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  • ISSN: 0973-4945; CODEN ECJHAO

    E-Journal of Chemistry

    http://www.e-journals.net 2010, 7(3), 861-869

    Groundwater Quality of Southeastern

    Brazzaville, Congo

    MATINI LAURENT and MOUTOU JOSEPH MARIE

    Department of Exact Sciences,

    E.N.S., Marien NGOUABI University, B.P 69 Brazzaville, Congo.

    matinilaurent@yahoo.fr

    Received 2 October 2009; Accepted 1 December 2009

    Abstract: The groundwater in southeastern Brazzaville (Congo) was analyzed for

    their fluoride contents and others related parameters in rainy season. The fluoride

    contents in water samples (wells and spring) can be gather in three classes in the

    study area: low, optimal, high. Fluoride concentration in water samples presents a

    low significant correlation with Ca2+. This suggests that fluoride in the groundwater

    come from fluoride-bearing minerals such as CaF2 (fluorite). Maps were drawn to

    show the geographical distribution of EC, Ca2+, Mg2+and F-. Factor analysis and

    cluster analysis were applied to the dataset. Factor analysis resulted in four factors

    explained 76.90% of the total groundwater quality variance. Factor 1 (hardness of

    the groundwater) includes total hardness, the concentration of K+, Ca2+ and pH.

    Factor 2 (low mineralization of the groundwater) includes concentrations of TDS,

    Cl-, SO42- and EC. Factor 3 (anthropogenic activities with the impact of agricultural

    fertilizers, farming activities, domestic wastewater, septic tanks) includes

    concentrations of Na+ and NO3-. Factor 4 (weathering of calcium minerals)

    includes concentrations of F-. For cluster analysis, Wards method and the

    Euclidean distance were used. The findings of the cluster analysis are presented in

    the form of dendrogram of the well water sites (cases). The discriminating

    parameters between clusters have been highlighted from the Student test. In

    majority, they are in accordance with those highlighted by factor analysis.

    Keywords: Fluoride, Groundwater, Sandstone aquifer, Factor analysis, t-Test.

    Introduction

    Fluoride is of interest, because of its effects on human health. Even small quantity of

    fluoride (< 0.7 mg/L) has beneficial effects to the teeth by hardening the enamel and

    reducing the incidence of dental caries1. Excessive intake of fluoride (>1.5 mg/L) results in

    dental and skeletal fluorosis2. Unlike many others elements, a large quantity of fluoride is

    ingested from drinking water and food. Many studies have reported that fluoride is one of

    the most undesired elements present in the underground water extracted for drinking3-5

    .

  • 862 MATINI LAURENT et al.

    Fluoride build-up in water is controlled by many factors like aquifer geology, contact

    times with fluoride-bearing minerals, agricultural fertilizers and climate. Fluoride mainly

    occurs in groundwater through fluoride-rich minerals, such as fluorite (CaF2), fluorapatite

    Ca5F(PO4)3, apatite Ca5(PO4)3(F, OH, Cl). It derives from dissolution of these minerals in

    the rocks and soils through which water interacts.

    The present study has been designed for the first time on the concentration of fluoride in

    groundwater in Southeastern Brazzaville, Congo, which provides baseline data for taking

    appropriate management measures to reduce the intensity of health disorders.

    The study area

    The study area is located between 151353 - 151410 East longitude and 4157.2 to

    41528.8 South latitude. The area is in the equatorial climate zone, with two seasons: rainy

    season (October to May) and dry season (June to September). Temperature in rainy season varies

    from 25 C to 36 C, while it is between 18 C and 24 C in dry season. The mean annual rainfall

    is 1470 mm. The vegetation is of savanna type (Loutetia demeusi) and presents a formation to

    sparse gramineous carpet with a shrubby layer of hymenocardia acida. The soils of the area are

    sandy and have been derived from Tertiary Silicate Sandstones of the Inkisi Serial. They are

    ferralitic and acid. Aquifer is shallow. Generally, the depth of wells does not exceed 2 m. The

    main natural recharge to groundwater is from precipitation (rainfall). Farming activities are

    present around some well water sites and also agricultural activities near the River Mfilou.

    Experimental

    Twenty seven samples of wells water and one sample of spring water were collected in three

    times in rainy season (from March 25 to April 5, 2007) from the study area. They were analyzed

    for pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH as CaCO3),

    Ca2+

    , Mg2+

    , K+, Cl

    -, SO4

    2-, NO3

    -, HCO3

    - and following standard methods

    6. The ratio Ca

    2+/Mg

    2+

    was also computed for all the groundwater samples. STATISTICA 7.1 software was used to

    perform factor and cluster analyses. Factor analysis was used to understand the correlation

    structure of collected data and identified most important factors contributing the data structure7.

    The data were standardized to produce a normal distribution of all variables8, whose mean and

    variance were set to zero and one respectively. The factor extraction was performed, using the

    method of principal components. Kaiser criterion9, which retains only the factors with

    eigenvalues greater than 1, was applied. The proportion of variance in all the groundwater

    parameters accounted for each factor was obtained by dividing the factors eigenvalue by the

    number of parameters. Interpretation of groundwater quality was facilitated, using the

    varimax rotation, which is a standard rotation method. Cluster analysis is also another data

    reduction method10

    that was used to classify entities or objects, with similar properties into

    groups called clusters. Objects within the clusters are similar, while objects in different

    clusters are dissimilar. This exploratory method enables to discover the data structure not

    only among observations, but also among variables. In this study, the Wards clustering

    method and the Euclidean distance was used as a similarity measure.

    Results and Discussion

    Table 1 presents the chemical composition of groundwater samples in the study area. It is

    observed that the pH in all the groundwater samples ranges from 3.85 to 6.08, with a mean

    of 5.22, indicating an acidic environment. The pH values are below the prescribed limits of

    6.5-8.5 for drinking. The results show that electrical conductivity is varied between

    75 S/cm and 431.20 S/cm, with a mean of 235.51 S/cm (at 25 C), indicating the

  • Groundwater Quality of Southeastern Brazzaville 863

    groundwater is slightly mineralized (Table 1). Wells, P6 and P14 located in northwestern

    and well P23 located in southern parts of the study area, presented in Figure 1, show the

    higher electrical conductivity value, which is attributable to the influence of domestic

    wastewater.

    526250 526300 526350 526400 526450 526500

    9529450

    9529500

    9529550

    9529600

    9529650

    9529700

    9529750

    9529800

    9529850

    9529900

    9529950S

    P1

    P2

    P3P4P5

    P6

    P7P8

    P9

    P10P11

    P12

    P13

    P14P15

    P16

    P17

    P18

    P19

    P20

    P21

    P22

    P23

    P24

    P25

    P2780

    100

    120

    140

    160

    180

    200

    220

    240

    260

    280

    300

    320

    340

    360

    380

    400

    420

    EC (S/cm)

    Figure 1. Contour map of EC (in S/cm) in the wells water and spring water.

    The TDS, which is an indicative parameter to assess the degree of water quality, is

    below 230 mg/L in the water samples. This is, within the recommended limit of 500

    mg/L for drinking purpose2. The TA ranges from 5 to 84.98 mg/L (mean of 26.21 mg/L).

    The TH in the groundwater samples is in the range of 5 to 60 mg/L (mean of 29.32

    mg/L) and indicates that the water belong to the soft category11

    . The concentration

    (mg/L) of calcium, magnesium, sodium, potassium, chloride, sulfate and nitrate is in the

    range of 4 to 30, 5 to 14, 1.13 to 36.25, 2 to 12, 5.4 to 44.0, 2 to 11, and 0.25 to 23.20

    mg/L with a mean of 16.03, 8.5, 10.81, 5.28, 20.24, 7.79 and 1.86 mg/L, respectively.

    Compared to WHO2, the concentration of the parameters quoted above are below the safe

    limit of 100, 150, 200, 200, 250, 200 and 50 mg/L for drinking, respectively. Since the

    chloride-rich minerals are not found in the study area, the higher concentrations of

    chloride in the groundwater could be caused by pollution sources such of domestic

    wastewater and septic tanks.

  • 86

    4

    MA

    TIN

    I LA

    UR

    EN

    T e

    t al.

    Table 1. Hydrochemical parameters of groundwaters in the study area.

    Code pH EC TDS TA TH Ca2+

    Mg2+

    Na K+ Cl

    - SO4

    2- HCO3

    - F

    - NO3

    - Ca

    2+/Mg

    2+

    S 3.90 93.92 49.88 40.00 5 4 12 2.53 3.2 19.53 2 48.80 0.42 0.56 0.20 P1 3.98 251.20 133.00 5.00 20 12 10 9.84 5.8 32.23 7 6.10 0.29 1.08 0.72

    P2 4.00 104.92 55.54 5.00 10 8 12 17.43 2.0 18.10 4 6.10 0.19 3.90 0.40

    P3 4.22 100.84 53.46 30.00 15 6 13 8.49 3.1 12.35 7 36.60 0.37 0.

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