<P> The tobacco industry has reduced tar and nicotine yields in cigarette smoke since the 1960s . This has been achieved in a variety of ways including use of selected strains of tobacco plant, changes in agricultural and curing procedures, use of reconstituted sheets (reprocessed tobacco leaf wastes), incorporation of tobacco stalks, reduction of the amount of tobacco needed to fill a cigarette by expanding it (like puffed wheat) to increase its "filling power", and by the use of filters and high - porosity wrapping papers . However, just as a drinker tends to drink a larger volume of beer than of wine or spirits, so many smokers tend to modify their smoking pattern inversely according to the strength of the cigarette being smoked . In contrast to the standardized puffing of the smoking machines on which the tar and nicotine yields are based, when a smoker switches to a low - tar, low nicotine cigarette, they smoke more cigarettes, take more puffs and inhale more deeply . Conversely, when smoking a high - tar, high - nicotine cigarette there is a tendency to smoke and inhale less . </P> <P> In spite of the changes in cigarette design and manufacturing over the last 50 years, the use of filters and "light" cigarettes neither decreased the nicotine intake per cigarette, nor lowered the incidence of lung cancers (NCI, 2001; IARC 83, 2004; U.S. Surgeon General, 2004). The shift over the years from higher - to lower - yield cigarettes may explain the change in the pathology of lung cancer . That is, the percentage of lung cancers that are adenocarcinomas has increased, while the percentage of squamous cell cancers has decreased . The change in tumor type is believed to reflect the higher nitrosamine delivery of lower - yield cigarettes and the increased depth or volume of inhalation of lower - yield cigarettes to compensate for lower level concentrations of nicotine in the smoke . </P> <P> Cellulose acetate is non-toxic, odorless, tasteless, and weakly flammable . It is resistant to weak acids and is largely stable to mineral and fatty oils as well as petroleum . It is biodegradable and the raw material is a renewable natural polymer expected to find application for other uses in the future . Smoked cigarette butts contain 5--7 mg (~ 0.08 - 0.11 gr) nicotine (about 25% of the total cigarette nicotine content), children ingesting> 2 whole cigarettes, 6 cigarette butts or a total of 0.5 mg / kg (~ 0, 0035 gr / lbs) of nicotine should be admitted to a hospital . Cellulose acetate is hydrophilic and retains the water - soluble smoke constituents, of which many are irritating (acids, alkali, aldehydes, and phenols), while letting through the lipophilic aromatic compounds . </P> <P> Smoked cigarette butts and cigarette tobacco are toxic to water organisms such as the marine topsmelt (Atherinops affinis) and the freshwater fathead minnow (Pimephales promelas). </P>

When did the first filtered cigarette come out