Human health risk assessment of atmospheric pollutant emissions from open field burning of rice residues

Burning rice straw as agriculture waste in open fields is a common practice in several Asian countries as part of annual rice cultivation cycle. This process results in a significant emission of air pollutants into the atmosphere. Hence, the aims of this study were: identifying the concentrations of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) in gaseous and particulate phases, source identification and health risk assessment of residential living around open burning area in three key agricultural regions of northern Iran (including Mazandaran, Gilan and Golestan) during the summer-fall seasons in 2022. Gaseous-phase samples (PAHs and BTEX) were collected using a SKC pump with XAD-2 and charcoal adsorbent tubes, while particulate-phase PAH samples bound to PMs were captured using a cascade impactor. Air toxics were then analyzed using gas chromatography equipped with flame ionization detector (GC-FID). The results showed that Mazandaran province had the highest concentrations of PMs among all samples at the open burning sites. For particulates PAHs Mazandaran exhibited ∑16 PAHs bounded on PM_10, PM_2.5, TSP of 3495.1 ± 274 ng/m³, 3478.1 ± 329.75 ng/m³ and 4150 ± 310 ng/m³ at open burning respectively. For gaseous samples from non and open burning areas, the concentration of ∑16 PAHs in Mazandaran province were 4.3 ± 0.74 ng/m³ and 2718 ± 57.3 ng/m³, respectively. The concentrations of total BTEX in Mazandaran during the rice straw open burning phenomenon, were 802.58 ± 75.55 μg/m³. To assess the health risks, incremental lifetime cancer risk (ILCR) was calculated for PAHs; and lifetime cancer risk (LTCR) and hazard quotient (HQ) of BTEX in children and adult were determined. Calculated ILCR for adult and children in Mazandaran were 2.32E-04 and 1.62E-05 which were unacceptable compared to U.S. EPA limits of 1.0 E-06. For BTEX, LTCR value exceeded the acceptable threshold and the HI in child of Mazandaran was determined more than 1. There is limited field research in the world and no study conducted in Iran about human health risk of rice straw open burning. Our results revealed that the highest values of ILCR and LTCR allocated to the open burning phenomenon in Mazandaran; moreover, the source diagnosis ratio illustrate the correlation to rice straw open burning emissions.