Does kitty litter contain harmful substances

 Q6: Why do they put silica dust in cat litter if it’s so dangerous? #CatHealthChat
[...] 2. Avoid clumping cat litter. My cats (RIP) used clumping cat litter. It is bad. Not only does it contain silica, which is a carcinogen when inhaled (and you know how the cats can kick up that litter dust), but clumping cat litter also contains sodium bentonite which clumps up to 15 times it’s size. Think of that non-biodegradable yuck hanging out in the landfills. Read more about it on Moderncat. [...]
On this website for example, the author begins by saying that dust from silica cat litter is a definite danger:
Some cat litters may trigger allergic reactions in both humans and felines. This often happens after inhaling silica dust, a common byproduct found in many clay-based litters. In a we outlined the main problems with clay litter – and this is just one more reason to keep your family away from it! in clay based clump cat litter, silicon constitutes most of the dust particlesMany mass market cat litters contain significant amounts of silica dust which has ..dust bothers you, you should go for pine, recycled paper, or silica cat litter.
Results: Dust particles obtained from seven commercial cat litters have an identifiable appearance and elemental ratio (primarily aluminum and silica). The same pattern is observed in particles obtained from lung wash wash fluid of cats, and significantly more silica particles were obtained from cats with respiratory disease than cats without respiratory disease.When you pour clay litter (clumping or regular) into a litter pan a puff of dust floats up towards you and streams throughout the room. You are inhaling these particles directly through your nose. The residual litter dust is inhaled indirectly as it travels throughout the room and around your home. However, your cat is under constant exposure to silica dust since each time he uses the box he inhales these particles directly into his lungs. Plus he is also inhaling the indirect dust floating in the home atmosphere.Interpretive Summary
Inhaled silica dust has been implicated as a cause of lung cancer and other respiratory diseases in humans and several animal species. Electron microscopy and x-ray spectroscopy were used to identify and characterize dust particles from seven brands of commercially available clay cat litters and to identify, characterize and quantify particles in the lung wash fluid of six cats with and six cats without signs of respiratory disease. Dust particles from clay cat litter have an identifiable appearance and elemental ratio (primarily aluminum and silica) and the same pattern was observed in particles obtained from lung wash fluid. Significantly more silica particles were obtained from cats with than without respiratory disease. This suggests an association between presence of silica particles and respiratory disease, but it is unknown whether silica dust particles contribute to respiratory disease or accumulate because of interference with normal lung ciliary function.In cats, respiratory diseases such as bronchial asthma, chronic bronchitis, viral, bacterial and pyogranulomatous pneumonia, and pulmonary neoplasia are commonly diagnosed (12). The incidence of primary lung tumors in cats is rare. It is estimated that 1-2% of the general cat population has asthma or chronic bronchitis, however, in some pure breeds, such as the Himalayan and Siamese it may be as high as 5% (13). Despite treatment, these problems may progress and can lead to life-threatening episodes and chronic respiratory disease. In the United States, the majority most of household cats are exposed to silica dust on a daily basis since more than 95% of cat litter is a form of silica (6). Although dusty cat litter has been suggested as exacerbating respiratory problems in cats, no research to date has demonstrated the presence of inhaled silica in airway secretions in cats or the presence of silica in primary lung tumors. The study reported here used scanning electron microscopy and x-ray spectroscopy (14) to analyze particles obtained from tracheal washings (TW) and bronchoalveolar lavage (BAL) fluid of 6 cats with and 6 cats without signs of respiratory disease. Respiratory secretions rather than lung biopsies were chosen to document the presence of silica because it is an accepted method in diagnosing human cases (11) and lung biopsies were not warranted for workup of the respiratory signs.