Oyster shell reduces PAHs and particulate matter from incense burning

This is the first report showing reduction of particle matter and PAHs from incense burning by addition of oyster shell. Worshiping ancestors and gods by burning incense sticks and joss paper is a very important tradition in many Asian regions. More than 45 % of families in Taiwan burn incense twice a day. Unlike joss paper burning, most of the incense burning occurs indoors, thus creating a risk for human health. Previous reports have indeed evidenced toxicity of incense, notably due to particulate matter and polycyclic aromatic hydrocarbons (PAHs). However, there are few methods to reduce particle matter and PAHs from incense burning. We hypothesize that oyster shell may be used to reduce incense fumes toxicity. Indeed a large amount of unused oyster shell is discarded due to increasing seafood consumption. Here, two types of incense were made in the laboratory, and then 5-30 % of oyster shells were added to the incense to study the reduction of particle matter and PAHs. Results show that reduction of particle matter and PAH emission increased with oyster shell addition. The reduction of emission factors is -35 % for mean particle matter, -21 % for particle-phase PAHs, and -37 % for benzo[a]pyrene equivalent concentration (BaPeq), using 30 % oyster shell additive. The addition of 10 % oyster shell reduces the burning time by 8.3 min, increases the burning rate by 3.4 mg/min, and reduces particle matter by 6.4 mg/g incense, particle-phase PAHs by 0.67 mu g/g incense, and BaPeq by 0.23 mu g/g incense. The reductions of particle matter, particle-phase PAHs, and BaPeq correspond to about 640 metric tons, 67, and 23 kg, respectively, per year. Our findings will help to produce safer and cleaner incense.