The scavenging activity of three fulvic acids (named XWCS-1, XWCS-4, and XWCS-8 according to time taken for ozonolysis) obtained by ozonolysis of humic acid extracted from Xinjiang (China) weathered coal and a fulvic acid (named XWCFA) extracted from the same coal towards reactive oxygen species such as superoxide radical (O-2(.-)) and hydroxyl radical ((OH)-O-.) was investigated with an electron spin resonance (ESR)-spin trapping method using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. O-2(.-) was generated with a hypoxanthine-xanthine oxidase system. (OH)-O-. was generated by three different methods; (i) FeSO4-hydrogen peroxide (H2O2) system, (ii) Cu(en)(2)-H2O2 system, and (iii) UVB photolysis of H2O2. At physiological pH, XWCS-1 had the greatest O-2(.-) scavenging activity, followed by XWCS-4, XWCS-8 and XWCFA. XWCFA had the greatest *OH scavenging activity among the four fulvic acids, whereas XWCS-1 and XWCS-4 enhanced the production of *OH from a metal-catalyzed hydroxyl radical generating system, suggesting that these molecules act as prooxidants in the presence of metal ion. (C) 2004 Elsevier B.V. All rights reserved.