PPG Industries' chlorine production facility in Natrium, W.Va., which releases more than 400 pounds of mercury into the air and the Ohio River annually, is one of just five such plants in the United States still using an inefficient, polluting technology invented in 1894.

If those five "renegade" facilities switched from mercury-based to available mercury-free production methods, they could eliminate almost 4,400 pounds of the pollution a year, according to a report released yesterday by Oceana as part of its campaign to reduce worldwide emissions of the toxic metal that accumulates in fish and can wind up on dinner plates.

Although the mercury-free technology is expensive to install, the Oceana report says it would use up to 37 percent less electricity, be more efficient, could result in increased production, and would eliminate costly mercury waste management and disposal charges.

The report estimates conversion costs can, in most cases, be recovered in five years.

"PPG's dirty little secret is that changing technology is not as big of a challenge as they seem to imply," said Jacqueline Savitz, director of Oceana's Campaign to Stop Seafood Contamination and co-author of the report. "Their refusal to switch to mercury-free technology -- a cost-effective solution adopted by the majority of plants around the world -- is an outrage that should concern citizens and shareholders alike."

The international conservation organization said that since 1974, more than 100 chlorine production facilities have switched to one of two alternative technologies that do not use or discharge mercury into the air or water. And by 2004, mercury-free technology was used to make 90 percent of the chlorine in the United States.

Betsy Mallison Bialosky, a PPG Industries spokeswoman, said the company has no plans to stop using the mercury-based chlorine production process at its Natrium facility, 20 miles from Pennsylvania's western border, and termed it a "business decision."

She said the company's customers demand the pure caustic soda chemical product -- termed "rayon grade" in the industry -- for making such things as pharmaceuticals, disinfectants, rubber products and paints.

"Our mercury-cell unit at the Natrium plant manufactures the highest purity caustic available for our customers," Ms. Bialosky said. "What's more, we strongly believe that mercury-cell technology can continue to be operated in a manner protective of human health and the environment."

She said the company will spend about $3 million by the end of the year to reduce mercury discharges from the facility, which opened in 1943, with a mercury-free diaphragm operation that was upgraded in 1984. The mercury cell process, which makes chlorine and caustic soda by pumping saltwater through mercury to produce a chemical reaction, was installed in 1957.

Ms. Bialosky said PPG has reduced mercury releases at Natrium from 1,248 pounds in 2004 to a little more than 400 pounds in 2005.

That's still more than is released by any of the 36 coal-fired power plants in Pennsylvania, and continues to be the largest source of mercury discharges into water in West Virginia and its third largest source of mercury air emissions.

PPG already has converted its chlor-alkali plants in Canada and Taiwan to mercury-free processes, and is in the process of converting its Louisiana facility. Ms. Bialosky said that conversion will cost the company $100 million, and isn't feasible in Natrium because the plants serve different markets.

PPG's commitment to the mercury process in Natrium was on display last month in the West Virginia courts where the company lost an appeal of a West Virginia Environmental Quality Board decision denying it a two-year waiver of state pollution limits for mercury discharges into the Ohio River.

But the West Virginia Department of Environmental Protection has proposed granting PPG's request for a "mixing zone" for mercury discharges into the Ohio River. Instead of measuring the discharges at the end of its pipe, such a zone would allow measurement downriver, after the mercury has been diluted.

According to the state agency's proposal, the average monthly discharge limit would be allowed to increase from 12 to 143 parts per trillion.

Oceana said PPG discharges about 32 pounds of mercury annually into the Ohio River, which is the drinking water source for many communities downriver from the plant.

The other four mercury-cell chlorine plants are Ashta Chemicals in Ashtabula, Ohio; Olin Corp.'s plants in Charleston, Tenn., and Augusta, Ga.; and ERCO Worldwide in Port Edwards, Wis.

All five states where the plants operate have issued fish consumption advisories because of high mercury levels in their streams, rivers and lakes. The five chloride-alkali facilities are among the biggest mercury emitters in those states.

Mercury is a dangerous neurotoxin that can affect humans who eat fish and seafood. If mercury builds up in the body it can cause problems that range from loss of sensory and thought processes, to inability to walk, loss of balance, increased risk of heart disease and death.