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Dear EarthTalk: What is the “de-extinction” movement all about -- Bill Mitchell, New York, NY

De-extinction—bringing back extinct animal and plant species—is a term that conservation biologists and environmentalists have been bandying about for a decade or so. But only recently have advances in genetic sequencing and molecular biology transformed de-extinction from theory into something that we are all likely to see in our own lifetimes.

Or so
Revive & Restore, a project of the Stewart Brand’s California-based non-profit Long Now Foundation, likes to think. The group is creating a movement around de-extinction, and is taking the lead on efforts to bring back the passenger pigeon while helping out on other ongoing efforts to restore other extinct species including European aurochs, Pyrenean ibexes, American chestnut trees, Tasmanian tigers, California condors, even wooly mammoths.

The main rationale behind bringing back these long gone species and others is to preserve biodiversity and genetic diversity, undo harm that humans have caused in the past, restore diminished ecosystems and advance the science of preventing extinctions.

While de-extinction may seem only theoretical at this point, biologists are already knocking on its door. In 2003, Spanish researchers used frozen tissue from the last Pyrenean ibex, which had died three years earlier, to clone a new living twin (birthed by a goat). While the baby ibex died of respiratory failure within 10 minutes of its birth—a common problem in early cloning efforts—the de-extinction movement was officially born.

Revive & Restore expects to see much more progress in the coming decade given the recent focus on the topic by geneticists, conservation biologists and environmentalists. The group is working with researchers around the world to put together a list of “potentially revivable” species. Some of the criteria for whether a given species is a good candidate for revival include how desirable it would be to have it around, how practical it would be to bring it back, and whether or not “re-wilding” (returning it to a natural environment) would be possible.

First up for
Revive & Restore is the passenger pigeon, which was hunted from a population of billions in the 19th century to extinction by 1914. The group has enlisted the help of bird experts around the world to contribute to the project, and in February 2012 convened a meeting at Harvard University to coordinate the next steps. Currently Revive and Restore is busy sequencing the DNA of the passenger pigeon’s nearest living relative, the band-tailed pigeon, and is simultaneously gathering DNA from some 1,500 preserved passenger pigeon specimens. The group hopes to combine this biological and genetic material to reintroduce the once abundant species.

In response to critics who question the logic of bringing back extinct species in a world potentially unprepared to host them, Brand, founder of the
Whole Earth Catalog, counters that it’s our job to try to fix “the hole in nature” we created. “It’s our fault that some of these crucial species have been completely wiped out, so we should dedicate our energy to bringing them back,” he says. “It may take generations but we will get the wooly mammoth back.”

CONTACT: Revive & Restore,

EarthTalk® is written and edited by Roddy Scheer and Doug Moss and is a registered trademark of E - The Environmental Magazine ( Send questions to: Subscribe: Free Trial Issue:





Dear EarthTalk: I was wondering how toxic chlorine is, because my well water was just chlorinated yesterday and today the smell is still strong. I have a 4-year-old daughter and I’m concerned.

                                            -- Rose Smith, via e-mail

According to the
U.S. Environmental Protection Agency (EPA), chlorine levels of four parts per million or below in drinking water—whether from a private well or municipal reservoir—are acceptable from a human health standpoint. Inexpensive home drinking water test kits (from $5 on up) that can detect levels of chlorine and other elements in water are widely available from online vendors. Administering the tests is easy and can provide parents with a way to involve kids in science for a practical purpose right at home.

Chlorine was first used in drinking water to reduce waterborne infectious diseases in Jersey City, New Jersey more than a century ago. It was so effective at destroying potentially harmful bacteria and viruses that the practice soon spread far and wide. Today some 98 percent of water treatment facilities in the U.S. use some form of chlorine to clean drinking water supplies. The
American Water Works Association (AWWA), a trade group representing water utilities across the country, credits the presence of chlorine in drinking water with a 50 percent increase in life expectancy for Americans over the last century. Indeed, some consider the chlorination of drinking water to be one of history’s greatest public health achievements.

But others aren’t so sure that any chlorine in drinking water should be considered safe. Opponents of chlorination point to studies linking repeated exposure to trace amounts of chlorine in water with higher incidences of bladder, rectal and breast cancers. The problem lies in chlorine’s ability to interact with organic compounds in fresh water to create trihalomethanes (THMs), which when ingested can encourage the growth of free radicals that can destroy or damage vital cells in the body. Besides cancer, exposure to THMs has been linked to other health issues including asthma, eczema, heart disease and higher miscarriage and birth defect rates.

Those with their own private wells who are skittish about chlorine have other options for disinfecting their water. One baby step would be to replace chlorine with chloramine, an ammonia derivative that doesn’t dissipate into the environment as rapidly as chlorine and has a much lower tendency to interact in bad ways with organic compounds in the water. However, traces of chloramine in the water may not be to everyone’s liking either, because it causes rashes after showering in a small percentage of people and can apparently increase lead exposure in older homes as it leaches the heavy metal off old pipes.

Another option, though somewhat costly, would be to purchase a machine to purify the water. Ozonation units, which disinfect by adding ozone molecules to water and leave no residues, start at around $9,000. Another choice would be a UV light treatment machine—at $6,000 or more—which cancels out viruses and bacteria by passing the water through UV light rays. The Clean Water Store is a reputable vendor and good online source for such water treatment equipment.

Perhaps the most sensible and affordable approach is to filter the water at the faucets and taps. Carbon-based tap- or pitcher-mounted filters can work wonders in removing impurities from drinking water. They can even be installed on shower heads for those with sensitive skin.

CONTACTS: AWWA,; The Clean Water Store, / Issue 145 - September 0850
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