Novel risk assessment of Cd in earthworms and leeches based on bioavailability through in vitro digestion/Caco-2 and MDCK cells

Little data are available about the extent of bio-accumulation of heavy metals in traditional animal medicines (TAMs). In the present study, the oral bioavailability of cadmium (Cd) in earthworms and leeches was investigated through in vitro PBET digestion/Caco2 and MDKC cell models. We are the first to create an innovative assessment strategy which has capacity to offer a more precise evaluation of Cd-associated health risks in TAMs, by combinational usage of bioavailable Cd levels, the duration and frequency of the exposure to TAMs obtained by questionnaire data, as well as safety factor of TAMs. Our data showed that the percentage of bioavailability for Caco-2 cells in earthworms and leeches ranged from 3.29–14.17% and 4.32–12.61%, respectively. The percentage of bioavailability of MDCK cells in earthworms and leeches ranged from 4.83–15.74% and 6.53–15.04%, respectively. After adjusting by the bioavailability of Cd to target hazard quotient (THQ), excitingly, our findings manifested that the health risks induced by the ingestion of earthworms and leeches were acceptable in the clinic. Our novel strategy has capacity to offer a more realistic and accurate assessment of Cd-associated health risks in TAMs. Besides, our key findings suggest that bioavailability characterization cannot be ruled out and health risks should be assessed on the basis of the bioavailable Cd levels rather than total levels.