The mobility of arsenic and its species in selected herbs

The aim of the study was verifi cation of the response of chamomile (Matricaria recutita (L.) Rauschert), peppermint (Mentha x piperita) lemon balm (Melissa offi cinalis L.), and sage (Salvia offi cinalis L.) on the elevated contents of inorganic As species in soils. The ability of herbs to accumulate arsenic was tested in pot experiment in which soils were contaminated by As(III) and As(V). The As(III), As(V), AB (arsenobetaine), MMA (monomethylarsonic acid) and DMA (dimethylarsinic acid) ions were successfully separated in the Hamilton PRP-X100 column with high performance-liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) techniques. The study examined total arsenic contents in soil and plants, as well as the mobility of the arsenic species from the soil into the studied plants. Peppermint demonstrated the highest arsenic concentration and phytoaccumulation among studied plants. The sequential chemical extraction showed that arsenic in the contaminated soil was mainly related to the oxide and organic-sulfi de fractions. The results showed that the oxidized arsenic form had a greater ability to accumulate in herbs and was more readily absorbed from the substrate by plants. Research has shown that soil contaminated with As(III) or As(V) has different effects on the arsenic content in plants. The plant responses to strong environmental pollution varied and depended on their type and the arsenic species with which the soil was contaminated. In most cases it resulted in the appearance of the organic arsenic derivatives. The mobility of arsenic and its species in selected herbs 87 As in the environment are still increasing, due to the industrial development and economic growth. In Polish rivers, the content of As(III) in water was even 2.36 μg∙L-1 in the Kłodnica River (Jabłońska-Czapla 2015a) or 3.83 μg∙L-1 in the Biała Przemsza River (Jabłońska-Czapla 2015b). Human exposure to arsenic can cause various detrimental health effects, such as dermatological, pulmonary, cardiological, genetic, genotoxic or mutagenic (Selene et al. 2003). For humans, water and food are the main arsenic sources. When compared to its inorganic forms, the organic compounds of As are relatively non-toxic to humans. Inorganic arsenic forms are metabolized in the human body to their methylated species (in the methylation process) and removed at least partly, together with urine (Vahidnia et al. 2007). The application of hyphenated techniques such as high performance-liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) allows for speciation analysis (Cai et al. 2017, Das et al. 2001, Donner et al. 2017, Hong et al. 2018, Jabłońska-Czapla et al. 2014a, Jabłońska-Czapla et al. 2015, Jabłońska-Czapla 2015b, Marcinkowska et al. 2016, Templeton et al. 2000, Zheng et al. 2003). It is necessary for the hyphenated methods used in the arsenic speciation analytics (at low concentration levels) to be both appropriately selective and sensitive (Hong et al. 2018). In the literature there are many studies on the instrumental methods used for the speciation of arsenic chemical species. Most of them are based on the chromatographic separation techniques, such as HPLC (Asaoka et al. 2012, Cornelis et al. 2003, Ellis and Roberts 1997, Moldovan et al. 1998, Pantsar-Kallio and Manninen 1997, Roig-Navarro et al. 2001, Ronkart et al. 2007). Fractionation is a method enabling differentiation of operationally defi ned element forms, while the sequential extraction procedure allows to separate trace metals into chemical forms that can be released into the solution under different environmental conditions. One of the most frequently used types of sequential extraction is either the extraction scheme suggested by the Institute for Reference Materials and Measurements (BCR) (Tokalioglu et al. 2003) or Tessier’s chemical extraction procedure (Tessier et al. 1979). Plants growing on polluted substrate absorb metals and metalloids (Pavlovic et al. 2006, Ruzickova et al. 2015, Voyslavov et al. 2013, Zheljazkov and Nielsen 1996, Zheljazkov et al. 2006, Zheljazkov et al. 2008a, Zheljazkov et al. 2008b, Zurayk et al. 2001). Plants partially metabolize arsenic into its methyl species. Due to the easiness of arsenic accumulation in plants (Samecka-Cymerman and Kempers 2000), its toxicity and plant tolerance for this element, the number of speciation study were carried out in: Acer platanoides (Budzyńska et al. 2018), Pteris vittata (Wang et al. 2002), radish (Raphanus sativus) (Tlustos et al. 2002), bean (Phaseolus vulgaris) (Sukanya et al. 2018) and even Xerocomus badius (Niedzielski et al. 2013). However, the As transformations in mushrooms are different from the higher plants (Kalač 2010). The proportional dependence of the arsenic content in plants on the presence of soil indicates a passive mechanism. The plant uptake of arsenic depends strongly on the plant species and soil physicochemical conditions. In the case of a substrate (or air) contamination with arsenic compounds, its content in plants increase even up to several thousand mg∙kg-1 (Niedzielski et al. 2000, Koukamp et al. 2016). Inside plants, as arsenic speciation analysis showed, As can affect growth and productivity due to a plethora of morphological, physiological, biochemical, and molecular alterations (Abbas et al. 2018). Unfortunately, there is little research in the world literature on the arsenic speciation in herbs, which are very popular, eagerly consumed, and collected from contaminated areas. Arsenic from the soil can be absorbed and stored in plants growing on such a substrate. Its migration from the soil into the plant tissues is a key step in the process of food contamination with the element. Although the migration rates of arsenic from the soil to many plants have already been investigated, the research on the dynamics of its occurrence in the soil and its migration and absorption by herbs such as peppermint (M. x piperita), chamomile (M. recutita), lemon balm (M. offi cinalis), and sage (S. offi cinalis) is limited. The World Health Organization (WHO) recommends that the daily arsenic dose in food should be 0.05–12.46 μg per day for total arsenic and 0.21–0.83 μg per day for its inorganic form (Kabata-Pendias and Pendias 1999). In the present study the concentration of As including organic [MMA(V), DMA(V), AB] and inorganic (As(III), As(V)) arsenic forms in leaves and steams of selected herbaceous plants was investigated. Selected herbs are used in the production of herbal teas and other dietary supplements. In our experiment, the ability of four herbs to accumulate potential risk element was tested in a pot experiment in which soil was contaminated by different arsenic species (As(III) and As(V)). The study was also conducted to demonstrate how soil contamination with inorganic arsenic species (As(III) or As(V)) affected the content of organic and inorganic forms of this metalloid in selected herbs. The main objectives of the experiment were i) to verify the tolerance of chamomile, peppermint lemon balm, and sage plants to increased risk element contents in soil which can be affected by various arsenic species contamination, ii) to estimate the potential risk of increased arsenic contents for herbs production as a medicinal plants as well as possibility of herbs cultivation in arable soil contaminated with arsenic, and iii) to fi nd relationship between the content of arsenic species in soil and the corresponding herbaceous plants. Materials and methods Sample preparation In the study plants i.e. chamomile (M. recutita), peppermint (M. x piperita), lemon balm (M. offi cinalis), and sage (S. offi cinalis), were planted (May 2015) in isolated containers. The soils in the containers were enriched with appropriate inorganic As(III) and As(V) species. The soils were contaminated in such a way that 2 g∙L-1 of the appropriate arsenic form was added to 9.8 kg of soil. Thus, the arsenic concentration of approx. 200 mg∙kg-1 in the soil was obtained. The control samples were also planted (plants growing on the same but not enriched soil). The plant samples were collected at the vegetation peak. After sampling they were washed with deionized water and separated into stems and leaves. For comparative purposes, commercially available herbal teas were purchased at the pharmacy: chamomile fi x, peppermint fi x, sage fi x, lemon balm fi x. Samples of herbal teas (fi x) were prepared as plant samples. 88 M. Jabłońska-Czapla, R. Michalski, K. Nocoń, K. Grygoyć Reagents and standard solutions The following substances were used for analyses: dihydro sodium arsenate heptahydrate ACS reagent (Sigma-Aldrich, Spain), sodium arsenite purum p.a. ≥99% (Sigma-Aldrich, Sweden), disodium methyl arsenate analytical standard (Supelco, USA), arsenobetaine ≥95% NMR (Fluka), dimethylarsinic (Supelco, USA), ultrapure nitric acid (65%, Merck, Germany), ultrapure ammonium nitrate (Merck, Germany). The calibration solutions were prepared each time through diluting suitable standard solutions on an analytical balance. The multi-elemental standards no. XXI and VI (Merck, Germany) were used when determining total arsenic and other metal(loid)s with ICP-MS. The ICP-MS spectrometer was optimized daily with a 10 g∙L-1 solution (Mg, Cu, Rh, Cd, In, Ba, Ce, Pb, U) in 1% HNO3 Elan 6100 Setup/Stab./Masscal. Solution (Perkin-Elmer). All solutions and standards were prepared with the Milli-Q-Gradient ultrapure deionized water (Millipore, Merck, Germany), whose electrolytic conductivity was <0.05 μS∙cm-1. Analytical method applied The basic physicochemical soil tests such as: sieve analysis (PN-ISO 11277:2005), pH, Eh and conductivity measurements (PN-ISO 10390:1997), total arsenic determinations in the soil, and plant digest (PN-EN ISO 17294-2:2016-11), and speciation analysis of arsenic in the plant extracts were conducted. For the basic research, a multi-parameter CX-401 meter (Elmetro