Quality deterioration of an Indian urban water source near an open dumping site

Historically it is found that urbanization started at the banks of the rivers and the major needs including freshwater, food transportation, and disposal of waste were satisfied. Thus, urban rivers are considered to be one of the most important features in an urban region and sometimes it is considered as an identity of that region (Francis 2012). But with the increase in urbanization, the quality of the urban stretches is deteriorating, which is a critical problem that has to be looked into (Wang et al. 2012). The possible sources for this deterioration include the discharge of sewage and effluents, agricultural runoff, and uncontrolled solid waste dumping near riverbanks (Singh et al. 2004, 2018, 2019; Zavaleta et al. 2021). Urban rivers can also contain a high amount of toxic and hazardous elements like heavy metals (Balaji & Thirumaran (2019). This study evaluates the quality of a river flowing through an urban zone comprising tourist destinations, agricultural areas, industries, residential zones, educational institutions, commercial parks, and a municipal solid waste (MSW) plant, which is now an open dumping site. The river plays a vital role as a host for drinking water in adjacent urban areas. However, according to the Comprehensive Report on Prevention and Control of Pollution in the Kadambrayar River, an Action Plan for Rejuvenation, 2018, the river was found to be polluted, and the pollution stretch was identified. The current study evaluated the pollution intensity in the Kadambrayar River along with the characterization of the dumping site. This study will help to assess pollution so that remedial measures can be taken for the abatement of pollution.

Sampling was performed from the river in the year 2020–2021 during the post-monsoon season at regular intervals. Before sampling, a reconnaissance of the study area was conducted to determine the sampling stations and identify possible pollution sources. Preliminary knowledge of the catchment area is needed before the application of tools to the variables measured for correct validation and interpretation (Alberto et al. 2001).

Eight sampling stations were chosen and grab sampling of water was conducted in triplicate from the cross-section of the river. To analyze the water quality parameters, samples were taken in clean 1-L polypropylene bottles rinsed with deionized water, and for analyzing the coliforms, the samples were taken in separate sterile bottles. The pH, temperature, and conductivity were measured on-site using a portable analyzer (Hanna pH meter; Thermo Scientific, EXPERT CTS Meter). To analyze the dissolved oxygen (DO) and biochemical oxygen demand (BOD), the oxygen was fixed on-site in 300-mL BOD glass bottles and titrated at the laboratory. The collected samples were preserved in an insulated box to prevent any changes in quality and transported to the laboratory. The other quality parameters were analyzed in the laboratory within 48 h of collection, following standard methods (APHA 2012). The reagents were prepared according to standard methods (APHA 2012). The trends of various parameters were compared using secondary data available from the Comprehensive Report on Prevention and Control of Pollution in Kadambrayar River: An Action Plan for Rejuvenation, 2018 (Action Plan for Rejuvenation 2018). A statistical analysis using the Pearson Correlation method for the physicochemical water quality variables was done based on the results obtained.

Grab samples were collected from these stations to determine the presence of heavy metals (As, Cr, Cd, Pb, Hg, and Cu) in the river. Among the heavy metals, As, Cd, Pb, Cr, Cu, and Hg are considered to be important because of the adverse health implications on human health when exposed (ATSDR 2015). Water samples were collected in 500-mL sterile inert bottles from the river, and Van Veen Grab sampler composite sediment samples were collected from the middle and shoreline of the river at stations S0, S1, S5, S7, and S8, representing each part of the river where possible sources of pollution exist (De Groot et al. 1982). The samples were analyzed for the presence of heavy metals using Inductively Coupled Plasma Mass Spectrometry (ICPMS) (Agilent 7700 Series ICP-MS). The spatial distribution of the key results was plotted using GIS to understand the variations in the variables.

Because the present study focuses on the decrease in quality of the river near the dumping site, the characterization of the dumpsite in terms of the leachate characteristics and the composition of waste is necessary. Fresh representative municipal waste samples were randomly collected from the piles of dumped waste at the dumping site. Sampling was conducted at regular time intervals for 3 months in which four samples of 1 kg each were collected from different parts of the dumping site. The samples collected from the raw waste were reduced to subsamples using the quartering method for a representative sample and manually sorted to determine the waste composition (Trulli et al. 2018). Subsamples, each weighing approximately 10 g, were extracted from a representative composite sample to determine moisture content. In addition, the leachate samples were collected in 1-L inert bottles from the pools of leachate formed from the waste at different sites adjacent to the river. There is no proper scientific treatment for leachate at dumping sites. The leachate was analyzed for BOD, chemical oxygen demand (COD), and heavy metals using ICPMS (Agilent 7700 Series ICP-MS).

The values obtained for the various water quality parameters observed in the Kadambrayar River are tabulated in Table 1, in which the minimum and maximum values obtained are compared with the standard limits as per the different agencies. From the statistical analysis using the Pearson Correlation method for the physicochemical water quality variables (Supplementary material, Tables S1 and S2), it was found that there was a strong correlation between BOD, COD, DO, nitrate, ammoniacal nitrogen, and phosphate. Most of the parameters were within the limits, but the most important parameters, such as DO, BOD, and Coliforms (total and fecal coliforms), failed to satisfy the limits at all stations. The presence of the water hyacinth covers considerably influenced the reduction in nutrients, which might be the cause of the low concentrations of nitrate and phosphate, even though the pollution load was high. This causes a decrease in temperature, pH, DO, and nutrients in surface water, thereby deteriorating water quality and threatening aquatic life (Rai & Munshi 1979; Howard & Harley 1997; Güereña et al. 2015; Dersseh et al. 2019). Therefore, this aquatic plant can be used as a bioindicator of pollution (De Laet et al. 2019).

The study has incorporated various standards to compare the values obtained for various variables. Most standard limits were referred from IS 10500:2012 (BIS 2012), which is the Indian standard for drinking water as per BIS and IS 2296:1992 (BIS 1992) which is the Indian standards for surface water quality according to various uses. The WHO (World Health Organization) and ICMR (Indian Council of Medical Research) standards in water are used for Electrical conductivity and Phosphate respectively as the limits were not available in the previously mentioned IS standards.

The high concentration of BOD may be due to the discharge of sewage or effluents into rivers (Penn et al. 2003). From the reconnaissance in the study area, it was observed that the upstream area was a tourist spot and an agricultural rural area devoid of any industries, except for an amusement park. However, the waste from poultry and other farming practices, along with sewage from nearby residential areas, might have resulted from the high BOD. The Edachira drain (stations S6 and S7) flows through the most important part of the city which includes IT parks. Commercial industries, restaurants, and effluents are discharged to rivers where some of the establishments have effluent treatment plants (ETPs). The highest COD of 696 mg/L was obtained from samples from the Edachira drain. The drains transport the effluent discharge to the river, which can affect the water quality (An Action Plan for Rejuvenation 2018). The drain joins the river at the Kadambrayar Bridge (station S5), which flows downward to Brahmapuram, where the open dumping site is located adjacent to the river. As per the details from the study conducted by Abhirami et al. (2021) as of December 2020, 314 tons of waste is generated by Cochin Corporation and transported to Brahmapuram.

Based on laboratory analysis results, the moisture content of different sample wastes in Brahmapuram ranges from 30 to 50%. This could result in a higher amount of leachate (Arunbabu et al. 2017). Paul & Paul (2021) evaluated MSW management in Kochi and reported that the percolation of leachate from the Brahmapuram dumping site polluted the Kadambrayar River. The results obtained by analyzing the leachate BOD, COD, and heavy metals are tabulated in Table 2. In a study by Arunbabu et al. (2017), the presence of metals such as Fe (60.938 mg/L), Cu (0.107 mg/L), Ni (0.531 mg/L), Zn (0.273 mg/L), Pb (0.017 mg/L), Cr (0.125 mg/L), Hg (0.005 mg/L), and As (0.061 mg/L) was reported in the leachate from Brahmapuram in 2015. In the present study, dangerous heavy metals such as arsenic (0.24 mg/L) and chromium (2.74 mg/L) were found. Iron, nickel, and other metals such as mercury, copper, lead, cadmium, and zinc were not found. Other elements include boron, gallium strontium, and titanium. However, in the present study, the concentration of arsenic was approximately four times higher and that of chromium was 22 times higher than that in the previously stated study. The BOD/COD ratio of leachate is considered an indicator of biological treatability, and a high ratio indicates that the leachate should be more treatable (Miller & Clesceri 2002). This study found that the BOD/COD ratio of leachate collected in 2021 was 0.55. ArunBabu et al. analyzed the leachate at the Brahmapuram dumping site in 2015 and found a high BOD/COD ratio of 0.69. The site does not have any treatment facilities for the leachate produced from waste (Arunbabu et al. 2017), and the high ratio highlights the possibility of biological treatment. Ganesan (2017) analyzed the management of solid waste in landfill sites and reported that there is a great environmental threat from the Brahmapuram open dumping site to the Kadambrayar River.

In the Kadambrayar River, heavy metals were found in sediments collected from all stations (Table 4). Five metals were compared to the values in the EPA guidelines, and it is clear that the sediment sample was heavily polluted with Cr, As, and Cu at station S0 near the dumpsite (Table 4), in the order Cr > As > Cu. Other metals, such as lead and cadmium, were less than the given limits as per the EPA guidelines for a non-polluted scenario (Ogbeibu et al. 2014). At other stations upstream, the concentrations were negligible compared to the downstream concentrations.

Thus, it can be understood that upstream the presence of arsenic and chromium was negligible and safe limits compared to downstream, which indicates the contribution of the uncontrolled open dumping site as a major source of heavy metals to the river causing heavy metal pollution. Heavy metals in sediments enter the food web through benthic fauna in the ecosystem. The heavy metals thus accumulate over time and during resuspension, and the metals can be transported further, thus acting as a good source of contamination (Chowdhury et al. 2004, 2016; Wu et al. 2014; Wang et al. 2015). Joseph et al. have identified trace metals in the sediments of Chitrapuzha located downstream of the Kadambrayar River (Joseph & Chacko 2006) and ultimately joined the Ramsar site Vembanad lake, where heavy metals were reported by Shyleshchandran et al. (2018).

Heavy metal pollution has been reported in similar studies, where the surface water quality is detrimentally affected near an open dumping site. Studies that focused on the surface quality near landfills or dumping sites reported that the quality near the site is highly polluted (Parvin & Tareq 2021). A study by Jahan et al. (2016) near Matuail landfill sites on reported that the DO in surface water near the site decreased which will threaten the fish over there as the area is a source for fisheries. A study by Azim et al. However, Azim et al. 2011) however stated that most variables were under safe limits near the same landfill site, except Cr (1.03 mg/L) and DO (2.3 mg/L). A study by Alam et al. (2020) in the Mogla Bazar landfill site found that Pb was above the safe limit in surface water near the site. A study by (Hossain et al. 2014, 2018) reported that the surface water in the surroundings of the Rowfabad landfill site contains a high concentration of iron, chromium, and cadmium.

In this study, by analyzing the quality of a stretch of the Kadambrayar River, which flows through an urbanized and industrialized region of a city during the post-monsoon season in 2021, it can be concluded that

• The river is infested with aquatic weeds, especially water hyacinth, which can be considered a bioindicator of pollution.

• The key parameter such as DO, BOD, and Coliforms which can be considered as a measure of the health of the river system fails to comply with the standard limits as per the surface water quality standards IS2296:1992. The presence of fecal coliforms is also confirmed which indicates fecal pollution in this drinking water source.

• An increasing trend is shown in the BOD values in the river compared to the previous year's data, and a decreasing trend is observed downstream. Thus, when compared to the upstream it can be understood that the downstream is more polluted in terms of the depletion of DO and BOD levels.

• The concentrations of arsenic and chromium obtained at the stations located downstream near the dumpsite were beyond the standard limits.

• The Edachira drain, located upstream, contributes to a significant level of pollution in the river by transporting sewage and effluents.

• There is no treatment for leachate at the dump site, and leachate along with runoff is a major source of pollution downstream of the river (at station S0, which joins river Chithrapuzha).

Apart from the regular monitoring of the river to control the pollution in the river. Timely sediment dredging of the river and removal of water hyacinth at infested places will enhance the flow of the river and thus the natural aeration will improve the quality of the river (Wang et al. 2012). The leachate at the dumpsite should be treated and phytoremediation is one of the low-cost methods (Arunbabu et al. 2017). The study will thus help in a better understanding of the pollution and its sources in the river; therefore, remedial measures can be framed for improving water quality for sustainable development.

We thank the Kerala State Irrigation Department, Kerala State Pollution Control Board, Kerala Water Authority, and Cochin Municipal Corporation for their assistance in sampling and data collection.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.