Three decades of biomonitoring airborne Pb in a rural area with the epiphytic lichen Ramalina lacera: A retrospective study

The present paper analyzes the results of a biomonitoring study that used the epiphytic lichen Ramalina lacera to estimate the environmental pollution impact of anthropogenic activity in terms of Pb content. Thalli of the lichen growing on carob twigs were collected in November 2001 in a relatively unpolluted forest near HaZorea, Ramat Menashe Hills, Northeast Israel, and transplanted to 11 rural and suburban sites around a coal-fired power plant near the town of Hadera. The lichens were retrieved in August 2002 and were found to contain smaller amounts of Pb than reported in the relevant literature. A comparative analysis of Pb amounts in thalli of R. lacera in the control site in HaZorea over the years 1974-2002 detected high values for Pb in July 1982 subsequent to extraordinarily extensive activity of motor vehicles, mostly using leaded gasoline, in June of the same year. The Pb values remained relatively high until 1993. Only in the years 1994-2002 did the Pb values decrease to a level resembling the first series of data obtained in the years 1974-1981. It is apparent that a decade and more were needed to "forget" the polluting event, and that the data obtained in this period (1982-1993) were irrelevant to the availability of Pb pollutants. Despite the gradual increase of the total number of motor vehicles in Israel, the Pb values in lichens decreased due to the introduction of unleaded gasoline in September 1990. Additional retrospective studies dealing with Pb in lichens are discussed.