Journal of Earth, Environment and Health Sciences

: 2016  |  Volume : 2  |  Issue : 2  |  Page : 66--69

Toxicological Effects of Heavy Metal Cadmium on Two Aquatic Species: Rutilus rutilus and Hypophthalmichthys molitrix

Aliakbar Hedayati 
 Department of Fisheries, Faculty of Fisheries and Environment, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

Correspondence Address:
Aliakbar Hedayati
Assistant Professor, Department of Fisheries, Faculty of Fisheries and Environment, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan


Introduction: Cadmium (Cd) is toxic to fish at low doses and never beneficial to an organism. As Caspian roach (Rutilus rutilus) and silver carp (Hypophthalmichthys molitrix) are two key fish species, the aim of this study was to gather data on different sensitivities of few inland fish to Cd to use them in the ecotoxicity experiment studies. Subject and Methods: All samples were exposed to the different doses of cadmium chloride (0, 0.2, 1, 2, 6, 10, and 15 ppm). Mortality was recorded after 24, 48, 72, and 96 h and the median lethal concentration (LC50) amount and its confidence limits (95%) were measured by Finney’s method of probit analysis. Results: Toxicity experimenting statistical endpoints indicated that lowest observed effect concentration in roach was higher than silver carp (2 and 1 ppm, respectively), which means that no observed effect concentration was also higher for roach than silver carp (6 and 2 ppm, respectively), and LC50 was also different between species (5.26 and 6.58 ppm for roach and silver carp, respectively). Conclusion: Our results showed that Cd is toxic for these fish, especially roach; therefore, we suggest using this fish species for toxicity experiment of heavy metals as a suitable indicator of toxicological studies.

How to cite this article:
Hedayati A. Toxicological Effects of Heavy Metal Cadmium on Two Aquatic Species: Rutilus rutilus and Hypophthalmichthys molitrix.J Earth Environ Health Sci 2016;2:66-69

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Hedayati A. Toxicological Effects of Heavy Metal Cadmium on Two Aquatic Species: Rutilus rutilus and Hypophthalmichthys molitrix. J Earth Environ Health Sci [serial online] 2016 [cited 2024 Mar 2 ];2:66-69
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Pollutants can be separated into four parts: halogenated hydrocarbons, nonhalogenated hydrocarbons, organic metals, and nonorganic metals. Organic and nonorganic metals can again be separated into three principle parts: bulk metals, essential (trace) metals, and nonessential (heavy) metals.[1] Most metals do not form stable alkylated forms, but some (e.g., copper, Cu, and mercury, Hg) have high affinity for organic material and may be found associated with organic macromolecules in water environments.[2] However, there is the need to consider the behavior of the heavy metals in the environments. Essential metals, elements that all animals need to exist, include iron (Fe), Cu, zinc (Zn), manganese (Mn), molybdenum (Mo), and nickel (Ni). Although the lack of one or more of these essential metals is not uncommon in terrestrial organisms, such deficiencies have not been seen in aquatic animals.[3]

Nonessential metals, elements for which there is unknown function, include cadmium (Cd), mercury (Hg), lead (Pb), silver (Ag), and gold (Au).[3] The fact that heavy metals cannot be destroyed through biological degradation and are able to accumulate in the environment makes these chemicals harmful to the water environment and then to humans who are dependent on the water products as sources of materials.[4]

Heavy metals can accumulate in the body of water animals and these tissue doses of heavy metals can be of public health concern to both fish and humans.[4] Heavy metals, the main sewage of factories activities, are of first concern as they resist in the environments, move up the food chain, and lead to many disasters.[4]

It is necessary to evaluate the species sensitivity to these metals to draft ecosystems management studies.[5] The median lethal concentration (LC50) experiments are conducted to calculate the susceptibility and survival of fish to particular toxic materials such as heavy metals. Higher LC50 amount are less toxic, so higher doses are needed to produce 50% mortality in fish.[2] The heavy metals that are toxic to fish at very low doses and never beneficial to living organisms include Hg, Cd, and Pb.[6] Today, few studies have been conducted on the mortality effects of Cd on aquatics, so the purpose of this study was to evaluate lethal effects of Cd as potential dangerous materials to measure mortality effects of these metal on some farmed inland fish, silver carp (Hypophthalmichthys molitrix), and sea ranching species, Caspian roach (Rutilus rutilus).

 Materials and Methods

Lethal toxicity experiments were conducted on silver carp (∼45 g and 18 cm) and roach (∼3.5 g and 7 cm). Only suitable fish, as indicated by their activity and external features, were kept in fiberglass tank.

Fish were moved to a 400-L aerated tank equipped with aeration with 200 L of experiment medium. All fish were adapted for 7 days in a 15 fiberglass tank at 25°C under 12:12 L:D photoperiod. Adapted samples were fed twice a day with a commercial feed at equilibrium.[4]

Dead fish were quickly removed with plastic forceps to avoid possible deterioration of the water quality.[7] Cadmium-experimented doses were 0, 0.2, 1, 2, 6, 10, and 15 ppm; accidentally selected 21 species were exposed for 96 h in the fiberglass medium.

Experiment tanks were not renewed during the test and no food was provided to the fish. The number of mortalities were measured at times 0, 24, 48, 72, and 96 h.[1] Lethal toxicity experiments were carried out to measure the 96 h LC50 for Cd, according to Hotos and Vlahos.[8] Mortality was recorded after 24, 48, 72, and 96 h and LC50 amount and its confidence limits (CLs, 95%) were measured. Percentages of fish mortality were measured for each Cd dose at 24, 48, 72, and 96 h of study.

Also LC50 amount were measured from the data obtained in lethal toxicity test, by Finney’s method of “probit analysis” and with SPSS (IBM SPSS Software, version 19, NJ, USA) computer statistical software. In Finney’s rules, the LC50 amount is derived by arithmetically fitting a regression equation and also by graphical interpolation by taking logarithms of the experiment chemical dose on the x-axis and the probit value of percentage mortality on the y-axis. The 95% CLs of the LC50 amount obtained by Finney’s method were measured with the formula.[9]

The LC1,10,30,50,70,90,99 amount were derived using simple substitution probit of 1, 10, 30, 50, 70, 90, and 99, respectively, for probit of mortality in the regression equations of probit of mortality vs. Cd. The 95% CLs for LC50 were estimated by using the following formula: LC50 (95% CL) = LC50 ± 1.96 [SE (LC50)].[10] The standard error (SE) of LC50 is measured from the following formula: [INSIDE:1] where b = the slope of the Cd/probit response (regression) line; p = the number of Cd used; n = the number of animals in each part; and w = the average weight of the observations.[8] At the end of the lethal experiment, the lowest observed effect concentration (LOEC) and no observed effect concentration (NOEC) were measured for each endpoint measured. In addition, the maximum acceptable toxicant dose was estimated for the endpoint with the lowest NOEC and LOEC.[10],[11]

This work was maintained by Ethical Committee of Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran (no. 6177515-5). To minimize suffering of species, all samples were exposed with clove essence, low concentration for anesthesia, hypothermia prior to euthanasia, and eventually spinal cord dislocation for euthanasia.

 Results and Discussion

The mortality of current species for Cd doses 0, 0.2, 1, 2, 6, 10, and 15 ppm were tested during the study times at 24, 48, 72, and 96 h [Table 1] and [Table 2]. Samples exposed during 24–96 h had significantly evaluated number of dead species with high dose. There were significant differences in number of dead fish during 24–96 h. There were 100% mortality at 40 ppm dose within the 96 h after dosing for all fish, and no mortality at 2 and 5 ppm within the exposure times for all samples. It is evident from the results that the Cd dose has a direct effect on the LC50 amount of the exposed species. The roach had a lower 96-h LC50 value of the heavy metal and silver carp had the highest.[1]{Table 1}{Table 2}

Median lethal doses of 1, 10, 30, 50, 70, 90, and 99% used in experiments are described in [Table 3] and [Table 4]. Data of doses that lead to mortality (or survival) were collected for each exposure dose in a toxicity experiment at different exposure times (24, 48, 72, or 96 h). Data can be plotted in other ways; the straight line of best fit was then drawn through the points. These were time–mortality lines.{Table 3}{Table 4}

The dose of heavy metals in fish is related to several parameters, such as the natural habits and foraging behavior of fish,[12],[13] food status, source of a particular toxin, distance of the fish from the contaminant source and the resistance of other metals in the environment, temperature, transport of ion across the membrane and the metabolic rate of the fish, and the seasonal difference in the taxonomic composition of different food levels affecting the level and accumulation of metal in the aquatics tissue.[12]

Toxicity experimenting statistical endpoints are shown in [Figure 1]. LOEC in Caspian roach was more than silver carp (2 and 1 ppm, respectively), which means that NOEC was higher for Caspian roach than silver carp (6 and 2 ppm, respectively); however, LC50 was different between fish (5.26 and 6.58 ppm for roach and silver carp, respectively).{Figure 1}

Comparing our study with those available in the open source data, we can show the sensitivity of studied fish especially roach to Cd. Onorati et al.[14] reported 96-h LC50 range of 2.91–4.28 ppm of Cd for Corophium orientale. Indeed, Hedayati et al.[15] found the LC50 range of 1.85–5.30 ppm of Cd for C. volutator.[3]

Similarly, the 96-h LC50 amount of water is different from ion to ion and from sample to sample.[15] Gill and Pant[16] also found 96-h LC50 levels of 20.0 and 12.65 ppm Cd for Puntius conchonius and Pleuronectes flesus, respectively. Spehar[17] found 96-h LC50 amount of 28.0 and 2.5 ppm Cd for Mugil cephalus and Jordanella floridae, respectively. Das and Banerjee[18] showed 300.0 and 175.0 ppm Cd for Labeo rohita and Heteropneustes fossilis, respectively. However, 100% mortality was reported in Cyprinus carpio after 3–4 weeks of exposure to 2 ppm of Cd.[19]

The susceptibility of aquatics to a particular ion is a very important point for LC50 amount. The fish that is highly exposed to the toxicity of one ion may be less or even nonsusceptible to the toxicity of another ion at the same way of that ion in the environment.[15] Also, the ion that is highly toxic to aquatics at low dose may be less or even nontoxic to other samples at the same or even higher dose. Das and Banerjee[18] confirmed 300 ppm Cd for the 96-h LC50 of H. fossilis, whereas in the current study, the 96-h LC50 was lower than this level.

The degree of our fish to lower doses of Cd may be attributed to the altered physiological response of all samples to the specific ion and the amount of solubility of ions. The species exposed to Cd can compensate for the contaminants. If it cannot successfully compensate for pollutant effects, an altered physiological stage may be reached in which the aquatics continue to function and, in extreme cases, the acclimation response may be increased with a subsequent effect on fitness.[15]

Owing to the few open sources on the effects of Cd on the respective LC50 amount of aquatic animals, the results of this study have not been compared with those of other researchers and discussed accordingly. However, some justifications have been provided following different researches.


However, in this study, the LC50 amount is different from each fish and the accumulation of Cd in the body of species depends upon many parameters; it is evident from the current research that doses of Cd and physiological response of these samples affect the LC50 amount of species. It may be because of the increased resistance of one fish to Cd through adaptation. During adaptation, some proteins are released in the body of sample that detoxify the metals. This may lead to higher levels of Cd being needed to lead effects, resulting in higher LC50 levels.

The selection of current samples may be an important way to evaluate the effects of contaminant in water environments; two fish used in our test demonstrated their ability for this test. In general, comparing the sensitivity of these fish to common reference metals, it can suggest application of aquatics for toxicity determinations as a suitable model of toxicological tests. Also it needs to conduct more research with specific pollutants on these two fish to determine their suitability for detecting toxicity, as well as tests involving a complex mixture of contaminants, to determine researches monitoring water environments.

Financial support and sponsorship

This work was technically and financially supported by the Gorgan University of Agriculture Sciences and Natural Resources, Gorgan, Iran, as a research grant.

Conflicts of interest

There are no conflicts of interest.


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