Toxic waters, struggling fish

The Ganga, India's poisoned lifeline

The Ganga basin, often cited as a lifeline for India and its people, spreads over 860,000 km³ – about 26.3 percent of the total geographical area of the country and 43 percent of the Indian population resides near the banks of the Ganges. The basin stretches over eleven states from Uttrakhand, Himachal Pradesh, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, Rajasthan, Madhya Pradesh, Chhattisgarh and West Bengal.

The river supports the livelihoods of 36 percent of the total population of the country and spreads out into a number of tributaries to form the highly productive Indo-Gangetic basin, which mainly supports agricultural activities besides other activities such as fishing.

However, the Ganga basin is also highly polluted and this has severe implications for the riverine communities that depend on the river for their livelihoods and animals that depend on its waters for their survival. Pollution through agricultural activities, urbanisation, and industrialisation not only compromise the water quality, but also harm aquatic health.

The World Wildlife Fund (WWF) has rated Ganga as one of the world’s top 10 rivers at risk from pollution, and one that is on the verge of losing its biodiversity.

Pesticides in the Ganges waters- death traps in disguise

Pesticides have been found to be one of the important polluters of the river waters due to their high application in the agricultural fields along the river basin. The total usage of pesticides in Ganga basin between year 2012–2017 was 72,741 MT, which is as high as 27 percent of the countries’ total pesticide consumption.

Studies have shown that pesticide use is not only a threat to humans, but also animals such as fish that reside in its waters. The fish that traditionally dominated the river Ganga are Labeo Rohita (Rohu), Cirrhinus Mrigala (Mrigal), Labeo Calbasu (Kalbasu), Mystus Oar, Mystus Seenghala (Singi/Singhara), Wallago Attu, and Hilsa Ilisha (Hilsa).

However, reduced flow, change in habitat, pollution have affected fish production in the riverine system. Invasive species have are fast replacing the traditional ones and include common carp (Cyprinus Carpio), African catfish (Clarias Gariepinus), sucker mouth catfish (Pterygoplichthys Spp.), Tilapia (Orecohromis Mossambicus), grass carp (Ctenopharyngodon Idella), silver carp (Hypophthalmichthys Molitrix) etc.

Recent studies show that around 21000 MT of pesticides are applied in the basin annually and among these, insecticides dominate followed by herbicides and fungicides. In the insecticide category, organochlorines were predominantly used till 1990, after which the use of organophosphate formulations has increased. The consumption pattern of pesticides shows that in year 2014, insecticide use was 80 percent, followed by herbicide 15 percent and fungicide 2 percent. Phosphamidon, butachlor, mancozeb, quinalphos, monocrotophos, paraquat, endosulfan, isoproturon are commonly found pesticides.

Impact of pesticides on fish in the Ganga

Many of these pesticides have chemicals that persist in the waters for a long time and have a negative effect on many animals large and small residing in the waters by altering their cellular structure and functions informs this paper titled 'Oxidative, biochemical and histopathological alterations in fishes from pesticide contaminated river Ganga, India' published in Nature Scientific Reports.

Studying the impact of river pollution on animals living in the waters can be useful as an indicator to regularly monitor the pollution status of the river and its impact on the ecology of the river, often referred to as ecological risk assessment. Regular investigation of the pesticide status in aquatic ecosystem can be greatly useful to reframe the policy of manufacture and use of pesticides in the country, argues the paper.

Histological changes in the organism exposed to the contaminants have been considered as the best tool for evaluating the toxic effects of river contamination on the ecology and health of the river. Gills are important indicators of fish health and that of the river as they are primary organs for oxygen uptake which remain in continuous contact with the toxins present in the water, and are thus good indicators for detecting impact of pollution on fish. The liver is also another important organ in fish that shows histopathological changes upon exposure to contaminants.

The paper discusses the findings of a study carried out to evaluate the effects of pesticides on two commonly edible fish namely Rita rita (a type of catfish) and Cyprinus carpio (commonly known as the carp) collected from two different sites of pesticide contaminated river Ganga namely Devprayag Rishikesh and Narora.

The study findings:

Dissolved oxygen was below the set value of 5 mg/l by ICMR at both the sites suggesting that the water was polluted with contaminants. High BOD values at both the sites indicated a large proportion of agricultural, domestic sewage and organic load. Low pH at Narora station could be due to a high degree of organic load by bacteria at high temperature resulting in the increased level of carbon dioxide in water which in turn led to low pH concentration.

The study showed evidence of cellular damage in the fish due to water polluted with pesticides. A significant increase in the catalase activity was observed in gill and liver of both Rita rita (a type of catfish) and Cyprinus carpio (commonly known as carp) from both the sites indicative of oxidative stress that can induce cellular damage in fish.

The findings of this study show that river pollution can not only spell doom for fish health and the health of the river, but also affect the livelihoods of communities that depend on the river for fishing. Urgent efforts to reduce the influx of harmful chemicals such as pesticides into the rivers through stringent regulatory mechanisms is essential to prevent risks to human health and livelihoods as well as the biodiversity of the Ganges. 

The gill and liver histopathological changes observed in fish did not reflect specific contaminants. However these could be greatly useful as  biomarkers or indicators in fish to detect pesticide contamination of water sources in the future, argues the paper.