Article pubs.acs.org/JAFC
Concentrations of Trace Elements in Organic Fertilizers and Animal Manures and Feeds and Cadmium Contamination in Herbal Tea (Gynostemma pentaphyllum Makino) Sumontha Nookabkaew,† Nuchanart Rangkadilok,*,†,‡,⊗ Norratouch Prachoom,§ and Jutamaad Satayavivad†,‡,⊗ †
Laboratory of Pharmacology, Chulabhorn Research Institute (CRI) and ‡Environmental Toxicology Program, Chulabhorn Graduate Institute (CGI), Kamphaeng Phet 6 Road, Lak Si, Bangkok 10210, Thailand ⊗ Center of Excellence on Environmental Health and Toxicology (EHT), CHE, Ministry of Education, Bangkok 10400, Thailand § Inter-University Program on Environmental Toxicology, Technology and Management, Asian Institute of Technology, Chulabhorn Research Institute, and Mahidol University, Bangkok, Thailand ABSTRACT: Thailand is predominantly an agriculture-based country. Organic farming is enlisted as an important national agenda to promote food safety and international export. The present study aimed to determine the concentrations of trace elements in commercial organic fertilizers (fermented and nonfermented) composed of pig and cattle manures available in Thailand. Pig and cattle manures as well as animal feeds were also collected from either animal farms or markets. The results were compared to the literature data from other countries. Fermented fertilizer composed of pig manure contained higher concentrations of nitrogen (N) and phosphorus (P) than fertilizer composed of cattle manure. High concentrations of copper (Cu) and zinc (Zn) were also found in fertilizers and manures. Some organic fertilizers had high concentrations of arsenic (As), cadmium (Cd), and lead (Pb). The range of As concentration in these fertilizers was 0.50−24.4 mg/kg, whereas the ranges of Cd and Pb were 0.10−11.4 and 1.13−126 mg/kg, respectively. Moreover, pig manure contained As and Cd (15.7 and 4.59 mg/kg, respectively), higher than their levels in cattle manure (1.95 and 0.16 mg/kg, respectively). The use of pig manure as soil supplement also resulted in high Cd contamination in herbal tea (Gynostemma pentaphyllum Makino; GP). The Cd concentration in GP plants positively correlated with the Cd concentration in the soil. Therefore, the application of some organic fertilizers or animal manures to agricultural soil could increase some potentially toxic elements in soil, which may be absorbed by plants and, thus, increase the risk of contamination in agricultural products. KEYWORDS: organic fertilizer, pig and cattle manures, arsenic, cadmium, Gynostemma pentaphyllum
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INTRODUCTION The agricultural sector in Thailand has long been playing its important role in terms of serving the global demand for both basic and processed agricultural products. The top five agricultural products (by quantity) are sugar cane, paddy rice, cassava, oil (palm fruit), and maize.1 Increased crop production for food supply largely requires the use of fertilizers or chemicals as supplement of essential nutrients for growing plants. The intensive chemical use in commercial farming has a direct impact on the farmers’ and/or consumer’s health and quality of life. These have led to the seeking of alternative farming methods that are considered to be safer to both human health and the environment. Therefore, the promotion of organic agriculture has been increasing worldwide because of its environmentally friendly properties, safety, and economic benefits. Organic farming can be practiced in any farming system. It uses organic matter as the only fertilizer, and pests and weeds are controlled by cultural practices, including organic chemicals made from herbs.2 The objective of organic farming is to restore soil fertility. In addition, the application of organic farming may lead to an improvement of water quality and food safety, which have been deteriorated by the heavy chemical use in agricultural areas. Application of inorganic and organic fertilizers increases essential nutrients in soil for growing crops. Animal manures © XXXX American Chemical Society
such as pig, cattle, and chicken manures are used as organic fertilizers as they are valuable sources of organic matter and major and minor plant nutrients, including metal ions such as iron (Fe) and copper (Cu).3−5 However, the long-term or overapplication of animal manures as organic fertilizers may result in contamination by some potentially toxic elements such as arsenic (As), cadmium (Cd), and lead (Pb) in agricultural soils and water resources. When these contaminated soils and water are used for growing crops, for example, rice, vegetables, and herbal medicines, these potentially toxic elements can enter into the food chain, affecting food quality and safety. Accumulation of these elements in agricultural or herbal products is of concern due to the adverse health effects on humans. Wang et al.6 studied Cd contamination in a long-term (>20 years) experimental field in northern China with different fertilizer treatments and an annual crop rotation of winter wheat and summer maize. Their results indicated that various extents of Cd accumulation were observed in the soil, and the accumulation was mainly affected by atmospheric dry and wet deposition and fertilization. Application Received: December 30, 2015 Revised: March 21, 2016 Accepted: March 29, 2016
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DOI: 10.1021/acs.jafc.5b06160 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
powder samples were kept in tightly closed plastic containers and stored at 4 °C until analysis. Plant Sampling (G. pentaphyllum). This herbal tea was selected because it contained a high concentration of Cd from our previous study15 and it is one of the most popular herbal tea products (apart from green tea and mulberry tea) consumed for medical purposes or maintaining good health. Aerial parts of GP (20−30 cm above surface soil) were harvested from a medicinal plant farm in Ratchaburi province (central western Thailand). The farmer grows GP plants in plant nurseries using organic fertilizers and his own agricultural practices. Generally, pig and cattle manures are also used as soil supplement in this farm. Herbal extracts are used as insecticides. GP plants were harvested at flowering stage. After harvesting, GP plants (two commercial cultivars; GP1 and GP2) were washed and dried in an oven at 50 °C for 2 days. Soil samples were also collected from each individual plot in which GP plants were grown. After drying, the plant and soil samples were ground into powder and kept in a plastic bag at 4 °C until analysis. Microwave-Assisted Acid Digestion. Suprapur nitric acid (65%) and hydrochloric acid (37%) (Merck, Darmstadt, Germany) were used for digestion of samples; all glassware and digestion vessels were soaked in AnalaR nitric acid (10%). High-purity water obtained through a MilliQ purification system (Millipore, Bedford, MA, USA) was used during digestion and also for rinsing the equipment. For ICP-MS, standard solutions of elements were obtained from Fisher Scientific (Loughborough, UK). A microwave digestion system MARSX (CEM Corp., Matthews, NC, USA) with a rotor for 12 polytetrafluoroethylene (PTFE) digestion vessels (XP-1500) was used for sample digestion. The dried powder samples of 0.2500 g were weighed into a dried and clean digestion vessel. Then, both 6.0 mL of 65% nitric acid and 2.0 mL of 37% hydrochloric acid were added into soil, manure, and fertilizer samples, whereas only 6.0 mL of 65% nitric acid was added into animal feeds and plant samples. The vessels were closed and placed on the rotating platform of the microwave oven before the digestion process started. The digested conditions of the samples were set at 1200 W maximum power, ramp time of 30 min, temperature of 190 °C, pressure of 170 psi, and holding time of 40 min. Two replicates were made for each sample. After cooling for 30 min, the vessels were opened carefully. Each digested solution was filtered through a Whatman filter no. 42 and further diluted to 100 mL (soil, manure, and fertilizer) or 50 mL (plant and feed) with high-purity water and then stored in a polyethylene bottle for analysis. The certified reference material and reagent blank were digested and diluted in the same manner. The digested solutions were stored in polyethylene bottles at 4 °C until analysis. ICP-MS Analysis. The digested solutions were then analyzed by Agilent 7500c inductively coupled plasma−mass spectrometry (ICPMS) (Agilent Technologies Co. Ltd., Palo Alto, CA, USA) for the determination of elements according to U.S. EPA method 6020 (U.S. EPA, 1998). Instrumental conditions for ICP-MS were as follows: radio frequency power, 1500 W; carrier gas flow rate, 1.09 L/min; makeup gas flow rate, 0.11 L/min; plasma gas flow rate, 15 L/min; spray chamber, double-pass Scott-type; nebulizer, Babington; and reaction cell gas, H2 at 4.5 mL/min and He at 5.0 mL/min. Rhodium was used as an internal standard. Certified reference material (San Joaquin soil SRM 2709a, NIST, Gaithersburg, MD, USA) was used to check the accuracy of the analytical procedures used in this work. Our analytical data along with the certified values showed that there is a good agreement for most elements between the experimental values and certified values (recovery was in the range of 77.4−99.7%) except Cr and Pb. The observed Cr and Pb concentrations in the SRM 2709a were slightly lower than the certified values (70.8 and 63.0%, respectively). This may be due to the weak condition of acid digestion for both elements in soil. All samples were also determined for the concentrations of total phosphorus (TP), total potassium (TK), total Kjeldahl nitrogen (TKN), pH, and electrical conductivity (EC) by the Laboratory of Soil Sciences, Department of Agriculture, Kasetsart University, Bangkok, Thailand. Statistical Analysis. The data are presented as the mean ± standard error of the mean (SEM). Comparison was carried out between different types of manures and between fertilizer and its manure. Statistical
of cattle manure was found to increase soil organic matter, total and available nutrients, pH, and electrical conductivity (EC) and was involved in the accumulation of heavy metals in corn.7 It also led to a high deficiency of Zn and high accumulation of Cd in the soil, which would be a risk for the safety of corn seed production in northwestern China. Gynostemma pentaphyllum Makino (GP; Cucurbitaceae), also known as Jiaogulan (in China) or Panjakan (in Thailand), is a climbing, perennial vine plant that grows in several parts of Asian countries including China, Vietnam, Japan, and Malaysia.8 GP has been reported to have a wide range of pharmacological effects including antidiabetic, hypolipidemia, antigastric ulcer, anticancer, prevention of cardiovascular disease, and immunomodulatory effects.9−14 Our previous study15 reported that the concentration of Cd was detectable at high level (>0.30 mg/kg) in 14 of 16 GP herbal tea products collected from Thai markets. Most GP products, both local and imported samples, were contaminated with Cd at higher levels than the standard maximum value for herbal tea in Thailand (Notification of the Ministry of Public Health No. 280, 2004; Cd < 0.30 mg/kg). This plant may accumulate Cd from the growing environment such as soil and water as well as from the use of some fertilizers. In addition, cleaning and processing of herbal tea leaves may be other sources for Cd contamination in this herbal tea. Chronic exposure to Cd is a risk factor for chronic kidney disease.16,17 In a study of Korean adult population (1797 adults, age ≥20 years, year 2011), exposure to low levels of Cd was positively associated with chronic kidney disease, especially in adults with hypertension or diabetes.18 In U.S. adults, higher cumulative Cd exposure may be related to subtly decreased performance in tasks requiring attention and perception, particularly among those adults whose Cd exposure is primarily through diet.19 Chronic occupational exposure to Cd (as reflected by high urinary Cd levels) was found to influence in a dose-dependent manner the slowing of psychomotor functions and the increase of complaints consistent with peripheral neuropathy and complaints about equilibrium and ability to concentrate.20 Therefore, determination of Cd and other potentially toxic elements in the plant raw material initially before further processing to the herbal tea product is also essential. The application of some fertilizers, especially the use of animal manures, may increase Cd concentration in soil available for absorption by plants. In the present study, different types of organic fertilizers and animal manures were collected to determine the concentrations of both essential and potentially toxic elements. Some animal feeds, as possible sources of elements in manure, were also collected and analyzed. In addition, the impacts of organic fertilizer application and element concentrations in GP plants were investigated in this study.
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MATERIALS AND METHODS
Sample Collection (Fertilizers and Animal Manures). Organic fertilizer samples (fermented fertilizer of pig manure (FPM), n = 3; fermented fertilizer of cattle manure (FCM), n = 8; nonfermented fertilizer of cattle manure (NFCM), n = 15; total fertilizers, n = 26) were purchased from different local markets in Bangkok, Thailand. Pig and cattle manures, which included 16 pig manures (PM) and 15 cattle manures (CM), were collected from animal farms in Chiang Mai, Nakornpathom, Chonburi, Ratchaburi, and northeastern provinces (Surin, Buriram, and Chaiyapum) of Thailand. In addition, different animal feeds (including feed raw materials, for example, corn and rice meal, n = 15) were sampled from animal farms and markets in Nakornpathom, Nonthaburi, and Bangkok. All samples were air-dried for 48 h and then ground into powder using an agate mortar. These B
DOI: 10.1021/acs.jafc.5b06160 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry Table 1. Characteristics of Organic Fertilizers Available in Thailand
a
samplea
pH
total Kjeldahl nitrogen (TKN) (%)
total phosphorus (%)
total potassium (%)
electricity conductivity (EC) (dS/m)
fermented PM (n = 2) fermented CM (n = 8) nonfermented CM (n = 5)
6.70 7.96 7.28
2.56 ± 0.26 1.17 ± 0.26 1.28 ± 0.32
1.60 ± 0.41 0.38 ± 0.10 0.53 ± 0.33
1.21 ± 0.78 1.22 ± 0.53 0.86 ± 0.49
2.36 ± 0.21 1.22 ± 0.53 0.86 ± 0.49
PM, compost of pig manure; CM, compost of cattle manure.
Figure 1. Concentrations of essential elements in organic fertilizers and animal manures: (A) concentrations of Mg, Ca, and Fe; (B) concentrations of Mn, Cu, and Zn. Comparison was carried out between different types of manures and between fertilizer and its manure. Statistical analysis of the data was performed using one-way ANOVA with significant differences as (∗∗∗) p < 0.001, (∗∗) p < 0.01, and (∗) p < 0.05. analysis of the data was performed using one-way ANOVA with significant differences at p < 0.001, 0.01, and 0.05.
pig manure had concentrations of N and P but not of K higher than those in cattle manure. They also indicated that poultry manure had the highest concentrations of N and K. The animal manures used in fertilizers are expected to improve the availability of the nutrients in soil for growing plants. Essential Elements in Organic Fertilizers and Manures. The manures of pig and cattle were composed of macronutrients with PM having the highest concentrations of Mg, Ca, Cu, and Zn and CM with the highest Mn and Fe concentrations (Figure 1). Similarly, a study in Austria (Table 2) showed that most essential elements including Mg, Ca, Cu, and Zn were found at higher concentrations in pig manure than in cattle manure.22 Moral et al.4 collected pig slurries from a total of 36 farms in Vega Baja in the Valencia region of Spain at different production stages
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RESULTS AND DISCUSSION Chemical Compositions of Organic Fertilizers. The results showed that the average pH value of fermented fertilizers of pig manure (FPM; pH 6.70) was lower than the average pH of fertilizers composed of cattle manures (both fermented and nonfermented fertilizers (FCM and NFCM); pH 7.28−7.96) (Table 1). In addition, FPM had average concentrations of nitrogen (N) and phosphorus (P) and EC values higher than those of FCM and NFCM, whereas the average concentrations of potassium (K) in all fertilizers were found to be at the same level. These results agree with Odedina et al.,21 who reported that C
DOI: 10.1021/acs.jafc.5b06160 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
D
a
3009 518−7900
6744 3851−8746
18687
7063
88.5 52.9−180
20600
9300
988 616−1393
10251 9855−10950
6577 5165−8311
6602 4530−10977
32100
14400
3382 1652−4963
34099 10463−110086
Ca
12384 7503−22918
Mg
Values represent minimum−maximum. ND, not detectable.
pig manure present study (n = 16) mean range England and Wales (1999)23 Austria (2007)22 China (2013)25 cattle manure present study (n = 15) mean range England and Wales (1999)23 Austria (2007)22 China (2013)25 dairy feed present study (n = 1) England and Wales (1999)23a China (2013)25a pig feed present study (n = 17) mean range England and Wales (1999)23a China (2013)25a corn (n = 4) mean range rice meal (n = 3) mean range
sample
12.4 2.20−28.8
2.57 1.70−4.70
136 16.6-311 17.9−217 ND−392
57.0 2.8−79.6 ND-45.9
18.2 8.62−47.2 62.3 51 56.1
410 64.5−1539 351 282 299.6
Cu
64.8 55.7−78.0
25.5 20.3−29.3
338 72.8−1979 150−2920 15.9−2042
271 21−289 10.3−378
85.4 46.4−155 209 164 212.6
909 162−5500 575 1156 599.1
Zn
179 98.5−224
46.1 17.0−94.0
587 292−1454
680
1970
4589 1273−15639
2080
2917 653−8451
Fe
3.33 0.80−8.40
0.95 0.10−3.10
15.0 0.70−37.7
