A lot of people work in places that aren't as safe as they should be, or could be.

April 28 was World Day for Safety and Health at Work. It's an annual observance of the U.N.'s workers' agency, the International Labor Organization. As we hear from VOA's Art Chimes, the threats to workers range from hearing loss and back injuries to cancer caused by toxic chemicals.

How safe are you on your job?

Most of the world's working people face some kind of danger on the job, according to Dr. Maritza Tennessee of the Pan American Health Organization, or PAHO.

"Two-thirds of the workers are exposed to unsafe and unhealthy working conditions. Many of those workers are exposed to carcinogens in the workplace. Twenty-five percent of the whole, global burden of disease is due to environmental and occupational risk."

She's quoting findings there from the World Health Organization.

Cancer prevention specialist Devra Davis showed PAHO staffers pictures representing the chromosomes of identical twins to demonstrate how environmental factors can affect our DNA.

At age three, the twins' chromosomes look, well, nearly identical.

"But look at what happens to them at age fifty," she said. The top and bottom two do not even look related to one another. And yet they are coming from one egg that splits into two. This is a clear indication that when it comes to the environment and our health, genes give us the gun, but the environment pulls the trigger."

Devra Davis heads the Center for Environmental Oncology at the University of Pittsburgh. She's also the author of the recent book, The Secret History of the War on Cancer.

The changes in our DNA come from exposure to our environment ? it could be sunlight or a medical X-ray, or cancer-causing substances that are found in work places around the world.

Take the people who grow flowers. Floriculture has become a big business in many countries. Colombia and Kenya are two big exporters. To maximize production, the plants are grown in greenhouses. Davis says that also increases the danger to workers.

"Floriculture is pesticide-intensive. It involves greenhouses with plastic sheets over them. Imagine if somebody put a plastic sheet over us right now, and pumped it full of [pesticide] sprays. That's what goes on in a plastic-covered greenhouse."

Dangerous chemicals don't just affect the workers who are directly exposed to them. Workers who don't use protective clothing can bring home toxic materials they are exposed to on the job. And it can cause genetic damage that is passed on to children.

"But as to fathers' exposure, paternal exposure to pesticides increases the relative risk of brain tumors two-point-three fold," Davis said. "Fathers who work as painters or in woodworking also have increased risk of cancer in their children. What happens to fathers before they become fathers affects the health of their children."

Pregnant woman are often banned from hazardous jobs, but toxic chemicals can do damage before a woman becomes pregnant, or before she realizes she's pregnant.

Davis specializes in cancer, but of course that's not the only on-the-job hazard.

Workers also face potential hearing loss, back pain, lung disease and injuries. In fact, injuries are the biggest cause of the loss of healthy years of life, a statistic used by public health experts.

The International Labor Organization says 2.2 million people die annually from work-related accidents and disease, and the U.N. agency puts the direct and indirect costs at $1.25 trillion ? about four percent of world GDP.