Bagarius bagarius, and Eichhornia crassipes are suitable bioindicators of heavy metal pollution, toxicity, and risk assessment

Analytical method validation

The results of the precision study with relative standard deviation (RSD), and accuracy are shown in Table 1. Through the precision study we found the value of RSD as less than 5%. Moreover, accuracy was done with percent recovery experiments. The results showed that the percentage recoveries for spiked samples were in the range of 95.7–103.7%.

Physicochemical properties and water quality index

The investigations of the water quality properties of the Narora channel are shown in Table 2. The temperature, TDS, turbidity, and alkalinity were within the standards of the country¹⁸ and WHO¹⁹ (taken from UNEPGEMS). While pH and dissolved oxygen (D.O) were above the recommended standards indicating poor water quality. Moreover, the detected heavy metals were in the following order Ni > Fe > Cd > Zn > Cr > Cu > Mn. Among these heavy metals Mn, Cu, and Zn were within the recommended limits whereas Cr, Fe, Ni, and Cd were crossing the limits¹⁸ contributing to the poor quality. Furthermore, the WQI calculation will give more insights into the overall quality of water as it explains the combined effect of several physicochemical properties¹². Its calculation is done simply by converting numerous variables of water quality into a single number^12,20. In addition to this, WQI simplifies all the data and helps in clarifying water quality issues by combining the complex data and producing a score that shows the status of water quality^2,12,21. The WQI classifies water quality status into five groups such as if WQI < 50 indicates excellent quality; WQI = 50–100 designates good quality; WQI = 100–200, shows poor quality; WQI = 200–300 reflects inferior quality; and if WQI is above 300 then it is unfit for drinking¹². In the current study, the WQI was calculated to be 4124.83, which did not fall in the set WQI groups. The WQI results show that Narora channel water in the investigated rural area is unsuitable for drinking as well as other domestic purposes. This too high WQI value at Narora channel water could be correlated to Ni and Cd which proves to be the main culprits due to their high qi values of 885.04 and 3196.26, respectively which leads to high SI and consequently high WQI. The high Ni and Cd content may be due to the effluents of several types of sources like sugarcane and iron factories, cement dust, mechanical workshops, and agricultural activities, etc. near the bank which drain their partial or untreated effluents into the channel. The wastes from domestic sources further contribute to pollution. In the upper Ganga region from Brijghat to Narora very poor water quality was reported by Prasad et al.⁷ Tabrez et al.² also found very high WQI in Kshipra River at Dewas segment, Madhya Pradesh, India. Giao et al.²² reported worse quality of water in low-lying areas of the Vietnamese Mekong Delta. The other rural, as well as urban regions of India, also do not meet the national guidelines of water quality in natural freshwater resources^3,12,23. Furthermore, the rural regions of the Colombian Caribbean represent poor water quality²⁴. Such investigations highlighting water quality problems become more meaningful when integrated with the assessment of adverse impacts on the health outcomes of bio-indicator organisms inhabiting the ambiance. Therefore, endemic fish Bagarius sp. and a plant E. crassipes were chosen for further investigations.

Bioaccumulation and MPI in Bagarius bagarius

The average body length from the snout to the tip of the caudal fin of the exposed fish was found to be 22.7 ± 0.9 cm, the average weight was 145.73 ± 1.3 g and that of the reference fish was 18 ± 0.6 cm and 128 ± 0.96 g respectively.

Fish Bagarius sp. accumulated significant concentrations of heavy metals in the muscle, gills, liver, and kidney (Table 3). In muscle, Cd (94 mg/kg.dw) showed the highest accumulation, and Mn (12.9 mg/kg.dw) accumulated the lowest. Likewise, in gills (96.3 mg/kg.dw) and kidney (72 mg/kg.dw), Cd accumulation was highest while Mn shows lowest accumulation 13.45 mg/kg.dw and 9 mg/kg.dw in both the organs respectively. In the liver, Cu (102 mg/kg.dw) accumulation was highest and Mn (20 mg/kg.dw) lowest. However, the MPI calculation showed that the liver (58.29) has the highest burden of heavy metals among all the tissues followed by the gills (54.66), muscle (52.50) and the lowest load in the kidney (33.73) (Fig. 1). The interpretation derived from the bioaccumulation and MPI results is that liver is the most vulnerable target organ of heavy metals may be because of its involvement in all the metabolic processes. It also takes part in the detoxification of toxicants²⁵. Moreover, gills and muscles proved to be the next target organs for heavy metal toxicity. Seemingly, the liver and gills were unable to excrete these heavy metals fully because they might have bound with the macromolecules and enzymes. Muscle contained high concentrations of metals which may be due to the reason that their metabolization occurs in the liver and part of them binds with the myoglobin and remain in the muscle tissue. The lowest heavy metal load in the kidney indicates that the kidneys function efficiently to remove these metals. Similar results were also observed by Khan et al.²³ and Mahamood et al.³ in Oreochromis niloticus and Labeo rohita living in the river Yamuna repectively. Moreover, Tabrez et al.¹¹ also found liver and gills as target organs in the same genus Mystus tengara and vittatus. Kose et al.²⁶ reported higher metal levels in the gills and liver of fish Carassius gibelio collected from dam lakes and Sakarya river, Turkey.

Condition indices

Various condition indices of fish Bagarius sp. are given in Table 4. In the present study lower values of condition factor (K), hepatosomatic index (HSI), and kidney somatic index (KSI) were found as compared to the reference fish. These condition indices present a simple tool to surveil the health of fish in field studies. The most common among them are K, HSI, and KSI. K represents the general well-being of the fish and the low value of K shows inferior environmental quality. Moreover, HSI relates the weight of the liver to the body weight of fish. It gives more precise information relating to the function of the liver in response to the environment. Furthermore, kidneys play excretory, endocrine, hematopoietic as well as reticuloendothelial roles. Therefore, KSI also helps in determining the health of fish.

Glucose, glycogen, and protein assays

Blood based biomarkers are very informative in predicting the health of the fish or the entire population therefore, they are routinely used in biomonitoring studies²⁷. In the present investigation, an increase (47.22%) was observed in the glucose levels in blood and serum glycogen (74.69%) in exposed Bagarius sp. However, the serum protein and liver glycogen concentrations got lowered by − 63.41% and − 79.10% in the exposed fish than in the reference fish (Fig. 2). It is well-known that heavy metals generate reactive oxygen species which cause stress by influencing several physiological processes. Carbohydrates and protein are energy sources. Glucose provides instant energy whereas glycogen is the reserve energy. So during stress conditions increase in glucose and serum glycogen indicates their utilization and mobilization from other tissues to the blood. Moreover, the decrease in serum protein and liver glycogen is also pointing in this direction. It is also reported that when glucose is in short supply in the body, a non-carbohydrate source would metabolize to glucose which could lead to its higher levels. Recently, Tabrez et al.² reported depletions of all energy sources, glucose, glycogen, and protein in the serum of Labeo rohita living in the polluted Kshipra River. Bhilave et al.²⁸ also found lower levels of glucose, glycogen, and protein under the effect of chronic heavy metals exposure. Lately, in Heteropneustes fossilis the As₂O₃ and PbCl₂ exposure lead to disturbance in the carbohydrate metabolism²⁹.

Heavy metals uptake by Eichhornia crassipes, bioaccumulation factor, transfer factor and mobility factor

Like inhabiting fauna, the flora also bioaccumulates heavy metals in different parts. The bioaccumulation data of E. crassipes leaves, stalk, and roots are presented in Table 5. This plant grows rapidly in polluted waters. The leaves, stalk, and roots accumulated the highest amounts of Cd 56 mg/kg.dw, 75 mg/kg.dw, and 81 mg/kg.dw respectively, while the Cr showed the lowest accumulation in all these parts 1 mg/kg.dw, 1.2 mg/kg.dw, and 1.8 mg/kg.dw respectively. According to MPI calculation (Fig. 3), the roots (21.50) contained the highest heavy metal load followed by the stalk (18.60) and then leaves (16.87). The high metal burden in roots pointed towards their habitat that they always remained immersed directly in the surrounding water. The plant part which is farther from the medium contained a lower load. Recently, Tabrez et al.² and Singh et al.¹⁵ also found similar results in E. crassipes. The BAF, TF, and MF of E. crassipes are presented in Table 6. The highest BAF was reported for Mn and the lowest for Cr. The highest TF was found for Ni (1.57), and the lowest for Cu (0.66), Zn (1.30) also had TF above 1, whereas the rest of the heavy metals had comparable TF and it was below 1. Furthermore, the maximum MF values were observed for Mn for both roots to stalk (324.35) as well as stalk to leaves (211.53). However, it followed the order as Mn > Cd > Cu > Zn > Fe > Zn > Ni > Cr from root to stalk; and Mn > Cd > Zn > Cu > Fe > Ni > Cr from stalk to leaves.

These factors BAF, TF, and MF are utilized to monitor the level of anthropogenic pollution in plants and their surrounding medium^{2,15,32,34,35}. BAF shows the concentrations of heavy metals bioaccumulated by plants from the water. If the BAF > 1 it indicates hyperaccumulation³⁶. So, in the present study, all the concerned heavy metals were hyperaccumulated in the plant. The TF elucidates the capability of the plant to translocate the accumulated metals to its other parts. The roots of E. crassipes showed the highest translocation capacity for Ni (1.57) as well as Zn (1.30) to other parts. If the value of TF exceeds 1, then it represents the high accumulation efficiency^37,38, therefore, plants will be considered as the hyperaccumulators for the Ni and Zn. Although the Cd was the highest accumulated metal in the plant, it could have been because of its may be because of its low TF. Whereas, TF values lower than 1 for Cr, Mn, Fe, Cu, and Cd pointed out that this plant’s roots act as a non-hyperaccumulator for these heavy metals. Furthermore, the highest MF values were depicted for Mn in both cases which reflects that E. crassipes can suitably be used for phytoextraction of Mn as well as for Cd, Zn, Fe, Ni, and Cu. The BAF, TF, and MF of Cr are low in the present study, which implies that roots are limiting the Cr. Moreover, if the BAF ≤ 1.00 then it shows the capability of absorption only rather than accumulation^36,37. In addition, if the values of BAF, TF, and MF exceed 1, plants can also work for phytoextraction. Furthermore, if the BAF > 1 and TF < 1, represents that plant is a good phytostabilizer as well^35,37,39. In the present study, it was observed that E. crassipes can also work as a good phytostabilizer for Cr, Mn, Fe, Cu, and Cd.

Human health risk assessment

Freshwater ecosystems are polluted everywhere by anthropogenic activities so it become a prime concern worldwide mainly due to the issues of water quality and seafood contamination. Hence to evaluate the possible health hazards, a health risk assessment was carried out in the form of target hazard quotient (THQ), hazard index (HI), and target cancer risk (TR) by consumption of Bagarius sp. from the Narora channel (Table 7). Non-cancer risk is represented by THQ and Cd shows the highest THQ in both adult males (3.21 × 10⁻²) and females (3.66 × 10⁻²) and minimum by Fe in both males (2.03 × 10⁻⁵) and females (2.31 × 10⁻⁵) adult individuals respectively. Moreover, the THQ value above 1 indicates that the exposed population could suffer from non-carcinogenic risks in their life duration. In the present study, the THQ for all the concerned metals was below 1, so the Bagarius sp. could not pose any non-cancer risk but it shows the level of concern for Cd. Furthermore, the HI is the total THQ, and in the present study, it indicates lower non-cancer risks for males (39.80 × 10⁻³) whereas females (45.38 × 10⁻³) were facing comparatively higher non-cancer risks. This different risk pattern could be due to their low weight because other parameters were the same. In the present study, cancer risk was calculated for Cr and Ni only. For Cd, the carcinogenic slope factor is not available. Ni posed a higher cancer risk to the exposed population than Cr. In males, the TR Ni value was 3.96 × 10⁻⁵ and in females, it was 4.52 × 10⁻⁵, while Cr represented 8.54 × 10⁻⁶ in males and 9.74 × 10⁻⁶ in females. Between both, groups females were at higher risk for cancer as well. In line with the present investigation, gender differences were also noted by Tchounwou et al.⁴⁰ and Balali-Mood et al.⁴¹. In general, the toxicity caused by heavy metals leads to several disorders which may be acute as well as chronic. The disorders may be of an immune and nervous system, gastrointestinal, renal disturbances, lesions in vessels and skin, birth defects, and may even lead to cancer. Several authors have reported that simultaneous exposure to a variety of metals either through water or food has synergistic effects^42,43,44. Moreover, there are reports on hormonal imbalance caused by Cr and Cd, that both of them interfere with thyroid and steroid metabolism and caused thyrotoxicosis⁴⁵.

Strategies to minimize heavy metal pollution in the Narora channel

The growing pollution load (heavy metals) of the river Ganga has attracted the attention of researchers as well as others who are concerned with the vulnerability of the environment.

Narora is a town and it is situated on the bank of the river Ganga. According to the Town and Country Planning Department, Uttar Pradesh as per the 2001 census the population of Narora was 20,376 (https://uptownplanning.gov.in/article/en/introduction-of-regulated-area-narora). It has occupied by petrol pumps, drug stores, small-scale sugarcane mills, water pumping and treatment plant, mechanical workshops, intensive agricultural and cropping areas around the bank of canal, etc. Moreover, an Atomic power plant is also present adjacent to this canal. The government made this canal mainly for irrigation of the crop fields of Narora and also to feed the atomic power plant. Additionally, as per the reports of the National Ganga River Basin Authority (NGRBA) Narora town has no sewage facility, consequently leading to the direct release of the town’s wastewater except the power plant into the canal. This further adds to the pollution load of the river Ganga and its canal. Table 8 shows the presence of different heavy metals in the different stretches of the river Ganga.

The present study has already reported the poor water quality condition and poor health status of the indicator organisms of the canal. Although, no non-cancer risk was found but the exposed population may have cancer risk due to Ni and Cr. Furthermore, it too brings about an unhygienic, unhealthy, situation in the town which is threatening public health. Thus, for the abatement of the pollution of this canal or the Ganga river and also to provide healthy conditions there must be a provision of a well-planned sewage/ drainage system in the town.

Besides, it has already been reported that industrial and domestic wastewaters are the predominant sources of heavy metals in the environment^46,47. In 1986 the government of India launched the Ganga Action Plan intending to clean Ganga and its tributaries unfortunately, they have had little success in achieving their objectives and goals.

Therefore, another way of improving the water quality of this study canal is through phytoremediation. The present study already reported E. crassipes as a suitable hyperaccumulator. No doubt, it is a prolific grower and can cause harm to the water body by creating dense mats on the surface, clogging, and blocking it, affecting navigation through the water body, irrigation of the crops, etc. But we have to exploit its hyperaccumulation and phytoextraction capability and its rapid growth can be controlled by time to time mechanical harvesting method and then it can present an attractive source of green, low-cost, remediation tool. In an interesting study by Jones et al.⁴⁸ where they grow the E. crassipes plant to explore its phytoremediation potential for heavy metals for the clean-up of the highly polluted tributary of Tawe river, a Nant-Y Fendrod. They conducted experiments in three levels (i) in situ study where water hyacinth was cultured within the river Nant-Y-Fendrod, (ii) bench scale trial where the plant was grown in the polluted river water and in synthetic solutions (iii) bankside study where the plants were grown in the treated river water. Their results were fascinating they successfully removed 21 heavy metals from the water. Among the methods used the bench scale demonstrated promising results with a higher removal rate of Al (63%), Zn (62%), Cd (47%), As (23%), and Mn (22%) whereas in insitu trial the average removal rate for Cd (15%), Zn (11%), and Mn (6%). Another study by Lissy and Madhu⁴⁷ also observed that if it grows collectively in a tank then it showed a 65% removal of heavy metals than in jars. Therefore, the present study suggested that the phytoremediation method by use of E. crassipes can be adopted for the abatement of the pollution load of the Ganga river in general and the Ganga canal in particular provided the harvesting of the plant should be done regularly. Moreover, the phytoremediation technique is sustainable, eco-friendly, cost-effective, and as well as requires low maintenance.

The present research investigated high concentrations of heavy metals in Narora channel water. Among heavy metals, Cr, Fe, Ni, and Cd were above the permissible limits. Ni and Cd are represented to be the main culprits which degraded the water quality. All the concerned heavy metals showed significant bioaccumulation in the fish Bagarius sp. and aquatic plant E. crassipes leading to metal mediated stress and consequent depletion of energy reserves. None of these metals do not pose any non-cancer risk but Cr and Cd raised the concern. Cr and Ni posed low cancer risk to the exposed population. Additionally, gender-specific differences were found in the health risk assessment study. This study clearly shows that water quality surveillance was not carried out in rural areas, as indicated by WQI analysis value. Moreover, techniques like bioremediation, phytoremediation, etc. should be employed time to time to maintain the quality of water and life.

Source: Ecology - nature.com