1. Introduction
Fish have been consumed by the Thai people for at least 3000 years as evidenced by a striped head fish fossil [
1]. As a food group, fish are important sources of high-quality proteins, minerals, vitamins, and essential omega-3 fatty acids [
2], as well as being unique dietary sources for cardioprotection due to docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids [
3]. Consequently, increased fish consumption is recommended to improve the health of all population groups.
Thailand’s economic growth has brought about extensive infrastructural and industrial development as well as the export industry promotion. Unfortunately, the absence of proper future planning has led to the deterioration of water sources and aquatic habitats due to the toxic elements used in industrial production (plastic, equipment, paint, PVC, and batteries), in agriculture (insecticide and fertilizer), and in medical/health industries (drugs, medical equipment, and cosmetics). While there are many types of toxic elements, arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) are of priority concern in terms of food safety standards [
4]. In particular, they play a prominent role in damaging the human nervous and urinary systems [
4,
5,
6,
7]. Long-term oral exposure to low levels of inorganic arsenic may cause dermal effects (such as hyperpigmentation and hyperkeratosis, corns, and warts) and peripheral neuropathy characterized by numbness in the hands and feet that may progress to a painful “pins and needles” sensation [
5]. Cadmium in the human body can cause renal tubular damage, glomerular damage, decreased bone mineralization, increased risk of bone fractures, decreased lung function, and emphysema. These effects typically occur after long-term exposure to cadmium. Lead in the human body can affect decreased cognitive function, alterations in mood and behavior, altered neuromotor and neurosensory function, decreased glomerular filtration rate, increased blood pressure, decreased activity of several heme biosynthesis enzymes, decreased sperm, and spontaneous abortion [
6]. Mercury is toxic to the nervous, digestive, and urinary systems. Therefore, Thailand’s Ministry of Public Health recognizes this danger and has mandated the maximum limit of As, Cd, Pb, and Hg in fish to be 2.0, 1.0, 0.3, and 0.5 mg/kg, respectively, based on the notification of Ministry of Public Health [
8].
In response to consumer health concerns, research studies have investigated toxic-element contamination in commonly consumed freshwater and marine fish species in Thailand. For example, arsenic concentrations in Nile tilapia, red tilapia, striped snaked fish, king mackerel, sea bass, and grouper from commercial markets in Bangkok were reported to be 0.50, 1.76, 0.31, 3.11, 11.65, and 4.42 mg/kg, respectively, while mercury concentrations were <0.50, <0.50, 0.90, 1.13, 0.75, and 1.37 mg/kg, respectively [
9]. Likewise, compared to the maximum limit, arsenic concentrations in king mackerel, sea bass, and grouper were reported to be higher than the maximum limit of 2 mg/kg, while mercury concentrations in striped snaked fish, king mackerel, sea bass, and grouper were higher than the maximum limit of 0.5 mg/kg [
9].
Toxic element contamination in fish may be dependent on several factors, such as the location of aquatic zones, the contamination levels of fishing sites, environmental conditions, characteristics of the fish, and even household cooking practices. To explore this consumer health issue in more detail, this study investigated levels of arsenic, cadmium, mercury, and lead in commonly consumed fish using inductively coupled plasma mass spectrometry (ICP-MS-MS) and assessed the risk of exposure for Thailand’s consumers through the consumption of these fish species.
3. Results
3.1. Moisture and Toxic Element Contents
The moisture contents of the fifteen fish species ranged from 69.62 to 86.64% depending on the type of fish (
Table 2). The total As, Cd, Hg, and Pb contents of the fish are shown in
Table 2.
The arsenic content of freshwater fish ranged from 0.01 to 0.48 mg/kg fresh weight (FW). The three fish species containing the highest arsenic content were striped snake-head fish (0.48 ± 0.14 mg/kg FW), red tilapia (0.15 ± 0.10 mg/kg FW), and Nile tilapia (0.10 ± 0.07 mg/kg FW). For marine fish, the arsenic content ranged from 0.46 to 8.51 mg/kg FW, with the highest levels found in grouper (8.51 ± 1.60 mg/kg FW), long-tail tuna (1.92 ± 0.27 mg/kg FW), and king mackerel (1.36 ± 0.26 mg/kg FW).
The cadmium content in freshwater fish was lower than the limit of detection (<LOD, 0.0009 mg/kg FW), except for striped snake-head fish (<LOQ, 0.0062 mg/kg FW). For marine fish, the cadmium content was negligible in the range of LOD (0.0009 mg/kg FW) in seabass to 0.04 mg/kg FW in Indo-Pacific mackerel. The three highest cadmium contents were found in Indo-Pacific mackerel (0.04 ± 0.02 mg/kg FW), long-tail tuna (0.02 ± 0.02 mg/kg FW), and Atlantic mackerel (0.02 ± 0.01 mg/kg FW).
The mercury content in the freshwater fish was lower than the limit of quantitation (<LOQ, 0.0124 mg/kg FW), except for striped snake-head fish (0.02 ± 0.01 mg/kg FW). For marine fish, the mercury content was in the range of <LOQ in mullet to 0.38 mg/kg FW in grouper. The top three marine fish with highest mercury content were grouper (0.38 ± 0.17 mg/kg FW), king mackerel (0.09 ± 0.06 mg/kg FW), and long-tail tuna (0.07 ± 0.02 mg/kg FW).
All fish species contained lead in small amounts (<LOQ, 0.012 mg/kg FW).
3.2. Comparison of Toxic Element Content with Legal Standard
Most of the fish had toxic elements lower than the national standards [
8], except for long-tail tuna and grouper that had total arsenic contents of 1.92 and 8.51 mg/kg FW, respectively, which are higher than the standard (2 mg/kg). Grouper also had a mercury content of 0.55 mg/kg FW, which is higher than the standard (0.5 mg/kg).
3.3. Risk Assessment of Toxic Elements through Fish Consumption
From the national food consumption data, the consumption amount was present in cooked form. In this study, the toxic element contents in the raw fish were low, and cooking could not affect these elements. Hence, the yield factor (weight before and after cooking) was used to calculate the toxic element content of the cooked samples. Different from the other toxic elements, one more important piece of information required for conducting a risk assessment for arsenic was the percentage of inorganic arsenic in fish. To calculate exposure for assessments, inorganic arsenic content must be used. The calculation of risk using the % inorganic arsenic of total arsenic (% iAs) as based on previous research [
18,
19,
20] was applied. Fifteen types of fish were categorized into 5 food groups based on consumption data [
21], with the yield factor and % inorganic arsenic of each group as shown in
Table 3.
3.3.1. Long Scaly Freshwater Fish
The results of this study revealed that persons aged 0–2.9 years old and those who had high consumption had a margin of exposure lower than 100, indicating a high risk of concern for arsenic (
Table 4). Consumers in all age groups also had a margin of exposure lower than 100, which implies a high risk of concern for arsenic for consumers of long scaly freshwater fish. For cadmium, mercury, and lead, all population groups showed a percentage of risk less than 100, which implies safety from the risk of the consumption of long scaly freshwater fish.
3.3.2. Long Non-Scaly Freshwater Fish
For arsenic, all population groups had a margin of exposure higher than 100, which implies a low risk of concern from arsenic for all populations. For cadmium, mercury, and lead, all population groups had a percentage of risk less than 100, which implies safety from the risk that can be caused by these elements from the consumption of long non-scaly freshwater fish.
3.3.3. Flat Scaly Freshwater Fish
For arsenic (
Table 5), the populations had a margin of exposure lower than 100, which implies a high risk of concern but only for some age groups (all age groups, except 18–64.9 years, for boiled fish and those aged 3–12.9 years for fried fish) and in extreme cases (97.5th percentile, high amount of consumption, and high arsenic content in fish). For consumers only, all age groups with consumption of high content of arsenic in fish, except for those persons aged 35 years or older for boiled fish and those aged 18 years or older for fried fish, had an MOE lower than 100, which implies a high risk of concern for arsenic. Some age groups (0–5.9 years old in boiled fish and 3–5.9 years old in fried fish) who had high consumption of average arsenic content in marine fish also had an MOE lower than 100, which can be assumed a high risk of concern from arsenic.
For cadmium (Cd), mercury (Hg), and lead (Pb), all groups of the population had a percentage of risk less than 100. This can be assumed as a low risk of concern that might be caused by cadmium, mercury, and lead from the consumption of flat scaly freshwater fish.
3.3.4. Marine Fish
For arsenic (As) (
Table 6), the results revealed that for the population per capita in all ages with a high amount of consumption, except the case of average arsenic amounts in marine fish at the age of 65 years and older in both boiled and fried fish and 13–17.9 years old in fried fish, the MOE was lower than 100, which can be assumed a high risk of concern from arsenic for eaters of marine fish. In addition, some age groups (0–5.9 years old in boiled fish and 0–2.9 years old in fried fish) with high consumption of an average mercury content in marine fish also had an MOE lower than 100, which can be assumed to be a high risk of concern from arsenic. Eaters in all age groups also had an MOE lower than 100, which can be assumed to be a high risk of concern from arsenic for eaters of marine fish.
For mercury (Hg) and population per capita, only the population aged 0–2.9 years old with high consumption of a high mercury content in marine fish had a percentage of risk lower than 100, which can be assumed as a low risk that might be caused by mercury from the consumption of marine fish. For eaters only, all age groups with consumption of a high content of mercury in fish, except those 65 years older in fried fish, had a percentage of risk lower than 100. Also, some age groups (0–12.9 years old in boiled fish and 0–2.9 years old in fried fish) with high consumption of an average mercury content in marine fish had a percentage of risk lower than 100. This can be assumed as a low risk that might be caused by mercury from the consumption of marine fish in cases of a high mercury content in marine fish.
For cadmium (Cd) and lead (Pb), all groups of the population had a percentage of risk less than 100. This can be assumed as safety from risk that can be caused by cadmium and lead from the consumption of marine fish.
3.3.5. Indo-Pacific Mackerel
For arsenic (As), only the population per capita in the age of 3–5.9 years with a high amount of consumption and the age of 0–2.9 years in an extreme case (a high amount of consumption and a high arsenic content in fish) had an MOE lower than 100, which can be assumed a high risk of concern from arsenic. For eaters only, all ages with a high amount of consumption, except the age of 18–64.9 years with high consumption of an average mercury content in mackerel, had an MOE lower than 100 together with the age of 3–5.9 years with average consumption of a high arsenic content in mackerel, which can be assumed a high risk of concern from arsenic, as shown in
Table 7.
For cadmium (Cd), mercury (Hg), and lead (Pb), all groups of the population had a percentage of risk less than 100. This can be assumed as safety from risk that can be caused by cadmium, mercury, and lead from the consumption of Indo-Pacific mackerel.
5. Conclusions
All studied toxic elements (As, Cd, Hg, and Pb) in the studied fish were found to be below the legal Thai standard, except grouper, which had the highest mercury content that did not comply with the legal standard. The risk assessment showed no risk from cadmium and lead in the studied fish. Most fish samples posed a high risk of concern regarding arsenic exposure, except the long, non-scaly freshwater fish group. The high-risk group of Indo-Pacific mackerel is mostly in an eaters-only group with high consumption while the high risk of flat-scaly freshwater fish only occurs when flat-scaly freshwater fish have a high arsenic content. On the other hand, the eaters-only group was identified as the high-risk group for marine fish, and long-scaly freshwater fish especially in children aged 0–5.9 years had a high risk of concern from arsenic. These results showed the possibility of the adverse effects of exposure to toxic elements from the consumption of the studied fish. Marine fish also had a high risk from mercury exposure for most of the eaters-only group, especially when consuming fish with a high mercury content. Information on potential foods contaminated with toxic elements should be provided to consumers to prevent adverse effects on human health. Food safety authorities should regularly monitor the levels of toxic element contamination in high-risk food products.