В Пуне уровень бактериальных аэрозолей в домах превысил международные нормы

Pune: Researchers from Savitribai Phule Pune University (SPPU) have conducted a single site study and observed indoor bacterial aerosol levels well above international residential guidelines. It is one of the first size-resolved baseline pictures of household bioaerosol exposure in an Indian city. Bioaerosols are microscopic biological particles, such as bacteria and fungi, that float in the air and can be breathed in. Akshay Kale and P Gursumeeran Satsangi of SPPU chemistry department carried out the study that was published in the journal Aerobiologia. They sampled air at a residential home in Pashan over six months — Jan-June 2022 — using a six-stage cascade impactor that separated airborne bacteria and fungi by particle size. Indoor and outdoor readings were taken across winter and summer, with 24 sampling runs and 144 plates analysed. Satsangi said, “Indoor bacterial concentrations peaked at 3,097 colony forming units (CFU) per cubic metre in summer and 2,131 CFU per cubic metre in winter — both above the 500 CFU per cubic metre benchmark set by the American Industrial Hygiene Association for residential settings.” . Outdoor bacterial levels were lower than indoor readings, but also crossed the threshold in both seasons. “Fungal aerosols showed the reverse pattern and stayed within guideline limits throughout,” she said. Satsangi said natural forces constantly cleaned the air outdoors: UV radiation from sunlight, rain and wind all help break down or disperse bacteria before they build up. None of that happened indoors — so bacteria from everyday human activity (skin, breath, movement), pets, poor air circulation and contaminated surfaces just accumulated, especially in a house with limited ventilation. Researchers also modelled how deep these particles penetrated the lungs of children and adults, and how breathing route changed that. “When children breathed through the nose — as during rest — deep lung deposition was 34%-36% lower than when breathing through the mouth, which tends to dominate during exertion such as play,” she said. Researchers didn’t measure lung deposition directly in people — but they calculated it. “We estimated how much bacteria/fungi would settle in different parts of the respiratory tract — nose, throat, bronchi and deep in the lungs — using the pollution levels plus standard scientific formulas (based on breathing rate, particle size and exposure time). The observation was done under two scenarios: breathing through the nose (like when resting) versus through the mouth (like during exercise or play),” Satsangi said. They ran the calculation separately for children and adults, since kids breathed differently and were exposed differently over time. That’s how they arrived at the finding that nose-breathing kept a lot more of the bacteria out of a child’s deep lungs compared to mouth-breathing. Despite the elevated raw bacterial counts, the study’s calculated hazard index — a standard risk-screening metric that factored in exposure time, breathing rate and other variables — stayed below one for both bacteria and fungi, indoors and outdoors, across both seasons. A hazard index below one generally indicated the exposure was not flagged as a health concern under the framework. However, researchers said it shouldn’t be read as a clean chit of health: bioaerosols behaved differently from chemical pollutants and there’s no universally accepted reference concentration to judge the biological risk. They also found the hazard index was around 72% higher indoors than outdoors — linked to residents spending longer hours at home (roughly 13 hours a day) than outside, combined with the higher baseline microbial load found indoors. The study is based on a single house in one Pune neighbourhood over a one six-month cycle. It relied on culture-based counting methods that don’t capture non-culturable organisms — limitations the researchers themselves flagged. They have called it a baseline data set that can inform future, broader indoor air quality research and residential guidelines, rather than a conclusive risk assessment on its own.