Shandong Province is an important area of production for the export of apples in China, comprising one-third of the country's export volume. Yantai City in Shandong Province is also known as “Apple City”. By 2019, the total area of apple cultivation in Yantai had reached 129,500 ha, and production accounted for 60% of the province (
Currently, waste apple wood is used to make charcoal and composite materials (Jindo et al., 2014; Kowaluk et al., 2019; Najibeh et al., 2020). A broader use of these materials is the cultivation of edible mushrooms. As early as 1996, Jo et al. (1996) added 15% of apple wood chips to the medium for
Mushrooms can become enriched with heavy metals, and there are some health risks associated with the excessive consumption of mushrooms that contain large quantities of heavy metals (Mohsen et al., 2021). Li et al. (2011) found that by artificially adding Pd to the medium, the mycelia of
This study investigated the resources of waste apple wood in Yantai, Shandong Province, China's main area for the production of apples and examined the contents of heavy metals and pesticide residue. Waste apple wood as the main raw material enables the cultivation of two wood-rotting edible mushrooms –
The materials for the cultivation of edible mushrooms, including apple sawdust, oak sawdust, corn cob, cottonseed husk and wheat bran, were all purchased from QixiaXurui Biological Technology Co., Ltd (Yantai, China).
A total of 21 sampling areas were established in the main apple producing areas (Qixia, Penglai, Haiyang and Muping) in Yantai, Shandong Province, including 13 sampling areas in Qixia, 3 in Penglai, 2 in Haiyang and 3 in Muping (Figure 1). A total of 73 apple wood samples were collected. The collected samples were left to dry in the sun and then cut into thin pieces with a profile cutting machine. A few pieces were randomly selected based on the size of the apple wood. The small branches were cut short by pruning. The sliced apple wood or short branches were placed in a Petri dish in a 60°C-blast dryer fan and baked until a constant weight, crushed and then sifted through a 0.5 mm sieve.
The global positioning system (GPS) localisation map of the sampling region.
Formulations for
Number | Cultivated species | Formula |
---|---|---|
1 (CK) | Cottonseed husk 80%, corn cob 3%, wheat bran 15%, gypsum 2% and water content 60% | |
2 | Apple sawdust 50%, cotton seed husk 20%, corn cob 20%, wheat bran 8%, gypsum 2% and water content 60% | |
3 (CK) | Oak sawdust 80%, wheat bran 18%, gypsum 2% and water content 60% | |
4 | Apple sawdust 80%, wheat bran 18%, gypsum 2% and water content 60% |
CK, control check.
The microwave digestion method was used to pretreat samples to detect heavy metals and other mineral elements (Siwulski et al., 2017; Falandysz and Treu, 2019). The digestion tube was cleaned according to the manufacturer's instructions (Multiwave3000; Austria Antompa Co., Ltd, Shanghai, China). A total of 0.3 g sample (0.3 g apple wood and cultivated raw materials and 0.2 g
A total of 179 pesticide residues were detected in 21 apple wood samples. The samples were pretreated as described by ‘GB23200.113-2018 National Food Safety Standard – Determination of 208 Pesticides and Metabolites Residues in Foods of Plant Origin – Gas chromatography – Tandem Mass Spectrometry Method’ and ‘GB/T 20770-2008 Determination of 486 Pesticides and Related Chemical Residues in Grains – Liquid chromatography-tandem mass spectrometry (LC-MS-MS) Method’. Gas chromatography-mass spectrometry (GCMS-TQ8040 NX, Shimadzu, Tokyo, Japan) and liquid chromatography-tandem mass spectrometry (6460 Triple Quad LC/MS; Agilent Technologies, Santa Clara, CA, USA) were used to measure the pesticide residues.
Microsoft Excel 2007 (Redmond, WA, USA) and SPSS 17.0 (SPSS, Inc., Chicago, IL, USA) were used for data processing and statistical analysis, respectively. A Pearson's correlation coefficient was used for the correlation analysis. The contents of pesticide residues and heavy metals were calculated by dry weight (mg · kg−1 dw). The results represent the means of three replicates ± SD (
The contents of 10 heavy metals (Pb, Cd, Hg, As, Cr, Ni, Zn, Fe, Mn and Cu) in the 73 apple wood samples collected were measured (Table 2).
Analysis of the contents of heavy metal elements in apple wood samples.
Heavy metal | Detection rate (%) | Detection range (mg · kg−1) | Average (mg · kg−1) | Standard deviation | Coefficient of variation (%) |
---|---|---|---|---|---|
Pb | 100 | 0.14–41.51 | 2.37 | 5.15 | 217.26 |
Cd | 72.60 | 0.08–2.23 | 0.20 | 0.31 | 159.79 |
Hg | 91.78 | 1.4–0.0031 | 0.057 | 0.17 | 292.96 |
As | 86.30 | 0.17–6.14 | 0.60 | 0.75 | 125.91 |
Cr | 97.26 | 0.12–16.12 | 3.49 | 2.75 | 78.70 |
Ni | 100 | 1.30–21.82 | 4.73 | 3.29 | 69.45 |
Zn | 100 | 1.12–115.15 | 18.55 | 19.48 | 105.02 |
Fe | 100 | 107–8,709 | 486.61 | 1,081.55 | 222.26 |
Mn | 100 | 20.3–204.62 | 84.73 | 43.93 | 51.85 |
Cu | 100 | 5.97–235.93 | 34.38 | 34.80 | 101.21 |
Cd was not detected in 20 of the samples, and the detection rate was 72.60%. Six samples did not have detectable Hg, and its detection rate was 91.78%. Ten samples lacked detectable As, and the detection rate was 86.30%. Two samples lacked Cr, which was detected in 97.26% of the samples. All the samples contained Pb, Ni, Zn, Fe, Mn and Cu (Table 2).
The average contents of Pb, Cd, Hg, As, Cr, Ni, Zn, Fe, Mn and Cu were 2.37 mg · kg−1, 0.20 mg · kg−1, 0.057 mg · kg−1, 0.60 mg · kg−1, 3.49 mg · kg−1, 4.73 mg · kg−1, 18.55 mg · kg−1, 486.61 mg · kg−1, 84.73 mg · kg−1 and 34.38 mg · kg−1, respectively. The inter-sample standard deviation and variation coefficient of each element were large, which reflected the large differences between samples (Table 2). The contents of heavy metals in the top five apple wood samples are also shown in Table 3. Some of the samples had extremely high levels of contamination, indicating that contamination is an individual phenomenon.
Top five contents of each heavy metal element in apple wood samples (mg · kg−1).
Ranking | Pb | Cd | Hg | As | Cr | Ni | Zn | Fe | Mn | Cu | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | Sample number | Content | |
1 | 27 | 41.51 | 57 | 2.23 | 32 | 1.4 | 69 | 6.14 | 19 | 16.12 | 4 | 21.82 | 57 | 115.15 | 27 | 8,708.92 | 38 | 204.62 | 19 | 235.93 |
2 | 19 | 18.48 | 36 | 1.05 | 38 | 0.25 | 57 | 1.99 | 46 | 12.58 | 49 | 14.02 | 41 | 81.62 | 19 | 3,963.58 | 41 | 188.95 | 46 | 134.28 |
3 | 32 | 7.03 | 41 | 0.90 | 19 | 0.23 | 2 | 1.51 | 27 | 9.70 | 72 | 12.78 | 27 | 61.07 | 4 | 1,251.47 | 43 | 183.50 | 34 | 126.23 |
4 | 16 | 3.81 | 56 | 0.68 | 60 | 0.22 | 36 | 1.4 | 4 | 8.82 | 33 | 11.48 | 19 | 58.07 | 32 | 1,105.65 | 44 | 180.38 | 32 | 107.42 |
5 | 4 | 3.16 | 24 | 0.60 | 69 | 0.19 | 27 | 1.10 | 32 | 8.80 | 64 | 10.50 | 36 | 56.03 | 46 | 641.30 | 66 | 176.62 | 73 | 90.45 |
As shown in Table 4, the maximum positive correlation between the contents of Pb and Fe occurred in the 73 apple wood samples, with a similarity coefficient as high as 0.988. The contents of Pb, Fe and Cu positively correlate with each other and are not correlated with the contents of As, Cd and Ni, indicating the joint accumulation of Pb, Fe and Cu in apple wood.
Correlation analysis of the content of each element in apple wood samples.
Element | Pb | Cd | Hg | As | Cr | Ni | Zn | Fe | Mn |
---|---|---|---|---|---|---|---|---|---|
Cd | 0.031 | ||||||||
Hg | 0.156 | 0.080 | |||||||
As | 0.059 | 0.386** | 0.133 | ||||||
Cr | 0.530** | 0.124 | 0.336** | −0.001 | |||||
Ni | 0.056 | −0.090 | 0.054 | −0.076 | 0.378** | ||||
Zn | 0.361** | 0.733** | 0.162 | 0.207 | 0.446** | 0.203 | |||
Fe | 0.988** | 0.050 | 0.118 | 0.065 | 0.560** | 0.112 | 0.394** | ||
Mn | 0.249* | 0.125 | 0.235* | 0.211 | 0.171 | 0.050 | 0.216 | 0.243* | |
Cu | 0.346** | 0.104 | 0.452** | −0.027 | 0.626** | 0.025 | 0.292* | 0.342** | 0.250* |
Among the 179 pesticide residues detected, five types, including thifensulfuron-methyl, rimsulfuron, nicosulfuron, iprodione and benfuracarb, were not reported because the quality control results did not meet the requirements. Among the remaining 174 pesticide residues, only 11 types of pesticide residues, including chlorpyrifos, cyhalothrin, cyper methrin, difenoconazole, tebuconazole, chlorbenzuron, carbendazim, imidacloprid, acetamiprid, cymoxanil and prochloraz were detected, while the remaining 163 pesticide residues were not detected (Table S1 in Supplementary Materials).
Chlorpyrifos was detected in all the apple wood samples, with the content ranging from 0.01 mg · kg−1 to 0.75 mg · kg−1. Chlorpyrifos is an insecticide that is widely used in apple cultivation (Ho et al., 2020), which explains why all the samples contained detectable amounts of chlorpyrifos.
Carbendazim was detected in 19 samples and ranged from 0.015 mg · kg−1 to 4.86 mg · kg−1, and the detection rate was 90.48%. Tebuconazole was detected in 16 samples ranging from 0.017 mg · kg−1 to 0.44 mg · kg−1, and the detection rate was 76.19%. Imidacloprid was detected in 14 samples ranging from 0.031 mg · kg−1 to 0.32 mg · kg−1, and the detection rate was 66.67%. Acetamiprid was detected in 13 samples ranging from 0.01 mg · kg−1 to 0.11 mg ·kg−1, and the detection rate was 61.90%. Chlorbenzuron was detected in eight samples and ranged from 0.037 mg · kg−1 to 0.21 mg · kg−1 and the detection rate was 38.10%. Only cyhalothrin was detected in two samples at 0.14 mg × kg−1 and 0.19 mg ·kg−1, respectively; cypermethrin was detected in two samples at 0.11 mg · kg−1 and 0.19 mg · kg−1, respectively; difenoconazole was detected in two samples at concentrations of 0.034 mg · kg−1 and 0.083 mg · kg−1, respectively, cymoxanil was detected in two samples at concentrations of 0.056 mg · kg−1 and 0.083 mg · kg−1, respectively. Their detection rate was 9.52%. Prochloraz was detected in one sample at a content of 0.04 mg · kg−1, and the detection rate was 4.76% (Table 5, Table S2 in Supplementary Materials).
Analysis of the contents of pesticide residues in apple wood samples.
Pesticide residues | Detection rate (%) | Detection range (mg · kg−1) | Average (mg · kg−1) | Standard deviation | Coefficient of variation (%) |
---|---|---|---|---|---|
Chlorpyrifos | 100 | 0.01–0.75 | 0.16 | 0.19 | 119.64 |
Cyhalothrin | 9.52 | 0.14–0.19 | 0.17 | 0.04 | 21.43 |
Cypermethrin | 9.52 | 0.11–0.19 | 0.15 | 0.06 | 37.71 |
Chlorbenzuron | 38.10 | 0.037–0.21 | 0.12 | 0.07 | 59.87 |
Carbendazim | 90.48 | 0.015–4.86 | 0.70 | 1.12 | 157.31 |
Imidacloprid | 66.67 | 0.031–0.32 | 0.10 | 0.08 | 76.69 |
Acetamiprid | 61.90 | 0.01–0.11 | 0.04 | 0.03 | 76.88 |
Difenoconazole | 9.52 | 0.034–0.083 | 0.06 | 0.03 | 59.23 |
Tebuconazole | 76.19 | 0.017–0.44 | 0.13 | 0.13 | 97.43 |
Cymoxanil | 9.52 | 0.056–0.083 | 0.07 | 0.02 | 27.47 |
Prochloraz | 4.76 | 0.04 | 0.04 |
The main nutrient in apple sawdust is crude fibre, which has low contents of proteins and lipids and almost no carbohydrates. It can be used as a carbon source to cultivate wood rot edible mushrooms (unpublished). However, apple wood is agricultural waste and may have heavy metal pollution. Therefore, the raw materials were analysed for the presence of heavy metals and other mineral elements. The contents of As (0.43 ± 0.19 mg × kg−1) and Hg (0.021 ± 0.0082 mg × kg−1) in apple sawdust was higher than those in other cultivation materials, which could be caused by the accumulation of As and Hg in the tree owing to the long-term use of some pesticides in apple orchards (Ian et al., 1994). The Mn content in the sawdust of wild oak was as high as 198.80 ± 33.24 mg × kg−1, and the content of Pb (0.90 ± 0.19 mg × kg−1) was relatively high. The Ni content of corn cob (61.45 ± 10.58 mg × kg−1) was significantly higher than that in other cultivation materials. In terms of other mineral elements, the content of P (11,736.02 ± 2,074.40 mg × kg−1) in bran was much higher than that of sawdust, cottonseed husks and corn cobs, and the content of Ca in sawdust was relatively high (Table 6).
The content of heavy metal elements and other mineral elements in culture material samples (mg · kg−1 dry weight).
Element | Apple sawdust | Oak sawdust | Cottonseed husk | Corn cob | Wheat bran |
---|---|---|---|---|---|
Pb | ND | 0.90 ± 0.19 | ND | 0.15 ± 0.05 | ND |
Cd | 0.26 ± 0.20 | 0.23 ± 0.04 | 0.04 ± 0.01 | 0.07 ± 0.02 | 0.05 ± 0.02 |
Hg | 0.021 ± 0.0082 | 0.014 ± 0.0045 | 0.0038 ± 0.00035 | 0.019 ± 0.003 | 0.0054 ± 0.0016 |
As | 0.43 ± 0.19 | 0.16 ± 0.025 | 0.24 ± 0.046 | 0.27 ± 0.11 | 0.16 ± 0.037 |
Cr | 2.00 ± 0.71 | 3.20 ± 0.26 | 1.89 ± 0.19 | 1.82 ± 0.12 | 1.99 ± 1.02 |
Ni | 11.42 ± 1.22 | 19.02 ± 0.34 | 3.40 ± 1.30 | 61.45 ± 10.58 | 11.27 ± 4.23 |
Zn | 36.56 ± 2.76 | 12.17 ± 1.50 | 29.17 ± 1.40 | 46.34 ± 13.76 | 95.55 ± 15.54 |
Fe | 469.52 ± 47.26 | 534.98 ± 46.71 | 133.18 ± 2.36 | 707.34 ± 26.48 | 389.38 ± 117.62 |
Mn | 56.45 ± 10.76 | 198.80 ± 33.24 | 43.43 ± 2.88 | 70.44 ± 6.63 | 151.94 ± 21.69 |
Cu | 42.37 ± 12.00 | 30.76 ± 2.18 | 22.04 ± 2.08 | 102.79 ± 29.97 | 30.02 ± 7.20 |
P | 285.89 ± 74.33 | 421.20 ± 11.30 | 965.73 ± 194.83 | 1,892.39 ± 245.57 | 11,736.02 ± 2,074.40 |
K | 2,976.74 ± 491.72 | 996.00 ± 63.02 | 9,184.94 ± 514.20 | 7,001.17 ± 1,652.27 | 12,811.04 ± 1,902.13 |
S | 1,011.27 ± 202.44 | 1,375.46 ± 34.10 | 1,453.87 ± 163.89 | 2,933.34 ± 272.59 | 4,044.84 ± 441.75 |
Ca | 11,220.94 ± 2,918.93 | 18,263.25 ± 445.73 | 3,370.71 ± 263.35 | 3,097.61 ± 599.40 | 1,476.53 ± 264.57 |
Mg | 1,120.56 ± 169.58 | 1,241.33 ± 282.32 | 1,721.86 ± 376.95 | 1,166.53 ± 252.63 | 4,234.88 ± 492.44 |
Se | 0.030 ± 0.0058 | ND | 0.043 ± 0.0087 | 0.032 ± 0.0036 | 0.0364 ± 0.011 |
ND: not detected.
A total of 179 pesticide residues were tested for each cultivation material. Chlorpyrifos (0.56 ± 0.075 mg × kg−1), acetamiprid (0.16 ± 0.020 mg × kg−1) and phoxim (0.053 ± 0.0047 mg × kg−1) were only detected in apple sawdust. Phoxim (0.058 ± 0.0047 mg × kg−1) was detected in bran, and pesticide residues were not detected in the other culture materials (Table 7).
Pesticide residue contents of culture raw material samples (mg · kg−1 dry weight).
Pesticide residues | Apple sawdust | Oak sawdust | Cottonseed husk | Corn cobs | Wheat bran |
---|---|---|---|---|---|
Chlorpyrifos | 0.56 ± 0.075 | ND | ND | ND | ND |
Acetamiprid | 0.16 ± 0.020 | ND | ND | ND | ND |
Phoxim | 0.053 ± 0.0047 | ND | ND | ND | 0.058 ± 0.0047 |
ND, not detected.
The contents of heavy metals and other mineral elements (Pb, Cd, Hg, As, Cr, Ni, Zn, Fe, Mn, Cu, P, K, S, Ca, Mg and Se) in the fruiting body samples of
The contents of Zn and Fe in
Contents of heavy metal elements and other mineral elements in
Formula 1 (CK) | Formula 2 | Formula 3 (CK) | Formula 4 | |
---|---|---|---|---|
Pb | ND | ND | ND | ND |
Cd | 0.11 ± 0.04 | 0.17 ± 0.02 | 1.06 ± 0.12 | 0.19 ± 0.03 |
Hg | 0.12 ± 0.03 | 0.033 ± 0.0024 | 0.018 ± 0.0028 | 0.028667 ± 0.0045 |
As | 0.52 ± 0.035 | 0.059 ± 0.010 | 0.48 ± 0.035 | 0.72 ± 0.094 |
Cr | ND | 0.60 ± 0.06 | 0.86 ± 0.19 | 1.34 ± 0.27 |
Ni | 0.16 ± 0.05 | 1.62 ± 0.24 | 3.00 ± 0.36 | 9.29 ± 0.78 |
Zn | 65.95 ± 8.50 | 75.47 ± 5.03 | 108.43 ± 7.97 | 90.22 ± 8.63 |
Fe | 69.18 ± 16.13 | 92.35 ± 6.26 | 95.47 ± 10.40 | 51.51 ± 7.86 |
Mn | 8.03 ± 0.30 | 7.25 ± 1.42 | 16.83 ± 3.15 | 14.89 ± 2.64 |
Cu | 12.63 ± 0.86 | 8.47 ± 2.20 | 26.03 ± 4.69 | 13.35 ± 2.44 |
P | 9,244.25 ± 1,133.32 | 9,275.98 ± 697.41 | 9,737.44 ± 1,277.03 | 9,470.33 ± 658.03 |
K | 16,654.00 ± 2,968.71 | 18,212.00 ± 936.16 | 18,507.33 ± 2,236.68 | 11,271.36 ± 2,829.37 |
S | 4,037.00 ± 249.92 | 4,186.00 ± 75.45 | 24,796.33 ± 4,636.61 | 16,388.44 ± 2,085.69 |
Ca | 178.24 ± 17.15 | 132.01 ± 10.57 | 908.50 ± 61.21 | 851.67 ± 31.13 |
Mg | 1,115.00 ± 148.58 | 1,463.33 ± 97.01 | 1,479.67 ± 320.01 | 889.33 ± 38.44 |
Se | 0.028 ± 0.0061 | 0.162 ± 0.034 | 0.096 ± 0.013 | 0.0605 ± 0.012 |
ND, not detected.
Fruiting body samples of
Apple sawdust and oak sawdust were used as the main materials to cultivate
Comparison of the biological efficiency of edible mushrooms cultivated with apple sawdust and other materials.
Formula 1 (CK) | Formula 2 | Formula 3 (CK) | Formula 4 | |
---|---|---|---|---|
Biological efficiency % | 112.17 ± 4.23** | 89.70 ± 2.04 | 80.79 ± 1.89 | 81.62 ± 1.40 |
CK, control check.
Previous studies on the use of agricultural waste to cultivate edible mushrooms focused on yield or nutritional content. For example, Patricia et al. (2014) used the invasive aquatic plant water hyacinth (
Cr and Ni are not specified in the Chinese national standard. However, the European Food Safety Authority proposed a maximum daily intake of 0.0028 mg · kg−1 body weight for Ni (Benford et al., 2015; Oskar et al., 2021). Thus, the maximum weekly intake of Ni was 0.0196 mg · kg−1 body weight. Calculated based on an average weight of 60 kg, the safe content of Ni per person per week is 1.176 mg. The content of Ni in this study was calculated based on the dry weight of the mushrooms and assuming an average moisture content of 90%. The mushrooms with the highest amount of Ni (9.29 ± 0.78 mg · kg−1 dry weight) when fresh were approximately 0.929 mg · kg−1. Based on data from the National Bureau of Statistics of China (
This study only used waste apple sawdust to cultivate two edible mushrooms,