State environmental regulators say toxic emissions by larger Indiana polluters fell 18 percent, or 20.6 million pounds, last year.

The Indiana Department of Environmental Management disclosed the 2009 data this month, citing the U.S. Environmental Protection Agency’s newly released Toxic Release Inventory, or TRI.

Electric-generating utilities accounted for 50 percent of the state’s pollution, with 49 percent from manufacturers.

The TRI data aren’t considered a comprehensive measure of pollution, however, in part because reporting is limited to firms that make or process more than 25,000 pounds of chemicals on the toxics list or use more than 10,000 pounds of the chemicals in a given year.

It’s also unknown to what extent the lower numbers stem from better practices among polluters—or to what degree emissions reflected reduced manufacturing output during the recession.

Many businesses have found ways to switch to safer chemicals or to eliminate them altogether, “and many have increased the efficiency of their processes to reduce or virtually eliminate chemical use,” IDEM Commissioner Tom Easterly said in a statement.

Overall, the Indiana manufacturing sector reduced toxic emissions 19 percent last year, while electric utilities curbed pollution 13 percent, according to TRI data.

The state’s coal-burning electric utilities have been upgrading their pollution-control devices in the last decade to comply with tougher federal and state limits on sulfur and nitrogen dioxide.

Last week, Indianapolis Power & Light asked state utility regulators to collect an additional $8 million from ratepayers to cover cost overruns on a flue gas desulfurization project at its Petersburg generating station, now estimated to cost $128 million.

The TRI data do not measure non-industrial activities that generate toxics, such as vehicle exhaust, which contains chemicals like toluene and xylene.  The data are more useful in identifying trends in chemical use and ways to modify industrial processes.