Health and environmental consequences of crop residue burning correlated with increasing crop yields midst India’s Green Revolution

The Green Revolution (GR) in India and other South Asian countries dramatically increased crop yields over the past half-century, transforming food security and supporting population growth. However, negative environmental consequences have become increasingly apparent, including deforestation due to land conversion, soil degradation, and salinization. The extensive use of pesticides and fertilizers, while contributing to the GR's success, also introduced toxic and persistent chemicals harmful to human health and ecosystems. While studies have explored the health impacts of the GR, the interconnected effects on the environment and human health remain understudied. The GR in India is characterized by a rapid rise in staple crop production (wheat, rice), and cash crops (cotton, jute), resulting in substantial post-harvest residues. In India, over 25% of urban households rely on biomass for cooking and heating, with agricultural residues contributing 16-20% to total indoor solid fuel emissions. Crop residue burning, especially in the Indo-Gangetic Plain (IGP), significantly impacts air quality and the health of local residents. Biomass burning is a major source of polycyclic aromatic hydrocarbons (PAHs), with India being the second largest emitter globally after China. Agricultural residue burning accounts for a significant portion (92.5%) of PAH emissions in India, contributing 20-25% of total emissions from all sectors. This practice is widespread in northwestern IGP during rice and wheat harvesting, causing severe PAH contamination. This study investigates the PAH contamination and health effects in India since the onset of the GR, focusing on benzo[a]pyrene (BaP) emissions from indoor and outdoor residue burning and other agricultural activities. The study models and analyzes BaP concentrations from various emission sectors across India from 1965 to 2014 and estimates the cumulative lifetime lung cancer risk (ILCR) for each Indian state.

Existing literature highlights the environmental degradation associated with the Green Revolution in India, including deforestation, soil degradation, and water salinization. The increased use of pesticides and fertilizers is also noted as a source of environmental and health problems. Studies have examined the air pollution caused by crop residue burning, particularly in the Indo-Gangetic Plain (IGP), identifying it as a major source of polycyclic aromatic hydrocarbons (PAHs) and other pollutants. Previous research has shown the significant contribution of biomass burning to PAH emissions in India and its impact on air quality and human health. However, there's a knowledge gap regarding the long-term, integrated effects of the GR on both environmental and human health, particularly concerning the specific contribution of crop residue burning to carcinogenic PAH exposure.

This study utilized a modified version of the CanMETOP (Canadian Model for Environmental Transport of Organophoric Pesticides) model to predict ambient air BaP concentrations and atmospheric transport from 1965 to 2014. The model's domain was reduced to cover India and surrounding regions with a higher spatial resolution (1/4° latitude by 1/4° longitude). The model was run from 1960 to 2014, with 1960-1964 serving as a spin-up period. BaP air concentrations from 1965 to 2012 were analyzed. The model incorporated various input parameters including BaP emission inventory, meteorological data (wind speed, pressure, precipitation), and terrain data. Two model scenarios were implemented: a "NO-GR" scenario using fixed BaP emissions from the agricultural sector in 1960, and a "GR" scenario using time-varying emissions from 1965 to 2014, reflecting the changing agricultural practices and yields during the Green Revolution. The incremental lifetime cancer risk (ILCR) was calculated for each 1/4° × 1/4° grid using EPA methodology, incorporating factors like human inhalation rate, exposure duration, body weight, and the carcinogenic potency factor (CSF) for BaP. Monte Carlo simulations were conducted to account for uncertainties in the input parameters. Data on crop yields, crop residue burning, and BaP emissions were obtained from various sources, including FAOSTAT, the PKU-PAH inventory database, and MODIS satellite remote sensing data (fire mask and land cover). Lung cancer incidence rates (LCIRs) from the Indian Council of Medical Research were used for comparison with the modeled ILCRs. Multivariate regression models were used to analyze the relationship between crop yields, BaP emissions, and ILCR, and to evaluate emission reduction scenarios.

The study found a strong positive correlation (r = 0.9) between total crop yield and agricultural BaP emissions in India from 1965 to 2014. BaP emissions from agricultural sectors increased from 106.5 tons in 1965 to 229.5 tons in 2014. The modeled ambient BaP air concentrations were highest in the Indo-Gangetic Plain (IGP), northwestern, and southern India, regions with high crop yields and population density. In several states (Haryana, Punjab, Himachal Pradesh, Meghalaya, Manipur), BaP levels exceeded the Indian national standard. Open-field burning of agricultural residues during rice and wheat harvesting, and slash-and-burn agriculture contributed significantly to BaP contamination. The annual mean BaP concentration averaged over India increased from 0.29 ng m⁻³ in 1965 to 0.74 ng m⁻³ in 2014. The ILCR from agricultural BaP emissions increased from 3.8 × 10⁻⁷ in 1965 to 9.66 × 10⁻⁶ in 2014, showing a 2.59% annual increase rate. A statistically significant correlation (p < 0.001) was observed between state mean ILCRs and non-smoker lung cancer incidence rates (r² = 16.7%). The spatial patterns of ILCR and lung cancer incidence rates showed significant overlap, suggesting a strong association. The comparison between ILCRs and death rates caused by lung cancer showed a high correlation (r = 0.96, p < 0.001), indicating that BaP emissions from agricultural activities is a significant contributing factor to lung cancer incidence.

The findings demonstrate a clear link between the intensification of agriculture during the Green Revolution in India and increased BaP contamination and lung cancer risk. The significant increase in crop yields has been accompanied by a substantial rise in BaP emissions from crop residue burning, posing a substantial public health concern. The study's results highlight the need for policies and interventions to reduce crop residue burning, which could significantly reduce the burden of lung cancer in India. The strong correlation between modeled ILCR and observed lung cancer incidence rates strengthens the evidence for a causal link between BaP exposure and lung cancer risk. The spatial distribution of ILCR highlights the disproportionate impact on regions with high agricultural productivity and population density. The model simulations underscore the potential for significant reductions in lung cancer risk through effective control of crop residue burning. While the study focuses on BaP, it's important to consider the broader impact of PAH emissions on other health outcomes. Future research could investigate the combined effects of various pollutants from agricultural practices and other sources on human health.

This study demonstrates a significant association between the Green Revolution's increased crop yields in India and heightened BaP contamination and lung cancer risk due to crop residue burning. The results strongly support the implementation of policies and practices to mitigate crop residue burning, reducing BaP emissions and subsequently, the public health burden associated with lung cancer. Future research could investigate alternative crop residue management strategies, explore the synergistic effects of multiple air pollutants, and refine the models to enhance their accuracy and predictive capabilities.

The study relies on modeled BaP concentrations and ILCRs, which are subject to uncertainties associated with model inputs and parameter estimations. The availability and quality of data on crop residue burning and lung cancer incidence varied across different regions and time periods. While the study demonstrates a strong association between BaP exposure and lung cancer, it does not establish definitive causality. Other factors could contribute to lung cancer incidence, and further research is needed to fully disentangle the complex interplay of factors.