Evaluating relationships between mercury concentrations in air and in Spanish moss (Tillandsia usneoides L.)

Measurement of mercury vapor is essential given that it is transported globally, and once deposited can be converted to methylmercury, a dangerous neurotoxin. A study was conducted in southeastern Georgia and northern Florida, USA to determine whether Spanish moss, an epiphytic vascular plant common to the southeastern United States, has the ability to retain mercury in its tissues over time, and to detect atmospheric mercury at relatively low concentrations from nonpoint sources. Spanish moss plants exposed to 10× and 100× ambient concentrations of mercury vapor increased tissue concentrations by 13.7 ± 11% and 74.1 ± 17% respectively, and then retained the mercury over two weeks following removal from the source. There was a strong trend of increasing Spanish moss mercury concentrations with increasing air concentration in resident populations across urban, rural inland, coastal and industrial sites. Transplanted Spanish moss around an industrial site contaminated with mercury exhibited a 164.8 ± 8.7% increase in mercury concentration after two weeks. Mercury concentration of Spanish moss transplanted to rural inland sites also increased after two weeks, while the change in transplant concentration at coastal sites was more variable. This study shows that Spanish moss possesses characteristics important for use as a bioindicator of atmospheric mercury, and can potentially be adapted as a tool for obtaining time-integrated atmospheric mercury data to add to existing atmospheric mercury monitoring programs.