Heavy Metal Pollution In Commercially Available Chinese Herbal Medicines From Kunming Market And Source-to-end Methods For Heavy Metal Removal

Chinese herbal medicines?CHMs?have been used to treat various diseases for thousands of years in China.As natural drugs with low toxicity,CHMs are more and more popularly used all over the world.With the development of global industrialization,the soil environment is polluted by various heavy metals.At the same time,the problem of heavy metal pollution in CHMs is getting serious.The pollution of heavy metals in CHMs not only restricts the development of CHMs in the international market,but also leads to the decline of the quality of traditional Chinese medicine and threatens people's health.Therefore,it is particularly important to investigate the heavy metal pollution of CHMs in the market and to prevent and control the heavy metal pollution in CHMs.This paper firstly examined the pollution status of heavy metals in commercially available CHMs in Kunming,Yunnan Province,and then studied the removal of heavy metals from soil itself?the source?and CHMs themselves?the end?of heavy metal pollution in CHMs.The following three aspects are studied:?1?Sixty CHMs were purchased from pharmacies in Kunming,and the contents of Cu,Cd,Pb,Zn,As and Hg were detected.The pollution situation of each heavy metal was analyzed through the limiting values of the“Green Trade Standards of Importing&Exporting Medicinal Plants&Preparations”?WM2-2001?.According to the chemical forms analysis of Cd with serious pollution in 8 CHMs?Cyathulae radix,Drynariae rhizoma,Peucedani radix,Homalomenae rhizoma,Dryopteris setosa,Polygonati rhizoma,Lilii bulbus and Linderae radix?and the dissolution of heavy metals in decoction of 4 CHMs?Typhonii rhizoma,Linderae radix,Homalomenae rhizoma,and Cyathulae radix?,the risk of heavy metals in CHMs to human health was comprehensively evaluated.?2?Several kinds of leaching agents?H₃PO₄,K₂CO₃,CH₃COOK,KH₂PO₄,HNO₃ and KNO₃?were used to elute metal-contaminated soils,and the best leaching agents and conditions were selected.The changes of chemical forms of heavy metals and physico-chemical properties of soil before and after leaching treatment were analyzed.Finally,the effectiveness of soil remediation was detected by planting?Mentha haplocalyx?,which can accumualte heavy metals with a strong ability.?3?Three kinds of adsorbents?chitosan,permutite and activated carbon?were used to adsorb Cd in decoction of CHMs.Adsorption kinetics and isothermal adsorption were used to analyze the adsorption process.The main results indicated as follows.1.The results of heavy metal analyses in 60 CHMs showed that the concentrations of Cd,Hg and Cu in some CHMs exceeded the limiting values of the“Green Trade Standards of Importing&Exporting Medicinal Plants&Preparations”?WM2-2001?,with exceedance ratios of 38.8%,8.3%and 1.7%,respectively.The majority of Cd was integrated with pectates and protein in CHMs,and the other five Cd chemical forms followed the order of water-soluble>insoluble heavy metal phosphates>oxalate>residual>inorganic form,indicating that Cd had relatively low bioactivity and toxicity.The average dissolution rates of Zn,Cu,Cd,Hg,As and Pb in the four CHMs were 47.4%,33.8%,20.5%,6.1%,5.4%and 4.8%,respectively.The calculation results of hazard quotients?HQs?for Cd and Hg showed that the CHMs did not pose a threat to human health.2.The results of soil washing by leaching agents showed that HNO₃ had a relatively good effect on the removal of Cd and Pb.The removal rates of Cd and Pb in soil by 1%HNO₃ were 75.7%and 60.6%,respectively,when the leaching temperature was 35?,the leaching time was 90 min and the leaching solid-liquid ratio was 1:10.Compared with the original soil,the total nitrogen and available phosphorus in the leached soil increased significantly,but the total phosphorus,total potassium,available nitrogen,available potassium and organic matter in the soil decreased significantly.The chemical forms of Cd in soil before leaching were mainly present as iron-manganese oxide bound state?F₃,32.37%?,exchangeable state?F₁,29.93%?and carbonate bound state?F₂,26.39%?.After leaching with 1%nitric acid,the chemical form of Cd was mainly present as F₁?62.68%?.When Ca?OH?₂ was used to regulate the pH value of leached soil to neutral,the chemical forms of Cd in soil were mainly present as residue?F₅,30.38%?and F₃?25.48%?.The chemical forms of Pb in soil before leaching were mainly present as F₃?44.61%?and F₅?40.57%?.After leaching with 1%nitric acid,the chemical forms of lead were mainly present as F₅?44.66%?and F₁?34.23%?.After adjusting pH to neutrality with Ca?OH?₂,the chemical forms of lead in soil were mainly present as F₅?52.32%?and F₃?33.45%?.The determination of plant height,root length and biomass of mint showed that the growth status of mint planted with soil leaching and pH adjustment did not change significantly,and the contents of Pb and As in the above-ground and underground parts of mint decreased significantly,but the contents of Cd,Cu and Zn showed no significant difference.3.The result of Cd removal from decoction of CHMs showed that the Cd concentration in the decoction of CHMs treated by three kinds of adsorbents?chitosan,permutite and activated carbon?met the limiting value(0.005mg L^-1)set by"Hygienic Standard for Drinking Water"?GB 5749-2006?.Among the three adsorbents,chitosan had the best adsorption effect.When the dosage of chitosan was 1g?i.e.the ratio of adsorbent to decoction of CHM was 1:25?,the removal rate of Cd reached 70%.Three adsorbents were more suitable for describing their isothermal adsorption of Cd in decoction of CHMs by Freundlich isothermal model.The second-order kinetic adsorption model was more suitable for describing the kinetic adsorption of Cd in decoction of CHMs by three adsorbents.In summary,Cd,Hg and Cu concentrations in some CHMs in Kunming market exceeded the limiting value,and Cd had the highest exceeding rate.However,the Cd chemical forms in CHMs with exceeding Cd were mainly present as pectin and protein binding state,which has low biological activity and toxicity,so the risk posed to human health was very low.The Cd and Pb in soil could be effectively removed by 1%HNO₃,and the total nitrogen and available phosphorus in soil were significantly increased,but the total phosphorus,total potassium,available nitrogen,available potassium and organic matter in soil were significantly reduced.Therefore,It is necessary to readjust the soil pH value.When Mentha haplocalyx was planted in the soil after readjusting pH value by Ca?OH?₂,the concentrations of Pb and As in both above-ground and underground parts of plant were significantly reduced.Chitosan had the best removal effect on Cd in decoction of CHMs,and its isothermal adsorption process was more suitable to be described by Freundlich isothermal model.