|Rice Straw Burning - 84
HAZARDOUS CONSTITUENTS OF RICE STRAW SMOKE
Research was conducted from 1980 to 1983 by the Department of Environmental Technology to determine if rice straw smoke contained constituents that might be hazardous to human health. The procedure used was to expose whole smoke or fractions of smoke to a bacterium which mutates (changes form) in the presence of a carcinogen, or cancer-causing substance. This test is only an indicator, not proof that a substance is a carcinogen. Not all compounds that react to this test are carcinogens. Most carcinogens, however, do cause the bacterium to mutate. The tests are conducted at two levels. Directacting mutagenic activity occurs in the presence of the compound with the bacterium. Indirect activity requires the presence of an enzyme to activate the compound before mutations can occur.
No direct mutagenic activity was found with either rice or barley straw smoke particulate matter collected from the field, although some indirect mutagenic activity was found. A comparison was made between smoke collected adjacent to a burning field and smoke collected downwind from the burning field. Samples collected downwind showed reduced indirect mutagenic activity in comparison with collections made adjacent to the field. Another comparison was between smoke exposed to simulated sunlight for 24 hours and smoke not exposed to sunlight. Simulated sunlight reduced the level of indirect mutagenic activity. It appears that natural environmental exposures reduce mutagenic activity.
In still other comparisons, extracts from rice smoke were compared with extracts from wood stove smoke and cigarette smoke particulate matter. The wood smoke particulate matter extracts showed a much higher level of direct mutagenic activity than the rice straw smoke particulate matter. Cigarette and rice smoke particulate matter extracts showed only indirect mutagens, although the cigarette smoke was at a level about five times higher than field rice straw smoke.
From the standpoint of human health, an important consideration is that exposure of most of the population to rice smoke is only brief and sporadic while many people are exposed to cigarette smoke on a chronic or daily basis. In addition, rice smoke is rapidly diluted as it moves downwind from its source. No rice pesticides or breakdown products from pesticides have ever been detected in rice smoke.
BURNING METHODS REDUCE AIR POLLUTANTS
The failure to find economical uses for rice straw had left burning as the only economical system of rice straw disposal. The Rice Research Board has supported research to find burning methods that reduce the amount of smoke entering the atmosphere.
From 1969 to 1974, new burning techniques were studied in rice fields and in the laboratory. These studies concluded that:
By using the appropriate burning procedures in combination with short-statured, stiffer straw varieties, reductions over preregulated burning methods can be as much as 80 percent for particulate matter, over 65 percent for gaseous hydrocarbons, and over 80 percent for carbon monoxide. Although ideal burning procedures and conditions are not always possible, the method of rice straw burning now in general use has eased the air pollution problem.
IMPROVED WEATHER AND WIND PREDICTIONS TO REDUCE AIR POLLUTANTS
Since 1981, the Rice Research Board has funded a project to improve air quality during the sfraw burning season by gathering better weather information and communicating it to air pollution control district officers. Participants in this project include the Air Resources Board, Central Computer Operations, a technical advisory committee, air pollution control districts, Nowcasting and Fife Environmental. The goal is to develop a rapid communication and decision-making system that protects air quality and airport visibility, reduces the number of days with smoke problems and public complaints, makes better use of good ventilation days for straw burning, and increases the amount of straw that can be burned.
More control has been shifted to local air pollution control districts. There is now greater flexibility in the system, burn hours have been shortened to reduce air quality problems, weather forecasts are more frequent and reliable, the number of burn days has increased, and all the air quality measures have improved.
The air quality indicators used in these studies were coefficients of haze, hours of smoke recorded at valley airports and complaints received by the Air Resources Board. The recent burning program has reduced the coefficient of haze 30 percent, airport smoke observations 65 percent and complaints 75 percent compared with these same indicators in 1980.
The agricultural burning guidelines of the California Administrative Code were amended as a result of these grower-supported studies. A variable acreage allocation is made depending on atmospheric conditions instead of the previous limit of emissions to 335 tons per day on permissive burn days. The daily acreages of open burning are made by the Air Resources Board based on meteorological conditions. They are prorated among all air pollution control districts.
LUNG ASSOCIATION GIVES RICE INDUSTRY CLEAN AIR AWARDS
The Rice Research Board, as representative of the California rice industry, received 1984 clean air awards from the Sacramento and Superior California chapters of the American Lung Association. The awards were made for industry efforts over the past five years to reduce smoke over urban areas during the fall rice straw burning season.
Rice growers have invested more than three million dollars in smoke reduction efforts. More than one million has been spent to reduce smoke from burning, and two million have been spent for research on alternative uses for rice straw. The cooperative work leading to improved weather and wind prediction capabilities and the better burning procedures has been the most successful effort to reduce the smoke problem. ° .,