COVID-19 Lockdown in Israel: The Environmental Effect on Ultrafine Particle Content in the Airway

Abstract

Inhaled ultrafine particle (UFP) content in exhaled breath condensate (EBC) was observed as an airway inflammatory marker and an indicator of exposure to particulate matter (PM). The exceptional decline in air pollution during the COVID-19 lockdown was an opportunity to evaluate the effect of environmental changes on UFP airway content. We collected EBC samples from 30 healthy subjects during the first lockdown due to COVID-19 in Israel (March-April 2020) and compared them to EBC samples retrieved during April-June 2016 from 25 other healthy subjects (controls) living in the same northern Israeli district. All participants underwent EBC collection and blood sampling. Ambient air pollutant levels were collected from the Israeli Ministry of Environmental Protection's online database. Data were acquired from the monitoring station closest to each subject's home address, and means were calculated for a duration of 1 month preceding EBC collection. UFP contents were measured in the EBC and blood samples by means of the NanoSight LM20 system. There was a dramatic reduction in NO, NO₂, SO₂, and O₃ levels during lockdown compared to a similar period in 2016 (by 61%, 26%, 50%, and 45%, respectively). The specific NO₂ levels were 8.3 ppb for the lockdown group and 11.2 ppb for the controls (p = 0.01). The lockdown group had higher UFP concentrations in EBC and lower UFP concentrations in serum compared to controls (0.58 × 10⁸/mL and 4.3 × 10⁸/mL vs. 0.43 × 10⁸/mL and 6.7 × 10⁸/mL, p = 0.05 and p = 0.03, respectively). In this observational study, reduced levels of air pollution during the COVID-19 lockdown were reflected in increased levels of UFP airway contents. The suggested mechanism is that low airway inflammation levels during lockdown resulted in a decreased UFP translocation to serum. Further studies are needed to confirm this hypothesis.

Keywords: COVID-19; EBC; NO2; UFP; air pollution; lockdown.

Figure 1

NO₂ and EBC-UFP levels in the lockdown group vs. the control group. NO₂ exposure level as measured in environmental stations located near the subjects’ home addresses during April 2016 (A) and during the first lockdown in April 2020 (B). NO₂ 1-month average exposure level (ppb); green dots x ≤ 5.8, yellow dots 5.8 < x ≤ 7.8, orange dots 8.7 < x ≤ 12.7, red dots x > 12.7. Biological monitoring of EBC-UFP content in relation to environment stations during April 2016 (C) and during April 2020 (D). UFP concentrations in EBC (10⁸/mL); blue dots x ≤ 0.4, light blue dots 0.4 < x ≤ 0.66, white dots 0.66 < x ≤ 0.95.

Figure 2

UFP and CRP levels in biological samples of the study population (n = 55). (A) Ultrafine particle concentrations in exhaled breath condensate and (B) in serum. (C) C-reactive protein concentrations in serum.

Figure 3

UFP content in inflamed respiratory epithelium-suggested mechanism. Increased epithelial permeability in inflamed airways allows more UFP to penetrate and translocate into the lung parenchyma and circulation, leading to a reduced concentration of UFP in EBC samples. Created with BioRender.com.