Using response surface methodology to assess the effects of iron and spent mushroom substrate on arsenic phytotoxicity in lettuce (Lactuca sativa L.)

► As in soils obviously reduces the root growth of lettuce. ► Incorporation of Fe in artificial soils induced EC50 of As to lettuce root elongation. ► SMS increased lettuce root elongation in both As-treated and non-As treated soils. ► However, SMS also decreased EC50 of As via its interaction with Fe. ► Response surface model fits for interpreting interactions of factors in soils.