Week of 4/10/2005

Dear EarthTalk: Is the pressure-treated wood used for decks, picnic tables and backyard play structures harmful to human health?

—Christy Silver, Cleveland, OH

Pressure-treated wood contains the preservative chromated copper arsenate (CCA), an arsenic derivative that is used to protect the wood and prolong its life. Also used commercially as a pesticide, CCA is regarded by many homeowners and construction professionals as a godsend for preserving outdoor wood structures against harsh weather and termites. But it is also on environmentalists" watch lists as a potential health hazard due to its arsenic content.

According to the US Environmental Protection Agency (EPA), arsenic, although a naturally occurring element found in the Earth's crust, is poisonous. Prolonged exposure can cause vomiting, diarrhea and skin abnormalities. The EPA also considers arsenic to be a human carcinogen, with long-term exposure increasing the risk of skin cancer and tumors of the bladder, kidney, liver and lung.

Recent studies have shown that rainwater can release arsenic-laden CCA from the treated wood, potentially contaminating any soil or groundwater below. Also, especially after a heavy rain, a fine coating of CCA residue can build up directly on the wood's surface, which in turn can be picked up on hands and clothing, potentially exposing family members to small but persistent doses of arsenic.

But while the EPA may classify arsenic itself as a toxin, it does not believe that periodic contact with pressure-treated wood poses any "unreasonable" risk. The agency has, however, issued new safeguards for protecting workers who come into contact with CCA on a daily basis. Even the nation's largest producer of pressure treated wood, Arch Wood Protection Inc., advises taking precautions when working with, using and cleaning up its products, acknowledging that "exposure to CCA may present certain hazards."

If you already have pressure treated wood around your home, applying an oil-based stain once every couple of years will help keep the CCA from seeping out. Additionally, you should keep children and pets out of under-deck areas where arsenic may be present. Also, don't grow edible plants near any pressure treated wood structures, and always follow safe handling guidelines (including the use of gloves and dust masks) when using it in building projects.

For those who may be starting from scratch, there are several safer alternatives to pressure treated wood. According to the Berkeley, California based Green Resource Center, yellow cypress, yew, tamarack, hemlock, white cedar and redwood are naturally rot-resistant, as are plastic and wood-plastic composite building materials. Meanwhile, wood boards that are treated with alternative techniques that don't use CCA are free of the arsenic problem. Alkaline Copper Quartenary, sold under the trade name NatureWood, is one safer option, as is Copper Azole, which is sold under the trade name Natural Select.

CONTACTS: EPA Arsenic Toxicity Assessment, www.epa.gov/ttn/atw/hlthef/arsenic.html ; Green Resource Center, (510) 845-0472, www.greenresourcecenter.org ; NatureWood, (800) 241-0240, www.osmose.com/wood/usa/preserved/naturewood/product/ ; Natural Select, (866) 789-4567, www.naturalselect.com.


Dear EarthTalk: Why have shark attacks been on the rise in recent years?

—J. Tibbetts, Boston, MA

Despite a slight downturn during the last few years as a result of hurricanes keeping people out of the water, the number of shark attacks on humans has indeed risen steadily over the last century. In fact, the nearly 500 shark attacks recorded around the world in the 1990s was double that which occurred in the previous decade, and that trend seems to be continuing apace into the new millennium.

The largest increase in shark attacks has been along the southeastern seaboard of the United States. The summer of 2001 witnessed sharks moving in to shallower waters and striking people near the shoreline. In just three weeks there were 20 attacks and two deaths—often in water no more than three feet deep.

Unproven theories abound regarding this phenomenon. Some experts postulate that the human-caused decline in ocean fish is causing sharks to venture closer to shore in search of food. Others believe that sharks" territories are shifting due to changes in ocean temperatures resulting from global warming.

Whether or not these theories have merit, no one doubts that humans are venturing further and further out to sea to swim, surf, snorkel and dive, increasing the chances of run-ins with sharks. Surfers are especially at risk because their shiny black wetsuits look like tasty seals to sharks. Also, surfers spend lots of time waiting for waves in the "splash zone" just offshore, where sharks tend to congregate to look for prey.

"An ever growing number of people spend their vacation at the oceanside, so that both the probability of encountering a shark and the respective danger of an accident also increases," says Dr. Alexander Godknecht, president of the Shark Foundation. Godknecht believes the 100 or so shark attacks last year to be a very small number and that mainstream media hype makes them appear to happen more often than they really do.

George Burgess, director of the International Shark Attack File (ISAF) at the Florida Museum of Natural History, agrees, arguing that the average North American is about 15,000 times more likely to be killed in a car accident than in a shark attack. "Bees, wasps and snakes cause far more fatalities a year," he adds. "And the annual risk of death from lightning is 30 times greater than that from a shark attack."

Burgess points out that, despite the increase in shark attacks, shark populations are actually in decline globally, mostly due to human overfishing which has depleted their sustenance. Along the Atlantic coast of the U.S. some shark species have declined as much as 70 percent over the last 20 years. "The number of shark attacks is rising every year while the shark population is dwindling—it's not rocket science to see that something is provoking them. We're swamping the near-shore environment," Burgess concludes.

CONTACTS: Shark Foundation, www.shark.ch; International Shark Attack File, www.flmnh.ufl.edu/fish/Sharks/ISAF/ISAF.htm .