Questions answered

By Sherry Seethaler

SAN DIEGO UNION TRIBUNE
November 24, 2004

QUESTION: What happens to the particles of worn tire tread? Are they polluting our atmosphere?

– Dorothy McSwain, San Dieg

ANSWER: Substantial numbers of particles arise from the wear of brake pads and tires. Probably hundreds of thousands of tons of tread particles are worn off tires on American vehicles each year.

Research by scientists at General Motors found that most particles were large enough that they settled within 15 feet of the pavement edge. Tires contain natural and synthetic rubber, carbon black (soot) and various chemicals added to cure the rubber.

Bacteria and exposure to the elements help to degrade tire particles over time. However, some of the chemical additives in tires do persist in the environment. It is not clear how significant this is as source of pollution.

Smaller particles that can remain airborne for longer may pose health problems for those living near highways. One study showed that up to 6 percent of airborne particles near a highway were rubber. Particles can cause or aggravate respiratory illnesses including bronchitis and asthma.

Natural rubber (latex) in tire particles could cause allergies in people sensitive to latex.

What causes the outside of the yolk of hard-boiled eggs to turn green?

– Philip Flavin, Kyoto, Japan

The green color is iron sulfide. It is produced when iron from proteins in the egg yolk reacts with hydrogen sulfide from proteins in the egg white.

Iron is stored by special proteins in the yolk because it is needed by a developing chick. Sulfur is found in certain amino acids – the building blocks of protein. Proteins in the egg white are particularly rich in sulfur-containing amino acids.

Cooking breaks down some of the proteins in the egg, causing hydrogen sulfide to be released from the white and iron to be released from the yolk. These two chemicals react where they meet.

Using newer eggs and cooling the eggs rapidly after cooking can minimize greenness, which, as Seuss' Sam-I-Am can tell you, is perfectly harmless.

copyright 2004 The San Diego Union Tribune