Abstract: 1,2,4-Trichlorobenzene (1,2,4-TCB) and tetrachloroethene (PCE) were chosen to study their competitive effect on 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB) sorption by three soils/sediments from South China with different fractions of natural organic matter (NOM) employing a batch technique. Results showed that cosolutes 1,2,4-trichlorobenzene and tetrachloroethene exhibited apparent competition against 1,2,4,5-tetrachlorobenzene in all of the three sediments. 1,2,4-Trichlorobenzene was more effective competitor than tetrachloroethene because the structure of 1,2,4-TCB is very close to that of 1,2,4,5-TeCB. Furthermore, the extent of competition depended on the rigidity of sediment NOM matrixes. The more reduced and condensed the matrixes are, the larger extent of competitive effect would the corresponding sediment show at a given sorbed volume of competitor. [Copyright &y& Elsevier]