Insecticide Toxicity in Paddy Agroecosystems, Impacts on Soil Health, and Microbial Bioremediation Strategies: A Review
Abstract
Paddy (Oryza sativa) rice cultivation in India extensively employs chemical insecticides to manage insect pests such as stem borers, leaf folders, and planthoppers. While effective in controlling pests, several commonly used active ingredients, including fipronil, chlorantraniliprole, lambda-cyhalothrin, and thiamethoxam, exhibit persistence in soil ecosystems and pose toxicity risks. This review synthesizes current knowledge on the types of insecticides used, their persistence and toxicological profiles, effects on soil microbial communities critical for fertility, and potential risks to human health. Furthermore, it evaluates microbial bioremediation as a promising strategy to mitigate pesticide residues and restore soil health. In view of the above, sustainable pesticide management practices integrated with bioremediation approaches are needed to balance crop protection and ecosystem health.
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Introduction
Rice (Oryza sativa), a staple for over half the world'spopulation, is predominantly grown in flooded paddy fields, covering approximately 167 million hectares globally. In India, rice serves as a cornerstone staple crop, playing a pivotal role in national food security and rural livelihoods. Persistent threats from pests, including the rice stem borer, leaf folder, brown plant hopper (BPH), and green leafhopper (GLH), undermine yields and necessitate robust control measures (Litsinger et al., 2009). Farmers apply an estimated 2–3.5 million tonnes of pesticides annually, with insecticides comprising 61%, herbicides 22%, and fungicides 11% of usage (Aktar et al., 2009). Common contaminants in paddy fields include organophosphates (e.g., chlorpyrifos, malathion), carbamates (e.g., carbofuran), organochlorines (e.g., endosulfan, DDT), triazines (e.g., atrazine), and pyrethroids. These persist due to high organic matter and anaerobic conditions in flooded soils, leading to bioaccumulation in rice grains and runoff into waterways (John & Prakash, 2002).
Chemical insecticides, featuring active ingredients such as fipronil, chlorantraniliprole, lambda-cyhalothrin, and thiamethoxam, have become integral to pest management protocols. Despite their efficacy, evidence highlights their environmental persistence and ecological toxicity, particularly disrupting soil health and non-target biota (DeLorenzo et al., 2001). Risks to human health arise from occupational exposure and dietary residues in harvested rice, with impacts ranging from neurotoxicity and endocrine disruption to millions of pesticide-related deaths since 1960, disproportionately affecting rural Asia (Kumar, 2017). Environmental degradation includes reduced soil microbial diversity and biodiversity loss, as pesticides inhibit bacterial abundance in irrigated rice fields (Gupta et al., 2022). Traditional remediation methods (e.g., incineration, chemical oxidation) are costly and generate secondary pollutants, whereas microbial bioremediation—using indigenous or augmented microbes—degrades xenobiotics via enzymatic pathways, offering substantial cost savings and eco-compatibility (Bhagawati et al., 2020). 1.1 Objectives and Scope of this Review: This narrative review aims to: (1) synthesize contemporary evidence on the persistence and toxicity profiles of major insecticides used in Indian paddy fields; (2) critically analyze their cascading effects on soil microbial communities and related fertility functions; and (3) evaluate the current state, practical challenges, and future potential of microbial bioremediation as a restorative strategy within this specific agroecosystem.