Introduction

In Bangladesh, ground and surface water are the primary sources of water and Halda River is the most important source of surface water (Hasan et al., 2019). Among the significant primary sources of water in Bangladesh, the Halda River is very special for Indian carp fish’s such as Catla catla, Labeo rohita, Labeo calbasu, Cirrhinus mrigala, etc. Indian carps naturally breed only in this tidal river (Patra & Azadi, 1985; Tsai et al., 1981). A number of factors like seasonal, environmental and hydro-morphological characteristics favor for spawning of carps. Studies showed that the interaction of various factors make a different hydrological condition which probably stimulate and prompt the carp breeding in the Halda River (Patra & Azadi, 1985). In addition, the soil profile of the Halda river contains sand 41.00% to 54.43%, silt 20.70% to 29.70%, clay 20.92% to 29.10%, organic matter 3.29% to 4.36%, and carbon 1.12% to 2.52% (Fontana, 2022).

Similar to other rivers, the water of Halda is used for various purposes including recreation, transportation, household uses, drinking water supply, fishing, carrying off, and assimilation of wastes from agricultural lands, domestics, municipalities, industries, streets, and roads run-off (Kabir et al., 2013). The Halda River become undesirably affected due to its direct link to the Karnaphuli River which is vastly polluted by the wastes from various sources such as municipalities and industries (Ali et al., 2016; Karim et al., 2019). In addition, anthropogenic activities (Hatje et al., 1998) factors threatening the Halda River lives (Azadi & Alam, 2013). Consequently, the natural carp fish breeding capacity of the Halda River is adversely disrupted.

Unplanned textile mills, power plant, paper mill, tannery, etc., and their accidental use of chemicals are the main causes of excessive metals in the aquatic ecosystems (Ahmed et al., 2019) and makes the Halda river water polluted. Department of Environment (DoE) and Water Resource Planning Organization (WARPO) regulate water pollution according to Bangladesh Water Act 2013 (Arifuzzaman et al., 2019). Moreover, the rising Bay of Bengal Sea water also enter the Halda through Karnaphuli river and destroying carps breeding (Illius, 2021). However, it is concerned that the metal contamination with some other vital factors in the water body might have been caused due to the anthropogenic sources along with the natural environment (Safiur Rahman et al., 2021). Water contamination due to the presence of organic and inorganic pollutants as well as the life-threatening microbes has become a national issue in Bangladesh. Therefore, the physicochemical and biological quality of the river water determines its utility for diverse application and the level of water pollution (Higgins & Burns, 1975).

There are few studies on the physiochemical parameters of Halda River water in Bangladesh. Moreover, there is also a lack of microbiological study on Halda River water. Therefore, a combined study, comprising both physiochemical and microbiological quality of this water source is needed to control pollution and manage sustainable water resources for aquaculture and ecosystem management.

The primary aim of this study was to assess the microbiological contamination, concentration of metals like- lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu), and physicochemical properties such as temperature, pH, Electrical Conductivity (EC), Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), and Total Dissolved Solids (TDS) of Halda River water in Chattogram, Bangladesh. Therefore, this research work will play a great role in addressing the public health concerns and aquatic lives in the Halda River.

Materials and Methods

Sampling sites

Sampling sites were selected based on point and non-point sources of contamination, climate, etc. Five sampling sites were selected randomly considering the location as representative of the water quality parameters wished to investigate. These are Mohara water treatment plant (22°24′53″N 91°53′03″E), point of Krishna Khal (22°25′44″N 91°52′48″E), West site of Modunaghat Bridge (22°26′02″N 91°52′17″E), East site of Modunaghat bridge (22°26′06″N 91°52′22″E) and Ramdash Hat point (22°27′32″N 91°51′26″E) (Figure 1) in Chattogram, Bangladesh.

Figure 1.

GPS position of Chattogram (Banglapedia, 2014) and GPS position of sampling sites.

Results

Physicochemical parameters of water samples

To assess the water quality of Halda River, different physicochemical parameters were analyzed. The seasonal variation of different physicochemical properties of the Halda River water samples are summarized in Table 1. The temperature in the study period at different points was found in the range from 22.5ºC to 27.67ºC and pH value of water samples was found from 6.9 to 7.53. In addition, EC value was found within the range from 50 to 283.33 µScm⁻¹. The DO, BOD, COD value of collected water samples represented a variation of 6 to 14.67 mgL⁻¹, 2 to 8 mgL⁻¹, and 40.43 to 107.63 mgL⁻¹ respectively at different sites throughout the study period. The recorded TSS value ranged from 818.33 to 3,180 mgL⁻¹, TDS ranged from 90.67 to 726.67 mgL⁻¹. We observed that the minimum recorded TS (total solids) were 1,039.33 mgL⁻¹, where maximum TS were 3,897.33 mgL⁻¹. However, the turbidity of the Halda river water samples ranged from 40.09 to 355 NTU among the studied sites.

Table 1.

At a Glance the Measured Value of Physicochemical Properties of the Water Samples of Halda River in February, May, and December 2019.

Determination of heavy metal concentrations

To explore the pollution level of Halda River water by inorganic pollutants, the heavy metal concentrations were determined and shown in Table 2.The results revealed that the average concentration of Pb, Cd, Cr, Ni at all study sites in the month of February, May, and December were below detection limit except at Ramdash Hat point in May, where the concentration of Pb (6.765 ± 0.244 µgL⁻¹) and Cr (3.17 ± 0.168 µgL⁻¹) was lower than the maximum standard limit 10 and 50 µgL⁻¹ respectively (WHO, 2011). Noticeable concentrations of Cu were recorded both at Mohara water treatment plant point (4.622 ± 0.080 µgL⁻¹) and Ramdash Hat point (10.338 ± 0.232 µgL⁻¹) in February but did not exceed the WHO permissible limit (<40 µgL⁻¹) (WHO, 2011). Therefore, no pollution due to heavy metals was observed during the present investigation.

Table 2.

Heavy Metal Profile of the Water Samples of Halda River in February, May, and December 2019.

Microbiological assessment of water samples

In this study, a number of microbiological parameters were investigated to analyze the water quality of the Halda river and the results are shown in Table 3. The observed Total Bacterial Count (TBC) of water samples was found in the range from 7.2 × 10³ to 3.83 × 10⁵ CFU/mL. Moreover, the recorded Total Coliform (TC) and Fecal Coliform (FC) of the water samples of Halda River were in the range from 5.4 × 10² to 2.2 × 10⁴/100 mL and 0.7 × 10² to 3.9 × 10³/100 mL.

Table 3.

Microbiological Analysis of the Water Samples of Halda River in February, May, and December 2019.

Identification and characterization of selected bacterial isolates

In this study, 25 bacterial colonies were isolated from water samples and based on their cultural and morphological characteristics 10 isolates (designated as HSA2, HSA4, HSB1, HSB2, HSC1, HSC3, HSD2, HSD3, HSE2, and HSE3) were randomly selected for identification. The isolates were taxonomically identified using 16S rRNA gene-based analysis (Table 4, Figure 2), morphological and biochemical characteristics. Results of 16S rRNA gene sequence of HSA2, HSB1, HSB2, HSC1, HSD2, HSD3, HSE2, and HSE3 strains showed maximum similarity to the genus Bacillus and HSA4 and HSC3 strains showed maximum similarity to the genus Comamonas and Acinetobacter, respectively. Phylogenetic relationship analysis of these isolates with the top hit strains from NCBI database also supports this (Figure 2). Identification by morphological, biochemical, physiological properties of these isolates ( Supplemental Table 1 and  2) were also found consistent according to Bergey’s Manual of Determinative Bacteriology (Buchanan & Gibbons, 1974).

Table 4.

Taxonomic Similarity Inferred From the Sequence Identity of Their 16S rRNA Genes. NCBI Accession Numbers are given in Parentheses.

Figure 2.

Evolutionary relationship analysis: The evolutionary history was inferred by using the Maximum Likelihood method and Tamura-Nei model (Tamura & Nei, 1993). The tree with the highest log likelihood (−6107.99) is shown. Initial tree for the heuristic search were obtained automatically by applying Neighbor-Join and BioNJ algorithms to a matrix of pairwise distances estimated using the Tamura-Nei model, and then selecting the topology with superior log likelihood value. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. This analysis involved 20 nucleotide sequences. Codon positions included were 1st + 2nd + 3rd + Noncoding. There were a total of 1,562 positions in the final dataset. Evolutionary analyses were conducted in MEGA11(Tamura et al., 2021).

According to NCBI database the 10 strains have been approved as novel strain viz. Bacillus wiedmannii strain HSA2, Comamonas jiangduensis strain HSA4, Bacillus halotolerans strain HSB1, Bacillus safensis strain HSB2, Bacillus subtilis strain HSC1, Acinetobacter modestus strain HSC3, Bacillus subtilis strain HABIBD2, Bacillus marisflavi strain HSD3, Bacillus aerius strainHSE2, and Bacillus megaterium strain HABIBE3 (NCBI accession numbers are mentioned in Table 4).

Antibiotic susceptibility assay of the identified isolates

The results of antibiotic susceptibility assay are shown in Table 5. Bacillus wiedmannii strain HSA2 showed resistance against six antibiotics (multi-drug resistance) viz: cefalexin, ampicillin, amoxicillin, ceftazidime, ceftriaxone, and imipenem. Comamonas jiangduensis strain HSA4, Bacillus halotolerans strain HSB1, Bacillus safensis strain HSB2, Bacillus subtilis strain HSC1, Bacillus subtilis strain HABIBD2, Bacillus marisflavi strain HSD3, and Bacillus megaterium strain HABIBE3 were found to form variable zone of clearance against all the antibiotics used in the current study. Acinetobacter modestus strain HSC3 was resistant against cefalexin, ampicillin, and sensitive to other antibiotics. Bacillus aerius strain HSE2 was also sensitive to all the antibiotics except ceftazidime.

Table 5.

Antibiotic Susceptibility Assay for the Identified Isolates Against Some Commercially Available Antibiotics.

Discussion

Now-a-days, water pollution is one of the greatest health problems in the world, especially in developing countries. Therefore, physicochemical and microbiological properties of surface water of the Halda River are considered as vital features of the water quality standards. According to the EQS (1997), the standard range of temperature of surface water is 20°C to 30°C. In this study, the temperature was found within the EQS standard limit. During spawning time, the temperature was also within the EQS standard limit in all sites (Table 1) (Ahmed et al., 2010; Hasan et al., 2019; Karim et al., 2019; Patra & Azadi, 1985)

On the other hand, the measured pH value was within permissible limit of surface water (Asian Development Bank [ADB], 1994; Ayres & Westcot, 1985; WHO, 2011). However, the results of the current study are in concurrence with other reports (Ahmed et al., 2010; Bhuyan & Bakar, 2017; Khan et al., 2020; Patra & Azadi, 1985).

During this study period, the average EC value was within the standard level of EC of most natural water (Department of Environment [DoE], 1997). The conductivity of most natural water generally ranges from about 50 to 1500 µScm⁻¹ (Uddin et al., 2014). The WHO standard value is also reported as 1,000 µScm⁻¹(WHO, 1993b). Our results of EC were found (Table 1) within the permissible limit (Ahmed et al., 2010; Bhuyan & Bakar, 2017; Karim et al., 2019; Patra & Azadi, 1985). In addition the EC value was reported in Karnaphuli River (Dey et al., 2017) which is a matter of concern as the Karnaphuli River water intrudes into the Halda River.

According to WHO (1993a), EQS (1997), and others the standard value of DO in surface water is 4 to 6.5 mgL⁻¹(De Anil, 2005; DoE, 1997; Khan et al., 2020 Chen et al. (2012) reported that the DO concentrations of healthy water remain above 6.5 to 8 mgL⁻¹ and this represents the good quality of river water. In the present investigation, the DO value in the spawning time was 6 to 8.67 mgL⁻¹, which shows the suitable DO concentration for spawning. The dissolved oxygen (DO) is an indication of available gaseous oxygen present in the water body, which is necessary for many forms of life. Considering the present study, it is showed that the solubility of oxygen in water decreases as temperature increases in May, and the colder water during February and December have the capability to hold higher concentrations of DO. The DO value found higher in February and December as sampling was done at the time of high tide and due to this high flow causing turbulence from opposite direction which increases DO level. Moreover, nonpoint source pollution due to heavy rain fall occurs during the month of May in Bangladesh. As a results rainfall picking up natural or anthropogenic (human-made) pollutants and depositing them into water resources that reduce the DO value in the month of May. On the other hand, the BOD level of the Halda River water represents the river is moderately polluted (Connor, 2016). High BOD was found such a point where canals like Krishna Khal, Madari Khal (near Ramdash Hat point) connect to the Halda River and especially at the sites of Mohara water treatment plant sampling point, where Halda connects to the polluted Karnaphuli River and water intrudes into Halda River during high tide (Ahmed et al., 2010; Islam et al., 2017). Comparing with previous findings, it showed that the BOD of the Halda River water is increasing day by day.

However, COD of water samples showed great variance among the sampling sites. In the present study, the recorded COD values are highly deviated from the WHO standard value (10 mgL⁻¹) (Table 1). The recorded higher COD value indicates the breaking down of organic and inorganic material entering the river incessantly. The high COD value was reported by Uddin et al. (2014) in the Jamuna River, Dey et al. (2017) in the Karnaphuli River and Karim et al. (2019) in the Halda River. Studies revealed that Halda River is being polluted with organic substances which are showing increased COD value (Ahmed et al., 2010; Bhuyan & Bakar, 2017) which are close to the values found in the present study.

In the study period, average TSS of water samples at different points was measured (Table 1) which is mostly deviated from the Bangladesh standard for TSS (150 mgL⁻¹) of inland water. In comparison with the previous studies, it can be noted that suspended solids in the Halda River water are increasing day by day (Ahmed et al., 2010; Islam et al., 2016). The suspended solids from various sources including sand lifting, industrial and domestic discharges, etc., causing the river to be polluted (Hussain, 2020; Islam et al., 2017).

In addition, the recorded Total Dissolved Solids (TDS) in the study period were within the Bangladesh Standard for TDS of inland surface water (1,000 mgL⁻¹). But there are concern matters about the TDS value of the river water which is gradually increasing day by day (Ahmed et al., 2010). Due to the increased amount of suspended solids, the Total Solids (TS) of the river was also higher than ever before and the average TS value of the Halda River water in the sampling months at different sampling points ranged from 1,590.07 to 2,952.4 mgL⁻¹, which is a sign of pollution (Islam et al., 2016; Sarwar et al., 2010). Moreover, the present study revealed that the average results of turbidity of water samples indicates that the Halda River water was highly turbid than the permissible limit (5 –25 NTU) (Karim et al., 2019).

Based on the present investigation, there was no pollution found in the Halda River water with lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu). Therefore, almost in all sampling sites on the Halda River water, the concentration of heavy metals were attributed to the WHO permissible limit (WHO, 2011) (Table 2). Ahmed et al. (2010) studied the Halda River water did not find any toxic heavy metal except manganese. Similarly, Islam et al. (2016) also reported that there was no pollution from Cd, Cr, Ni, and Cu in Halda River water.

Before the present work, only a few groups described the presence of microbial contamination of Halda River water. In this study, higher count of TBC was recorded in May during the spawning season. This may be due to excessive nutrient run-off or microbes washing off from land with rainwater flow along with wastes containing bacterial contamination from different sources, such as unplanned industrialization near the river, local market on the bank of river, domestic discharge, connectivity of canals, flowing of sea water through Karnaphuli, etc. (Ahmed et al., 2019; Illius, 2021; Islam et al., 2016; Safiur Rahman et al., 2021). Moreover, previous studies reported that higher bacterial count was observed in different river water of Bangladesh (Real et al., 2017; Saha et al., 2009; Tuhi et al., 2017).

According to WHO standard, the maximum permissible limit of TC is 5 × 10³/100 mL (WHO, 1993a). The Total Coliform count in the Halda water samples mostly were within this limit except at Krishna Khal point and Mohara water treatment plant point (Table 3) in May, which was highly polluted with Coliform where the Halda connects to the Karnaphuli River. Therefore, this pollution may be from Karnaphuli River which was reported with high count of Total Coliform (Dey et al., 2017) as water enters into the Halda River during high tide (Islam et al., 2016). However, among the sampling sites, water samples from Mohara water treatment plant were found highly polluted by fecal coliform than other sampling sites. Pollution at Mohara water treatment plant point may be from Karnaphuli River (Dey et al., 2017) as sampling was done at the time of high tide and water from Karnaphuli River intruded into Halda River (Islam et al., 2016). Higher count of fecal coliform was also found in the west site of Modunaghat Bridge.

Ten bacteria were identified from the Halda River water (Table 4). The occurrence of Bacillus, Acinetobacter, and Comamonas during this study in water samples is of primary importance because the river water may be contaminated from different sources. The contamination may be from the local market, Modunaghat Bazar, domestic and discharges from different sources through canals that are connected to Halda River. However, Bacillus halotolerans strain HSB1, Bacillus safensis strain HSB2, Bacillus subtilis strain HSC1, Bacillus marisflavi strain HSD3, and Bacillus megaterium strain HABIBE3 in this study are highly salt tolerant ( Supplemental Table 2), possibly they are from sea water or tannery wastes. Oyelakin et al. (2016) isolated Comamonas jiangduensis from the fish Brycinus longipinnis at Eggua Station in Yewa River, Nigeria as a potential pathogen. However, all the identified strains were tested for their antibiotic sensitivity against commercially available disk of antibiotics. It is a matter of concern that Bacillus wiedmanniistrain HSA2 showed resistance against a number of commercially available antibiotics. Previously reported that Bacillus wiedmannii is a psychrotolerant and have strong cytotoxic effect (Miller et al., 2016). A recent study also reported the toxic effect of this bacterium (Zhao et al., 2019).

Conclusion

This study can be concluded that the Halda River water is being polluted from the intrusion of Karnaphuli River water and discharges from various industrial sources. This can significantly affect the growth, distribution and physiology of fish and other lives of this unique natural carps breeding gound of Bangladesh. Considering the physicochemical pollution level, occurance of high microbial load and pathogenic bacteria indicates that the Halda River water is becoming unsafe for drinking and domestic purposes. To minimize the contamination and pollution level of Halda River, a great effort from different authorities such as locals, farmers, agriculturists, municipal, industrialists, ministries of government is needed. This can be achieved by the proper treatment and discharge of agricultural, industrial, sewage wastes, wastes from mills or factories. So, proper management and planning for water quality monitoring is necessary to maintain a healthy ecosystem of Halda River. Moreover, regular monitoring and evaluation of water quality of the Halda River are also recommended.