Heavy metals contamination at whitespots – conlig, newtownards, northern ireland

Journal of Natural Sciences Research www.iiste.org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online)

Vol.3, No.5, 2013

45

Heavy metals contamination at Whitespots – Conlig,

Newtownards, Northern Ireland.

Chukwuemeka Kingsley Egbuna 1*

Bolarinwa Ajibola 2 Ishaq Ayoola Louis

3

1. Department of Civil Engineering, University of Bristol, UK

2. Department of Geology, University of Brighton, UK

3. School of Built Environment, University of Brighton, UK *Email of corresponding author: [email protected]

Abstract

This study was conducted to investigate and examine the dispersion of heavy metals at the lead mine of

Whitespots – Conlig, Newtownards, Northern Ireland. Seven vertical profiles namely; profiles A, B, C, D, E, F

and G, were measured at depths between 0cm to 80cm and were tested for soil moisture content, soil pH, PXRF

spectrometer, XRD spectrometer and Inductively Coupled Plasma Mass spectrometer (ICP-MS), with all tests

done in duplicate. The finding shows that Pb and other heavy metals accumulate at the topsoil of profiles B 0-

22cm, C 0-20cm and A to depth 63cm. The process of dispersion occurs as lateral migration of contaminated

materials, which partly accumulated at topsoil via surface runoff across the meadow. This process is regulated by

the clay-rich and organic-rich soil composition, the soil pH condition of neutral to slightly alkaline which

allowed immobilized Pb and other heavy metals to be adsorbed onto soil particles and a small percentage of

leaching to take place. The mobile elements K, Fe and Zn which percolated downward were however

precipitated in the slightly alkaline to neutral soil. The concentration of the carbonates and heavy metals

indicated a lateral dispersion process by surface flow transfers and deposition of particles via an entry point onto

the field and also as a result of topographic gradient.

Keyword: Lead, PXRF, minerals, metals, DTPA Extraction

1.0 Introduction

Elevated levels of heavy metals from metalliferous mines are found in and around disused mines sites due to

discharge and dispersion of mine wastes into the ecosystem (Alloway, 1995; Jung, 2001). Heavy metals which

are contained in residues of mining and metallurgical operations are frequently dispersed by wind and or water

after their disposal (Adriano, 2001). These areas experience severe erosion problems caused by wind and water

runoff and to which soil texture, landscape topography; regional and micro-climate operate an important role

(Chopin et al., 2003 and Razo et al., 2004).

The contamination of soil by Pb and other heavy metals in and around a mine site is dependent on the

geochemical characteristics and the extent and degree of mineralization of the tailings (Johnson et al., 2000). The

release of metals by sulphide oxidation is weakened by precipitation, sorption reactions and co-precipitation

(McGregor et al., 1998 and Berg et al., 2001) in and around the site. The dispersions of these metals released and

their inputs into soil profile and sediments (Kim et al., 2002) are subjected to examination as well as the physical

transport process involved (Navarro et al., 2007). It has been established that bio-availability of heavy in soils is

dependent on the solubility of minerals and chemical species present (Kambata-Pendias and Pendias, 1984),

hence, soil pH and soil buffering capacity appear to be important controls on metal bio-availability (Alloway,

1990; Gee et al., 2001). Pb contamination can cause health problems via ingestion and or inhalation to plants and

humans because of its organic compounds which are toxic. This paper thus, investigates and examines the

dispersion of heavy metals at the lead mine of Whitespots – Conlig, Newtownards, Northern Ireland.

2.0 Study Materials

Site study

The Whitespots – Conlig lead mines is an abandoned mine site near Newtownards, Northern Ireland, which

occupies an extensive area consisting of spoil heaps, tailings impoundments, capped mine shafts as well as the

architectural features of the engine house and chimney stacks. The mine site contains materials such as

hydrothermal vein minerals, notably galena, chalcopyrite, barite, dolomite, calcite and harmotome which help to

identify the origin of its mineralization (Nawaz and Moles, 2006).

Previous studies at a metalliferous mine site shows the accumulation of Pb as well as other heavy metals in

surrounding soils (Sidle et al., 1991) vegetation (Johnson and Eaton, 1980; Chambers and Sidle, 1991), local

water ways (Merrington and Alloway, 1994), and of this mine site, uptake of heavy metals by plant and

translocation to human food chain (Levy et al., 1992).

In recent times, the Department of the Environment for Northern Ireland after due consultation with the Council

for Nature Conservation and Countryside, decided to make the mine area an area of special scientific interest by


Vol.3, No.5, 2013

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reason of geological features, hence declaring it to be ‘Whitespots Area of Special Scientific Interest’ (Martin,

1998) and also develop it as a country park (Moles et al., 2004).

3.0 Methodology

Seven vertical profiles namely; profiles A, B, C, D, E, F and G, were measured at depths between 0cm to 80cm.

Profile G is at a near-by field where previous work had also been done and it is intended to give a background

representation of the field contaminated by heavy metals. These profiles were analysed for XRD, DTPA, PXRF

and soil moisture content and pH. All tests were done in duplicates and it was observed that the variations

between both results were not more than 2%.

The XRD is a method for characterising the mineralogy of rocks and soils and can be used to derive quantitative

mineralogy data. The soil samples were homogenised, oven dried and ground to particles of about 0.002mm. It is

important to have a finely ground sample with a flat surface so that the XRD accurately measures the molecular

structure or compound of the soil sample. Semi-quantitative estimates of the proportions of mineral constituents

of the soil samples are obtained in percentages by the computer program X’Pert Pro.

Di-ethylene-triamine penta-acetic acid (DTPA) is a soil test which is useful to extract the portion of Zn, Fe, Mn

and Cu which is similar to the amounts that are bio-available in the soil. Heavy metals have higher affinity for

chelating agent than soil, hence, metal contaminants dissolve during the extraction process (Hong et al., 2002).

This is because the chelating agent combines with free metal ions in solution and as such forming soluble

complexes, thus, reducing activities of free ions in solution. Accumulation of chelated metals in the solution is

an indication of extraction function of both ability of metal ions in soil and ability of soil to replenish those ions.

The purpose of using the DTPA is to dissolve certain heavy metals by preventing through precipitation their

removal and then release the absorbed metals that are in sediments of the soil.

The Portable X-ray Fluorescence spectrometry (PXRF) is used for analysing the elemental composition of rocks

and sediments (Jenkins, 1999). Its analysis is derived from excitation of electrons by incident X-radiation. The

energy emitted as fluorescence and the wavelength spectra forms the characteristics of atoms of specific

elements (Weltje and Tjallingii, 2008). The instrument is used for both in-situ and ex-situ methods of analysis.

The processed data output reveals the minerals with highest concentration within the threshold of soil sample

analysed (Ramsey and Boon, 2011).

4.0 Results

4.1 Soil Moisture content and soil pH

The range of soil pH and its moisture content of 44 soil samples over the 7 profiles are shown in table 1. The soil

pH range indicates most of the soil sample content is neutral and a deviation between slightly alkaline to slightly

acidic as it is location dependent. The classification of the pH values deduced plays an important role in the

mobility of metals in the soil, this is because they govern directly or indirectly the complex reactions of metal

cations, ion –exchange as well as other metal binding formations and solubility. Profiles A and C are mainly

neutral while profiles B, D, E, F indicate a shift towards slightly alkaline depth soils as a result of ingress of

carbonate – rich tailings material into the meadow. Profile G, is neutral to slightly acidic and its location is at a

background representative location to the field and by contrast cannot be affected by the carbonate materials

from the tailings spoil heaps.

All the profiles (A-G) have variations in distribution of soil moisture, the profile A is most characterised by

clayey soil texture, and has a very high dry mass of 45% in core depth 57cm-63cm. At this depth the soil is light

brown clay and its moisture characterisation indicates it is moderately plastic when wet, hence, it is close to the

field capacity after gravitational percolation has taken place. By indication of this, the water content is not only

stored for plant use but also as an agent of metal transportation within the soil. This can also be described for the

highest moisture content depth profile D 37cm-50cm with weight loss of 52% indicating moisture content is

above field capacity, which results from the nearness of the depth profile to the close-by spring.

4.2 Portable X-ray Fluorescence spectrometry (PXRF)

The data obtained via the PXRF in-situ and ex-situ analysis indicated 17 elements and 20 elements respectively.

For the in-situ data, 2 elements (S and As) were measured below detection limit while ex-situ data, 8 elements

(S, Co, As, Rb, Sr, Zr, Cd, Sn) were measured from no data to below detection limit and above detection limits.

Correlation between the data results of in-situ and ex-situ analysis varies with disparity as low as 3ppm (profile

G, Cu) and as high as 38,953ppm (profile B, Pb). The variation in values encountered by the output data is

shown in table 2.

The variations in the ppm values between the in-situ and ex-situ data could be attributed to some inherent

interference which caused disturbances to the detection limits and precision use of the instruments. This

interferences is as a result of the particle size, homogeneity, and surface conditions of the soil for in situ

measurements and moisture content, grinding of air-dried soil sample, chemical matrix effect (for example when


Vol.3, No.5, 2013

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Fe will absorb more Cu X-rays, thus making Cu levels enhanced in the presence of Fe (Mclean and Bledsoe,

2004) and precipitation.

4.2.1 In situ

The variations in trends of elements measured by the PXRF shows that Pb (68093ppm) and Ca (56751ppm)

recorded highest in the topsoil of profile B, but gradually decreases between depth 20-30cm down the vertical

profile. Fe records 24107ppm at the topsoil but shows variations with distributions in depths as it moves

downward the profile. K, Zn and Cu recorded highest measurements of 10815ppm, 2049ppm and 586ppm

respectively (fig. 1). Fe recorded the highest reading 28398ppm at depth 20cm of the profile with least reading

13761ppm recorded for depth 50cm. Ca and K exhibit similar trend patterns with varying measurements. At

depth 50cm the least readings were observed for Ca 3715ppm and K 4180ppm. Pb, Zn and Cu had low readings

within this depth profile (fig. 2).

4.2.2 Ex situ

The processed laboratory graphic analyses of soil samples were splited into two to show clearly the visible

elements and the variations within the depth profiles.

The processed output of the PXRF spectrometer indicates a very high detection of Pb and Ca in profile A and a

gradual decrease in profile B. This detection of metals gradually decreases along the other profiles. Fe appears

although low but with a 40000ppm as its highest detection and a constant variable in all the depth profiles.

Profile A is closest to the entrance of the tailings wash onto the field hence the major factor for highest detection

by the PXRF spectrometry. As the variables of the metals decrease across the excavated transect, it should be

noted that elements with little detections by the spectrometer is as a result of the detection limits of the analyser.

It therefore means that these elements with little or no detection, for example profile D where detection limits of

Cu, Zn and Pb, it would simply mean the elements have low values (ppm) that are not considered to be read-able

by the spectrometer. Rainwater and surface wash of the tailings are the prime form of deposition of these heavy

metals across the different depth profiles of the soil (figures 3 and 4).

4.3 XRD spectrometry

Minerals detected by the X-ray diffraction spectrometry are quartz, cerussite, calcite, dolomite, clinochlore,

plagioclase. Clinochlore ((Mg,Fe2+

)5AI(Si3AI)O10(OH)8), from mineralogy group of chlorite, is derived from

country rock, that is greywacke and shale which was metamorphosed to form chlorite together with mica (but

not shown by XRD analysis) and attains the highest semiquant of 100%. The clinochlore and the quartz are

derived in the parent material of the soil, as such the constituent of high detection by the XRD machine. Profiles

A, B, and C differ in terms of mineral proportion to profiles D, E and F, and while profile G as well as in depicts

in abundance of the detected minerals. The cerussite, calcite and dolomite are discharged into the soil mainly

from the source which is the tailings wash from the adjacent spoil heaps. This can be described given that in

profile A the contaminant (calcite) can be seen while it in other profiles may have possibly dissolved below

detection limits in other profiles. They are all carbonate minerals, yet they posses different solubility such that

calcite mineral readily dissolves than dolomite and cerussite with the use of rainwater percolating into the soil

(figures 5 and 6).

Plagioclase is another mineral forming the parent material of the soil. This mineral was detected by the XRD

spectrometer, the mineral indicates variations in proportions, however its detection can be seen in profile A

depth 57-80cm, while in profile B detection was further closer to the topsoil than profile B 28-76cm. Profile C is

of the same pattern as to profile B, and detection was also seen closer to the topsoil at depths 20cm to 70cm of

the soil profile. All other profiles had detection from the topsoil to beneath the depth profiles.

4.4 DTPA Extraction

The selected soil depth samples analysed were chosen based on the wide variations in proportion of distributed

heavy metals within the depth profiles. Due to time constraints the ICP spectrometer was used as against the use

of AAS however, the existing literature by Lindsay and Norvell, (1978) did specify the use of AAS and

appropriate standards. The concentrations of Pb, Fe, K, and Cu are highlighted in table 3. The result indicated

shows a high bio-availability of Pb in the entire depth profiles within the soil sampled as it decreased from

profile A depth 50-57cm (86mg/l), 57-63cm (62mg/l), to 63-68cm (35mg/l). This can also be described for K

and Cu whereas Fe only had concentrations at depth 57-63cm (1mg/l) and 63-68cm (8mg/l).

At profile B, Pb and Fe concentrations increased from sampled depth 16-22cm; to 22-28cm; 125mg/l to 143mg/l

and 0mg/l to 4mg/l respectively, while K and Cu decreased from 14mg/l to 12mg/l and 13mg/l to 5mg/l

respectively as well. Profile C experiences a variation in proportion of the heavy metals in the sampled depth

profiles. Depth 17-20cm denotes the highest concentration of Pb, 0-9cm for K and Fe while 9-17cm for Cu. Fe

has no concentration in depth 9-17cm and it took an increase in depth 17 to 27cm from 2mg/l to 8mg/l. Profile E

had concentrations of from the top sampled soil depth in Pb 106mg/l and K 12mg/l and decreased into the 19-


Vol.3, No.5, 2013

48

29cm however, from 9-19cm to 19-29cm there was an increase from 16mg/l and 3mg/l to 19mg/l to 4mg/l for Fe

and Cu respectively.

5.0 Discussion

The results obtained for soil moisture contents shows a wide variation with the soil profile of the meadow. Each

profile experiences an irregular sequence in moisture content distribution. This however, could be attributed to

the amount of water incorporated within the soil pores, soil composition, and retention capacity. The result of the

pH values of water are in slight contrast to the findings of Moles et al., (2004) which differ on the range of

sample classification. In Moles et al. findings, pH values range between 6.6-8.1 which reveals they were neutral

to slightly alkaline while the findings from samples analysed in this study, shows pH value range between 6.23-

7.54 indicating slightly acidic to slightly alkaline water content. This however shows a change in solubility of

cerussite which although have fine grain size, yet, have existed in the tailings materials for over 150 years

(Moles et al., 2004).

The source of the contaminated soil is the lead rich tailings which have undergone erosion by wind, rain and

visibly scrambling at the surface; thus causing re-distribution of metal particulates or soluble metals to pollute

the surrounding surface soils and vertical depth profiles. Currently, the tailings material is deposited in the

depositional plume in a meadow on the south side of the site (Moles et al., 2000). The dispersion of heavy metals

have moved in from the entry point across the field and percolated into the soil profile core depths. The core

depth profiles investigated and examined is in agreement to Moles et al., (2004) findings which reveal that

vertical depth 0-20cm of profiles A, B and C are contaminated by the mechanically redistributed tailings

material. However, at core depths 22cm downward the profiles B-F depicts they are undisturbed.

The mobility of minerals deduced in this study shows that of all the mineral carbonates (cerussite (PbCO3),

calcite (CaCO3), dolomite (CaMg(CO3)2), Pb which is predominantly formed in cerussite and has a low

solubility which is supported by neutral to alkaline pH, disperses vertically farthest as seen at profile A depth 57-

63cm than the other carbonate minerals at all other profiles.

The DTPA extraction of heavy metals varies in abundance of Pb, low detections of K, Fe and Cu. The result

indicates a decrease in depth for Pb at depth profile A, while a change in proportion (increase and decrease)

within other depth profiles for which no detection or range in quantification earlier persists in the PXRF result.

These variations are as a result of slaked lime added to reagents to buffer the soil pH, complexation with soluble

organic matter followed by precipitation.

The study shows that Pb and other heavy metals accumulate on surface soils, and with variations in abundance

in topsoils of profiles B 0-22cm, C 0-20cm and profile A, percolated to depth 63cm. The immobilization of Pb

beneath these depths is associated with the adsorption onto solid phases and precipitation processes on clay-rich

and organic-rich soils. Only a small percentage of the total Pb would be leached while other mobile elements K,

Fe and Zn would be removed at neutral to slightly alkaline soil pH through precipitation. Profiles D, E, F and G,

had no visible evidence of tailings input, which is synonymous to below detection limits and low detection limits

of the XRD and PXRF spectrometer. Hence, surface runoff, which can transport soil particles containing

contaminating materials, aids lateral migration of heavy metals across the meadow. Subsequently, with

conditions of the soil pH being neutral to slightly alkaline, soil particles adsorbs heavy metals while the more

mobile elements precipitate within the soil.

6.0 Conclusion

Although the site is already contaminated with toxic metals, it is nonetheless imperative to forestall further

contaminations of soil horizons, given that there have been varying increases in contaminations investigated. It is

very important to prevent further erosion and re-deposition of the tailings materials at the AMS from dispersing

into the field and surrounding areas. More so, the site should restrict the use of motorbikes at areas where the

spoil heaps are eroding rather a separate area should be developed for the motorbike activities. The tailing

materials should be prevented with appropriate soil plants as well as flow drainage system to cap the surface

wash into a separate site which can be used for further studies. Educating the public on the awareness of health

risks involved in heavy metal consumption is very important within the mine site and at global level.

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Table 1: Soil moisture contents and Soil pH result values.

Profile

A B C D E F G

Moisture

content %

13 - 45

12 – 33

12 – 32

31 – 52

10 – 38

18 – 42

18 – 29

Soil pH Neutral Neutral –

slightly

alkaline

Neutral Neutral –

slightly

alkaline

Neutral –

slightly

alkaline

Neutral –

slightly

alkaline

Neutral –

slightly

acidic

Table 2: Comparisons between the PXRF in-situ and ex-situ readings

Profiles

K Ca Fe Cu Zn Pb

in

situ ex situ

in

situ ex situ in situ

ex

situ in situ

ex

situ in situ

ex

situ

in

situ ex situ

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

B 10815 11319 56751 51338 586 831 586 831 2049 3072 68093 107046

D 9467 9060 6145 6799 28398 35489 72 135 158 286 2755 3802

E 11166 9354 7048 11664 29153 38624 121 176 302 471 3038 4899

F 7376 9318 7538 11146 22607 35371 202 320 117 194 2207 3737

G 11562 13526 1857 3435 36067 48051 109 142 39 42 590 584

Table 3: Metal concentration in soil samples after DTPA extraction

mg/l

Profile depth Pb K Fe Cu

A 50-57cm 86 14 0 14

A 57-63cm 62 10 1 5

A 63-68cm 35 7 8 4

B 16-22cm 125 14 0 13

B 28-36cm 143 12 4 5

C 0-9cm 139 31 6 4

C 9-17cm 134 17 0 11

C 17-20cm 180 17 2 3

C 20-27cm 131 6 8 4

E 9-19cm 106 12 16 3

E 19-29cm 67 7 19 4


Vol.3, No.5, 2013

51

Figure 1: In situ measurements for Pb, Zn, K, Ca, Fe and Cu in the vertical depth profile B.

Figure 2: In situ measurements for Pb, Zn, K, Ca, Fe and Cu in the vertical depth profile D.

UNITS

X-axis Profile

Y-axis ppm

UNITS

X-axis Profile

Y-axis ppm


Vol.3, No.5, 2013

52

Figure 3: Ex-situ measurement of Ca, Fe and Pb using the PXRF spectrometer

Figure 4: Ex-situ measurement of K, Cu and Zn using the PXRF spectrometer

UNITS

X-axis Profile

Y-axis ppm

UNITS

X-axis Profile

Y-axis ppm


Vol.3, No.5, 2013

53

Figure 5: Semi-quantitative output of quartz, cerussite and calcite minerals analysed.

Figure 6: Semi-quantitative output of dolomite, clinochlore and plagoiclase minerals analysed.

UNITS

X-axis Profile

Y-axis cm

UNITS

X-axis Profile

Y-axis cm

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