Characterization of hazardous Constituents of Rice Straw Smoke 82

Characterization of Hazardous
Constituents of Rice Straw Smoke-82

Project Leader and Principal UC Investigators

D.P.H. Hsieh, and J.N. Seiber, Department of Environmental Toxicology, UC Davis

The primary purpose of this project is to determine the biological activity of rice straw smoke from open field burning. The four objectives are: (1) to identify components in four fractions of smoke particulates collected in a burning tower at the University of California, Riverside, and having the highest activity in the Ames Mutagenicity Assay, (2) to compare these four fractions in terms of composition and mutagenicity with those from samples collected adjacent to an open field. (3) to determine changes in composition and mutagenicity when smoke particulates were exposed to air and light and (4) to extend the environmental analyses to smoke particulate samples collected downwind from an open field burn, from other types of grain stubble and from diesel engines.

Terry Mast, Department of Environmental Toxicology, finds the mutagenicity of breakdown products from rice smoke to be relatively low compared to other emissions in the environment.

The laboratory analytical methods used were capable of separating the collected smoke into over 75 compounds. These methods and results were reproducible. The rice straw smoke particulate matter collected from the burning tower at UC Riverside had a higher level of mutagenic activity than field collected samples. This may have been caused by the high ozone and oxidant present in the Riverside atmosphere at the time the straw was burned.

No direct-acting mutagenic activity was found either in rice or barley straw smoke particulate matter. Direct-acting mutagenic activity by the Ames Mutagenicity Assay causes mutation without oxidation by the rat liver enzymes in the test system. Indirect activity requires the enzymes to show mutagenic activity. Not all compounds that are active in the Ames test are carcinogens or substances that cause cancer. However, most known carcinogens are active according to the Ames test. The Ames test is widely used as an indicator of substances that may cause cancer but is not a sufficient test.

No direct-acting mutagenic activity was found either in rice or barley straw smoke particulate matter.

A comparison was made of both direct and indirect mutagenic activity by the Ames test of rice smoke particulate matter collected directly adjacent to a field burn and 400 yards downwind from the burn. The downwind samples showed slightly less indirect mutagenic activity than samples collected adjacent to the field. No direct mutagenicity was obtained from any field samples. However, direct mutagenicity was obtained from rice straw smoke collected in the Riverside burning tower and from diesel soot particulate matter.

The level of mutagenic activity of field samples exposed to sunlight for 24 hours was reduced compared with samples kept in the dark. These results indicate that "weathering" of rice straw smoke particulate matter in the atmosphere may reduce mutagenic activity, but these results require further testing. Other studies remaining to be completed are further identification of fractions from field samples and a comparison of rice straw smoke particulate matter with tobacco and wood smoke. However, results to date indicate rice smoke mutagenic activity to be relatively low compared to other emissions in the environment.