Heavy metals are present in fluvial sediments of the Picher Mining Field in northeast Oklahoma as a result of lead and zinc mining between 1904 and 1970. The underground mine workings began to fill with water when mining and dewatering ceased, and acid mine water began discharging into Tar Creek from boreholes and air shafts in 1979. The U.S. Geological Survey collected sediment samples in 1983-84 from Tar Creek and found concentrations of lead up to 6800 ppm and of zinc up to 14,000 ppm. These metals and others pose serious health hazards for the local communities.

The purpose of our study was to determine if concentrations in Tar Creek have changed since the mid-1980s of lead, zinc, cadmium, copper, nickel, and iron. We collected stream sediments in the same locations as the earlier USGS study and used the same techniques for sampling and lab analyses to ensure comparable data. Concentrations remain at 109-862 ppm for lead and 3500-17,000 for zinc. Heavy metal concentrations decreased in upstream sites because of drainage diversion projects constructed after 1984. Heavy metals increased in downstream sites for two possible reasons. Particle sizes may have decreased from 1983-84 to 2000 and smaller sizes generally adsorb higher concentrations. Alternatively, additional heavy metals could have been added to Tar Creek from the floodplain and tailings during large floods. Remediation efforts have met with limited success; clean-up is prohibitively expensive; residents in former mining communities may need to be relocated.