Joint toxicity of sulfamonomethoxine and Cd on seed germination and root elongation of crops in soil

The single and joint effects of sulfamonomethoxine(SMM) and cadmium(Cd) on seed germination rate and shoot/root elongation of wheat(Triticum aestivum L.) and tomato(Solanum lycopersicum) in yellow fluvo-aquic soil were investigated.In the single-factor experiments,there was a dose-response relationship between the concentration of SMM or Cd and the inhibitory rate of crop root elongation and shoot elongation(P0.05),but no correlation was found between the concentration of each pollutant and the inhibitory rate of crop seed germination(P0.05).The inhibitory effect of each pollutant on root and shoot elongation was much stronger than those on seed germination.SMM showed a much higher toxic effect on crops than did Cd.The IC50(half inhibition concentration) values of SMM on root elongation of wheat and tomato were 33.7,49.3 mg/kg,respectively,the corresponding values of Cd were 507.3,599.8 mg/kg,respectively.In the joint effect tests,SMM and Cd showed a synergic effect on root and shoot elongation when the concentration of Cd was at 200 mg/kg.However the synergic effect was not significant with the increase of SMM concentration(P0.05);At the high concentration of Cd(500 mg/kg),joint toxicity of SMM and Cd was more dependent on Cd.