EXAMINING EFFECTIVE EXPOSURE TIME AND BIOACCUMULATION RATE OF A SENSITIVE AND ACCURATE ACTIVE BIOMONITOR (RAMALINA SINENSIS) FOR ATMOSPHERIC SUSPENDED PARTICULATES

Ramalina sinensis (RSI) is a good active biomonitor for atmospheric element deposition, but effective exposure time is yet unknown for this lichen.We transplanted RSI from a "clean" site to Tangshan, an industrially polluted city in China, during winter heating period.Three exposures time spans were used: two 2-month exposures (NJ2: Nov. 2016-Jan.2017; JM2: Jan.-Mar.2017) and one 4-month exposure (NM4: Nov. 2016-Mar.2017).We measured concentrations of 47 elements.Exposed concentrations were higher than unexposed concentrations for almost all elements.Exposed to unexposed ratios (EU) and pollution load index at local scale (PLIsite) were greater in NM4 and NJ2 exposures than in JM2 exposure for 44 elements.Observed EUNM4 ratio was lower than expected for most elements.Pollution load index at regional scale (PLIzone) had a NJ2:JM2 ratio similar to the average and cumulative daily mean concentrations of atmospheric suspended particulate matters (PMs).These results suggest that bioaccumulation primarily occurred within two months, indicating a retention time of less than two months and reaching an equilibrium by the end of this period.In conclusion, RSI is a sensitive and accurate active biomonitor for atmospheric suspended PMs, with an effective exposure time span of 2-4 months, during which RSI element concentrations vary proportionally to atmospheric suspended PMs.