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Litter And The Environment


Pet Camp and Cat Safari owner does some homework for his facility
By Mark Klaiman

Litter ScoopRetailers are always asked about the pros and cons of various litters as they relate to a cat’s litter box environment—will there be dust, will there be tracking, will there be a smell? It is only recently, however, that this discussion was extended to include the effect of litter (and cat waste) on our environment.

For the last several years Pet Camp has participated in a unique program to find an alternative way to dispose of dog poop. As Pet Camp’s work in the dog poop field has gotten wider attention, clients and others have started to ask us about cat waste. They all want to know about cat litter and cat waste, and what is the greenest way to deal with them.

As is often the case with environmental issues, there is no perfect solution.

Types of Litter
Traditional clay-based cat litter, introduced in the mid-1940s, is made from natural clay, extruded into pellets and dried. In the mid-1980s a particular type of clay—sodium bentonite —was introduced as clumping cat litter. Clay litter continues to be the dominant type of cat litter sold in the United States, and more than 60 percent of the clay litter is of the clumping variety.

A second type of popular cat litter is silica gel based. Silica gel has millions of tiny pores on its surface, enabling it to absorb up to 40 times its weight in moisture.

The last main type of cat litter is plant based. Included within this category are litters made from corn, wheat, beet pulp, pine and other plant materials. The newest member of the cat litter family, though not yet in widespread use (and won’t be discussed here), is “recycled” litter, which is made out of products such as newspaper or pine saw dust.

Clay-based Litters
Clay-based cat litter must be mined. The United States Geological Society estimates that 85 percent of the 2.54 million tons of clay used in this country every year is used for absorption of pet waste, with cat litter being the dominant. There are about 20 companies operating such mines in 10 states. (For detailed information on clay mining operations, see “U.S. Geological Survey, Minerals Information 1996” and “U.S. Geological Survey Minerals Yearbook 2001” both by Robert L. Virta.)

As with all mining operations, there is an environmental impact. Because sodium bentonite mining is only economical when the material is close to the surface, the impact of this mining is similar to other strip-mining operations. In strip mining the top layer of soil (called the overburden) is removed and then the clay is taken out.

Most sodium bentonite clay is mined using only a scraper or bucket loader. The result of this operation is a depression or a pit that must then be reclaimed. While laws mandate the reclamation of land impacted by mining operations, there remain heated disputes over the extent and timing of such reclamation efforts and whether the environmental impacts of strip mining can ever be addressed through reclamation.

After being mined, the clay is then transported to a second facility, where it is dried. Only then is it processed into a powder or flake to be used as cat litter. The environmental impact of clay litter production, in addition to the mining itself, includes the transportation of the clay to the drying facility as well as the use of petroleum products to generate sufficient heat needed to dry the clay.

Of course, after it is used, the litter must be disposed of. Clay cat litter is sent to landfills where its sits for an eternity. Since one assumes all cat clay litter purchased and used eventually gets thrown out, we are talking about a huge amount of cat litter ending up in landfills every year. The net result is that clay-based cat litter has a sizable environmental impact in both its manufacture and disposal.

Silica Gel-Based Litters
How about the other options? Silica gel is a patented formula that makes sodium silicate more porous. This litter is made from silica dioxide, the type of sand found in quartz. It is then mixed with oxygen and water to make silica gel.

Originally patented in 1919 for use in gas masks during WWI, silica gel is currently used for much more benign purposes. Since it is made from sand, silica gel also has a mining component. (For more background information on silica gel, see “Demystifying Silica Gel” by Steven Weintraub, Object Specialty Group Postprints, vol. 9, 2002.)

Silica gel, because it is lightweight, is often manufactured in other countries and then shipped to the United States. It thus has a transportation component not present in clay litter. The big upside to silica gel is that it does not need to be changed as frequently as clay-based litter. In fact, in many single-cat households, the litter only needs to be changed once a month. Thus the disposal implications of silica gel litter, in terms of landfill volume, is considerably less than that associated with clay based litter.

One of the potential environmental downsides of silica-based litter is that while the litter needs to be changed infrequently, fecal material must be removed from the cat litter and disposed of on a regular basis. Recently there have been concerns expressed in California that when cat feces is flushed down the toilet (a very viable option for those using silica gel litter) a parasite in the feces, toxoplasma gondii, may be responsible for killing sea otters. Wastewater treatment facilities are not designed to address toxoplasma, and the thought is that the otters may be getting ill from eating mussels and other filter feeders that concentrate the toxoplasma.

The Monterey Bay Aquarium and others in California have expressed concern about toxoplasma. These concerns lead to an amendment to the California Fish and Game Code that provides:

  • The Legislature finds and declares that several types of nonpoint source pollution are harmful to sea otters, and that scientific studies point to links between cat feces, the pathogen T-ghondii, and sea otter mortality.  The Legislature further finds and declares that efforts to reduce the flushing of cat litter and car feces are steps toward better water quality in sea otters’ natural habitat.
  • Any cat litter offered for sale in this state shall contain one of the following statements:
  • “Encouraging your cat to use an indoor litter box, or properly disposing of outdoor cat feces, is beneficial to overall water quality. Please do not flush cat litter in toilets or dispose of it outdoors in gutters or storm drains.”
  • A general statement that encourages the disposal of cat feces in trash and discourages flushing cat feces in toilets or disposing of them in drains. (See California Fish and Game Code Section 4501).

As part of its educational outreach regarding toxoplasma, the Monterey Bay Aquarium suggests that guardians of indoor/outdoor cats provide an outdoor litter box as well as an indoor one. 

Of course, those using silica gel litter could simply dispose of their cats’ feces in the garbage, but that adds more waste to landfills.

Plant-Based Litters
Plant-based litter is probably the least environmentally offensive cat litter. Certainly there are plusses and minuses of the various plants used to create the litter, but generally those concerns do not trump the overall advantages when compared to clay- or silica-based litter. Plant-based litter is marketed as both biodegradable and flushable. But these claims may be overstated.
Flushing plant-based litter along with cat feces has the same potential toxoplasma issues noted above. Further, as anyone who has ever suffered through a stopped-up drain, putting anything, even something described as “flushable,” down the drain increases the likelihood that you will be dealing with a drain problem later. For that reason, many users of “flushable” plant-based cat litter will dispose of it the old fashioned way—throw it out.

The question becomes, what happens to biodegradable cat litter once you throw it out. Does it actually biodegrade?

It turns out that the answer depends on where you throw it out. Claims of biodegradable and compostable are premised on the user actually composting the used cat litter or using the spent cat litter as mulch in a garden. (Retailers should warn customers that if they use these litters as mulch they must remove the feces from the litter and dispose of the feces in the trash.)

From an environmental point of view, one must remember that none of the claims of biodegradable and compostable take into account the more common practice of placing the used cat litter in the trash bin and having it end up at the landfill– just like the clay-based and silica-based cat litter does. When biodegradable cat litter ends up at the landfill, it does eventually break down (assuming it is not wrapped in a plastic bag), but it does not “biodegrade” as the American Society for Testing and Materials uses that term nor as it is used by most state codes.

While no study has been conducted directly evaluating how such liter breaks down in landfills, studies performed by W.L. Rathje at the University of Arizona confirm that most modern landfills are packed very tightly, contain little soil and not very much oxygen. These environmental conditions greatly inhibit biodegradation of even products that in other environments would biodegrade.

Further, municipalities operating compost facilities often exclude animal waste and cat litter from such operations. For example in my hometown of San Francisco, kitty liter or animal feces” may not be placed into a compost bin for collection.  Thus, this litter neither “biodegrades” nor is “composted” in normal usage.

Retailer Issues
What is the conscientious cat lover to do? Is there a good way to dispose of cat litter or even just cat feces? There is no easy answer that is applicable to everyone.

Like the conscientious cat lover, the conscientious retailer is faced with some difficult questions and not-so-easy solutions. While clay-based cat litter remains the dominant form of litter in the market (largely based on its inexpensive price per pound), it may be the most expensive in terms of its impact on the environment.

At the same time, litter often costing much more may not meet all of the environmental goals of the purchaser. The newer generation of plant-based cat litter is a better answer than older clay-based cat litter, but they are not a perfect solution, nor do we have enough data to determine if cat feces should be flushed or trashed.

The conscientious retailer is left in the position of having to explain the pros and cons of each approach to the cat lover. This approach takes time and energy—but doesn’t all quality customer service, and isn’t that what we all want to deliver?

Mark Klaiman runs green facilities Pet Camp and Pet Camp Cat Safari in San Francisco. 

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