Heavy metal pollution is a very aggravating problem affecting both aquatic and terrestrial ecosystems worldwide. Several rivers are known to be affected by this pollution and problems are more with the rivers which are given sacred importance, as they are highly exposed to human interventions. Our very prestigious and holy river Ganga is the largest river of the Indian subcontinent, with spiritual significance in Indian culture and has the highest exposure to several such anthropogenic pollutants. After traveling 2525 km and covering 8,61,404 km2 of the drainage basin, through Uttarakhand, Uttar Pradesh, Bihar, Jharkhand and West Bengal, it discharges its water into Bay of Bengal. But the river has faced major sequential and spatial challenges in its waters and biodiversity in recent times due to poor sanitation, agricultural runoff, household waste and the rapid pace of anthropogenic activities. Heavy metals are one of the most indestructible pollutants, having a long life span that pollutes and extends to the next trophic levels in the ecosystem (Maurya et al., 2016). Aquatic organisms including fish, zooplankton, benthic algae etc. are frequently exposed to heavy metals and show significant metal accumulation variance. Not only this, but heavy metal pollution adversely affects the self-purification and antimoicrobial properties of Ganga water and its flora and fauna diversity, resulting in changes of physical, chemical & biological properties and affect the river ecosystem (Usmani et al., 2017). Different sites and seasonal studies have reported that carcinogenic metals like As, Cd, Cr, Hg, Ni and Pb, were exceeding the WHO permissible limit for potable Ganga water (Sinha et al., 2007; Pandey et al., 2010; Katiyar et al., 2011) and concluded that Ganga water is unfit for human consumption even for household works.
The River Ganga is home to about 140 species of fishes including exotic varieties (Sarkar et al., 2012) and are the ultimate recipients, endangered by natural toxins and one of the leading bio-indicators of these metal pollution (Khanna et al., 2007). Gills and oral ingestion contaminated food and sediment particles are the main sources of entry, while the liver, kidneys, gills, muscles, skin and brain are the main organs of their accumulation (Vaseem et al., 2013). As a potential source of protein, essential minerals, vitamins, and unsaturated fatty acids (Medeiros et al., 2012) in the human diet, about 20 kg year− 1 per capita fishes are consumed worldwide and 50% of global consumption by Indians, contributes − 8–9 kg per year for fish eaters (FAO, 2022). Numerous hazardous elements bio accumulate and biomagnifies in the fishes of Ganga (Mitra et al., 2012; Singh, 2014). These metals after going through food chain can also enter the human system and contribute to a serious health risk to a person through environmental and food exposure causing various health problems. Minamata disease in Japan due to mercury poisoning is a worldwide phenomenon. Itai Itai disease due to cadmium poisoning is another well-known example.
The WHO in 2010 classified lead (Pb), cadmium (Cd), mercury among the top ten chemicals of major public health concern (WHO, 2010). They affect vital organs such as the kidneys, liver, and brain causing nephrotoxicity, hepatotoxicity, and neurotoxicity. Inside the body, some metals bind to sulfur-containing enzymes and disrupt their function. Some may lead to oxidative stress due to their potential to generate free radicals (Jaishankar et al., 2014). Exposure to high cadmium may lead to kidney damage and bone fractures (Jarup, 2003; Maurya et al., 2016). Prolonged exposure to arsenic in drinking water is strongly associated with increased risk of skin cancer, as well as other types of cancer, as well as other skin lesions such as hyperkeratosis and pigmentation changes (Jarup, 2003). Al complexed with Amyloid β disrupt Ca2+ homeostasis and inhibits mitochondrial respiration in the neuronal cells by interfering with enzymes of electron transport chain, ultimately leading to neuronal cell death (Drago et al., 2008). Metal toxicity depends on the dose absorbed, the route of exposure, and the duration of exposure, whether negative or chronic. Deliberate use of arsenic in the case of attempted suicide or accidental exposure to child may also result in severe toxicity (Mazumder, 2008). High doses can lead to death, usually within 2 weeks after the onset of symptoms. The acute lethal dose of arsenic in human is 0.6mg/kg/day (ATSDR, 1989; Ratnaike, 2003). Cadmium exposure to humans can cause kidney damage and effects on bone, may easily lead to fracture (Jarup et al., 2009).
The current study was conducted in the Varanasi region of Uttar Pradesh, one of the busiest industrialized cities in India. The city discharges its HM-containing contaminants into the river through many wastewater treatment plants. The specific aim of the present study is to examine the load of metals especially lead (Pb), manganese (Mn), chromium (Cr) and cadmium (Cd) in water and tissues such as gills, muscle and liver of different fish species of the Ganga River that are frequently used for human consumption in Varanasi region. Our aim is also to find out the heavy metal load in river Ganga (water and fishes) and the potential health risk for the consumers due to the consumption of heavy metal contaminated fishes.