Great cormorant (Phalacrocorax carbo) as Monitor of Heavey Metals Contamination in Hara Biosphere Reserve

Introduction
Environmental pollution, especially marine pollution, is one of the complex and minatory problems that human is facing at the present time. Many of human activities have irrecoverable outcomes and affect the marine environment in such a way that destruction of marine zones has become a significant warning. One of the most important ecosystems in Iran is Hara biosphere reserve, located in the southern part of the country, and in the northwest of Qeshm Island in the protected zone of Hara. Since it is situated near the city of Bandar Abbas (the largest southern port of Iran in the Persian Gulf) and because ofits location at the margins of the northern coast of Qeshm Island (the largest island and commercial-industrial free zone of the country in the Persian Gulf), this region has been subjectedto urban and industrial pollutions. One of the most important pollutant sources, which has jeopardized the life of this ecosystem with serious threats in the recent decade, is the entry of heavy metals from various pollutant sources. Heavy metals are the most important contaminants that enter into the sea through rivers and shore zones and aggregate in the aquatic body through the food chain.
Most of these elements are not necessary for animals but have high toxic properties. One of the most imperative problems about heavy metals refers to their insoluble characteristic in the body. Indeed, heavy metals never excrete from the body, but they sediment in fat, muscles, bones, and joint tissues and may cause illnesses and various other phenomena. Birds, in comparison with other animals, are much more sensitive to environmental pollution. They may distribute chemicals, such as heavy metals, through direct connection or using polluted water or food. In other way, because of their indirect connection to polluted sources, they can determine the level of toxic element concentration in the marine ecosystem food chain. Therefore, the birds’ pollution of heavy metals can be used to anticipate the pollution level in the food chains. Among different tissues, mostly the soft tissues of birdsareused for the monitoring operation.
In many studies, the tissues of muscle, liver, kidney, spleen, heart, lungs, fat, blood, brain, and bone, and in some others, the feather and egg have been used toinvestigate the concentration of heavy metals in the environment. The selection criteria for choosing the suitable bird species (generally the suitable environmental monitors) include: sedentary species, proper distribution, easy identification, long life, availability during the whole year, carnivorous species, stability against fluctuations, and physiochemical features.
The birds that have most of these characteristics are not numerous. In fact, the maximum reflection of the heavy metals ratio is the purpose of these limitations and therefore, according to the above conditions, Great Cormorant (Phalacrocorax carbo) was selected as a suitable species to evaluate the heavy metals concentration. Great Cormorant is a species dependent on the aquatic ecosystem with a plentiful population and a wide distribution. In addition, its special piscivorous behavior has been always attractive for researchers.
The purpose of the present study is to compare the concentration of heavy metals (i.e. nickel, cadmium and lead) in the kideny, muscle and liver of the great cormorant between the male and female cormorants, and also to compare the concentration of heavy metals between the mature and immature cormorants.
Materials and Methods
Hara Biosphere Reserve is located in the south of Iran in the Strait of Khuran, between Qeshm Island and the mainland of Iran, in the Persian Gulf, and with 86,581 hectares area. Its latitude and longitude coordinates are 36°40' to 37° and 55°21' to 55°52' E, respectively. It is situated in the Mehran River delta and hosts the largest seabirds along the Persian Gulf shoreline and, therefore, it would represent a center of biodiversity in Iran. The variety in this biosphere reserve and its unique mangrove trees provides a diverse habitat for birds like egrets, herons, pelicans, and plovers. Based on the available statistics, in 2010, the biosphere reserve had been the host of 36 species and 13,000 water birds and wader birds. Hara also serves as a breeding and spawning habitat for fishes, shrimps, and other crustaceans.
After primary studies about the studied areas, we collected 12 Great Cormorant samples in November and December 2012 from Hara biosphere reverse.
After collection, we separated kideny, muscle and liver then, placed in the oven at 65 °C for 24 hours. In the digestion phase, 8 ml of nitric acid (65%) and 2 ml of perchloric acid (60%) (i.e. at the ratio of 4:1) were added to each sample (1 gram of the weighted sample). In a hot-block digester, they were digested firstly at 40 °C for 1 hour and then, at 140 °C for 3 hours. Afterwards, samples were screened by Whatman paper No. 1 and the solution’s volume reached 25 ml by using distilled water. At the end, all samples were kept in the refrigerator in polyethylene jars in order to later evaluate heavy metals concentration by atomic absorption machine.
In order to ensure about accuracy of the digestion process, in each digestion round, there was a control sample to subtract the sizable results from concentration of the metal in different samples. In this study, measurement of heavy metals concentration was performed by atomic absorption machine (model contrAA 700).
Discussion of Results
The results revealed that The maximum and average concentrations belonged to lead and the minimum related to nickel. Also the results indicated that the average of heavy metals were highest in kideny and lowest in muscle.
In this study, the high lead concentration in some of the samples from Hara biosphere reserve demonstrated this fact that the birds’ environment is under extreme pressure due to existence of lead.
Lead is a contaminant, which can be found everywhere and enters into the sea through various industrial wastes from the printing industry, oil refinery, etc. Human activities, along with the developments of the oil refinery and petrochemical plants, added to zinc and lead factories in Qeshm, and marine transportation in the south of Iran, may play the most important roles in absorption of this metal in the tissues of this bird.
The existence of heavy metals in the tissues of the great cormorant in Hara biosphere reserve can be due to the presence of oil refineries and usage of petrol nearby the studied area.
Burger and Gochfeld (2000) indicated that the undesirable effects of lead in birds occurs atthe concentration of 4000 ppb, althoughaquatic birds are able to tolerate even the concentrations higher than this level. If the lead concentration in birds’ tissues reaches over 4000 ppb, it would bring some problems, such as the decrease in the bird’s perception, decrease of chickens’ survival, inability in recognizing the sibling species, and the behavioral and nutritional problems. The behavioral problems of birds resulting from cadmium occur at the concentrations much lower than the lead and mercuryconcentrations.
In this research, the T-test results were used for comparing the concentration differences between two genders and it was shown that there is a significant difference among nickel and lead concentrations in three tissues of males and females (P < 0.05), but the results of the T-test showed that there is a significant difference between nickel and cadmium concentrations in adult and juvenile cormorants (P < 0.05).
Conclusions
The results revealed that The maximum and average concentrations belonged to lead and the minimum related to nickel. Also the results indicated that the average of heavy metals were highest in kideny and lowest in muscle. The results revealed that age factor affected on cadmium and nickel accumulation and sex affected on nickel an lead accumulation in all of Great Cormorant´s tissues. Heavy metals levels are below the range to cause behavioral change or reduce reproduction.