Bioconcentration of mercury by mushroom Xerocomus chrysenteron from the spatially distinct locations: Levels, possible intake and safety

Ecotoxicology and Environmental Safety 107 (2014) 97–102

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Bioconcentration of mercury by mushroom Xerocomus chrysenteron from the spatially distinct locations: Levels, possible intake and safety Anna Dryżałowska, Jerzy Falandysz n University of Gdańsk, 63 Wita Stwosza Str., PL 80-952 Gdańsk, Poland

art ic l e i nf o

a b s t r a c t

Article history: Received 22 March 2014 Received in revised form 15 May 2014 Accepted 16 May 2014 Available online 11 June 2014

Concentrations of mercury were determined in specimens of Red Cracking Bolete (Xerocomus chrysenteron) (Bull.) Quél. and overlying soil (0–10 cm) collected from 22 spatially distributed sites in Poland during 1996–2013 to assess the potential of this species to bioconcentrate Hg and possible intake by humans. The mean Hg concentrations ranged from 80 to 630 for caps and from 28 to 380 ng/g dry matter (dm) for stipes. Decrease in the potential of this mushroom species to bioconcentrate Hg both in caps and stipes was observed when the Hg content in soil substratum increased from 15 to 75–94 ng/g dm. A maximum median value for bioconcentration factor (BCF) of Hg determined for caps was 18 for soil with Hg content at 15 ng/g dm and decreased to 0.97–3.8 for soils that contained Hg at 37–94 ng/g dm. Caps of X. chrysenteron consumed at a volume of 300 g daily in a week can yield an exposure amount of Hg at 0.0168–0.1323 mg (0.00024 to 0.00189 mg/kg body mass); these values are well below the provisionally tolerated weekly intake (PTWI) for inorganic Hg. & 2014 Elsevier Inc. All rights reserved.

Keywords: Bioconcentration Forest Fungi Mercury Organic food Wild food

1. Introduction Mercury, like arsenic, cadmium, lead etc. is known as hazardous to man in all its physical and chemical forms but some inorganic Hg compounds, such as HgSe and HgS (cinnabar), because of low solubility and dissociation are supposed to be difficult in up-take by man and animals. But exceptions as in reported case of HgS are possible (Huang et al., 2007). In mushrooms from
1 too25% of total Hg is methylmercury (MeHg) (Falandysz, 2012a and 2012b; Rieder et al., 2011), while inorganic forms of Hg have not been characterized until now. Dietary selenium plays protective role against MeHg toxicity (Ralston and Raymond, 2010; Yoneda and Suzuki, 1997). For man, the environmentally relevant Hg compound in foodstuffs is the highly toxic MeHg (Olivero, et al., 2002; UNEP, 2013). A long lasting spread of Hg due to anthropogenic sources is an ongoing process and efforts have been undertaken to reduce its emission to the environment (UNEP, 2013). The airborne Hg can be preferentially trapped from tropospheric depositions across an elevation gradient (Stankwitz et al., 2012; Zhang et al., 2013), and this phenomenon can be the cause of the elevated contents of Hg in mushrooms having shallow mycelium from a pristine regions of high mountains with “circum-polar” weather condition (Falandysz et al., 2014).

n

Corresponding author. E-mail address: [email protected] (J. Falandysz).

http://dx.doi.org/10.1016/j.ecoenv.2014.05.020 0147-6513/& 2014 Elsevier Inc. All rights reserved.

Mercury in soils occurs naturally at trace concentration and in the past two centuries the emissions from anthropogenic activities have increased the volume of Hg available in the global ecosystems (UNEP, 2013) and the rates of depositions on land vary spatially (Stankwitz et al., 2012). Mercury concentrations o0.050 ng/g are considered to be of geochemical background for soils in Poland (PIG, 2013). Nevertheless, Hg content in the upper layer (0–10cm and 0–15 cm) of soils in forests in the “background” areas in many regions of Poland is above 0.05 ng/g dm (Falandysz et al., 2003a, 2007a, 2007f, 2012a and 2012b). Both inorganic Hg and MeHg in soils can be efficiently taken up and sequestered by fungi in fruit bodies (Falandysz et al. 2001a, 2002a, 2002b, 2002c, 2002d; Fischer et al., 1995; Rieder et al., 2011), while in fungal flesh inorganic Hg is usually in dominant form (Fischer et al., 1995; Rieder et al., 2011). Fruit bodies of mushrooms are usually rich in sulfur, and the range of S in fruit bodies of 27 species in Canada was reported to be between 0.073% and 1.4%, dry matter (Nasr et al., 2012). Mushrooms always contain Se and some species are rich both in Se (45 ng/g dm) and Hg (Falandysz and Borovička, 2013). Both Se and S (contained in thiol groups of cysteine amino acid in peptides and proteins) may possibly bind a portion of Hg/MeHg in the flesh of mushrooms and cause Hg precipitation as sparingly soluble compounds (HgSe, HgS) but no evidence is known to support such hypothesis. The global pollution with Hg is a matter of high concern, because human economic activities have boosted it's atmospheric diffusion and subsequent aerial deposition at the global scale. As

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A. Dryżałowska, J. Falandysz / Ecotoxicology and Environmental Safety 107 (2014) 97–102

reported by UNEP, 2013, the environmental pollution with Hg worldwide started nearly two centuries ago and this have had toxic consequences on vulnerable wildlife from the top of the food webs. In parallel to the ongoing global Hg problems and its toxicity, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) recently established a new value of Provisionally Tolerable Weekly Intake (PTWI) for inorganic Hg, which is 0.004 mg/kg body mass (bm) (JECFA, 2010) (0.24 mg for man of 60 kg bm and 0.28 mg for man of 70 kg bm). That new PTWI standard is based on the assumption that inorganic Hg is the predominant form of Hg in foods other than fish and shellfish. And that assumption applies to some degree also to wild-grown mushrooms for which inorganic Hg is at
90–99% of total Hg content (Rieder et al., 2011). Mentioned value of PTWI is close to a reference dose (RfD) of 0.0003 mg Hg kg1bm daily (7  RfD ¼ 0.0021 mg Hg kg/bm or 0.126 mg for man of 60 kg bm and 0.147 mg for man of 70 kg bm) that was established by the Environmental Protection Agency (USA) for non-carcinogenic effects of Hg (US EPA, 1987). The PTWI fo MeHg by the JECFA is 0.0016 mg/kg bm (JECFA, 2007) (0.096 mg for man of 60 kg bm and 0.112 mg for man of 70 kg bm). Nevertheless, adequate Se supply and availability can diminish risk of MeHg taken from food due to Se and MeHg interactions (Ralston and Raymond, 2010). Previous studies showed that data on Hg in some species of edible wild-grown mushrooms of various feeding strategy (mycorrhizal, saprophytic, parasitic) from background areas shows higher contamination–with mean levels reaching from around 0.1 to 0.7 mg/kg fresh product (Alonso et al., 2000; Chojnacka et al., 2013; Falandysz et al., 2011; Melgar et al., 2009; Nasr et al., 2012; Tüzen and Soylak, 2005; Vetter and Berta, 1997), when compared to grains. In a study in Poland, the barley, oat, wheat, rye and maize contained Hg (average mean weighted values for product) at 0.008 mg/kg n ¼599; 0.008 mg/kg n ¼274; 0.005 mg/kg n ¼1659; 0.005 mg/kg n ¼1510 and 0.006 mg/kgn ¼ 119; and plant foodstuffs such as potatoes, leafy vegetables, tubers and fruits at 0.005 mg/kg n ¼73; 0.016 mg/kgn ¼163; 0.005 mg/kg n ¼ 209; 0.002 mg/kg n ¼239 and 0.004 mg/kg n ¼160; and meats such as beef, pork and poultry muscle meats at 0.008 mg/kg n ¼2495; 0.006 mg/kg n¼ 3780 and 0.003 mg/kg n ¼286, respectively (Szprengier-Juszkiewicz, 1994). The soil substrate is a major source of Hg absorbed via mycelia and rhizomorphs by mushrooms and translocated to fruit bodies (Falandysz et al., 2013). The calculated values of bioconcentration factor (BCF)1 of Hg available for several species of mushrooms are usually above unity (BCF 41), e.g. for Amanita muscaria, A. rubescens, Russula ochrolucea, Suillus grevillei, Boletus edulis and many others (Chudzyński et al., 2009; Drewnowska et al., 2012a, 2012b; Frankowska et al., 2010; Melgar et al., 2009; Nasr and Arp, 2011). Some mushrooms weakly bioconcentrate Hg, e.g. for Cantharellus cibarius from many background areas, the BCF was close to 1 (Falandysz et al., 2012b), and species of Lactarius family, e.g. Lactarius rufus, bio-excluded Hg (BCF o1) (Falandysz and Chwir 1997; Falandysz et al., 2004). Red Cracking Bolete (X. chrysenteron) (Bull.) Quél. as well as X. badius (Boletus badius) and X. subtomentosus are three species that are collected in Poland in large quantities both by fanciers and in domestic gourmet as well as by commercial collectors for sale each year (Chojnacka et al., 2012; Jarzyńska et al., 2012). Mushroom X. chrysenteron is a species that is common in central, western and southern regions of Europe (Gumińska and 1 BCF is a value of quotient of Hg content of mushroom (whole fruit body or its morphological part) to soil or other substratum in which mycelia develops; it helps to assess potential of species to pick-up chemical element and is calculated on dry matter basis.

Wojewoda, 1985). In this study we examined accumulation and contamination of the fruit bodies of X. chryzenteron with total Hg and in the beneath soils collected from various regions of Poland and probable intake of element by human consumers.

2. Materials and methods 2.1. Materials collection Matured specimens of X. chryzenteron that are in good condition (no infected by insects and apparent molds) and fit for culinary processing and soils taken from below the fruit bodies were collected from 22 spatially distantly distributed sites in Pomerania, Mazury, Kujawy and Świętokrzyskie lands of the northern, northeastern and central parts of Poland in 1996—2013 (Fig. 1; Table 1). Mushrooms (separately caps and stipes), and soil samples were examined individually or in pools. The number of individual and pooled samples and number of specimen and soil samples in pools are given for each site and year in Table 1. The carpophores were cleanup from any adhered plant and soil particles with plastic knife. The caps with skin and stipes (stalks) were air-dried for 2–3 days at room temperature under clean condition, and then they were oven dried at 65 1C to constant weight and further ground in porcelain mortar to fine powder. Dried and ground mushrooms were archived in sealed and brand new polyethylene bags under clean and dry condition. Moisture content of dried fungal material kept for long-term was 6.0 7 0.1% (n¼ 98) as determined gravimetrically after drying of the sub-samples at 105 1C in a separate study. The cost-effective approach in analysis of contaminants in environmental and food materials is pooling the samples and this was found suitable when examining Hg in mushrooms. All specimens collected at certain locations were pooled to make one sample and it consisted separately of caps and stipes (Table 1). 2.2. Hg determination Determination of total Hg content of mushrooms and soils was by direct material thermal decomposition, coupled with gold wool trap, desorption and cold vapor - atomic absorption spectroscopy (CV-AAS) analysis (Jarzyńska and Falandysz, 2011; Nnorom et al., 2012). The mercury analyzer type MA-2 with and without the auto-sampler (Nippon Instruments Corporation, Takatsuki, Japan) was employed. The reagents were of analytical reagent grade. Deionized water (resistivity 410 MO cm) was used for the preparation of the solutions. Mercury standard solution (100 mg/L, Inorganic Ventures) and L-cysteine (98%; Nacalai Tesque) were used. For the stabilization of mercury standard solution, the L-cysteine solution was used. To prepare 0.001% L-cysteine solution, 10 mg of L-cysteine was weighed, placed in 1000 mL flask and then water and 2 ml of nitric acid (HNO3, 65%, Suprapurs, Merck) were added. 1 ml of 100 mg/L solution was extracted and diluted to 100 mL with 0.001% L-cysteine solution. In this way, a solution of 1 μg /mL was prepared. Blank, 50, 100, 150 and 200 μL of 1.0 μg Hg/mL standard solution were injected into the analyzer for the calibration curve. The conditions used for CV-AAS according to the instructions by manufacturer were as follows: heating temperature  850 1C; detection - dual beam AAS; determination  7 min; and wavelength  253.7 nm. A running analytical control and assurance quality (AC/AQ) were performed through the analysis of blank samples and one certified fungal reference materials (CRMs). Three blank samples were examined with each set of real samples of fungal material when using MA-2 and auto-sampler and two blanks with a set of ten soil samples using MA-2 without auto sampler. In the same manner blank samples and CRM samples were examined. The declared total Hg content of certified reference material CS-M-1 (dried fruit-bodies of mushroom Suillus bovinus; Institute of Nuclear Chemistry and Technology, Warsaw, Poland) is 174 718 ng/g dm, while our measurements during this study showed 1857 10 ng/g dm (n¼ 3). The limit of detection (LOD) in our study was 3 ng/g dm, and the quantification limit (LOQ) was 5 mg ng/g dm. All data were statistically treated, using the “Statistica version 8.0” computer software package. Nonparametric u test of Mann–Whitney was used to test for possible statistically significant differences between the variables.

3. Results and Discussion 3.1. Mercury in X. chrysenteron All fruit bodies of X. chryzenteron contained Hg and the mean values for most of the sites and years ranged from 80 to 630 for caps and from 28 to 380 ng/g dry matters (dm) for stipes (Table 1). A statistically significant difference was observed in level of mushroom contamination depending on the site (0.05 op

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Fig. 1. Location of the X. chryzenteron and soil sampling sites in Poland (the names of the sites are given in Table 1).

Table 1 Total mercury in fruit bodies of Xerocomus chrysenteron (ng/g dm) and values of the quotients QC/S, BCF (arithmetic mean 7 SD, range and median, respectively). Place no.

Place name, year of collection and number of samples and specimens examined (in parentheses)

1

Pomerania, Nearshore Landscape Park, 2006 n ¼15(52)a

2

Pomerania, Darżlubska Forest, 2003 n¼ 5

3

Pomerania, County of Luzino, Strzebielino, 2006 n¼ 15

4a

Pomerania, TLP b, Witomino (S-W) and Kacze Łegi Reserve, 2006 n¼ 15(25)

4b

Pomerania, TLP, Witomino (N), 2006 n¼ 15(36)

4b

Pomerania, TLP, Witomino (S), 2006 n¼ 15(34)

4c 4c 4d 4d 4d 5 6

Pomerania, Pomerania, Pomerania, Pomerania, Pomerania, Pomerania, Pomerania,

TLP, Polanki, 2001 n¼ 1(12) TLP, Oliwa, 2010 n¼ 1(10) TLP, Niedźwiednik, 1996 n ¼1(8) TLP, Niedźwiednik, 2002 n¼ 2(19) TLP, Niedźwiednik, 2010 n ¼1(15) Gdańsk-Kowale, 2010 n¼ 1(8) Łapino, 2005 n¼ 1(15)

Hg

BCF

Fruit bodies

Fruit bodies

Caps

Stipes

Soils

QC/S

Caps

Stipes

230 7 96 (210) 53–380 2707 5 (270) 260–270 1807 56 (180) 90–260 1807 75 (160) 87–300 2007 36 (210) 120–230 260 7 40 (260) 190–320 200 630 260 290 (100–490) 540 580 260

1607 46 (180) 73–210 260 7 10 (260) 250–270 1407 59 (140) 53–240 997 44 (86) 46–210 1407 59 (120) 91–150 230 7 32 (230) 160–280 100 380 150 170 (52–290) 300 290 140

637 22 (75) 14–83 157 1 (15) 15–16 287 12 (27) 9.0–65 417 11 (37) 31–71 537 20 (57) 25–81 267 7 (23) 16–37 WD WD WD WD WD WD WD

1.4 7 0.7 (1.2) 0.73–3.1 1.17 0.1 (1.0) 0.92–1.3 1.4 7 0.4 (1.1) 0.9–2.3 1.8 7 0.5 (1.7) 1.1–3.0 1.5 7 0.6 (1.5) 1.2–1.8 1.17 0.2 (1.2) 0.80–1.3 2.0 1.8 1.7 1.7–1.9 1.8 2.0 1.9

4.2 72.3 (3.7) 0.68–9.8 18 71 (18) 17–19 7.8 75.7 (7.1) 1.4–26 4.4 72.1 (3.8) 2.2–8.6 4.2 72.4 (3.7) 1.7–8.3 11 73 (11) 5.7–17 WD WD WD WD WD WD WD

3.8 7 2.0 (2.4) 0.93–11 177 1 (18) 16–18 6.3 7 5.1 (5.1) 0.82–23 2.5 7 1.3 (2.0) 1.3–5.7 2.8 7 1.3 (2.4) 1.3–5.6 9.7 7 2.9 (8.7) 6.1–16 WD WD WD WD WD WD WD

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Table 1 (continued ) Place no.

Place name, year of collection and number of samples and specimens examined (in parentheses)

Hg

BCF

Fruit bodies

Fruit bodies

Caps 7 8 9 10 11

Pomerania, Pomerania, Pomerania, Pomerania, Pomerania,

12 13 13 14 15 16

Pomerania, Koteże, 2006 n¼ 1(10) Pomerania, Tucholskie forests, Lubichowo, 2005 n¼1(15) Pomerania, Tucholskie forests, Lubichowo, 2006 n¼ 1(15) Pomerania, Chełmno, 2001 n¼ 1(16) Pomerania, Kobylarnia n/Bydgoszcz, 2000 n¼ 1(16) Mazury, Kiwity, 2002 n ¼16(44)

17 17

Mazury, Piska Forest, 2002 n ¼1(15) Mazury, Piska Forest, 2006 n¼15(18)

18

Kujawy Land, Commune of Bukowiec, Tuszynki, 2006 n¼ 11

19

Kujawy Land, Dobrzejewice forests, 2006 n¼ 16

20

Kujawy Land, Ciechocinek region, 2011 n ¼15

21

Kujawy Land, Włocławek region, Mielęcin, 2006 n¼ 15(70)

22

Świętokrzyski Land, Starachowickie forests, Lipie, 2000 n ¼15

Notes: a b

Jodłowno/Pomlewo, 2013 n¼ 1(51) Mojusz, 2007 n¼ 1(15) Dziemiany, 2005 n¼1(15) Wysoczyzna Elbląska, 2003 n¼ 1(14) Kępice, 2003 n¼ 15(15)

460 200 100 490 2707 46 (270) 140–330 220 180 88 430 100 1307 34 (130) 66–220 140 1307 83 (110) 62–410 917 34 (83) 37–130 1307 34 (130) 66–220 1207 21 (110) 100–150 807 16 (78) 51–110 360 7 93 (340) 200–580

Stipes

120 72 210 1607 30 (160) 120–230 WD 150 59 647 36 (61) 18–130 28 647 26 (57) 30–96 1207 34 (120) 59–170 737 33 (70) 40–97 807 30 (70) 60–130 597 13 (61) 36–80 2707 76 (240) 170–450

Soils

QC/S

Caps

Stipes

WD WD WD WD 317 15 (26) 11–70 WD WD WD WD WD 467 14 (45) 19–69 WD 337 14 (33) 9–54 587 15 (53) 39–89 457 14 (45) 19–68 257 2 (24) 21–27 967 73 (82) 23–230 1007 32 (94) 65–200

WD 1.7 1.4 2.3 1.6 70.31 (1.7) 1.1–2.2 WD WD WD 2.9 1.8 2.8 72.5 (1.9) 1.0–11 5.0 2.0 70.7 (1.9) 1.2–4.3 0.86 70.55 (0.79) 0.2–2.2 1.9 70.8 (1.7) 1.3–3.1 1.6 70.3 (1.6) 1.1–1.9 1.4 70.8 (1.4) 0.21–2.5 1.4 70.2 (1.4) 1.1–1.6

WD WD WD WD 117 5 (11) 3.7–21 WD WD WD WD WD 3.2 7 1.4 (2.8) 1.3–5.8 WD 4.9 7 3.8 (3.9) 1.6–15 1.7 7 0.8 (1.6) 0.7–3.3 3.17 1.3 (2.8) 1.4–5.9 5.0 7 1.1 (4.8) 3.8–7.1 1.5 7 0.4 (0.97) 0.65–2.1 3.7 7 1.3 (3.8) 1.9–6.6

WD WD WD WD 6.5 7 3.1 (5.5) 2.6–12 WD WD WD WD WD 1.4 7 0.8 (1.2) 0.53–3.2 WD 2.6 7 2.3 (2.1) 0.90–10 2.17 0.6 (2.1) 1.3–2.9 0.777 0.60 (0.68) 0.30–1.9 3.3 7 0.9 (2.7) 2.5–4.9 1.17 1.1 (0.93) 0.27–3.2 2.7 7 1.1 (2.5) 1.6–5.6

nn

For composite [n¼ 1(X)] samples, each value is a mean of three separate determinations.

Number of samples and number of specimens (in parentheses) TLP, Trójmiejski Ladscape Park; WD (without data)

o0.01; Mann–Whitney U test), while for several sites the level of contamination was similar (p 40.05). More contaminated with Hg were specimens collected from the upland location, the Starachowice forest of Świętokrzyski land (place 22), while significantly less were specimens from two areas at the Kujawy land (places 18 and 21) (Fig. 1; Table 1). In some earlier studies dedicated to X. badius specimens from the Świętokrzyskie land, they were also more contaminated when compared to specimens from several locations in the northern part of the country, while most contaminated were those from upland and southernmost regions (Falandysz et al., 2012a). 3.2. Hg soil substrate and values of BCF At three of the fourteen sites where soils were sampled, the median value of Hg in soils was up to two folds above the value of 50 ng/g dm and other sites were from around 50 ng/g dm down to 15 ng/g dm (Table 1). The maximum median value in soils of 94 ng Hg/g dm was for a site in Świętokrzyskie land and Świętokrzyskie mountains (place 22; Fig. 1), which is more or less uphill when compared to sites from the northern part of country in this study. Also for the site of Mielęcin (place 21) in Kujawy land the median value was well above 50 ng/g dm, i.e. at 82 ng/g dm and for the Nearshore Landscape Park (place 1; Fig. 1) that could be considered as not contaminated (background) area, the median of Hg was 75 ng/g dm.

Clearly when the content of Hg in soil substratum increased, there is a corresponding decrease in the potential of species to bioconcentrate this element both in caps and stipes. In case of caps, the maximum median value of BCF was determined as 18 for soil content at 15 ng/g dm and decreased down to 0.97 and 3.8 for soils contaminated at 37 to 82 ng/g dm, respectively (Table 1). Based on the values of BCF for Hg obtained for several populations of X. chrysenteron in this study, it can be noted that this species is not an excluder (BCF o1) but accumulator and has some capacity to sequester Hg, and depending on site the values of BCF were up to 20. And available data for mushrooms of the same genera such as X. badius and X. subtomentosus showed similar absolute values and tendency of BCF depending on soil Hg content, and hence also a similar capacity to accumulate Hg (Chojnacka et al., 2012; Falandysz et al., 2012a). Those data agree with observation for the Spanish populations of X. chrysenteron and X. badius by Melgar et al. (2009), where a value of BCF for whole fruit bodies was roughly at 30. A large variation in Hg content between spatially distant populations of X. chryzenteron shows that there may be no homeostasis for this element in its flesh and fungus attempts to exclude Hg when emerging at soils where “background” contamination increased even at relatively narrow range from 15 to 94 ng Hg/g dm and/or there are not enough ligands to be absorbed in parallel, all other chalcophile elements. This feature seems to be common also to X. badius and X. subtomentosus (Chojnacka et al., 2012;

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Falandysz et al., 2012a). While at the sites with high deposition rates of Hg from a point source(s) such as fumes from Cu and Hg smelters, the exposure and contamination with Hg are evidently higher but the number of observations is very limited (Bargagli and Baldi, 1984; Svoboda et al., 2000). 3.3. X. chrysenteron as a source of Hg in diet For the assessment of risks in inorganic Hg intake from food is used as Hg reference dose (RfD) of 0.0003 mg/kg body mass (bm) daily developed by the Environment Protection Agency of the United States of America (US EPA, 1987). Also is used a value of Provisionally Tolerable Weekly Intake (PTWI) of inorganic Hg which is 0.004 mg/kg bm and equivalent to 0.00057 mg/kg bm/ day (JECFA, 2010). The PTWI for methylmercury (MeHg) is 0.0016 mg/kg bm (JECFA, 2007). Based on the range of the mean Hg values of this study, a meal made of 300 g of fresh caps of X. chrysenteron from the regions surveyed can be considered to be providing from 0.0024 to 0.0189 mg Hg (a dose 0.000034 to 0.00027 mg/kg bm for an individual of 70 kg bm) and this is 1.1–8.8 times below the RfD for inorganic Hg. Wild grown mushrooms are consumed more frequently usually in mushrooming season and in the country side regions while less frequently or rarely in other seasons of the year (Zhang et al., 2010). And amount of mushrooms in a meal is rarely greater than 500 g (fresh mushrooms) (Chudzyński et al., 2011). Caps of X. chrysenteron if consumed by fanciers at volume of 300 g daily in a week period can provide Hg at 0.0168 to 0.1323 mg Hg (0.00024 to 0.00189 mg/kg bm), and these values are well below those of PTWI for inorganic Hg. The values of RfD and PTWI of Hg used in assessment are based on data where inorganic Hg or MeHg as sole toxicants were at high excess to possible protective compounds (thiols, Se and antioxidants) contained in feed or food consumed. Mushrooms usually contain Se and it is found in certain species in elevated content (often in parallel with Hg) (Falandysz 2008). Mushrooms can be also rich in sulfur (Nasr et al., 2012; Rudawska and Leski 2005) and interactions between Hg and Se and S and other dietary components are possible, which can diminish toxicity from Hg sequestered, e.g. because of low absorption. Nevertheless, data on contents and absorption of Hg and its interrelationships with Se and other chalcophile elements as well as beneficial antioxidants contained in mushrooms are absent.

4. Conclusions Mercury noted in fruit bodies of Red Cracking Bolete that emerged at “background” areas across of Poland in 1996–2013 was at levels safe for consumers.

Acknowledgments This study is based on PhD thesis by Anna Dryżałowska that in part was supported by the National Science Centre under Grant no. 0706/B/P01/2011/40. Technical support by Katarzyna Bargłowska, Ada Borkowska, Justyna Chorążak, Karolina Czapiewska, Iza Domin, Joanna Gozdek, Aleksandra Gutfrańska, Magdalena Kiełpińska, Karolina Kokot, Aleksandra Konkel, Magdalena Kubaszewska, Edyta Kułdo, Katarzyna Młynarkiewicz, Aleksandra Mostrąg, Aneta Naczk, Karolina Napierała (Jackiewicz), Daniela Orzłowska, Alina Pękacka, Wioletta Witka-Jeżewska, Renata Załęcka is acknowledged.

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