/ μl for HCB.

Recovery standard was added at the beginning of the process while an internal standard was added to the keeper (dodecane).

Some amount of solvent was injected into the system to flush it prior to sample measurement.

As the program was started, the temperature gradually increased and the low boiling point solvent evaporates by passing through a long capillary made of silica of about 50m long.

The machine was run on a selective ion monitoring mode for higher sensitivity.

The injection volume used was 2 μl.

The mobile phase which is an inert carrier gas (Helium) pushes the analyte through the stationary liquid in the column phase repeatedly as in a cyclic process at flow rate of 1ml/min.

Separation is based on difference in temperature for boiling points and mass to charge ratio.

The retention time was monitored for each of the samples.

Solvent was used to flush-off any carry over sample that may remain in the machine.

Chromatogram spectra were obtained for each sample.

The basic principle of the GC-MS relies on a mobile phase inert gas carrier to carry the analyte through the system in to the heated column where the sample is vaporized without decomposing the analyte. The temperature is raised to elute the analyte which gets detected at the detector and generates an electrical signal. The signal goes to a data system where a chromatogram is generated (Zhang, 2007).

QUALITY CONTROL/QUALITY ASSURANCE

Gloves were worn prior to sample collection and throughout the period of analysis in the laboratory.

A quality control measure carried out during homogenization and preparation process was the spiking of the sample with a recovery standard so as to check for error arising from the loss of analytes of interest.

The glass equipment and aluminium foils were baked at 450oC.

The analytical apparatus and equipment were rinsed with acetone and hexane to ensure the removal of contaminants.

Iso-octane was added during evaporation to prevent the sample from drying up.

The sample was introduced with a different pipette while a different pipette was used to introduce solvent for rinsing the vials so as to avoid contaminating the sample.

A recovery standard was introduced in to the GC-MS prior to analysis to monitor losses that may arise while an internal standard was introduced with the keeper to monitor injection and machine variability.

GC system was flushed after each batch of measurement to wash-off any carry over sample that may affect measurement.

RESULTS AND DISCUSSION

Table 1: Soil Characteristics

Sample name

Wet soil / g

After 105 °C / g

After 550 °C / g

LEC courtyard 1

44.77

24.41

21.91

LEC courtyard 2

41.78

24.03

21.75

Woodland 1

42.82

26.22

22.73

Woodland 2

42.32

25.67

22.18

To calculate for the concentration of the chemicals in soil, the approach given below was used.

The calculated or derived amount was multiplied by the amount spiked and the value obtained.

Then an average percentage of the dry weight of the soil was calculated and used to divide the amount in the sample so as to obtain the concentration of each of the chemicals.

For example for LEC SOIL 1 the calculated amount of HCB is 140.036pg/ul

Amount spiked =25ul for 625 pg/sample.

Mass of wet soil=29.3g

After 105oC the amount of dry soil is calculated thus:

LEC courtyard (1) 24.41/44.77 *100 = 54.5

LEC courtyard (2) 24.03/41.78 *100 = 57.5 Average =56%

Therefore, weight of dry mass = 56/100 *29.3 =16.4 dry soil.

To obtain concentration of HCB = 140pg/ul *25ul =3500pg/sample

Concentration in soil =3500pg/16.4 =213.4pgg-1 HCB in soil.

To calculate for recoveries: For example LEC SOIL 1 for 13C-pcb101 with a calculated value of 16.5.

Amount spiked =25ul for 625pg/sample

Recovery =16.5*25 = 412.5*100/625 =66%

To obtain the concentration of chemical in organic matter

After 550oC the amount of dry soil is calculated thus:

LEC courtyard (1) 21.91/24.41*100 = 89.76%

100-89.76 =10.24

LEC courtyard (2) 21.75 /24.03*100 = 90.5%

100-90.5 =9.5 Average = 9.9%

For example for LEC SOIL 1 the calculated amount of HCB is 140.036pg/ul

To obtain concentration of HCB = 140pg/ul *25ul =3500pg/sample

For 9.9% of 16.4g of dry soil gives the organic matter content = 1.62

Concentration in organic matter = 3500pg/1.62 = 2160.5pgg-1 HCB in organic matter.

Example LEC VEG 1 mass =20.44g

To obtain the concentration of chemical in vegetation using 20% dry weight of vegetation

For example for LEC VEG 1 the calculated or derived amount of HCB is 61.1pg/ul*25ul =1527.5pg/sample

For 20.4g wet vegetation: 20/100*20.4 = 4.08 dry weight.

Concentration of HCB in LEC VEG 1 = 1527.5pg/sample/4.08 dry weight = 374.4 pgg-1.

The methods above were used to generate values for all the other compounds and the recovery standards.

Table 2: Mass of Wet and Dry Soil, and Concentration of POPs in LEC and Wood Land Soil.

Samples

Mass of wet soil

Mass of dry soil

HCB

p.p'-DDT

pcb 101

pcb 153

pcb 180

Units

(x)g wet soil

(x)g dry soil

pgg-1

pgg-1

pgg-1

pgg-1

pgg-1

LEC Soil 1

29.32

16.4

213.4

201.9

326.1

802.3

384.6

LEC Soil 2

30.12

16.9

222.8

630.8

397.8

1039.2

695.4

LEC Soil 3

30.43

17.0

139.7

169.1

321.8

722.2

298.9

Total

89.88

50.3

575.9

1001.8

1045.7

2563.7

1378.9

Average

29.96

16.77

191.97

333.93

348.57

854.57

459.63

Wood Land Soil 1

30.0

18.3

176.6

638.9

218.6

348.5

105.3

Wood Land Soil 2

30.85

18.8

166.9

800.0

212.4

391.8

150.9

Wood Land Soil 3

32.18

19.6

103.7

862.4

203.2

432.6

148.3

Total

93.034

56.7

447.2

2301.3

634.2

1172.9

404.5

Average

31.01

18.9

149.07

767.1

211.4

390.97

134.83

Figure 6: Bar chart representing the concentration of POPs in LEC and Woodland Soil

Table 3: Mass of Wet, Dry Soil and Organic Matter and POP Concentration in the Organic Matter.

Samples

Mass of wet soil

Mass of dry soil

Mass of organic matter

HCB

p.p'-DDT

pcb 101

pcb 153

pcb 180

Units

x(g)wet soil

(x)g dry soil

x(g) in dry soil

pgg-1

pgg-1

pgg-1

pgg-1

pgg-1

LEC Soil 1

29.32

16.4

1.62

2160.5

2044.8

3300.9

8121.9

3893.5

LEC Soil 2

30.12

16.9

1.67

2254.5

6383.2

4025.4

10516.5

7035.9

LEC Soil 3

30.439

17.0

1.68

1413.5

1711.2

3255.9

7308

3025.3

Total

89.88

50.3

4.97

5828.5

10139.2

10582.2

25946.4

13954.7

Average

29.96

16.77

1.66

324.47

567.27

590.57

1447.7

779.2

Wood Land Soil 1

30.0

18.3

2.47

1308.7

4733.8

1619.4

2581.9

780.4

Wood Land Soil 2

30.85

18.8

2.54

1235.2

5928.1

1530.5

2822.8

1087.6

Wood Land Soil 3

32.18

19.6

2.65

766.9

6378.3

1502.8

3200

1097.2

Total

93.03

56.7

7.66

3310.8

17040.2

4652.7

8604.7

2965.2

Average

31.01

18.9

2.55

1103.6

5680.1

1550.9

2868.2

988.4

Figure 7: Bar chart representing Concentration of POPs in LEC and Woodland Organic matter.

Table 4: Percentage Recoveries for LEC and Woodland Soil

Recovery Standard-Radio labelled (%)

Samples

13C-PCB 101

13C-PCB 153

13C-PCB 180

LEC Soil 1

66%

69.20%

65.20%

LEC Soil 2

104.40%

94.40%

91.92%

LEC Soil 3

95.90%

86%

78.40%

Wood Land Soil 1

86%

76%

66%

Wood Land Soil 2

88.40%

91.60%

84.40%

Wood Land Soil 3

101.20%

94.00%

91.20%

Table 5: Mass of Wet and Dry Vegetation, and POP Concentration in the Vegetation Sample

Samples

Mass of wet veg.

Dry mass of veg.

HCB

p.p'-DDT

pcb 101

pcb 153

pcb 180

Units

x(g) wet veg

x(g) dry veg

pgg-1

pgg-1

pgg-1

pgg-1

pgg-1

LEC Veg 1

20.44

4.08

374.4

432.6

495.1

495.7

117

LEC Veg 2

20.895

4.18

431.2

861.8

767.3

925.2

221.3

LEC Veg 3

20.0588

4.02

309.7

ND

454.6

488.2

77.7

Total

61.39

12.28

1115.3

1294.4

1717

1909.1

416

Average

20.46

4.09

371.77

431.47

572.33

636.37

138.67

Wood Land Veg 1

20.95

4.19

386.6

472

472.6

420

89.4

Wood Land Veg 2

20.415

4.08

286.8

512.3

405

430

71.7

Wood Land Veg 3

27.91

5.6

436.7

537

356.5

385.2

86

Total

69.28

13.87

1110.1

1521.3

1234.1

1235.2

247.1

Average

23.09

4.62

370.03

507.1

411.37

411.73

82.37

Figure 8: Bar chart representing Concentrations of POPs in LEC and Woodland vegetation.

Table 6: Percentage Recoveries for LEC and Woodland Vegetation.

Recovery Standard-Radio labelled (%)

Samples

13C-pcb 101

13C-pcb 153

13C-pcb 180

LEC Veg 1

103.60%

110.80%

105.20%

LEC Veg 2

111.60%

109.20%

98.80%

LEC Veg 3

77.20%

82.80%

44%

Wood Land Veg 1

100.80%

91%

85.20%

Wood Land Veg 2

75.20%

76.40%

70%

Wood Land Veg 3

111.20%

102%

96.40%

The result presented shows that the recoveries were reasonably good, which suggests that the homogenization and clean-up and general analytical processes were cautiously undertaken. The concentration for the PCB congener 13C-pcb153 was found to have the highest concentration in LEC and woodland soil samples compared to the other compounds while the concentration of p.p'-DDT was comparatively higher in woodland soil samples for both dry soil samples and organic matter content.

The result also shows that the woodland soil has more organic matter content compared to the LEC soil samples. The higher organic matter content is expected of the woodland because of the complex microbial interaction and decomposition that may be orchestrated by leaf litter, root exudates within the microbial populations.

LEC soil samples had more water content compared to the wood land soil as the results of the dry weight of samples reveals this. It has been demonstrated that increase in organic matter from 0.5-3% resulted in doubling the available water capacity (Hudson, 1994) also an increase in water retention in sandy soil was observed with an increase in organic matter content (Rawls, 2003). Expectedly, woodland soil with more organic matter content should have more water capacity but result of the analysis seems to prove otherwise. This could be that the LEC soil has a structure that enhances its water retention.

The result of the vegetation samples points out that the PCB congener 13C-pcb180 has the lowest concentration both in LEC and woodland soil compared to the other compounds.

The experiment had a bit of limitation because some of the concentrations of compounds measured were well above calibration range which could introduce doubt to the linearity of the regression curve. A possible way to correct for this in subsequent analysis is to dilute the concentration of the samples.

CONCLUSION

The detection of these POPs (HCB, DDT, PCBs) within the Lancaster campus which has no historic production status confirms the stated characteristics of POPs which pre-disposes them to long range atmospheric transport, persistence and air-surface exchange. The results obtained are reliable but not very robust because of some limitations such as lack of use of replicate samples, field blanks and equipment blanks. If these were employed in the analytical process, it would have been able to compensate and track for errors such as that observed in LEC vegetation sample 3. Time limitation was another constraint to this experiment resulting in some routine protocols not being carried out. These contaminants exist in trace amounts so utmost precaution was taken during the analysis. The study detected POP concentration in both soil and vegetation samples in varying amounts with some compounds such as p.pDDT and PCB153 being comparatively higher than others. Most concentrations of POPs in the wood land appear lower than that of LEC probably due to vegetative cover of the woodland trees which could receive the depositions from the atmosphere there by reducing the amount that reaches the soil in the woodland site. Also, LEC court yard is closer to human activities while woodland appears relatively distant. This experiment corroborates studies carried out in this field of study has added to knowledge.

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