Study On The Ecotoxicity Of Roxarsone In Soils

Roxarsone, an animal feed additive, was widely used in poultry production. It was excreted unchanged in the manure and introduced into environment when animal litter was applied to farmland as fertilizer, which would pollute soils and arsenic amount of plants in soils may be more than the food hygienic standard.In the research, the effects of roxarsone on the microorganism in soils and the growth of cabbage and tomato planted in polluted soil were studied. A HPLC method was developed for determining residues of roxarsone in soils and the sorption of roxar-sone in soils.Different roxarsone concentrations (0,20,50,80,150 mg/kg) were designed for researching the effects of roxarsone on microorganism in soil and growth of two plants pakchoi cabbage and tomato. The soil respiration was some enhanced during 4～6d after treating by roxarsone, but there was no significant difference(P>0.05). Compar-ing with the control group, the inhibitory effects on soil nitrification were more obvi-ous with the roxarsone dose increased. The 80 mg/kg and 150mg/kg groups had sig-nificantly inhibitory effects over the whole experiment periods(P<0.05). The soil ammonification was weakened in 20 mg/kg and 50mg/kg roxarsone groups after treated 2d(P<0.05), and was strongly weakened at 80mg/kg and 150mg/kg doses(P<0.01).The low concentrations of roxarsone, such as 20,50,80mg/kg would stimulate the growth of tomatoes while high concentrations such as 150,250mg/kg of roxarsone had distinct restrain effects to pakchoi cabbage and tomato. The arsenic amount of cab-bage and tomato arrived peak value about 50 days, and the tissues of two plants contents increased with the roxarsone addition in the soil. However, roxarsone residual amount of soils decreased slowly by HPLC test, there were more than 10mg/kg in soil up the sixtieth day.The sorption of roxarsone in the Ap,Bt1 and Bt2 soils was researched through shaking to reach equilibrium. The adsorption isotherms of roxarsone in soils fitted the Freundlich equation well, and the adsorption values of roxarsone were calculated by Freundlich equation. The adsorption coefficient (Kf) in Ap, Bt1 and Bt2 were 0.1824, 0.5152,0.9616 respectively, which indicated the sorption capacity of soil Bt2 > Bt1 >Ap. The sorption capacity of Ap soil was decreased with the pH increasing, the sorption of roxarsone on Bt soil showed no pH dependence.