Abstract
The elemental concentration of K, Fe, Cu, Mn, Zn, Pb, Cd, Ni, Sn, Br, Sr, Ti, Rb, As, Th, an U in eleven wild growing mushroom species collected from various regions of Turkey were determined by using non-destructive nuclear analytical techniques like tube-excited energy dispersive X-ray fluorescence and gamma ray spectroscopic measurements. The highest element concentrations for K, Fe, Cu, Mn, Zn, Pb, Cd, Ni, Sn, Br, Sr, Ti, Rb, As, Th, and U were 50977 ± 3982, 2971 ± 749, 99.1 ± 5.5, 71.3 ± 49.1, 266 ± 109, 5.6 ± 0.1, 3.08 ± 0.91, 3.6 ± 0.7, 1.6 ± 0.1, 27.2 ± 19.7, 19.9 ± 2.1, 602. ± 166, 72.4 ± 24.5, 3.7 ± 0.7, 1.8 ± 0.9 and 0.42 ± 0.13 mg/kg dry mass, respectively.
INTRODUCTION
It is known that wild growing mushrooms can accumulate many different elements of toxicological and nutritional in high concentrations such as mercury, cadmium, lead, copper, arsenic, potassium, nickel, zinc, manganese, etc.[Citation1–4] Therefore, mushroom has been used as a good bioindicator by various researchers to determine the environmental pollution. On the other hand, wild edible mushrooms are becoming increasingly important in our diet for their nutritional and pharmacological characteristics.[Citation5] Wild growing mushrooms have been a popular delicacy in many countries. The consumption of wild edible mushrooms has been increasing, especially in Central and Eastern Europe, in which the average annual consumption may exceed 10 kg for some individuals due to a good content of proteins as well as a higher content of trace minerals.[Citation3–4] Turkey consumes significantly fewer wild growing mushrooms than those from European countries, Russia, North America and Japan. However, Turkey has a large edible mushroom potential and is becoming an important exporter of wild edible mushrooms. Therefore, it is necessary to investigate the levels of toxic and essential elements in wild edible mushrooms. There are a number of papers dealing with elemental concentrations in many Turkish edible mushroom species.[Citation5, Citation6–15] For the elemental concentrations in mushroom samples, flame, graphite furnace and cold vapor atomic absorption spectrophotometer (FAAS, GFAAS and CVAAS) and inductively coupled plasma-optical emission spectrometer (ICP-OES) were used in these studies. Especially, ICP-OES is considered excellent technique for the determination of major, minor, and trace elements in foods.[Citation16] On the other hand, there are no reports in the open literature about the occurrence of thorium and uranium element in wild growing mushroom species in Turkey.
In this study metal element, concentration in some wild mushroom species was determined using tube-excited energy dispersive X-ray fluorescence (EDXRF). The EDXRF is a promising analytical technique for determining elemental contents in mushrooms because the technique is not only non-destructive, fast, sensitive, and capable of simultaneous multi elemental analysis, but also ensure that mushroom can be quantitatively analyzed without damage. The EDXRF is that it does not require any special sample preparation, as is the case for the techniques like AAS and ICP-OES. This method can be directly applied in dried and palletized samples, avoiding sample digestion dissolution by toxic and corrosive acids. Furthermore, the short analysis time required for this method makes it suitable for routine analysis. In recent years, XRF has been used for wild edible mushrooms,[Citation17] various food materials,[Citation18,Citation19] some vegetables,[Citation20] some plants.[Citation21,Citation22]
Thorium, uranium, and potassium concentration in mushroom species was analyzed using gamma-ray spectrometric technique. As known, gamma-ray spectroscopy is a rapid, non-destructive and commonly used technique for gamma-ray emitting radionuclide analysis. This technique is particularly suitable for analyzing elemental concentration of K, Th, and U. The aim of this present study was to determine the concentrations K, Fe, Cu, Mn, Zn, Pb, Cd, Ni, Sn, Br, Sr, Ti, Rb, As, Th, and U in eleven mushroom species collected from uncontaminated agricultural lands and forests belong to 14 different locations (K. Maras, Mersin, Denizli, Izmir, Muğla, Isparta, Istanbul, Kırklareli, Canakkale, Samsun, Tokat, Kırsehir, Ankara, Erzurum) in Turkey.
MATERIALS AND METHODS
Sample Preparation
In this study, the wild-growing mushrooms corresponding to 11 mostly edible species gathered from 15 locations belonging to different ecosystems in Turkey were analysed. Mushroom species include Morchella esculenta, Boletus edulis, Craterellus cornucopioides, Cantharellus cibarius, Netria cinnabarina, Lepiota cristata, Stropharia coronilla, Lycogola epidendron, Agaricus porphyrocephalus, Marasmius oreades and Agaricus bisporus. Five samples of each species were collected between 2004 and 2005. One complete fruiting body of a mushroom was taken as a sample. The fruiting bodies were cleaned, cut, pulverized with a cooking blender and dried in a temperature-controlled furnace at 105°C for 20–24 h to remove moisture. For EDXRF analysis, each pulverized mushroom sample of 5 g was formed into stable pellets with no binder using a SPEX DIE with die diameter of 1.25” (32 mm) under 20 ton/inch2. For gamma-ray spectroscopy, the dry powdered samples were stored in airtight (sealed) cylindrical plastic containers (4-cm diameter and 3.9-cm height). These were kept for at least four weeks so as to ensure that 226Ra and 228Ra attain radioactive equilibrium with their respective daughters.
Methods
The elemental concentration of the samples, except K, Th, and U was carry out using High performance Oxford ED-2000 EDXRF spectrometer which consists of air cooled X-ray tube having a rhodium anode with a high-voltage power supply of up to 50 kV, a liquid nitrogen cooled Si(Li) detector and a multi channel analyzer. The EDXRF system is fully controlled by a computer using the software package XpertEase, which includes pre-programmed analytical parameters, full spectrometer control, data library and X-ray mathematical models and controls all the ED2000 spectrometer functions, was based on the Windows operating environment.
The Si(Li) detector whose resolution is 170 keV at 5.9 keV was placed at 45° to the beam direction for detecting the characteristic X-rays emitted from the target. Quantitative calculations were made through the fundamental parameters method. [Citation17] The experimental parameters were obtained by calibrating the whole system by means of standard reference materials of known elemental concentrations, IAEA V-10 (hay flour), NIST 157a (tomato leaves), NIST 1571 (orchard leaves) and IAEA- 359 (cabbage). Each sample was analyzed using solids (S - V, Sn - Ba, 100 s, 231 μA), steel (Ca- Cu, 100 s, 499 μA), medium element (Ca -Mo, 100 s, 77 μA) and very heavy element (Nb - Nd, 100 s, 1000 μA) conditions. The system has automatic energy calibration in each condition.
For estimating natural radioactivity present in the each mushroom sample, a high resolution HPGe gamma ray spectrometry system, which was equipped with a coaxial p-type HpGe detector (GC11021) with an active volume of 451 cm3 manufactured by Canberra Inc. The HpGe detector has a relative efficiency of 110%, an energy resolution of 2.1 keV at 1332.5 keV of 60Co and of 1.3 keV at 122 keV of 57Co, and a peak-to-Compton ratio of 85:1. For gamma ray shielding, a front opening split-top shield (Canberra Model 767) was used to reduce background. The detector was interfaced to the DSA-1000 Digital Spectrum Analyzer, which was a full featured 16 K channel Multichannel analyzer on advanced digital signal processing techniques (DSP), and operates through Genie-2000 gamma spectroscopy software.
Energy calibration of the detector was performed using point sources (60Co, 137Cs, and 241Am). Absolute efficiency calibration of the gamma spectrometry system was carried out using the IAEA reference materials RG-set and Soil 375. The reference material and the sample containers were placed on top of the detector for counting. The same geometry was used to determine peak area of samples and references. Background measurements were taken and subtracted in order to get net counts for the sample. The counting time for each sample and background was 60,000 s to obtain the gamma ray spectrum with good statistics. The specific activity of 40K were measured directly by its own gamma-ray at 1460.8 keV, while activities of 238U and 232Th were calculated based on the weighted mean value of their respective decay products in equilibrium. The specific activity of 238U was measured using the 351.9 keV gamma rays from 214Pb and the 609.3 keV from 214Bi. The specific activity of 232Th was measured using the 911.2 keV from 228Ac and 583.2 keV from 208Tl. The obtained activity results corrected for gamma ray self-attenuation effects due to differences in density and composition of both sample and reference material. The specific activities of 238U, 232Th and 40K can be converted into the elemental concentrations of U (in mg/kg), Th (in mg/kg) and K (in percent) using data given IAEA-TECDOC.[Citation23]
RESULTS AND DISCUSSION
The mean elemental concentrations with their standard deviations dry mass (mg/kg) for eleven different species of wild growing mushrooms are presented in . The concentrations of Fe, Cu, Mn, Zn, Pb, Cd, Ni, Sn, Br, Sr, Ti, Rb, and As were determined by tube excited EDXRF spectrometry, while the gamma-ray spectrometry was used for determining the concentrations of K, Th, and U. The elemental concentrations in studied mushroom samples were found to be 20898–50977, 64.1–2971, 12.7–99.1, 7.4–71.3, 69.5–266.2, 1.2–5.6, 1.4–3.1, 3.18–3.58, 1.44–1.57, 4.2–27.2, 2.3–19.9, 7.0–602.8, 3.6–72.4, 2.6–3.7, 0.56–1.78, and 0.33–0.42 mg/kg for potassium, iron, copper, manganese, zinc, lead, cadmium, nickel, tin, bromine, strontium, titanium, rubidium, arsenic, thorium and uranium, respectively. It was observed from the results that differences in elemental uptake for the several species do exist for almost all the elements. The biggest differences were observed for Ti, presenting variations from 602.8 mg/kg in Cantharellus cibarius 7.0 mg/kg for Lepiota cristata. Smaller differences were observed for K, Cd, Ni, Sn, As, Th and U.
Table 1 The mean concentrations of K, Fe, Cu, Mn, Zn, and Pb in the mushroom samples analyzed (in mg/kg−1, dry mass), (mean ± SD)
Table 2 The mean concentrations of Cd, Ni, Sn, Br, and Sr in the mushroom samples analyzed (in mg/kg−1, dry mass), (mean ± SD)
Table 3 The mean concentrations of Ti, Rb, As, Th, and U in the mushroom samples analyzed (in mg/kg−1, dry mass), (mean ± SD)
Toxic metals in mushroom samples were Cd, Pb, Cu, As, and Ni. Cd and Pb present only in Morchella esculanta, Boletus edulis, Craterellus corncopioides, Cantharellus cibarus, while As and Ni present only in Morchella esculanta, Boletus edulis, Cantharellus cibarus and Boletus edulis, Craterellus corncopioides, respectively. Minimum and maximum levels of Cd and Pb were determined as 1.4 and 3.1 mg/kg and 1.2 and 5.6 mg/kg, respectively. The Cd content of Morchella esculanta, Boletus edulis, Craterellus corncopioides and Cantharellus cibarus was higher than the literature values. [Citation9,Citation13 Citation–14] A higher content of Cd was reported for Boletus edulis, Cantharellus cibarius, Marasmius oreades and Morchella esculanta. [Citation24] Copper presents the highest concentration (99.1 mg/kg) for Nectria cinnabarina and the lowest (12.7 mg/kg) for Lepiota cristata. Kalač and Svoboda[Citation4] reported that Cu concentrations in the accumulating species are usually 100–300 mg/kg dry matters, which is not considered a health risk. Cu level of several mushroom species was in agreement with those found in literature.[Citation9,Citation13] Lead presents the highest concentration (5.6 mg/kg) for Cantharellus cibarius and the lowest (1.2 mg/kg) for Morchella esculanta. These results conform to FAO/WHO[Citation25] standards for Pb. Ni levels were found only Boletus edulis (3.6 mg/kg) and Craterellus corncopioides (3.2 mg/kg). Ni levels were lower than literature values for Agaricus bisporus,[Citation12–13,Citation15] Stropharia cornilla, and Marasmius oreades.[Citation7,Citation12] Arsenic was observed in Morchella esculanta (2.6 mg/kg), Boletus edulis (3.7 mg/kg) and Cantharellus cibarus (3.4 mg/kg). These values were about three times higher than those for Boletus edulis and Cantharellus cibarus.[Citation24]
The iron concentrations in the mushroom samples varied from 64.1 to 2970.6 mg/kg, and the highest concentration was obtained in Cantharellus cibarius. Iron contents in the studied samples were much higher than literature values for Agaricus bisporus, [Citation10,Citation12,Citation13,Citation15] Agaricus porphyrocephalus,[Citation8] Morchella esculanta,[Citation12,Citation14] while Fe content was in agreement with Marasmius oreades.[Citation7] Fe contents were much lower than literature values for Nectria cinnabarina and Lycogola epidendron.[Citation5]
The lower and higher manganese contents were 7.4 mg/kg in Marasmius oreades and 71.3 mg/kg in Cantharellus cibarius, respectively. The reported Mn values in the literature for wild growing mushrooms were 14.2–69.7, 7.1–81.3, 16–64, 3.0–56.2, 6.8–63.6, 21.2–103.0, and 12.9–93.3 mg/kg, [Citation5,Citation7,Citation8,Citation10,Citation12,Citation13,Citation15] respectively. Mn values in this study were in agreement with those reported in the literature.
Zinc has a biological significance for living organisms and mushrooms are known as good zinc accumulators.[Citation11] The Zn concentrations in the mushroom samples ranged from 69.5 mg/kg (in Boletus edulis) to 266.2 mg/kg (in Agaricus bisporus). The Zn content was not determined in Canharellus cibarius. The Zn contents in the samples studied in this work were higher than literature values in these cited references,[Citation7,Citation8,Citation10,Citation12–15] while Zn content was lower than value of Boletus edulis.[Citation9]
The lowest content and the highest content level of potassium were 20897.9 mg/kg (Agaricus porphyrocephalus) and 50977.5 mg/kg (Canharellus cibarius), respectively. These results are in agreement with the values reported in the literature.[Citation3,Citation10] Strontium content ranged from 2.3 to 19.9 mg/kg and the highest concentration was obtained in Cantharellus cibarius. The concentration of thorium and uranium varied from 0.6 to 1.8 mg/kg and 0.3 to 0.4 mg/kg, respectively. The highest concentrations of Th and U were obtained in Stropharia cornilla and Morchella esculanta, respectively. These values are in agreement with the reported in the literature.[Citation26]
CONCLUSIONS
Metals (Cu, Cd, Ni, Pb, As, Fe, Mn, Zn, Ti, Rb, Sr, K, Br, and Sn), bromine, thorium and uranium concentration levels of eleven mushroom species collected from uncontaminated agricultural lands and forests belong to 14 different locations in Turkey were analyzed using non-destructive nuclear analytical techniques like tube excited EDXRF and gamma-ray spectroscopy. The present study also confirms that elemental concentration in mushroom was species-dependent and local-dependent. This study also showed that major advantages of EDXRF over inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrophotometer (AAS) include the ease of analysis of solid samples without need for rather tedious and potentially hazardous procedures. The simultaneous detection of the whole elements is another advantage. However, the sensitivity of EDXRF for light elements is very poor, which is one of the drawbacks of EDXRF; this is why the elements P, S, and Cl were almost not referred to in this study.
ACKNOWLEDGMENTS
This study was supported by Turkish Atomic Energy Authority (TAEA). The authors wish to thank Dr. Ahmet Varinlioglu, Chemist in TAEA for his useful discussion and comments.
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