Radicals in the church

To the Editors:

Public health is seriously threatened by exposure to ambient and indoor particulate matter (PM). Epidemiological studies have demonstrated that long-term exposure is associated with lung cancer and other pulmonary diseases 1. In vitro studies have demonstrated the involvement of polycyclic aromatic hydrocarbons (PAH), inflammation and oxidative stress in these adverse health effects 2–4. As free radicals are also known to play a crucial role in these processes, we developed an electron spin resonance (ESR)-based methodology to quantify the radical-generating capacity of PM. We applied this methodology in order to evaluate the effect of burning candles and incense, known sources of indoor air PM 5, on the radical-generating capacity of PM in a Roman Catholic church (Onze Lieve Vrouwe Basiliek, Maastricht, The Netherlands).

PM passing through a size-selective inlet with a 50% efficiency cut-off at a 10-µm aerodynamic diameter (PM₁₀) was sampled in a small chapel before and after 9 h of continuous candle burning (the normal daily practice). Additionally, in a large basilica, PM₁₀ was sampled before and after a simulated service with incense burning. Radical-generating capacity and total PAH concentrations were analysed and compared to those of PM₁₀ from high-traffic locations. Free-radical formation was measured by placing the filters directly into the ESR apparatus, after adding the spin trap 5,5-dimethyl-1-pyrroline-N-oxide.

It was found that PM₁₀ concentrations before candle/incense burning are three-fold higher as compared with the outdoor values (table 1⇓), and clearly exceed the 24-h average European Union standard of 50 µg·m⁻³. Moreover, incense and candle burning were found to increase PM₁₀ concentrations up to levels exceeding 1,000 µg·m⁻³. The average oxygen radical-generating capacity of PM₁₀ from high-traffic locations was remarkably lower as compared with that of PM₁₀ sampled before and after candle or incense burning. The post-service measurements in the church show that the burning of incense generates an additional ESR signal that is typical for a carbon-centred radical, whereas oxygen-radical formation decreases concomitantly. This suggests that the interaction between oxygen free radicals and other organic substances present in incense-derived PM results in the formation of this other type of radical. Furthermore, a signal of an unidentified free radical is found after burning incense and, even more pronounced, after burning candles in the chapel. A search in the US National Institute of Environmental Health Sciences (NIEHS) spin trap database 6 did not link this ESR signal to any known type of free radical. Pre-service PAH levels in both church and chapel were higher as compared with the outdoor measurements, and increased by a factor of four and 10 after burning incense and candles, respectively.

In view of the exceptionally high particulate matter passing through a size-selective inlet with a 50% efficiency cut-off at a 10-µm aerodynamic diameter and high polycyclic aromatic hydrocarbons levels found in this church, combined with a high radical-generating capacity, it cannot be excluded that regular exposure to candle- or incense-derived particulate matter results in increased risk of lung cancer or other pulmonary diseases. Further research is needed to characterise the genotoxic potential of the unidentified radicals and to evaluate the actual health risk associated with exposure to this mix of free radicals and carcinogenic polycyclic aromatic hydrocarbons.