Assessment of seasonal fluctuation in heavy metal contamination in sediments and surface water of Narmada River, India

In recent years, the escalating presence of heavy metal contamination in aquatic ecosystems has raised significant concerns due to its toxicity, pervasiveness, and accumulation. This issue has garnered substantial attention and awareness, underscoring the growing need for immediate action. The main source of heavy metal contamination in river sediments and surface water is either anthropogenic or natural sources. Anthropogenic sources of heavy metal are untreated domestic wastewater, agricultural fertilizer and pesticides, and industrial discharges. Meanwhile, natural sources of heavy metal result from rock-weathering and soil. River pollution arises from various sources, including the discharge of sediments and suspended solids, such as soil from cultivated fields, construction and logging areas, urban environments, and eroded riverbanks during intense rainfall. The shifting of river channels, urbanization-induced encroachment of river banks, and other natural factors can alter the topographical features of a basin, thereby potentially impacting the quality of both river sediments and water (Singhal et al. 2024).

In their natural state, rivers and other aquatic systems experience eutrophication, a natural aging process that progressively introduces sediments and organic material into these water bodies (Karbassi et al. 2008; Varol & Şen 2012; Bhuyan et al. 2019). The introduction of these sediments into water bodies impairs fish respiration, diminishes plant productivity and water depth, and leads to the suffocation of aquatic organisms and their habitats (Xu et al. 2021; Ma et al. 2023; Wang et al. 2023). Additionally, contamination in the form of organic substances infiltrates waterways through various means, such as sewage, foliage, mowed grass, and runoff originating from livestock feedlots and pastures.

To comprehensively assess the contaminant load of a river, it is imperative to simultaneously investigate sediments and surface water. The aqueous phase and river sediments get a distribution of metal that is released into a river system throughout its conveyance by point or non-point sources (Zhuang et al. 2018).

Because of the combined effects of adsorption, hydrolysis, co-precipitation, and the presence of fine particles, only a limited fraction of unbound metal ions stay in water and large quantities of them are deposited in the sediment (Sakan et al. 2009). When harmful and persistent chemical pollutants with slow decomposition rates are discharged into the river water, sediments act as a top pollutant key store for such contaminants. Flow regulation influences natural flow patterns in river basins, impacting the flood pulse phenomenon. This pulse, rich in water, sediments, and nutrients, nourishes agricultural land, inland fisheries, as well as instream and wetland ecosystems, serving as a vital element for life and crucial ecosystems within the Lower River basin (Gao et al. 2022). Based on the limnological conditions, the sediment can function as both a supplier and a receiver of metals. River sediments serve as habitats for diverse aquatic animals and plants, playing a crucial ecological role in the aquatic environment while also serving as reservoirs for pollutants. This can lead to the accumulation of metal residues, potentially posing health risks if these contaminants enter the human food chain (Zhuang & Lu 2020; Wang et al. 2023). In aquatic systems, sediments serve the dual role of potential secondary sources and transporters of pollutants. The retention of metals in river sediments has the capacity to be a perpetual future pollutant. Sediments play an important role in the chemical characteristics of rivers. Rivers are the major means of transport of water and sediments from continents to oceans (Chen et al. 2016). To evaluate the appropriateness of the river for particular uses, it is crucial to examine the chemical properties and concentrations of metals in the sediment. Analysing the chemical composition of sediments in a river system aids in gauging anthropogenic pollution and understanding its potential environmental ramifications (Guan et al. 2018; Ma et al. 2023). Agriculture is one of the main sources of livelihood in India with lands located on the banks of rivers. During the rainy season, agricultural water with soil came into the river, and the concentration of heavy metals (As, Cu, Fe, Ni, and Zn) in river sediments increased (Brito et al. 2020; Zhuang & Lu 2020). The river system exhibits a distinct feature regarding the fluctuation of flow, sediment loading, and morphological processes across seasons. Additionally, significant floods and tectonic events within the river system have contributed to creating a complex morpho-dynamic environment (Sarker et al. 2023). In natural ecosystems, metals are typically present in low concentrations, usually ranging from nanogram to microgram per litre. However, there is a growing concern about high concentration levels of heavy metals in recent times, posing a threat of environmental pollution due to their toxicity and accumulation in aquatic habitats.

Studies have highlighted the adverse effects of heavy metal accumulation in plants and animals, including humans, elucidating the impact through the food chain. Unlike many pollutants, heavy metals are non-biodegradable and undergo a global ecological cycle, with natural waters serving as the primary pathways ( Zhuang et al. 2018; Zhuang & Lu 2020; Wang et al. 2023). Heavy metals have been categorized based on their source of origin into three primary groups: anthropogenic metals (As, Co, Cr, Cu, Ni, Pb, and Zn), crustal metals (Fe and Mn), and marine-related metals (Na, Ca, and Mg) (Wijesiri et al. 2019).

Seasonal variation is a primary factor in evaluating the concentration of heavy metals in river sediments and surface water. Seasons are categorized based on the level of rainfall intensity: (a) monsoon season (heavy rainfall), (b) pre-monsoon season (light to moderate rainfall), (c) post-monsoon season (light rainfall), and (d) winter season (little to no rainfall) (Awasthi et al. 2024).

Sediment and surface water contamination assessment studies have been utilized globally during the past few decades (Olivares-Rieumont et al. 2005; Sekabira et al. 2010; Salah et al. 2012; Sin et al. n.d.; Varol & Şen 2012; Islam et al. 2015; Xu et al. 2017; Xie et al. 2020; Xu et al. 2021); however, few studies have been reported on heavy metal contamination with seasonal variation in the sediments and surface water of rivers (Lim et al. 2013; Qiao et al. 2013; Singh & Pandey 2014; Zohreh Mirsalari 2014; Bhuyan & Bakar 2017; Hussein et al. 2020). Hence, it is imperative to conduct comprehensive research on sediment and surface water quality to assess the potential threat posed by heavy metal contamination and the associated carcinogenic risks (Chen et al. 2016; Patel et al. 2018; Da Silva et al. 2019; Ahamad et al. 2020; Xie et al. 2020; Xu et al. 2021).

The Narmada River is vital to Central India but faces threats from harsh climate and human activity, endangering flora, fauna, and water quality and river sediments. The Narmada basin, a crucial water resource region, supports millions of livelihoods and diverse ecosystems (Tiwari et al. 2024). Climate changes directly affect river sediments and water quality, increasing the risk to the ecosystem. Rising temperatures and extreme weather worsen pollution levels (Rehana & Dhanya 2018). Temperature fluctuations and their resulting impacts from climate change pose significant threats to human survival, ecological communities, and socioeconomic progress worldwide. In recent decades, there has been a pronounced global temperature rise, disrupting the delicate balance of nature and precipitating extreme shifts in weather patterns (Shawky et al. 2023). Predictions indicate rising water temperatures and extreme weather events exacerbating pollution. With estimates suggesting a potential 1.4 °C increase by 2040, tropical countries could see significant impacts on surface water and sediment quality (Hernández et al. 2022).

Cluster analysis (CA) has gained widespread recognition as a valuable tool for identifying, classifying, and understanding the relationships among sampling stations.

Therefore, the objectives of this study are:

• To determine the concentration of heavy metals in the sediments and surface water by utilizing ICP-MS in four different seasons.

• To assess the heavy metal in sediments by utilizing CF, PLI, GF, and EF indices.

• To find out the source of contamination in the study stretch of the Narmada River.

• To assess the environmental risks of these heavy metals and compare the other rivers.

The Narmada River ranks as the fifth-longest river in the Indian subcontinent and it is called the lifeline of Madhya Pradesh. Over time, numerous small towns and large cities have flourished along their banks. Unfortunately, due to various human activities, such as the discharge of domestic and dairy industrial waste and natural drainage, the river's water quality has deteriorated significantly. Therefore, it is essential to analyse the quality of sediment and surface water of the Narmada River.

The first sampling station, Jamtaraghat (S-1), is near the Pariyat tributary and several dairy industries. The second, third, and fourth stations – Gwarighat (S-2), Tilwaraghat (S-3), and Bhedaghat (S-4) – are located near urban areas. The fifth and sixth stations, Ghugharaghat (S-5) and Parmatghat (S-6), are situated close to agricultural and rural regions. The distances between the first four stations are each 5 km, with the distance from the fourth to the fifth being 10 km, and from the fifth to the sixth being 15 km. Thus, a total stretch of 40 km has been selected for this study.

Samples of sediments and surface water were gathered from sampling sites over four distinct phases: firstly, May 2021 (pre-monsoon or summer climate); secondly, July 2021 (monsoon or rainy climate); thirdly, September 2021 (post-monsoon); and fourthly, January 2022 (Winter) during the year 2021–2022. The samples of water were collected in an acid-washed one-lit polyethylene bottle. Samples of sediments were collected from four composite samples, each weighing approximately 200 g. After sampling, samples of sediments were immediately enclosed within uncontaminated polyethylene bags and transported to the laboratory where both samples were stored at a temperature of 4 °C. In preparation for the analysis of sediment samples, the samples underwent an air-drying process. Subsequently, plant fragments and stones were eliminated by sieving the dried sample through a 2 mm mesh. The analytical procedure was followed to EPA protocol 3050B, involving acid digestion for sediments, sludges, and soils (Environmental Protection Agency n.d.). This method utilizes a combination of hydrogen peroxide and nitric acid for complete metal digestion. The next step involved utilizing ICP-MS to ascertain the concentration of metals within the sediments and surface water samples.

Previous analyses of heavy metals in the Narmada river's sediments were conducted in 2008 (Jain et al. 2008) and 2010 (Sharma & Subramanian 2010), while the quality of heavy metals in surface water was assessed in 2021 (Mishra & Kumar 2021). To maintain the continuity of these analyses, it is urgently required to examine both the sediment and surface water quality of the Narmada River.

In the explication of geochemical data, the selection of background value is crucial. Many authors have utilized the average shale value as a reference background value (Müller et al. 1997; Sekabira et al. 2010; Islam et al. 2015). However, due to the absence of data regarding background values for the Narmada River sediment and the enclosed area under investigation, this study adopts a meticulous approach and computes background values by averaging the metal concentrations in uncontaminated sediments within the study region (Sakan et al. 2009; Varol 2011; Varol & Şen 2012).

The I_PLI value represents the level of metal sediment pollution. When I_PLI > 1 indicates pollution exists; otherwise, if I_PLI < 1, there is no metal pollution (Islam et al. 2015; Bhuyan et al. 2019; Wang et al. 2023).

Fe serves as the reference element for geochemical normalization, the interpretation of I_EF values is as follows: I_EF < 1 implies no enrichment; <3 indicates minor enrichment; 3–5 suggests moderate enrichment; 5–10 implies moderately severe enrichment; 10–25 signifies severe enrichment (Sakan et al. 2009; Varol 2011; Wang et al. 2023).

The findings on the seasonal fluctuation of heavy metal concentrations in sediment across different stations are presented in Table 1. As concentrations ranged between 0.02 and 0.07 mg/kg, stations second, third, fourth, and sixth exhibited the highest concentration during the monsoon season, and station fifth had the lowest concentration during the pre-monsoon season. Co concentrations spanned from 0.55 to 1.39 mg/kg, peaking at station third in the post-monsoon and being lowest at station six during the monsoon. Cr concentrations ranged between 1.33 and 3.33 mg/kg, with station third registering the highest concentration during the post-monsoon season and station six recording the lowest concentration during the monsoon season. Cu concentrations spanned from 0.84 to 2.97 mg/kg, with the third station having the highest during the monsoon and station six displaying the lowest during the pre-monsoon. Fe concentrations varied between 309.68 and 1,133.82 mg/kg, with station first exhibiting the highest concentration in the monsoon season and station six having the lowest concentration in the pre-monsoon season. Mn concentrations ranged between 12.03 and 23.97 mg/kg, with station third registering the highest concentration during the pre-monsoon season and station six recording the lowest concentration during the monsoon season. Ni concentrations spanned from 0.32 to 0.95 mg/kg, with station third displaying the highest concentration during the monsoon and station fifth recording the lowest during the pre-monsoon. Pb concentration spanned from 0.08 to 0.20 mg/kg, with the third station exhibiting the greatest concentration during the pre-monsoon season, while station fifth had the lowest concentration during the monsoon season. Zn concentrations varied between 0.69 and 2.09 mg/kg, with station third exhibiting the highest concentration during the monsoon and stations first and fifth recording the lowest concentration during the pre-monsoon season.

The findings concerning the seasonal fluctuation of metal concentrations in surface water across different stations is shown in Table 2. Co concentrations ranged from 0.02 to 0.04 μg/l, with the highest levels observed at station third during the post-monsoon period and the lowest at stations first, second, fourth, fifth, and sixth. Fe concentrations varied between 0.01 to 0.03 mg/l, with station first exhibiting the highest concentration in the monsoon season and stations second, third, fourth, fifth, and sixth having the lowest concentration. Ni concentrations spanned from 0.05 to 0.11 μg/l, with station fourth displaying the highest concentration during the post-monsoon and station sixth recording the lowest during the pre-monsoon. Zn concentrations varied between 0.27 and 0.49 μg/l with station third exhibiting the highest concentration during the post-monsoon and station sixth recording the lowest during pre-monsoon.

The concentration of As, Cr, Cu, and Pb was falling below the detection limit, and the concentration of Fe was also falling below the detection limit (indicated by symbol –) during the pre-monsoon season at stations fourth, fifth, and sixth and during the winter season at stations fifth and sixth.

The value of average concentration was calculated by averaging the values for all four seasons. Based on the average concentration results, the order of metal concentration was as follows: Fe > Mn > Cr > Cu > Zn > Co > Ni > Pb > As. The concentration of Fe was exhibited higher at the station first because of the involvement of natural crustal activities. In contrast, at station third, the concentrations of As, Co, Cr, Cu, Mn, Ni, Pb, and Zn had increased significantly due to human-induced activities. Concerning the seasonal variations in sediment composition, heavy metal distribution in sediments exhibited distinct patterns. For metals As, Cu, Fe, Ni, and Zn, their concentrations follow the sequence monsoon > post-monsoon > winter > pre-monsoon. In contrast, Co and Cr displayed a distribution pattern of post-monsoon > winter > pre-monsoon > monsoon, while Mn and Pb exhibited a distribution pattern of pre-monsoon > winter > post-monsoon > monsoon. During the monsoon season, the interaction between agricultural runoff water and river water led to an increase in the concentrations of As, Cu, Fe, Ni, and Zn in sediments, due to their presence in fertilizers and pesticides and crustal metal activities. During the post-monsoon season, higher human activities contributed to elevated concentrations of Co and Cr. The pre-monsoon period witnessed increased concentrations of Mn and Pb due to higher evaporation rates during summer. Four metals (As, Co, Cr, and Ni) out of nine metals have the potential risk of carcinogenicity but the concentration of these four metals is below the prescribed limit. So they did not pose a carcinogenic risk.

The average concentration results reveal that station first exhibited higher concentrations of Fe. Station third exhibited an elevated concentration of Co and Zn, while station four recorded the highest concentration of Ni. Based on the metal concentration findings, the hierarchy of concentration was as follows: Zn > Ni > Co > Fe. Concerning the seasonal fluctuations in surface water quality, the distribution of heavy metals exhibited distinct patterns. Co, Ni, and Zn displayed the following order of prevalence: post-monsoon > winter > monsoon > pre-monsoon. Conversely, Fe exhibited a distribution pattern of monsoon > post-monsoon > winter > pre-monsoon.

The significance of this study is crucial for both environmental protection and climate change. The river system displays a unique characteristic concerning heavy metal contamination, influenced by seasonal variations and human activities. Understanding seasonal variations aids in developing effective pollution management strategies and emphasizes the need to address contamination within broader climate change initiatives. Applied climatology explores how climate interacts with various phenomena, its impact on humans, and the potential for climate manipulation to meet human needs (Sarker 2022).

The I_CF exhibited an average value of 1.38, with a range between 1.50 and 2.17. The lowest I_CF value was observed at station sixth for metal Fe and the highest I_CF value was recorded at station third for metal Cu. The findings of the I_CF indicate that there was low contamination to moderate contamination. The average I_PLI value was 1.37, indicating a spectrum ranging from no metal pollution to the presence of pollution. The average I_gai value was −0.15, ranging from −0.81 to 0.53. The lowest I_gai value for Fe was recorded at the sixth station, whereas the highest was detected at the third station for Cu. Urban activities had minimal impact on contamination levels at both the sixth and fifth stations, resulting in the lowest I_gai values observed there. These results indicate a spectrum ranging from uncontaminated to moderately contaminated metal levels. The average value of I_EF was 1.12, ranging from 0.70 to 1.51. The lowest I_EF value was detected at station first for metal Zn, and the highest was recorded at station third for metal Cu. The I_EF results indicate a range from no enrichment to minor enrichment.

A comparison of the heavy metal concentration in sediments and surface water to other selected rivers is shown in Table 3. The concentration of heavy metals in the Narmada River sediment to other selected rivers was low and below the permissible limits as per the World Average Shale value. The maximum concentration of Co, Fe, Ni, and Zn in surface water was low to comparisons to other selected rivers and below permissible limits as recommended by WHO. The concentration of As, Cr, Cu, Mn, and Pb in surface water was below the detection limit. In a previous study of heavy metals in the sediments of the Narmada River (Jain et al. 2008; Sharma & Subramanian 2010), the levels of Cr, Cu, Fe, Mn, Ni, Pb, and Zn were higher compared to the present study and this difference is attributed to the previous study covering a larger stretch of the river, which included more urban areas. In the present study, Jabalpur is the fourth city from the origin of the Narmada River, with Anoopur, Dindori, and Mandala being the first, second, and third cities, respectively. There was not a significant disparity in the concentration of heavy metals in surface water between the present and previous studies (Mishra & Kumar 2021).

The main aim of this investigation was to assess the concentrations of heavy metals (As, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) within the sedimentary deposits and surface water of the Narmada River. The observed trends in metal distribution throughout the different seasons exhibited distinguishable patterns. Regarding seasonal variations in sediments, the distribution of the heavy metals followed the order of monsoon > post-monsoon > winter > pre-monsoon for As, Cu, Fe, Ni, and Zn. Conversely, Co and Cr showed a distribution pattern of post-monsoon > winter > pre-monsoon > monsoon, and Mn and Pb showed a distribution pattern of pre-monsoon > winter > post-monsoon > monsoon. Regarding seasonal variations in surface water, the distribution of the heavy metals followed the order of post-monsoon > winter > monsoon > pre-monsoon for Co, Ni, and Zn. Fe showed a distribution pattern of monsoon > post-monsoon > winter > pre-monsoon.

The concentration of all these heavy metals in sediments and water were within the permissible limit, after assessment of heavy metals (As, Co, Cr, and Ni) revealed that there was no carcinogenic risk and there is no adverse effect on climate changes. The results of sediment pollution indices indicated that the sediment quality varied from unpolluted to minimally polluted. The sources of contamination were identified as being associated with human activities, natural crustal processes, and agricultural activities-derived metal inputs. This research represents the comprehensive study of heavy metal contamination in sediments and surface water of the Narmada River.

The advantages of this study are:

• Assessing contamination levels and identifying peak contamination periods.

• Gaining insights into the influence of natural and human factors on contamination levels.

• Promoting community awareness and education.

• Highlighting potential health risks associated with contamination levels.

The limitations of this study are:

• The possibility that this stretch may not fully represent the variability of the entire river system.

• Assessment challenges arise due to the limited historical data available for the Narmada River.

• Omission of flora and fauna from the study.

• Absence of contamination modelling in the analysis.

The author is grateful for the support given by the Principal, Jabalpur Engineering College, Jabalpur, M.P., for the support given for conducting the study.

Conceptualization, acquisition of data, preparation of graphs and tables by the first author (D.C.R.), analysis and interpretation of data by the second author (R.C.), drafting and analysis by the third author (A.V.), and final approval of manuscript by all authors.

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.