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Aquatic Toxicology 150 (2014) 9–16

Contents lists available at ScienceDirect

Aquatic Toxicology

j ourna l ho me pa ge: www.elsev ier .com/ locate /aquatox

etal accumulation and oxidative stress biomarkers in liverf freshwater fish Carassius auratus following in vivo exposureo waterborne zinc under different pH values

uijuan Qu, Mingbao Feng, Xinghao Wang, Li Qin, Chao Wang,unyao Wang ∗, Liansheng Wang

tate Key Laboratory of Pollution Control and Resources Reuse, School of Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China

r t i c l e i n f o

rticle history:eceived 21 December 2013eceived in revised form 12 February 2014ccepted 16 February 2014

eywords:ntioxidant defenseetal content

arassius auratusinc

a b s t r a c t

In this study, laboratory experiments were conducted to investigate the combined effect of zinc and pHon metal accumulation and oxidative stress biomarkers in Carassius auratus. Fish were exposed to 0.1 and1.0 mg Zn/L at three pH values (5.0, 7.25, 9.0) for 3, 12, and 30 d. After each exposure, the contents of threetrace elements (Zn, Fe and Cu) were determined in liver. Generally, longer exposure to zinc (12 d and 30 d)increased hepatic Zn and Cu deposition, but decreased Fe content. Increasing accumulation of Zn in thetissue was also observed with increasing zinc concentration in the exposure medium. Moreover, hepaticantioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT) and glutathioneperoxidase (GPx), together with the level of glutathione (GSH) were measured to evaluate the oxidativestress status. The decreases in the four measured biochemical parameters after 3 d exposure might reflect

H the failure of the antioxidant defense system in neutralizing the ROS generated during the metabolicprocess, while the recovery of the antioxidants at days 12 and 30 suggested a possible shift toward adetoxification mechanism. With regard to the influence of pH on zinc toxicity, the general observationwas that the living environment became more stressful when the water conditions changed from anacidic state toward a near-neutral or alkaline state.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

The contamination of aquatic environment by metals is the con-equence of industrial, agricultural and anthropogenic activities,uch as an urban runoff, sewage treatment, and domestic garbageumps, thus aquatic organisms are exposed to unnaturally high

evels of these metals (Heath, 1987; Pinto et al., 2003; Sampaiot al., 2008). Elevated concentrations of metals can be toxic toquatic life because they are able to induce oxidative stress byccelerating the generation of highly reactive oxygen species (ROS),ncluding superoxide radical (O2

•−), hydrogen peroxide (H2O2),ydroxyl radicals (OH•), and singlet oxygen species (1O2). If notetoxified, these ROS can oxidize proteins, lipids and nucleic acids,ften leading to damage in different cellular targets or even cell

eath (Lushchak, 2011).

Organisms have developed antioxidant defense systemhat helps them to cope with ROS. The antioxidant defense

∗ Corresponding author. Tel.: +86 25 89680358.E-mail addresses: wangzy@nju.edu.cn, wangzun315cn@163.com (Z. Wang).

ttp://dx.doi.org/10.1016/j.aquatox.2014.02.008166-445X/© 2014 Elsevier B.V. All rights reserved.

system consists of both enzymatic and non-enzymaticcomponents. The key enzymes responsible for the detoxifica-tion of ROS are superoxide dismutase (SOD), catalase (CAT) andglutathione peroxidase (GPx). SOD catalyzes the dismutationof O2

•− into H2O2, which is eliminated by CAT into H2O andO2. GPx also participates in the decomposition of hydrogenperoxide. The non-enzymatic component mainly refers to thoselow-molecular-weight antioxidants including reduced glutathione(GSH), tocopherol, ascorbic acid and carotenoids. Especially, GSHcan protect against oxidative stress through the quenching ofoxyradicals by its sulfhydryl group (Winston and Di Giulio, 1991).Changes in the activities or levels of these oxidation-relatedparameters have been successfully used as biomarkers for expo-sure to metallic contaminants (Regoli et al., 2002; Sanchez et al.,2005; Basha and Rani, 2003; Fatima and Ahmad, 2005).

Copper, iron, and zinc are essential trace elements required forthe function of many cellular enzymes and proteins (Kozlowski

et al., 2009). For example, copper and zinc are critical elementsof SOD while iron is an integral component of CAT. Under normalphysiological conditions, these microelements are kept in dynamicbalance. However, homeostasis for these major metal ions may be

1 oxicology 150 (2014) 9–16

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Table 1Chemical species distribution (%) of zinc in experimental media of study.

Species of zinc (%) pH = 5.0 pH = 7.25 pH = 9.0

Zn2+ 83.96 82.79 4.98ZnOH+ 0 0.78 2.58Zn(OH)2 0 0.24 43.60Zn(OH)3

− 0 0 0.15ZnCl+ 0.13 0.13 0ZnSO4 15.65 15.42 0.96Zn(SO4)2

2− 0.25 0.25 0.02ZnCO3 0 0.23 42.52

0 R. Qu et al. / Aquatic T

isturbed when organisms were stressed by xenobiotics (Webert al., 1992; Moiseenko and Kudryavtseva, 2001). Alterations in theetabolism of Cu, Fe and Zn will disrupt normal cellular functions,

eading to disorders in the antioxidant defense system (Stohs andagchi, 1995). Therefore, concentration changes of these essentialetals may reflect the toxicity of an exposure situation and could

e used as indicators for exposure to pollutants.Among aquatic organisms, fish are generally considered to be

he most relevant organism for pollution monitoring in aquaticcosystems (Van der Oost et al., 2003). Although zinc is an impor-ant trace element in fish nutrition, excessive waterborne zinc canave severe impacts on fish species, causing morphological alter-tions in the gills, osmoregulatory disturbances and liver damageVan Dyk et al., 2007; Giardina et al., 2009; McGeer et al., 2000).

any studies had earlier been conducted to explore the effect ofinc exposure on the antioxidant defense system in a variety ofsh (Atli and Canli, 2010; Hansen et al., 2007; Firat et al., 2009;heng et al., 2011). Nevertheless, response to zinc-mediated oxida-ive stress in environmentally relevant situations is still a relativelylank field which needs special attention since environmental fac-ors can have a considerable effect on the toxicity of zinc. Especially,ater pH may influence metal bioavailability therefore the toxicity

o aquatic life by altering metal speciation (Hogstrand, 2012; Lorot al., 2012), and toxicity changes with respect to pH are often metalnd organism specific.

In the present paper, we will focus on the combined effect of zincnd pH on fish in order to provide critical information for the envi-onmental risk assessment of Zn in various aquatic environments.he widely distributed freshwater goldfish Carassius auratus wassed as the test organism. In fish, biochemical processes associatedith detoxification are triggered in the liver since it is the site ofultiple oxidative reactions and maximal free radical generation

Gul et al., 2004; Avci et al., 2005). Hence, liver was chosen as thearget organ. The objective of the current research was to assess the

etal accumulation and antioxidant defense in liver of C. auratusollowing in vivo exposure to waterborne zinc under three pH val-es. For this purpose, the concentration of the bioelements (Zn, Fend Cu) in liver was determined, and the activities of three antioxi-ant enzymes (SOD, CAT and GPx) and the level of a non-enzymaticntioxidant (GSH) were measured.

. Experiment

.1. Acclimatization

C. auratus (weight: 30.15 ± 4.35 g) were purchased from a localquatic breeding base. Prior to the experiments, fish were acclima-ized for at least 10 d in aquaria containing 150 L tap water whichad been dechlorinated by active carbon. During the acclima-ization period, they were fed twice a day with commercialellets, and food residues and metabolic wastes were removedaily. The water quality parameters were as follows: tempera-ure: 20 ± 1 ◦C, pH: 7.25 ± 0.25, conductivity: 340.6 ± 16.4 �s/cm,otal hardness: 135.5 ± 9.3 mg CaCO3/L, alkalinity: 40.7 ± 5.2 mgaCO3/L. Ion levels were measured as: Na+: 11.2 ± 0.2 mg/L, K+:.34 ± 0.07 mg/L, Mg2+: 7.74 ± 0.02 mg/mL, Ca2+: 41.07 ± 0.82 mg/Lnd Cl−: 28.3 ± 1.2 mg/L. Moreover, the three microelements in theater were measured as: Zn: 5.90 ± 0.75 �g/L, Fe: 10.30 ± 2.41 �g/L

nd Cu: 1.47 ± 0.16 �g/L. The aquariums were aerated with airtones attached to an air compressor to saturate with oxygen. Thistudy was approved by the Ethics Committee of Nanjing University,

nd all experimental procedures were performed in accordanceith the Guide for the Care and Use of Laboratory Animals of this

nstitution. When the total mortality was less than 1%, the experi-ents were started.

ZnHCO3+ 0 0.17 0.55

Zn(CO3)22− 0 0 4.65

2.2. Exposure protocol

The experiments were conducted in forty-five glass tanks(28 cm × 60 cm × 36 cm), with each tank containing 30 L of testsolution or 30 L of dechlorinated tap water. A total of 135 acclimatedfish were randomly divided into 9 groups, where 15 fish in eachgroup were uniformly distributed into five parallel tanks. The groupof fish was exposed to control (no zinc addition in natural dechlo-rinated tap water, pH 7.25), low pH-acid medium (pH 5.0), highpH-alkaline medium (pH 9.0), 0.1 mg Zn/L in acid medium (pH 5.0),0.1 mg Zn/L in natural medium (pH 7.25), 0.1 mg Zn/L in alkalinemedium (pH 9.0), 1.0 mg Zn/L in acid medium (pH 5.0), 1.0 mg Zn/Lin natural medium (pH 7.25), or 1.0 mg Zn/L in alkaline medium (pH9.0) for 3, 12, and 30 d. Five parallel samples for each treatment afterevery period of exposure were obtained by taking out one goldfishfrom each tank. The experimental fish were fed daily with com-mercial pellets during the toxicity tests but were fasted 24 h priorto biochemical analysis. Water was always aerated and renewed50% every day to minimize metal loss. Aqueous zinc concentrationswere monitored with a flame-atomic absorption spectrophotome-ter (SOLLAR M6, Thermo, USA) during the experimental period,similar to our previous study (Qu et al., 2013). The two zinc expo-sure concentrations were chosen to be higher than the reportedvalue 7.6–11.6 �g/L in surface water from Nanjing section of theYangtze River (Wu et al., 2009) but within the permissible limit1.0 mg/L for drinking water as prescribed by Ministry of Environ-mental Protection of the People’s Republic of China. The final pHof 5.0 or 9.0 was achieved by adding 1.2 mol/L HCl or 2.0 mol/LNaOH solution, and 0.001 mol/L HCl or 0.05 mol/L NaOH solutionwas dropwise added at an appropriate rate to set the pH to within±0.1 of the desired value. When the water was renewed, the pHwas immediately readjusted to maintain the test conditions. Basedon the measured water quality parameters, Zn speciation analysisfor each pH (Table 1) was performed using Visual MINTEQ soft-ware (ver. 3.0, beta, KTH, Department of Land and Water, ResourcesEngineering, Stockholm, Sweden; courtesy of J.P. Gustafsson, RoyalInstitute of Technology, Stockholm, Sweden).

2.3. Sample preparation and biochemical assays

At days 3, 12, and 30, five fish per treatment were randomlysampled, dissected in ice to obtain liver samples. Liver tissues wererinsed with cold physiological saline (0.9% NaCl) to remove theadherent blood, and dried in filter paper. For biochemical param-eters, the liver was weighed, and then homogenized (1:10, w/v)in cold saline using an IKA T10 homogenizer (IKA, Germany). Thehomogenates were centrifuged (Eppendorf, Germany) at 4000 × gfor 15 min at 4 ◦C, and the supernatants were used for the assess-

ment of various biochemical parameters.

The enzyme (SOD, CAT, GPx) activities, GSH level and proteincontent in the supernatants were measured using the Diagnos-tic Reagent Kits according to the manufacturer’s instructions. SOD

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R. Qu et al. / Aquatic T

ctivity was measured at 550 nm using the xanthine oxidaseethod (McCord and Fridovich, 1969). CAT activity was determined

y monitoring residual H2O2 absorbance at 405 nm (Goth, 1991).Px activity, estimated by the rate of GSH oxidation, was measuredt 412 nm (Hafeman et al., 1974). Reduced GSH level was assayedt 412 nm following the method of Tietze (1969) by using 5,5′-ithiobis-2-nitrobenzoic acid (DTNB) reagent. DTNB was reducedy free sulfhydryl groups of GSH to form yellow colored compound-thio-nitrobenzoic acid (TNB). The protein content was measuredt 595 nm by the Coomassie Brilliant Blue dye binding techniqueBradford, 1976), with bovine serum albumin as a standard. Allhe absorbance was recorded with a TU-1810 UV-Vis spectropho-ometer (Persee, China). Specific activity of enzymes is expresseds U/mg protein, while GSH level is denoted by �mol/g protein.

.4. Metal measurements

At each sampling time, the remaining liver samples were imme-iately freeze-dried and then digested with nitric acid and sulfuriccid (4:1, v/v) at 120 ◦C for at least 2 h. Cooled digestates wereiluted to 20 mL with 1% HNO3. The concentrations of Zn, Fe and Cu

n the tissue were measured using a flame atomic absorption spec-rophotometer (SOLLAR M6, Thermo, USA). Calibration curves wereonstructed daily based on five standards. Digestion blanks indi-ated negligible contamination. All measurements were performedn duplicate and metal concentrations are presented as mg/kg dry

eight (d.w.).

.5. Statistical analysis

Results were expressed as mean ± standard deviation (SD). Prioro the statistical analysis, all data were checked for normality ofistribution using the Shapiro–Wilk test and for homogeneity ofariance using the Levene test. Differences between groups werenalyzed using one-way analysis of variance (ANOVA) followed byuncan’s test, and the significance level was considered at P < 0.05.ll statistical analyses were performed using the SPSS statisticalackage (ver. 17.0, SPSS Company, Chicago, USA).

.6. Integrated biomarker response

The Integrated Biomarker Response (IBR) (Beliaeff and Burgeot,002), a method for combining all the measured biomarkeresponses into one general stress index, was applied to assess theotential toxicity of different exposure protocols to fish. The pro-edure of IBR calculation is described here briefly: (1) Data weretandardized according to the formula Y = (X − m)/s, where X is thealue of each biomarker response, m is the mean value of theiomarker, and s is the standard deviation of the biomarker. (2)sing standardized data, Z was calculated as Z = Y in the case ofctivation or Z = −Y in the case of inhibition. Thus, the minimumalue (Min) was obtained for each biomarker. (3) The score (S)as computed as S = Z + |Min|, where S ≥ 0 and |Min| is the abso-

ute value of Min. (4) Calculation of star plot areas by multiplyinghe obtained value of each biomarker (Si) with the value of the nextiomarker, arranged as a set, dividing each calculation by 2. (5)umming up all values, and the corresponding IBR value is obtaineds IBR = {[(S1 × S2)/2] + [(S2 × S3)/2] + [(S3 × S4)/2] + [(S4 × S1)/2]}.

. Results

.1. Metal accumulation

Table 2 listed the hepatic Zn, Fe and Cu content in C. auratusfter exposure to zinc under different pH values. From Table 2 wean see that the waterborne zinc exposure resulted in increased Ta

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12 R. Qu et al. / Aquatic Toxicology 150 (2014) 9–16

Fig. 1. The activity of antioxidant enzymes (SOD, CAT and GPx) and the level of the non-enzymatic antioxidant GSH in liver of C. auratus exposed to waterborne zinc underd dard

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ifferent pH at the three timepoints (3, 12 and 30 d). Data are shown as mean ± stanetter (a–f) are significantly different (P < 0.05).

n content in all the test groups. Compared with the blank control,ignificant Zn accumulation was observed in the pH(5.0)-Zn(1.0)nd pH(7.25)-Zn(1.0) group after 3 d exposure, in all the zinc-reated experimental groups after 12 d and above (except forhe pH(5.0)-Zn(0.1) group after 30 d). Under exposure conditionsithout extra addition of zinc, Zn concentration was significantlyecreased in the pH(5.0) group after 12 d (reduced by 23.5%), whilehe other pH control groups showed no statistically confirmedhanges. Moreover, except for the pH(5.0)-Zn(0.1), pH(9.0)-Zn(0.1)nd pH(5.0)-Zn(1.0) group after 3 d, Zn concentration in other co-xposure groups was significantly higher than that in the respectiveH control group. When zinc was added into the exposure water,n accumulation in liver increased in the following order: pH(7.25)roup > pH(9.0) group > pH(5.0) group for 3 d exposure, and pH(9.0)roup > pH(7.25) group > pH(5.0) group for 12 d and 30 d exposure.enerally, Zn concentration in the group treated by 1.0 mg/L Zn wasigher than the corresponding group treated by 0.1 mg/L Zn at theame pH level, and most of the differences were statistically signifi-ant. Especially, at day 30, the pH(7.25)-Zn(1.0) and pH(9.0)-Zn(1.0)roup was 1.8 and 1.5 times the Zn content of the pH(7.25)-Zn(0.1)nd pH(9.0)-Zn(0.1) group.

A general decrease in hepatic Fe content was found in all experi-ental groups. After 3 d exposure, significant difference from blank

ontrol was observed in the pH(5.0)-Zn(0.1) and pH(9.0)-Zn(0.1)roup. Although concentrations of Fe in co-exposure groups werell lower than the respective pH control groups, the changes wereot significant. After 12 d and above, all fish following exposureo the combination of zinc and pH showed significant decreasesn hepatic Fe contents, when compared to control. For the groupsxposed to pH alone, significantly decreasing Fe concentration wasnly observed in the pH(5.0) group at day 12.

Hepatic Cu content determined in all experimental fish includ-

ng the pH(5.0) and pH(9.0) group was significantly lower thanhat of the blank control after 3 d. Comparing the co-exposureroups and the corresponding pH control, we can see that Cuontent decreased significantly in the pH(5.0)-Zn(0.1) group and

error (SD), n is 5 for each data point. Values that do not share the same superscript

increased remarkably in the pH(9.0)-Zn(1.0) group. As the expo-sure time lengthened to 12 d and 30 d, the situation was somewhatdifferent. Significant increases relative to controls were observedin all co-exposure groups with the exception that the differ-ence between the pH(5.0)-Zn(0.1) group and the blank controlwas non-significant. For example, Cu content in the pH(5.0)-Zn(0.1), pH(7.25)-Zn(0.1) and pH(9.0)-Zn(0.1) group after 12 d wasincreased by 16.4%, 35.3% and 48.7%; and this trace element waseven increased by 65.6%, 127.0% and 132.3% in the pH(5.0)-Zn(1.0),pH(7.25)-Zn(1.0) and pH(9.0)-Zn(1.0) group at day 30. At a specificpH level, Cu content in the 1.0 mg Zn/L group was usually higherthan the 0.1 mg Zn/L group, and sometimes even statistical sig-nificant difference was observed between paired groups, e.g., thepH(5.0)-Zn(0.1) and pH(9.0)-Zn(0.1) group after 3 d exposure.

3.2. Antioxidant defense

Activities of antioxidant enzymes (SOD, CAT and GPx) in liver ofC. auratus following exposure to waterborne zinc under differentpH values were presented in Fig. 1(A–C). Blank control values forSOD, CAT and GPx at day 3 were measured as 123.89 ± 6.97 U/mgprotein, 26.51 ± 2.62 U/mg protein and 145.90 ± 4.66 U/mg pro-tein, respectively. The corresponding values were first increasedto 193.93 ± 14.14 U/mg protein, 40.84 ± 4.24 U/mg protein and287.61 ± 14.09 U/mg protein at day 12, and then decreasedto 65.54 ± 2.94 U/mg protein, 24.77 ± 6.27 U/mg protein and99.60 ± 7.87 U/mg protein at day 30.

All the zinc-treated groups showed significant decreases in SOD,CAT and GPx activity after 3 d exposure, when compared to con-trols. For those fish only exposed to pH, significant difference fromblank control was found in pH(9.0) group for CAT activity and inpH(5.0) group for GPx activity. The groups at pH 5.0 always exhib-

ited the smallest decreases of all three biochemical parameters ascompared with respective pH controls. To be specific, SOD activ-ity was reduced by 37.9% and 38.9%, CAT activity was reduced by42.6% and 37.1%, GPx activity was reduced by 31.6% and 42.9% in the

R. Qu et al. / Aquatic Toxicol

0

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ig. 2. Integrated biomarker response (IBR) of all parameters measured in liverissue of C. auratus following co-exposure to zinc and pH.

H(5.0)-Zn(0.1) group and pH(5.0)-Zn(1.0) group, respectively.oreover, SOD, CAT and GPx activity in the 0.1 mg Zn/L expo-

ure group had little difference with the corresponding 1.0 mg Zn/Lroup except that there was significant difference between theH(5.0)-Zn(0.1) and pH(5.0)-Zn(1.0) group for GPx activity.

After 12 d exposure, changes in antioxidant activities (SOD,AT and GPx) were more complex. SOD activity increased toear control levels in pH(5.0)-Zn(0.1) and pH(5.0)-Zn(1.0) group,hile the other six groups still exhibited statistically significantecreases. Compared with the blank control, the largest reductionf the enzyme activity was found in the groups exposed to zincnder alkaline conditions. In fact, SOD activity was determineds 95.08 ± 4.66 U/mg protein and 116.72 ± 7.87 U/mg protein forhe pH(9.0)-Zn(0.1) group and pH(9.0)-Zn(1.0) group, respectively.esides, the addition of zinc into the exposure water all causedignificant changes in SOD activity except for the pH(5.0)-Zn(0.1)roup which was not significantly induced. For CAT activity,here was no significant difference among the three pH controlroups. Significantly inhibited CAT activity relative to controls wasbserved in all zinc-treated groups with the pH(5.0)-Zn(0.1) groups an exception. Moreover, CAT activity in 1.0 mg Zn/L treatedroups was significantly lowered by comparison with the cor-esponding 0.1 mg Zn/L treated groups. The activity of GPx wasack to normal in the pH(5.0), pH(9.0)-Zn(0.1) and pH(5.0)-Zn(1.0)roup. However, other groups still showed significantly reducedPx activity. When zinc was added into water, significant differ-nce from respective pH controls was commonly found. Then, afterhe longest exposure duration 30 d, all three antioxidant enzymeseached control levels in test groups.

The level of the non-enzymatic antioxidant GSH in C. auratus fol-owing co-exposure to zinc and pH was illustrated in Fig. 1D. After

d exposure, significant decreases in GSH level were observed in allinc exposure groups, while GSH level was significantly increasedn the pH(5.0) group as compared to the blank control. Furthermore,SH level in 1.0 mg Zn/L exposure groups was almost identical to

hat in 0.1 mg Zn/L exposure groups. By contrast, only the pH(9.0)-n(1.0) group showed significantly decreased GSH level at day 12.inally, GSH level in all experimental groups returned to controlalue after 30 d.

.3. Integrated biomarker response

The integrated biomarker response values in the experimentalsh were shown as a star plot in Fig. 2. As the exposure time

ogy 150 (2014) 9–16 13

increased, the IBR value for each zinc-treated group decreased andreached a minimum (less than 3.0) at day 30. According to thisindex, the rank of the most affected group could be ordered as:pH(9.0)-Zn(1.0) > pH(9.0)-Zn(0.1) > pH(7.25)-Zn(0.1) > pH(7.25)-Zn(1.0) > pH(5.0)-Zn(1.0) > pH(5.0)-Zn(0.1) for 3 d; pH(9.0)-Zn(1.0) > pH(7.25)-Zn(1.0) > pH(7.25)-Zn(0.1) > pH(9.0)-Zn(0.1)>pH(5.0)-Zn(1.0) > pH(5.0)-Zn(0.1) for 12 and 30 d. For the pHcontrol groups, the largest IBR value was only 0.73.

4. Discussion

It is known that the pH of aquatic systems can be decreasedor increased by a variety of anthropogenic sources, includ-ing agriculture, urbanization, industry, and mining (USEPA,http://www.epa.gov/caddis/ssr ph4s.html). Low and high waterpH per se are potentially toxic to fish since low pH inhibits the netuptake of both Na+ and Cl− through the gills and stimulates passivediffusive effluxes of these ions, while high pH may block ammoniaexcretion and accelerate CO2 excretion (Wood, 2001). In this work,C. auratus shows high tolerance to changes in water pH becauseno fish in the pH control groups (pH 5.0 and 9.0) died during theexperiment. However, both acidic and alkaline water environmentsare stressful to the test organism, as shown by some significantchanges in the hepatic microelements contents and antioxidantslevels of the control fish kept in water with pH 5.0 and 9.0. Signifi-cantly decreasing Zn, Fe and Cu concentration was more commonlyseen in the liver of C. auratus exposed to acid water than thoseexposed to alkaline water, probably suggesting that hepatic metalhomeostasis was more easily disrupted by low pH. On the otherhand, levels of some antioxidants in the fish exposed to pH 5.0 and9.0 water was significantly inhibited or promoted, which indicatedthe sensitivity of antioxidant system to water pH fluctuations. Panet al. (2008) proposed that SOD, CAT and GPx activity in Dugesiajaponica all changed evidently when medium pH deviated from 7.0(pH becomes acid or alkaline). Overall, our observations demon-strated that pH itself can also cause effects on metal accumulationand oxidative stress parameters. Hence, it is necessary to includepH controls when evaluating the effect of metals at different pHvalues.

Zinc plays a physiological role in major metabolic pathways,either as cofactor or to stabilize enzyme structures. For example,it is required for enzymes such as phosphatases, glutamate dehy-drogenase or superoxide dismutases. In the present study, hepaticZn levels were increased in all zinc-treated groups. This can beexplained in two ways: first, liver is the main target for accumu-lation of heavy metals, as proved by Cogun et al. (2006); second,zinc can trigger ROS production and cellular oxidation which pro-motes further zinc release (Kozlowski et al., 2009). Moreover, Znaccumulation in liver of C. auratus increased with increasing con-centration of zinc in the exposure medium. Firat et al. (2009) alsoobserved higher Zn level in the gill and liver of Oreochromis niloticusat larger waterborne zinc concentration. The competition betweenH+ and Zn2+ for binding sites on biological surfaces usually resultsin decreased accumulation of Zn in the tissue at lower pH (Campbelland Stokes, 1985). This theory is applicable to describe our results.In our experiment, modeling of zinc speciation showed that for anygiven zinc exposure concentration, there is much more free Zn2+

ion at low pH values, which is generally considered as the mostbioavailable form. However, when fish were exposed to zinc underdifferent pH values, liver Zn accumulation was less in low pH com-pared to high pH, i.e. accumulation of Zn in the tissue was inhibited

in the presence of the hydrogen ion.

The metal analysis results demonstrated that after longer expo-sure time (12 d and 30 d), waterborne zinc exposure decreasedthe hepatic Fe content but improved the Cu content. A possible

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echanism is that zinc can alter the metabolism of these bioele-ents, finally leading to the redistribution of them (Bray and

ettger, 1990). In addition, the data acquired from our experi-ents clearly indicated that hepatic Zn, Fe and Cu contents were

elated to waterborne zinc concentration, pH level of the water,nd the experimental duration. However, the precise mechanismas unknown and further researches should be done to investi-

ate the distribution, function and biological availability of theseioelements after the co-exposure.

Many aquatic organisms are able to live in metal-contaminatednvironments. This ability is related to their defense mechanismshat allow detoxification (Sheehan et al., 2001), and the antioxi-ant protection (Geret and Bebianno, 2004). Previous studies havehown that the antioxidants may be induced or inhibited underhemical stress, depending on the type and concentration of theenobiotic, the intensity and the duration of the stress applied,nd the exposed organism (Cheung et al., 2001; John et al., 2001).t is not a general rule that an increase in xenobiotic concentra-ion enhances the efficiency in antioxidant defenses. The resultsf this study revealed that both enzymatic and non-enzymaticntioxidants in C. auratus responded rapidly to zinc-mediatedtress. After 3 d exposure, waterborne zinc exposure tended toeduce the hepatic SOD, CAT and GPx activity as well as GSHevel.

SOD is a metalloenzyme that plays a key role in the defensegainst ROS. The total SOD activity that we measured mainly referso the activity of Cu,Zn-SOD, the major isoform in the cytosol,ucleus and peroxisomes. Cu,Zn-SOD is prone to oxidative mod-

fication and inactivation by the toxic reactive oxygen speciesSharonov and Churilova, 1992). The excess production of super-xide radicals or their transformation product H2O2 can cause thexidation of the cysteine in SOD that deactivates it as a result. Thus,he observed decrease in SOD activity may suggest damage to theOD protein due to ROS overproduction by zinc. CAT is an enzymeocated in peroxisomes which facilitates the removal of H2O2 (Vaner Oost et al., 2003). According to the former research resultsPandey et al., 2001; Atif et al., 2005), the suppressed CAT activ-ty observed in the liver of C. auratus could be explained by the fluxf superoxide radicals resulting from the oxidative stress caused byxposure to zinc.

GSH, a major cytosolic non-protein thiol, is involved in the cel-ular defense against the toxic action of xenobiotics, oxyradicalsnd metal cations (Meister and Anderson, 1983). It is hypothesizedhat the presence of heavy metals will induce increased synthesisf GSH to protect against the resulting oxidative stress from metalxposure. Hence, the down-regulation of GSH level is a signal indi-ating the inability of liver to successfully scavenge oxyradicals.xposure to heavy metals has been shown to cause a time andose-dependent increase or decrease of GSH concentrations in var-

ous fish species (Sayeed et al., 2003; Ali et al., 2004). Because GPxs a GSH-dependent enzyme, changes in GSH level may affect thectivity of GPx. Therefore, it seems that the decrease in GSH leveled to inactivated GPx activity. GPx inhibition was also reportedn livers of various fish after exposure to organic compounds or

etals (Fatima et al., 2000; Oruc and Uner, 2000; Talas et al.,008). Earlier researches demonstrated that GPx activity can beecreased by negative feedback either from excess of substrate oramage induced by oxidative modification (Tabatabaie and Floyd,994), and a reduced GPx activity in a given tissue could indicatehat its antioxidant capacity was exceeded by the accumulation ofydroperoxide products.

Generally, antioxidants act in a coordinated manner to ensure

ptimal protection against oxidative stress (Michiels et al., 1994).he inhibition of these antioxidants in the liver of exposed fishight reflect a possible failure of the antioxidant system in scav-

nging H2O2 and lipid hydroperoxides produced in this tissue.

ogy 150 (2014) 9–16

Different from the above-mentioned effects, antioxidantenzyme activity (SOD, CAT and GPx) and GSH level experiencedthe recovery process at day 12 and finally reached control levelsafter 30 d exposure. This may reflect the attempts of the antiox-idant defense system to neutralize metal-induced highly reactiveintermediates. The back-to-normal level of the four antioxidantsshows a possible shift toward a detoxification mechanism underlong-term exposure to zinc. Maracine and Segner (1998) pointedout the protective processes at the molecular and cellular levelmay result in acclimation to toxic metal stress under conditionsof chronic, low-dose exposure. Consequently, we may infer thatlong-term living in the environment with co-exposure to pH andzinc leads to adaptation in the exposed organism C. auratus.

It is noteworthy to mention that compared with the situationin near-neutral and alkaline water, changes in the four measuredoxidative stress biomarkers at pH 5.0 was always the minimumfor both high-concentration and low-concentration groups after 3 dand 12 d treatment. This phenomenon indicated that the exposedfish suffered less injury in acidic environments. This highlights theneed to study the defense mechanisms of the antioxidant system inorder to elucidate differences in the zinc-induced oxidative stressbetween acid and alkaline conditions.

Up to now, very little study has been conducted on oxidativestress responses to zinc in fish (Hogstrand, 2012). Unlike thoseredox-active metals (copper, iron, etc.), zinc cannot induce ROSgeneration via redox reactions such as Haber–Weiss and Fentonreactions. Although the exact mechanism involved in zinc-inducedoxidative stress still remains unknown, several possible mecha-nisms have been proposed before. Gioda et al. (2007) suggestedthat the oxidative stress-inducing potential of zinc may be relatedto DNA fragmentation, and the interaction with endogenous lowmolecular weight thiols and proteins. Another explanation involveschanges in antioxidant enzymes activities (Pedrajas et al., 1995;Gioda et al., 2007). Besides, the zinc ion may also account for theobserved oxidative stress responses (Loro et al., 2012). It is nowclear that free Zn2+ plays an important role in the cell signalingpathways associated with oxidative stress. The increase in cytosolicZn2+ concentration will activate the intracellular zinc sensor (Mtf1)which finally leads to increased gene expression of a suite of tar-get genes coding for several key antioxidants, either through directinduction or downstream events (Hogstrand, 2012). These antiox-idants include SOD, CAT, GPx, and GSH. Thus, it is possible thatthe changed (sometimes significantly) levels of the four antioxi-dants (SOD, CAT, GPx, and GSH) in fish following zinc exposure atthree pH values reflected this direct action of Zn2+ as a cell signalingmolecule, because hepatic zinc concentrations were increased in allzinc-treated groups (Table 2). According to the direct action expla-nation, the fact that exposure to zinc in the alkaline medium is morestressful can be explained by the higher zinc accumulation at pH9.0.

As shown in Fig. 1, the biomarker responses in the goldfish werecompletely different under different exposure protocols. Thus, forcomparison, four biomarker responses were standardized and com-bined into one general stress index termed IBR. The IBR indexprovides a simple tool for a general description of the “health sta-tus” of organism, combining the different biomarker signals. Itsusefulness was previously demonstrated in environmental stud-ies, regardless of the considerable variability in the biomarker setsused, contamination profiles and species (Broeg and Lehtonen,2006; Damiens et al., 2007). Generally, the higher the IBR value is,the more stressful the environment is. The IBR calculation resultsindicated that zinc was less toxic to the goldfish in an acidic envi-

ronment: on one hand, the IBR value at pH 5.0 was smallest at agiven zinc exposure concentration; on the other hand, the increasein IBR value for zinc-treated groups was smaller at pH 5.0 than atpH 7.25 and pH 9.0 when compared with respective pH controls. By

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omparing IBR values obtained at different waterborne zinc con-entrations, we found that zinc-induced stress has become moreerious with the increasing exposure concentration. In addition,he relatively small IBR value for all experimental groups at day 30

ay suggest the strong self-adaptive ability of the fish.

. Conclusions

In conclusion, the present study showed that metal contentsnd antioxidant levels in liver of C. auratus were affected by zincxposure at different pH values. The hepatic Zn, Fe and Cu contentsaried with the waterborne zinc concentration, pH level of theater, and the experimental duration. Generally, Zn and Cu depo-

ition in liver was increased after 12 d and 30 d treatment, whilee was found to be spoiled. With regard to changes in enzymaticnd non-enzymatic antioxidants, we observed that SOD, CAT andPx activities as well as GSH level were reduced after 3 d expo-ure, and they gradually recovered to control levels after 30 d. Thisay suggest a possible development of oxidative stress induced

y co-exposure to waterborne zinc and pH in the early exposureeriod and a possible adaptive response to the harmful environ-ent after long-term exposure. Moreover, our work indicated that

he exposed fish suffered less injury in acidic environments. Thus,H should be considered in laboratory assessments of field metaloxicity. Overall, response of antioxidants to zinc exposure was

ore rapid than accumulation of metals. Further investigationshould be designed to interpret relationships between liver concen-rations of bioelements and antioxidative responses in the goldfish.

cknowledgments

This research was financially supported by the National Natu-al Science Foundation of China (No. 21377051), the Major Sciencend Technology Program for Water Pollution Control and Treat-ent of China (No. 2012ZX07506-001) and the Scientific Research

oundation of Graduate School of Nanjing University (2013CL08).

eferences

li, M., Parvez, S., Pandey, S., Atif, F., Kaur, M., Rehman, H., Raisuddin, S., 2004. Flyash leachate induces oxidative stress in freshwater fish Channa punctata (Bloch).Environ. Int. 30, 933–938.

tif, F., Ali, M., Kaur, M., Rehman, H., Raisuddin, S., 2005. Modulatory effect of cad-mium injection on endosulfan-induced oxidative stress in the freshwater fish,Channa punctata Bloch. Bull. Environ. Toxicol. Contam. 74, 777–784.

tli, G., Canli, M., 2010. Response of antioxidant system of freshwater fish Ore-ochromis niloticus to acute and chronic metal (Cd, Cu, Cr, Zn, Fe) exposures.Ecotoxicol. Environ. Saf. 73, 1884–1889.

vci, A., Kac-maz, M., Durak, I., 2005. Peroxidation in muscle and liver tissues fromfish in a contaminated river due to a petroleum refinery industry. Ecotoxicol.Environ. Saf. 6, 101–105.

asha, P.S., Rani, A.U., 2003. Cadmium-induced antioxidant defense mechanism infreshwater teleost Oreochromis mossambicus (Tilapia). Ecotoxicol. Environ. Saf.56, 218–221.

eliaeff, B., Burgeot, T., 2002. Integrated biomarker response: a useful tool for eco-logical risk assessment. Environ. Toxicol. Chem. 21, 1316–1322.

radford, M.M., 1976. A rapid and sensitive method for the quantitation of micro-gram quantities of protein utilizing the principle of protein-dye binding. Anal.Biochem. 72, 248–254.

ray, T.M., Bettger, W.J., 1990. The physiological role of zinc as an antioxidant. FreeRadic. Biol. Med. 8, 281–291.

roeg, K., Lehtonen, K.K., 2006. Indices for the assessment of environmental pollutionof the Baltic Sea coasts: integrated assessment of a multi-biomarker approach.Mar. Pollut. Bull. 53, 508–522.

ampbell, P.G.C., Stokes, P.M., 1985. Acidification and toxicity of metal to aquaticbiota. Can. J. Fish. Aquat. Sci. 42, 2034–2049.

heung, C.C.C., Zheng, G.J., Li, A.M.Y., Richardson, B.J., Lam, P.K.S., 2001. Relationships

between tissue concentrations of polycyclic aromatic hydrocarbons and antiox-idative responses of marine mussels, Perna viridis. Aquat. Toxicol. 52, 189–203.

ogun, H.Y., Yuzereroglu, T.A., Firat, O., Gok, G., Kargin, F., 2006. Metal concentrationsin fish species from the Northeast Mediterranean sea. Environ. Monit. Assess.121, 431–438.

ogy 150 (2014) 9–16 15

Damiens, G., Gnassia-Barelli, M., Loques, F., Romeo, M., Salbert, V., 2007. Integratedbiomarker response index as a useful tool for environmental assessment evalu-ated using transplanted mussels. Chemosphere 66, 574–583.

Fatima, M., Ahmad, I., Sayeed, I., Athar, M., Raissudin, S., 2000. Pollutant-inducedover-activation of phagocytes is concomitantly associated with peroxidativedamage in fish tissues. Aquat. Toxicol. 49, 243–250.

Fatima, R.A., Ahmad, M., 2005. Certain antioxidant enzymes of Allium cepa asbiomarkers for the detection of toxic heavy metals in wastewater. Sci. TotalEnviron. 346, 256–273.

Firat, O., Cogun, H.Y., Aslanyavrusub, S., Kargin, F., 2009. Antioxidant responses andmetal accumulation in tissues of Nile tilapia Oreochromis niloticus under Zn, Cdand Zn + Cd exposures. J. Appl. Toxicol. 29, 295–301.

Geret, F., Bebianno, M.J., 2004. Does zinc produce reactive oxygen species in Rudi-tapes decussatus? Ecotoxicol. Environ. Saf. 57, 399–409.

Giardina, A., Larson, S.F., Wisner, B., Wheeler, J., Chao, M., 2009. Long-term andacute effects of zinc contamination of a stream on fish mortality and physiology.Environ. Toxicol. Chem. 28, 287–395.

Gioda, C.R., Lissner, L.A., Pretto, A., da Rocha, J.B.T., Schetinger, M.R.C., Neto, J.R.,Morsch, V.M., Loro, V.L., 2007. Exposure to sublethal concentrations of Zn(II) andCu(II) changes biochemical parameters in Leporinus obtusidens. Chemosphere69, 170–175.

Goth, L., 1991. A simple method for determination of serum catalase activity andrevision of reference range. Clin. Chim. Acta 196, 143–151.

Gul, S., Belge-Kurutas, E., Yildiz, E., Sahan, A., Doran, F., 2004. Pollution corre-lated modifications of liver antioxidant systems and histopathology of fish(Cyprinidae) living in Seyhan Dam Lake, Turkey. Environ. Int. 30, 605–609.

Hafeman, D.G., Sunde, R.A., Hoekstra, W.G., 1974. Effect of dietary selenium onerythrocyte and liver glutathione peroxidase in the rat. J. Nutr. 104, 580–587.

Hansen, B.H., Romma, S., Garmo, O.A., Pedersen, S.A., Olsvik, P.A., Andersen,R.A., 2007. Induction and activity of oxidative stress-related proteins duringwaterborne Cd/Zn-exposure in brown trout (Salmo trutta). Chemosphere 67,2241–2249.

Heath, A.G., 1987. Water Pollution and Fish Physiology. CRC Press, Florida, USA, p.245.

Hogstrand, C., 2012. Zinc. In: Wood, C.M., Farrell, A.P., Brauner, C.A. (Eds.), Homeo-stasis and Toxicology of Essential Metals – Fish Physiology, vol. 31A. Elsevier,San Diego, pp. 135–200.

John, S., Kale, M., Rathore, N., Bhatnagar, D., 2001. Protective effect of vitamin E indimethoate and malathion induced oxidative stress in rat erythrocytes. J. Nutr.Biochem. 12, 500–504.

Kozlowski, H., Janicka-Klos, A., Brasun, J., Gaggelli, E., Valensin, D., Valensin, G., 2009.Copper, iron, and zinc ions homeostasis and their role in neurodegenerativedisorders (metal uptake, transport, distribution and regulation). Coord. Chem.Rev. 253, 2665–2685.

Loro, V.L., Jorge, M.B., da Silva, K.R., Wood, C.M., 2012. Oxidative stress param-eters and antioxidant response to sublethal waterborne zinc in a euryhalineteleost Fundulus heteroclitus: protective effects of salinity. Aquat. Toxicol. 110,187–193.

Lushchak, V.I., 2011. Environmentally induced oxidative stress in aquatic animals.Aquat. Toxicol. 101, 13–30.

Maracine, M., Segner, H., 1998. Cytotoxicity of metals in isolated fish cells: impor-tance of the cellular glutathione status. Comp. Biochem. Physiol. A 120, 83–88.

McCord, J.M., Fridovich, I., 1969. Superoxide dismutase: an enzymatic function forerythrocuprein (hemocuprein). J. Biol. Chem. 244, 6049–6055.

McGeer, J.C., Szebedinszky, C., McDonald, D.G., Wood, C.M., 2000. Effects of chronicsublethal exposure to waterborne Cu, Cd or Zn in rainbow trout. 1: Iono-regulatory disturbance and metabolic costs. Aquat. Toxicol. 50, 231–243.

Meister, A., Anderson, M.E., 1983. Glutathione. Annu. Rev. Biochem. 52, 711–760.Michiels, C., Raes, M., Toussaint, O., Remacle, J., 1994. Importance of Se-glutathione

peroxidase, catalase, and Cu/Zn-SOD for cell survival against oxidative stress.Free Radic. Biol. Med. 17, 235–248.

Moiseenko, T.I., Kudryavtseva, L.P., 2001. Trace metal accumulation and fish patholo-gies in areas affected by mining and metallurgical enterprises in the Kola Region,Russia. Environ. Pollut. 114, 285–297.

Oruc, E.O., Uner, N., 2000. Combined effects of 2,4-D and azinphosmethyl on antiox-idant enzymes and lipid peroxidation in liver of Oreochromis niloticus. Comp.Biochem. Physiol. C 127, 291–296.

Pan, H.C., Fan, J., Wang, F.F., Sun, Z., 2008. Effect of medium pH on populationgrowth, asexual reproduction and activity of six enzymes of Dugesia japonica.Acta Hydrobiol. Sinica 32, 339–344.

Pandey, S., Ahmad, I., Parvez, S., Bin-Hafeez, B., Haque, R., Raisuddin, S., 2001. Effectof endosulfan on antioxidants of freshwaterfish Channa punctatus Bloch: 1. Pro-tection against lipid peroxidation in liver by copperpre-exposure. Arch. Environ.Contam. Toxicol. 41, 345–352.

Pedrajas, J.R., Peinaldo, J., Lopez-Barea, J., 1995. Oxidative stress in fish exposed tomodel xenobiotics. Oxidatively modified forms of Cu, Zn-superoxide dismutaseas potential biomarkers. Chem. Biol. Interact. 98, 267–282.

Pinto, E., Sigaud-Kutner, T.C.S., Leitao, M.A.S., Okamoto, O.K., Morse, D., Colepicolo,P., 2003. Heavy metal-induced oxidative stress in algae. J. Phycol. 39, 1008–1018.

Qu, R.J., Wang, X.H., Feng, M.B., Li, Y., Liu, H.X., Wang, L.S., Wang, Z.Y., 2013. Thetoxicity of cadmium to three aquatic organisms (Photobacterium phosphoreum

Daphnia magna and Carassius auratus) under different pH levels. Ecotoxicol.Environ. Saf. 95, 83–90.

Regoli, F., Gorbi, S., Frenzilli, G., Nigro, M., Corsi, I., Focardi, S., Winston, G.W., 2002.Oxidative stress in ecotoxicology: from the analysis of individual antioxidantsto a more integrated approach. Mar. Environ. Res. 54, 419–423.

1 oxicol

S

S

S

S

S

S

T

T

6 R. Qu et al. / Aquatic T

ampaio, F.G., Boijink, C.L., Oba, E.T., Santos, L.R.B., Kalinin, A.L., Rantin, F.T., 2008.Antioxidant defenses and biochemical changes in pacu (Piaractus mesopotami-cus) in response to single and combined copper and hypoxia exposure. Comp.Biochem. Physiol. C 147, 43–51.

anchez, W., Palluel, O., Meunier, L., Coquery, M., Porcher, J.M., Ait-Aissa, S., 2005.Copper-induced oxidative stress in three-spined stickleback: relationship withhepatic metal levels. Environ. Toxicol. Pharmacol. 19, 177–183.

ayeed, I., Parvez, S., Pandey, S., Bin-Hafeez, B., Haque, R., Raisuddin, S., 2003. Oxida-tive stress biomarkers of exposure to deltamethrin in freshwater fish, Channapunctatus Bloch. Ecotoxicol. Environ. Saf. 56, 295–301.

haronov, B.P., Churilova, I.V., 1992. Inactivation and oxidative modification ofCu,Zn-superoxide dismutase by stimulated neutrophils: the appearance ofnew catalytically active structures. Biochem. Biophys. Res. Commun. 189,1129–1135.

heehan, D., Meade, G., Foley, V.M., Dowd, C.A., 2001. Structure, function andevolution of glutathione transferases: implications for classification of non-mammalian members of an ancient enzyme superfamily. Biochem. J. 360, 1–16.

tohs, S.J., Bagchi, D., 1995. Oxidative mechanism in the toxicity of metal ions. FreeRadic. Biol. Med. 18, 321–336.

abatabaie, T., Floyd, R.A., 1994. Susceptibility of glutathione peroxidase and glu-tathione reductase to oxidative damage and the protective effect of spin trapping

agents. Arch. Biochem. Biophys. 314, 112–119.

alas, Z.S., Orun, I., Ozdemir, I., Erdogan, K., Alkan, A., Yilmaz, I., 2008. Antioxidativerole of selenium against the toxic effect of heavy metals (Cd+2, Cr+3) on liver ofrainbow trout (Oncorhynchus mykiss Walbaum 1792). Fish Physiol. Biochem. 34,217–222.

ogy 150 (2014) 9–16

Tietze, F., 1969. Enzymic method for quantitative determination of nanogramamounts of total and oxidized glutathione: applications to mammalian bloodand other tissues. Anal. Biochem. 27, 502–522.

Van der Oost, R., Beyer, J., Vermeulen, N.P.E., 2003. Fish bioaccumulation andbiomarkers in environmental risk assessment: a review. Environ. Toxicol.Pharmacol. 13, 57–149.

Van Dyk, J.C., Pieterse, G.M., van Vuren, J.H.J., 2007. Histological changes in the liverof Oreochromis mossambicus (Cichlidae) after exposure to cadmium and zinc.Ecotoxicol. Environ. Saf. 66, 432–440.

Weber, D.N., Eisch, S., Spieler, R.E., Petering, D.H., 1992. Metal redistribution inlargemouth bass (Micropterus salmoides) in response to restrainment stress anddietary cadmium: role of metallothionein and other metal-binding proteins.Comp. Biochem. Physiol. C 101, 255–262.

Winston, D.W., Di Giulio, R.T., 1991. Prooxidant and antioxidant mechanisms inaquatic organisms. Aquat. Toxicol. 19, 137–161.

Wood, C.M., 2001. Toxic responses of the gill. In: Schlenk, D.S., Benson, W.H. (Eds.),Target Organ Toxicity in Marine and Freshwater Teleosts, vol. 1. Taylor andFrancis, London, pp. 1–89.

Wu, B., Zhao, D.Y., Jia, H.Y., Zhang, Y., Zhang, X.X., Cheng, S.P., 2009. Pre-liminary risk assessment of trace metal pollution in surface water fromYangtze River in Nanjing Section, China. Bull. Environ. Contam. Toxicol. 82,

405–409.

Zheng, J.L., Luo, Z., Chen, Q.L., Liu, X., Liu, C.X., Zhao, Y.H., Gong, Y., 2011.Effect of waterborne zinc exposure on metal accumulation, enzymatic activ-ities and histology of Synechogobius hasta. Ecotoxicol. Environ. Saf. 74,1864–1873.