Martha Castillion, a Chicago resident for nearly 20 years and grandmother of a 2-year-old toddler, boils her water for drinking and cooking.

"I don't like my kids to be contaminated," she said.

She lives in Little Village -- the site of one of Chicago's biggest sources of pollution, the coal-burning Crawford Generating Station -- and home to one of the city's largest immigrant communities. As thousands of Chicagoans took to the streets on May Day to support immigrant workers rights, Castillion joined the Little Village Environmental Justice Organization to draw attention to the often toxic communities in which they live.

"It's a proven fact that people affected most by pollution are people of color," said Kim Wasserman, 30, coordinator for the local not-for-profit organization.

A recent Harvard School of Public Health study found that air pollution from the Crawford plant and neighboring Fisk plant in Pilsen causes more than 40 deaths and 2,800 asthma attacks annually. And according to the American Lung Association of Metropolitan Chicago, the city's asthma hospitalization rate is double the national average.

A spokeswoman with the association said the mortality rate from asthma for African American and Latino populations is four to six times that for Caucasians. Wasserman said she and more than two dozen volunteers participated in Tuesday's march because it's "mind-boggling to compare how city planning happens" in Little Village to what transpires in wealthier, predominantly white Chicago neighborhoods.

The organization's Web site says Little Village's zip code ranks third for worst air pollution in the Chicago metropolitan area.

"This government marginalizes our community. They throw us scraps," Lorena Lopez, 26, said.

An organizer with the Little Village not-for-profit, Lopez cited a controversial city plan to convert an Environmental Protection Agency Superfund site into a neighborhood park.

Once used by a company that made asphalt roofing products, the site is polluted with a group of chemicals thought to cause cancer. She said the Chicago Park District acknowledges that, compared with other parts of the city, Little Village has less green space. But she said current plans to clean-up the site are inadequate.

At the end of the month, she said, city representatives intend to meet with the community to discuss plans for the new park. The organization says neighborhood factories and chemical sites increase the prevalence of asthma, lead poisoning, diabetes and high blood pressure in the highly immigrant community.

Nearly once a month, volunteers lead "Toxic Tours" to local companies like Meyer Steel Drum Co. and MRC Polymers, Inc., and give Little Village visitors an opportunity to witness first-hand how toxins are released into the community.

Eddie Monarrez, 16, a youth volunteer and guide for the "Toxic Tour," said the program helps correct misconceptions about environmental justice.

"[This] isn't about being a treehugger," he said. "This is something so important. Something we need to work on."

Marisol Davila, 18, a freshman at Dominican University and the daughter of undocumented immigrants, marched with the Little Village organization because she hopes the rally will bring attention to hidden environmental and health issues in immigrant communities.

"A lot of people in my neighborhood have asthma," she said. "I'm here because I'd like there to be some kind of reform."