Aquatic ecosystems are lifelines for humans and our planet. They help regulate climate and hydrological cycles, support biodiversity and food webs and provide water for drinking, agriculture, and industry. But these systems are under siege from pollution, climate change, and especially toxic heavy metals.
A recent study that assesses the concentrations of heavy metals (HMs) in freshwater bodies and their correlation with zooplankton populations and human health in West Bengal finds that heavy metals affect zooplankton populations negatively, showing that they can serve as indicators of the presence of heavy metals in the water. Both children and adults face health risks due to heavy metals.
Freshwater ecosystems are powered by a complex web of life and include small-sized or microscopic plants known as phytoplankton (primary producers) that capture sunlight to make food. Zooplankton are microscopic animals like rotifers, cladocerans (water fleas), and copepods that feed on phytoplankton and are in turn eaten by fish and insects, which are preyed upon by larger fish and birds.
Each link in this chain is vital. Disrupt one, and the whole system begins to unravel. Zooplankton are highly sensitive to changes in water chemistry, can serve as early warning systems for pollution and toxicity and are essential for nutrient cycling and energy transfer. Monitoring their diversity and abundance helps scientists assess the health of freshwater bodies—and predict future risks.
Protecting freshwater bodies from contamination is crucial for India, where 740 million rural people depend on freshwater and about 38 million suffer from waterborne diseases. Seventy-two per cent of disease outbreaks due to drinking contaminated water occur in the states of Maharashtra, followed by West Bengal, Madhya Pradesh, Punjab, and Karnataka.
The present study, titled ‘Integrated zooplankton and heavy metal analysis as indicators of pollution threats in freshwater ecosystems of West Bengal’ published in Nature Scientific Reports, was done in the East Medinipur district in West Bengal, where Local residents rely heavily on surface water bodies for their daily needs. Of the 3% of land covered by water bodies, 67% of the population uses ponds for household purposes, 13% use canals, and 7% depend on waterlogged areas. More than 60% of the population in the region are affected by waterborne and skin diseases due to the regular use of these water resources. Medical expenses in the region have soared to 30% of total household expenditure.
Water from four sites namely, Tamluk, Haldia, Egra and Contai in the district, was tested for contaminants. The water resources included culture ponds used for both domestic purposes and aquaculture; waterlogged areas used for agriculture and aquaculture; and canals and drainage areas used for discharging market waste and toxic substances from various small industries.
Water pollution due to heavy metals was very high in the studied samples
Haldia exhibited the highest level of heavy metal pollution, with 40.47% of heavy metals posing potential health risks to adults and children.
Non-carcinogenic health risk assessments for the seven heavy metals revealed that nickel (Ni) and zinc (Zn) posed the highest potential health risks for both children and adults at all the sites.
Canal water systems posed the most health risks to children and adult groups due to high quantities of industrial effluents that were contaminated with heavy metals.
Heavy metal pollution led to a significant decline in zooplankton population, posing a threat to aquatic ecosystems. The study found that zooplankton populations could serve as early warning indicators of ecosystem stress due to pollution in freshwater ecosystems.
This dual-parameter approach that included biological and chemical analysis helped identify hidden pollution threats that could have been missed by chemical analysis alone. This dual parameter approach can also help in enabling communities, scientists and policy makers to work together to tackle water pollution by using a combination of chemical and biological indicators that are relatively cheap and can be done much faster than chemical analysis.
The study argues for:
An urgent need to design cost-effective remediation techniques to improve water quality in the region
Conduct research to explore the relationship between zooplankton abundance, chemical indicators that identify elevated levels of heavy metals posing health hazards to humans, and GIS-based studies to better understand the situation.
The need for industrial sectors, agricultural bodies, and other stakeholders to comply with environmental standards and regulations to prevent contamination.
Municipalities to establish designated areas for domestic waste disposal and introduce water purification processes to protect communities.
Regulation on the use of chemical fertilisers and pesticides
Public awareness campaigns at the village level to help reduce pollution in aquatic ecosystems
When water grows sick, it speaks through its smallest inhabitants. The vanishing of zooplankton is not just an ecological loss; it is a mirror held up to our choices. If we can read these signs through science, community action, and care, we can begin to cleanse what we have clouded. For in every drop of living water lies both the memory of what once was and the possibility of renewal.