Si and Ii are the standard permissible and the highest desirable values for each parameter, respectively. These values are used to calculate the Heavy Metal Pollution Index (HPI) as follows:

n

Hpi= ∑ Mi-Ii x 100

I=1 S-Ii

where Mi is the measured concentration of the $i$th parameter.

Si and Ii values for some of the heavy metals you are interested in, based on the World Health Organization (WHO) standards are:

| Heavy Metal | Si (µg/L) | Ii (µg/L) |

| ----------- | --------- | --------- |

| Pb | 10 | 0 |

| As | 10 | 0 |

| Cr | 50 | 0 |

| Cd | 3 | 0 |

| Cu | 2000 | 1000 |

| Zn | 3000 | 2000 |

| Ni | 70 | 20 |

| Mn | 400 | 50 |

For the USEPA standards, refer to the National Recommended Water Quality Criteria table(2), which lists the freshwater and saltwater criteria for various pollutants, including heavy metals. The criteria are expressed as the concentration of dissolved metal in water. However, these criteria are not directly comparable to the Si and Ii values, as they are derived from different methods and data. You may need to convert the criteria to the total metal concentration using the conversion factors provided in Appendix A(2). Alternatively, you can use the MetALiCC-MAP tool(3) to calculate the aquatic life criteria for metals based on your site-specific water chemistry data.

Source(s)

1. Water Quality Assessment and Environmental Impact of Heavy Metals in ...

2. National Recommended Water Quality Criteria - US EPA

3. Aquatic Life Criteria and Methods for Toxics | US EPA

4. Metals | US EPA

5. Heavy Metal Definition and List - ThoughtCo

6. PARTITION COEFFICIENTS FOR METALS IN SURFACE WATER, SOIL, AND WASTE

7. Groundwater quality, heavy metal pollution, and health risk ... - Springer

8. A Reassessment of Regulatory Reference Values and Background ... - IAFNS