# Risk Assessment of Metals in Black Fungus and Culture Substrates Based on Monte Carlo Simulation
## 5 Conclusions  
This study evaluated the background value of heavy metals in auriculus auriculus fruiting bodies and raw materials and the risk assessment of dietary intake of auriculus auriculus, and made a preliminary discussion on the sources of heavy metals in auriculus. The main research results are as follows:  
1. As, Pb, Cd and Cr were detected in auriculus auriculus auriculus, and the cumulative quantity showed Cr > Pb > As > Cd, and there was no significant difference between auriculus auriculus samples collected from the base and the market (\(p\) > 0.05), indicating that there was no external risk during storage and transportation. 2. In this study, the background values of four heavy metals in auricularia auriculata were determined, and the background values of As were 0.010-0.320 mg/kg, Pb 0.051-0.792 mg/kg, and Cd 0.019-0.236 mg/kg. The background value of Cr ranges from 0.06 to 3.41 mg/kg. The over-standard rate of As, Pb and Cd in black fungus was 1.68%, 0.59% and 0.59% respectively. Since there is no limit standard for Cr, the reference grain limit has an over-standard rate of 37.99%. In view of this, it is recommended to develop the limit standard for Cr in black fungus as soon as possible. 3. The background values of the four heavy metals in the main raw materials were determined. As in sawdust was between 0.006-0.097 mg/kg, Pb was 0.124-1.44 mg/kg, Cd was 0.059-0.902 mg/kg, and Cr was 0.300-6.500 mg/kg, and Cr > Pb > Cd > As. In soybean meal, As was 0.005-0.008 mg/kg, Pb ranged from 0.020-0.300 mg/kg, Cd 0.011-0.125 mg/kg, Cr 0.042-1.147 mg/kg, and Cr > Pb > Cd > As. The contents of As in rice bran ranged from 0 to 0.892 mg/kg, Pb from 0.090 to 1.150 mg/kg, Cd from 0.010 to 0.087 mg/kg, Cr from 0.280 to 6.900 mg/kg, and Cr > Pb > As > Cd. In wheat bran, As was 0.005-0.097 mg/kg, Pb 0.010-1.840 mg/kg, Cd 0.010-0.169 mg/kg, Cr 0-8.000 mg/kg, and Cr > Pb > Cd > As. The content of heavy metals in lime and gypsum is the highest in Cr, followed by Pb, and less in As and Cd. 4. Without considering irrigation water and external factors, the contribution of raw materials to heavy metals mainly came from sawdust, followed by rice bran and wheat bran. The contribution rate of Pb is as follows: sawdust 82.32% > rice bran 7.63% > wheat bran 7.05% > lime 1.39% > gypsum 1.05% > soybean meal 0.39% > corn flour 0.17%. The contribution rate of Cd was 77.83% sawdust > rice bran 7.82% > wheat bran 6.62% > gypsum 2.80% > lime 2.36% > soybean meal 2.22% > corn flour 0.34%. The contribution rate of Cr was 81.35% sawdust > rice bran 8.49% > wheat bran 6.01% > lime 1.34% > gypsum 1.19% > corn flour 1.06% > soybean meal 0.57%. 5. Risk assessment results showed that the risk of heavy metals As, Pb, Cd and Cr in black fungus through dietary intake was higher in minors than in adults. The average risk quotient of As, Pb, Cd and Cr ingested by the black fungus pathway in the juvenile population was 0.1281, 0.0315, 0.0338 and 0.1326, respectively, and the comprehensive pollution index was 0.3260. However, at the high exposure levels of 97.5% sites and 99% sites, the risk quotient of single element was within the safe level, and the risk quotient of comprehensive pollution index was 1.1500 and 1.4466, respectively, in the light pollution level. The average risk quotient of As, Pb, Cd and Cr ingestion in the adult population through black fungus pathway were 0.0766, 0.0188, 0.0202 and 0.0794, respectively, and the comprehensive pollution index was 0.1950, which was within the overall safety level. However, at the high-exposure level of 99% sites, the risk quotient of single element was within the safe level, and the risk quotient of comprehensive pollution index was 0.8649, which was at the warning limit. To sum up, this study established a Monte Carlo simulation-based non-parametric probability assessment system for heavy metals in auriculus auriculus. The hazard degree of heavy metals in auriculus auriculus on dietary intake of different populations was evaluated by the target hazard coefficient method.