Lead concentrations in major U.S. rivers declined from 1974 to 1985 in two-thirds of the 300 sites tested by the U.S. Geological Survey. The downward trends were statistically significant for 30% of the stations. Preliminary evaluation of more recent data indicates that lead concentrations are continuing to decline.
Higher lead concentrations were measured at some sites in the Texas Gulf and lower Mississippi Valley regions but were due largely to lower river flow. A few water samples exceeded the Environmental Protection Agency established limit of 50 ppb, and none were from sources of drinking water supplies.