Quantitative Analysis and Risk Assessment of 5 Heavy Metal Elements in Birch Bark Medicinal Materials Based on Inductively Coupled Plasma Mass Spectrometry

The birch bark medicinal material powder sample （0.25 g） was taken, and 7 mL of nitric acid was added. The mixture was left overnight, and pre-digested at 120 ℃ for 20 min, then placed in a microwave digestion instrument and digested at 180 ℃ for 20 min by heating program. After cooling to room temperature, the mixture was acidified to 1 mL at 120 ℃ and made its volume up to 50 mL with 2% （volume fraction） nitric acid solution. After shaking well, the 5 heavy metal elements （lead, cadmium, arsenic, mercury, and copper） in the solution were determined by inductively coupled plasma mass spectrometry, with an online addition of a mixed internal standard solution containing germanium, bismuth and indium. The contamination status of birch bark medicinal materials by heavy metals were evaluated using the single-factor pollution index method and the Nemerow comprehensive pollution index method. The potential human health risks posed by heavy metals were assessed based on 3 indicators, including the maximum tolerable daily intake, the target hazard quotient, and the carcinogenic risk factor. As shown by the results, linear relationships between the ratios of the corresponding response intensity to the internal standard response intensity and mass concentrations of the 5 target elements were kept in definite ranges, with detection limits （3s/k） in the range of 0.000 2−0.005 mg·kg⁻¹. Test for precision was conducted on an antual sample, with RSDs （n=6） of the determined values less than 5.0%. Test for recovery was made by the standard addition method, giving results in the range of 90.9%−106%. The method was applied to the analysis of 30 batches of birch bark medicinal material samples. The results showed that there were certain differences in the contents of the 5 target elements among samples from different producing areas and different batches. The single-factor pollution index and the Nemerow comprehensive pollution index were less than 0.8 and 0.7, respectively, indicating that the pollution degrees of birch bark medicinal materials were at safe level. The health risk assessment showed that the maximum tolerable daily intakes were lower than the provisional tolerable daily intakes, and the carcinogenic risk factors were significantly below 1×10⁻⁶ mg·（kg·d）⁻¹. However, the target hazard quotients of lead element in 3 batches of samples from Inner Mongolia were greater than 0.01, suggesting that lead element in birch bark medicinal materials may pose a potential non-carcinogenic risk, which should be subject to continuous monitoring.