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 B lacklick Run (BLK) and Herrington Creek Tributary (HCRT), two streams in we stern Maryland (MD). Samples were analyzed for total mercury (Hg), methylme rcury (MMHg), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb). Hg concentrations generally fell between 50 and 100pM. comparable to concentra tions in wet deposition measured at other MID sites. While Hg concentration s decreased with rainfall amount, a similar washout trend was not seen for MMHg. Cd, Pb, As. and Se concentrations were comparable overall to those me asured in the region. Concentrations of Hg, Cd, and Pb in throughfall were similar between sites and equivalent or higher than wet deposition concentr ations. As and Se concentrations were similar in throughfall at the two sit es, 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 collect ions, four storm events were sampled. These measurements demonstrate the im portance of storm events in trace metal transport. especially for Hg. Pb an d MMHg. For these metals, a strong correlation between metal and suspended particulate concentration was evident. Retention efficiencies of the waters heds 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. (C) 2001 Elsevier Science Ltd. All rights reserved.