Heavy Metal Pollution Index (HPI)
Industrialization and effluent society consumes various metals in day to day activities by exposing the modern technological society to heavy metals in unusually high concentrations in both physical and chemical forms. Though the optimum dose of heavy metals is required for biological system, if it exceeds, the toxicity persists. The toxicity of heavy metals leads to interference of cells and malfunction of enzymatic system in diverse ways depending upon nature of heavy metals. Monitoring of heavy metal pollution in the environmental matrix in ground and surface waters assumes significance in the context of human health. The assessment of heavy metals is included with water quality parameters in order to assess overall pollution of water. Monitoring of heavy metal pollution in the drinking water id very important in a developing town like Tirupati.
The pollution parameter monitored for the assessment of the quality of any system gives an idea of the pollution status with reference to that particular parameter. With such type of assessment, understanding of overall pollution of a particular system with respect to number of parameters is difficult. Quality indices are to be usually employed to get a composite influence of all the parameters of overall pollution. Quality indices make use of series of judgements into a reproducible form and compile all the polutio parameters into some convenient approach. Horton (1965) defined quality index as an overall quality reflecting the composite influence on quality of a number of individual quality characteristics. Number of quality indices were developed to estimate characteristics of surface water with water quality parameters (Horton 1965; Bottom et al. 1978; Brown et al. 1972; Lee and Hward 1965; Lohani and Todino 1984; Ott 1978; Tiwari and Mishra 1985). Recentlly pollution index of heavy metals is also gaining importance in surface waters (Joung et al. 1979; Nishidia and Miyai 1982).
This communication discusses the application of weighted arithmetic average mean method for indexing to assess the overall pollution of the heavy metals in ground water useful for drinking purpose. The concentration of four important heavy metals (Copper, Cadmium, Lead and Zinc) were monitored in Tirupati town at twelve important sampling stations for three seasons in a year.
Uses and Limitation:
It is used as a tool to assess overall water quality with respect to the heavy metals pollution level in ground and surface water for drinking and other aquatic purposes. The index is highly useful to get rightful conclusion of overall quality of water with a systematic rating. It is also used for comparative purposes of quality characteristics at different stations and also to discuss the quality criteria of particular area in detail.
Categorization Table:
The permissible or critical pollution index value for drinking water is 100 (Mohan et al. 1996). According to Edet and Offiong (2002) HPI is classified into three classes as follows:
Standards Required
Any regional water quality standards for drinking purpose could be used for this model.
Variables Selection
As the name of this model clearly indicates that this refers to the heavy metal toxicity,any possible heavy metal could be considered for this pollution index. For instance: Fe, Co, Ni, Cu, Ni, Zn etc.
Calculation of Heavy Metal Pollution Index:
The HPI (Heavy Metal Pollution Index) model (Mohan et al. 1996) is given by Eq. (1)
\begin{eqnarray*}
HPI =\frac{\sum_{i=1}^{n} W_i Q_i}{\sum_{i=1}^{n} W_i} \ \\
\end{eqnarray*}
Where, Qi is the sub-index of the ithparameter. Wi is the unit weightage of the ith parameter and n is the number of parameters considered. The sub-index (Qi) of the parameter is analysed by
Eq. (2)
\begin{eqnarray*}
Q_i = \sum_{i=1}^{n} \frac{{M_i (-) I_i}}{(S_i – I_i)} \ * 100 \
\end{eqnarray*}
Where, Miis the monitored value of heavy metal of ith parameter, Iiis the ideal value of the ith parameter and Si is the standard value of the ith parameter.
Case Studies based on Heavy Metal Pollution Index
References
Tiwari, A. K., Singh, P. K., Singh, A. K., & De Maio, M. (2016). Estimation of heavy metal contaminationin groundwater and development of a Heavy Metal Pollution Index by using GIS technique. Bulletin ofEnvironmental Contamination and Toxicology. https ://doi.org/10.1007/s0012 8-016-1750-6.