Oxidative response to Cd and Pb accumulation in coastal fishes of Pattani Bay

Abstract

Bioaccumulation of heavy metals can cause physiological and biochemical alterations in aquatic animals. Accumulation of Cd and Pb and oxidative response in the liver and muscle of fish species; Scatophagus argus, Plotosus lineatus, Netuma thalassina and Mugil cephalus were evaluated. Accumulation of Cd, Pb and oxidative response indicated by malondialdehyde (MDA) were significantly higher in the liver than muscle in all coastal fish species. Antioxidative parameters, such as reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD), varied. S. argus exhibited the highest levels of Cd and Pb accumulation, both in the liver and muscle. Simultaneous activation and depression of oxidative defense mechanism was depicted in S. argus’s liver which indicated by positive correlation of Pb to CAT activity and negative correlation of Pb to SOD activity. Positive correlation was significance for Cd and Pb accumulation in the liver and muscle of M. cephalus, which may be used for pollution biomonitoring. The present study indicated the oxidative response to Cd and Pb accumulation was emphasise in liver, while oxidative response varied in each coastal fish species.

Highlights

• Accumulation of Cd, Pb, and oxidative status, i.e., lipid peroxidation level indicated by malondialdehyde (MDA), was significantly higher in the liver than muscle in 4 coastal fish species (Scatophagus argus, Plotosus lineatus, Netuma thalassina, and Mugil cephalus).

• S. argus exhibited the highest levels of Cd and Pb accumulation, both in the liver and muscle, when compared to other three coastal fish species. The liver’s oxidative response to Pb was high in S. argus, and represented simultaneous activation and depression of antioxidative defense mechanism.

• A significant positive correlation was revealed for Cd and Pb accumulation in the liver and muscle of M. cephalus, which may be used for pollution biomonitoring.

Keywords:

• Bioaccumulation
• lipid peroxidation
• oxidative stress
• cadmium
• lead
• Pattani Bay

Introduction

Pattani Bay is a developing site planned by the government, with more than 200 factories in addition to coastal aquaculture, a seafood-bank establishment, and seaport development (Sowana et al. 2011). The increase of pollution release near the sea is unavoidable. Solid waste and wastewater contamination from land activity may influence the quality of aquatic ecosystems, which is vital to ensure health protection for humans and wildlife (Espejo et al. 2019). Bioaccumulation of heavy metals in aquatic animals’ tissue can be used to monitor water pollution according to whether accumulation is higher in the tissue than in surrounding water or sediment. Bioaccumulation can indicate biomagnification according to ages of animals, exposure period, or the maintenance of accumulation in their bodies by continuously eating contaminated food or prey. Human health is not the only concern in terms of contaminated food; aquatic animals’ health is also threatened by heavy metal accumulation (Zhao et al. 2022). Chronic exposure to heavy metals, bioaccumulation, and magnification of heavy metals can reduce animals’ quality of life, including alteration of metabolism, reduced growth rate and reproductive ability, and increased mortality (Authman et al. 2015). Heavy metal accumulation in animal’s tissue and variety linkage of cellular toxicity is mentioned. Researches have emphasis the involvement of heavy metal in oxidative damage, inflammatory response and apoptotic induction (Zhao et al. 2020; Yu et al. 2021). Metal-induced oxidative stress in cells can be partially responsible for the toxic effects of heavy metals. Under oxidative stress, cells display various dysfunctions due to reactive oxygen species (ROS)-induced lipids, proteins and DNA damages. (Ercal et al. 2001). Therefore, the detoxification process and oxidative response mechanisms are vital as major cellular processes to counteract the harm induced by a variety of noxious materials.

Oxidative stress in aerobic life is an unavoidable process, and balancing of ROS is normally controllable. However, there are a variety of ROS-inducing factors, which sometimes challenge the limitation of oxidative defense mechanisms. Mitochondria play a major role in respiration and ROS’ endogenous sources. Environmental exposure to harmful substances or toxic chemicals disrupts the mitochondrial function and prompts release of ROS. Contaminant-stimulated ROS formation results in oxidative damage in fish and initiates a mechanism of toxicity in pollution exposure (Chowdhury and Saikia 2020). Large amounts of free radical formation and exceeding the limit of oxidative defense mechanisms can lead to various types of deterioration, including changes in cell redox status, oxidation of proteins and lipids, alteration of cells’ function, and death (Livingstone 2003). Similar to those in mammals, fish’s oxidative defense mechanisms include the enzymatic system and low–molecular-weight antioxidants (Migdal and Serres 2011). These processes are activated in response to a deteriorating environment and harmful conditions. As an aquatic pollutant, heavy metals are indicated for oxidative stress induction, but oxidative defense mechanisms are impaired when exposed to heavy metals, i.e. lead (Pb) and cadmium (Cd) (Sevcikova et al. 2011).

Cd is a non-essential metal with unclear biological function. In aquatic environments, Cd is released mostly from industrial activity (Järup 2003). Cd causes severe toxicity to fishes regarding to oxidative stress-inducing effects of Cd in mitochondrial electron transport chain blockage and led to ROS formation (Garai et al. 2021), alteration of reduced glutathione (GSH) level, influence on cells’ thiol status, and lipid peroxidation (Stohs and Bagchi 1995). In addition, Cd’s alteration effects on mitochondrial function participate in superoxide radical formation and influence antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). CAT activity is reduced following Cd exposure by direct binding of Cd to CAT (Roméo et al. 2000). Pb is a major environmental pollutant and considered one of the most hazardous heavy metals, found in paint, cosmetics, medicines, food supplements, and petroleum-based fuels (Stohs and Bagchi 1995). Pb causes oxidative damage directly to cell membranes, auto-oxidation of haemoglobin, and decreased glutathione peroxidase (GPx) activity (Ercal et al. 2001). Pb-induced oxidative stress also reported to cause synaptic damage and neurotransmitter malfunction in fish (Lee et al. 2019).

Heavy metals can be deposited in various fish organs, e.g. liver, kidneys, spleen, digestive tract, gill, and muscle, which vary in their ability to respond to oxidative stress. The present study was intended to compare oxidative status according to natural accumulation of Cd and Pb in organ meat, not usually consumed but responsible mostly for detoxification and oxidative response, such as the liver (Hurtado-Carneiro et al. 2021), and in frequently edible parts such as the muscle of fish. Therefore, we determined the natural oxidative response to Cd and Pb accumulations in these two organs of four coastal fish species from Pattani Bay, Gulf of Thailand.

Materials and methods

This study was approved by Animal Ethic Committee, Faculty of Veterinary Science, Kasetsart University (ID#ACKU61-VET-071).

Sample collection

Four fish species, namely Scatophagus argus (n = 15), Plotosus lineatus (n = 18), Netuma thalassina (n = 14), and Mugil cephalus (n = 30), were collected during Aug, 2020–Feb, 2021 from Pattani Bay, Gulf of Thailand (Geographic coordinates: 6°54'51.0"N 101°17'12.0"E). Three sampling sites (SSs) were selected around the bay: Ban Budee (SS1), Ban Tanyong (SS2), and Ban Datoh (SS3), as shown in Figure 1. Fish samples obtained from the local fishing boat and they were kept in a cool box with ice and transported immediately to the laboratory, Faculty of Science, Kasetsart University, Bangkok, Thailand. All fish were dissected for livers and muscle. The fresh organs were weighed before further processing of the tissue’s metal bioavailability and oxidative status analyses.

Figure 1. Four coastal fish species (S. argus, N. thalassina, P. lineatus and M. cephalus) with depth range and sampling sites form Pattani Bay, Gulf of Thailand (according to www.maps.google.com).

Sample preparation and heavy metal analysis

Tissue samples were oven dried at 65 °C and grinded with mortar and pestle. Dried samples (0.5 g) were added to 5 ml concentrated nitric acid (70%) and placed under a hood at 25 °C overnight for digestion. Further digestion was performed in 150–180 °C water baths for three hours (Baird and Bridgewater 2017). All digested samples were diluted to a volume of 25 mL with deionised water (Milli-Q). Cd and Pb were analysed in each sample using flame atomic absorption spectrometry (FAAS; 240B: Agilent Technologies).

Heavy metal standard solutions (1000 mg/L) were purchased from Merck (Germany). All working solutions were prepared in deionised water (ranging from 0.05–2.00 mg/L for Cd and 0.50–20.00 mg/L for Pb). Concentrations of heavy metals were determined using corresponding calibration curves.

Quality control and assurance

FAAS methods for Cd and Pb were validated for limit of detection (LOD) and limit of quantification (LOQ) based on sample replication measurement in a blank solution. The LOD and LOQ were calculated using the linear regression of the calculation curve for each metal. They are computed as LOD = 3SD/b and LOQ = 10SD/b, where SD is the standard deviation of the response and b is the slope of calibration curve (Alankar and Vipin 2011). LOD and LOQ values were 0.002 and 0.006 mg/L for Cd and 0.020 and 0.060 mg/L for Pb, respectively. The precision in terms of recovery percentages was 96.50% for Cd and 97.50% for Pb. The average accuracy of Cd and Pb measurements was higher than 99.95%.

Oxidative status analysis

Biochemical analysis reagents used in the present study were purchased from Chemical Express Co., Ltd. Merck Millipore (Samutprakarn, Thailand).

Organ tissues were washed with cold normal saline and homogenised in a 10% w/v phosphate buffer saline (50 mM, pH 7.4). Half of each organ tissue homogenate was kept for MDA and GSH assays. We centrifuged the rest of the organ tissue homogenate at 10,000 g at 4 °C for 10 min and then analysed the supernatant for total protein level and SOD and CAT activity.

The total protein was determined using Lowry’s assay (Lowry et al. 1951) by mixing 0.2 ml of the supernatant with 2 ml of solution D (ratio 48:1:1) (2% w/v Na₂CO₃ in 0.1 N NaOH: 0.5% w/v CuSO₄-5H₂O in distilled water: 1% w/v C₄H₄KNaO₆-4H₂O) and incubating it for 10 min before adding 0.2 ml of 1 N Folin-Ciocalteu reagent (1:1). After 30 min of incubation, the mixture was read at 600 nm. Protein concentration was calculated using the standard curve of bovine serum albumin 0, 0.0045, 0.018, 0.009, 0.035 and 0.0181 mg/ml (y = 0.0424x − 0.0029; R² = 0.9917).

MDA was measured in the organ tissue to determine the lipid peroxidation level. In brief, we mixed 0.2 mL of organ tissue homogenate with 4% sodium dodecyl sulphate, 1.5 mL of 20% acetic acid, and 1.5 mL of 0.5% thiobarbituric acid. The mixture was heated at 95 °C for 1 hr. and then centrifuged for 10 min at 3,500 rpm x g before reading the supernatant at 532 nm. MDA concentration was calculated using the standard curve of MDA concentration 0, 3.61, 6.02, and 12.04 µM (y = 14.1x − 0.6558; R² = 0.9810). We presented organ tissue MDA concentration as µM/mg of protein (Sakamula and Thong-Asa 2018).

GSH was measured by mixing 0.1 mL of homogenate with 10% tricarboxylic acid and centrifuging it for 10 min. Then, 0.5 mL of supernatant was mixed with 5, 5′ -dithios 2-nitro benzoic acid. The final volume was increased to 3 mL using PBS before reading it at 412 nm. We calculated GSH concentration using the standard curve of GSH concentration 0, 0.02, 0.04, and 0.06 µM (y = 0.669x − 0.0102; R² = 0.9955). We presented organ tissue GSH concentration as µM/mg of protein (Manyagasa and Thong-asa 2019).

SOD activity was measured by mixing 0.1 mL of supernatant with 0.1 mL of EDTA (0.0001 M), 0.5 mL of carbonate buffer (pH 7.9), and 1 mL of epinephrine (0.0003 M). We read the absorbance every 30 sec at 480 nm for 3 min. Enzyme activity was presented as U/mg of protein, using the standard curve of SOD concentration 0, 0.0058, 0.0294, 0.117, and 0.294 µg/ml (y = 0.0015x + 0.0001; R2 = 0.998). Standard SOD activity was 6,150 U/mg (Merck, Germany) (Sakamula et al. 2022).

Enzyme activity of CAT was determined using 50 µL of supernatant, increasing the volume to 3 mL with 0.05 M PBS (pH 7.4) containing 0.01 M H₂O₂. We read the absorbance every 30 sec at 240 nm for 3 min, and we calculated CAT activity with reference to the extinction coefficient of H₂O₂ and presented it as U/mg of protein (Thong-Asa and Bullangpoti 2020).

Statistical analysis

All data were interpreted as mean ± standard error of mean (S.E.M). We conducted one-way analysis of variance and used Fisher’s PLSD post hoc test for group comparison. The correlation between organs’ heavy metal concentrations and biochemical parameters was also tested. We considered a p-value less than 0.05 statistically significant.

Results and discussion

Heavy metal accumulation

The bioavailability of Cd and Pb in the liver and muscle of all fish species is indicated in Figures 2 and 3. The comparison of Cd and Pb accumulation between organs of each fish species depicted a similar pattern; Cd and Pb were concentrated in the liver rather than muscle. In S. argus, Cd and Pb concentrations in the liver were significantly higher than in the muscle (p < 0.0001 and p < 0.001, respectively). In P. lineatus, N. thalassina, and M. cephalus, Cd concentration in the liver was significantly higher than in muscle (p = 0.0350, 0.0020, and 0.0083, respectively), and similar results were found for Pb concentration in the liver when compared to muscle (p = 0.0018, 0.0021 and 0.0015, respectively). Our result indicated that the liver accumulates Cd and Pb at a significantly higher rate than the muscle in all fish species. This finding been indicated in other work (Rajeshkumar and Li 2018), and our result emphasis major involvement of liver in heavy metal accumulation. In addition, for the metal detoxification process, it is well known that gills, skin, and the digestive tract are responsible for the absorption of waterborne xenobiotic chemicals. Then, blood transportation is vital for excretion in the liver, kidneys, and gills, and the liver and bones act as storage locations (Junejo et al. 2019). Fish livers are indicated as the major detoxification sites for metals. After successful solubility and conjugating processes in the liver, metals are delivered to excretion sites (Ardeshir et al. 2017). However, some metals are difficult to eliminate, which can lead to accumulation in fish’s tissues. The liver is the major organ in storage of heavy metals (Malik et al. 2010), and bound forms of intracellular storage—i.e. metallothionein-bound, ferritin-bound, and bound within vesicle-granules—have been indicated (Deb and Fukushima 1999). Several studies have indicated relationships of metal bioaccumulation in various fish tissues, with species-specific results (Malik et al. 2010;; Bat et al. 2018; Rajeshkumar and Li 2018). In the present study, correlation tests indicated a significant positive correlation between liver and muscle tissues for Cd and Pb in M. cephalus (Table 2). In P. lineatus, the significant positive correlation is depicted only for Pb. However, other fish species (S. argus and N. thalassina) showed no tissue correlation for these heavy metals. The present study is limited by the cellular parameters of each fish species; therefore, the result of the correlation test may suggest that Pb accumulation in only M. cephalus and P. lineatus liver and muscle can be used for pollution biomonitoring.

Figure 2. Histogram for liver’s Cd, Pb, MDA, GSH, CAT and SOD of four coastal fish species, * indicates statistical significance. Cd: cadmium; Pb: lead; MDA: malondialdehyde; GSH: reduced glutathione; CAT: catalase; SOD: superoxide dismutase.

Figure 3. Histogram for muscle’s Cd, Pb, MDA, GSH, CAT and SOD of four coastal fish species, * indicates statistical significance. Cd: cadmium; Pb: lead; MDA: malondialdehyde; GSH: reduced glutathione; CAT: catalase; SOD: superoxide dismutase.

In addition, as shown in Figure 2, a comparison of the liver’s Cd and Pb concentrations among four coastal fish species depicted the highest accumulation belonging to S. argus. The significant difference in Cd (p < 0.0001, <0.0001, and <0.0001) and Pb (p = 0.0045, 0.0051, and 0.0361) accumulation was indicated by comparing S. argus to P. lineatus, N. thalassina, and M. cephalus, respectively. We compared the muscle’s accumulation of Cd and Pb among fish species, and results were similar to those from the liver (Figure 3). The significant difference of Cd (p = 0.0162, 0.0052, and 0.0473) and Pb (p = 0.0083, 0.0046, and 0.0361) accumulation in muscle was indicated by comparing S. argus to P. lineatus, N. thalassina, and M. cephalus, respectively. Varying organ accumulation of Cd and Pb among the four fish species may be related to their feeding habits. S. argus, which displayed a significantly high concentration, is an omnivore that feeds on worms, crustaceans, insects, and plant matter (Froese and Pauly 2018). Carnivores like N. thalassina and P. lineatus exhibited the lowest level of heavy metal accumulation in the liver and muscle. Higher accumulations of heavy metals are frequently found in some omnivores (as well as detritivores and herbivores) rather than carnivorous fish (Tesser et al. 2021). However, in the present study, fish ages and exposure time were unclear. Moreover, the difference of fish species due to species-specific factors—i.e. susceptibility (accumulation level and tolerance), detoxification metabolic ability, habitats, diet, and trophic level—must be considered (Garai et al. 2021).

Tissue’s oxidative response

Malondialdehyde was used to indicate the status of tissue’s lipid peroxidation. MDA levels in liver increased significantly when compared to the muscle in all fish species: S. argus (p < 0.0001), P. lineatus (p = 0.0083), N. thalassina (p = 0.0066), and M. cephalus (p = 0.0086). This result established major involvement of the liver in lipid peroxidation and the oxidative stress response. The lipid peroxidation product e.g. MDA increased during the degradation of polyunsaturated fatty acids. The mechanism of Cd-induced MDA is still not fully clarified and may involve a sulfhydryl group and antioxidant enzyme reduction. It has been indicated that Cd does not generate ROS directly but can alter GSH levels, which influence thiol status and affect the metallothionein level in liver, facilitating the membrane’s lipid peroxidation (Sevcikova et al. 2011). Pb was indicated as a weak inducer of lipid peroxidation in the liver in some fish species, while a similar effect was depicted with Cd for metallothionein activation, which may be involved in the accumulation process (Campana et al. 2003). Further comparison of the liver’s MDA among fish species indicated that liver MDA of S. argus was significantly higher than P. lineatus (p = 0.0018) and N. thalassina (p = 0.0065) but not M. cephalus (p = 0.0717). In the muscle, the MDA level of M. cephalus was significantly higher than P. lineatus (p = 0.0010) and N. thalassina (p = 0.0034), but not S. argus (p = 0.2312). These results indicate that the liver displays a high level of lipid peroxidation in S. argus, and the muscle displays a high level of lipid peroxidation in M. cephalus. Both fish species were highly responsive to oxidative stress, indicated by MDA levels higher than in carnivorous species such as P. lineatus and N. thalassina. However, natural responses to oxidative stress indicated by MDA levels in each fish species were quite different due to species-specific factors such as susceptibility to oxidative stress inducers, metabolic quality and quantity for detoxification, and oxidative response (Kuzina and Kuzin 2021). Although high levels of Cd and Pb accumulation as well as MDA were found in S. argus and M. cephalus but not the other two species, the correlation test indicated no positive correlation for liver’s MDA and Cd or Pb accumulation, while muscle’s MDA level in P. lineatus exhibited a significant positive correlation to Cd accumulation (Table 3). This may suggest that only P. lineatus clearly exhibited an increase of lipid peroxidation level in response to Cd accumulation in the muscle and that P. lineatus’ s muscle may be more sensitive to Cd accumulation for lipid peroxidation than the other species in the present study. However, further studies are needed for molecular explanation of the specific difference in tissues’ oxidative defense mechanisms.

Table 1. Sampled fish species and their ecology (according to www.fishbase.se).

Species	Common name	Family	Diet	Habitat type
Scatophagus argus	Spotted scat	Scatophagidae	Worms, crustaceans, insects, plant matter	Harbors, natural embayment, brackish estuaries
Plotosus lineatus	Striped eel catfish	Plotosidae	Crustaceans, molluscs, worms, fish	Coastal benthic, estuaries, tide pools, open coasts
Netuma thalassina	Giant catfish	Ariidae	Crabs, prawns, mantis shrimps, fishes, molluscs	Estuaries
Mugil cephalus	Flathead gray mullet	Mugilidae	Detritus, micro-algae, benthic organisms, zooplankton	Coastal waters, estuaries, rivers

Reduced glutathione was available as the reducing agent or as the electron and H donor for the redox reaction. GSH levels tended to increase more in the liver than the muscle, and a significant difference was indicated only in P. lineatus (p = 0.0082) and M. cephalus (p = 0.0003). Our result suggests that the antioxidative defense mechanism is highly activated in the livers of these two coastal fish species. GSH is reported to play a key role in the oxidative-induced toxicity of Cd, which some enhances GSH level in the liver, including the synthesis and uptake of amino acid substrates and activation of biosynthetic enzymes (Eroglu et al. 2015). Alteration effect of Cd on GSH levels and cells’ thiol status (Stohs and Bagchi 1995), and decreased glutathione peroxidase activity were indicated (Ercal et al. 2001). Different GSH levels were observed in response to Cd and Pb in different fish species (Garai et al. 2021). In the present study, the liver’s GSH levels among fish species was not significantly different (p > 0.05, Figure 2), and a correlation test depicted significant positive correlation between liver’s GSH level and Pb concentration only in N. thalassina (Table 2). This may suggest that N. thalassina’s liver glutathione metabolism is closely related to Pb accumulation.

Table 2. The correlation test of Cd, Pb concentrations between liver and muscle.

	Liver vs. muscle
Coastal fish species	Cd		Pb
	Correlation	p-value	Correlation	p-value
Scatophagus argus	0.470	0.1776	0.093	0.8056
Plotosus lineatus	0.146	0.5702	0.725	0.0004^a
Netuma thalassina	−0.171	0.5668	−0.402	0.1579
Mugil cephalus	0.836	<0.0001^a	0.839	<0.0001^a

^aindicates statistical significance.

It has been reported that heavy metals cause a decrease of CAT enzyme activity (Roméo et al. 2000). The evaluation of antioxidative enzymatic activity in the present study did not involve a control or a group unexposed to heavy metals. Therefore, we not interpreted the increase or decrease. CAT activity indicated no significant difference between liver and muscle tissues in the present study (p > 0.05,). In addition, the liver’s CAT activity among fish species indicated no significant difference (p > 0.05, Figure 2), while a significant positive correlation was found for Pb concentration and the liver’s CAT activity in S. argus (Table 3). It may be that only S. argus clearly exhibited increased CAT enzymatic activity in response to increased Pb accumulation in the liver.

Alteration of SOD activity after heavy metal exposure has been indicated (Sevcikova et al. 2011). Comparing SOD activity indicated that the liver’s SOD activity was significantly higher than the muscle’s in S. argus (p < 0.0001), and a comparison among fish species showed a significant increase of liver’s SOD activity in S. argus compared to P. lineatus (p = 0.0001), N. thalassina (p = 0.0062), and M. cephalus (p = 0.0062), respectively (Figure 2). However, a significant negative correlation was found between Pb concentration and SOD activity in S. argus (Table 3). These results confirmed S. argus’s oxidative response dominates in the liver rather than the muscle in response to oxidative stress (indicated by MDA) as well as antioxidation (indicated by SOD). However, antioxidative responses indicated by SOD activity in the liver decrease when Pb concentration increases. The comparison of muscle’s SOD activity among fish species indicated the highest activity in N. thalassina. Significant differences were found when comparing N. thalassina to P. lineatus (p = 0.0001), M. cephalus (p = 0.0033), and S. argus (p < 0.0001). No correlation was found between metal concentrations in the muscle and SOD activity of all fish species. Our results showed varying SOD activity in response to heavy metals in fish tissue, and more research is needed to elucidate expression levels of SOD in various organs of each fish species.

Table 3. The correlation test of Cd, Pb concentration and tissue’s oxidative status.

Coastal fish species		Cd		Pb
Scatophagus argus		Correlation	p-value	Correlation	p-value
MDA	Liver	0.327	0.3678	−0.345	0.3410
	Muscle	−0.158	0.6729	−0.37	0.3540
GSH	Liver	0.260	0.4811	0.413	0.2454
	Muscle	−0.558	0.0958	−0.521	0.1268
CAT	Liver	0.201	0.5889	0.807	0.0031^a
	Muscle	0.502	0.1446	0.547	0.1044
SOD	Liver	−0.454	0.195	−0.644	0.0430^a
	Muscle	−0.389	0.2779	−0.162	0.6648
Plotosus lineatus		Correlation	p-value	Correlation	p-value
MDA	Liver	0.275	0.3087	−0.203	0.4582
	Muscle	0.514	0.0278^a	−0.177	0.4896
GSH	Liver	0.312	0.2116	0.455	0.0641
	Muscle	0.141	0.6222	−0.128	0.6556
CAT	Liver	−0.186	0.4658	−0.211	0.4057
	Muscle	0.067	0.7952	−0.122	0.6348
SOD	Liver	−0.065	0.8022	−0.090	0.7258
	Muscle	−0.216	0.3957	−0.061	0.8127
Netuma thalassina		Correlation	p-value	Correlation	p-value
MDA	Liver	−0.108	0.7185	−0.469	0.0912
	Muscle	0.388	0.1748	−0.076	0.8015
GSH	Liver	−0.079	0.7939	0.887	<0.0001^a
	Muscle	0.061	0.8386	0.173	0.5617
CAT	Liver	−0.411	0.1469	−0.223	0.4514
	Muscle	−0.058	0.8462	0.320	0.2717
SOD	Liver	−0.455	0.1036	−0.382	0.1816
	Muscle	−0.085	0.7777	0.337	0.2450
Mugil cephalus		Correlation	p-value	Correlation	p-value
MDA	Liver	−0.458	0.0102^a	−0.435	0.0155^a
	Muscle	−0.309	0.0971	−0.388	0.0335^a
GSH	Liver	0.042	0.8255	−0.222	0.2417
	Muscle	0.040	0.8342	0.028	0.8855
CAT	Liver	0.177	0.3527	0.171	0.3700
	Muscle	0.162	0.3963	0.159	0.4056
SOD	Liver	−0.341	0.0648	−0.227	0.2302
	Muscle	0.257	0.1726	−0.017	0.9288

^aindicates statistical significance. 

Cd: cadmium; Pb: lead; MDA: malondialdehyde; GSH: reduced glutathione; CAT: catalase; SOD: superoxide dismutase.

Our present study indicated the bioavailability of Cd and Pb as well as the natural response to oxidative stress indicated by MDA level were mostly contained in the liver rather than muscle. However, findings were inconclusive regarding the oxidative response indicated by GSH level and CAT and SOD activities in liver or muscle, as well as the comparison among fish species. Because the study was based on the natural oxidative response, a variety of factors must be considered, i.e. individual response, differences of threshold and tolerance for heavy metal accumulation, and specific tissue metabolic processes.

Conclusions

Accumulation of Cd and Pb was high in the liver and low in the muscle of coastal fish species; S. argus, P. lineatus, N. thalassina, and M. cephalus. Natural oxidative responses indicated by MDA levels imply domination of the liver for lipid peroxidation. Varying antioxidative statuses were indicated by GSH, CAT, and SOD among coastal fish species, and we indicated the close relationship between metal accumulation and oxidative status.

Ethical approval

This study was approved by Animal Ethic Committee, Faculty of Veterinary Science, Kasetsart University (ID#ACKU61-VET-071).

Author contribution

Wachiryah Thong-asa conceived and designed research, biochemical analysis, analysed all data, artworks and wrote the manuscript. Phanwimol Tanhan conceived and designed the experiments, contributed reagents, materials, sample collection, and performed experiments. Niyada Lansubsakul collected samples and performed experiments. Kanjana Imsilp, conceived and designed the experiments, sample collection, and performed experiments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data are available upon reasonable request.

Additional information

Funding

Financial support from Faculty of Veterinary Medicine, and International SciKU Branding (ISB), Faculty of Science, Kasetsart University, Thailand.