Juliet Eilperin reports in the Washington Post this morning on a problem that will only get worse when Congress mandates more ethanol production through an expanded renewable fuel standard.

Atrazine, the second most widely used weedkiller in the country, is showing up in some streams and rivers at levels high enough to potentially harm amphibians, fish and aquatic ecosystems, according to the findings of an extensive Environmental Protection Agency database that has not been made public.

The analysis -- conducted by the chemical's manufacturer, Syngenta Crop Protection -- suggests that atrazine has entered streams and rivers in the Midwest at a rate that could harm those ecosystems, several scientific experts said. In two Missouri watersheds, the level of atrazine spiked to reach a "level of concern" in both 2004 and 2005, according to the EPA, and an Indiana watershed exceeded the threshold in 2005.

Much of the data on atrazine levels has remained private because Syngenta's survey of 40 U.S. watersheds was done in connection with the EPA's 2006 decision to renew its approval of the pesticide. The Washington Post obtained the documents from the Natural Resources News Service, a District-based nonprofit group focused on environmental issues.

Most atrazine is used on corn. EWG documented a widespread problem with atrazine (and other weedkillers) in finished drinking water 12 years ago, through a testing program we conducted during the "spring spike" in 29 cities (most in the midwest).

In one sample we tested back then, an amount about that of a glassful of water, we found 12 weedkillers or herbicide metabolites.

USGS has detected atrazine more or less everywhere they've tested over the years. But those samples mostly came from larger water bodies. The results Eilperin reports come from a special survey by the manufacturer that includes smaller streams.

How long has this contamination been taking place? Well, atrazine came onto the U.S. market in 1958, the year Elvis went into the army.

Hat tip to the Natural Resources News Service for uncovering the unpublished data.