# Risk Assessment of Metals in Black Fungus and Culture Substrates Based on Monte Carlo Simulation
## 2 Materials and Methods
### Dietary Risk Assessment Model  
The target hazard quotient (THQ) method established by the United States Environmental Protection Agency (USEPA) was used to evaluate the potential risk to human health caused by different heavy metals when consumers eat black fungus. The THQ method assumes that the heavy metal absorption is equal to the ingested dose, and calculates the ratio of the ingested pollutant dose to the reference dose. A single heavy metal coefficient THQ value \(<\) 1 indicates that the intake of heavy metals in black fungus poses no significant health risk to the exposed population. When THQ \(\geq\) 1, it indicates that the intake of heavy metals in black fungus poses health risks to the exposed population. The higher the THQ value, the greater the risk to human health arising from the intake of heavy metals in black fungus. The THQ method can also further evaluate the impact of pollutants in products on the health risks of adults and children, and the parameter settings for different age groups in the method are different. Therefore, it is possible to distinguish the degree of health risk for intake of cadmium in black fungus between different age groups.  
The @Risk 8.0 software was used to assess the risk of heavy metals in auriculae, and the heavy metal pollution data were randomly selected to calculate the heavy metal dietary risk quotient of different populations. The simulation method was Monte Carlo simulation with 10,000 simulations. The distribution of the dietary risk quotient of auricularia auricularia in different heavy metal populations was obtained by calculation.  
1. Risk description formula The target risk quotient of heavy metals in black fungus is calculated as follows: \[\text{THQ}=\frac{\text{EF}_{\text{r}}\times\text{ED}\times\text{F}_{\text{IR}} \times\text{C}\times\text{F}_{\text{P}}\times\text{F}_{\text{m}}}{\text{R}_{ \text{fD}}\times\text{W}_{\text{AB}}\times\text{AT}_{\text{n}}}\times 10^{-3}\]  
THQ: target risk quotient; EFr (d\(\cdot\)a\({}^{-1}\)): exposure frequency; ED (a): exposure persistence; F\({}_{\text{IR}}\) [g\(\cdot\)(d\(\cdot\)person)\({}^{-1}\)]: per capita daily dietary intake of edible fungi; C (mg\(\cdot\)kg\({}^{-1}\)) black fungus heavy metal content; F\({}_{\text{P}}\): processing factor; F\({}_{\text{m}}\): variation factor; R\({}_{\text{fD}}\) (mg\(\cdot\)kg\({}^{-1}\).bw): reference dose; W\({}_{\text{AB}}\) (kg\(\cdot\)person\({}^{-1}\)): body weight per capita; A\({}_{\text{Th}}\) (d): mean cancer-free response time.
2. Expose the source of assessment data Exposure frequency and duration, per capita dietary intake of edible fungi, heavy metal content in black fungus, processing factors, variation factors, per capita body weight and mean cancer-free response time were all associated with risk description formula. Daily reference dose: According to nutrition and chronic diseases among residents in China in 2015, the report data are RfD (Cd) = 1 \(\times\) 10\({}^{-3}\) mg\(\cdot\)kg\({}^{-1}\).d \({}^{1}\), RfD (As) = 3 \(\times\) 10\({}^{-4}\) mg\(\cdot\)kg\({}^{-1}\).d\({}^{-1}\), and RfD (Pb) = 3.5 \(\times\) 10\({}^{-3}\) mg\(\cdot\)kg \({}^{-1}\).d\({}^{-1}\). The recommended optimal intake (AI) RfD (Cr) in the _Reference Intake of Dietary Nutrients for Chinese Residents_ (2013 edition) is 3 \(\times\) 10\({}^{-3}\) mg\(\cdot\)kg\({}^{-1}\).d\({}^{-1}\).
3. Heavy metal pollution classification standards As to Table 3.