Introduction

Heavy metals (HMs) are defined by having an elemental density (ED) exceeding 5 g cm3 and an atomic number (Z) surpassing 20, as stipulated by Aliand and Khan in 2018. These metals, acknowledged for their non-biodegradable, cytotoxic, mutagenic, or carcinogenic properties, pose significant environmental contamination risks1,2,3. The growth of manufacturing and agricultural industries has notably contributed to the contamination of water with metals, impacting both the environment and living organisms4,5. Previous researchers demonstrated that various sources emit heavy metals by contaminating both freshwater and saltwater, thereby affecting aquatic life6,7,8.

Different metals that infiltrate ground and surface water exhibit detrimental effects on aquatic life and human health. For instance, lead (Pb), widely utilized in paints, explosives, protective coatings, building materials, and wine due to its density, malleability, and erosion resistance, is particularly concerning9. The pollution of river networks with heavy metals stands out as a major contemporary environmental challenge globally, resulting from a combination of socioeconomic and industrial activities10,11. In the context of fluvial environments, this pollution can arise from geological weathering, atmospheric deposition, or the release of industrial, domestic, urban, or agricultural discharges12,13. In three-quarters of urban areas in Asia, Africa, and Latin America, industrial or urban wastewater irrigation is a common reality14. In today's modern world, environmental contamination is the biggest problem. Among other environmental pollutants, HMs are well-known and cause more worry because of their toxicity to aquatic and terrestrial life15. Human activities have released a significant number of HMs into the environment16,17,18,19. However, HMs, are persistent and harm the health of living things20,21. HMs from mining operations agriculture, and industries discharged into rivers are trapped by sediments that transit and bio-magnify HMs causing severe diseases in fish and human beings22,23,24,25,26. The heavy metal poisoning of many inland water environments has grown recently, according to Otchere25. Even though 70% of the Earth's surface is made up of water, freshwater resources are quickly running out26. Further reducing the availability of clean, fresh water sources is the rapid industrialization and lifestyle changes that have led to the contamination of these watery resources with a wide range of pollutants27.

Drinking water contaminated with metals can have long-lasting and short-term impacts, including lowered immunity, oxidative stress, gastrointestinal ulcers, and even cancer. Mercury (Hg), Copper (Cu), Zinc (Zn), Arsenic (As), Chromium (Cr), Nickel (Ni), Cobalt (Co), Cadmium (Cd), Lead (Pb), and others are toxic HMs that can be dangerous28. Natural and manmade activities, HMs accumulation in fish increase throughout the world, and its potential threat to health29,30. Infected drinking water causes over 0.84 million people to die from diarrhea each year, according to a WHO report from 2018. Pakistan, the world's sixth most populous nation, is likewise grappling with severe water31. While some of the HMs, such as Pb, Hg, and Cd, are biologically nonessential and highly poisonous to living things, low quantities of others are necessary for the growth and development of living things. Even necessary metals can become harmful if their concentration exceeds the allowable limit32,33,34. Similar to this, metals in sediments can come from a variety of sources, including air deposition, mining deposits, bedrock weathering and erosion, and industrial and agricultural effluents35,36. Contaminants that contain HMs constantly enter rivers from rapid urbanization, agricultural activities, and industrialization37.

Environmental pollution stands as the primary threat to public health in Pakistan, as highlighted by Shakir38. The water bodies within the country frequently exhibit the presence of heavy metals (HMs) such as mercury (Hg), iron (Fe), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), nickel (Ni), and arsenic (As). These metals have detrimental effects on aquatic life and become incorporated into the food chain, as indicated by Hussain39. While certain heavy metals like lead (Pb), cadmium (Cd), and mercury (Hg) lack known biological functions in fish, others such as iron, zinc, and copper play essential roles in fish metabolism40. The primary sources of metals and metalloids, whether natural or anthropogenic, consistently introduce these substances into aquatic bodies, posing significant threats to human and ecological health due to their toxic nature41. The release of heavy metals from sediments into water and their accumulation in fish depend on factors such as the solubility of the metals and processes like adsorption or precipitation42. The escalating population ratio contributes to the increasing levels of heavy metals, exacerbated by mismanagement of solid waste, agricultural practices, mining activities, and sanitation issues in the study area, negatively impacting the quality of the Panjkora River. The current study focuses on assessing the concentration of heavy metals in water and fish samples from the Panjkora River, aiming to determine the potential health risks associated with heavy metal ingestion through fish consumption in the study area.

Materials and methods

Description of study area

The study was carried out in River Panjkora, located in District Dir lower, which lies in the Hindukush range at 71°, 31°–72°, 14′ east and 34°, 37°–35°, 07′ north43. It is around 2700 feet above sea level. It is considered a major lifeline of the area, originates from Kohistan in the district of Upper Dir, and flows southward to Lower Dir.

The total population of 767,409, and most of the population is located on the bank of the river. Sewage, industrial, and agricultural wastewater are entering into rivers without treatment, these are the main sources of water pollution in the study area. Dir is split into the Upper Dir and Lower Dir districts (Fig. 1). The software ArcGIS (version 10.5) was used to draw the country, province, and detail study area discussed here. Dir's topography is dominated by mountains and hills that are a part of the Hindukush ranges. The mountain ranges run from north to south and from northeast to southwest along the northern borders with Chitral District. The Panjkora River enters the district from the northeast and flows southwest along the Bajour Agency's border until it joins the Swat River. Several streams in the Lower Dir and Dir River, the major stream of the Upper Dir, combine to form Panjkora River.

Figure 1
figure 1

Shows the sampling collection site in the study area (Dir Upper and Lower). The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Sampling techniques

The random sampling technique was used for the current study. The samples were taken from seven different locations in River Panjkora. Three samples were collected from the Upper Dir area (Wari, Sheringle, and Thal) and four samples were collected from the Dir Lower area (Khall, Timergara, Shagokas, and Bosaq) respectively. From each location, one fish and one water sample were collected for HM analysis. The rest of the samples were collected from the tributaries of river Punjkora. From each tributary one sample was collected and the following are the main tributaries of river Punjkora i.e. Ushiri Lamchar, Dhok Darra Khwar, Dir River, Shalgah Khwar, Jhakar Khwar, Kunai Khwar, Gumbir, Toor Camp respectively.

Water sampling and analysis

Water samples were gathered in a polythene bottle. The bottles were clean, well-washed, and airtight. The water samples were collected from at middle position and the depth of water samples was 1 foot below the surface water. A total of fifteen samples were collected along the tributaries of river Panjkora. The samples were collected between March 2021 and April 2022. All samples were gathered in a 1-L bottle and preserved with 5 ml NHO3. Samples were sent to the "Advance Hydro-Geochemistry Laboratory, Department of Environmental Sciences, Quaid-I-Azam University Islamabad" for atomic absorption spectrophotometry. The samples were kept at 4 °C in the aforementioned laboratory and were examined within three months44.

A 250 volumetric flask was filled with 100 ml of water to remove the turbidity, and 5 ml of NHO3 (55%) was added to increase the sample's acidity. The acidified samples in the fume hood evaporated to a volume of 20 ml on a heated plate. After that, the samples were removed from the hot plate and left to cool at room temperature. The cooled samples received an additional 5 ml of NHO3, which was then again evaporated to produce 20 ml. After chilling at room temperature, the samples are diluted to 100 ml with tape water. Atomic absorption spectrophotometry (Spectra AA 2000) was employed to detect heavy elements like Zn, Pb, As, Cd, Fe, and Mg in the samples. To create the standard curves, characteristic standard solutions for each HMs were made and aspirated into a flame atomic absorption spectrophotometer (Spectra AA 2000). The curve is used to read the concentration of a particular HMs. To measure the concentration of HMs, ppm units were used.

Fish sampling and analysis

The sample of fish was collected from the seven locations of the river Panjkora by a skilled fisherman and washed several times with distilled water. The sample was sealed in plastic bags with an ice box and transported to the laboratory for further analysis. In the laboratory, the fish sample was dissected with stainless scissors and forceps. The muscle of the fish was cut into small pieces and then dehydrated in the oven at 80 °C to obtain a constant weight. The dry sample converts into a fine powder with the help of mortar and pestle and is stored in desiccators until digestion. After this, 1 g of the sample was digested with 6 ml of 60% HNO3 and 3 ml of 35% H2O2 in a digestion flask for one hour. After that, the sample was cooled and filtered with Whatman filter paper 42. Finally, the filtrate obtained was diluted to 50 ml by adding deionized water in a volumetric flask and shifted for HMs analysis through an atomic absorption spectrophotometer. The analysis was performed in triplicate for quality assurance45.

Human health risk assessment of HMs via consumption of fish

Different methods have been used for the determination of the risk associated with the consumption of contaminated fish. Estimated daily intake is one of the most common methods to help identify the number of pollutants consumed daily. For determining health risk related to HM via the consumption of fish were determined by using the following indices46,47.

Estimated daily intake of HMs (EDI)

Daily intake of HMs via consumption of fish was determined by using the following equation:

$${\text{EDI}}=\frac{{\text{CM}}\times {\text{FIR}}}{{\text{WAB}}}$$
(1)

where EDI is the estimated daily intake of HMs, CM means the concentration of HMs in fish mg/kg wet weight, and FIR is the fish intake rate in the study area. It was considered 10 g/person/day because no information was available on daily fish intake and WAB representing the average body weight was taken 60 kg reported for fish from river Chenab, Pakistan48.

Health risk index (HRI)

Health risk due to the eating of contaminated fish with metal was determined by using HRI. The value of HRI less than 1 is said to be safe for the exposed population. Where HRI above 1 means that there is a chance of non-carcinogenic effect on the exposed population. To determine HRI, the following equation was used49.

$${\text{HRI}}=\frac{{\text{EDI}}}{\mathrm{ RFD }}$$
(2)

where RFD is the Oral Reference Dose of the metal (mg/kg/day) and EDI is the estimated daily intake of HMs via fish consumption. RFD is an approximation of the daily tolerable exposure to which a person is expected to have without any adverse health effects during a lifetime. Values of RfD for Fe (0.7 mg kg−1per day), Pb (0.03 mg/kg/day), Mn (0.14 mg/kg/day), Zn (0.30 mg/kg/day), Cd (0.001 mg/kg/day), and As (0.0003 mg/kg/day) were taken from Integrated Risk Information System50,51.

Target cancer risk (TCR)

The target cancer risk was calculated using the equation below. The carcinogenic risk of HMs is calculated using the target cancer52.

$$TCR=\frac{\mathrm{EF }\times {\text{ED}}\times {\text{FIR}}\times {\text{CM}}\times {\text{CPSo}}}{{\text{WAB}}\times {\text{ATc}}}$$
(3)

where TR is the target cancer risk, EF exposure frequency (365 days/year), ED exposure duration (70 years), FIR fish ingestion rate (10 g/person/day for this study CM concentration of HMs (mg/kg) WAB average body weight (60 kg) ATc is the averaging time, carcinogens (365 days/year for 70 years) used by USEPA53.While CPSo is the carcinogen potency slope factor which was determined by USEPA. While Mn, Fe, and Zn do not cause any carcinogenic effect, their CPSo has not yet been established by USEPA, so TR was only calculated for As, Cd, and Pb in order to determine carcinogenic risk. The CPSo values for Pb are 0.009, Cd 0.6, and for As 1.5. TR value is also equal to CPSo × EDI54.

Spatial distribution of HMs

Spatial distributions of heavy metal i.e., Fe, Pb, Mn, Zn, Cd, and As were shown with the help of IDW software. The highest and lowest values were shown with the help of the map. The color shows the concentration of different parameters in the study area55.

Statistical analysis

Different statistical methods are used, namely, variance and standard deviation. Data were analyzed by different software such as MS Word, Excel, Sigma Plot, and SPSS56,57. The ArcGIS (version 10.5) were used to draw country, province and study area detail maps.

Results

Assessment of HMs in water and fish

The concentration of heavy metal in water and fish in Thal Komrat valley are presented in Fig. 2. The concentration of Mn, 0.05 was detected in Thal Komrat valley (point A 1). Commonly, the concentration Pb was 1.21 detected in fish (point A 2).

Figure 2
figure 2

Concentrations of HMs in the water and fish of river Punjkora in Thal Komrat.

The concentration of HMs in water and fish samples of river Panjkora are presented in Fig. 3. The lowest values of HMs (Fe, Mn, and As) were found 0.01, 0.01, and 0.1 mg/L respectively in the water of Sharingal (point B 2). Similarly, at the location, Sheringal (point B 2), the concentrations of HMs (Pb, and Zn,) in fish samples were measured (2.04, 1.28, mg/L) respectively (point B 2).

Figure 3
figure 3

Concentrations of HMs in the water and fish of river Punjkora in Sharingal.

The concentration of HMs measured in the water of the river Punjkora at location Wari (point C) are presented in Fig. 4. The iron concentration was not detected at point C Wari. In the same way, the concentration of HMs (Fe, Pb, Mn, Zn, Cd, and As) was also measured in fish samples (0.43, 2.08, 0.29, 1.27, 0.13, 0.12 mg/kg) respectively at the location of Wari (point C).

Figure 4
figure 4

Concentrations of HMs in the water and fish of river Punjkora in Wari.

The concentration of HMs in water and fish samples of river Punjkora in Khall are presented as Fig. 5. The concentration of HMs was measured in the water of the river Punjkora. Similarly, the highest concentrations of Pb, were 1.89, mg/L in the fish at the location of Khall (point D).

Figure 5
figure 5

Concentration of HMs in the water of river Punjkora in Khall.

The number of HMs in water and fish samples of river Punjkora at location Timergara is shown in Fig. 6. The lowest concentration of Cd was 0.008 mg/L in Timergara (point E). The concentrations of Fe and Pb were not detected at point E Timergara. The value of Mn was 1.94 mg/L was detected in the location of Timergara (point E).

Figure 6
figure 6

Concentration of HMs in the water of river Punjkora in Timergara.

The concentration of HMs in the water and fish sample of river Punjkora in Shagokas (point F) is presented as Fig. 7. The concentrations for Fe and As were not detected at this point. Similarly, the concentrations of selected HMs were also measured in the fish samples of river Punjkora. The highest value of Pb were recorded in the fish at the location of Shagokas (point F).

Figure 7
figure 7

Concentrations of HMs in the water and fish of river Punjkora in Shagokas.

The number of HMs in the water and fish sample of river Panjkora in Bosaq (point G) is shown in Fig. 8. The concentrations of selected HMs were measured in the water of the river Punjkora. The concentrations of Fe, Pb, and As were not detected. Similarly, the concentrations of HMs, were also measured in fish of river Punjkora. The lowest value of As was recorded in the fish samples at the location of Bosaq (point G).

Figure 8
figure 8

Concentrations of HMs in the water and fish of river Punjkora in Bosaq.

Spatial distribution of HMs in tributaries and river Panjkora

The concentration Fe in the study area is presented in the Fig. 9. The concentrations of Fe were spatially distributed in the study area. The concentration of Fe in the tributaries of the river Panjkora river i.e., Dir River, Jhakar Khwar, Kunai Khwar, Gumbir, Toor Camp were shown with help of map While the concentration of Fe in Ushiri Lamchar, Dhok Darra Khwar, and Shalgah Khwar was not detected in water samples. Figure 10 shows the concentration of Pb in different tributaries of river Panjkora. The value of Pb was 0.05 mg/L and was detected in Dir River.

Figure 9
figure 9

Show the spatial distribution of Fe in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Figure 10
figure 10

Show the spatial distribution of Pb in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

In Fig. 11 the concentration Zn in the study area is presented. In the tributaries of river Panjkora the lowest vale of Zn was 0.01 detected in Gumbir. In Fig. 12 Mn concentration in water tributaries were spatially distributed in Upper and Lower Dir. The concentration of Mn in Shalgah Khwar was not detected in the study area.

Figure 11
figure 11

Show the spatial distribution of Zn in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Figure 12
figure 12

Show The spatial distribution of Mn in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Figure 13 shows spatial distribution of heavy metal cadmium in different tributaries of river Panjkora. The concentration of Cd was distributed spatially. Figure 14 show spatial distribution of As concentration in the study area. Respectively, the concentration of As in Dir River, Shalgah Khwar, Jhakar Khwar, were not detected in these tributaries of river Punjkora.

Figure 13
figure 13

Show the spatial distribution of Cd in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Figure 14
figure 14

Shows the spatial distribution of As in the study area. The software ArcGIS (version 10.5; https://malagis.com/arcgis-enterprise-105-download.html) was used to draw the map of the country, province, and detail study area.

Health risk assessment

Risks to human health via consumption of HMs contaminated fish were determined by using health risk indices EDI and HRI by using Eqs. 1, 2, and 3, respectively and their results are given in Tables 1, 2, and 3.

Table 1 EDI of HM via consumption of contaminated fish.
Table 2 HRI of HM and their mean via consumption of fish.
Table 3 Target cancer risk (TCR) of HM in the study area.

The results of the estimated daily intake of HMs via contaminated fish are given in Table 1. The maximum daily intake of Fe, Pb, Mn, Zn, Cd, As were occurring at 0.08, 0.451, 0.105, 0.32, 0.04, 0.03 mg/kg/day in points E, E, D, and G, D, G, D while the minimum daily intake occurs of 0.03, 0.20, 0.048, 0.15, 0.02 and 0.008 in point C, G, B, G, C, C. So, it was clear from the result that the maximum daily intake of HMs occurred for Pb and Zn. Similarly, the daily intake of HMs in all sample points of the river Panjkora follows the order of Pb > Zn > Mn > Fe > Cd > As. The EDI values for Pb, Cd, and As were found higher than their corresponding reference doses. While the rest HMs have lower EDI than the reference dose, so they do not pose non-carcinogenic health risks in the short term.

The health risk index (HRI) for individual HMs calculated from Eq. 2 and presented in the Table 2. The results showed that the mean HRI for Fe, Pb, Mn, Zn, Cd, and As were found 0.079 mg/kg/day, 10.56 mg/kg/day, 0.541 mg/kg/day, 0.782 mg/kg/day, 26.85 mg/kg/day and 62.91 mg/kg/day. HRI values for Fe ranged from (0.121–0.042) Pb (15–8.33) Mn (0.75–0.342) Zn (1.06–0.5) Cd (31–40) As (100.0–27.66). The highest mean HRI in all sample locations was recorded for As, Cd, and Pb. Overall, the HRI value of HMs decreased in the order of As > Cd > Pb > Zn > Mn > Fe. While the rest of the heavy metals Fe, Zn, and Mn have HRI < 1 while in point D, Zn has HRI greater than 1 so the exposed population is safe. The high HRI values of these metals are due to the high daily intake of HMs in the given area.

The results for TCR calculated from Eq. 3 are shown in Table 3. The target cancer risk was calculated only for As, Cd, and Pb because the CPSo value was only calculated for these metals while the other metals Fe, Zn, and Mn have no CPSo value so the TCR value was not calculated for the TCR value for Pb as found 0.002862 or 2.8 × \({10 }^{-3}\), for Cd its value was 0.016 or 1.6 \(\times {10}^{-2}\) and for As the TCR was calculated 0.028 or 2.8 \(\times {10}^{-2}\). The highest value was calculated for As 0.028 or 2.8 \(\times {10}^{-2}\), while the lowest found for Pb was 0.002862 or 3.8 × \({10}^{-3}.\)

Discussion

Throughout the world, pollution of water with HMs is the main problem58. HMs is the most toxic source of water pollution in the river Punjkora. Most of the heavy metals in the water were above the permissible limits of that prescribed by WHO and Pak-EPA. The results show that the concentration of HMs in water such as Fe and As were detected less as compared to Pb, Mn, Zn, and Cd. The concentration of Fe was 0.01 mg/L in Sheringal Khall and Thall while in Wari, Bosaq, Shagokas and Timergara the concentration of Fe was not detected. The value of Fe was high in the tributaries of the river was 0.02 mg/L in Dir River and Gumber. The average concentration of Fe in upstream and downstream were 0.56 and 0.96 mg/L in the water of Tembi River59. The concentration of As was not detected in Bosaq and Shagokas and the concentration of As was 0.04 and 0.03 mg/L in Kunai Khwar and Gumbir tributaries. In Bangladesh Korotoa River, the concentration of As was 46 mg/L60.

Our study shows that the concentration of Pb were 0.06, 0.06, 0.05, 0.04, and 0.03 mg/L in Sheringal, Shagokas, Usheri Lamchar, Dir River, and Thall. In river Ganga, Lead is very toxic, and its concentration was higher in water (37–163 μg/L61. The values of Mn were 0.09, 0.08, 0.06, and 0.06 mg/L in Dir River, Ushiri Lamchar, Dhok Darra Khwar, Timergara. In river Ekiti the concentration of Mn were 0.12–0.3062. The concentration of Zn were 0.06, 0.06, 0.05, 0.05 were recorded in Ushiri Lamchar, Dir river, Dhok Darra Khwar, and Thall respectively, the lowest concentration was 0.01 mg/L in Gumbir. The concentration of Zn was 0.526 mg/L in water at at river Nile63. The concentration of Cd was 0.023 mg/L in Dir River, ushiri Lamchar, while the lowest vale was 0.001 mg/L in Dhok Darra Khwar, Jhakar Khwar, Kunai Khwar. In in Niger River water River the concentration of Cd was 50 mg/L in Nigeria’s64. The highest value of As was recorded in Gambir, while the concentrations in Shalgah Khwar, Jhakar Khwar, Shagokas, and Bosaq were not detected. The concentration of HMs was high in the tributaries and put pressure on river Panjkora.

The species of fish, i.e., Crossocheilusdiplocheilus, was selected due to the high consumption ratio within the study area. The concentrations of Fe, Pb, Mn, Zn, Cd, and As were also measured in fish because bioconcentration of HMs is taking place. The results show that the concentration of HMs was also measured in fish from the selected point of Panjkora river. The concentration of Fe was 0.51 and 0.44 mg/L in Shagokas and Bosaq. The lowest concentration of Fe was 0.18 mg/L in Khall. The ranged of Fe from 1.45–4.56 and 0.12–0.42 µg/g in fish (Districhodus rostratus) and (Heterotis niloticus) from river Benue in Nigeria65.

In Shagokas the highest value of Pb was 2.71 mg/L in Timergara. in the lowest value of Pb was 1.21 mg/L were detected in the Thall region. In different rivers, Pb concentrations were detected in the muscles of fish. The range of Pb was 0.337–0.810 mg/L in River Kabul66. Commonly, the highest value of Mn was 0.63 mg/L in Thall and Timergara. the lowest value of 0.29 mg/L was detected in Wari region. The concentration of Mn 34.98 ± 1.01, 22.42 ± 0.70, 29.09 ± 0.91, 125.81 ± 2.57, 27.89 ± 1.69 mg/kg ww Puntius ticto, Puntius sophore, Puntius chola, Labeo rohita, Glossogobius giuris from Buriganga river, Bangladesh67.

Respectively, the highest value of Zn 1.94 mg/L was detected in Timergara while the lowest value was 0.95 mg/L in Thall. The highest value of Cd was 0.24 mg/L in Thall region while the lowest value was 0.12 mg/L in Khall. The highest average values of Cd in fish (Schizothorax plagiostomus) were 1.4 ± 0.39 and 1.4 ± 0.44 µg g−1 in Swat Barandu River68The concentration of As was 0.18 mg/L was detected in Timergara while the lowest value was 0.05 mg/L in Khall. The value of As were 0.0091, 0.0025, 0.018, 0.0043, 0.0098 mg/Kg in Tor macrolepis, Glyptothorax stocki, Cyprinus carpio, Cirrhinus mrigala, Schizothorax plagiostomus in Swat river69.

The main source of HMs in the study area was anthropogenic activities such as mining, agricultural activities, municipal waste, domestic effluents, and industries. On another hand, there is no proper method used for the disposal of solid waste and all waste which was generated in the study area, enters into water bodies directly or indirectly. Rapid industrialization, urbanization, and agricultural activities are also the main sources of HMs. Due to continuous discharge, it pollutes the river with HMs70. On the other hand, rainwater is considered the main source of HMs because the study area is a sloping region. Rainwater is directly entering the river. Surface water is the main source of heavy metals that accumulate in fish71. The study area is the mountainous region, and the mountainous region has a rich source of metals and minerals. The mountain of Gwaldai area has 80% Pb, Bajaur Agency Has 35% Mn and Ushiri Valley has 16% Cu and mining activities are under processing which is the main cause of HMs. In the Swat region, surface water heavy metals such as Cd, Cr, Ni, and Pb demonstrated increasing pollution from upstream to downstream. This thread may be linked to the existence of fmafic and ultramafic rock formations, ongoing mining activities, as well as agricultural and industrial development downstream in the region of Sawat72.

The river Punjkora is considered the final disposal point of this waste. The waste (sewage and indusutrial wastewater) which was generated in Sharingal, Wari, Khall, and Timergara was disposed of on the bank of the river Punjkora. In Pakistan, agricultural runoff, and industrial and municipal waste have no proper way of disposal. Due to improper disposal HMs concentrations, i.e., Cu, Hg, Ni, Cd, As, Fe, Pb, and Zn were increasing day by day, which produced a bad impact on aquatic life and finally it will enter into the food chain. Commonly, this increases the level of HMs in water. Naturally, HMs entered into water bodies through rock due to their differences in chemical combinations. Besides these sources, the main sources of HMs in water were also in natural40.

Risk assessment

Risk assessment for HMs via consumption of fish was determined by using parameters viz, EDI, HRI, and TCR. These risk assessment criteria were developed in the US by the EPA to determine the potential health risks posed by any chemical contaminants when exposed for an extended period of time73. The result of HRI from river Panjkora is shown in (Tables 1 and 2). In the study, a high daily intake of HMs was recorded for As, Cd, and Pb, which was found above their corresponding reference dose set by USEPA. Among these, more intakes occurred for Pb. While EDI for Fe, Zn, and Mn was found below their corresponding reference dose. A study conducted the daily intake of Pb (4.9 mg/kg bw/day) and Cd (0.30 mg/kg bw/day) in river Panjkora similarly they recorded the estimated daily intake (mg/kg bw/day) of Pb and Cd in river Swat and river Barandu as: 3.8, 0.23; 2.5, 0.23 respectively which was also found higher than the present study29. The estimated daily intake of Pb and As was recorded as 1.20 and 0.45 mg/kg/bw/day for fish in Cempaka Lake, Malaysia74,75. This value of Pb and As was also higher than in the present study.

In the present study, HRI values were found greater than 1 for As, Pb, and Cd. while for Mn, Fe, and Zn HRI was found less than 1 except Zn which has HRI > 1 in point D. HRI less than 1 means the exposed population has no noticeable adverse health effects, whereas HRI greater than 1 means that there is a risk of non-carcinogenic effects, with an increasing probability as the value increases76,77. The high HRI values result from the high EDI of the metals involved. The HRI value for Pb, As, and Cd in all sampling points is greater than 1, indicating a high risk of adverse health effects, especially for children and pregnant women from the consumption of fish products from this river.

Ekere, also, equally recorded HQ > 1 for some of the metals considered in this study in the rivers studied78. Studies conducted by Islam also revealed that HI values greater than 1 should produce public health distress for consumers of fishery yield79,80. From the results of the present study, HRI values were > 1 indicating potential health risks from consuming fish in river Panjkora The finding of this study is a source of distress due to potential health risk consequences from the intake of HMs via consumption of fish from river Panjkora.

The TCR calculated in this study showed that all metals were above the guideline value set by USEPA, which implies that fish consumption from river Panjkora is risky and may have the probability of cancer. The TR was categorized as TR ≤ 10−6 = Low; 10−4 to 10−3 = moderate; 10−3 to 10−1 = high and TR ≥ 10−1 = very high78. In this study, the TR value of Cd and As is high (\({10}^{-2}\)) while TR of Pb is moderate (\({10}^{-3}\)) which shows high cancer risk to the exposed population.

Conclusions

In the study area, there is no proper sanitary system for the disposal of wastewater. On the other hand, all solid wastes which were generated in the study area were thronged to river water and its tributaries directly or indirectly. This waste produces an extra burden on the quality of water and increases the concentration of HMs in water. So, the present was conducted on HMs in water and fish in river Punjkora. Commonly, all of the HM’s concentrations were higher than normal, especially Pb concentrations were high so many times from normal because different anthropogenic activities were the main cause such as mining, industries, and car washing. Besides this, the concentrations of HMs in fish were high so many times in the study area. HRI assessment was carried out by using the health risk indices EDI, HRI, and TCR. Their results showed that fish intake from river Panjkora are not safe because the HRI value was found greater than 1. Similarly, carcinogenic health risk also showed a high risk of cancer. So, it was concluded from this study that fish products from river Panjkora is not safe for human consumption. Therefore, efforts should be made by the government to ensure the treatment of waste effluents from different sources before discharge into river Panjkora.