Small amounts of some toxic metals tend to accumulate
in the food chain and can damage living things. In the past,
most toxic metal pollution came from mining activities and
individual sources, such as wastewater-treatment plants and
smoke-stack emissions. Federal and State regulations have
resulted in the reduction of toxic metals from these
sources. Metals tend to attach themselves to dirt and
sediment, and thus, they are still present in the stream
beds and banks of many urban streams.
Concentrations of toxic metals in stream sediments could be reduced if