Comparison of effect of CdS QD and ZnS QD and their corresponding salts on growth, chlorophyll content and antioxidative capacity of tomato.

When applied in the same concentration to tomato plants, cadmium sulfate (CdSO 4) and zinc sulfate (ZnSO 4 ) were transported from soil to roots and from roots to shoots more readily than their nano counterparts: cadmium sulfide quantum dots (CdS QD) and zinc sulfide quantum dots (ZnS QD). Compared to the CdS QD, he higher rate of transport of CdSO 4 resulted in a greater negative effect on growth, chlorophyll content, antioxidant properties, lipid peroxidation and activation of antioxidant defence systems. Although ZnSO 4 was transported more rapidly than ZnS QD, the overall effect of Zn addition was positive (increase in total plant mass, stem length, antioxidant content and decrease in lipid peroxidation). However, these effects were more pronounced in the case of ZnS QD, suggesting that the mechanisms underpinning the activity of ZnS QD and ZnSO 4 were different. Thus, the risk of phytotoxicity and food chain transfer of the two elements depended on their form (salt or nanoform), and consequently their effects on plants' growth and physiology were different.