Promoting plug-in hybrids and saving sea sponges.

As I understand it, "hybrid" cars make use of an electric motor that never needs to be plugged in. But how do those proposed "plug-in" hybrids I've been hearing about work?--Jen Seminara, Omaha, NE

The mass-market gasoline-electric hybrids made by Toyota, Honda and others use an electric motor in conjunction with a gas engine. The electric motor can run the car at slow speeds (as in the Toyota Prius) or work largely as a power booster to a smaller-than-usual gas engine (the Honda Civic Hybrid). Contrary to popular belief, hybrids don't need to be plugged in because the on-board battery is constantly being charged by the gas engine and by the motion of the wheels and brakes.

The so-called "plug-in hybrids," until now mostly built by enthusiasts, take this technology a step further. By adding the ability to charge up an auxiliary battery pack from a standard household outlet, typically overnight, plug-in hybrid cars relegate the gas engine to back-up status and instead let the electric motor do most of the work.

Proponents claim that these "gas-optional" cars can A be twice as fuel efficient as current hybrids, achieving 150 miles per gallon or more. Additionally, they say, powering up plug-in hybrids with wall sockets results in far less pollution (from the power plants providing the electricity) than an equivalent gasoline-powered car spews out its tailpipe. Meanwhile, plug-in hybrids recharged from rooftop solar power systems might approach being the world's first mass-market "zero emission" vehicles.

Convincing the public that plug-in hybrids are the way of the future is the challenge of a loose network of advocacy groups led by the California Cars Initiative (CalCars). CalCars explains that when gas prices reach $3 per gallon, traditional cars cost eight to 20 cents per mile. Plug-in hybrids used for all-electric local travel would cost only two to four cents per mile.

CalCars is lobbying major automakers to introduce plug-in options on future hybrid models, and has built showcase examples that achieve 100 miles per gallon using Toyota's Prius. Meanwhile, goaded by a campaign led by the Texas-based utility Austin Energy, a growing list of state and local governments say they would seriously consider buying plug-in hybrids for their fleets. CONTACT: Austin Energy, [phone], www.austinenergy.com; CalCars, www.calcars.org.

Is it true that some sponges used for cleaning and bathing are real sea sponges? If so, are they endangered by our using them? Which are more eco-friendly, real or synthetic?--Lin Heidt, Canmore, Albert

While it is true that real sea sponges have been in use since the Roman Empire, synthetic alternatives made primarily from wood pulp became commonplace by the middle of the 20th century. Today, most of the sponges we use are made from a combination of wood pulp (cellulose), sodium sulphate crystals, hemp fibers and chemical softeners.

Another common type of artificial sponge is made of polyurethane foam. These sponges are manufactured in a process that relies on ozone-depleting hydrocarbons (set to be phased out by 2030). Also, polyurethane can emit formaldehyde and can form cancer-causing dioxins when incinerated.

Some real sea sponges are still sold today, used for everything from cleaning car and boat exteriors to removing make-up and exfoliating the skin. The product of at least 700 million years of evolution, sea sponges are among the world's simplest living organisms. They survive by filtering microscopic plants and oxygen from the water, growing slowly over many decades. Commercially, they are prized for their natural softness and resistance to tearing, and their ability to absorb large amounts of water. Scientists know of more than 5,000 different species, though we only harvest a handful of them, such as the exfoliating honeycomb (Hippospongia communis) and the silky smooth Fina (Spongia officinalis).

Environmentalists are concerned about protecting sea sponges, especially because we still know so little about them. For example, researchers are optimistic that chemicals emitted from some living sea sponges could be synthesized to create new arthritis treatments and might even be cancer fighters. And sea sponges serve as the primary food source for endangered hawksbill sea turtles.

According to the Australian Marine Conservation Society, sea sponges are under threat not only from over-harvesting but also from sewage discharge and stormwater run-off, as well as from scallop dredging activity. Global warming is also now a factor. CONTACT: Australian Marine Conservation Society, www.amcs.org.au.