Mercury, Fatty Acids Content and Lipid Quality Indexes in Muscles of Freshwater and Marine Fish on the Polish Market. Risk Assessment of Fish Consumption

Mercury content and fatty acids in muscles of Perca fluviatilis L. (European perch), Leuciscus idus L. (ide), Cyprinus carpio L. (European or common carp), Oncorhynchus mykiss Walb. (rainbow trout), Platichthys flesus L. (European flounder). and Clupea harengus L. (bream) from the Polish market were investigated. The total mercury was processed with AAS. The fatty acids were analyzed by gas chromatography. The concentration of mercury in muscles varied from 0.006 to 0.138 mg/kg and decreased as follows: perch ≈ ide > flounder > herring ≈ bream ≈ rainbow trout > carp (p ≤ 0.05). There were only significant positive correlations between body weight and mercury content in muscle tissue of carp (r = 0.878), flounder (r = 0.925) and herring (r = 0.982) (p ≤ 0.05). The atherogenic index (AI), thrombogenicity index (TI) and flesh-lipid quality index (FLQ) were calculated as follows 0.33–0.70 (IA), 0.16–0.31 (IT) and 13.01–33.22 (FLQ). Hypocholesterolemic (OFA) and hypercholesterolemic fatty acids (DFA) in muscles of fish ranged from 18.26 to 23.01 and from 73.91 to 78.46, respectively. In most cases, there were not significant correlations between size (body weight and total length) and fatty acids in the muscles of the examined fish (p > 0.05). The Target Hazard Quotient (THQ) values were below 1, which shows that there is no non-carcinogenic health risk to the consumer by consuming the examined fish.


Introduction
Fish are an important sources of biologically valuable proteins, fats, fat-soluble vitamins and n-3 polyunsaturated fatty acids with five and six double bonds in the carbon chain [1]. The results of prospective cohort studies indicate that consuming fish or fish oil containing the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is associated with decreased cardiovascular death risk, whereas the consumption of vegetable oil-derived n-3 fatty acid α-linolenic acid is not as effective [2]. Long-chain fatty acids can be classified into n-3 fatty acids and n-6 polyunsaturated fatty acids which are beneficial to health, because they have anti-inflammatory properties and decrease the risk of cardiovascular disease, cancer, hypotriglyceridemia and increase HDL cholesterol [3][4][5][6][7]. They also (along with nutrients such as carotenoids, vitamins A, D, E, C and zinc, selenium and iron) influence immune system activity [8]. Saturated fatty acids such as lauric (C12:0), myristic (C14:0) and palmitic (C16:0) acid increase total and LDL-cholesterol concentrations [9,10].

Sample Preparation
Perch (Perca fluviatilis L.), ide (Leuciscus idus L.), carp (Cyprinus carpio L.), rainbow trout (Oncorhynchus mykiss Walb.), flounder (Platichthys flesus L.) and herring (Clupea harengus L.) were bought on the Polish market. The samples of fish were collected the same day. The body weight and total length were measured (Table 1). Muscles (without skin) were dissected from the dorsal part and stored until analysis in the refrigerator at −18 • C. For large bream, perch, ide, carp and rainbow trout, the samples were prepared from muscles taken from one specimens, whereas for flounder and herring, samples were prepared from muscle tissue taken from two fish.
Ethical statement: according to European and Polish Law, the research done on the commercially catch fishes tissue is free to obtain permission on Local Ethical Commision.

Mercury
Duplicate samples of muscles were weighed into quartz boats (270 mg ± 0.0001 g) and transferred from an analytical auto-sampler. The total mercury was processed with atomic absorption spectrometry thermal decomposition using a Milestone DMA-80 (with dual-cell) instrument (Milestone, Sorisole, Italy). The samples are first dried at 160 • C by 60 s and then underwent decomposition in a furnace in an oxygen atmosphere (temp. 650 • C by 60 s). The time between the end of drying and the beginning of decomposition (650 • C) is 120 s. The absorption wavelength was 253.65 nm (detection limit-0.005 ng Hg) and detector was a UV enhanced photodiode instrument. The analysis method was tested by measuring the elements in reference material: BCR CRM 422 (muscles of cod Gadus morhua (L.)) with a certified mercury value. The recovery rate percentage was 100.2% (n = 4).

Fat and Fatty Acids Analysis
Approximately 1 g samples (±0.0001 g) in duplicate were dried to a constant weight at 105 • C in glass sample tubes with frits and transferred to weighed beakers. The lipids from the fish muscles (without skin) and liver were extracted according to the hot extraction method using an E-816HE automatic extractor. The analysis consisted of three steps (extraction, rinsing, drying). After the extraction was finished, all of the solvent (petroleum ether) was collected in the tank. Fat was dried in beaker at 100 • C to a constant weight and was then weighed.
The content of fat (%) was calculated according to pattern: x = [(b − a) × 100]/c, where: a = weight of flask (g), b = weight of flask with extracted fat (g), c = weight of samples (g).
The lipids were extracted according to the Folch's procedure [26]. The studied material was broken up and mixed. 2 g of sample was homogenised for 1 min with 20 mL of methanol. Next, 40 mL chloroform was added and the procedure was continued for 2 min. The prepared mixture was filtered to a 250 mL glass cylinder. The solid residue was re-suspended in 60 mL chloroform: methanol (2:1 v/v) and homogenized again for 3 min. After filtering, the solid was washed once more with 40 mL chloroform and once with 20 mL methanol. The combined filtrate was transferred to the same cylinder. 0.88% sodium chloride in water (determining 1/4 volume of filtrate) was added to the total filtrate and then shaken and left overnight. The upper layer was removed and to the lower layer a water:methanol mixture (1:1 v/v) was added and the washing procedure was repeated. The remaining layer was trickled by anhydrous sodium sulphate and distilled by means of aggregate for distillation of solvents. The fatty acid methyl esters were prepared from total lipids with the Peisker method with chloroform:methanol:sulphuric acid (100:100:1 v/v) [27].
The fatty acids of methyl esters of each sample were analyzed using a 7890A chromatograph (Agilent Technologies, Waldbroon, Germany) equipped with a flame-ionization detector (FID) under the following conditions: capillary column (dimension 30 m × 0.25 µm with a 0.32 mm internal diameter, liquid phase Supelcowax 10 (Supelco, Bellefonte, PA, USA), temperature: flame-ionization detector −250 • C, injector −230 • C, column −195 • C, carrier gas-helium with a flow rate 1.5 mL/min. Individual fatty acids were identified by comparing the relative retention time peaks to the known Supelco standards.
2.3. The Llipid Quality Indexes Were Calculated from the Fatty Acids Composition Using the Following Formulae The AI indicates the relationship between the sum of the main saturated fatty acids and that of the main classes of unsaturated fatty acids, the former being considered proatherogenic (favoring the adhesion of lipids to cells of the immunological and circulatory system), and the latter antiatherogenic (inhibiting the aggregation of plaque and diminishing the levels of esterified fatty acid, cholesterol, and phospholipids, thereby preventing the appearance of micro and macro coronary diseases) [28][29][30] (AI) = [C12:0 + (4 × C14:0) + C16:0]/(n-3PUFA + n-6PUFA + MUFA) PUFA-polyunsaturated fatty acids MUFA-monounsaturated fatty acids C12:0-lauric acid, C14:0-myristic, C16:0-palmitic.

Index of Thrombogenicity (TI)
The TI shows the tendency to form clots in the blood vessels. This is defined as the relationship between the prothrombogenetic (saturated) and the antithrombogenetic fatty acids (MUFA, n-6 PUFA and n-3PUFA) [28][29][30]: The FLQ indicates the percentage correlation between the main n-3 PUFA (EPA + DHA) and the total lipids. The higher value of this index is an indicator of the higher quality of the dietary lipid source [31,32]: EDI-the estimated daily intake (µg/kg body weight/day) = C × IR/BW TWI-Tolerable Weekly Intake = EDI × 7 C-the average concentration of heavy metals in food stuffs (µg/g wet weight) IR-the daily ingestion rate (g/daily) The fish consumption was 12.1 kg per capita/year [33] BW-the average body weight (60 kg) [34]

Target Hazard Quotient (THQ)
The THQ assesses the non-carcinogenic health risk of consumers due to the intake of heavy metal polluted fish using the oral reference dose (RfD = 3.00 × 10 −4 ) [35,36]. The non-cancer risk model is used in this study because mercury is not classifiable as a human carcinogen. When THQ < 1 there is health benefit from fish consumption and the consumer is safe, whereas THQ > 1 suggests a high probability of adverse human health risks: Efr-the Exposure Frequency (365 days/year) ED-the Exposure Duration (70 years) FiR-the Fish Ingestion Rate (g/person/day) C-the average concentration of heavy metals in food stuffs (µg/g wet weight) RfD-the oral reference dose (mg/kg/day) (USEPA 2017) BW-the average body weight of local residents (60 kg) [34] TA-the average exposure time (365 days/year × ED)

Statistical Analysis
Significant interspecific differences in the content of fatty acids and mercury in the muscles were calculated using a one-way analysis of variance ANOVA (Duncan's test) after testing for homogeneity of variance (test Levene's). Differences were found to be significant at p ≤ 0.05. The correlation coefficients between the content of Hg and fatty acids in muscles of fish were calculated using the STATISTICA 10 software (StatSoft, Kraków, Poland). Similarly, the correlation coefficients between the content of Hg and fatty acids in muscle tissue of fish and their size (body weight and total length) were evaluated using the STATISTICA 10 software. The significance level of p ≤ 0.05 was used.
Muscles of bream were characterized by a significantly higher content of saturated fatty acids SFA (32.94%) (p ≤ 0.05), whereas the content of monounsaturated fatty acids MUFA (54.54%) was significantly higher in muscle tissue of herring (p ≤ 0.05) than in the other fish examined ( Table 2). In the case of bream and perch as representative wild freshwater fish, the muscles of these fish contained significantly more n-3 PUFA and n-3 HUFA than marine fish (flounder and herring), cultured fish (carp and rainbow trout) and ide inhabiting different aquatic ecosystems (river and lakes) (p ≤ 0.05). The values n-3 PUFA in muscle tissue of bream and perch were 37.46% and 38.62%, while the contents of n-3 HUFA were 35.00% and 36.57%, respectively. However, the muscles of bream, carp and rainbow trout had significantly higher content of n-6 PUFA (15.48%, 15.10% and 15.03%, respectively).
A significantly lower amount of hypocholesterolemic fatty acids was observed in muscles of rainbow trout (18.26%) and flounder (20.34%) (p ≤ 0.05) than other fish examined, although there were no significant differences between muscle tissue flounder and carp, ide, and bream (p > 0.05) ( Table 2). hypercholesterolemic fatty acids contents in the muscles of fish were as follows: flounder (78.46%) ≈ carp (77.55%) ≈ ide (77.33%) and carp ≈ ide ≈ herring (76.07%) ≈ perch (75.73%) and herring ≈ perch ≈ bream (74.88%) ≈ rainbow trout (73.91%). The muscles of herring had significantly higher index of atherogenicity (0.70) than other fish studied (p ≤ 0.05), whereas the muscle tissue of carp had a significantly higher index of thrombogenicity (0.31) (p ≤ 0.05). There were also significant differences between the value of flesh-lipid quality in perch (33.22) and other fish examined (p ≤ 0.05). Table 1. Mercury and total lipids content (mean ± SD, range), and linear correlation coefficients (r) between body weight or total length and content of mercury in muscles of fish. n-Number of fish; SD-standard deviation; a, b, c, d-significant differences at p ≤ 0.05. The same letter indicates a lack of significant differences between the muscles fish species (p > 0.05); p-significance levels for the correlation between the content of mercury in muscles of fish and their body weight or total length. Table 2. Lipid content (%) and fatty acids composition (% of total fatty acids) in muscles of different fish species.

Fatty Acids Bream Perch Ide Carp Rainbow Trout
Flounder Herring    Muscle tissue of perch and ide contained more mercury (0.139 and 0.109 mg/kg, respectively) than other fish studied (p ≤ 0.05) ( Table 1), while a representative marine fish such as flounder had more mercury than herring (0.021 mg/kg), bream (0.016 mg/kg), rainbow trout (0.015 mg/kg) and carp (0.006 mg/kg) (p ≤ 0.05). The differences in the content of mercury in muscles of herring, bream and rainbow trout were not significant (p > 0.05). However, the muscles of carp contained a significantly lower mercury concentration than other fish examined (p ≤ 0.05). The mercury content in muscles of the examined fish did not exceed maximum residue level (0.5 mg/kg).
Positive correlation coefficients were found between mercury levels in the muscles and the fish weight and length (Table 1). However, significant correlations were found between body weight and the content of mercury in muscle tissue of carp (r = 0.878, p = 0.050), flounder (r = 0.925, p = 0.008) and herring (r = 0.982, p = 0.0005).
Negative correlations were noted between the total length and the content of C18:2 (n-6) in muscles of bream (r = −0.845, p = 0.034), as well as between the total length and AI (r = −0.890, p = 0.018) or TI (r = −0.812, p = 0.050) in muscles of ide ( Table 3

Human Health Risk Assessment
The THQ for mercury in different fish species is presented in Table 4. THQ values were below 1 which shows that there is no non-carcinogenic health risk to the consumer by consuming the examined fish. The EDI of mercury from the 33.16 g portions of fish was: 0.009 µg/body weight (bream), 0.076 (perch), 0.060 (ide), 0.003 (carp), 0.008 (rainbow trout), 0.031 (flounder) and 0.012 µg/body weight (herring). The weekly intake of mercury (232.12 g of fish portion) accounts for 1. 50  n-Number of fish; EDI-the estimated daily intake (µg/kg body weight/day); EWI-the estimated weekly intake (µg/kg body weight/weekly); THQ-Target Hazard Quotient; * TWI-Tolerable Weekly Intake for inorganic mercury expressed as mercury = 4 µg/kg body weight, ** TWI for methylmercury expressed as mercury is 1.3 µg/kg body weight.

Discussion
Previously findings reported by Łuczyńska and Krupowski [37] showed that mercury content in muscles of fish from the Polish market varied between some species. The muscles of predatory (perch and pike) and non-predatory freshwater fish (bream) contained higher levels of mercury than marine fish (flounder and mackerel) (p ≤ 0.05). Similarly, predatory freshwater fish (i.e., pike) had more mercury than non-predatory fish (i.e., bream). For bream and flounder, a contrary regularity was found (Table 1). Muscle tissue perch from the Vistula River (Toruń, Poland) contained more mercury (0.36 mg/kg) than muscles of bream (0.054 mg/kg) [38]. Muscles tissue of flounder contained a higher concentration of mercury (0.036 mg/kg) than muscles of herring (0.032 mg/kg) [39]. Voigt [40] observed differences between the content of mercury in the muscles of the pelagic open-sea species (herring) and inshore species (perch) (Western Estonia). According to the same author perch contained more mercury than herring. The observations of above authors are close to those found in the present study. Kenšová et al. [41] also found the highest concentration of mercury in muscles of predatory fish (asp Aspius aspius L., eel Anguilla anguilla L., pike Esox lucius L., and perch). The same authors showed that among non-predatory fish (carp, bream, tench Tinca tinca L. and roach Rutilus rutilus L.) the lowest mercury content were noted in carp. Zrnčić et al. [42] studied 14 different fish species belonging to four groups according to feeding habits (among others: ide, carp and bream). The authors found that the differences between the content of metals examined, including mercury, in the four groups (herbavore, omnivore, piscivore and plankton-feeding fish) were significant. These results are consistent with those in present study (Table 1). Popov et al. reported that interspecies differences in the content of metals, including mercury, are most likely caused by peculiarities in the feeding habits of fish (Russia) [43]. According to those authors, the contents of mercury in muscles of perch, bream and ide were 0.033, 0.035 and 0.014 mg/kg. There were statistically significant differences between content of mercury in muscles of herring (0.0658 mg/kg) and carp (0.0373 mg/kg) bought in Polish market (p < 0.05) [44]. Muscle tissue of carp from the Neretva River (Croatia) had higher values of mercury (0.190 mg/kg) than carp from the Polish market studied by the above authors [45]. The fish (carp and rainbow trout (Poland)) contained 0.036 mg Hg/kg [46]. According to Mazej et al. [47] the muscles of perch from Velenjsko (Slovenia) had four times higher content than muscle tissue of carp (0.03 mg/kg). Lidwin-Każmierkiewicz et al. [48] found that muscle tissue of perch from West Pomerania (Poland) contained more mercury (0.03 mg/kg) than carp and bream (0.01 mg/kg). Those authors did not observe differences between the mercury concentration in muscles of carp and bream. However, Kenšová et al. [49] noted a significant differences between the content of mercury in muscles of carp and predatory fish species (asp Aspius aspius L., pike Esox Lucius L. and pikeperch Sander lucioperca L.) caught in the Vȇstonice Reservoir (Czech Republic) (p < 0.01), but did not find significant differences between the mercury concentration in muscle tissue of carp and bream (p > 0.01) or any dependence of metal content on fish weight, age or sex. For the muscle tissue of fish from Puck Buy, perch (0.110-0.130 mg/kg) contained higher values of mercury than other fish, i.e., bream (0.040 mg/kg) flounder (0.031-0.053 mg/kg) and herring (0.049 mg/kg) [50]. The same authors found a positive relationship (p < 0.05) only between total body length and weight and mercury content in muscles of flounder. Baeyens et al. [51] found strong positive correlation between the length of flounder and the concentration of mercury (r = 0.71). This is in accordance with the results of the present study, but only in relation to correlation of mercury content in muscles of flounder with body weight.
The content of mercury in muscle of perch from Lake Gusinoye and the Selenga River (Russia) significantly depended on the fish length and weight (r = 0.62-0.90, p < 0.01) [52]. According to Łuczyńska [53], the positive correlation between the body weight and the total mercury levels in muscles of perch from Lake Łańskie, Pluszne, Dłużek and Maróz (r = 0.967, 0.963, 0.876 and 0.967, p < 0.001, respectively) was slightly higher than that between mercury and body length (r = 0.933, 0.950, 0.781 and 0.916, p < 0.001), respectively). A positive correlation between the concentration of mercury in muscles of perch from the southern Baltic and weight or length (p < 0.01) was found by Szefer et al. [54]. Mercury content in muscles of predatory fish belonging to five species (asp, Aspius aspius L.; eel Anquilla anquilla L.; perch; pike, Esox Lucius L.; pikeperch, Stizostedion lucioperca L.) from the Želivka Reservoir was correlated with weight (r = 0.330, p < 0.001) [55]. The above findings were not confirmed by the results of this studyof perch.
There were also significant positive correlation between mercury content and fish body size (ide, carp and bream) [42]. A significant correlation coefficient between the concentration of mercury in muscle tissue of bream from Lake Balaton and their length (r = 0.8459, p < 0.0001) was also observed by Farkas et al. [56]. This is in accordance with the examined results, but only in the case of carp.
According to Łuczyńska et al. [57], the content of fat and fatty acids varied both between and within species. The muscles of bream and perch contained 1.03 and 0.89 of total lipid, respectively. The fat content in fillets of carp and bream from Inland waters was 3.24% and 7.13%, respectively [58]. These results are higher to those for the fish examined ( Table 1). The muscle tissue of rainbow trout studied had lower content of fat than meat of rainbow trout from extensive farming (3.13%) and intensive farming (5.39%) [59] and fish of the same species from Polish market (6.84%) [60]. Polak-Juszczak and Adamczyk [61] found that muscles of bream, perch and herring contained 3.14%, 0.12% and 2.61% of fat. This literature data was not confirmed the presented findings.
Ljubojevic et al. [58] found differences between the content of MUFA, PUFA, n-3 PUFA and n-6 PUFA in muscles of bream and carp (p < 0.01). According to these authors fillets of bream contained more MUFA and n-3 PUFA than carp fillets, and lower amounts of PUFA and n-6 PUFA. These results are close to those for MUFA and n-3 PUFA in muscles of the fish studied (Table 2). Polak-Juszczak and Komar-Szymczak [62] studied the fatty acids profiles in muscles of bream, perch and herring from the Vistula Lagoon (Poland). They authors found that the content of SFA, MUFA and PUFA in muscle tissue of those fish were as follows: herring > bream ≈ perch; bream > herring > perch and perch > herring > bream, respectively. In turn, Kołakowska et al. [63] observed that these groups in muscle lipids of rainbow trout, carp and flounder was as follows: flounder > rainbow trout > carp (SFA); carp > flounder > rainbow trout (MUFA) and rainbow trout > flounder > carp (PUFA). The results observed by Polak-Juszczak and Komar-Szymczak [62] and Kołakowska et al. [63] are in not accordance with the results of the present study. Similarly, the previously findings reported by Łuczyńska et al. [60] did not confirm the regularity of these fatty acids in muscles of carp, rainbow trout and bream from Polish market.
According to Ehsani et al. [64], monounsaturated fatty acids (MUFA) in fillets of rainbow trout were the highest, followed by polyunsaturated (PUFA) and saturated fatty acids (SFA). These results are not consistent with those of the present study, because the content of PUFA in muscles of the examined fish was higher than the content of MUFA (Table 2). Karaçali et al. [65] showed that MUFA in muscles of carp (Turkey), independent of seasonal variations, was at the higher amount (45.67-50.17%) than SFA (25.29-28.13%) and PUFA (17.87-26.73%). These findings are not in agreement with those reported by Donmez [66] for muscles carp living in Porsuk Dam, Turkey (SFA > MUFA ≈ PUFA). However,Ćirković et al. [67] found that muscles of carp in raised in poly-culture (Serbia) had more PUFA than SFA and MUFA. According to these authors, nutrient composition, varies widely among fish species, especially the profile of fatty acids related to their consumption habits (herbivorous, omnivorous and carnivorous). Polak-Juszczak and Komar-Szymczak [62] observed that muscle tissue of bream had more MUFA than PUFA and SFA, whereas the muscle of herring had more PUFA than MUFA and SFA, and these groups in muscles of perch were as follows PUFA > SFA > MUFA. The results of authors are close only to those for perch examined. Stancheva et al. [68] noted that carp from the Danube River contained higher levels of n-3 PUFA in comparison with n-6 PUFA. These results are in good agreement with the data from the present study on the same fish species.
Ouraji et al. [69] and Stancheva et al. [68] reported that higher values of AI and TI (>1.0) are detrimental to human health. The value of these parameters in muscles of carp, both studied by Stancheva et al. [68] (0.65 and 0.36, respectively) and in the present study, were lower than 1.0. The FLQ value (6.84) in the muscle tissue of carp reported by Stancheva et al. [68] was lower than those noted in present study. Indices such as AI and TI in fillets of rainbow trout with three different average weights ranged from 0.20 to 0.28 and from 0.88 to 1.28, respectively [64]. These values are superior to those for rainbow trout studied in the present study. The same author found that fish weighing about 480 g and 350 g contained lower AI and TI values than the low-weight fish, and that the content of DHA in fillets of rainbow trout decreased with weight. For the examined rainbow trout, DHA decreased with increased their weight, but the correlation was not significant.
A consumer who eats 232.12 g of weekly portion of fish meat ingests less mercury than the TWI [23], which means that it does not pose any health risks. The THQ of mercury in species examined for adult was also less than 1. Addo-Bediako et al. [70] reported that THQ < 1 suggests that adverse health effects are unlikely, whereas THQ > 1 suggests a high probability of adverse health effects. This shows that the fish from Polish market are safe for consumers. Although the greatest contribution of harmful exposure to mercury for humans is through eating fish, we should comprehensively address the subject and take into account the multiple sources of exposure. For example mercury content in fresh fruit and vegetables from independent agrarian production ranged between 0.0011 and 0.0039 mg/kg (Poland) [71]. However, vegetable products, products for infants and children and wheat cereal products contained 0.001-0.008 mg/kg. These values did not affect health and were generally below the levels set forth in food legislation (0.01 mg/kg) [72]. The results observed by Duma et al. [73] also showed that the analysed products collected each year during 2002-2010 from selected farms in the Podkarpackie Province (Poland) did not present a risk to human health because the content of mercury (<0.001-0.003 mg/kg) in the tested products (milk, pigs, pork) did not exceed the maximum admissible values. Mercury, which has been acknowledged as a serious human toxin, was absent in the fruits and vegetable in Lagos state (Nigeria) [74]. Mercury content had no hazardous effect on human health and environment pollution in Shahre-Ray regions (Iran) because the mean concentrations of mercury in five leafy vegetables was 0.027 mg/kg dry weight [75]. The same authors found that mercury also had a low concentration in soil and water as compared with WHO/FDA references. The concentration of Hg in various vegetables (roots, stems, leafy, fruits, cereals and legumes) grown in four major industrial and urban cities (Tabouk, Riyadh, Damamm and Jazan) in Saudi Arabia was not detected in selected legume species from the northern district while it was at low levels in leafy vegetables (except parsley, which recorded the maximum mercury value (0.048 mg/kg dry weight) [76]. According to these data, fish are more likely to be exposed to the toxic effects of mercury and contain more than other raw materials and food products.

Conclusions
The examined fish are better dietary sources of n-3 PUFA. Despite this, n-3/n-6 ratio in marine fish was higher than other fish examined, which is associated with a small amount of n-6 PUFA in lipid muscles of this group. Furthermore, all fish species had more hypercholesterolemic fatty acids relative to hypocholesterolemic fatty acids and may be an important dietetic fish food from a cardiovascular disease point of view. The dietetic quality indices of lipids (index of flesh-lipid quality, atherogenicity and thrombogenicity) was no more than 1.0 which according to the data literature is detrimental to human health. In conclusion, the fish examined did not exceed the maximum acceptable level of mercury and were a beneficial source of PUFA, especially n-3 PUFA may be recommended for human health consumption, especially since the Target Hazard Quotient (THQ < 1) showed there is a non-carcinogenic health risk to the consumer.