Health risk assessment of the heavy metal levels in marketed Liza aurata (Risso, 1810) from the Urla Coast (Eastern Aegean Sea, Türkiye)

Located on the Aegean coast of western Turkey and of strategic importance in terms of maritime transportation and trade, the Gulf of Izmir is also an important production area where intensive fishing activities continue. The gulf, which has a surface area of approximately 410.3 km², is located between 38°20′–38°40′ north latitude and 26°30′–27°10′ east longitude. Due to the large number of fishing ports and harbors, a large portion of commercial fishing in the province of Izmir is concentrated in this region. While the gulf offers breeding, feeding, and growth areas for many aquatic species, it also attracts attention with its coastal fishing activities that continue throughout the year. In this area, where coastal fishing methods are prevalent, the fish caught are usually offered for consumption in local markets, with auctions held in the morning hours (Tokaç, 2017). This situation ensures that the aquatic products obtained from the region reach consumers directly and necessitates the evaluation of the effects of possible pollutants on human health.

Samples were obtained seasonally between 2017 and 2018 from individuals of L. aurata caught within the scope of commercial fishing activities carried out on the Urla coast of Izmir Bay and offered for sale at the Urla auction (Fig. 1). The fish samples used in this study were selected to reflect the actual consumption chain in the region. Fish were taken on the first day of fishing. In each sampling period, dead fish were collected from fishermen and immediately brought to the laboratory in polyethylene containers filled with ice. In this study, a total of 80 L. aurata, 10 for each season, were used to determine metal concentrations. The average total length of the fish samples was 24.49 ± 1.03 cm, and the average total weight was 250.49 ± 15.73 g. Approximately 5 g pieces were separated from the dorsal surface muscle, liver, and two gills of each fish sample using clean stainless steel instruments. Each tissue sample was measured as wet weight (0.0001 g) using the XB 22OA, Precisa (Zurich, Switzerland) instrument and stored in a freezer at -20°C until analysis. The samples were dissolved in concentrated HNO₃:HClO₄ (5:1) (extra pure Merck) according to the method of Bernhard (1976) and filtered. Heavy metal concentrations (Cd, Cu, Pb, Zn) were analyzed using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) (Perkin Elmer 2000 DV, Waltham, MA, USA). All samples were analyzed in triplicate to measure precision. Blank samples were always analyzed under the same conditions as the samples. The results are expressed as mg kg⁻¹ wet weight. Standard solutions were prepared using Merck multi-element standard solutions (Darmstadt, Germany). DORM-2 shark muscle certified reference material was analyzed as a calibration verification standard, and recovery rates for each of the four elements in fish ranged from 96% to 106%, demonstrating good accuracy of the method.

Figure 1

Sampling location.

The normal distribution of the data was tested using the one-sample Kolmogorov–Smirnov test. The homogeneity of variances was tested using Levene’s test. Tukey HSD (Honestly Significant Difference) and Tamhane Tests were applied to determine the differences between tissue samples and sampling periods. Statistically significant differences were expressed as p < 0.05. All analyses were performed using SPSS 25.0 (IBM Corp., Armonk, NY, USA).

Evaluation of the possible risk of pollutants to human health is mainly based on prediction or identification of the adverse effects of toxicants on human health (Babuji et al., 2023). The EDI, EWI, target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR) are parameters normally used for evaluation of the possible impact of heavy metals on human health by the United States Environmental Protection Agency (US EPA) (2007). These evaluation parameters can vary depending on factors such as the amount of metal intake, duration of exposure, the average body weight (BW), and the reference dose from mouth (RfD), US EPA (2007). Two integrated indices were estimated based on the non-carcinogenic and carcinogenic effects of heavy metal accumulation. While the non-carcinogenic index is used to evaluate the adverse effects of heavy metals on health, the carcinogenic index is used to evaluate the potential of certain metals to increase the risk of cancer.

The EWI and EDI heavy metal exposure due to fish consumption were determined for human health risk assessment and were also compared with the provisional tolerable weekly intake (PTWI). The weekly metal consumption that is acceptable as PTWI is established by the Food and Agriculture Organization/World Health Organization (FAO/WHO) and the Joint Expert Committee on Food Additives (JECFA) (FAO/WHO, 2010, 2011). The PTWI is the estimate, from all sources, of the amount of a substance in food or drinking water, expressed as an amount per BW that can be ingested weekly over a lifetime without appreciable health risks (mg · kg⁻¹ or μg · kg⁻¹ BW). EWI for the intake of fish muscle (g) was estimated using the following formula, and then EDI was obtained by dividing the EWI value by 7. In Türkiye, the average per capita consumption of aquatic products was 5.5 kg in 2017, 6.3 kg in 2019, and 6.7 kg in 2021, while the annual per capita consumption of aquatic products was revealed as 7.3 kg in 2022, which increased by 12% in comparison to the previous year according to the data from TUIK (2023). The annual average per capita consumption of aquatic products in Türkiye is 7.3 kg or 20 g · person⁻¹ · day⁻¹. EWI=WFC×MCBW{\rm{EWI}} = {{{\rm{WFC}} \times {\rm{MC}}} \over {{\rm{BW}}}}

MC: Concentration (average amount of metal in fish muscle tissue, mg · kg⁻¹) WFC: Consumption rate (g) BW: Indicates BW (kg).

Non-carcinogenic health risks posed by mullet consumption for Turkish consumers were evaluated according to the THQ. THQ expresses the non-carcinogenic risk of metal levels taken into the body. The formula used in the THQ calculation is given below (Abdel-Kader & Mourad, 2022; Korkmaz et al., 2019; Mol et al., 2017; Taş et al., 2024): THQ=EF×ED×IR×MCRfD×BW×AT×10-3{\rm{THQ = }}{{{\rm{EF \times ED \times IR \times MC}}} \over {{\rm{RfD \times BW \times AT}}}}{\rm{ \times 1}}{{\rm{0}}^{{\rm{ - 3}}}} where EF is Exposure frequency (365 days · year⁻¹), ED is Exposure duration (year) (in case of a 70-kg adult exposed to metals through consumption for 30 years), IR is the Daily fish consumption rate, MC is the Determined metal concentration (mg · kg⁻¹), AT is the Average exposure duration (365 days × 30 years— non-carcinogenic), BW is body weight, RfD is the Oral reference dose (mg · kg⁻¹, day), and 10⁻³ is the unit conversion factor US EPA (2024). Oral reference dose (RfD) values of metals are given as 0.001; 0.04; 0.004; 0.3 (mg · kg⁻¹, day) for Cd, Cu, Pb, Zn, respectively, as per US EPA (2009). The value expressed as the total THQ value of all metals investigated is calculated as Σ THQ. A Σ THQ >1 indicates that there are non-carcinogenic health risks for consumers (US EPA, 1989): ΣTHQ=(THQCd+THQCu+THQPb+THQZn)\Sigma {\rm{THQ}} = ({\rm{THQCd}} + {\rm{THQCu}} + {\rm{THQPb}} + {\rm{THQZn}})

In addition, the carcinogenic health risks associated with consuming grey mullet by Turkish consumers were evaluated according to the carcinogenic risks (CR) framework. CR refers to the increase in the risk of an individual developing cancer throughout their life as a result of exposure to a potential carcinogen. This risk is calculated using the cancer slope factor (CSF), which determines the level of environmental exposure and the carcinogenic potential of the relevant chemical (Abbas, 2023). According to the US EPA (1989), acceptable lifetime carcinogenic risk levels for human health generally range between 10⁻⁴ and 10⁻⁶. Carcinogenic risk is interpreted as CR < 1 × 10⁻⁶ insignificant risk; 1 × 10⁻⁶ < CR < 1 × 10⁻⁴ lower acceptable risk range, and 1 × 10⁻³ < CR < 1 × 10⁻¹ high carcinogenic risk levels (Le et al., 2023). The specific CR value of a metal is calculated based on the CSF and the amount of exposure of the individual. Such risk assessments are critical for understanding the potential effects of heavy metal pollution on public health and for developing preventive policies. The lifetime carcinogenic risk was calculated using the formula given below (US EPA (2024); Ahmed et al., 2015). In this calculation, CSF values defined for toxic metals such as Pb and Cd were used. However, since there are no reliable CSFs defined for essential elements such as Zn and Cu and since these metals are physiologically required at certain levels in the body, CR calculations for Zn and Cu were not performed in this study. In this formula, for Cd and Pb, 0.380; 0.0085; the relevant slope factors of mg · kg⁻¹ · day⁻¹ were used (Azadeh et al., 2022; Mohammadi et al., 2024; Pan et al., 2019): CR=EF×ED×MC×IR×CSFBW×AT×10−3{\rm{CR}} = {{{\rm{EF}} \times {\rm{ED}} \times {\rm{MC}} \times {\rm{IR}} \times {\rm{CSF}}} \over {{\rm{BW}} \times {\rm{AT}}}} \times {10^{ - 3}} where CR is carcinogenic risk, EF is exposure frequency (365 days · year⁻¹), ED is exposure duration (years), MC is concentration of heavy metals in mg · kg⁻¹ in fish muscle, IR is daily fish consumption rate, BW is body weight, AT is average exposure duration (365 days × number of exposure years, assuming 70 years for carcinogenic), 10⁻³ is the unit conversion factor, and CSF is the oral cancer slope factor provided by US EPA (1989).

In this study, heavy metal accumulation in L. aurata was investigated, and it was determined that the metal concentrations varied in different tissues. The average heavy metal accumulation of Cd, Cu, Pb, and Zn in the muscle, gill, and liver tissues of L. aurata is presented in Table 1, and their distribution according to seasons is presented in Figs. 2–5. According to the findings, metal concentrations followed the order of Zn > Cu > Pb > Cd in all tissues. In other words, Zn was detected at the highest concentration in all sampling periods and all tissue types, followed by other metals, respectively. Although positive and statistically significant relationships have been reported between the total length, BW, and metallothionein level in the liver cytosol of fish and metal accumulation in general (Oliveira et al., 2010; Wosnick et al., 2021), no significant relationship was found between the length and weight of L. aurata individuals and heavy metal accumulation in this study (p > 0.05).

Figure 2

Seasonal distribution of Zn concentrations (mg · kg⁻¹ ww) in liver, gill, and muscle tissues of L. aurata.

Figure 3

Seasonal distribution of Cu concentrations (mg · kg⁻¹ ww) in liver, gill, and muscle tissues of L. aurata.

Figure 4

Seasonal distribution of Pb concentrations (mg · kg⁻¹ ww) in liver, gill, and muscle tissues of L. aurata.

Figure 5

Seasonal distribution of Cd concentrations (mg · kg⁻¹ ww) in liver, gill, and muscle tissues of L. aurata.

For a long time, the examinations have been used to estimate the health risk to humans from heavy metal content in numerous fish species. Although toxicological limits may not have been surpassed for the average consumer, the health risk of heavy metal exposure may appear for heavy consumers of a particular fish species (Leblanc et al., 2005). Consequently, the weekly (EWI) and daily (EDI) dietary exposures were calculated for L. aurata and compared with the PTWI. Moreover, non-carcinogenic health risks (THQ and Σ THQ) and carcinogenic health risks (CR) were estimated for consumers, and the results are listed in Table 3.

In this study, fish samples were assessed for potential impact of the heavy metals on human health; the EWI for heavy metals was compared with the PTWI of individuals with a BW of 70 kg (adult). The EWI of Cd was above the 70 kg adult PTWI. The EWI for 2017 was 0.648 mg · week⁻¹, whereas the PTWI limit is 0.49 mg · week⁻¹. This difference became even larger in 2018: the EWI value was calculated to be 0.904 mg · week⁻¹. This indicates that exposure to Cd in both years was higher than the permissible levels in the short term. The rise in Cd accumulation with time also suggests that Cd requires careful surveillance on health perspectives. The estimated EWI values of Pb in 2017 and 2018 were 1.296 mg · week⁻¹ and 1.276 mg · week⁻¹, respectively, which were also lower than the PTWI (1.75 mg · week⁻¹). These findings indicate that exposure to Pb was not excessive during the time frame studied. Although the determined ones are below the admissible ones for public health, the values obtained, which are relatively closer to the limit values, do not exclude carrying them out carefully for the purpose of monitoring Pb contamination. The EWI of Cu in 2017 and 2018 was computed as 1.096 mg · week⁻¹ and 1.168 mg · week⁻¹, respectively. These levels are substantially lower than the PTWI of 245 mg · week⁻¹. The values obtained indicate that the ingestion of L. aurata is safe in relation to Cu, and the levels of exposure do not pose any health risk. The estimated EWI values for Zn in both years were well below the PTWI limit (490 mg · week⁻¹) Cd, in particular, was found to exceed the permissible limits more frequently than other metals. In this regard, strategies for environmental monitoring and source control of Cd are crucial.

When non-carcinogenic health risks (THQ and Σ THQ) for consumers were examined, the THQ values for 2017 were calculated as Cd: 0.092, Cu: 0.004, Pb: 0.044, and Zn: 0.004, respectively. In 2018, these values were Cd: 0.129, Cu: 0.004, Pb: 0.045, and Zn: 0.004. The THQ value of no metal exceeded 1 in both years. These results reveal that consumption of the examined fish is within acceptable limits in terms of non-carcinogenic health risks. Total Target Hazard Quotient (ΣTHQ) was found to be 0.144 for 2017 and 0.182 for 2018. The fact that ΣTHQ values are below 1 indicates that the combined toxic effects resulting from the combined effect of metal accumulation do not pose a significant risk to public health. However, Cd is seen to have the highest THQ contribution in both years; this is an indicator that will require regular monitoring of cadmium in fish in this region.

In this study, carcinogenic risk (CR) was assessed for Cd and Pb, representing the potential long-term carcinogenic effects of these metals. CR reflects the probability of developing cancer from lifetime exposure. The values were Cd: 3.52 × 10⁻⁵ and Pb: 1.58 × 10⁻⁶ in 2017, and Cd: 4.91 × 10⁻⁵ and Pb: 1.55 × 10⁻⁶ in 2018. Although the CR values calculated for Pb slightly exceeded the threshold of 1 × 10⁻⁶ in both years and technically fall into the “low acceptable risk” category, they remain very close to the ‘negligible risk’ level. This indicates that under current conditions, Pb does not pose a significant public health risk, although long-term exposure should be monitored. The CR values calculated for Cd fall within the range of 1 × 10⁻⁶ < CR < 1 × 10⁻⁴, which is interpreted as a “low acceptable risk’. Overall, since the CR values for both metals remain below the maximum lifetime risk threshold of 1 × 10⁻⁴ accepted by the US EPA, they do not indicate a significant carcinogenic risk to public health. However, Cd is identified as a critical metal that should be carefully monitored under long-term exposure scenarios.