According to the International agency for Research on Cancer, cadmium (Cd) is considered as a human carcinogen. Cadmium may induce cell death by apoptosis in various cell types, although the underlying mechanisms are still unclear. Nowadays, the cytotoxic potential of heavy metals is commonly evaluated by different cellular endpoints as reactive oxygen species formation, cell viability or cell death. Heavy metals cytotoxicity testing is based on in-vitro methods such as MTT assay, for the colorimetric detection of mitochondrial activity, propidium iodide-staining of DNA, as cell death marker, fluorometric detection of ROS generation to evaluate the stress response and colorimetric detection of cytokine secretion for the inflammatory reaction by ELISA method. In this work, we present a label-free digital holography (DH) based technique as an in-vitro cytotoxicity assay, which overcomes the limitations of conventional in vitro test based on color or fluorescence read outs. In particular, we show how DH is able to quantify the evolution of key biophysical parameters of cells during the exposure to cadmium. Murine embryonic fibroblasts NIH 3T3 are chosen here as cellular model for studying the cadmium effects. The results demonstrate that DH is able to retrieve the temporal evolution of different key parameters such as cell volume, projected area, cell thickness and dry mass, thus providing a full quantitative characterization of the cell physical behaviour during cadmium exposure. This demonstrates DH as an elegant label-free tool for heavy metals toxicity analysis.