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. 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.
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 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.