Toxicity of Water- and Organic-Soluble Wood Tar Fractions from Biomass Burning in Lung Epithelial Cells

Abstract

Widespread smoke from wildfires and biomass burning contributes to air pollution and the deterioration of air quality and human health. A common and major emission of biomass burning, often found in collected smoke particles, is spherical wood tar particles, also known as “tar balls”. However, the toxicity of wood tar particles and the mechanisms that govern their health impacts and the impact of their complicated chemical matrix are not fully elucidated. To address these questions, we generated wood tar material from wood pyrolysis and isolated two main subfractions: water-soluble and organic-soluble fractions. The chemical characteristics as well as the cytotoxicity, oxidative damage, and DNA damage mechanisms were investigated after exposure of A549 and BEAS-2B lung epithelial cells to wood tar. Our results suggest that both wood tar subfractions reduce cell viability in exposed lung cells; however, these fractions have different modes of action that are related to their physicochemical properties. Exposure to the water-soluble wood tar fraction increased total reactive oxygen species production in the cells, decreased mitochondrial membrane potential (MMP), and induced oxidative damage and cell death, probably through apoptosis. Exposure to the organic-soluble fraction increased superoxide anion production, with a sharp decrease in MMP. DNA damage is a significant process that may explain the course of toxicity of the organic-soluble fraction. For both subfractions, exposure caused cell cycle alterations in the G2/M phase that were induced by upregulation of p21 and p16. Collectively, both subfractions of wood tar are toxic. The water-soluble fraction contains chemicals (such as phenolic compounds) that induce a strong oxidative stress response and penetrate living cells more easily. The organic-soluble fraction contained more polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs and induced genotoxic processes, such as DNA damage.

The Toxic Effect of Water-Soluble Particulate Pollutants from Biomass Burning on Alveolar Lung Cells

“…All tests were performed in A549 cells, a commonly used tumorigenic cell line. Pardo et al [13] compared the toxicity of wood tar materials in both A549 and BEAS-2B cells, finding that BEAS-2B were slightly less responsive to the toxic effects of biomass burning than A549. Other studies, however, stated that BEAS-2B is more responsive to toxicity than A549 [31,32].…”

“…Other studies, however, stated that BEAS-2B is more responsive to toxicity than A549 [31,32]. Pardo et al [13] justify the use of A549 cells by stating that BEAS-2B cells are immortalized by integrated SV40 virus and present a low sensitivity, suggesting that the choice of BEAS-2B over A549 is disputable.…”

“…These compounds have a short lifetime in the atmosphere (several hours up to a few days) and they are ubiquitously present in fog and precipitation [10,11]. In addition, two different subfractions (watersoluble vs. organic-soluble) of wood fuel pyrolysis brown carbon (BrC) were tested and shown to be toxic to epithelial lung cells [12][13][14].…”

2021 Climate and Health Review – Uncharted Territory: Extreme Weather Events and Morbidity

“…Research in 2021 contributed to strengthening the evidence that PM 2.5 from wildfire smoke-which may contain residue from burned buildings and other materials-is also more toxic than ambient PM 2.5 . A review highlighted that wildfire smoke contains many of the carcinogenic components of cigarette smoke 39 , and an experimental study found it to induce both oxidative stress and DNA damage 40 . An observational study in Southern California found 10-fold more respiratory hospitalizations in those exposed to wildfire PM 2.5 compared to those exposed to the same amount of ambient PM 2.5…”

Cytotoxicity and chemical composition of women's personal PM2.5 exposures from rural China

“…A549 cells are one of the most commonly used cell lines for in vitro research on the mechanisms of PM health effects, 24,25 and studies comparing A549 and non-cancerous human lung epithelial cells have observed similar trends in toxicities of different PM samples. 26,27 The cells were grown in a humidied atmosphere with 5% CO 2 at 37 C.…”