Residues and Dietary Risk Assessment of Imidacloprid in Bamboo Shoot (Phyllostachys praecox), Winter Jujube (Ziziphus jujuba Mill. cv. Dongzao), Dendrobium officinale Kimura et Migo, and Fritillaria

Abstract

The widespread use of pesticides poses significant risks to food and environmental safety. Imidacloprid is one of the most effective neuroactive neonicotinoid insecticides and is effective against a broad spectrum of piercing–sucking pests. A rapid, efficient, and high-throughput analysis method for the determination of imidacloprid was developed in four minor crops with six matrices (bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria) by solid-phase extraction and HPLC-MS/MS. The procedure showed satisfying recoveries (72~111%) and RSDs (1~13%). A total of 288 samples were tested in China (Aba and Luan). Imidacloprid residues were 100% detected in fresh and dry D. officinale and winter jujube, with concentrations ranging from 0.048 to 1.550 mg·kg⁻¹. Imidacloprid residues were also abundant in fresh and dry Fritillaria (maximal concentration of 0.021 and 0.063 mg·kg⁻¹, respectively), followed by bamboo shoot, which had the lowest detection rate of imidacloprid (6%). Using the risk quotient (RQ) method, the long-term (RQ_c) and short-term (RQ_a) dietary risks of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria were further monitored. Based on the imidacloprid residues in this paper, the RQ_c and RQ_a were 15.03% and 0.0008~1.7604%, respectively. The RQ values were far less than 100%, showing that Chinese consumers face little health risk as a result of imidacloprid intake.

1. Introduction

The demand for controlling pests and diseases has often been addressed by an increase in the usage of pesticides, especially in some developing countries because of a general lack of stringent regulations on pesticide production and use. Past studies have shown that only a small proportion of pesticides are active on target crops due to application technique, plant properties, and droplet rebound. About 80% of pesticides are lost, which can lead to soil, sediment, and freshwater ecosystem pollution, and can even have a negative impact on human health [1,2]. Therefore, pesticide residue detection is increasingly important for monitoring environmental pollution, which is directly related to human health.

Neonicotinoids, which have low toxicity to mammals and high activity against pests and insects (whiteflies, aphids, beetles, and some Lepidoptera species), have become the most frequently used insecticides worldwide [3]. In 2014, the neonicotinoid market exceeded 3 billion and accounted for about 25% of the global pesticide market [4,5]. Imidacloprid was the first neonicotinoid insecticide developed for commercial use [6], and it accounted for 41.5% of the entire neonicotinoid market in 2009, making it one of the most popular insecticides in the world [7,8].

Numerous studies have demonstrated that imidacloprid was the most frequently detected pesticide among neonicotinoids. For example, according to a survey conducted in Hangzhou, China (HZC), 7 neonicotinoids were confirmed in 134 fruit and vegetable samples, with imidacloprid being the most commonly detected (66% frequency) [9]. Yuan et al. stated that imidacloprid was detected with the highest detection rate (92%) in 12 samples of Taiwanese tea, with the highest concentration of 0.75 mg·kg⁻¹, exceeding the standards of China (0.5 mg·kg⁻¹) and the EU (0.05 mg·kg⁻¹) [10]. The results of Yu et al. [11] showed that imidacloprid residue concentrations were up to 0.005~0.12 mg·kg⁻¹ in Zizania latifolia and purple sweet potato. Higher use of imidacloprid in various crops increases the risk of human exposure, and there are some adverse effects on human health, such as chronic diseases and birth defects [12,13,14]. Moreover, studies have found that imidacloprid had many direct serious adverse effects on non-target organisms (especially honeybees) [15]. Therefore, the investigation of imidacloprid residues is of significant importance to ensure food safety and human and ecosystem health.

Minor crops refer to those with a limited cultivated area, limited consumption, and limited economic benefit compared with major crops [16]. The use of pesticides to control diseases and pests in minor crops is a significant global issue that has an impact on the quality and safety of minor agricultural products due to the limited type and number of pesticides registered for these target crops [17]. There are many kinds of minor crops in China, including 12 classes of 375 species, such as seasonings, medicinal plants, feed, and flowers [18]. Therefore, the food security of minor agricultural products is very important to the Chinese. What is more, this is very much in line with Xi’s “broad food view” concept in the 20th National Congress of the Communist Party of China [19]. For minor crops, bamboo shoot, winter jujube, D. officinale, and Fritillaria were chosen as representative commodities in this study. At present, imidacloprid has been registered and permitted to control bamboo shoot aphids, winter jujube miridae, D. officinale aphids, and Fritillaria grubs [20], but there has been little investigation on imidacloprid residues in these crops. Therefore, in order to improve the quality and safety of minor agricultural products as well as the healthy development of our characteristic agriculture, we should further pay more attention to the problem of pesticide residues in minor crops.

Currently, GC or LC with a mass spectrometer (MS) or tandem mass spectrometer (MS/MS) has been routinely used in the development of analytical methods for neonicotinoid residues [21]. The purpose of this study was to: (i) establish a method for the determination of imidacloprid residues in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria; (ii) investigate the residual levels of imidacloprid by established methods in 288 samples collected from Aba (Sichuan Province, China) and Luan (Anhui Province, China); and (iii) conduct a short-term and long-term dietary risk assessment for Chinese consumers based on the results of the food consumption data and the residue levels. These data provide a reference for the safe use of imidacloprid.

2. Materials and Methods

2.1. Chemicals and Reagents

Imidacloprid standard (99% purity) was acquired from Zhejiang Tide Crop Technology Co., Ltd. (Hangzhou, China). LC-grade acetonitrile, methanol, methylbenzene, and acetone were purchased from Merck KGaA (Darmstadt, Germany). Analytical grade acetonitrile and formic acid were purchased from Shanghai Lingfeng Chemical Regent Co., Ltd. (Shanghai, China). Nylon syringe filter (0.22 μm) was purchased from Tianjin Bonna-Agela Technologies Co., Ltd. (Tianjin, China). Sep-Pak Vac NH₂ cartridge (6 cc/500 mg), Sep-Pak C₁₈ cartridge (6 cc/500 mg), and Sep-Pak florisil cartridge (6 cc/500 mg) were obtained from Waters Technologies (Shanghai, China).

2.2. Preparation of Standard Solutions

A standard stock solution was prepared by dissolving accurately weighed 0.0508 g of imidacloprid standard in 50 mL volumetric flasks with LC-grade acetonitrile to obtain a final concentration of 1006 mg·L⁻¹. Standard working solutions for plotting calibration curves were prepared by serial dilution of the stock solution of imidacloprid in acetonitrile. All solutions were labeled and stored in dark glass bottles at 4 °C.

2.3. Sample Collection

Bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria were randomly collected from markets, the indicated cultivation regions, and e-commerce companies in the major production regions of Aba (Sichuan Province, China) and Luan (Anhui Province, China). A total of 288 samples were collected from June to November 2021, half from Aba and half from Luan. Each sample was at least 5 kg (dry D. officinale and dry Fritillaria were each 1 kg) in weight and classified by quartering. All samples were stored at −20 °C until analyzed.

2.4. Sample Extraction and Clean-Up

2.4.1. Sample Extraction

Several grams of chopped and homogenized samples (bamboo shoot, winter jujube, fresh D. officinale, and fresh Fritillaria: 5.0 g; dry D. officinale and dry Fritillaria: 2.0 g) were accurately weighed into an 80 mL centrifuge tube, and 40 mL of acetonitrile was added. The mixture was vigorously shaken at 350 r·min⁻¹ for 10 min. NaCl (5 g) was added to the sample followed by shaking for 5 min, and 4 mL of acetonitrile layer was transferred into a round-bottom flask and then concentrated to nearly 1 mL with a rotary vacuum evaporator at 40 °C.

2.4.2. Sample Clean-Up

The Sep-Pak Vac NH₂ cartridge was preconditioned with 4 mL of acetonitrile–methylbenzene (75/25, v/v). Then, 1 mL extract solution was loaded onto the cartridge. The residue of the extracts was re-washed 3 times with 6 mL of acetonitrile–methylbenzene (75/25, v/v) and then loaded onto the cartridge, and 15 mL of acetonitrile–methylbenzene (75/25, v/v) was added directly to the cartridge. The eluates were collected in a round-bottom flask and evaporated to near dryness in a vacuum rotary evaporator at 40 °C and completely dried under nitrogen purge. Ultimately, the residues were re-dissolved with 10 mL (dry D. officinale and dry Fritillaria in 4 mL) of acetonitrile–water (60/40, v/v), and the mixtures were filtered through a 0.22 μm nylon syringe filter for HPLC-MS/MS analysis.

2.5. HPLC-MS/MS Analysis

The HPLC-MS/MS analysis used a triple-quadrupole mass spectrometer (XEVO TQ MS, Waters, Riddle, OR, USA) in positive electrospray ionization (ESI+) mode. A reversed-phase column (Acquity HPLC BEH C₁₈, 2.1 × 100 mm, 1.7 μm) was used for the chromatographic separation. The mobile phase was acetonitrile/aqueous 0.1% formic acid (60:40, v/v) at a flow rate of 0.2 mL·min⁻¹. The sample injection volume was 5 μL. The column temperature was kept at 35 °C, and the temperature in the sample manager was set to 10 °C. Typical instrumentation conditions: source temperature: 150 °C, desolvation temperature: 400 °C, cone gas flow: 50 L·h⁻¹, desolvation gas flow: 800 L·h⁻¹. Multiple reaction monitoring (MRM) mode was used for detection. The m/z 256.07→m/z 209.13 (collision energy: 14 eV) and m/z 256.07→m/z 175.06 (collision energy: 20 eV) were employed in the quantification and identification of imidacloprid, respectively.

2.6. Validation Study

Matrix effect (ME), linearity, limit of detection (LOD), limit of quantification (LOQ), and precision and accuracy were examined for assessing the practicability of the proposed method. The existence of ME affected the selectivity and sensitivity of analytical methods and consequently the accuracy and precision of the results. The linearity was determined via matrix-matched curves established by testing a series of calibration standards in the matrix and solvent. The LOD was set as the lowest concentration of the matrix-matched curve, and the LOQ was set as the lowest spiked level. The precision and accuracy of this method were checked by recovery experiments with satisfactory recovery (70~120%) and precision (relative standard deviation, RSD < 20%) [22], which were conducted by fortifying blank bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria with the standard solutions at 3 different spiking levels. Each spiking level was repeated five times.

2.7. Statistical Analysis and Dietary Risk Assessment

Matrix effects were calculated with Equation (1) [23]:

ME (%) = (slope_(matrix) − slope_(solvent))/slope_(solvent) × 100%,

(1)

where slope_(matrix) and slope_(solvent) are the slopes of the calibration curves of matrix and solvent standards, respectively. |ME| < 20% represents moderate effects, 20% ≤ |ME| ≤ 50% represents medium effects, and |ME| > 50% represents strong effects [24].

The long-term exposure assessment of imidacloprid was calculated according to Equations (2) and (3) [25]:

NEDI = ∑ (MN × FI),

(2)

RQ_c (%) = (NEDI/ADI × bw) × 100,

(3)

The short-term exposure assessment of imidacloprid was calculated according to the following Equations (4) and (5) [25]:

NESTI = HR × LP,

(4)

RQ_a (%) = (NESTI/ARfD × bw) × 100,

(5)

where NEDI is the national estimated daily intake (mg bw), MN is the median residues detected in this study (mg·kg⁻¹), FI is the reference daily food intake (kg·day⁻¹), bw is the body weight of an average adult Chinese person, and ADI (mg·kg⁻¹ bw) is the acceptable daily intake. NESTI is the national estimated short-term intake (mg), HR is the highest residue level (mg·kg⁻¹), LP is the maximum daily consumption (kg·d⁻¹), ARfD is the acute reference dose (mg·kg⁻¹ bw), and RQ is the risk quotient. If RQ exceeds 100%, there might be a risk [26].

3. Results and Discussion

3.1. Method Optimization and Validation

3.1.1. Optimization of Extraction Solvents

In pesticide residue analysis, the choice of extraction solvent is pivotal to the extraction effect. We tested acetonitrile and acetone as extraction solvents to determine the imidacloprid residues. We added 0.1 mg·kg⁻¹ imidacloprid into the blank matrix in 5 replicates (n = 5) which stood for 30 min. After the target and the matrix were fully absorbed, 40 mL of acetonitrile or acetone was added to extract imidacloprid. Finally, the extraction efficiency of the two extraction solvents was evaluated with the recovery ± RSD. The results are shown in Figure 1A. The average recoveries of imidacloprid in all matrices were 83~104% with RSD between 3% and 6% using acetonitrile as the extraction solvent, and the average recoveries were 73~110% with RSD between 4% and 8% using acetone as the extraction solvent, which all met the experimental criteria. Compared with acetone, acetonitrile had less impurity interference and was easier to obtain. Therefore, acetonitrile was selected as the extraction solvent in this experiment.

3.1.2. Optimization of Purification Methods

At present, purification methods mainly include solid-phase extraction (SPE) and QuEChERS extraction. The QuEChERS method was used to determine simple substrates such as vegetables and fruits [27]. Considering the large differences among the four minor crops (bamboo shoot, winter jujube, D. officinale, and Fritillaria), we chose SPE as the purification method. In the SPE purification method, different SPE cartridge types have different functional groups and retention mechanisms. In this study, the effects of different SPE cartridges including C₁₈, florisil, and NH₂ on the purification of four minor crops were investigated using 5.0 g samples (dry D. officinale and dry Fritillaria, 2.0 g) spiked with imidacloprid at 0.1 mg kg⁻¹. A total of 40 mL of elution solvent (acetonitrile–methylbenzene (v/v, 75/25) for the NH₂ cartridge; hexane–acetone (v/v, 90/10) for the florisil cartridge; and methanol–water (v/v, 90/10) for the C₁₈ cartridge) was used for the elution of imidacloprid. The purification efficiency was also illustrated by recovery, which was calculated by dividing the peak area of imidacloprid from a pre-extraction spiked sample by the peak area of imidacloprid from a post-extraction spiked sample. As shown in Figure 1B, the recovery of the C₁₈ cartridge was too small (21~62%) to achieve a suitable purification efficiency. C₁₈ mainly extracts weakly polar compounds (polycyclic aromatic hydrocarbons, phthalates, and polychlorinated biphenyls), while imidacloprid is a polar compound, which may be the cause of the low recovery [28]. When the SPE cartridge was a florisil cartridge, the recoveries of bamboo shoot, winter jujube, fresh D. officinale, and fresh and dry Fritillaria were all suitable (79~92%) but not of dry D. officinale (60% lower recovery). Moreover, compared with the C₁₈ (21~62%) and florisil (60~92%) cartridges, the NH₂ cartridge had a higher recovery (81~108%). Therefore, we ultimately chose NH₂ for the purification method for our research.

3.1.3. Optimization of MS Parameters

In order to improve the selectivity and sensitivity of the instrument, the main ion parameters (cone voltage, collision energy, etc.) were optimized. The imidacloprid standard solution with a concentration of 0.2 mg·L⁻¹ was mixed with the mobile phase (acetonitrile/aqueous 0.1% formic acid = 50:50, flow rate: 0.2 mL·min⁻¹) in the combined mode and injected into the mass spectrometer. The parent ion was found by adjusting the capillary voltage and the cone voltage. The intellistart automatic optimization function was used to obtain the optimal cone voltage and collision energy, and the qualitative ion and quantitative ion pairs were determined. The detailed optimized parameters are summarized in Section 2.5.

3.1.4. Method Validation

To evaluate the performance of the established method, the method was validated in terms of the matrix effect (ME), linearity, precision and accuracy, limit of detection (LOD), and limit of quantification (LOQ).

The ME resulting from the matrix co-eluting components was unavoidable when measuring pesticide residues, which can be evaluated by comparing the solvent calibration curves and matrix-matched calibration curves [29]. The results in

Table 1. Linearity range, linear equation, regression coefficient (R²), and matrix effect (ME) of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria.

Matrix	Linearity Range/mg·L−1	Linear Equation	R2	ME/%
Bamboo shoot	0.0001~0.1	y = 17048060x + 699	0.9999	2.15
Winter jujube	0.0001~0.1	y = 37657079x + 3966	0.9987	−8.11
Fresh D. officinale	0.00005~0.1	y = 16343565x + 458	0.9995	−14.37
Dry D. officinale	0.00005~0.1	y =38362227x + 641	0.9999	−17.92
Fresh Fritillaria	0.0001~0.1	y = 16081276x + 676	0.9988	−16.26
Dry Fritillaria	0.0001~0.1	y = 37213329x + 496	1.0000	−25.36

show a significant signal suppression effect for imidacloprid in dry Fritillaria (ME = −25.36%). The other matrices observed were moderate, with the bamboo shoot at 2.15%, winter jujube at −8.11%, fresh D. officinale at −14.37%, dry D. officinale at −17.92%, and fresh Fritillaria at −16.26%. These results indicated that the signal response of imidacloprid was influenced by the above matrices, especially dry Fritillaria. Therefore, to acquire more reliable results, the quantification of imidacloprid residues was performed with matrix-matched calibration in this study. To compensate for the ME, the linearity of the method was performed by using matrix-matched standard solutions at 7 concentrations within 0.00005/0.0001~0.1 mg·L⁻¹. Linearity was evaluated using the regression coefficient (R²), and it was determined by plotting the peak area (y) against the concentrations (x) of imidacloprid. All the R² values of bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria ranged from 0.9987 to 1.0000, which satisfied the requirements of the residue analysis.

To evaluate the precision and accuracy of the present method, three concentration levels of imidacloprid standard solution (

Table 2. Recovery, relative standard deviation (RSD), limit of quantitation (LOQ), and limit of detection (LOD) for imidacloprid in three spiked levels from bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria.

Matrix	Spiked Level /mg·kg−1	Recovery /%	RSD /%	LOQ /mg·kg−1	LOD /mg·kg−1
Bamboo shoot	0.01	99	7	0.01	0.0001
	0.1	102	4
	3	98	1
Winter jujube	0.01	107	6	0.01	0.0001
	0.5	88	1
	5	89	3
Fresh D. officinale	0.01	104	5	0.01	0.00005
	0.5	85	3
	2	90	3
Dry D. officinale	0.01	111	5	0.01	0.00005
	0.5	103	3
	3	87	3
Fresh Fritillaria	0.01	87	13	0.01	0.0001
	0.05	88	2
	3	93	3
Dry Fritillaria	0.01	79	4	0.01	0.0001
	0.2	82	4
	3	72	1

) were spiked into the blank bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria samples in five replicates. The representative chromatograms of the blank, matrix-matched standard solution, and fortified samples for the different commodities are shown in Figure 2. The average recoveries ranged from 72% to 111% (98~102% for bamboo shoot, 88~107% for winter jujube, 85~104% for fresh D. officinale, 87~111% for dry D. officinale, 87~93% for fresh Fritillaria, and 72~82% for dry Fritillaria), with the associated relative standard deviations (RSDs) in the range of 1~7%, 1~6%, 3~5%, 3~5%, 2~13%, and 1~4% for the respective matrices. These results confirmed that the method met the requirements of the validation criteria. LOD was 0.0001 mg·kg⁻¹ in bamboo shoot, winter jujube, and fresh and dry Fritillaria and 0.00005 mg·kg⁻¹ in fresh and dry D. officinale. The LOQ in all matrices was 0.01 mg·kg⁻¹ corresponding to the lowest spiked concentration. The results showed that the analytical method had good linearity and reliability and could accurately detect imidacloprid.

3.2. Residues of Imidacloprid in Bamboo Shoot, Winter Jujube, Fresh and Dry D. officinale, and Fresh and Dry Fritillaria

Using the established method, we measured the residues of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria collected from Aba (Sichuan Province, China) and Luan (Anhui Province, China) with 48 samples per matrix. The results are shown in

Table 3. Minimal, maximum, and median concentrations and detection rates of imidacloprid in collected samples.

Matrix	Min /mg·kg−1	Max /mg·kg−1	Median /mg·kg−1	Detection Rate /%	MRL /mg·kg−1
Bamboo shoot	n.d. *	0.050	0.050	6	0.1
Winter jujube	0.048	1.550	0.500	100	5
Fresh D. officinale	0.192	0.966	0.552	100	2
Dry D. officinale	0.887	1.280	1.080	100	3
Fresh Fritillaria	n.d.	0.021	0.018	50	0.05
Dry Fritillaria	n.d.	0.063	0.056	75	0.2

* n.d. = non-detect.

. Imidacloprid was found in all of the matrices, indicating frequent use of imidacloprid in the four minor crops. The detection rate of imidacloprid in the 6 substrates was: fresh D. officinale (100%) = dry D. officinale (100%) = winter jujube (100%) > dry Fritillaria (75%) > fresh Fritillaria (50%) > bamboo shoot (6%); the maximum concentration was: winter jujube (1.55 mg·kg⁻¹) > dry D. officinale (1.28 mg·kg⁻¹) > fresh D. officinale (0.966 mg·kg⁻¹) > dry Fritillaria (0.063 mg·kg⁻¹) > bamboo shoot (0.05 mg·kg⁻¹) > fresh Fritillaria (0.021 mg·kg⁻¹); and the median concentration was: dry D. officinale (1.08 mg·kg⁻¹) > fresh D. officinale (0.552 mg·kg⁻¹) > winter jujube (0.5 mg·kg⁻¹) > dry Fritillaria (0.056 mg·kg⁻¹) > bamboo shoot (0.05 mg·kg⁻¹) > fresh Fritillaria (0.018 mg·kg⁻¹). It can be seen that, compared with fresh and dry Fritillaria and bamboo shoot, the detection rates and detection concentrations of fresh and dry D. officinale and winter jujube were higher. Moreover, the difference between the maximum imidacloprid concentration of winter jujube (1.55 mg·kg⁻¹) and fresh Fritillaria (0.021 mg·kg⁻¹) was 74 times, and the minimum imidacloprid concentration of dry D. officinale (0.887 mg·kg⁻¹) was 42 times greater than the maximum imidacloprid concentration of fresh Fritillaria. It can also be seen that the residues of imidacloprid in the different crops varied greatly, which might be affected by various factors, including crop type, pesticide dosage, weather conditions, etc. [30,31]. In different states of the same crop, the residues of imidacloprid were also different. For example, imidacloprid residues in dry D. officinale (or dry Fritillaria) were higher than in fresh D. officinale (or fresh Fritillaria), which might be caused by drying reducing the water content [32]. In addition, imidacloprid may be metabolized into 6-chloronicotinic acid and imidacloprid-olefin in the environment, which still has high toxicity to target pests [33]. In all matrices, imidacloprid did not exceed the maximum residue limit (MRL) set by the national standard GB 2763-2021 [26], indicating that the residues of imidacloprid in the Aba and Luan samples were within a reasonable range.

3.3. Dietary Risk Assessment of Imidacloprid in Bamboo Shoot, Winter Jujube, Fresh and Dry D. officinale, and Fresh and Dry Fritillaria

Currently, the presence of pesticide residues in food has drawn mounting concern from the public. Consequently, risk quotient (RQ) values were calculated in order to assess the dietary exposure risk for Chinese consumers. RQ refers to a point estimate of the measured or predicted exposure concentration divided by a toxicity reference value. Typically, if RQ values are >100%, it indicates an unacceptable risk for common consumers. If RQ values are < 100%, it presents an acceptable risk to human health.

3.3.1. Long-Term Consumer Exposure

Based on the residue results obtained in this study, dietary exposures for different food categories were calculated. All residue data and food categories are shown in

Table 4. The long-term dietary risk assessment of imidacloprid in different food.

Food Category	Commodity	FI 1 /kg·day−1	MRL 2 /mg·kg−1	Source of Reference Limit	NEDI 4 /mg	ADI 5 /mg·kg−1	RQc 6 /%
Rice cereals and rice products	rice	0.2399	0.05	China	0.012	ADI × 63
Wheat cereals and wheat products	wheat	0.1385	0.05	China	0.006925
Other cereal grains	maize	0.0233	0.05	China	0.001165
Potatoes	potato	0.0495	0.5	China	0.02475
Dried beans and their products	beans(dry)	0.016	0.05	China	0.0008
Dark-colored vegetables	spinach	0.0915	5	China	0.4575
Light-colored vegetables	bamboo shoot	0.1837	0.05	MN 3	0.009185
Pickles		0.0103
Fruits	winter jujube	0.0457	0.5	MN	0.02285
Nuts		0.0039
Livestock and poultry		0.0795
Milk and milk products		0.0263
Egg and egg products		0.0236
Fish and fish products		0.0301
Oilseeds and oil	peanut kernel	0.0327	0.5	China	0.01635
Animal-origin oil and fat		0.0087
Sugars and starch	sugarcane	0.0044	0.2	China	0.00088
Salt	tea	0.012	0.5	China	0.006
Soy sauce	dry D. officinale	0.009	1.08	MN	0.00972
Total		1.0286			0.5681	3.78	15.03

¹ FI, recommended dietary food intake for its corresponding food classification; ² MRL, maximum residue limit of the relevant registered crops in China obtained from GB 2763-2021; ³ MN, the median concentration in this random sample test; ⁴ NEDI, national estimated daily intake; ⁵ ADI, acceptable daily intake; ⁶ RQ_c, the long-term dietary exposure risk probability.

. Based on the GB 2763-2021 reports, the acceptable daily intake (ADI) of imidacloprid was 0.06 mg·kg⁻¹ bw [26]. The average adult body weight was 63 kg [34]. The default assumption was that all of the registered crops were treated with imidacloprid. The total national estimated daily intake (NEDI) for imidacloprid was computed using the median residues (MNs) detected in this study. We classified bamboo shoot into the light-colored vegetables, winter jujube into the fruits, and D. officinale and Fritillaria into the soy sauce group (in accordance with the principle of maximizing risk, dry D. officinale was selected as the soy sauce group). As displayed in Table 3, the MNs of imidacloprid in bamboo shoot, winter jujube, and dry D. officinale were 0.05, 0.5, and 1.08 mg·kg⁻¹, respectively. The maximum residue limits (MRLs) of imidacloprid in the relevant registered crops in China were the same as the matched intake concentrations for the food category [26]. Thus, the total NEDI of imidacloprid was 0.5681 mg. Therefore, the RQ_c (the long-term dietary exposure risk probability) was 15.03%. As this was not beyond 100%, the result indicated that the long-term dietary exposure risk of imidacloprid was acceptable.

3.3.2. Short-Term Consumer Exposure

The short-term dietary risk assessment was conducted using maximum residual concentrations and the maximum consumption of bamboo shoot, winter dates, fresh and dry D. officinale, and fresh and dry Fritillaria to simulate a worst-case scenario. The highest residue (HR) was acquired from the maximum residue concentration of imidacloprid in our study. The HRs of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria were 0.05, 1.55, 0.021, 0.063, 0.966, and 1.28 mg·kg⁻¹, respectively. The consumption of large portion (LP) data of bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria were obtained from the Chinese Food Guide Pagoda, the Chinese Pharmacopoeia, and the Food and Agriculture Organization of the United Nations (FAO) [35,36,37]. The acute reference dose (ARfD) for imidacloprid was 0.4 mg·kg⁻¹ [38]. Thus, the national estimated short-term intake (NESTI) and RQ_a (the short-term dietary exposure risk probability) for Chinese consumers of bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria were 0.0250 mg and 0.10%, 0.4436 mg and 1.76%, 0.0002 mg and 0.0008%, 0.0006 mg and 0.0025%, 0.0580 mg and 0.23%, and 0.0154 mg and 0.06%, respectively (

Table 5. The short-term dietary risk assessment of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria.

Matrix	HR 1/mg·kg−1	LP 2/kg	NESTI 3/mg	RQa 4/%
Bamboo shoot	0.050	0.500	0.02500	0.0992
Winter jujube	1.550	0.2862	0.44361	1.7604
Fresh Fritillaria	0.021	0.0100	0.00021	0.0008
Dry Fritillaria	0.063	0.0100	0.00063	0.0025
Fresh D. officinale	0.966	0.0600	0.05796	0.2300
Dry D. officinale	1.280	0.0120	0.01536	0.0610

¹ HR, highest residue; ² LP, large portion; ³ NESTI, national estimated short-term intake; ⁴ RQ_a, the short-term dietary exposure risk probability.

). No RQ_a exceeded 100% which indicated that the short-term dietary exposure risk of imidacloprid in bamboo shoot, winter dates, fresh and dry D. officinale, and fresh and dry Fritillaria was acceptable for Chinese consumers.

4. Conclusions

In this study, solid-phase extraction (NH₂ cartridge) coupled with the HPLC-MS/MS method was developed for the determination of imidacloprid in the four minor crops (bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria). Imidacloprid residues in 288 samples collected from Aba (Sichuan Province, China) and Luan (Anhui Province, China) were detected using this method, and the risk of dietary exposure was assessed based on the research results.

The results showed that the method exhibited satisfactory performance regarding linearity (R² > 0.9987), accuracy (72~111% in all cases), and precision (RSDs < 13% in all cases) and provided a guarantee for the monitoring of imidacloprid in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria in large quantities. Imidacloprid residues in the collected samples were detected in low amounts (none exceeded MRL) in all matrices, but detection rates of up to 100% were found in winter jujube and fresh and dry D. officinale, followed by dry Fritillaria (75%), fresh Fritillaria (50%), and bamboo shoot (6%). Moreover, using the risk quotient (RQ) method, long-term and short-term dietary risk assessments of imidacloprid in China were performed. The results indicated that the RQ values were below 100% (RQ_c, 15.03%; RQ_a, 0.0008~1.7604%), showing that the dietary exposure risk of imidacloprid used in bamboo shoot, winter jujube, fresh and dry D. officinale, and fresh and dry Fritillaria was acceptable for Chinese consumers.