Soil and plant contamination with pesticides and heavy metals have significant effects on human health. There may be an interaction effect (synergistic or antagonistic) between them that can increase the risk of their presence in certain amounts. A pot experiment was conducted using four pesticides (acetamiprid, emamectin benzoate, imidacloprid, and thiamethoxam) applied on Lew mallow (Chorcoruis olitorus) plants grown on contaminated and uncontaminated soils. Some heavy metals and pesticide residues were determined. Treating plants with different pesticides increased the soil content of pesticide residues, and the increases were much higher in previously contaminated soils compared with the uncontaminated ones. Soil content of pesticide residues in contaminated soil can be arranged in descending order as follows: acetamiprid > thiamethoxam > imidacloprid > emamectin benzoate with increases by 707, 373, 287, and 124%, respectively, compared to the control. The highest antagonism was found between Acetamiprid and soil Zn, Emamectin benzoate and soil Pb, Imidacloprid and Mn in soil and plant, Thiamethoxam and plant Zn. The highest synergistic relationships were found between Acetamiprid with Pb and Ni in plant, emamectin benzoate with Mn and Cd, in soil and plant’s Mn, imidacloprid and plant Zn, thiamethoxam and Pb in soil and Cd in plant.