1. Introduction
Nowadays, it is believed that the vegetables and food obtained from them are a crucial part of the daily human diet [
1]. These products are considered one of the best sources of essential nutrients and bioactive compounds [
2]. In addition, many studies suggest that the intake of vegetables positively affects consumer health. Regular consumption of vegetables can positively affect the prevention of many diseases, such as cancer (colorectal and breast cancer [
3,
4]) and cardiovascular diseases [
5].
Red beetroot (
Beta vulgaris L.
subsp. vulgaris) is one of the most popular vegetables with a valuable source of vitamins, minerals, and bioactive compounds [
6]. Due to the high contents of phytochemicals, intake of this vegetable may indicate positive, beneficial effects for consumers. Red beetroot shows anti-neurodegenerative, antitumor, anti-inflammatory, antibacterial, antiviral, cardioprotective, and lipid peroxidation inhibitory activities [
7]. Moreover, this vegetable is trendy in the food industry. It produces many red beetroot products or additives (drinking and concentrated juices, yoghurts, and frozen foods) and prepares natural red dyes [
6]. On the other hand, red beetroot may contain other compounds, such as perfluoroalkyl substances (PFASs) [
2].
These molecules are a wide range of synthetic organofluorine compounds which have been based used in the industry [
8]. They are a group of organofluorine compounds, aliphatic hydrocarbons, in which all or almost all hydrogen atoms are replaced with fluorine. They consist of a hydrophobic alkyl chain of varying lengths (typically C4 to C16) and a hydrophilic end group, which may be fully or partially fluorinated. PFASs are classified as persistent and bioaccumulative substances [
9]. They are a diverse group of compounds with high thermal, chemical, and biological inertness [
10,
11]. PFASs remain stable in the presence of acids, bases, oxidants, and reductants. Furthermore, they exhibit high resistance to degradation by photolytic or metabolic processes and microbial decomposition. Nevertheless, their widespread use led to contamination of the environment, which, as a consequence, led to the exposure of these compounds in humans and animals [
8,
12]. PFAAs are ubiquitous in various environmental media and are distributed globally. Due to their ability to migrate, they can be transferred from water to soils, taken up by plants, and thus enter the food chain. These substances enter the human body through the digestive, respiratory systems, and skin. Moreover, they are not metabolized and accumulate in the body [
13]. Furthermore, direct and indirect contact with PFAS-containing materials such as oil and water-resistant materials, detergents, paints, and fabrics causes high exposure of humans to their toxic properties [
11]. In living organisms, high absorption levels and low elimination rates of PFASs have been observed [
14].
Researchers confirmed that PFASs exist in human and animal tissues and blood (serum or plasma). Studies indicated that anionic PFASs were detected primarily in the human plasma/serum [
15]. Biomonitoring of PFASs in the human body started in 2000. Many PFASs have been detected in human matrices, most commonly in blood samples [
16,
17]. In recent years, a number of papers have confirmed the occurrence of these compounds in breast milk [
18], seminal plasma [
19], umbilical cord blood [
20], and liver [
21]. However, in contrast to most other persistent organic pollutants (POPs), they do not tend to accumulate in fat tissues but bind to serum albumin and other cytosolic proteins and accumulate mainly in the liver, the kidneys, and bile secretion [
22,
23]. In addition, positive associations were observed between levels of PFOS and PFOA detected in serum, and total cholesterol, low-density lipoprotein cholesterol, thyroxine and thyroid hormone concentrations [
24,
25].
PFASs are extensively applied in various industrial and consumer goods. Fluorosurfactants are more effective and efficient in surface activity than their hydrogenated analogues. These and other properties, such as high thermal, chemical, and biological stabilities, make PFASs perfect material for industrial and domestic applications [
26,
27]. Typical applications encompass the automotive and aviation industries (hydraulic fluids, low-friction bearings and seals, and materials for car interiors), construction technology (paints and coating additives and glues), biocides (herbicides and pesticides), electronics (flame retardants, weather resistant coatings, and insulators), household products (wetting and cleaning agents, nonstick coatings, and components of cosmetic formulations), medical articles (stain and water repellents in surgical equipment, raw materials for implants), and packaging materials (oil and grease repellent materials) and textiles (impregnating agents for fabrics, leather, and breathable membranes) [
11,
28,
29].
Due to the presence of PFAAs in ambient air, various consumer products, drinking water, and food, it has become necessary to assess their potential impact on human health accurately. Researchers have reviewed the occurrence of highly fluorinated compounds in human matrices in recent years, and there is indisputable evidence that their bioaccumulation potential in tissues is high [
30,
31]. However, there is uncertainty regarding the accumulation processes themselves and the acute or chronic toxicity effects due to variation of observed toxic response to PFAAs between species and genders within tested species. Varieties of PFASs have been detected in human blood (both in serum and plasma) [
8,
17,
32,
33] as well as in the umbilical cord [
34,
35] and maternal [
36,
37] blood. Besides blood, some PFASs have also been found in other human tissues. PFASs were predominantly found in the liver [
38,
39]. Furthermore, studies show some accumulation potential in the lungs, kidneys, bones, and the brain [
40]. Numerous recent studies have confirmed their presence in seminal plasma [
19], breast milk [
41] of lactating mothers, and umbilical cord blood, all drawing attention to their influence on the human reproductive system. In conjunction with the bioaccumulation and biomagnification potential of PFASs, these long half-lives can give rise to various processes within the living cell and lead to concern over their potential hazard to human health. Because of their capacity to modify surface properties, even on the molecular level, it is essential to elucidate their toxicity and toxicokinetic activity [
42].
Both PFOA and PFOS have shown moderate acute toxicity via ingestion. The oral LD50 levels assessed for PFOS were 230 and 270 mg kg
−g bw for male and female rats, respectively [
43]. In contrast to PFOS, PFOA is moderately toxic. The LD50 value in rats ranged from 430 to 680 mg kg
−g bw [
44]. The suspected toxic effects of PFASs include the following: liver toxicity, including liver hypertrophy [
45,
46]; liver cancer [
47]; disruption of lipid metabolism due to their effect on serum cholesterol and triglyceride levels [
16,
48]; function of the immune system, causing atrophy of the thymus and spleen or suppressed antibody responses [
49,
50,
51]; function of the endocrine system due to their effects on thyroid hormone levels (triiodothyronine (T3) and thyroxine (T4)) [
52,
53]; induction of adverse neurobehavioral reactions [
54]; tumor formation [
55]; prenatal and neonatal toxicity [
16]; decreased birth weight and size [
56]; and even obesity [
57]. Several studies cover the putative modes of action of PFASs on a cellular level, but these mechanisms still need to be fully defined. Nevertheless, due to the structural similarities of PFASs to endogenous fatty acids, these reactions can be partly attributed to their morphology, more precisely to activity resulting from their chemical structure. PFASs are characterized by the high tendency to noncovalent, intracellular binding to β-lipoproteins, albumin, and other plasma proteins, such as fatty acid-binding protein (L-FABP) [
22]. The proliferation of peroxisomes is one of the main reasons for liver toxicity observed in laboratory animal studies.
Considering all the aspects, this study aimed to determine the perfluoroalkyl substances' content in fermented red beetroot juice and human body fluids (blood plasma and urine) before and after intake of this product. The novelty of the work lies in linking dietary exposure to PFASs and blood parameters, bringing a new perspective to our understanding of these compounds. To our best knowledge, this paper is the first detailed and cross-sectional investigation of selected perfluoroalkyl substances in human body fluids after exposure to fermented red beetroot juice.
3. Materials and Methods
3.1. The Chemicals, reagents, and study material
Gradient reagents, including methanol, acetonitrile, formic acid, and water, were purchased from Sigma Chemical Co. (St. Louis, MO, USA). A native standard mixture of PFASs containing seven perfluorocarboxylic acids (PFCAs) such as perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) and three perfluoroalkane sulfonates (PFSAs), namely perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS) and perfluorooctane sulfonate (PFOS) prepared in methanol, with chemical purity of >98% each, purchased from Wellington Laboratories, Inc., (Guelph, ON, Canada). The isotopically labelled internal standards (ISs): perfluoro-n-[13C8] octanoic acid (13C8-PFOA) in methanol, with chemical purity of >98%, and sodium perfluoro-1-[13C8] octane sulfonate (13C8-PFOS) in methanol, with chemical purity of >98%, were obtained from Wellington Laboratories, Inc., (Guelph, ON, Canada). Auxiliary equipment such as MPW-351R Centrifuge (MPW Med. Instruments, Warsaw, Poland), Vacuum Concentrator Plus (Eppendorf AG, Hamburg, Germany) and ultrasonicator were used for sample preparation.
Stock, intermediate and working standard solutions of native PFASs and internal standards (13C8-PFOA and 13C8-PFOS named IS1 and IS2, respectively) were prepared in MeCN. Intermediate and working standard solutions of native PFASs with concentrations of 100 ng/mL and 1 ng/mL, respectively, were prepared by diluting the standards with the mixture of 20% MeOH in water (v/v) with the addition of 1% (v/v) of FA. Internal standard solutions were prepared according to the above procedure.
Fermented red beetroot juice was specially prepared for this study by the fruit and vegetable processing company s headquartered in Poland.
3.2. Characteristic of participants and study design
The subjects who met the inclusion criteria (body mass index (BMI) under 30; without gastrointestinal disturbances, including gastric and duodenal ulcers; they could not participate in other clinical trials within 90 days before the survey, take drugs, abuse alcohol, be pregnant and breast-feeding, or take any medications or vitamin supplements), and they had to be certified healthy at a medical interview were accepted to the study. Ultimately, 24 healthy subjects, 5 males and 19 females, aged between 24 and 40, participated in the experiment (
Table 4).
The study was conducted for six weeks (42 days). For 42 days, once a day, volunteers consumed a dose of the fermented beetroot juice (200 mL/60 kg of body weight) directly after breakfast. Every 7 days, the health status of all volunteers was assessed by the doctor, and they received the fermented beetroot juice for the next week. Under fasting conditions, before consumption (sample zero), and at the end of the experiment, the blood samples were taken into heparinized vacutainers and then centrifuged (500 × g, 15 min, 1000 × g, 10 min, 4°C). According to the above sampling scheme (0 and 42 days), urine samples were collected from the volunteers. After that, the separated plasma and collected urine were frozen and stored at 80°C until analysis. The study design is presented in
Figure 2.
3.3. Ethical aspects
The experimental design and procedure were accepted by the Bioethical Committee at the Faculty of Medical Science of the University of Warmia and Mazury in Olsztyn (Poland, No. 7/2015). All volunteers were fully informed about the potential benefits and risks and signed an informed consent form. Moreover, the study was conducted under medical supervision in the NZOZ Atarax Clinic in Olsztyn, Poland.
3.4. Plasma and urine samples preparation
The content of perfluoroalkyl substances was determined in the plasma and urine samples. The plasma samples were prepared according to Rotander et al. [
68]. Briefly: 200 µL of plasma with 4 µL of ISs solution (2.5 µg mL-1) was extracted with 1.5 mL 100% acetonitrile (MeCN) using ultrasonication followed by vortex extraction, centrifugation and evaporation to dryness in a vacuum concentrator. The residue was reconstituted with 100 µL of MeOH. Before the micro-HPLC-MS/MS analysis, samples were diluted fivefold in deionised water with 1% (v/v) of FA addition to the final volume of 500 µL. The same analytical procedure was applied to blank samples. Each sample for the assay was prepared in triplicate.
The urine samples were prepared according to Perez et al. [
69]. Briefly: 500 µL of urine with 3.2 µL of ISs solution (2.5 µg mL-1) was mixed. Precipitation of traces of protein was induced by mixing the samples with acetonitrile (1:1). After centrifugation at 4000 rpm for 10 min, 400 µL of the supernatant was transferred to a PP tube and evaporation to dryness in a vacuum concentrator. The residue was reconstituted with 80 µL of MeOH. Before the micro-HPLC-MS/MS analysis, samples were diluted fivefold in deionised water with 1% (v/v) of FA addition to the final volume of 400 µL. The same analytical procedure was applied to blank samples. Each sample for the assay was prepared in triplicate.
3.5. Instrumental analysis
The investigated substances were analyzed by micro-HPLC/MS/MS with negative ion electrospray ionization (ESI) and Multiple Reaction Monitoring (MRM) mode. Chromatographic separation was carried out using an Eksigent LC200 System (AB SCIEX, Concord, Canada). The column used was HALO C18 column 50 mm x 0.5 mm x 2.7 µm (Eksigent, Concord, Canada), and it was termostated at the temperature of 45 °C with the mobile phase flow rate of 20 µL/min. A binary gradient consisting of water (A) and MeCN (B) (both with 0.1 % FA) was applied. The gradient was set as follows: 40% B (0-0.5 min), 40-90% B (0.5-3.0 min), 90% B (3.0-4.0 min), 90-40% B (4.0-4.2 min) and 40% B (4.2-5.0 min). The injection volume was 5 µL. The autosampler temperature was set at 40 °C. The mass spectrometer used was QTRAP 5500 with ESI (AB SCIEX, Concord, Canada). The optimal sensitivity for the investigated PFASs was obtained under the following settings: curtain gas flow: 25 L/min, collision gas flow: 9 L/min, ion spray voltage: -4500 V, temperature: 350 °C, 1 ion source gas flow: 30 L/min, 2 ion source gas flow: 35 L/min, declustering potential range: -30 to -85 V, entrance potential: -10 V, collision energy range: -10 to -65 eV and collision cell exit potential range: -10 to -38 V [
70]. Quantitative analyses were performed using the multiple reaction monitoring (MRM) mode. Data analysis was done with Analyst Software (AB SCIEX, Concord, Canada) (version 1.5.2).
3.6. Analysis of blood parameters
The analysis of blood samples was conducted by the Medical Diagnostic Laboratory of the Provincial Specialist Hospital in Olsztyn, Poland. The blood hematology parameters included leukocytes, erythrocytes, hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular/cellular hemoglobin concentration (MCHC), platelets, red cell distribution width (RDW-CV), platelet distribution width (PDW), mean platelet volume (MPV), and platelet large cell ratio (P-LCR), also was measured blood biochemistry parameters which included lipid profile (total cholesterol, triglycerides, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and glycated hemoglobin.
3.7. Statistical analysis
Statistical analysis were performed using Statistica software (v. 13, StatSoft, Tulsa, Ok, USA). The normal distribution of the data was evaluated using a Shapiro-Wilk W test. The tested groups showed a non-normal distribution, therefore, quantitative variables are expressed as median (P25-P75). Comparisons within the groups, between the baseline and after the exposure to the fermented red beetroot juice, were performed using Wilcoxon signed-rank tests. Correlations between the concentration of individual PFASs, total acids, total sulfonates, total PFASs and blood parameters (leukocytes, erythrocytes, hemoglobin, hematocrit, MCV, MCH, MCHC, platelets, RDW-CV, PDW, MPV, P-LCR, total cholesterol, cholesterol HDL, cholesterol LDL, triglycerides, glycated hemoglobin) were analyzed using a Pearson correlation coefficient test. Statistical significance thresholds were set at p < 0.05 (*) and p < 0.01 (**). The strength of the correlation was described as fair (<0.3), moderate (0.3 to <0.5), good (0.5 to <0.7), or very good (≥0.7) [
71].