The risk element uptake by chamomile (Matricaria recutita (L.) Rauschert) growing in four different soils

German chamomile (Matricaria recutita (L.) Rauschert) belongs to the plants with a high tolerance to toxic elements. The ability of chamomile to accumulate risk elements was tested in a pot experiment in which four soils contaminated by different levels of arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn), differing in their physicochemical parameters, were used. The element mobility in the soils was affected predominantly by the cation exchange capacity (CEC) of the soils. Whereas As, Pb, and Zn were retained in roots, Cd showed good ability to translocate to the shoots, including anthodia, even in extremely Cd-contaminated soil without symptoms of phytotoxicity. The bioaccumulation factor for Cd calculated as the ratio of element content in the plant and the soil was the highest among the investigated elements. Between 5.5 and 35% of the total Cd was released to infusion, and its extractability decreased with increasing Cd content in anthodia. The essential oil composition suggested an alteration of the abundance of the individual compounds. However, no detectable contents of risk elements were found in the oil. Chamomile can be recommended as a suitable alternative crop for risk element-contaminated soils tested within this experiment, but only for production of essential oil. The risk element uptake by chamomile (Matricaria recutita (L.) Rauschert) growing in four different soils 13 that risk elements stimulate an increase in ROS (reactive oxygen species) formation, being affected especially by the given metal and exposure concentration (Petö et al. 2011). The plant-availability of elements in soil is affected by the physicochemical parameters of the soils, climatic conditions, plant genotype, and plant management (Kabata-Pendias and Pendias 2001, Tokalıoğlu et al. 2003). Thus, the element content in plants is not directly related to the total element content in the soil (Schwartz et al. 2001). Among the physicochemical and biological parameters affecting the plant-availability of risk elements, soil pH, redox potential, cation exchange capacity (CEC), content of carbonates, hydroxides and oxides of Fe and Mn, clay minerals, organic matter, plant species, vegetation cover and the activity of soil organisms and microorganisms should be mentioned (Alloway 1990, Ross 1994, Cheng and Mulla 1999, Adriano 2001, Kabata-Pendias and Pendias 2001). The effects of nutrient content on the growth and yield of German chamomile have already been reported (Mosleh et al. 2013). The connections between the nutrient supplement of the chamomile plants and the content of essential oil was published as well. Nasiri et al. (2010) proved the benefi cial effect of foliar application of Fe and Zn on both plant yield and essential oil content. In our experiment, the ability of German chamomile to accumulate potential risk elements was tested in a pot experiment in which four soils contaminated by different levels of As, Cd, Pb, and Zn and characterized by different physicochemical parameters were used. Moreover, the potential interactions with essential elements such as Cu, Fe, and Mn were assessed, as well as the extractability of both risk and essential elements into the infusion. Simultaneously, the composition of essential oil and reachability of the risk elements into the oil were assessed. The main objectives of the experiment were i) to verify the tolerance of chamomile plants to increased risk element contents in soils as affected by various soil properties and risk element contamination levels and ii) to estimate the potential risk of enhanced element contents for chamomile production as a medicinal plant as well as the possibility of chamomile cultivation in arable soil contaminated by risk elements. Material and methods Experimental design The plants were cultivated in pots with four soils differing in their main physicochemical characteristics and pseudototal (i.e. Aqua Regia soluble) risk element contents (Table 1). For the experiment the soils affected either by industrial activity (non-ferrous metals mining and smelting, chemical industry) – Chernozem 2 (50.69°N, 13.72°E), Fluvisol (50.52°N, 14.07°E), Cambisol (49.69°N, 14.01°E), or by land application of sewage sludge in the case of Chernozem 1 (50.12°N, 14.54°E) were used. All the soils were already investigated and the more detailed description of the soils and/or locations was published elsewhere (Száková et al. 1999, 2000). The soils were collected in each sampling point from a depth of 0–25 cm, air dried, sieved through a 5-mm plastic sieve, and homogenized. Laboratory soil samples for the determination of total and mobile concentrations of elements were air dried at 20°C, ground in a mortar, and passed through a 2-mm plastic sieve. The M. recutita (diploid variety Bohemia widely planted in the Czech Republic) plants were cultivated in 6-liter plastic pots with 5 kg of air-dry soil, and six replicates were used for each treatment. The Czech diploid variety Bohemia was licensed in 1952 and is classifi ed as the bisabololoxid genotype. The chamomile of the variety Bohemia has the certifi cation trademark no. CZ/00411/PDO – “Chamomilla Bohemica.” Bohemia typically contains 1.2% of essential oil. Mineral fertilizer NPK (0.5 g N, 0.16 g P, 0.4 g K per pot as inorganic salt solutions, representing ca. 300 kg N, 96 kg P, and 240 kg K per ha, respectively) was added before sowing. The experiment started at April 2008, and 5 plants were sown per pot. Soil moisture was regularly controlled and kept at 60% of the maximum water holding capacity (MWHC). Pots were placed in an outdoor weather-controlled vegetation hall protecting the pots against rainfall. Weed plants were regularly manually removed; other cultivation conditions such as light and temperature were not managed. The experiment was terminated at July 2008. The harvested biomass was divided into anthodias, shoots, and roots. Plant material was carefully washed in deionized water, dried at 60°C in a drying oven, homogenized, and analyzed. Analytical methods Determination of soil physicochemical parameters The pH value was determined in 0.01 M CaCl2 extract 1/10 (w/v = 5 g + 50 ml, Novozamsky et al. 1993). Cation-exchange capacity (CEC) was calculated as the sum of Ca, Mg, K, Na, Fe, Mn, and Al extractable in 0.1 M BaCl2 (w/v = 1 g + 20 ml for 2 hours) (ISO 1994). Total organic carbon (TOC) was determined spectrophotometrically after the oxidation of organic matter by K2Cr2O7 (Sims and Haby 1971). For the determination of potentially available portions of main nutrients in soils, the Mehlich III extraction procedure (0.2 M CH3COOH + 0.25 M NH4NO3 + 0.013 M HNO3 + 0.015 M NH4F + 0.001 M Table 1. The main characteristics of the experimental soils Soil type Texture Cox pH Ca# Mg# K# P# CEC¶ As$ Cd$ Cr$ Cu$ Ni$ Pb$ Zn$ % mg/kg mg/kg mg/kg mg/kg mmol/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg Chernozem 1 loam 3.45a 7.3a 5828a 146a 199a 82a 69.2a 20.7a 14.6c 82.1b 68.2b 34.8c 34.0a 133a Chernozem 2 loam 3.95a 6.8a 2668b 156a 192a 128b 224c 362c 1.0a 19.5a 24.4a 13.0a 99.6b 112a Fluvisol sandy loam 5.93b 4.4b 1026c 35b 120a 248c 176bc 27.6a 1.6a 100b 46.0b 21.3b 48.6a 207b Cambisol loam 3.88a 6.3a 2420b 108a 363b 81a 165b 124b 4.8b 27.7a 23.6a 17.8b 1276c 190b # plant-available element contents determined by Mehlich III extraction procedure (Mehlich 1984); ¶ cation exchange capacity; $ the pseudototal (Aqua regia soluble) concentrations of the investigated elements in soils; the averages marked by the same letter superscripts did not signifi cantly differ at p<0.05 within individual columns; n=6 14 J. Száková, M. Dziaková, A. Kozáková, P. Tlustoš ethylenediamine acetic acid (EDTA) at a solid/liquid ratio of 1/10 [3 g + 30 ml] for 10 minutes) was applied (Mehlich 1984). Determination of essential and risk elements in soils and plants Plant samples were decomposed using the dry ashing procedure as follows: An aliquot (~1 g) of the dried and powdered plant material was weighed into a borosilicate glass test tube and decomposed in a mixture of oxidizing gases (O2+O3+NOx) in an Apion Dry Mode Mineralizer (Tessek, Czech Republic) at 400°C for 10 hours. The ash was than dissolved in 20 ml of 1.5% HNO3 (Miholová et al. 1993). A certifi ed reference material CRM CTA-OTL-1 Tobacco leaves was applied for the quality assurance of analytical data. For the determination of the pseudototal element contents on soil, aliquots (~0.5 g) of air-dried soil samples were decomposed in a digestion vessel with 10 ml of Aqua Regia (i.e. nitric and hydrochloric acid mixture in a ratio of 1+3). The mixture was heated in an Ethos 1 (MLS GmbH, Germany) microwave-assisted wet digestion system for 33 minutes at 210°C. After cooling, the digest was quantitatively transferred into a 25 ml glass tube, topped up by deionized water, and kept at laboratory temperature until measurement. A certifi ed reference material RM 7001 Light Sandy Soil was applied for the quality assurance of analytical data. For the determination of mobile and element proportions, the soil samples were extracted with 0.11 mol l-1 solution of CH3COOH at a solid/liquid ratio of 1/20 (1 g + 20 ml) for 16 hours (Quevauviller et al. 1993). Chamomile infusions were prepared as follows: 1±0.001 g of dried anthodias was weighed out and put into standardized glass beakers. Then, 50 ml of boiled distilled water was poured into the glass beakers, after which they were covered by watch glasses. After 15 min, the extracted solution was fi ltered through fi lter paper (blue label) into test tubes and immediately measured (Street et al. 2006). All samples were analyzed in triplicates, and blanks represented 10% of the total number of samples. The determination of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in soil extracts, soil and plant digests, and plant infusions was carried out by inductively coupled plasma optical emission spectrometry with axial plasma confi guration (ICP-OES, Varian VistaPro