Quantification of aristolochic acids in agricultural soil and development of remediation methods

Abstract

Aristolochic acids (AAs) are nitrophenanthrene carboxylic acids naturally produced by the plants of Aristolochia species. They have been widely used to prepare herbal remedies until the AAs were shown to be highly nephrotoxic and carcinogenic to humans. Despite the prohibition of the use of AAs-containing Aristolochia plants in herbal medicine worldwide, emerging evidence suggests that exposure to AAs is a major global cause of nephropathy, renal failure and urothelial cancer, including Balkan endemic nephropathy (BEN), an environmentally derived disease threatening numerous people residing in farming villages near the Danube River in the Balkan Peninsula. The high incidence of BEN on the Balkan Peninsula is originally assumed to result from consumption of food crops co-harvested with Aristolochia clematitis L. seeds. However, we demonstrate here that AAs are persistent soil contaminants (t_1/2 ~ 6 months) in agricultural fields of Serbia that enter wheat and maize plants by root uptake, observing a strong pH-dependent relationship between the levels of AAs in soil and in food grains. We collected hundreds of wheat and maize grains with corresponding soil samples from six Serbian villages which were thereafter subjected to the qualitative and quantitative analyses of AAs. Results indicated that samples from villages endemic in BEN are more extensively contaminated with AAs and the contamination agrees with the local BEN incidence rates, presumably due to consumption of contaminated grain products by residents of these villages. Our results can benefit the identification of regions bearing higher human risk of exposure to AAs, it is anticipated that similar systematic surveys of soil and food in other endemic villages or countries would be initiated and published. The positive identification of AAs in soil and food not only sends out public health alerts to local government and residents, but also creates demands for solutions to eliminate AAs in the environment. Since the most probable source of AAs could be A. clematitis plants, the complete removal of these plants may appear to be one of the viable solutions. The issue of enormous manpower and resources required in the process is one major obstacle, but an even greater issue of existing AAs in soil still left unsolved. For the sake of long-term public health well-being, a soil remediation method is necessary in addition to the removal of AA-containing plants. Fenton’s reagent is chosen to remediate AAs-contaminated soil using chemical oxidation, taking advantage of its simplicity in operation, moderate cost and advanced oxidative potential, Fenton’s reagent has proved to be an efficient and popular remedy to treat soil contaminated by unwanted organic compounds like polycyclic aromatic hydrocarbons (PAHs). In this experiment, the AAs-removal efficiencies were evaluated by the post-treatment level of AAs in water and soil. Temperature, dosages of iron (II) ion and hydrogen peroxide and molar ratio between iron (II) ion and hydrogen peroxide were optimized to achieve the best degradation performance (> 95% removal). The course of Fenton reaction was also monitored for three hours, which clearly depicted its rapidity in attacking organic compounds. The optimized method was later applied on soil samples collected from endemic villages to demonstrate its ability to remediate AAs-contaminated soil. Finally, additional human exposure pathways to AAs were explored by analyzing flour and medicine samples. Wheat flour, maize flour samples were collected from local supermarket in Serbia, while traditional Chinese medicines were gathered from China, Hong Kong and Taiwan. Positive results (~15%) among these samples suggest that the extent of AA contamination in our daily life can be beyond our expectations and they may also explain the high chronic kidney disease incidence in China.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology