Molecular Soil Biology 2024, Vol.15, No.3, 118-128 http://bioscipublisher.com/index.php/msb 119 2 Historical Context of Pesticide Usage in Rice Cultivation 2.1 Evolution of pesticide use in agriculture The use of pesticides in agriculture has evolved significantly over the past century. Initially, pesticides were introduced to combat pests and increase crop yields, which was crucial for food security. Early pesticides included natural substances like sulfur and arsenic compounds. However, the development of synthetic pesticides in the mid-20th century, such as DDT and organophosphates, marked a significant shift. These chemicals were highly effective but also brought about environmental and health concerns due to their persistence and toxicity (Parsons et al., 2010). Over time, the adverse effects of these chemicals led to stricter regulations and the development of more targeted and less persistent pesticides (Tiwari et al., 2019; Onorati et al., 2022). 2.2 Specifics of pesticide application in rice fields Rice cultivation, being a water-intensive crop, presents unique challenges and practices for pesticide application. Pesticides are often applied directly to the water in paddy fields, which can lead to widespread contamination of water bodies and affect non-target organisms. Commonly used pesticides in rice fields include herbicides, insecticides, and fungicides. For instance, chlorpyrifos, a widely used insecticide, has been shown to persist in soil and affect soil microbes and nematodes adversely (Kumar et al., 2017). The overapplication of pesticides, sometimes exceeding recommended rates by up to 11 times, has been documented, leading to significant environmental risks. The use of pesticides in rice fields is also influenced by the type of rice cultivation system, with lowland rice fields showing higher impacts on human health and freshwater ecotoxicity compared to upland and terraced systems (Toolkiattiwong et al., 2023) (Figure 1). Lowland rice fields, due to their intensive farming practices, often use more fertilizers, herbicides, and pesticides, leading to a higher carbon footprint and gray water footprint, as well as more significant risks to human health and freshwater ecosystems. Studies have shown that the types and quantities of pesticides used in lowland rice fields are greater, primarily for commercial purposes, aiming for higher yields. These pesticides tend to persist in the soil, and their residues can cause long-term impacts on ecosystems through soil and water migration. In contrast, upland and terraced systems typically rely on natural conditions for cultivation and are mainly used for household consumption, resulting in lower pesticide usage and reduced environmental and health impacts. Figure 1 Environmental, human and ecotoxicological impacts of different rice cultivation systems (Adopted from Toolkiattiwong et al., 2023) 2.3 Case studies of historical pesticide impacts Several case studies highlight the historical impacts of pesticide use in rice cultivation. In Sri Lanka, a study assessing pesticide residues in water from rice paddies found that overapplication of pesticides led to high environmental risks and adverse effects on local fauna, including fish, amphibians, and insects (Gamaralalage et
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