Risk Assessment of Pesticides in Groundwater of India: An Integrated Index of Water Stress, Climate, and Biodiversity

Groundwater contamination risk is influenced by hydroclimatic constraints, abstraction-driven dilution capacity, and ecological sensitivity, rather than chemical levels alone. However, groundwater pesticide assessments generally prioritize sites based on measured concentrations. We developed a groundwater-focused Level of Concern (LOC) indicator that integrates cumulative pesticide mixture toxicity expressed as an ecological Risk Quotient (RQ) derived from reported groundwater concentrations and groundwater Predicted No-Effect Concentrations (PNEC_GW), baseline water stress (BWS) as a proxy for groundwater scarcity and reduced assimilative capacity, and composite tetrapod biodiversity richness as an index of ecological sensitivity. The aridity index (AI) was retained as a supporting context to interpret recharge limitations and the persistence or mobility of contaminants across climatic zones. The framework was applied across diverse Indian aquifer provinces spanning semi-arid, dry sub-humid, and humid regions, including the Indo-Gangetic Plains and stressed urban aquifers (Delhi; Farrukhabad, Agra, Kanpur, Unnao, Varanasi, Lakhimpur Kheri, Gorakhpur), semi-arid transition and irrigated belts (Jaipur in Rajasthan; Hisar, Ambala, Gurgaon in Haryana), humid floodplains (Nagaon and Dibrugarh in Assam), deltaic and coastal aquifers (North 24 Parganas and South 24 Parganas in West Bengal; Thiruvallur in Tamil Nadu), and hard-rock basalt systems in central India (Bhandara, Amravati, Yavatmal in Maharashtra).

Results show pronounced spatial heterogeneity and two dominant pathways of groundwater vulnerability. In semi-arid provinces with high to extremely high BWS, medium to very high pesticide risk classes align with constrained dilution and persistence, and these sites are predominantly categorized as medium concern (LOC=2). In humid alluvial systems, very high pesticide-risk classes can occur under low to high BWS, consistent with recharge-driven transport and strong groundwater–surface water connectivity. These locations also cluster in the medium concern class (LOC=2). High concern (LOC=1) is identified at Yavatmal, where semi-arid conditions and extremely high BWS coincide with cumulative stress. Low concern classifications (LOC = 3-4) are limited to Kanpur, Gorakhpur, and South 24 Parganas, where cumulative stress is lower under their respective BWS, RQ, and AI classes.