Document Type : Research Paper
Abstract
Abstract
1- Introduction
In between aquatic ecosystems, wetlands and rivers have a great ecological importance. Heavy metals from geological and anthropogenic sources are increasingly being released into natural waters. Contamination of aquatic ecosystems with heavy metals has seriously increased worldwide attention, and a lot of studies have been published on the heavy metals in the aquatic environment. Under certain environmental conditions, heavy metals may accumulate to toxic concentrations and cause ecological damage. Mercury is a special concern in marine ecosystems, where methylation occurs during the process of biotransformation and accumulates in biota. Mercury is a toxin to the central nervous system and it can readily cross the placental barrier. Lead is attracting wide attention of environmentalists as one of the most toxic heavy metals. The sources of lead release into the environment by waste streams are battery manufacturing, acid metal plating and finishing, ammunition, tetraethyl lead manufacturing, ceramic and glass industries printing, painting, dying, and other industries. Lead has been well recognized for its negative effect on the environment where it accumulates readily in living systems. Lead poisoning in human causes severe damage to the kidney, nervous system, reproductive system, liver and brain.
The aim of this study is determination of mercury concentration in the muscle, intestine, gonad and kidney of Rutilus rutilus, Hemiculter Leucisculus (Anzali wetland), and Alosa Caspia Caspia (Caspian Sea), and mercury and lead concentrations in the muscle of Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Schizocypris altidorsalis, and Schizothorax zardunyi (Hamun wetland). The results of this study were compared with global standards. As well as in this multispecies monitoring, health risk assessment of consumers by EPA/WHO instructions has been done. The main objective was to evaluate the potential health risks associated with heavy metals via consumption of fish from the wetlands using the Average Daily Dose for Intake Process (〖ADD〗_pot) and Hazard Quotient (HQ) from heavy metals.
2- Materials and methods
2-1- Case study
The Caspian Sea (Fig. 1), which is located in the northern I.R. Iran, is the largest lake in the world and is connected to the distant Baltic through canals and the River Volga. It is unique closed water basin, plays the important role in the establishment of the climate. The Anzali Wetland (193 km2) (Fig. 1), located on the southern coast of the Caspian Sea, is internationally known as an important wetland for migratory birds, and was registered as a Ramsar site in June 1975 in accordance with the Ramsar Convention. Hamun wetland, the largest freshwater expanse of the Iranian plateau, is listed in the Convention on Wetlands, Ramsar.
2-2- Sampling
The fish species including Rutilus rutilus, Hemiculter Leucisculus (from Anzali wetland), and Alosa Caspia Caspia (from Caspian Sea), Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Schizocypris altidorsalis, and Schizothorax zardunyi (Hamun wetland) randomly were collected.
Fish samples (20 samples from each species) were transferred to the laboratory and stored in refrigerator. Afterwards, the tissues were separated and dried.
2-3- Mercury and lead analysis
The dried samples were ground and changed into a homogenous powder and then the mercury concentration rate has been determined by advanced mercury analyzer, model 254. Lead concentration rate has been determined by Atomic Absorption Spectroscopy (AAS), Perkin Elmer 4100.
2-4- Health risk assessment by EPA/WHO method
2-4-1- Hazard Identification
Hazard identification involves gathering and evaluating toxicity data on the types of health injury or disease that may be produced by a chemical and the conditions of exposure under which injury or disease is produced. The subset of chemicals selected for the study is termed “chemicals of potential concern”. Data from acute, subchronic, and chronic dose-response studies are used.
2-4-2- Dose-Response Assessment
The dose-response assessment involves describing the quantitative relationship between the amount of exposure to a chemical and the extent of toxic injury or disease. The US EPA established the Reference Dose (RfD) as below:
RfD = (NOAEL or LOAEL)/(UF ×MF)
NOAEL: No Observed Adverse Effect Level
LOAEL: Low Observed Adverse Effect Level
UF: Uncertainly Factor
MF: Modifying Factor
2-4-3- Exposure Assessment
Applies a generalized dose-response relationship to specific conditions for some population. Characterizes the sources of an environmental hazard, concentration levels at that point, pathways, and any sensitivities. Exposure assessment involves describing the nature and size of various populations exposed to a chemical agent, and the magnitude and duration of their exposures. The exposure pathway of heavy metals to human through ingestion of contaminated food has been studied by many researchers. Average Daily Dose for Intake Process 〖ADD〗_pot is calculated as:
〖ADD〗_pot=( (C× IR×ED))/(BW×AT)
C: Concentration of toxic material
IR: Ingestion Rate
ED: Exposure Duration
BW: Body Weight
AT: Averaging Time
2-4-4- Risk Characterization/Risk calculation
The Average Daily Dose for Intake Process (〖ADD〗_pot) (Total Intake) is compared to the RfD. If 〖ADD〗_pot< RfD, then no problem. Hazard Quotient (HQ) is calculated as:
HQ=〖ADD〗_opt/RfD
3- Results and discussion
The concentrations of Hg in tissues of Rutilus rutilus, Hemiculter Leucisculus, and Alosa Caspia Caspia was measured (Table 1).There was no significant difference between the independent variables of gender, age and weight of the dependent variable is the amount of mercury in the tissues of the Rutilus rutilus. But between the length and the amount of mercury in the kidney of Rutilus rutilus, there was significant difference at 95% (p=0.015) (Figs 2 and 3).
Mean concentrations of Hg in muscle of Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Schizocypris altidorsalis, and Schizothorax zardunyi were 0.14, 0.28, 0.15, 0.15, 0.34 and 0.36 mg/kg respectively (Table 1). The results of laboratory analysis showed that there are significant difference between the concentration of mercury in the muscle between species (p<0.001).
Mean concentrations of Pb in muscle of Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix, Schizocypris altidorsalis, and Schizothorax zardunyi were 0.32, 0.39, 0.35, 0.72 and 0.81 mg/kg respectively (Table 1). There was no significant difference between lead concentrations of these species (p>0.05).
Table 1 shows ADDpot and HQ of heavy metals in muscles of fish samples from the wetlands. Among the fish species examined in this study, Hemiculter Leucisculus with a HQ value of 0.009 has the lowest potential health risk to mercury and Schizothorax zardunyi with a HQ value of 1.2 has the highest potential health risk to mercury. The HQ through the consumption of Schizocypris altidorsalis and Schizothorax zardunyi was higher than 1 (for mercury), indicating that there is potential health risk associated with the consumption of these fish from the hamun wetland. The results for lead concentration indicate that there is no HQ value > 1, indicating that humans would not experience any significant health risk if they only consume metals from these species of fish from the hamun wetland. The concentrations of mercury in all species were below the limits for fish proposed by United Nations Food and Agriculture Organization (FAO), World Health Organization (WHO), US Food and Drug Administration (FDA) and US Environmental Protection Agency (EPA), and European Union (EU) (Table 2). Lead concentrations in Ctenopharyngodon idella, Cyprinus carpio, Hypophthalmichthys molitrix were under the scope proposed by FAO, WHO, FDA, Turkish Acceptable Limits (TAL), United Kingdom Ministry of Agriculture Fisheries and Food (UK MAFF) and National Health and Medical Research Council (NHMRS), but lead concentration in Schizocypris altidorsalis, and Schizothorax zardunyi were higher than WHO and TAL (Table 2).
It should be noted that maximum consumption of 0.020 kg/day of Schizocypris altidorsalis and 0.019 kg/day of Schizothorax zardunyi there is no potential health risk (CRlim).
4- Conclusion
The results of the present study aimed to provide data from Caspian Sea, Anzali wetland, and Hamun wetland as indicators of natural and anthropogenic impacts on aquatic ecosystem as well as to evaluate the human hazard index associated with fish consumption. The human health hazard Quotient (index) showed that the cumulative risk greatly increases with increasing fish consumption rate, thus yielding an alarming concern for consumer health.
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