Air pollution and respiratory symptoms: results from three panel studies in Bangkok, Thailand.

Several studies in North American cities have reported associations between air pollution and respiratory symptoms. Replicating these studies in cities with very different population and weather characteristics is a useful way of addressing uncertainties and strengthening inferences of causality. To this end we examined the responses of three different panels to particulate matter (PM) air pollution in Bangkok, Thailand, a tropical city characterized by a very warm and humid climate. Panels of schoolchildren, nurses, and adults were asked to report daily upper and lower respiratory symptoms for 3 months. Concentrations of daily PM(10) (PM with a mass median aerodynamic diameter less than 10 microm) and PM(2.5) (airborne particles with aerodynamic diameters less than 2.5 microm) were collected at two sites. Generally, associations were found between these pollution metrics and the daily occurrence of both upper and lower respiratory symptoms in each of the panels. For example, an interquartile increase of 45 microg/m(3) in PM(10) was associated with about a 50% increase in lower respiratory symptoms in the panel of highly exposed adults, about 30% in the children, and about 15% in the nurses. These estimates were not appreciably altered by changes in the specification of weather variables, stratification by temperature, or inclusion of individual characteristics in the models; however, time trends in the data cause some uncertainty about the magnitude of the effect of PM on respiratory symptoms. These pollutants were also associated with the first day of a symptom episode in both adult panels but not in children. The estimated odds ratios are generally consistent with and slightly higher than the findings of previous studies conducted in the United States.

KCl potentiation of the virucidal effectiveness of free chlorine at pH 9.0.

In studies at 5 degrees C and pH 9.0, poliovirus 1 was inactivated about 15 times more rapidly by free chlorine (FC) in purified water in the presence of 1,262 mg of KCl per liter (approximately 0.0169 M) than in the absence of KCl. In the presence of 526 mg of KCl per liter, the virus was inactivated about seven times more rapidly by FC than in the absence of KCl. At a level of 21 mg/liter, KCl did not significantly potentiate the virucidal activity of FC in purified water. Although poliovirus 1 was inactivated almost three times more rapidly by FC in borate-buffered purified water than in purified water, the presence of the buffer did not alter the extent of potentiation by KCl. Most of FC exists as OCl- at pH 9.0. Tap water has been shown to markedly potentiate the polivirucidal effectiveness of FC at pH 9.0. For the same degree of virucidal potentiation of FC at this pH, a considerably greater quantity of KCl was required in purified water than the total salt content that appeared to be present in the tap water.

Potentiation of the virucidal effectiveness of free chlorine by substances in drinking water.

At 5 degrees C, poliovirus 1 was inactivated by free chlorine (FC) at pH 9.0 more than 10 times as rapidly in drinking water as in purified water. Because ions that comprise many salts potentiate the virucidal effectiveness of FC, we believe that ions and possible other substances in the drinking water potentiated the virucidal effectiveness of FC. Since viruses may be much more sensitive to chlorination in drinking waters than laboratory tests in purified waters have heretofore led us to believe, it may be possible to reduce the amounts of FC applied to many water supplies for disinfection and thereby perhaps reduce the quantities of halomethanes and other toxic compounds produced in these supplies by the chlorination process.

Potentiation of the poliocidal effectiveness of free chlorine by a buffer.

Poliovirus 1 was inactivated by free chlorine at pH 9.0 three times more rapidly in boric acid (0.05 M)-NaOH buffer than in purified (carbon-filtered, deionized) water. Thus, at a given concentration of free chlorine, it took three times longer to inactivate the same fraction of the poliovirus in purified water than in the boric acid-NaOH buffer. Conversely, in a given period of time, three times more chlorine was required to inactivate a given percentage of the virus in purified water than in the boric acid-NaOH buffer. Buffers are almost always used to control pH in disinfection studies with free chlorine and with other chlorine compounds also. The use of buffers for pH control in such disinfection studies may distort the resulting data and, at least for waters that contain little salt, may cause serious overestimation of the rates at which viruses are inactivated.