Cause-Effect Modelling of Crop Residue Burning on Urban School Children Health

Abstract

Clean air is a need of each human being to survive on planet earth. Due to rapid growth in modernization and life style, the ambient air is getting polluted due to mixture of hazardous substances such as toxic gases and fine suspended particulate matter having size several times lesser than the thickness of human hair. The exposure to these substances for a short or long duration caused chronic disorders such as asthma, shortness of breath and reduction in working capacity of respiratory system. According to previous studies, exposure to increased level of particulate matter having size less than 10µgm-3 in ambient air is responsible to affect the health of inhabitants of all age groups. The effects on children are more severe than other age groups due to their body structure and constraints. The children are unaware of their surrounding environment and their organs are under development. Their respiration system is unable to trap these substances due to weak defense system. Particulate matter is generated by improper combustion of fuels or garbage in ambient air. Typically, there are number of sources that are responsible. Agriculture crop residue burning is identified as the second largest source of air contamination in Punjab state (India) that is responsible for releasing of coarse and fine particulate matter in the air. Rice and wheat crop is the main cyclic crop of this area. As per NASA’s recent evidences, dense plums are identified in the area that is hypothesized to affect the lung capacity of human subjects. To study the effect of ACRB on human subjects, three schools (in Amritsar, Ludhiana and Mandi Gobindgarh) were selected in the region. Initially, 150 healthy human subjects (50 school going children in age group 10 to 14 years per school) were enrolled in the study. The repeated sampling of particulate matter (PM10 and PM2.5) and pulmonary function test (FVC, FEV1, PEF, FEF25-75% ) were done for three years from August 2013 to July 2016 using Aerosol spectrometer and spirometer. The sampling frequency was planned to cover non crop residue burning seasons and burning seasons. The sampling was done twice in a fortnight during non crop residue burning seasons and four times in burning seasons in a staggered manner at all sites. After collection of data, statistical analyses were done to observe the trends in physiological parameters of human subjects. Descriptive analyses were done using t-test and ANOVA test to observe the significant difference in categories. Mixed effect model has been used to predict the changes in physiological parameters of human subjects due to increased level of PM with adjustment of confounders and covariates. It has been observed from the results that the level of PM crossed the NAAQS during crop residue burning seasons. The concentration level of PM was higher in rice crop residue burning seasons than in wheat crop residue burning seasons. During both crop residue burning periods, a sharp increment has been observed in PM levels at all selected sites. It has been seen that the level of PM was higher in Mandi Gobindgarh than Ludhiana and Amritsar. The level of PM was higher in rice seasons due to unfavorable meteorological conditions. BMI wise, the subjects were surrogated in three categories to observe the changes in PFT parameters. All the male and female subjects were grouped separately on the basis of their respective BMI values i.e., either as NBMI (18-23 kgm-2), LBMI (less than 18 kgm-2) or HBMI (>23 kgm-2). FVC of NBMI subjects reduced marginally from 3.2% to 3.4%. The fall in FVC of HBMI subjects were however, greater from 3.6% to 4.2% while for LBMI it varied from 4.1% to 4.3% from their respective baseline values. the FEV1 of NBMI subjects decreased by 3.5% to 3.8% from their baseline values. The fall in FEV1 of HBMI subjects varied by 4.1% to 4.9% while that of LBMI it varied from 5.0% to 5.4% from the baseline value. The fall in PEF of HBMI subjects varied by 4.1% to 4.9% while that of LBM,I it varied from 5.0% to 5.4% from the baseline value. It has been observed from the trends that the PEF of all subjects decreased from their baseline values and the fall was greatest in LBMI subjects in comparison to HBMI and NBMI subjects by 50 to 55%. The FEF25-75% levels of all categories declined due to burden of PM levels. FEF25-75% of NBMI subjects reduced marginally from 1.7% to 1.9%, while the fall in FEF25-75% of HBMI subjects varied by 1.6% to 1.9%. The fall in FEF25-75% of LBMI subjects varied by 2.3% to 2.6% from the baseline value. It has been observed that the subjects of LBMI were affected more than NBMI and HBMI subjects at all sites. Site wise, the decrement was more in FVC and PEF at Mandi Gobindgarh site due to higher level of PM than Ludhiana and Amritsar site. SAC Theory has been to explain as plateau were observed in FVC levels of all BMI categories. It cannot be supported with experimental observations immediately, yet it is hypothesized that during increase in PM2.5 levels from 74µgm-3 till 81µgm-3, 82µgm-3 to 106 µgm-3,107µgm-3 to 117µgm-3 and more than 117µgm-3 the PM2.5 keeps on depositing in the successive pulmonary sacs in the lungs and the FVC observed does not show any fall in its values corresponding to these periods. Further investigations are required to prove this hypothesis. Hence, the sac theory proposed here is supported amply from the plateau getting noticed for children of all age groups and BMI categories.