Cockles are among the four traditional cultured bivalve mollusks in China. However, the high cadmium (Cd) content in cockles, its origins, and the associated health risks remain unclear. In this study, we employed a stable isotope tracer method to comparatively determine the toxicokinetics of Cd in two species: Tegillarca granosa and Scapharca subcrenata. Compared to T. granosa, S. subcrenata exhibited a higher Cd uptake rate constant and a lower elimination rate constant, providing a toxicokinetic explanation for its higher Cd concentrations. In both species, the viscera showed the highest Cd uptake rate constants and the longest biological half-lives, explaining the higher Cd concentrations found in these tissues. We further measured Cd concentrations in tissues of three economically important cockle species (Scapharca broughtonii, T. granosa, and S. subcrenata) collected from 20 sites along the Chinese coast. Over half of the cockle samples exceeded the Cd limit for bivalves set by China's food safety standards. Considering dietary habits and international and domestic Cd limit standards, we conducted a health risk assessment using the Monte Carlo method for the three cockle species. Based on the tolerable Cd intake levels recommended by international organizations, we estimated the daily safe consumption amounts for S. broughtonii, S. subcrenata, and T. granosa to be 1, 2, and 10 individuals, respectively. We also compared the total dietary Cd intake from rice in China. Our findings indicate that the additional health risk from Cd in cockles is non-negligible, with the highest risk associated with consuming S. subcrenata. Cockles are an important yet overlooked source of Cd exposure for populations in China's coastal regions. This study provides crucial information for the safe cultivation of cockles and for controlling the risks associated with their consumption.