In the life support system, water is a crucial component. It is a vital resource that sustains all forms of life, including humans, animals and plants. Water is used for drinking, cooking, cleaning, irrigation, industries and power generation. However, the availability of clean and safe water is becoming a major concern due to pollution and overuse.

This study investigates the quality of drinking water in and around Hojai district by analyzing various parameters crucial for human health. The various purpose such as parameters examined includes fluoride concentration, Nitrate levels, iron concentration and water hardness. Concerning contaminations, fluoride concentrations range from 0.01 mg/lt to 4/8 mg/lt, with implications for dental health. Nitrate concentrations in some rural areas are   found above 2 mg/lt , unfit for human consumption, Iron levels found in all sources range from  5.1 to 10,05 mg/lt, influencing taste and causing potential health issues, water hardness ranged from 50 mg/lt to 196 mg/lt, affecting  taste and potentially contributing to scaling issues in pipes and appliances.

Hojai district with its head quarter in Hojai town is spread across 1685 sq. kms within 26⁰00^/North latitude and 92⁰87^/ East longitude.  People of this district and around this district faces many problem due to surface water and groundwater pollution, flood is one of the main reason behind this problem.

The study’s goal is to warn the residents of the Hojai district not to drink contaminated water , which was validated by measurements of iron. Fluoride, and nitrate. The aim of the present study is to measure fluoride, nitrate, iron and hardness of some places in and around Hojai district and toxic effect of these .

Water bodies that support life are severely impacted by pollution and environmental degradation caused by human activities like industrialization and agriculture .

Water source in Kamrup district are heavily polluted with iron and fluoride. It is observed by Sutapa Chakrabarty and Hari Prasad Sharma(2011) [1]..  Iron was estimated by using Atomic Absorption Spectrometer (Perkin Elmer AA 200). Fluoride was measured by the SPADNS method at 570nm and Nitrate content was measured by the phenol-disulphonic acid method at 410nm using a UV–VIS spectrometer, Shimadzu 1240 model.

Available literature shows that groundwater in Assam are highly contaminated with iron[6] . The occurrence of fluoride contamination in Darrang, Karbi Anglong, and Nagoan districts of Assam in the form of fluorosis were already reported[7],[8],[9] . High level of fluoride and iron distribution in groundwater sources of certain districts of Assam has also been observed[9],[11]. The health problems arising as a result of fluoride contamination are far more widespread in India. Nearly 177 districts have been confirmed as fluoride-affected areas. Nitrate contamination in groundwater arises from intensive agriculture and use of chemical fertilizers, improper and unhygienic sanitation, landfills and irrigation of land by sewage effluents[10] . Nitrate (NO₃ ^- ) con nverted from nitrogenous fertilizers leaches readily to deep soil layers and ultimately accumulates into the groundwater system

Enetimi, Angaye and Okogbue (2016) conducted field research on physio-chemical quality assessment of river Orashi in Eastern Niger Delta of Nigeria and asserted that river quality assessment is essential to the sustenance of aquatic biodiversity, the environment and public health. They also indicated that mild anthropogenic activities have caused changes in parameters assessed such as iron, PH, magnesium, calcium with increase in total dissolved solids. Furthermore, they were of the opinion that if mitigation measures are not put in place, anthropogenic effects could rise beyond tolerant or permissive limits, which could affect the sustenance of the river. Bellingham (2012), in his study on physicochemical parameters of natural waters opined that the concentration levels of Pb, Cd, Fe and Mn were in surplus because fertilizers and pesticides used for agricultural activities, manufacturing land-use along the watershed area and other anthropogenic activities were the major causes for the elevated concentrations of the metals in rivers.

The groundwater samples were collected in  three seasons viz.  Pre-monsoon  season  (February-May), Monsoon season (June-September)  and Winter (October-January) starting from Feb2023  to Jan,2023. Water samples were collected in precleaned polythene containers of 5 liters capacity from   different sources in 15 locations. The  sources  includes  tube wells (from TW1 to TW20), ring wells (from RW1 to RW13), and supply water. Random selection was used to choose individual water samples, which were then combined in sterile, clean 5-litre polythene cans, rinsed with diluted HCl to create a representative sample, and kept in an ice box. During transit to the lab, samples were shielded from the sun, and metals were examined in accordance with standard protocol.

Nitrate content was measured by using a UV–VIS spectrometric technique (Hitachi 3210) by measuring the absorbance of the phenol-disulphonic acid nitrate complex at 410nm. The process typically involves a colorimetric analysis using chemical reagents that form a colored complex= with nitrate ions specifically using the Phenol Disulphonic acid (PDSA} method. The methodology involves a series of precise chemical reactions and measurements. Initially,  a water sample is mixed with a known amount of KNO, to introduce a nitrate standard for calibration. The sample is then treated with PDSA reagent, which reacts with nitrate ions to  form a yellow-colored complex. To ensure complete reaction and accurate measurement, potassium hydroxide is added to adjust the pH, and silver sulfate is introduced to remove any interfering substances by precipitating them. Following this, the sample is subjected to a color development phase, and EDTA is used to complex any residual metal ions that might interfere with the colorimetric analysis. After colour development, the intensity of the yellow colour is measured using a spectrophotometer of approximately 410 nm.  The concentration of nitrate nitrogen and nitrite in the sample is determined by comparing the absorbance of the sample to a calibration curve prepared from standard nitrate solution.

Iron in water samples were estimated estimated by phenanthroline method. Ferrous iron chelates with 1,10- Phenanthroline at 3.2 to 3.3 to form an orange-red complex. The intensity of this  colour is proportional to the iron content in the sample  and the later was read on a UV - spectrophotometer  (Hitachi 3210) operating the instrument at 510 nm in  photometry mode calibrating against a standard and a  blank.

Fluoride was measured spectrophotometrically by the SPADNS method at 570nm.  the process  involves a colorimetric analysis that provides a quantitative measurement of fluoride ions.  Initially, a water sample is treated with SPANDS (Sodium Phenolphtalein Phthalein) reagent,  which reacts with fluoride ions to form a colored complex. The sample is first adjusted to an  appropriate pH using a buffer solution to ensure optimal conditions for the reaction.  The addition of SPANDS reagent to the sample produces a blue-colored complex in the  presence of fluoride ions. The intensity of the blue color, which is directly proportional to the  fluoride concentration, is measured using a spectrophotometer at a specific wavelength.  typically around 570 nm. The concentration of fluoride in the sample is then determined by  comparing the absorbance of the sample to a calibration curve prepared using known fluoride  standards.

The table shows the average values of iron, fluoride and nitrare in mg/lt for one year, spanning from February,2023 to January,2021, in three distinct seasons: Premonsoon, monsoon and winter.

The analysis of total hardness across different water sources revealed notable variations River water exhibited moderate hardness, reflecting the influence of natural mineral content and surrounding geology. Groundwater showed high hardness, attributed to its extended contact with mineral-rich geological formations. Pond water demonstrated variable hardness levels, influenced by local mineral content and organic matter. Overall,the calcium levels in these waters are generally acceptable for drinking purposes and fall within standard data limit.

Concentration varied across water sources: river water had moderate levels, groundwater showed high calcium hardness,  and pond water varied widely. Overall, the calcium levels in these waters are generally acceptable for drinking purposes and fall within standard data  though treatment and source conditions influence their suitability.

Magnesium level varied across water sources: river water had moderate levels, groundwater shows high hardness. All measured magnesium levels are within acceptable drinking water standards.

CALCIUM AND CALCIUM HARDNESS 

To measure calcium and calcium hardness begin by preparing the water sample, ensuring it is well-mixed and filtered if needed. Add a buffer solution to the sample to maintain a stable pH, typically achieved with NaOH Introduce murexide, a calcium indicator that changes color in the presence of calcium ions. Titrate the sample with a standardized sodium EDTA solution, which binds to the calcium ions. The endpoint of the titration is indicated by a color change of the murexide from pink to blue. Calculate the calcium hardness based on the volume of sodium EDTA used, with results expressed in milligrams per liter (mg/L) as calcium carbonate  (CaCO₃). This method effectively quantifies both the concentration of calcium ions and the total hardness of the water sample.  This method provides a specific measure of calcium and calcium hardness by utilizing the selectivity of  murexide and the chelating ability of EDTA in a controlled pH environment.

Calculation: 

Calcium (mg/L) = T x400.5 x 1.05/V

Calcium hardness as CaCO₃, (mg/L) = Tx1000x1.05/V

Where, T = volume of titrant. mL

V= volume of sample. mL.

The process begins with the preparation of a buffer solution, which is essential for maintaining the pH at a level where EDTA effectively binds with the calcium and magnesium ions. Typically, a pH range of 10 to 11 is maintained using ammonia or a similar buffer.

First, a water sample is treated with hydroxylamine hydrochloride, which reacts with any interfering metal ions and helps to stabilize the s ample by eliminating potential interferences. Next, a small amount of Eriochrome Black T is added to the sample. EBT acts as an indicator, changing color upon binding with calcium and magnesium ions. In the presence of these ions, the solution turns red. The actual titration process involves adding a standardized EDTA solution to the sample. EDTA, a chelating agent, reacts with the calcium and magnesium ions, forming stable complexes. As EDTA is added, the red color of the EBT complex fades, and the endpoint is reached when the solution turns blue, indicating that all the calcium and magnesium ions have reacted with the EDTA. The volume of EDTA solution used to reach this endpoint is then measured, By applying the known concentration of the EDTA solution and the volume used in the titration, the total hardness of the water can be calculated, typically expressed as mg/L of CaCO_3.

This method provides an accurate measure of total hardness by quantifying the concentration of calcium and magnesium ions through complexometric titration, using EDTA as a chelating agent and EBT as an indicator for endpoint detection.

Total hardness (as CaCO₃, mg/L) mL= C x D x1000/ml of sample

 Where, C mL of EDTA required by sample for titration

 D= mg CaCO₃ equivalent to I mL EDTA titrant (l mg for 0.01M EDTA used here.)

METHODOLOGY FOR THE MEASUREMENT OF MAGNESIUM HARDNESS AND

MAGNESIUM

With both total hardness and calcium hardness values obtained, magnesium hardness is calculated by subtracting the calcium hardness from the total hardness.

Calculation:

Total Hardness (mg/L as CaCO3)= Total hardness( mg/L as CaCO3) -Calcium Hardness(g/L-as CaCO3)

Not only in Hojai but also in other places, the risk of ring mineral contamination has grown in recent years due to an increase in groundwater usage. Although fluoride is a naturally occuring mineral in water, its quantity has increased  for a number of reasons. The alteration in climate patterns is one of them. Long dry spells have led to less rain water seeping into the ground and replenishing the groundwater table. Indiscriminate cutting of trees – for construction purposes and otherwise – has added to the problem. With ample rainfall, the fluoride concentration in water remains normal but with lessening rain, the concentration goes up. Another major reason is the increase in drilling activity for hand pumps and borewell pumps. With the lowering of the water table, the drills are also going deeper, thereby closing in towards the granitic rocks that are rich in minerals like fluoride. Therefore, fluoride is making inroads into the water pumped up. Laboratory facilities for testing water samples has been upgraded in four districts (Karbi Anglong, Nagaon, Hojai, Kamrup), and ring wells have been constructed in Karbi Anglong, Nagaon and Kamrup districts for safer drinking water, even as more are coming up. Eleven village panchayats in Hojai district who were sanctioned funds for tubewells, have now been asked to make ring wells instead.  

The nitrate-N contents of water sample were found from  2.02 mg/lt to 7.76 mg/lt in TW  and  3.01 to 5.1 mg/lt in RW. The present study did not record any all season average concentration of nitrate-N above the permissible limit of 10 mg/lt.[4].

 The fluoride contents of water sample were found from 0.01 mg/lt to 4.8 mg/lt in TW  and .01 mg/lt to 0.2 mg/lt. In Tapatjuri and Modertoli the fluoride concentration is found above the permissible limit (WHO limit 1.5 mg/lt).[4]. The presence of Fluoride in drinking water at low concentration is considered essential in guarding against dental caries. However , excess fluoride results in bone diseases, mottling of teeth and lesions of the endocrine glands, thyroid, liver and other prgands.

In every tube well, pond water and ring well water iron is found above the WHO limit. The most of the water sources in the present study area were found to be unfit to consume as drinking water due to this metallic constituent. It was found that the groundwater in the current study area has a heterogeneous distribution of Iron. Excessive consumption may cause hemochromatosis, which can accumulate and cause tissue damage.

This study provides comprehensive  evaluation of water quality of some places in and around Hojai District by analysing Fluoride, Nitrate and Iron concentration. The study also assessed nitrate and fluoride, crucial for understanding the overall safety of the water supply. The tubewell water in the  present study area could not be recommended for direct consumption. According to available statistical data( PHE, Diphu sub-division 2000) at least 20000 children and young people are in the grip of Fluorosis in Assam. As prevention is the only known solution, massive health education is the need of the hour. Treatment of water is required before using the water for drinking purpose. At the same time drinking water may be supplied from the nearby village through pipe line to this twin fluoride affected area in Hojai district. Iron contents of the tube well water were recorded to be higher than WHO recommended value. The iron content in the ring wells is higher than permissible limit so ring well water was found to be unfit from potability consideration. Hardness measurement showed that calcium and magnesium levels were generally within acceptable ranges, with calcium hardness consistently meeting drinking water standards.

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