Pesticides Prevalent in Midwestern Streams.

• Position: AQUATIC TOXINS - Brief article

One hundred small streams in the Midwest were tested for pesticides and found to contain, on average, 52 pesticides per stream. More than 180 pesticides and their by-products were detected in small streams throughout 11 Midwestern states, some at concentrations likely to harm aquatic insects, according to a study by the U.S. Geological Survey, Reston, Va.

At least one pesticide in at least half of the 100 streams sampled exceeded a threshold predicted to cause harm to aquatic insects and other stream organisms, ranging from acute effects (like death after short-term exposure) to chronic effects (such as longer-term impairments to reproduction and development). Two to four pesticides exceeded that threshold in more than one-quarter of the streams.

Aquatic insects, such as mayfly and stonefly larvae, are critical to stream health because they are an essential link in the aquatic food web. Pesticides were not measured at levels predicted to be toxic to fish in 95 of the 100 streams tested. Potential impacts on human health were not...