Generation of reactive oxygen intermediates (ROI) such as O(2)(-), H(2)O(2), and *OH is known to be a major mechanism of damage in biological systems. This study investigated and compared effectiveness of scavenging ROI generated in fluoranthene (FLU) pre-fumigated Japanese red pine seedlings. Three kinds of eco-physiological assessments were used to express the impact of the different fumigants used inside the green house. Gas exchange measurements showed negative changes induced by 10 microM FLU on Japanese pine seedlings during a 10 d exposure period whilst no negative change was found during a 5 d exposure period. Moreover, during a 14 d FLU exposure incorporating ROI scavengers, results revealed that chlorophyll fluorescence, needle chemical contents and needle dry mass per unit area of the seedlings were affected. The negative effects of FLU on the conifer were dependent on both the dose and period of FLU fumigation. Peroxidase (PERO), superoxide dismutase (SOD) and mannitol (MANN) were all effective scavengers of ROI. MANN scavenged *OH, the most lethal of the ROI. For practicable use, MANN is more economical, and may be the best ROI scavenger among the three considered. It can be concluded that efficient scavenging of ROI in biological systems is important to mitigate the negative effects of FLU on Japanese red pine trees.