BACKGROUND: Little attention has been paid to the use of large-sized scrap cast iron for reduction of refractory organic pollutants at neutral pH and in the presence of dissolved oxygen (DO). RESULTS: Scrap cast iron and copper-modified cast iron with fresh surfaces have a high reactivity towards the reduction of 2,4-dinitrotoluene (2,4-DNT). The extent of conversion reached around 80% and 97% respectively, though it gradually decreased with repeated reactions to relatively stable values of 63% and 72%, and recovered once the reacted filings were cleaned by dilute acid. After 50 days reaction, no dissolved copper appeared in the copper-modified cast iron process. The mass loss of copper due to physical detachment reached 1.1% of the total coated copper within the initial 20 reaction days, and only 0.3% appeared in the next 30 days. 2,4-DNT oxidizes scrap cast iron to generate mainly FeFe(2)O(4) with DO, however, it oxidizes scrap copper-modified cast iron to generate mainly gamma-FeO(OH) and alpha-FeO(OH). CONCLUSION: Both samples of cast iron were successfully applied in the treatment of neutral wastewater containing 2,4-DNT with high reactivity and good repeatable efficiency. Electrode reaction rate was enhanced by the deposited copper, which has strong chemical and physical stability. (C) 2011 Society of Chemical Industry