GIS-based assessment of groundwater vulnerability to heavy metal contamination via water quality pollution indices in urban Aligarh, India

In this anthropocene era, deterioration in groundwater quality has garnered much attention from researchers worldwide. The major reason behind degrading water quality may be undoubtedly attributed to increasing industrialization and expanding urbanization (AInyinbor Adejumoke & Toyin 2018). For restoring ecosystem and benefit of mankind, it is necessary to protect the available groundwater reserves by undertaking all possible measures to prevent any further contamination. Generally, there exist two prime causes for groundwater vulnerability, either natural or anthropogenic. Natural factors comprise of hydrogeological conditions, soil parameters, seawater intrusion, etc. while the anthropogenic factors include overabstraction, effluent discharge from wastewater treatment plants, unlimited use of fertilizers, mining activity, waste dumps, industrial waste, etc. Among the anthropogenic factors, effluents from industrial outlets are the major source of groundwater pollution. Furthermore, few industries such as leather industry, textile industry, electroplating industry, and mining industry discharge wastes containing excessive organics as well as inorganic impurities containing specifically heavy metals.

In our ecosystem, a total of 35 metals exist, 23 of which are categorized as heavy metals. The presence of these heavy metals in drinking water, soil, or food can pose significant risks to human health, whether through the food chain or other pathways. Notable examples of these heavy metals include arsenic (As), lead (Pb), copper (Cu), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), and more. Heavy metals are defined by their high atomic weight (ranging from 63.5 to 200.6) and high density (exceeding 5) (Bazrafshan et al. 2015). The solubility of these heavy metals in water at different pH conditions further complicates the issue. Moreover, these inorganic pollutants are mostly non-biodegradable and might enter the food chain and accumulate in the living organism, resulting in serious environmental problems (Hunsom et al. 2005). Intake of these heavy metals through water exceed their permissible limits is known to cause serious human health issues. Therefore, these heavy metals need to be removed from drinking water supplies exceeding permissible limits. Recently various methods have been used to remove heavy metals from water and wastewater including chemical precipitation, membrane filtration, floatation, ion-exchange absorption, electrocoagulation, etc. (Niu et al. 2023).

In past years, several incidents were reported all over the world due to heavy metal toxicity and poisoning. Several case studies also exist where industrial accidents and tragedies happened linked to heavy metal poisoning of available water reservoirs affecting humans as Frailes mine, Aznacollor, Spain, which was later called the Donana disaster, in which 5 million cubic metres of acid wastewater and toxic sludge containing heavy metals such as lead, arsenic, and zinc dropped into the river Agrio, which continued to the Guadiamar River. Gaudiamar is the main water source for the Donana National Park. Various agricultural land, pastureland, woodland, river areas, and marshland alongside the Guadiamar River were affected. The matter came into light when sudden death of wildlife and aquatic life in large numbers (Pain et al. 1998). Thus, concerning such issues so as to avoid such tragedies periodic water quality assessment or examination is required so as to determine whether the available water from the referred-to reliable sources is safe from such toxic metals for drinking and other purposes.

The main objective of this study was to assess groundwater quality pertaining to heavy metals. Besides, the role of industries influents on contaminating groundwater quality in the urban Aligarh was also explored and investigated for any correlation if there. GIS-based maps were plotted for the assessment of groundwater vulnerability to heavy metal contamination via water quality pollution indices.

In recent decades, urbanization and industrialization have rapidly increased in this area, leading to a significant increase in water demand and consequently wastewater generation. This resulted in a major problem with the disposal of wastewater, as there is no proper natural drainage system. As a result, the city is often submerged, especially during the rainy season, and some parts of the city remain submerged throughout the year due to an ineffective drainage system (Rahman 2008). Aligarh is well known for its lock industry, with almost 5,506 industries including about 3,500 small industries, 2,000 medium industries, and 6 large-scale industries. To ensure sustainable development and promote a healthy living environment for its residents, effective management of the industrial activities resulting in pollution is indispensible for Aligarh (Rahman 2008; Mainier et al. 2015).

The aquifer system is comprised of three separate aquifers that have merged into one unified aquifer system. The first group of aquifers is composed of fine to medium-grade sand and is a source of fresh water for various sources of water supply such as handpumps, government tube wells, and shallow tube wells. The depth of this aquifer is located between 0 and 122 m below ground level. After the first group of aquifers, there is a thick layer of calcareous clay that separates it from the middle aquifer. The middle aquifer is located between 100 and 150 meters below ground level and due to the presence of calcareous clay, the water found in this aquifer is saline in nature. The third and final layer of the aquifer system is located between 130 and 300 meters below ground level. This layer is extensive in its geographical reach and is in a confined state, meaning that the water is isolated within the aquifer by surrounding layers of impermeable rocks. This layer of the aquifer has a medium sand size and the water found here is brackish to saline in nature (Khan & Khan 2019; Priyadarshi et al. 2020; Mohammad et al. 2022).

Studies on groundwater vulnerability in Aligarh were conducted to assess the presence of heavy metals in the area. All the samples were collected and analyzed as per standard methods to ensure the accuracy of the results. Briefly, the samples were collected in sterile 250-ml polyethylene bottles and treated with nitric acid (HNO₃) to eliminate the possibility of precipitation of heavy metals (Rowe & Abdel-Magid 2020). The study area was chosen as it appears to host various industries or is an emerging region with a diverse industrial landscape. All the data sets are comprised of primary data collected by physically visiting all the specified locations. The water samples were gathered in two rounds. Initially, samples were taken from 20 locations within the industrial drains. In a subsequent round, 17 samples were taken from different groundwater sources, such as hand pumps and submersible pumps in close area to the industries. The analysis of heavy metals was performed in the environmental engineering laboratory using an Atomic Absorption Spectrometer (Perkin Elmer PinAAcle 900F). Before analysis, each sample was filtered using Whatman-1 filter paper.

Numerous organizations and regulatory bodies worldwide have established guidelines to ensure the safe levels of heavy metals in drinking water. These standards and standardization efforts form the foundation for technical regulations. Notably, the World Health Organization (WHO) Guideline Values (GV), the United States Environmental Protection Agency (USEPA), the Bureau of Indian Standards (BIS), and the European Union Maximum Acceptable Concentration (EU MAC) guidelines and standards for drinking water quality, widely recognized on a global scale. These benchmarks serve as essential references to guarantee the safety and quality of drinking water. By adhering to these established guidelines, we can have confidence that the drinking water we consume meets the necessary standards for heavy metal concentration, as set forth by these esteemed organizations.

Table 1 provides water quality standards prescribed by the different internationally responsible organizations.

The contamination index (CDx) is a measure of the overall impact of various water quality factors that are harmful to drinking water (Mazhar & Ahmad 2020). To determine the level of contamination, the contamination factor of each component in a water sample that surpasses the acceptable limit is calculated and summed up. The highest value obtained is considered to be the maximum permissible level of contamination. This system categorizes the levels of contamination into six groups based on the CD values:

CD (0.3) represents an extremely pure level of contamination.

CD (0.3–1) also denotes an extremely pure level.

CD (1–2) indicates a slightly affected level of contamination.

CD (2–4) implies a moderately affected level.

CD (4–6) shows a severely affected level of contamination.

CD (>6) represents a severely contaminated area.

The heavy metal pollution index (HPI) is a method of determining the impact of heavy metals on the quality of water. It can be found by assigning a weight to each selected water quality factor, with the weight being proportional to the inverse of the recommended standard (S_i) for that particular parameter. This index provides a clear representation of the combined effect of heavy metals on the overall water quality and helps to identify and address any potential health hazards.

The HPI is divided into two categories to determine the quality of the water:

If the HPI < 100, it indicates that the water is safe for drinking.

If the HPI > 100, it implies that the water is polluted with heavy metals and is not safe for drinking purposes.

This system provides a clear and concise way to evaluate the overall quality of the water supply, making it easier to identify any potential health hazards and take appropriate action (Horton 1965; Mohan et al. 1996).

This study analyzed the presence of heavy metals in both industrial effluent and groundwater samples collected from various locations in urban Aligarh. It is important to note that metallic water contamination may be a direct consequence of the existence of metalliferous deposits in the soil and rock (Ghasera et al. 2021). However, the primary sources of heavy metals in the studied area groundwater are industrial activities, including various operations, such as lock manufacturing and polishing. The potential adverse effects of higher heavy metal levels on human health have become a pivotal point of this research study. As increased concentrations of heavy metals can pose a severe risk to human as well as plants and animals (Islam et al. 2018; Nath et al. 2018; Ojaswini et al. 2022).

To determine the distribution pattern of the concentration of different elements and to demarcate higher concentration zones, contour maps for various elements were generated using the ArcGIS 9.3 software. The water quality assessment has brought to light a concerning issue prominently contamination, with emphasis on the presence of lead (Pb), chromium (Cr), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and nickel (Ni). The heavy metals taken into consideration since, these are widely used in the industrial operations taking place in the surrounding area. It is apparent that these metals have made their way into the water, potentially stemming from their use in locks manufacturing. Table 2 presents statistical summaries of heavy metal concentrations in groundwater and industrial effluent, encompassing maximum, minimum, and average values. These statistics provide an overview of central tendency and variability in the data set.

These increased chromium levels observed in industrial wastewater may be attributed to the utilization of chromium in different lock manufacturing processes, such as polishing to give lustrous finish and provide protection against corrosion. During these manufacturing stages, residual chromium may find its way into drainage systems, leading to the high concentrations detected in industrial effluents.

The current presence of trace amounts of chromium in groundwater signifies the probable for infiltration. If this infiltration continues at the current rate, it has the potential to induce significant alterations in the quality of drinking water, potentially leading to a harmful situation.

There are certain toxicants classified as ‘light metals’ that pose a significant risk to the environment and ecosystems when present in high concentrations, and Ni is one such example (Ghasera et al. 2021). Nickel is found to be a probable carcinogenic substance that can have adverse effects on the lungs. Additionally, exposure to nickel is linked with a risk of skin allergies, fibrosis of the lungs, and respiratory cancer for the population (EPA 2002).

Additionally, conspicuous high-level nickel contamination is evident in the effluent from industries in various locality such as Rorawar, which records a concentration of 46.10 mg/l, Saifi Colony with 43.40 mg/l, and Karbala at 38 Makki Nagar, indicating a concentration of 6.7 mg/l. Interestingly, despite the notable concentration in industrial waste, groundwater levels remain comparatively low. This phenomenon could be attributed to the limited number of industries or recent industrial developments in area, or may be the industrial wastewater does not infiltrate the groundwater.

According to various researches, zinc is considered an essential element, has been linked to detrimental effects, including stomach lining damage, weakened immune responses, and reduced HDL cholesterol levels in the blood when its concentration exceeds 50 ppm (Marion 1998). There is a significant increase in the amount of zinc (Zn) in the effluents of several sectors, such as woollen mill, marble, paper mill, and glass industries have been identified as contributors to increased zinc in their effluents, surpassing the limits established by the National Environmental Quality Standards (NEQS). The zinc concentration decreased below the established limit, making it suitable for human consumption (Gyamfi et al. 2012).

The study reveals that zinc levels in groundwater range from 1.029 to 0.152 mg/l, with an average value of 0.154 mg/l. In contrast, in the industry effluent, these levels vary from 1.63 to 0.00 mg/l, with an average value of 0.051 mg/l. Importantly, all these measurements in both groundwater and industrial effluents are found to be below the established permissible limits set by the WHO and the BIS, indicating a positive trend in the urban area's zinc contamination scenario (Marion 1998).

The results obtained through two distinct analytical methods offer a well-defined assessment and categorization of various regions in terms of groundwater suitability for human consumption. The statistical calculations for both the HPI and CDx are presented in Table 4. Analyzing the HPI values for 17 locations revealed that 11 of them fall within the group with values below 100, indicating a lower level of contamination and suggesting that the groundwater is potentially safe for drinking purposes. These locations represent a substantial proportion, accounting for 64.7% of the total surveyed area. In contrast, the remaining six locations (Govind Nagar, Nivar Road, Rorawar Road, Mamoon Nagar (1), ADA colony, and Mamoon Nagar (2)), accounting for 35.3%, were identified as having HPI values exceeding 100. These elevated values are mostly attributed to higher concentrations of Nickel and Copper in groundwater, making it unfit for consumption.

The second method, the CDx, serves as an alternative method for analyzing water quality by quantifying traces of heavy metals. It plays a crucial role in categorizing groundwater quality. Based on the resulting values, it becomes evident that within the urban area of Aligarh, four locations (Eidgah (1), ADA colony, Mamoon Nagar B (2), and Sarai Rehman) fall into the category of high purity, accounting for 23.53% of the total locations. These areas exhibit negligible amounts of metals. Additionally, three locations (Eidgah (2), Prem Nagar, and Kalandi Puram) are deemed slightly affected, representing 17.6% of the total. The elevated values of copper along with iron and manganese contribute to the contamination. Furthermore, two locations (Aashiq Nagar and Labbaik Mosque) exhibit a moderate level of contamination due to the presence of nickel, constituting 11.7% of the total visited locations. Similarly, Nivri Mod and Eidgah Road were identified as being affected by a higher pollution level, also accounting for 11.7% of the total. In the Nivri Mod, nickel, iron, and manganese contributed, while on Eidgah Road, traces of zinc along with Iron, Manganese, and Nickel are responsible. Lastly, five locations were found to be severely contaminated, representing 29.4% of the total observed locations. In Govind Nagar, Nivar Road, Mamoon Nagar, and ADA colony, almost all seven metals were found in low to higher concentrations. Additionally, on Rorawar Road, nickel, iron, and manganese contributed, and in Mamoon Nagar B (1), nickel and copper raised the CDx values. A significant portion of the groundwater in the region is affected by industrial wastewater. Therefore, it is imperative to implement conservation measures to preserve groundwater for sustainable use in the future.

The primary objective of this study was to assess the impact of industrial effluent on the contamination of groundwater of urban Aligarh pertaining to heavy metals. Through comprehensive analysis and examination, this research aimed to shed light on the intricate relationship between industrial activities and the quality of groundwater, contributing valuable insights to the ongoing discourse on environmental sustainability. The highest contamination was observed for nickel and copper along with few traces of other metals in the groundwater. Conversely, in industrial wastewater, metals were present in the order of Ni > Cu > Mn > Cr > Fe > Pb > Zn, all exceeding the permissible limits. Both the HPI and CDx were successfully utilized for determining the overall degree of groundwater contamination. The analyzed water samples of various locations in urban Aligarh revealed that 64.7% of sites have groundwater safe for human consumption, while remaining 35.3%, was found affected by heavy metal traces beyond permissible limits. Moreover, the CDx values provided closer insights into the area, indicating that 23.53% of locations have pure water, 17.6% have slight contamination, 11.7% have a moderate level of contamination, 11.7% are severely affected, with an overall 29.4% of sites being extensively polluted. Furthermore, groundwater and industrial effluent monitoring results were utilized to create a map using interpolation techniques with ArcGIS software. The maps display the spatial distribution of heavy metal concentrations in urban Aligarh regions. The findings of this study suggest that the government should consider implementing specific treatment technologies or regulations, such as the centralized Effluent Treatment Plant, along with some tertiary treatment measures to effectively reduce the presence of heavy metals below the drinking water specifications.

This work is not supported by any funding or grant.

Each author made a significant contribution to the planning, collection, and analysis of the study's data. All authors participated in the development of the initial and final versions of the manuscript.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.