This study was performed to verify whether the exchange of the fuel used in the boilers of a
crude oil refinery located in Cubatão (SE Brazil) would result in alterations on gas exchange, growth and leaf
injuries in saplings of Psidium guajava 'Paluma'. The purpose of the refinery was to reduce the SO2 emission, but using
natural gas as fuel could increase the concentrations of O3 precursors in the atmosphere. Thus a biomonitoring was performed with a native species sensitive to O3. The plants were exposed in five areas (CM1, CM5, CEPEMA, Centro, and RP) at different distances to the refinery, both before and after the fuel exchange. We performed six exposures under environmental conditions, with length of ca. 90 days each. With the utilization of
natural gas, the saplings presented reductions in
carbon assimilation rate under saturating light conditions (Asat, μmolCO2m(-2)s(-1)) and the stomatal conductance (gs, molH2Om(-2)s(-1)), and increase in height, number of leaves, and dry mass of leaves and shoots. There were also reductions in root dry mass and in the root/shoot ratio. The saplings also presented O3-induced leaf
injuries. The responses of P. guajava 'Paluma' were altered after the fuel exchange as a result of a new combination of
pollutants in the atmosphere. The fuel exchange has not resulted in environmental benefit to the surrounding forest; it has only altered the contamination profile of the region.