Geological Survey (USGS) collected sediment cores from select lakes across the country from 1970 to 2008 as part of the National Water Quality Assessment program where they found decreasing trends in the legacy contaminants total dichlorodiphenyltrichloroethane (DDT), total PCBs, lead, and p,p’-dichlorodiphenyldichloroethylene (DDE), but an increasing trend in PAHs for which higher concentrations were found in urban areas ( Van Metre and Mahler, 2005 ; Mahler et al., 2006 ; Van Metre and Mahler, 2010 ).
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