Methylmercury and Total Mercury Content on Usnea Lichens in Nova Scotia: Assessing Mercury Stability with Controlled Irradiation and Temperature Change.

Research on mercury distribution is critical as methylmercury can bioaccumulate and biomagnify within food webs. Lichens and other vegetation have been used to monitor heavy metals in the atmosphere as an alternative to commercially available passive-adsorbing collectors. We present results from controlled lab experiments quantifying the stability of mercury on Usnea lichens and the total mercury and methylmercury content of 105 Usnea lichens collected across Nova Scotia, Canada. We discovered that mercury forms a stable association with Usnea lichens and minimal amounts were released (0.003 and 0.15% of total mercury) under a variety of short term (40 h) radiation and temperature conditions. We also found that there were significant detectable methylmercury concentrations in the lichens ranging from 0.1 to 18.4 ng/g d.w. which was 0.04 to 7.3% of the total mercury present. This work shows that Usnea lichens are stable passive air samplers for both total mercury and methylmercury.