Contamination Index (CI)
Drinking water is the most common pathway throughwhich populations are exposed to harmful elements ofanthropogenic or geological origin. The health-based criteriafor the quality of drinking water, set by nationaland international health organizations (Anon 1993,1994a,b), include limits on the number of potentiallyharmful microbes or bacteria (the harmless species Escheriacoli is used as indicator bacterium) and concentrationsof certain inorganic elements (As, F–, Rn) and ionicspecies (e.g., NO3–, UO22+). In addition to the health-relatedupper permissible concentrations or guide values,there are a number of technical and aesthetic target valuesfor household water. These properties impairing theutilization of water are color, smell, taste, and some physicaland chemical properties (low pH, high CO2 and Cl-concentrations) which induce the corrosion of concreteand metal or enhance precipitation and clogging in pipes.Household water may also contain ionic species and biotawhich, while not affecting human health directly, mayimpair water quality by enhancing the growth of microbesor by leaching harmful elements from waterpumps, containers, and pipes. Finnish soft and acidgroundwaters tend to corrode metals and other plumbingmaterials (Korkka-Niemi and others 1993), but corrosionis not a problem in the more strongly mineralized Slovakground water.
The quality of groundwater consumed in households hasbeen registered in the course of several national hydrogeochemicalmapping programs and monitoring networksin Finland and Slovakia. A few physical and chemicalcharacteristics and dissolved components were measuredin the field immediately after the collection of groundwatersamples. Later, in the laboratories, the sampleswere analyzed for the concentrations of tens of dissolvedelements and ionic species. The results were presented intables and assets of hydrogeochemical maps.Modern map production techniques visualize informativelythe distribution of each element and compound. Alarge number of separate maps do not, however, easilyprovide a general view of the level of groundwater contamination.As a means to such a general view, a methodfor calculating a contamination index, Cd, was developedat the Geological Survey of Slovak Republic by D. Bodišand S. Rapant (Rapant and others 1995). The method wasfurther refined at the Geological Survey of Finland.
One approach to the assessment and visualization of areascharacterized by anomalous or hazardous concentrationsof defined elements and ionic species is to calculateand depict on maps the degree of contamination througha contamination index, which takes into account both thenumber of parameters exceeding the upper permissiblelimits or guide values of the potentially harmful elements,and the concentrations exceeding these limit values.Calculation of the contamination degree, Cd, is madeseparately for each sample of water analyzed, as a sum ofthe contamination factors of individual components exceedingthe upper permissible value. Hence, the contaminationindex summarizes the combined effects of severalquality parameters considered harmful to household water.
Uses and Limitation:
In order to aid the depiction of level of groundwatercontamination at various regions on a map,a contamination index, (Cd), has been developedto provide a general view of the extent of ground water contamination.
Categorization Table:
Table 1 Three grade scale for degree of groundwater contamination
Standards Required
The upper permissible concentration for drinking water of any national and international water quality standards could be use.
Variables Selection
The selection of variable is based on two different purposes.
- To assess health risk: F–, NO3-, UO22-,As, B, Ba, Cd, Cr, Ni, Pb, Rn and Se
- For technical-aesthetic aspects: TDS, SO42- , Cl–, F–, NO3–, NH4+, Al,As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Sb, Seand Zn.
Calculation of Contamination Index:
The scheme for the calculation of Cd is the following:
\begin{eqnarray*}
C_i = \sum_{i=1}^{n} \ C^{fi} \\
\end{eqnarray*}
where \begin{eqnarray*}
C_{fi} =\frac{C_{Ai}}{C_{Ni}} \ – 1 \\
\end{eqnarray*}
Where Cfiis the contamination factor for the ith component, CAiis the analytical value of the ith component and CNi is the upper permissible concentration for ithcomponent, N representing the normative value.
Case Studies based on Contamination Index
The applicability of the contamination index Cd wastested in two areas, Finland and Slovakia, radically different in natural and geological conditions. Hydrogeochemicalmapping data and the upper permissible concentrationsor guide values set by national or internationalhealth organizations for household water were used inthe compilation. The contamination index Cd is ideal forevaluating and displaying cartographically the overall degreeof groundwater contamination. The proposed indexcould be used not only in mapping of groundwater contaminationbut also equally well be applied to map thecontamination in other components of the environment,such as surface waters, stream sediments, and soils. Suchevaluation, based on the monitoring of a large number ofdissolved elements and ionic species, provides a clearpicture of the qualitative properties and degree ofgroundwater contamination, useful for environmentalistsand administrative decision-makers alike.
Twenty water samples from a river system in southern Caspian Sea basin werecollected and analyzed for physicochemical parameters and metals (Cu, Zn, As, Cd, Pb, Ni andMn). In order to evaluate the risk potential of metal pollution in river water, use of two indicesnamely heavy metal pollution index (HPI) and contamination index (Cd) accompanied by clusteranalysis was taken in to consideration. Stations located within the upstream of the river (1 to 13)seemed to encounter low risk potentials while the downstream stations (14 to 20) approved tohold higher risks.The results also showed relativelymeaningful correlation among different metalswhich may be attributed to their same entry source, mainly mining and quarrying activities in thecentral parts of the basin following by municipal and industrial wastewater discharge to the riverin downstream. The convergence of both indices in this study was also of interest. Although themean values of both indices were below the critical values, severe precautions must be taken intoconsideration especially in the stations holding high risk potentials. Extreme use of river waterfor drinking, agriculture and industrial purposes within the water basin, relatively biota-richcharacteristic of the river and Caspian Sea asthe final sink ofthe river are among the mostsignificantreasons that make the river monitoring implementation inevitable.
Ground water is the most important source of domestic and irrigation purpose inboth rural and urban regions. The present study is carried out to find the groundwater quality by heavy metal concentration from three sites. Nine heavy metals wereselected (Cd, Pb, Cr, As, Cu, Hg, Se, Zn and Ni). It was showed that concentration valueswere 0.0016-0.0016, 0.003-0.00, 0.006-0.00, 0.00-0.004 and 0.002 mg/L, respectively.To assess ground water quality which contaminated by heavy metals, four indiceswere selected as follow: heavy metal pollution index (HPI), contamination index (Cd),metal enrichment index (MEI) and metal evaluation index (HEI). Results showed thatthe concentrations of heavy metals in water samples are within the permissible WHOlimits in drinking water. Three metals of them (AS, Hg and Se) were not detected in allsampling stations. MEI in the ground water samples show that Niis the highest metalenrichment value of -0.6. HPI of water samples in three sites were 20.57 which waslower than 100 the critical value for drinking water. Cdshows that the values varybetween -5.1 to -0.3 which indicate low contamination. HEI shows that the values inspring season vary from 0.001 to 0.66 and indicate low heavy metal pollution. Resultsshow that ground water of the present study is acceptable for drinking.
References
Nasrabadi T (2015) An index approach to metallic pollution in river waters. Int J Environ Res 9(1): 385-394.
El- Hamid HTA, Hegazy TA (2017) Evaluation of Water Quality Pollution Indices for Groundwater Resources of New Damietta, Egypt. MOJ Eco Environ Sci 2(6): 00045. DOI: 10.15406/mojes.2017.02.00045