Abstract: Nanoscale zero\|valent iron （NZVI） has been used to reduce polychlorinated biphenyls （PCBs）. However， the effect of dissolved organic matter （DOM） on the dechlorination of PCBs was not well recognized. This study examined the effect of three low weight molecule organic acids， including salicylic acid （SA）， tannic acid （TA） and gallic acid （GA）， which are widely present in soil， on the dechlorination and removal efficiency of 4\|ClBP by NZVI. After 96 h reaction， the dechlorination efficiency of 4\|ClBP by NZVI was 650%， and the removal efficiency was 740%. The dechlorination and removal efficiency of 4\|ClBP were 540% and 699% with SA， 612% and 708% with TA， and 546% and 695% with GA， respectively. The addition of SA inhibited the reduction of 4\|ClBP by NZVI. And in these four reaction system， pH increased rapidly firstly and then reached equilibrium quickly.

Key words: polychlorinated biphenyls, nanoscale zero\, valent iron, dechlorination, removal rate, low\, molecular weight organic acids