Concentration of mercury, methylmercury, cadmium, lead, arsenic, and selenium in the rain and stream water of two contrasting watersheds in western Maryland.

Weekly wet deposition and throughfall rain samples were collected in the Blacklick Run (BLK) and Herrington Creek Tributary (HCRT), two streams in western Maryland (MD). Samples were analyzed for total mercury (Hg), methylmercury (MMHg). arsenic (As), selenium (Se), cadmium (Cd), and Icad (Pb). Hg concentrations generally fell between 50 and 100 pM. comparable to concentrations in wet deposition measured at other MD sites. While Hg concentrations decreased with rainfall amount, a similar washout trend was not seen for MMHg. Cd, Pb, As, and Se concentrations were comparable overall to those measured in the region. Concentrations of Hg, Cd, and Pb in throughfall were similar between sites and equivalent or higher than wet deposition concentrations. As and Se concentrations were similar in throughfall at the two sites, though throughfall at BLK seemed to be punctuated with slightly higher concentrations of these two metals. Concentrations of Hg, MMHg, Cd, Pb, As, Se, and SPM were measured in monthly stream collections and compared with concentrations found in other MD rivers. In addition to the monthly collections, four storm events were sampled. These measurements demonstrate the importance of storm events in trace metal transport, especially for Hg, Pb and MMHg. For these metals, a strong correlation between metal and suspended particulate concentration was evident. Retention efficiencies of the watersheds for the metals were calculated for each watershed. Of all the metals, Hg is the most and As is the least strongly retained in the watershed.