Abstract:
Ambient (03) ozone concentrations were compared to ozone damage on milkweed
plants to determine if there was a correlation. Eight survey sites of at least 100 plants
each were located within 5 kilometers of Air Quality Index (AQI) stations in southern
Ontario. Sites were visited nine times from June-September (2007) and milkweed
leaves from 75 plants were assessed using methods pioneered in the United States.
Ambient 0 3 results were calculated into SUM65, seasonal cumulative 0 3, and total 03.
The 0 3 exposure indices SUM65 and cumulative 0 3 were tested statistically to
determine which index is biologically relevant to milkweed as an 0 3 damage indicator
species. The milkweed damage indices were incidence of leaves damaged per plant,
incidence of plants damaged per site, and total 0 3• The incidence of plants injured per
site was the best damage parameter with an F(1,28)=17.37, p=0.0003 for SUM65 and
F(1,28)=7.5, p=O.0106 for cumulative 03 .. Milkweed plants showed quantifiable ozone
damage with minimal spatial differences in damage and thus have potential use as a
biomonitor species in southern Ontario.
