INTRODUCTIONHeavy metals in contaminated food crops, evenat low concentrations, produce deleterious effects onhuman health [1]. Metals pollution naturally occurs inthe environment; however, human activities includingmining and other industries have particular effects onthe ecosystem, as well as the aquatic environment [2–4].Despite the progress in sewage effluent technologies,water contamination is still a threat in many developingcountries due to sewage discharge [5]. Heavy metals havean impact on aquatic ecosystems and eventually enter thehuman’s food chain [6]. Rainbow trout (Oncorhynchusmykiss L.), a native fish of North America, is known asone of the most valuable members of the Pacific trout thatbecame the main freshwater fish species farmed in Iran[7, 8]. The first farm of this fish in Iran was establishedin 1959. Its production increased from 599 tons in 1978 to140 000 tons in 2016, making Iran one of the worldleadingproducers of this salmon [9].Mercury, cadmium, and lead are known as toxicantsassociated with fish consumption [10]. They are listed assixth most dangerous contaminants by the InternationalProgram of Chemical Safety (IPSC) [11]. Lead poisoningcan affect various systems of the body including renal,haematological, cardiovascular, gastrointestinal, andreproductive systems [12]. Renal exposure to cadmiumresults in its deposition in proximal tubular cells andcauses renal failure due to decreased glomerularfiltration rates. Also, skeletal system anomalies occurdue to the secondary effects of renal dysfunction andaccumulation of lead in bones [13]. Methyl mercuryexposure through the consumption of contaminated fishin prenatal period leads to serious abnormalities suchResearch Article DOI: http://doi.org/10.21603/2308-4057-2019-2-329-338Open Access Available online at http:jfrm.ruHeavy metal content in farmed rainbow troutin relation to aquaculture area and feed pelletsMajid Majlesi1 , Janmohammad Malekzadeh1,* , Enayat Berizi2 ,Mehdi Akbartabar Toori11 Department of Nutrition Sciences, School of Health and Nutrition Sciences,Yasuj University of Medical Sciences, Yasuj, Iran2 Department of Food Hygiene and Quality Control, School of Nutrition and Food Sciences,Shiraz University of Medical Sciences, Shiraz, Iran* e-mail: malekjmd@yums.ac.irReceived May 13, 2019; Accepted in revised form August 27, 2019; Published October 21, 2019Abstract: Fish contamination by heavy metals, even at low levels, has an adverse effect on human health. Mercury (Hg), cadmium(Cd), and lead (Pb) are the most common heavy metals that contaminate sea foods. Rainbow trout is a fish species which is widelycultured in fresh water regions, e.g. in Yasuj, southwest of Iran. Heavy metal contamination was measured in three different cultureareas (A, B, and C), with three different feed pellets used in Yasuj farms (I, II, and III). The sampling was conducted during February-April 2018 and the metals were measured using cold vapour atomic absorption with a Perkin Elmer 4100. The mean values of Hg,Cd, and Pb levels in the muscular tissue of the samples were 0.022, 0.105, and 1.07 mg/kg, respectively. Concentrations of Hg andCd in edible tissues of rainbow trout were lower than the permitted values set by the WHO, the FDA, and the EC. The samplesfed on mixture pellets III showed a significantly higher Hg content and a lower concentration of Cd in the muscle tissue comparedto those given feed mixtures I and II (P < 0.05). Pearson correlation tests revealed significant correlations between the Cd and Pbconcentrations and the weight of the fish samples (r = –0.519, r = –0.580). The lowest Cd concentration (0.076 mg/kg–1) was found insite A located close to the spring and not polluted by sewage from urban or rural areas. The study showed a correlation between theconcentration of heavy metals in the fish samples and their weight, the degree of pollution, and the feeding mixture used in the farms.Keywords: Rainbow trout, heavy metals, mercury, cadmium, leadPlease cite this article in press as: Majlesi M, Malekzadeh J, Berizi E, Toori MA. Heavy metal content in farmed rainbow trout inrelation to aquaculture area and feed pellets. Foods and Raw Materials. 2019;7(2):329–338. DOI: http://doi.org/10.21603/2308-4057-2019-2-329-338.Copyright © 2019, Majlesi et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 InternationalLicense (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix,transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.Foods and Raw Materials, 2019, vol. 7, no. 2E-ISSN 2310-9599ISSN 2308-4057330Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338as cerebral palsy, mental backwardness, neurologicaldisorders, and infant mortality [14]. Fish, which isan important aquatic component of the human foodchain, has been a subject of investigation with regard tometal pollution [15]. Therefore, numerous reports havedescribed metal residues in types of fish species [16–20].The accumulation of heavy metals in fish tissues isinfluenced by a number of factors such as feeding habits,nourishment sources, habitat, age, and size [21–23]. Inthis study, concentrations of heavy metals (Hg, Cd, andPb) were assessed in fish feed mixtures and edible tissuesof rainbow trout farmed in three different culture areas.STUDY OBJECTS AND METHODSStudy area and sample collection. BetweenFebruary and April 2018, rainbow trout (Oncorhynchusmykiss L.) samples were collected from six farms (fivefishes from each farm) in three different culture areasin Yasuj, southwest of Iran (Fig. 1), the third leadingproducer of this trout in the world [9]. The culture areaswere located very close to the spring (site А: 30.502935,51.743184), downstream of cities and villages (siteB: 30.710630, 51.514926), and downstream of a ruralarea (site C: 30.789658, 51.329715). Their choice wasdetermined by the level of contamination probability.The farms used a raceway farming system, with watersupplied by the spring. All the farms practiced manualfeeding with commercial pellets two times a day. Thefish were collected randomly from two farms in eacharea (10 fishes in each site). The experiments wereapproved by the Animal Care and Use Committeeof Yasuj University of Medical Sciences (YUMS) incompliance with the ‘Guidelines for the Care and Useof Animals’. At first, the samples’ biological parameterswere recorded including wet body weight and totallength. Then, they were washed, preserved in ice-boxes,and transported to the Food Chemical Laboratory atYUMS for heavy metal (Hg, Cd, and Pb) determination.The fish were filleted, placed in polyethylene bags, andkept at −20°C prior to analysis.Four pellets of three types (I, II, and III) ofcommercially manufactured feed mixtures werefrequently applied in the aquaculture trout farms duringthe fish sampling (12 pellets) and studied to determinethe content of heavy metals.Analytical procedures. Both feeds and fillets wereoven-dried at 105°C for 1 h and then cooled. To measurethe level of heavy metals, the samples (dry weight) weredigested in a mixture of 6 mL concentrated HNO3 (superpure quality; Romil Ltd., Cambridge, UK) and 2 mLH2O2 (supra pure quality; Merck, Darmstadt, Germany)in a microwave digestion system (MARSXpress, CEM).When cooled to room temperature, the digested samplesolutions were filtered and adjusted to 50 mL withultrapure water. The levels of Hg, Cd, and Pb contentwere determined using cold vapour atomic absorptionwith a Perkin Elmer 4100 (FIMS 400 Perkin Elmer Inc.,USA). The blank samples were also processed to avoidpossible contamination during the analysis [22].Human health risk assessment. The estimateddaily intake (mg/kg bw/day) (EDI) of heavy metals wasmeasured to evaluate the daily/weekly intake of heavymetals by the human body through the consumptionof fish [24]. The daily intake of metals in adults wascalculated as:EDI (mg/kg bw/day) = (EF·ED·FIR·CF·CM)/(WAB·TA)×10–3 (1)Where EF and ED are the exposure frequency(365 days/year) and the exposure duration (60 years),respectively; FIR is the fish ingestion rate (25.2 g/day forIran); CF is the conversion factor to convert fresh weightto dry weight (0.208); CM is the metal concentration inFigure 1 Location of Yasuj, southwest of Iran and the study area (site A: 30.502935, 51.743184, site B: 30.710630, 51.514926,site C: 30.789658, 51.329715)331Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338the fish tissue (μg/g dry weight); WAB is the average bodyweight for adults (65 kg for Iran); and TA is the averageexposure time for non-carcinogens (EF·ED) [4].The percentage of provisional tolerable weeklyintake (PTWI) and target hazard quotient (THQ)were calculated for each heavy metal by the followingequations:PTWI = EWI/PTWI × 100 (2)THQ = EDI/RfD (3)where PTWI, EWI, and RfD are provisional tolerableweekly intake (mg/kg bw/week), estimated weeklyintake (mg/kg bw/week), and oral reference doses(mg/kg/day), respectively.When the THQ is less than one, the risk ofnoncarcinogenic toxic effects for exposed consumerpopulations is presumed to be low. When it is greater thanor equal to one, it is considered as a concern for consumerpopulations, indicating potential health risks [25].Biomagnification factor. The biomagnificationfactor (BMF) is the ratio between the concentration ofan element in fish and the concentration of this elementin its diet. The BMF was calculated by the followingequation: [26]:BMF = Cfish/Cfeed (4)where Cfish is a heavy metal concentration in fish edibletissues and Cfeed is a metal concentration in troutcommercial pellets.Statistical analysis. Statistical analysis wasperformed using the SPSS Statistics 19.0 softwarepackage. The mean and standard deviation (mean ± SD)levels of metal concentrations were reported for differentareas and foods. The differences between heavy metallevels in edible tissues of fish from different farmsand in different commercial foods were tested by theone-way analysis of variance (ANOVA), followed byDuncan’s post hoc test. The Pearson correlation testwas used to check for significant relationships betweenmetal concentrations, length, and net weight of fish.P < 0.05 was considered as the level of significance.RESULTS AND DISCUSSIONHeavy metal concentration in rainbow trout.Concentrations of heavy metals in edible tissues ofrainbow trout farmed in three different areas are shownin Fig. 2.The mean ± SD levels of Hg in the muscle tissuesof rainbow trout farmed in sites A, B, and C were 0.021± 0.0027, 0.023 ± 0.0026, and 0.024 ± 0.0027 mg/kg–1,respectively. The lower mercury level in site A,compared to the other two sites, had no significantdifference (P > 0.05). In addition, the meanconcentration of Cd in sites A, B, and C were 0.076,0.119, and 0.120 mg/kg–1, respectively. The lowest Cdconcentration was found in edible tissues of the fishesfarmed in locations close to the spring, not pollutedby sewage from urban or rural areas. The highest Pbconcentration was detected in site B (1.171 mg/kg–1),followed by sites C and A (0.893 mg/kg–1) (P < 0.05).The fishes cultured in sites B and C had significantlyhigher contents of cadmium and lead, compared to thosefarmed in site A (P < 0.05). The results indicated thatconcentrations of Hg and Cd were below the permittedvalues determined by [27–29]. However, the level of Pbin the muscle tissue of farmed trout exceeded the valueset by the WHO [30] (Table 1).Below the levels established by the WHO, theFDA, and the EC were heavy metal concentrations indifferent fish species studied in Turkey, in the BarentsSea commercial fish, the fish from Lake Chini inMalaysia, wild fresh water fish from the Khersan riverin Iran, rainbow trout and freshwater fish species fromLake Pamvotis in Greece [11, 31–35]. In addition, Batet al. reported that the Cd, Hg, and Pb concentrationsin Cyprinus carpio from the Karasu Stream, Sinop andin four fish species from Sarikum Lake were withincertified values allowed to consumers [36, 37].The Pb content was higher than the WHO allowedlevel in the fish cultured along the river’s upstream inFigure 2 Heavy metal levels in muscle tissue of farmedrainbow trout from three aquaculture sites (G: site A; Be: siteB; Ch: site C). All results are expressed as means ± SD for fivefish in each group. a and b: groups with different letters differsignificantly (P < 0.05)Table 1 Maximum permissible limit of heavy metals established by international organisationsHeavy metal, μg/g–1 In this study WHO (2007) FDA (2001) FAO (2007) EC Regulation No. 1881/2006Hg 0.022 0.5 0.05–1.0 0.5 0.5–1.0Cd 0.105 0.5 4.0 0.5 0.5Pb 1.070 0.5 1.7 2.0 1.0332Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338Ghadirabad, Pakistan, wild fresh water fish from theKhersan river in Iran, farmed and wild rainbow trout inthe Zayandeh Rood river in Iran, and fresh water fish inNorth Mexico (4298 mg/kg) [16, 19, 20, 33]. These datasupport the findings in our study. Table 2 demonstrates thecomparison of heavy metal levels in the muscle tissue ofrainbow trout from different locations reported in literature.However, lower Hg, Cd, and Pb levels in site A,compared to the other sites, indicated an importantrole of water supply in trout aquaculture with regard toheavy metals accumulation in fish tissues. The release ofindustrial wastewater and pollutants caused by humanactivities increased the lead content in Liza fish fromthe Karun River in Iran and from the coast of Cochinin India [44, 45]. It was also reported that wild carps inthe downstream areas of the Ravi and the Indus riversin Pakistan showed a high contamination by heavymetals [46, 47].Emara et al. observed significant differences in theCd and Pb accumulation in the muscle tissue of fish intwo distinct farms using different water sources [48].Based on health standards, the concentration of heavymetals such as lead was higher in Mugil cephalus andTrachurus mesiteraneus in the Gulf of Iskenderun [49].Wagner and Boman reported a greater amount ofcalcium and iron in the contaminated areas, comparedto non-industrial zones [41]. High levels of cadmiumand nickel were recorded in fish from Kuetsjarvi Lake(Russia) due to the contamination of surroundingregions and the proximity of smelting plants. A lowerconcentration of heavy metals in fish was detectedin the areas away from factories and contaminatingsources [52]. Power plants can reduce water aciditywhich causes an increase in the water solubility of leadand cadmium, resulting in high accumulation of themetals in aquatic organisms [11].Table 2 Heavy metal levels in edible tissue of rainbow trout from different locations according to literature data: mercury (Hg),cadmium (Cd), lead (Pb)Fish species Region Unit Heavy metals Ref.Hg Cd PbRainbow trout Hamadan, Iran mg/kg dw – 3.74 ± 4.24 14.07 ± 14.56 [38]Large sea trout Sinop fish market, Turkey mg/kg–1 wet wt 0.15–0.42 0.012–0.044 0.08–0.23 [39]Wild rainbow trout Khersan river, Iran mg/kg dw 0.023 ± 0.004 0.110 ± 0.028 1.120 ± 0.130 [33]Rainbow trout Gilan, Mazandaran andChabahar, Iran.μg/kg (ppb) 22.1 ± 0.8 36 ± 32.2 249.4 ± 88.6 [40]Farmed rainbowtroutChaharmahal-va-Baghtiari,Iranμg/g dw0.314 ± 0.195 0.097 ± 0.058 1.108 ± 0.400 [16]Wild rainbow trout Zayandeh-Rood river, Iran μg/g dw 0.292 ± 0.181 0.130 ± 0.068 1.201 ± 0.373 [16]Rainbow trout Khorramabad, Iran mg/kg dw 0.297 ± 0.04 0.123 ± 0.03 0.741 ± 0.02 [34]Rainbow trout Karakaya Dam Reservoir,Turkeyμg/kg ww – 0.00052 0.053 [41]Brown trout Munzur Stream, Tunceli,Turkeyμg/kg–1 0.01 ± 0.00 4.08–2.83 0.10 ± 0.00 [42]Rainbow trout Chaharmahal and Bakhtiari,Iranmg/kg–1 – – 12.40 [43]Rainbow trout Yasuj, Iran mg/kg–1 0.022 0.105 1.07 this studyTable 3 Health risk parameters for the Iranian population consuming farmed rainbow trout cultured in Yasuj compared to otherstudiesHealth riskparameterThis study [42] [50] [38] [51]Hg Cd Pb Pb Hg Cd Pb Hg Cd Pb Cd PbEDI, mg/kgbw/day0.17×10–5 0.84×10–5 0.86×10–4 0.77×10–3 0.008 0.039 4 0.007 0.007 0.004 0.12×10–4 0.18×10–4EWI, mg/kgbw/week0.12×10–4 0.59×10–4 0.6×10–3 0.54×10–2 – – – 0.049 0.048 0.027 0.87×10–4 1.30×10–4PTWI, mg/kgbw/week0.004 0.007 0.025 – – – – – – – – –PTWI, % 0.30 0.84 2.41 – – – – – – – 1.25 0.52RfD, mg/kgbw/day0.0003 0.001 0.004 – – – – – – – – –THQ 0.0059 0.008 0.021 0.22 0.037 0.014 0.097 – – – 12.46×10–3 9.28×10–3TTHQ 0.0349 – 0.146 – – – –EDI: Estimated Daily Intake; EWI: Estimated Weekly Intake; PTWI: Provisional Tolerable Weekly Intake; RfD: Oral Reference Dose;THQ: Target Hazard Quotient; TTHQ: total THQ333Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338Health risk assessment. Several parameters widelyused to assess human health risks include the estimateddaily intake (EDI), the estimated weekly intake (EWI),the target hazard quotient (THQ), and the provisionaltolerable weekly intake (PTWI). Health risk assessmentvalues including the EDI, the EWI, the THQ, and thePTWI with regard to farmed rainbow trout are presentedin Table 3. These parameters showed the followingpattern in all the samples under study: Pb > Cd > Hg.We found that the EDI, the EWI, the PTWI, and theTHQ obtained here were far below the recommendedamounts, compared to the set values (RfD and PTWI) orother studies (Table 3). The THQ values were lower thanone for all three studied metals. The findings indicatedthat the consumption of farmed rainbow trout in thestudy area does not pose a potential non-carcinogenicrisk to human health.Feeds and heavy metal concentrations. The mean± SD contents of heavy metals in the commercialfeed mixtures (I, II, and III) used in the rainbow troutfarms of this region are shown in Table 4. The resultsindicated some differences in commercial feeds basedon the content of heavy metals. Food I contained higherlevels of Pb (5.8 mg/kg–1) compared to the EuropeanCommission Regulations (EC) [53]. Using different rawmaterials in fish pellets resulted in some alteration ofheavy metal contents in fish feed mixtures.The mean concentrations of Hg, Cd, and Pbin muscle tissues of rainbow trout with regard to the typeof food consumed in each of the farms are presentedin Fig. 3.We observed that various commercial mixtures couldinfluence the accumulation of heavy metals in farmedrainbow trout. The concentrations of Hg, Cd, and Pb inthe fishes that consumed pellet II were 0.05, 0.076, and0.893 mg/kg–1, respectively. Using pellet III resulted ina higher content of mercury and a lower concentrationof cadmium, compared to the fishes fed on mixturesI and II (P < 0.05). On the whole, we concluded thatthe accumulation of heavy metals in fish was mainlyinfluenced by water, food, and sediment. However, theaccumulation of these elements in water and food isdue to various factors including ecology, metabolism,pollution of slope water, food, and sediment, as wellas other factors such as solubility, temperature, andinteraction of various parameters [54, 55].In our study, however, food intake had a significanteffect on the concentration of heavy metals inrainbow trout muscle tissue: the consumption ofpellet III resulted in a marked increase in mercuryand a considerable reduction in cadmium andlead. Researchers have reported that there is alarge association between the concentration ofheavy metals in fish and its nutritional habits [22].Mixture I had higher levels of Pb (5.8 mg/kg–1)compared to the values established by the EuropeanCommission Regulations (EC) [53]. Using differentraw materials to prepare feed pellets resulted in somealteration of heavy metal contents in the commercialfood mixtures. The accumulation of heavy metals infish depends on food habits, reproductive status, size,and sex [21, 56]. Deep sediments contain large amountsof heavy metals. Compared to the epipelagic organisms,benthos occupying the deepest layers of water is thelargest source of heavy metals [22].Biomagnification factor. The BMF values forall the metals were under 1 (Table 5). Actually,the concentrations of the examined metals in thecommercial pellets used in this region were higherthan those in the rainbow trout tissues. As Table 5demonstrates, the BMF values for the three metals hadthe following pattern: Hg > Pb > Cd (Table 5). The BMFwas applied to show the capability of a contaminant tobioaccumulate. When a metal BMF is less than one, itindicates that no biomagnification occurred in the biosystem [26]. The current study showed that the BMFvalues were lower than one for all the metals (Table 5),suggesting that these metal contaminants were notbiomagnified by rainbow trout from the diet. Thisfinding was similar to the result obtained by Varol et al.[57]. Nevertheless, biomagnification implies inadequateTable 4 Heavy metal levels in commercial feed mixturesconsumed by farmed rainbow trout in three differentaquaculture sitesFeedmixturesLead (Pb) Cadmium (Cd) Mercury (Hg)I 5.8 ± 0.365* 0.61 ± 0.093 0.075 ± 0.013II 4.52 ± 0.259 0.54 ± 0.106 0.063 ± 0.018III 4.15 ± 0.384 0.66 ± 0.076 0.071 ± 0.026All results are expressed as means ± SD (mg/kg–1) for three feedmixtures* indicates a higher level of lead in pellet I compared to the EuropeanCommission standardsFigure 3 Heavy metal concentrations in muscle tissue offarmed rainbow trout in relation to the type of commercialfeed mixture (C: pellet I; F: pellet II; B: pellet III). All resultsare expressed as means ± SD for six fish in each group. a andb: groups with different letters differ significantly (P < 0.05)Feed mixture334Majlesi M. et al. Foods and Raw Materials, 2019, vol. 7, no. 2, pp. 329–338information on the real threat from heavy metals in anaquatic food chain [58].Physical characteristics and heavy metal levels.Table 6 shows the biometric characteristics of thesampled rainbow trouts. The relationship between metalconcentrations and fish size (length and weight) is shownin Table 7. Increasing the weight and length of farmedtrouts generally reduced the concentration of the threeheavy metals. The Pearson correlation test revealedsignificant negative associations between the cadmiumand lead concentrations and the weight of the fishsamples (r = –0.519 and r = –0.580, respectively).Few studies have focused on the relationship betweenphysical characteristics and heavy metal accumulation.To the best of our knowledge, this is the first study onthe relationship between the length and weight of farmedrainbow trout and the concentration of mercury, lead,and cadmium. Most of the authors have found a negativerelationship between heavy metal accumulation and thesize of fish (length and weight). They suggested thatmetabolic activity is one of the most important factorsaffecting the accumulation of heavy metals in marinefish [59]. Higher metabolic activity in juvenile fish leadsto a higher accumulation of heavy metals [60, 61].The correlation between the spectroscopicparameters and the concentration of heavy metals hasbeen reported to be negative in various species of fish[61]. Heavy metal content in fish after a certain ageremains almost constant [62]. In contrast to our results,Widianarko et al. found that in sturgeon species in theCaspian Sea, a higher accumulation of heavy metalswith an increase in age, length, and weight of fish [63].In general, there is a consensus that metals in livingorganisms are detoxified and depleted by a specialmechanism, which is significantly dependent on theTable 5 Biomagnification factors of three metalsAquaculturefarmsLead (Pb) Cadmium (Cd) Mercury (Hg)Site A 0.15 0.11 0.28Site B 0.25 0.22 0.36Site C 0.37 0.22 0.38Table 6 Biometric characteristics of farmed rainbow troutsampled from different farming sitesFeed mixtures Length, cm Weight, gSite A 33.66 ± 2.33 504.66 ± 122.65Site B 28.16 ± 2.78 262.00 ± 77.80Site C 34.83 ± 5.07 446.33 ± 226.37All results are expressed as means ± SD for eight fish in each groupTable 7 Relationships between heavy metal concentrationsand farmed rainbow trout length and weightPhysicalcharacteristicsLead(Pb)Cadmium(Cd)Mercury(Hg)LengthPearson correlation–0.383 –0.296 –0.217sig. (two-tailed) 0.116 0.232 0.386WeightPearson correlation–0.580* –0.519* –0.266sig. (two-tailed) 0.012 0.027 0.286* indicates a significant correlation (P < 0.05)metabolism in the particular weight [64, 65]. Therefore,the negative relationship between heavy metalconcentrations and the size of fish does not necessarilymean that a certain amount of metals will accumulatein the body at the beginning of the growth, and no moremetals will be subsequently absorbed [66]. It has alsobeen suggested that the absorption of metals in lowcontaminatedwater sources is more affected by nutrition[67]. In other words, a significant reduction in theamount of heavy metals in organs at the maturity stageis due to a decrease in the daily fish diet with age [68].The fish at the highest nutritional level are expected tohave the highest accumulation of heavy metals [69, 70].CONCLUSIONAccording to the results of the study, the levels ofmercury, cadmium, and lead in the muscle tissue ofrainbow trout farmed in Yasuj were found to be belowthe permitted values. The findings showed that thehealth risk assessment parameters (EDI, EWI, THQ)were far below the recommended values. This indicatedthat the consumption of farmed rainbow trout in thestudy area did not have any adverse effect on humanhealth caused by heavy metal contamination.However, the release of urban and rural wastewaterand pollutants from human activities into the riversleads to increased levels of lead and cadmium in the fishfarmed in the downstream fields of the countryside andcities. Moreover, the application of various commercialpellets containing different levels of heavy metals canaffect the accumulation of these metals in farmed trout.CONFLICT OF INTERESTThe authors declare that there is no conflict ofinterest.ACKNOWLEDGEMENTSWe would like to thank Mr. E. Sharifpoor for histechnical assistance.