Hazardous waste, treated human sewage and farm chemicals are part of a dumping ground culture surrounding the San Joaquin Valley, but other deadly health risks slip under the radar.

Through a legal loophole, a company with global sales of $4 billion opened its West Coast distribution center in Visalia last year without having to follow a rule that curbs air pollution, much of it generated by traffic.

Critics, who sued over it, argue traffic and diesel truck exhaust from the 500,000-square-foot distribution center will create tons of air pollution. Air pollution kills several hundred people prematurely each year in the Valley.

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They say VWR International, a laboratory supply and distribution company, needs to use the cleanest trucks available or buy cleaner equipment for businesses in the area.

It's a classic case of big-city pollution being dumped into the Valley, say air-quality activists. The distribution center moved from the Bay Area to the Valley, where the air is more tainted than anyplace in the country except the South Coast Air Basin.

VWR shouldn't be allowed to leverage profits on the lungs of the people living here, says Fresno activist Kevin Hall, executive director of the Central Valley Air Quality Coalition.

"It's shocking," Hall said. "This is exploitation of the Valley's economic crisis."

Health researchers say diesel exhaust is carcinogenic. Diesel is now considered the biggest single contributor to air pollution in the Valley.

To help combat pollution from urban sprawl and traffic, the San Joaquin Valley Air Pollution Control District has a rule requiring new businesses to clean up or pay for cleanups in the area, as well as make a full accounting of the dirty air that will be created.

The 2005 rule forces new projects at the edges of town to pay fees for traffic and other types of pollution. The fees are used to help buy cleaner diesel engines for buses, tractors and trucks in the area.

But the air district says the rule doesn't apply in VWR's case. The company is exempt because there is no "discretionary decision" involved from the city -- such as a City Council vote on a conditional-use permit.

The VWR distribution center didn't need such a permit, Visalia officials say. The center is appropriately located in the city's industrial park that was zoned 20 years ago for this kind of use.

City attorney Alex Peltzer said the City Council voted on the zoning for that land in the 1990s. At that time, the environmental issues were debated and considered, he said. It is a common, legal practice throughout California, say many experts.

Peltzer added that objections to the VWR project are really about union issues. The Teamsters Joint Council 7 alleged union-busting activities when VWR moved to Visalia from Brisbane in the Bay Area.

"The Teamsters are trying to say that this is an environmental issue," Peltzer said. "It's really a union issue."

On Thursday, 61 employees of VWR in Visalia voted to join Teamsters Local 948. But a lawyer representing the Teamsters said there has been no change in the lawsuit the union filed against the VWR project. The lawsuit says the company should address air-quality issues.

Three public-interest groups -- the Coalition for Clean Air, Center for Environmental Health and the Association of Irritated Residents -- also are part of the suit.

A Tulare County judge dismissed it in 2011. But in September last year, the 5th District Court of Appeal in Fresno reinstated the case, saying the plaintiffs have the right to make sure the city follows environmental law. It is supposed to come back before the court in Tulare County.