Introduction

The tannery industry has shown remarkable extension and increasing pollutants to the aquatic environment during the last three decades. Total hardness (TH), biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), calcium, sodium, potassium, chloride, sulphate, and chromium are some of the component present in tannery effluent. The majority of underdeveloped nations do not treat the tannery effluents before they are dumped into the water supply. ^1,2 The survival of aquatic species that breathe through their gills will be harmed by high BOD levels, while high COD levels indicate that the wastewater is hazardous and contains organic material that is resistant to biological processes. Eutrophication may result from the high levels of electrical conductivity (EC) and nitrogen, which are hazardous to aquatic species^3,4.

One of the main new environmental issues in the production and disposal of chromium-contaminated sludge is the tanning sector. Nearly three thousand tonnes of chromium are emitted into the environment each year from tanneries in India, with a level of 3000-5000 mg/L in the aqueous effluent⁵. While the toxicity of a substance to small animals, fish, or other wildlife can be assessed by simply subjecting a small number of them to varying doses of contaminants in a laboratory setting. The most popular method is to expose animals that can be produced for commercial purposes and made widely available to pollutants that are of concern to humans. The indestructibility of heavy metals during bioremediation, unlike organic contaminants, and their negative consequences as pollutants are two of the most significant factors.

As industrialization grows, untreated garbage is dumped into aquatic environments, contaminating natural water with different metals and cause harmful impacts⁶. Since heavy metals are not biodegradable, understanding how they are absorbed, distributed, and remain in biological tissues is essential⁷. The most popular tanning agent is chromium. Because chromium is harmful, it must be determined in environmental sample because it is used to tan about 90% of all leather manufactured. Even though it is thought to be necessary for mammals to maintain metabolism, its biological, geochemical, and toxicological properties differ greatly from one another^8,9. The tanning process creates an extremely offensive-smelling waste that also contains a significant amount of salts, including chromium, sulphur dioxide, ammonia chlorides, and other salts. The wastewater has been dumped to open land or into waterways, heavily contaminating them with hazardous compounds and suspended and dissolved pollutants.

The aquatic organisms may take up pollutants from sediments, water, suspended particle and food items. In addition to fish infections, other factors that contribute to fish mortality include deteriorating water quality, industrial effluent, metallic contaminants, and pesticide residues. Fishery experts are of the opinion that the continuous discharge of persistent industrial pollutants is likely to cause serious damage to fishes in view of their toxic effect on respiration, growth, reproduction, spawning behaviour, egg mortality and fish survival^10,11. Channa punctatus, a freshwater fish, was chosen for the inquiry primarily because it is a crucial biological indicator of freshwater quality and is impacted by environmental deterioration on a global scale^12,13.

The significance of present research lies in addressing these gaps and contributing to a more comprehensive and up-to-date understanding of the issue. Researchers can provide a more accurate assessment of the environmental and public health risks associated with tannery effluents, as well as the efficacy of treatment technologies and the impact of regulatory measures. This knowledge can inform policy decisions, support sustainable practices in the tanning industry, and protect both aquatic ecosystems and human communities from the harmful effects of tannery effluents.

Material and Methods

Study Area: In the present study, the selected area was Sempatu in Tiruchirappalli district, which is situated between 10^o10’ and 11^o 20’ North and 78^o 10’and 79^o 0′ East in the centre part of the Tamil Nadu. There are about fifteen tanneries situated in this area among them the NM tannery is selected for the present research work. Untreated sewage and effluent from the tannery business contaminate the water

Collection of Samples: Samples were taken straight from the collection tank in a plastic container, transported to the lab with due care, and held at 20^oC for additional examination in order to determine the contamination status of tannery effluent water. A total of 18 months were spent collecting the water samples see in Figure 1.

Physicochemical Parameters: The samples’ physicochemical characteristics, including things like colour, odour, water temperature, pH, EC, TSS, TDS, BOD, COD, TH, calcium, sodium, potassium, sulphate, chloride and chromium. Colour: The colour of the site’s effluent water samples was visually assessed and noted. Odour: The odour of effluent water samples from the site was detected by smelling directly from water cans. Water temperature: Using a field thermometer, the temperature was determined at the time of sample collection. pH: The pH meter (Model Eltek Mx 61-A) was calibrated using different standard (pH 4.0, 7.0 and 9.2) solutions, thereafter the pH of samples were recorded. EC: It was measured using an EC metre from Elico, India; EC is a numerical indication of a sample’s capacity to conduct an electric current in soil and water.

TSS and TDS: The TSS and TDS were calculated by using standard procedure.

TSS or TDS = [(A-B) X 1000] / Sample volume (mL)

Whereas: A=Weight of filter and residue (g), B=Weight of crucible (g) and 1000 is constant.

BOD: The relative oxygen requirement of wastewater is assessed using standardised laboratory procedures in the BOD test. In this study, we adopted Winkler’s method¹⁴. COD: The COD is a measurement of the amount of organic material in the sample that is capable of being oxidised by a potent chemical oxidant¹⁴. TH: Using American Public Health Association Colour Scale techniques, the total hardness was determined and monitored¹⁴. Calcium, sodium, potassium, and sulphate: Using a flame photometer (Model Chemito-1000) and the Jackson method, the calcium, sodium, potassium, and sulphate of the samples were determined¹⁵. Chloride and chromium: The chloride and chromium contents of the effluent were estimated by argentometric method^14,16,17.

Results

Physico-chemical Parameters: Table 1 shows the information that was gathered regarding the physicochemical quality of the tannery effluent water samples.  The visually observed colour of the effluent water samples from the site are shown in Table 1. The odour of tannery effluent is found to possess sewage smell throughout the period of study (Table 1). The pH of aqueous solution represents the concentration of H+ ions. During the study period, the effluent’s pH fluctuated from 4.4-8.8, mean value 7.01±0.491 (Table 1 and Figure 1). The pH range was found to be acidic to basic, not good for the aquatic life. The water temperature of tannery effluent was found to vary from 29.3-38.0^oC, mean value 31.21 ± 1.45 (Table 1 and Figure 1). The minimum and highest recorded temperatures occurred in January and April, respectively. The EC of effluent water samples were found to vary from 1148-2905 micro/ mho/cm, mean value 2378.61±124.27 (Table 1 and Figure 1) during the study period. The values increased between August 2007 and June 2008, while the TSS in samples of tannery effluent water throughout the study period ranged from 710-1623 mg/L, mean value 1199.39±137.99 (Table 1 and Figure 1).

Figure 1: show PH, Temp and EC values of tannery effluent. Click here to view Figure

The TDS was high in all months, ranged from 7049-8500 mg/L, mean value 7669.17±141.99 (Table 1, Figure 2). The BOD value of samples ranged started 1060-1664 mg/L, mean value 1347.17±73.68 (Table 1 and Figure 2). High BOD values were recorded during the study period, which indicates the quality of tannery water was unfit for the use of people. The water samples’ COD values ranged from 3025-4982 mg/L, mean value 4029.83±163.56 (Table 1 and Figure 2). High COD values were recorded during the study period that indicates the bad quality of tannery water for any humans use. The TH of water samples were found to be ranging from 2200-3417 mg/L, mean value 2794.50±136.49 during entire period of research (Table 1 and Figure 2). Because of how hard it is, no home use is possible with the water. The total hardness of the samples was discovered to be extremely high during the post-monsoon period. Among the chemical properties especially the dissolved substances such as calcium and sodium was encountered in the water samples of the tannery effluent (Table 1). The calcium was found to be high from March to June 2008 (<800 mg/L) while it was (>800 mg/L), mean value 713.83±50.33 during the rest of the research time (Table 1 and Figure 2). Sodium was bring into being to be high (1200-1805 mg/L), mean vale 1634.83±75.06 in the month of June 2008 (Table 1 and Figure 2).

Among the chemical properties, especially the dissolved substances like potassium and chlorides were encountered in the water samples of the tannery effluent (Table 1). The potassium (Table 1 and Figure 2) was also high during May 2008 (112 mg/L) and low in the month March of 2007 (38 mg/L), mean value 78.44±9.05. The chloride range (Table 1 and Figure 2) was from 2330-4210 mg/L, mean value 3334.22±241.92 during the time of research, being high in the month of June 2008. Among the chemical properties especially the dissolved substances like sulphate and chromium was encountered in the water samples of the tannery effluent (Table 1). The sulphate content (Table 1 and Figure 2) varied from 830-1008 mg/L, mean value 952.17±15.06 respectively. The sulphate content was found to be high in January (1005 mg/L) and June (1008 mg/L) months respectively. The analysis of various metal content showed that the range of chromium was started 1.17-1.52 mg/L, mean value 1.327±0.132 (Table 1, Figure 2). The most significant behavioural pathology of Channa punctatus included restlessness, erratic darting movements occasionally, movement displays towards the aquarium’s bottom, and gradual loss of buoyancy that resulted in fish floating upside down and horizontally with their open mouths and gill opercula (Figure 2). It is found that the symptoms and mortality rate was increased with the increase in the dose and the pathological incidence was directly related to dose and duration of exposure. It indicate the loss of equilibrium due to Irregular and erratic movements that might be due to the damage in the brain associated with the maintenance of equilibrium. The symptoms were depending upon the nature of the toxicant and the dose dependent manner.

Figure 2: Shows TSS, TDS, BOD, COD, TS and Ca values of tannery effluent. Click here to view Figure

Table 1: Physico-chemical parameters of Tannery effluent collected from Sembattu area, Trichy, Tamilnadu. Click here to view Table

Figure 3: Shows Na, K, CI, S and Cr values of the tannery effluent and Effect on Chenna punctatus Click here to view Figure

Discussion

One of the most terrible ecological crises to which we are currently vulnerable is environmental pollution. India, which ranks seventh among the world’s industrialised developing nations, has a robust industrial infrastructure in a number of sectors, including chemicals, power, nuclear energy, petroleum, plastics, food, and pesticides¹⁸. The issue of environmental degradation is not limited to industrialised nations; it is now spreading to India¹⁹. The toxicants and other unfavourable chemicals eventually enter water bodies with rainwater and degrade the water media, creating an imbalance in the environment that causes ecosystems, particularly aquatic ones, to slowly deteriorate and result in unabated aquatic fauna mortality²⁰. The results of the current research demonstrate that the tannery effluent had a brownish and blackish appearance and an unpleasant scent. A similar study found that the tannery wastewater leaves behind a dark colour and pungent smell²¹.  In a similar vein, Jamal²² findings showed that a significant proportion of contaminants might transfer colour and odour to the receiving water. The wastewater was described as brownish and odourless in another study²³.

Aquatic toxicity testing is now an essential step in the process of determining environmental danger and the evaluation of toxic compounds since the aquatic environment serves as the final sink for all contaminants. International organisations, such as the Environmental Protection Agency¹⁹, have advised understanding a variety of bioassays to evaluate the ecotoxic hazards to non-target creatures and their surroundings. Pollution’s toxic effects result from disruption of an organism’s normal morphological and physiological processes. Pathogen, pesticide, and heavy metal stress all cause changes in the biochemical components of tissues, and these changes follow a certain pattern. An organism’s metabolic activity shows how biochemical energy is used to combat toxic stress²⁴. The use of fish as bio indicators for detecting pollution in the aquatic environment is common because fish are known to bio collect, concentrate, and biomagnify toxicants in their tissue²⁵.

The tannery effluent’s pH was found to be lower range. The water temperature level was found to be higher range. Similarly, Rabah and Ibrahim²⁶ reported a similar average pH of tannery effluent. This means in such level of pH the counts of microorganism high because most of them blooms well²⁶. According to a study, Varadarajan and Sneha ²⁷ The reported pH of the tannery effluent was 7.5. Therefore, The tannery effluent has a pH that is just barely alkaline. Fish do not thrive in the aquatic environment when tannery effluent with an alkaline pH is dumped into lakes, ponds, rivers, and other natural sources. The presence of carbonates, bicarbonates, hydroxides, borates, silicates, and phosphates in tannery effluent may be the cause of the substance’s alkaline nature^{28, 29}.

In this investigation, the level of EC in the effluent was found higher range, whereas the acceptable limit is 1500, this shows that the tannery effluent had a larger discharge of chemicals in the form of cations and anions. This might be caused by the tannery effluent’s high levels of acid-base and salt²². The tannery effluent’s chelating capabilities are altered by the higher EC, which also affects how readily available free metals are to aquatic species³⁰.

One important metric used to assess the effects of tannery effluent on water contamination is the estimation of BOD. Due to the significant amount of organic matter present, the effluent in the current study had found high levels of BOD. According to Noorjahan²¹ a high point of BOD was experimental in the tannery effluent. In another similar study high level of BOD was reported³¹.

To estimate organic matter the best method is COD test and total oxygen demand, determination by rapid test in the existence of organic matter. In current research, the level of COD was recorded higher range. The study of Noorjahan²¹ reported higher range of COD from the tannery effluent. The results of present study support the previous study³². Due to the high concentration of organic molecules in the effluent, which may not be affected by bacterial breakdown, the quantity of COD may have increased³³.

In the current study, the level of TDS was recorded for tannery effluent higher range value. Similarly, Noorjahan²¹ reported the higher range of TDS value. Similar findings from a different study with high levels of physicochemical factors, including TDS, COD, TSS, chloride, sodium, nitrate, pH, the high colour intensity in tannery effluent³⁴. TDS are mainly due to carbonates, bicarbonates, phosphates, sulphates, nitrogen, calcium, chlorides, iron and potassium³⁵. The high levels of TSS and TDS may be caused by the presence of insoluble organic and insoluble inorganic materials in the tannery effluent³⁶.

The level of TSS in the tannery effluent was measured in the current investigation found higher range, which exceeded the permissible levels less than two hundred. The tannery effluent becomes murky due to these TSS contaminants. The quality of the hides and skins treated in the tannery largely determines the composition of TSS found in tannery effluent²⁹. When compared to the allowed limit of two hundred for effluent discharge, the TSS level in the effluent was found to be greater. High TSS concentrations harm aquatic species, limit the variety of life in the aquatic system, and hasten oxygen depletion³⁷. A report claims that charges on the surface of small particles in the tannery effluent force the bigger TSS particles to remain suspended³⁸.

The studies shows TH of tannery effluent level was found high range was observed, which exceeded the permissible limit of six hundred. In the investigation, the level of calcium was found higher in the effluent, although the permissible limit is 75-200. The level of sodium was recorded higher range in the effluent, however the acceptable limit two hundred. In the present research, the higher range of potassium was found in the effluent, whereas the permissible limit is less the 8.3.  This is lower than the previous study²³. In the previous research, it was discovered that the soil watered with tannery water had significant levels of exchangeable calcium, sodium, and potassium²³.

In the current study, the level of chloride was observed higher range in tannery effluent, whereas the permissible limit is two hundred. Chlorides are added to tannery effluent, which slows the growth of aquatic organisms and, at high concentrations, can cause cell structure to break down. Rain-induced soil chloride loss causes it to re-enter the ecosystem and could end up in groundwater³⁹.

The level of sulphate was found higher range in the effluent samples, whereas the permissible limit is two hundred. The level of sulphates were exceeded the limit. Sulphate is a component of tannery effluent, according to the earlier study, and it results from the use of sulphuric acid or goods with a high sulphate level³⁹. Similar to this, Vijayanand⁴⁰ reported that the association of organic matter, calcium, magnesium, carbonates, bicarbonates, sulphates, chlorides, and nitrates increases the hardness of water.

One of the most serious new environmental problems brought on by wastewater treatment by-products is the disposal of chromium in the tanning industry. Chromium, iron, nickel, cadmium, zinc, manganese, and copper are among the elements that are contaminating the aquatic environment at increasing quantities in the tannery effluent. In the present study, the level of chromium was found higher range, although the permissible limit is 0.05. According to Rabah and Ibrahim’s analysis, the tannery effluent contained (0.26) milligrammes of chromium²⁶. High levels of chromium concentration are still hazardous to aquatic organisms and have been shown to change their food chains⁴¹.

In this study, Channa punctatus exposed to the tannery effluent at different concentrations showed severe and varied pathological symptoms depending upon the dose and nature of the toxicant. The most significant behavioural pathologies was restlessness, sporadic erratic darting movement, migrating to the aquarium’s bottom, rapid opercular motions, and gradually losing buoyancy, which led to fish floating upside down horizontally with their open mouth and gill opercula. Similar behavioural responses of Cyprinus carpio to industrial effluent were observed^42,43. Irregular and erratic movements indicate the loss of equilibrium that might be due to the damage in the brain associated with the maintenance of equilibrium.

Conclusion

The current analysis has confirmed that the tannery effluent’s physicochemical characteristics exhibit high concentrations of EC, TSS, TDS, BOD, COD, TH, sodium, calcium, chlorides, sulphates and chromium  that exceed the permissible levels. The physicochemical analysis showed that the morphological changes in the appearance of fish within tannery effluent water samples are because of variation in the salinity, odour and pH. Large volumes of mucous and excrement were discharged from the body, and behaviour changes like widely opened mouths, erratically moving operculums, and frequent up-and-down motion were noticed. The skin was also a poor shade. The current investigation thus showed the detrimental effects of tannery effluent on the aquatic ecosystem.

Acknowledgement

The authors thankfully acknowledge support from the NM tannery, Sembattu Pudukkottai, Trichy, Tamil Nadu to bring out the samples for do research. The authors would also like to articulate special appreciations to the Department of HGMB, BU, India.

Conflict of Interest

The authors declare that they have no conflict of interest.

Funding Sources

No funding source 

Authors’ Contribution

PK drafted the original manuscript and sample collection; MY provided critical suggestions;
SK and JI edited the manuscript. All authors read and approved the final manuscript.

Data Availability Statement

Not applicable

Ethics Approval Statement

Not applicable

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