Emerging organic contaminants and antimicrobial resistance in Bengaluru waters

Protecting water resources and reducing their pollution for safe human consumption and healthy ecosystems is an becoming an ongoing challenge in urban areas.

Recently emerging organic contaminants (EOC), including pharmaceuticals, lifestyle products, and industrial compounds in surface water and groundwater in urban areas such as Bengaluru are making the water undrinkable threatening human health and also contributing to antimicrobial resistance (AMR) informs this study titled 'Presence of emerging organic contaminants and microbial indicators in surface water and groundwater in urban India' published in Environmental pollution.

Surface and groundwater resources in Bengaluru

While surface water area in Bengaluru is shrinking due to land use and land cover changes, tanks remain an important feature of the city’s water infrastructure. The water quality of these tanks is highly variable. Measures were undertaken to rejuvenate tanks in recent years by removing silted bottom layers from the tanks and enhancing protection against encroachments and sewage inflows to improve water quality.

Groundwater is also another important water source in Bengaluru. Rainfall patterns affect groundwater levels with shallow groundwater levels in August/September (monsoon), and the deep levels around April, at pre-monsoonal onset. Historically, tanks were considered an important source of groundwater recharge.

While groundwater pollution has been assessed in Bengaluru in terms of major ions, metals and the presence of faecal indicators such as Escherichia coli,  there is little information on EOC concentrations and their relationship to AMR in Bengaluru’s surface water and groundwater.

This study makes a first of its kind combined assessment of emerging organic contaminants (EOC) and antimicrobial resistance (AMR) in the city of Bengaluru.

The study found that:

Surface water showed high contamination due to emerging organic contaminants

A total of 125 EOCs were detected with the artificial sweeteners - sucralose and saccharin, and the anticonvulsant carbamazepine being the three most frequently detected.

The highest number were detected in surface water sources such as the Vrishabhavathi river, Bellandur lake and the Byramangala reservoir. The lowest were found in rejuvenated lakes and tap water while those found in groundwater were low in comparison to the more polluted surface waters, but higher than those tap water or the rejuvenated tanks.

Medical and veterinary compounds were the highest among EOCs

Medical and veterinary compounds were the highest number of detected EOCs with the antidiabetic metformin in highest concentration. The largest subgroup was antibiotics followed by anticonvulsants.

The largest proportion were found in the more heavily polluted water sources such as the Byramangala reservoir, Bellandur lake, Vrishabhavathi river and in the rejuvenated tanks.

Agrochemicals were the second largest group

Herbicides, insecticides and fungicides were the second-largest group detected in the study. The herbicides atrazine, its metabolite desethyl-atrazine, and the insecticide degradate fipronil-sulfone were detected in majority of tap water samples and in the groundwater from the densely- piped areas near the Indian Institute of Science (IISc) and near the Sankey tank, but not in surface water of the tank.

The metabolite fipronil-sulfone was found in groundwater and tap water, while its parent compound fipronil was detected in surface water sources such as the Vrishabhavathi river and Byramangala reservoir, but not in tap water. The recommended concentration of pesticides exceeded in surface waters, groundwater, but not in tap water.

Industrial compounds were found in surface and groundwater

Despite Bengaluru’s high degree of industrialisation, only 12 industrial compounds were detected in the local surface waters and also in groundwater and tap water sample.  Most industrial compounds detected in groundwaters were surfactants belonging to the group of per- and polyfluoroalkyl substances (PFAS) such as perfluorooctane-sulfonate (PFOS), perfluorohexane-sulfonate, and perfluorobutane-sulfonate.

Few PFAS were detected in Vrishabhavathi river, Bellandur, Byramangala reservoir in higher concentrations than in groundwater and in the rejuvenated tanks, but no PFAS were detected in tap water.

Lifestyle compounds were the highest in surface water sources

Three artificial sweeteners sucralose, saccharin, acesulfame-K and the nicotine metabolite cotinine were detected in highest concentrations in the Vrishabhavathi river, Bellandur lake and Byramangala reservoir.

Antimicrobial resistance (AMR) risk was high in surface waters

Groundwater surface water connections influenced contamination

Out of 125 EOCs detected in this study, 62 were present in groundwater and a number of these could be linked directly to distinct recharge sources. For example, PFAS detected in groundwaters were likely recharged from surface water influenced by sewage, in which PFAS were detected at highest concentrations. PFAS were also detected in rejuvenated tanks, and recharge from tanks was another potential source for PFAS in groundwater.

Agricultural products such as atrazine and its metabolite desethyl-atrazine were detected in groundwater and tap water imported from the Cauvery basin indicating groundwater recharge from mains water leakage.

Thus urban groundwater recharge processes were anthropogenically dominated by surface water storage, water imports and pipe leakage, overlaying the more natural rainfall-driven recharge. The detection of recently introduced artificial sweeteners in all groundwater also indicated a high degree of system- connectivity.

Groundwater surface water connectivity increased vulnerability of Bengaluru to contamination

• The connectivity of the groundwater-surface water system, likely increased by heavy abstractions, and the presence of contaminants linked to a variety of recharge sources has critical implications for the quality of the groundwater resources which sustain domestic, agricultural and industrial water demand in areas where piped water is limited.

• High PFAS concentrations and the detection of 3 PFAS compounds in groundwater that were not detected in any of the other waters shows that urban groundwater systems in Bengaluru are vulnerable

• Medical/veterinary compounds, including 27 antimicrobials were the dominant pollutant class in the urban surface waters and, to a lesser extent, in groundwater.

• The highest prevalence of the AMR-indicator, intI1, was also found in the Byramangala reservoir while no risk of AMR development was found in tap water, groundwater and rejuvenated tanks

• Surface water bodies with recently implemented protection measures such as prevention of sewage inflows had fewer EOCs detected than other surface waters and were found to have much lower risk of AMR development thus indicating how relatively simply urban protection measures can protect freshwater quality.

Thus monitoring and limiting contamination occurring in surface waters and the Cauvery River water is crucial to protect groundwater resources in Bengaluru, argues the article.