Physicochemical parameters and heavy metal in surface water in Central Bangladesh

Pollution of surface water and heavy metals is one of the growing concerns worldwide due to industrialization and unplanned urbanization. The surface water pollution level was studied by assessing the physicochemical properties and heavy metal concentration of collected samples in Gazipur district. Maximum average temperature(35.200C±2.63), EC(1423µs/cm), and TDS(746.5mg/l) were observed in Kaliakoir upazila. These parameters were found minimum in Kapasia upazila. DO was found above 5mg/l in Sreepur, Kapasia and Kaliganj. Cr and Ni were too low to detect by the instrument. The maximum average concentration of Pb(925.6917µg/l), Mn(477.8625µg/l), and Na(11230.17µg/l) was observed in Kaliakoir upazila. However, no Fe was observed in Kaliakoir upazila. The maximum Fe concentration was Sreepur upazila (3531.6µg/l) followed by Sadar (1496.517µg/l) upazila. Maximum average Cd concentration was observed in Kapasia (41.28µg/l) followed by Kaliakoir (30.8767µg/l), Sadar (29.4283µg/l) and Sreepur (28.8042µg/l). Cu concentration was found maximum in Kaliganj (14.205µg/l) followed by Sadar (6.29µg/l) and Kaliakoir (3.893µg/l). However, Cu concentration was found nil in Kapasia. The maximum average concentration of Ca(29197.25µg/l) and Mg(8142.833µg/l) was observed in Kaliganj and the minimum concentration was observed in Sreepur upazila. The order of concentration of heavy metals in the study area is Ca>Na>Mg>Fe>Pb>Mn>Cd>Cu>Ni>Cr. From the findings, the physicochemical parameters of the surface water sources were found higher than the standards in most of the samples.


Introduction
During the last few decades, overpopulation, rapid urbanization, industrialization, and agricultural advancement have triggered some serious problems in the global environment [1], especially in developing countries [2].The pollution of air, water, and soil is increasing for different anthropogenic activities which are severely impacting the ecosystems [3][4][5].
Being a developing country Bangladesh is facing a rapid land use change from agriculture, forest, or fallow land to urbanization and built-up development [6].The capital city is located in the central part of the country and district Gazipur is in the north of the capital Dhaka and is highly concentrated in different industries such as textile and garments, plastic and chemical industries, glass and battery manufacturing industries, food processing industries, shoe making industries, tannery, steel plants, dairy, beverage, feed, pesticides, etc. [7][8].The effluents from those industries are mixed with different surface water bodies and contaminate the aquatic systems as well as soil environments [9].The IOP Publishing doi:10.1088/1755-1315/1297/1/012087 2 imbalance in population density in the central part from the rest of the country has led to rapid unplanned urbanization and industrial development in the peripheral area resulting degradation of aquatic resources [10][11].The situation is being worsened gradually due to the gradual increase of population in the area leading to continuous land use changes, unplanned urbanization, and industrialization.Surrounding rivers and different water bodies are more affected and accumulate different degradable and nondegradable wastes from municipal wastes, industrial effluents, wastes from hospitals, chemical fertilizers, and pesticides [12][13].The surface water quality is deteriorating due to different infectious agents, solid wastes, and carcinogenic heavy metals pollution.Moreover, the indiscriminate use of pesticides and chemical fertilizers for growing more crops for the growing population leads to heavy metal contamination in the soil as well as the aquatic environment [14].The water quality both physicochemical properties and aquatic biodiversity is deteriorating and some of them become polluted and unusable.However, the pollution level differs due to diversified effluents received from different industries and land use practices in specific areas.In the central part of Bangladesh, some of the areas have been declared Ecologically Critical Areas (ECA) by the Department of Environment [9].
Several researchers also reported that heavy metal and metalloid contamination in Bangladesh has become a major issue in recent years which is mainly associated with industrialization, urbanization, and extensive agriculture [12,[15][16].Being non-biodegradable, these heavy metals along with other persistent organic pollutants transfer from soil and water to different aquatic lives and food crops (such as rice, maize, wheat, potato, etc.) resulting in their entrance into the food chain [12].Aquatic lives and their reproductive ability are being threatened by contaminated water [9].This process continuously occurs due to human activities and biomagnification is being occurred.Humans are the ultimate receivers of these toxic elements and being suffered from different life-threatening health issues.
Although many studies have been focused on water quality assessment, heavy metal condition, and risk assessment, and their effects on lives in the central peripheral area of the capital.Nevertheless, the situation is being worsened gradually.Therefore, it is very time demanding and urgent to update the knowledge on the present situation of pollution status in the industrial hub Gazipur.Thus, the objective of this study was to investigate the physicochemical and heavy metal concentration status in surface water bodies of different upazilas in the Gazipur district.

Study area
The study was conducted in the Gazipur district (Figure 1) located in the central part near the boundary of the capital Dhaka city.The total area of district Gazipur is 1806.41km 2 of which 1515.41 sq km is land mass, 273.42 sq km reserved forest, and 17.53 sq km riverine area [17].It lies between 23.53˝ and 24.21˝ north latitude and 90.09˝ and 92.39˝ east longitude having a population of more than 3.5 million and about 1884 population per square kilometers with 5.2% annual growth rate.There are five subdistricts (Upazila) in Gazipur, namely, Gazipur Sadar, Sreepur, Kaliakair, Kapasia, Kaliganj, and Sreepur.The main rivers of Gazipur are the Shitalakshya, old Brahmaputra, Turag, Balu, Banar, and Bangshi.Different industries like readymade garments, dying and packaging industries, diesel plants, shoe factories, machine tool factories, brick field manufacturers, etc. are overcrowded in this district.The main agricultural crops are rice, jute, and sugarcane.Different pulse crops, mustard, wheat, different kinds of vegetables, and spices like turmeric, ginger, etc. are grown in this district.Agro-ecologically, the study area falls in AEZ-9 and 28 categories of FAO of the United Nations [18].

Sampling
A total of 60 water samples consisting of 12 samples from every five upazilas were collected for the study.Water samples were collected from ponds, lakes, rivers, and other surface water sources available in the study area.Sterilized dry screw-capped 500 ml bottles were used for sample collection.Before sampling, the bottles were pre-washed with 1:1 HNO3 and rinsed thrice with distilled water.The samples were filtered using filter paper Whatman 42 to remove suspended solids.For trace metal analysis, acidifications were performed with concentrated HNO3 (AR grade: 65% and density 1.38 kg/L), and the treated samples were preserved at 4 ºC.

Detection of physicochemical parameters and elements concentration
The physical and chemical parameters like, color, odor, temperature (℃), p H , electrical conductivity (EC), dissolved oxygen (DO), and total dissolved solids (TDS) were assessed for the evaluation of water quality status.Watercolor was categorized into 3 (three) classes, black, turbid, and brown to clear where black and turbid indicate polluted and the 3 rd indicates non-polluted water sources [10].The temperature (℃), p H , EC, TDS, and DO were measured in situ using a portable thermometer, pH meter (HANNA H198107), EC meter (DiST 3 HANNA H198303), TDS meter (AQUA Filter Tech), and DO meter (DO-5509 T.014544), respectively.The concentration of cadmium (Cd), lead (Pb), nickel (Ni), chromium (Cr), copper (Cu), manganese (Mn), iron (Fe), sodium (Na), magnesium (Mg), and calcium (Ca) were determined using atomic absorption spectrophotometer (AAS, PerkinElmer, PinAAcle TM 900H, USA) in the lab of the Dept of Agroforestry and Environment, BSMR Agricultural University, Gazipur.For the cation analysis of each sample, 3 replicates were performed and the instrument recalibrated after every 10 samples.For all the samples, the overall precision in percent relative standard deviation (RSD), was below 10.For heavy metals detection, 2 ml concentrated HNO3 acid per liter of water sample was added immediately to acidify the collected water samples followed by shaking homogeneously and preserving in a refrigerator at 4ºC.Later the water samples were filtered in the laboratory using fine filter paper (Whatman Filter Paper 41, Diameter 125 mm) for the removal of suspended materials.

Physicochemical properties of the surface water
More than half of the samples (53%) were found smelly in the study area.Only 16 samples (26.7%) represented brown to clear water and among the rest 73.3%, 32 (53.3%) were turbid and 12 (20%) were black in color.In a study by [10], only 26.7% sample represented non-polluted water sources in the study area.The physicochemical properties of the collected samples are presented in table 1 The temperature of the samples varied from 25.5 0 C to 41 0 C. The average temperature in the study area was (31.84 0 C±3.41).Upazila-wise maximum average temperature (35.20 0 C±2.63) was observed in Kaliakoir and minimum average temperature (30.26 0 C±2.27) was observed in Kapasia upazila.The p H of the water sample is neutral to alkaline ranging from 6.9 to 9.4.The average pH in the study area was 7.76.Among five upazila the highest pH value (9.4) was observed in Sadar.The average EC value was observed 680.975 µs/cm and ranged from 8.5 µs/cm to 2000 µs/cm.Average EC values were 841.25, 504.92, 1423, 225.54, and 410.167 µs/cm found in Sadar, Sreepur, Kaliakoir, Kapasia, and Kaliganj upazila, respectively.TDS value ranged from 20 to 1352 mg/l.The highest average TDS (746.5 mg/l) was observed in Kaliakoir and the lowest average TDS (114.03 mg/l) was observed in Kapasia upazila.The average Dissolve oxygen (DO) in the study area was 5.25 mg/l.At the upazila level, the maximum average DO was observed in Kapasia (5.91 mg/l), and minimum DO in Kaliakoir (4.65 mg/l).Average DO was found above 5 mg/l in the samples from Kapasia, Kaliganj, and Sreepur.From the study of physicochemical properties, the values of different parameters such as temperature, pH, TDS, EC, etc. were found lower in Kapasia.

Heavy metal concentration status of surface water in the study area
The data presented in table 2 showed the average concentrations of heavy metals of Pb, Cd, Cu, Cr, Mn, Ni, Fe, Ca, Mg, and Na from surface water sources like lakes, ponds, and rivers which are major collection points of water from different canals or drains of industrial effluents in different upazila of Gazipur district.From the results, Cr and Ni were found nil at all the upazilas except only 1 sample (109.4 µg/l) at Sreepur for Cr and 4 samples for Ni.The highest Fe concentration was observed in Sreepur upazila (3531.6 µg/L) followed by Sadar (1496.517µg/L), Kaliganj (1124.014µg/L), and Kapasia (716.325µg/L).However, no Fe was observed in Kaliakoir upazila.The U. S. Environmental Protecting Agency has set a standard value of Fe 0.30 mg/l or 300 µg/L (Ghannam et al. 2021).In the study area, Mn concentration varied from 2.079 to 1932 µg/l with an average of 302.05±397.94µg/l.The maximum Mn concentration of 477.8625 µg/l was observed in Kaliakoir upazila.Cd concentration of different water bodies (textile effluents, river water, etc.) varied from 0.76 to 80.53 µg/l.At the upazila level, the highest Cd concentration was observed in Kapasia (41.28 µg/l) followed by Kaliakoir (30.8767 µg/l), Sadar (29.4283 µg/l), Sreepur (28.8042 µg/l) and Kaliganj (23.6436 µg/l).Pb concentration was found highest in Kaliakoir (925.6917µg/l) followed by Kapasia (916.865µg/l), Sreepur (647.1458µg/l), Sadar (641.94µg/l) and Kaliganj (117.7425µg/l).Pb concentration varied from 1.68 to 1338 µg/l with an average of 649.88±444.76µg/l.In Kapasia, Cu concentration was nil.The highest Cu concentration was found in Kaliganj (14.205 µg/l) followed by Sadar (6.29 µg/l), Kaliakoir (3.893 µg/l), and Sreepur (3.0458 µg/l) upazila.The highest concentration of Ca (29197.25 µg/l) and Mg (8142.833µg/l) was observed in Kaliganj and the lowest concentration was observed in Sreepur upazila.For Na, the highest concentration was observed in Kaliakoir (11230.17µg/l), and the lowest concentration (8572.333µg/l) was observed in Kapasia.

Discussion
Although Bangladesh is an agricultural country, recently, industrial sectors are playing a vital role and strengthening the country's revenue by increasing the contribution to GDP.The unplanned industrial establishment has occurred rapidly concentrating the capital city.More than 80% of industries discharge effluents without treatment [10].Therefore, indiscriminate disposal of effluents is mixing with the surrounding water sources, wetlands, irrigation channels, agricultural fields, rivers, ponds etc., and contaminating the surface water [19].[11] reported that effluent production in the Gazipur district is higher compared with others.
Color and odor determine the physical status, acceptability, or rejection as well as its importance for the congenial aquatic environment or the ecosystem services of human welfare and aesthetic values [10].The untreated effluents (having colored and/or odored) discharged from different industries mix with the water channels and run to the rivers or water sources.This reduces the transparency of the water and affects primary productivity.Almost two-thirds (73.3%) of the samples in the study area represented turbid and black water.[10] also found that only 26.7% sample represented non-polluted water sources in the study area.Most of the water channels in Gazipur are ended at the lake or river carrying the effluents.The temperature ranged from 25.7 to 41 0 C in the study area.The average temperature in the study area was 31.84 0 C±3.41.Upazila-wise maximum average temperature (35.20 0 C±2.63) was observed in Kaliakoir and minimum average temperature (30.26 0 C±2.27) was observed in Kapasia upazila.During the last few decades, overpopulation, rapid urbanization, industrialization, and land use changes have been responsible for deforestation [2,20] which are major concerns in modern life.The pH of the collected samples ranged from 6.8 to 9.4 indicating neutral to alkaline conditions with average pH of 7.76.The study area lies within the Madhupur Tract (representing pH strong to slightly acidic).However, the reasons for a higher pH value might be for washing, bleaching, and mercerizing wastewater production from industries and mixing to the surface water sources and another reason might be the presence of biodegradable organic compounds that makes the water alkaline [21,8].This wastewater is mixed with the nearest water sources by channels and increases the base saturation.
EC is an estimate of the total amount of dissolved ions in water.The EC value is comparatively higher if the effluents from industries are mixed with water before getting enough time to dilute, or if construction wastes or municipal drainage lines ended at the water sources.A higher EC value is not suitable for aquatic life or for irrigation [8].From the collected samples, the average EC value was measured 680.975 µs/cm ranging from 8.5 µs/cm to 2000 µs/cm.The range is larger because of different sources of waterbodies such as from different type of industries.At the upazila level, the maximum average EC value was observed in Kaliakoir (1423 µs/cm), and the minimum was observed at Kapasia (225.54 µs/cm).The TDS value ranged from 20 to 1352 mg/l in the study area.The highest average TDS (746.5 mg/l) was observed in Kaliakoir and the lowest average TDS (114.03 mg/l) was observed in Kapasia upazila.The maximum desirable TDS value recommended by [22] is 500 mg/l and the maximum permissible limit suggested by [23] is 1000 mg/l.Except for Kaliakoir, the TDS value of all the upazila was found within the desirable limit.
Dissolve Oxygen (DO) refers to the amount of molecular oxygen dissolved in water.DO value indicates the suitability of water for aquatic life.The higher the DO value, is more suitable for aquatic life.DO value below 5 indicates that aquatic life is under stress [24][25].The average Dissolve oxygen (DO) in the study area was 5.25 mg/l.At the upazila level, the maximum average DO was observed in Kapasia (5.91 mg/l), and minimum DO in Kaliakoir (4.65 mg/l).Average DO was found above 5 mg/l in the samples from Kapasia, Kaliganj, and Sreepur.According to [7,[26][27], the acceptable DO for domestic use and aquaculture can be considered 4.0-6.0mg/l.From the study of physicochemical properties, upazila Kapasia was found better in terms of physical properties of water such as DO, Temperature, pH, and TDS.[28] reported that most of the industries are located in Kaliakoir and regularly discharge huge amounts of effluents and wastewater.These wastewaters directly enter the nearest river system (Turag and Bangshai) and pollute the river water.
Several heavy metals are available in trace amounts in the environment.Although some trace metals are essential (Fe, Cu, Zn, and Mn) and some are non-essential (Co, Ni), and some are toxic (Pb, As, Hg, and Cd) but the exposure of heavy metals to an elevated amount is harmful to plants, animals and ultimately for human health [29].Being non-biodegradable, these elements persist in the environment for à longer time and are biologically magnified through the food chain [30].However, if these trace elements are ingested in large quantities for a longer period of time, then they affect deadly to the neurological system (Co, Cu, Cr, Ni), kidney, liver (Pb, Cu, Cd), bones, teeth (Ni, Cd, Cu, Cr), skin and so forth by heavy metals and their carcinogenic and toxic effect.Agricultural production with contaminated water increases the accumulation of toxic metals in the crops and ultimately bioaccumulation is occurring through the food chain.Some of these metals are carcinogenic.Currently, the number of cancer patients in Bangladesh is increasing due to the bioaccumulation of toxic and heavy metals in the body [31].Food safety and crop quality are closely related to heavy metal pollution in the soil and water environment [32].
Among the studied 60 samples in the Gazipur district including all five studied upazila, cadmium (Cd) concentration varied from 0.76 to 80.53 µg/l.However, at upazila level, the maximum cadmium concentration (41.28 µg/l) was observed in Kapasia and the minimum was observed in Kaliganj (23.6436 µg/l).Cadmium is used in different industries like plastic, steel (as metal), batteries (as compounds), etc.The main source of daily exposure to cadmium is food through which the daily oral intake is 10-35 µg.In humans, the kidney is the main target organ for cadmium toxicity [33] where primarily cadmium accumulation occurs and has a long biological half-life of 10-35 years.The.The U. S. Environmental Protecting Agency has set a standard value of Fe 300 µg/l [34].In the study area, maximum average concentration of Fe (3531.6 µg/l) was observed in Sreepur upazila.Except Kaliakoir, the rest of the upazilas, have a Fe concentration >700 µg/l.
In the Gazipur district (all studied upazila), lead (Pb) concentration varied from 1.68 to 1338 µg/l with an average of 649.88±444.76µg/l.At upazila level, the average Pb concentration was found highest in Kaliakoir (925.6917µg/l) and lowest in Kaliganj (117.7425µg/l).The primary source of lead is IOP Publishing doi:10.1088/1755-1315/1297/1/0120878 plumbing in buildings and service connections.Water with low mineral content and high acidity corrodes pipes and fixtures [35].Lead is principally used in the production of lead-acid batteries, alloys, and solders, as antiknock and lubricating agents in petrol.Bangladesh Standards for Industrial Effluents sets a standard for Pb 10 µg/l [36].
The maximum Mn concentration of 477.8625 µg/L was observed in Kaliakoir upazila.Manganese (Mn) is mainly used in the manufacture of iron and steel alloys, and different manganese compounds such as sodium and potassium permanganate are ingredients in various products used for bleaching, cleaning, and disinfection.Nickel (Ni) is a nutritionally essential trace and naturally occurring element, that is used for the production of nickel alloys and stainless steel.Among the studied 60 water samples only 4 samples were found to have Ni.Among them, one sample was from Kaliakoir (5.9 µg/L), one from Sreepur (1.81 µg/L), and the rest 2 were from Kaliganj (119.4 and 45.57µg/L).
The average Cu concentration in the studied samples was 5.67 µg/l.At the upazila level maximum average Cu concentration was found in Kaliganj (14.205 µg/L) followed by Sadar (6.29 µg/L), Kaliakoir (3.893 µg/L), and Sreepur (3.0458 µg/L) upazila.In Kapasia Cu concentration was below detection level.Cu is mainly derived from agricultural activities i.e., fertilizer, pesticides, feed additives for poultry and livestock for disease control, etc.For these reasons, Cu content is generally found in higher concentrations in the farmland [37,32].
The maximum concentration of Ca (29197.25 µg/L) and Mg (8142.833µg/L) was observed in Kaliganj and the minimum concentration was observed in Sreepur upazila.For Na, the maximum concentration was observed in Kaliakoir (11230.17µg/L), and the minimum concentration (8572.333µg/L) was observed in Kapasia.According to the U.S. Environmental Protecting Agency, the recommended limit for Cd, Pb, Cr, and Ni in wastewater effluents are 10, 6, 50, and 20 µg/l, respectively [38].By exposing the polluted water people suffered from different health issues like waterborne diseases, skin diseases, and respiratory diseases.[9].
From the above discussion, it is quite clear that the surface water of the study area is deteriorating due to unplanned industrial development and indiscriminate discharge of effluents from different industries, and unoptimized use of agrochemicals.It cannot be denied that industrialization enhances employment status, increases income, improves living status, and accelerates the country's economic development.Thus, effective wastewater treatment and reuse is highly recommended.

Conclusions
More than half of the samples (53%) were found smelly.53.3% of samples were turbid and 20% were found black in color.Among five upazila, the maximum average temperature (35.20 0 C±2.63),EC (1423 µs/cm), TDS (746.5 mg/l), the maximum average concentration of Mn (477.8625µg/l), Pb (925.6917µg/l), and Na (11230.17µg/l) were observed in Kaliakoir upazila.Conversely, the values of different parameters such as temperature, pH, TDS, EC, etc. were found lower in Kapasia.Dissolved oxygen (DO) was found above 5 in the samples from Kapasia, Kaliganj, and Sreepur.The pH was above 7 at all the upazila.
Based on the study, it is concluded that the concentration of different physicochemical parameters in the surface water of the study area is above the WHO standards in most of the samples.The situation is deteriorating due to unplanned industrial development and indiscriminate discharge of effluents from different industries.For any country, industrialization enhances employment status, increases income, improves living status, and accelerates the country's economic development.Thus, effective wastewater treatment and reuse is highly recommended.
The findings of the study will be helpful for the local people by supplying information on the current status of water quality along with the situation of heavy metal contamination.The findings of this study will be helpful for environmental restorationists and local policymakers.

Table 1 .
. Physicochemical properties of water samples of the five upazilas of Gazipur district

Table 2 .
Upazila wise average concentration of heavy metals (μg/l) and some elements in surface water