Clumping litter
Close up of cat litter Clumping litters were first developed in the UK in the 1950s by the Fuller's Earth Union, later to become a part of Laporte Industries Ltd. The type of clumping litter developed by the FEU was calcium bentonite, a less swelling and less sticky type than American bentonite. Subsequently in America, clumping bentonite was developed in 1984 by biochemist Thomas Nelson. Most are made from granulated bentonite clay which clumps together when wet and forms a solid mass separate from the other litter in the box.
This solid clumped material can be scooped out and disposed of without changing the entire contents of the litter box. However, the entire contents should be changed on a regular basis to prevent buildup of bacteria; every four to six weeks is recommended. At the same time, the litter box itself should be disinfected.
Approximately 69% of the cat litter market consists of clumping litter. Clumping litter usually also contains quartz or diatomaceous earth (sometimes called diatomaceous silica, which causes it to be mistakenly confused with silica gel litter). Because of the clumping effect, it is not recommended to flush clumping litters down the toilet. The top two clumping litters in the United States according to sales data are Fresh Step and Tidy Cats.
In recent years, there are increasing claims that clumping litter can be harmful to pets because if it is ingested or inhaled, it swells and solidifies inside them. This is thought to be particularly dangerous for kittens, who are more likely to ingest cat litter and less likely to recover easily. However, other than anecdotal testimonial, there has been little evidence for the claim, and no confirmed cases in the scientific literature.
Clumping clay cat litters also contain crystalline silica, or silica dust, which is a known carcinogen according to California Proposition 65. It has been proven to not be of a significant risk to humans, but there are no regulations or studies to show the affect of silica dust on cats. Clay litter has also come under scrutiny due to the fact that the clay used in its production is commonly stripmined in an environmentally degrading process.