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Changes in people's dietary structure and consumption concepts have made wild vegetables rich in nutrition and have dietary and health care functions more and more popular. Wild vegetables are wild edible vegetables that grow naturally and are not artificially grown, and usually have certain medicinal properties. Such as dandelion (TaraxacummongolicumHand.Mazz.) With the effect of clearing heat and detoxification, reducing swelling and dissipating knots, diuresis and leaching, Ixeriscass has the effect of clearing heat and detoxification, cooling blood and reducing swelling, analgesic and anti-inflammatory. In addition to its special medicinal value, wild vegetables are also rich in nutrients, and studies have shown that they are rich in amino acids, proteins, fats, sugars, vitamins and minerals needed by the human body. The unique characteristics of wild vegetables meet the needs of people's pursuit of health, and have become dishes on the table, and wild vegetables grown in mountain forests, roadside groves, fields, parks, residential areas and other green spaces have become wild vegetable picking areas.
However, heavy metals present in natural environments such as soil, atmosphere and water will be enriched by the human body through the food chain, which may cause poisoning, cause diseases, and endanger human health. According to the limit standard of heavy metals in the "Safety Requirements for the Safety and Quality of Pollution-free Vegetables of Agricultural Products of the People's Republic of China", Wu Xiaohong et al. used the graphite furnace atomic absorption method to determine the content of lead and cadmium in wild vegetables in Nanjing, and found that the content of lead and cadmium in urban wild vegetables was mostly higher than the maximum limit. Sun Xiaohui et al. used graphite furnace atomic absorption method and atomic fluorescence spectrophotometry to determine the heavy metal content in five wild vegetables, including gray cabbage, cress, watercress, scissors and purslane, and found that the cadmium content of gray cabbage and cress exceeded the standard, and the content of lead and cadmium in purslane exceeded the standard.
It can be seen that while social progress is progressing, human activities have caused serious pollution to the natural environment, making the food safety of wild vegetables that are considered natural green foods worthy of attention when eaten. Some studies believe that the heavy metal pollution of copper, lead, zinc and cadmium in Beijing is mainly affected by human activities.
As a trace analysis technology, graphite furnace atomic absorption method has high atomization efficiency and better performance than other methods, and is widely used in the analysis of heavy metal content in different sample matrices. In this experiment, the copper and lead contents of wild vegetables in different regions of Beijing were determined by graphite furnace atomic absorption method under optimized instrument conditions after wet digestion, aiming to provide health risk evaluation for the food safety of wild vegetables in Beijing.
Materials and methods
TAS-990 atomic absorption spectrophotometer (Beijing General Instrument Co., Ltd.), equipped with GF-990 graphite furnace power supply and CW-1Y automatic temperature control cooling circulating water device (Beijing General Instrument Co., Ltd.), copper and lead element hollow cathode lamp (Beijing Shuguang Electronic Light Source Instrument Co., Ltd.), horizontal platform graphite tube (Beijing General Instrument Co., Ltd.), AAWinv2.1 operating software (Beijing General Instrument Co., Ltd.), high-purity argon(pressure 0.5 MPa), 10 μL pipette gun (German Eppendorf).
SX-4-10 type box-type resistance furnace and control box (Tianjin Teste Instrument Co., Ltd.), DB-3 stainless steel electric heating plate (Jintan Fuhua Instrument Co., Ltd.), 101-0AB type electric heating blower drying box (Tianjin Tester Instrument Co., Ltd.). The crucible used is burned empty in a resistance furnace at 250 °C for 4h, heated to 550 °C for 2h, 600 °C for 1h, cooled and continued the above process once, cooled and put into a dryer for use.
All glassware (volumetric flasks, graduated cylinders, pipettes, etc.) are washed and soaked with dilute nitric acid overnight, rinsed with deionized water, and dried in an air blast drying oven for use. Reference Materials for Compositional Analysis (GBW10014, GSB-5, Institute of Geophysical and Geochemical Exploration); Nitric acid (excellent grade pure, Sinopharm Chemical Reagent Co., Ltd.); Copper standard solution (GSB05-1117-2000) and lead standard solution (GSB07-1282-2000) are both 500μg/mL (Institute of Standard Samples, Ministry of Environmental Protection); Ultrapure water, its resistivity is 18.2MΩ·cm@25°C.
Instrument operating parameters
The working conditions of the atomic absorption spectrophotometer are shown in Table 1, and the heating procedure of the graphite furnace is shown in Table 2.
Table 1
Table 2
After the fresh samples of dandelion and bitter pickles were collected, they were rinsed with deionized water (to remove the surface material of wild vegetables), baked in a blast drying oven at 60 °C for about 30min to dry (dried with moisture on the surface of wild vegetables), chopped and mixed well. Weigh 1.0000g of the mixed sample, put it in a porcelain crucible, move it into a resistance furnace and ash it at 550 °C for 1h, add 5mL of nitric acid after cooling, heat it on the electric hot plate and stir carefully until dry, move it to the resistance furnace at 550 °C to continue ashing for 1h, add 2mL of nitric acid after cooling and heat it until there are no carbon particles in the residue, dissolve it 3 times with 1mL dilute nitric acid (1:5), filter it into a 10mL volumetric flask respectively, and dilute it to the scale with ultrapure water. Pipette the resulting 1mL solution, set the volume to 10mL, pipette 5mL through the 0.22μm filter membrane, and parallel each sample three times. Do reagent blank test and quality control experiment according to the same method, three times parallel.
Under the working conditions of 2.3, the standard curve of each element is made, and each sample is measured according to the standard curve. Each specimen is measured in 5 replicates.
Respectively, 1mL of copper and lead standard solution were sucked into a 100mL volumetric flask, and the volume was fixed to the scale with 0.5% nitric acid, and then diluted step by step into copper standard working solution with a concentration of 0, 50.0, 100.0, 150.0, 200.0ng/mL and a lead standard working solution with a concentration of 0, 20.0, 40.0, 80.0, 100.0ng/mL, respectively. The standard curves of copper and lead were plotted with concentration (c) as abscissa and absorbance (A) as ordinate, and the linear regression equation and correlation coefficient (r) were determined, and the results showed (Figure 1) that the absorbance and concentration of the elements to be measured of copper and lead showed a good linear relationship. where ACu=0.0064c+0.0852, r=0.9981; APb=0.0043c-0.0032,r=0.9996。
Precision and recovery experiments
The accuracy of the experimental method was investigated, the quality control experiment was carried out, and the component analysis standard was analyzed and determined according to the experimental method (n=3), and the reagent blank experiment was done at the same time. The results showed that the copper content (standard value was 2.7±0.2mg/kg) in the composition analysis standard was 2.76mg/kg, and the RSD was 2.15%. The content of lead in the compositional analysis standards (standard value 0.19±0.03 mg/kg) was 0.21 mg/kg and RSD was 1.89%. The experimental method accuracy meets the requirements.
The reliability of the experimental method was investigated, and the standard sample addition method was used to carry out the spike recovery experiment. Accurately weigh 1.0000g of component analysis standard, quantitatively add copper and lead standard solution, determine it according to the test method, do the reagent blank test at the same time, repeat three times, and calculate the recovery rate and relative standard deviation. The results showed that the recovery rate of copper was between 97.2%~99.5%, and the RSD was 2.51%. The recovery rate of lead element was between 99.1~102.5%, and the RSD was 3.24%. The test method is reliable.
Considering the prominence of heavy metal pollution in soil and crops on both sides of the road, the type of land use and agricultural structure in Beijing, and the characteristics of people's intake of wild vegetables, the two wild vegetables of bitter vegetables and dandelion were taken as the research objects, and wild vegetables were collected within an average of 10m on both sides of the traffic roads in six districts and counties of Changping, Haidian, Tongzhou, Shunyi, Fangshan and Yanqing, and wild vegetables were collected in Changping field area, Haidian mountain forest area, Tongzhou farmland area, Shunyi park area, Fangshan park area and Yanqing park area. Twenty sample sites were selected as representative samples for each region, and five sufficient amounts of bitter vegetables and dandelions were collected from each sample site. Samples were collected in April 2013.
Each sample is analyzed and tested according to the sample processing method and instrument working conditions, and the average value calculated three times is used as the copper and lead content of each sample, the average value of five samples per sample point is used as the copper and lead content of each sampling point, and the suspected copper and lead content values of each sampling point are excluded, and the range of copper and lead content in different sample collection areas in six districts and counties is shown in Table 3.
The results show that many wild vegetables are more likely to enrich heavy metal elements than ordinary vegetables, and heavy metals accumulate in the human body to a certain extent will cause poisoning, causing great damage to health. It can be seen from Table 3 that the copper content in bitter vegetables on both sides of the roads in the six districts and counties is between 3.90~14.83mg/kg and 0.23~1.82mg/kg.
The copper content in dandelion was between 4.26~14.54mg/kg and the lead content was between 0.17~0.61mg/kg; The copper content in bitter vegetables in fields, mountains and parks in six districts and counties was between 3.34~10.40mg/kg, lead content was between 0.06~0.29mg/kg, and the copper content in dandelion was between 2.91~6.16mg/kg and lead content was between 0.09~0.25mg/kg. It can be seen that the content of copper and lead in wild vegetables in the average 10m area on both sides of the traffic road is significantly higher than that in other sampling areas.
The U.S. EPA established a population health risk assessment method in 2000, through the parameter value to calculate the target hazard quotient (THQ), can evaluate the health risk of single heavy metal and polymetallic composite health risk at the same time, if the value is less than 1, indicating that the population has no obvious health risk, otherwise there is a health risk. The calculation formula is as follows, and the meaning and value of the parameters are shown in Table 4
Based on the calculation method and reference to domestic literature, according to the sample analysis results, the THQ of a single copper metal for adults and 0.690~2.624 for children, 0.229~2.453 for adults and 0.301~3.221 for children in an average 10m area of traffic roads on both sides of Beijing traffic roads were 0.229~2.453. The THQ of single copper metal for adults was 0.392~1.402, 0.515~1.857 for children, 0.081~0.392 for adults and 0.106~0.512 for children in wild vegetables in mountain forests, fields and parks in Beijing.
The THQ of copper-lead composite heavy metals in wild vegetables in the average 10m area of traffic roads in Beijing was 0.755~4.453 for adults and 0.991~5.845 for children. The THQ of copper-lead composite metal in wild vegetables in mountain forests, fields and parks in Beijing was 0.473~1.794 for adults and 0.621~2.369 for children. It can be seen that eating non-artificially grown wild vegetables in Beijing has obvious health risks to the population, and children are more likely to cause heavy metal health risks.
Table 3
Table 4
The content of copper and lead in wild vegetables in an average area of 10m on both sides of the traffic road was significantly higher than that in other sampling areas, indicating that the heavy metal pollution of copper and lead in wild vegetables in the average area of 10m on both sides of the traffic road was relatively serious. The results of the health risk evaluation of polymetallic composite show that the consumption of non-artificially grown wild vegetables in Beijing has obvious health risks to the population, and the heavy metal health risks caused by wild vegetables (especially children) are worthy of attention, and the occurrence of food safety problems is prevented.