Walmart and one of its supplier are turning plastic bags, bottles, cardboard and hangars into beds for dogs and litter boxes for cats, along with other eco-friendly pet products.

This is the latest example of what's called "cradle to cradle" design -- although the cradle in question here turns out to be a PoochPlanet Dog Bed, made from recycled plastic bottles.

"We're committed to creating zero waste," explains John Kunkel, senior buyer, pets for Walmart. One way to get there is to take things that Walmart throws away and instead of sending them to a landfill, make them into something useful.

Worldwise, a privately held pet products company based in San Rafael, CA, is supplying the eco-friendly gear to Walmart, the companies said yesterday. Besides the PoochPlanet beds, they include SmartyKat Cat Scratchers (made from recycled cardboard) and the SmartyKat Litter Accessories like the SmartyKat Litter LooLadle (made from recycled plastic hangars).

Worldwise has been a supplier to Walmart since 1996, when the giant retailer began selling its SuperScratcher, a cat scratcher made from corrugated cardboard and organic catnip. Aaron Lamstein, the company's co-founder and executive chairman, told me, "We're the No. 1 supplier of certified organic catnip in the United States."

(It never occurred to me that there was such a thing as certified organic catnip. As one of my high school teachers liked to say, you learn something new every day.)

Now, there's something silly and something serious about this latest initiative from Walmart.

It's silly because anyone who is committed to environmental responsibility would think long and hard about owning a cat or dog. To the best of my knowledge, no one has calculated the carbon impact of pets but it is clearly not trivial in the aggregate. A 2007 survey by the American Veterinary Medicine Association says Americans own are 72 million dogs, 82 million cats, 11 million pet birds and 7 million horses. You'll get a lot of arguments about this topic -- particularly if you write a book called Time to Eat the Dog: The Real Guide to Sustainable Living -- but pets obviously eat and poop**, two activities with undeniable impacts on greenhouse gas emissions, land use, stocks of fish in the ocean and the like. Of course, as a former owner of a dog (a golden retriever name Sophie, may she rest in peace), I'm well aware of the benefits that owning a pet can bring.