CHANGES IN ATMOSPHERIC TRACE-ELEMENT DEPOSITION IN THE FRASER VALLEY,BC, CANADA FROM 1960 TO 1993 MEASURED BY MOSS MONITORING WITH ISOTHECIUM-STOLONIFERUM

Moss monitoring, a common bioindication method, was used to investigat e temporal changes of atmospheric trace element deposition since the 1 960s in the Fraser Valley, British Columbia. Vancouver, Canada's third largest metropolitan area, is located in the west of the Fraser Valle y and has a significant effect on the air quality of the region. Chang es in atmospheric deposition of lead, cadmium, chromium, nickel, zinc, and manganese were estimated by analyzing local samples of the common woodland moss Isothecium stoloniferum Brid. collected during three di fferent time periods: 1960-1966, 1975-1980, and 1993. A significant de crease was found for lead, cadmium, chromium, nickel, and zinc, when s amples from 1960-1966 were compared with those collected in 1993. The declining metal levels are associated with a change in industrial acti vity, a reduction in fuel oil combustion for space heating, and abando nment of leaded gasoline. Manganese concentration in the moss samples increased significantly over the past 30 years. This increase might be related to the replacement of the antiknock additive, tetraethyl lead , with methylcyclopentadienyl manganese tricarbonyl. The present study shows how changes in human activity can affect and counterbalance inc reasing pressure from a fast-growing population in respect to trace el ement pollution.