To investigate the endogenous characteristics and consumption safety risk of semicarbazide (SEM) residues in farmed Scylla paramamosain.

A total of 239 mud crab samples were collected from aquaculture ponds along the coasts of Sanmen Bay and Yueqing Bay, covering 5 counties (cities): Ninghai, Sanmen, Wenling, Yuhuan and Yueqing. In addition, 119 water samples and 119 sediment samples were simultaneously collected.SEM residues were detected using high performance liquid chromatography-tandem mass spectrometry, yielding 478 valid data points in total.

No SEM was detected in any water or sediment samples, while the detection rate in Scylla paramamosain reached 92.1%, confirming that the detected SEM was confirmed to be mainly derived from the endogenous background. The detected values exhibited a typical positively skewed distribution, with 75.9% of samples concentrated in the dominant concentration range of 0.1–0.4 μg/kg, and only 0.45% of samples exceeded 1.0 μg/kg.Tissue distribution analysis revealed that SEM concentrations in the hepatopancreas were generally higher than those in muscle, but 51.2% of samples showed hepatopancreas/muscle ratios between 1 and 2, indicating a uniform distribution pattern characteristic of bound residues without extreme enrichment. No statistically significant differences were observed among regions (P>0.05), with both Sanmen Bay and Yueqing Bay belonging to endogenous background areas.Significant gender differences (P<0.05) were primarily regulated by the dynamic process of lipid transport to ovaries during the female reproductive cycle. Temporally, SEM concentrations exhibited regular fluctuations with reproductive rhythms, peaking in female hepatopancreas at 0.40 μg/kg in mid-September, coinciding with ovarian maturation. Food safety risk assessment indicated that the average SEM intake per Scylla paramamosain was approximately 50 ng, equivalent to only 1/300000 of the toxic reaction dose in experimental animals, indicating extremely low food safety risk.

SEM residues in farmed Scylla paramamosain from Sanmen Bay and Yueqing Bay represent an endogenous background phenomenon regulated by reproductive cycles, posing no systematic safety risk, and consumers can safely consume these products.