Background

Mercury is a persistent, toxic, and volatile heavy metal that is globally distributed via the atmosphere. While its elemental form (Hgº), is relatively harmless at ambient concentrations, its derivative organic forms, methyl mercury (MeHg) are potent neurotoxins that bioaccumulate in aquatic food webs, directly harming humans, animals, and the ecosystem structure on which both depend (Morel et al. 1998). Although watershed factors, as opposed to atmospheric deposition, can often dominate MeHg production (Mason et al. 2002), recent research has shown that freshly deposited atmospheric mercury is more likely to be converted to the toxic form (MeHg) than “old” mercury (Babiarz et al. 2003). Although the NCRN experiences some of the highest deposition of atmospheric mercury in the US (Mason et al. 2000a, Mason et al. 2000b), this mercury appears to be largely retained in NCRN watersheds (Mason et al. 1999; Lawson et al. 2001), and fish tissue concentrations appear to be decoupled from atmospheric deposition as a result (Benoit et al. 1998, Mason et al. 1999). Although Benoit et al. (1998) implicate high sulfide (which inhibits methyl mercury production at high levels in substrate) as one reason for this decoupling, researchers are uncertain as to what watershed factors maintain this decoupled state. Data analysis should compare mercury deposition results with fish tissue concentrations available from EPA as an indicator of the risk to the watershed from atmospherically deposited Hgn. Simultaneous increases in atmospheric mercury deposition and fish tissues will be evidence of atmospheric contributions to NCRN mercury methylation, while increases in only fish tissue concentrations may indicate that watershed factors are contributing NCRN mercury methylation.

Objectives

• Report on annual status and trends of mercury concentration and deposition in precipitation

Reports & Products
2009 Annual Air Report
2008 Annual Air Report
2006 Annual Air Report
2005 Annual Air Report
MDN Maps

Links
Protocol
Mercury Deposition Network

Contacts
Patrick Campbell
NCRN Network Coordinator
202.342.1443 ext. 229
202.342.1443 ext. 214

Measures

State and federal agencies, and others, who monitor mercury in wet deposition through the Mercury Deposition Network (MDN), use MDN’s monitoring protocol and follow the program’s quality assurance/quality control guidelines . MDN posts site-specific and programwide data on their website. The NCRN will obtain data summaries, interpretations and graphics available on the MDN website and proivide annual summaries to network parks.

Status

Mercury deposition data collection takes place at numerous sites in the Washington, DC metropolitan area. The NCRN will continue to access this data and provide summary information to network parks.