A first-ever attempt to quantify the the amount of toxic substances that reach — or have the potential to reach — the Bay reveals that hundreds of thousands of pounds of potentially harmful contaminants entering the Chesapeake originate from storm water runoff and air pollution.

The Chesapeake Bay Basin Toxics Loading and Release Inventory, in the works since 1989, includes information about toxic pollution from such diverse sources as industrial and waste water treatment plant discharges, pesticide applications, shipping spills, atmospheric deposition, and urban/suburban runoff.

“The Toxics Loading Inventory tells us we have to look harder at controlling the more pervasive sourcesa of chemicals, such as runoff and air pollution,” said Bill Matuszeski, director of EPA’s Chesapeake Bay Program Office. “Industry has made considerable progress in reducing overall chemical loadings and releases, but must concentrate on pollution prevention efforts and air pollution controls.

“We also know that people — all of us — living in the Bay region are part of the problem, too. Car exhaust contributes to the air pollution,” Matuszeski said, while storm water originates with “runoff from our streets, parking lots, and driveways.”

The inventory does not attempt to link the loads it quantifies to problems in the Bay. Severe toxic problems are not necessarily the result of high loads, but high concentrations in the water or sediment. The inventory does not assess whether loads, which may be dispersed over large areas, result in concentrations that would create toxic conditions for fish and other species.

Also, information used in the inventory is very incomplete. Loading information is extrapolated from data gathered for other reasons, and likely undercounts many contaminants. As a result, load estimates have large margins of error, and trying to determine the total amounts that originate from any particular source from the inventory is not possible. Officials hope that picture will become clearer in future updates to the report.

“Often, these estimates were developed using limited data covering various time periods and collected for purposes other than calculating loadings and releases,” said Joseph Macknis, monitoring coordinator with EPA’s Chesapeake Bay Program Office, who was largely responsible for drafting the report. “As a result, many of the loadings and releases presented in this initial version of the inventory are likely to be no better than order-of-magnitude estimates.”

Nonetheless, these relative comparisons help provide a picture, in relative terms, of what is entering the Bay.

Storm water contributes huge amounts of potentially toxic materials. An estimated 230,000 pounds of copper washes off streets and into the Bay and its tributaries each year — three times as much as what originates from point sources. Copper is one of 14 primary Bay “Toxics of Concern” — contaminants identified as having a high potential to impact the Chesapeake’s living resources. About 1.3 million pounds of zinc, a secondary Toxic of Concern, results from storm water runoff.

The report shows that potentially large amounts of some chemicals may reach the Bay directly through deposition from the air, the result of pollution from industries, power plants, and automobiles. It estimates annual airborne loadings of lead at 32,000 pounds, copper at 24,000 pounds, and chromium at 7,500 pounds.

The airborne deposition data was extrapolated from very limited information and the numbers have a large amount of uncertainty. The report suggests that the toxics contributed through the air — particularly in areas downwind of cities — are probably underestimated. The inventory also does not include estimates of loadings to the Bay resulting from airborne deposition of chemicals on the land within the Bay basin which may wash into rivers and streams and, ultimately, the Bay.

Point sources — end-of-pipeline discharges from waste water treatment plants and industry — appear to contribute less than either storm water runoff or airborne deposition. These loads may still be a problem, though, as they tend to be concentrated in urbanized and industrial areas.

The report also cautioned that because of the possibility of spills, toxics from boats and shipping pose a risk to the Bay. The report said more information was needed about toxics related to shipping and boating on the Bay, as toxic materials are both transported over the water and are used in various cleaners, disinfectants, and sewage treatment systems on boats.

Besides loading estimates, the inventory includes information about two other pathways through which toxics reach the Bay — releases and “fall line” loads.

The release category includes information about metals and organic chemicals that are discharged into the environment. That includes pesticides and information from the EPA-mandated Toxics Release Inventory which requires larger businesses to report information about certain chemicals they discharge to the air, water, or land.

Releases, though, are different than loadings because they do not necessarily end up in the Bay. For example, while the report shows that 2.3 million pounds of the pesticide atrazine are applied onto croplands in the Bay watershed, estimates made from the river monitoring program in 1990 and 1991 detected only 3,000 to 16,000 pounds of the herbicide, indicating that only a fraction of the amount used reached the Bay.

Over time, though, the release data will indicate trends in use and discharges of toxics that will help determine whether certain activities should be targeted for reductions.

The report also includes information about the loads of toxics entering the Bay from the Susquehanna and James rivers. These “fall line” loads — so named because they are measured at the geological fall line that divides the coastal plain from the Piedmont — give an idea about the amount of toxics entering the Bay from upland areas. Fall line loads, though, provide no information about whether those materials result from runoff, industries, or other sources.

Despite its shortcomings and caveats, officials say the inventory provides a general sense about the relative importance of different toxics sources — information that may help set priorities for the development of a new Basinwide Toxics Reduction Strategy that is to be completed later this year.

“It will play a role in terms of telling us what kinds of sources we should target,” said Rich Batiuk, toxics coordinator with the EPA’s Chesapeake Bay Program Office.

For example, Batiuk said, the data indicates a need to change from the “point source mentality” that has often guided toxics regulatory programs toward a new focus on better controlling storm water. Although storm water requirements have become more stringent in recent years, those discharges historically have not been dealt with as aggressively. “It’s expensive and it’s tough to deal with,” Batiuk said.

Also, more emphasis may be placed on air pollution, he said. In particular, more work is needed to determine whether air pollution downwind from large urban centers is a major source of toxics.

The report, besides serving as an initial baseline for toxic loads to the Bay, also identified “information gaps” regarding toxic loads which may help state and federal agencies establish better information-gathering techniques.

The report also says the data provides a “simple tool” for determining whether existing programs are effective at reducing toxics reaching the Bay.

The inventory will be updated every two years. The next report is due in March 1996.