Determine of Mercury Levels in Various Tissues of Common coot (Fulica atra) and Common teal (Anas cerecca) Considering to the Age and Sex in the Fereydunkenar International Wetland

Document Type : Research Paper


The aim of this study is to determine of mercury levels in various internal organs of the Fereydunkenar International Wetland’s birds for the first time and to determine the influence of this metal on their health.
This study has been done in the Fereydunkenar international wetland where is the most important wetland habitat of the central areas of Hyrcanian ecosystem. Fereydunkenar International Wetland with 5427 hectares area has located in the southern Caspian. This wetland also is the overwintering habitat of only surviving flock of Western Siberian Crane in Iran, every year attracts about one-third of overwintering birds species (150 species), that will migrate the northern geography latitudes to Iran. Bird samples were collected in autumn 2011.
Samples collected from tow species (Common coot: n = 15 and Common teal: n = 16). The birds were biometrics (total body length and weighing). Sex and age of birds was identified. Finally liver, kidney and breast muscle of each bird was completely separated from the body and were kept until beginning to analyze in temperature - 20 ° C. Then 0.2 g of each tissue (liver, kidney, and breast muscle) was transferred in 50 mL Teflon containers with lid and 5 ml of nitric was added to it. Then the samples were transferred to the microwave and temperature of microwave reached the 180° C temperature with a gentle slope during 40 minutes and maintained at this temperature for 20 minutes. Then, the temperature of the microwave was reduced with a gentle slope to cool the samples. After cooling, the solution was passed through filter paper to obtain a clear solution. Next, the clear solution obtained was increased with two time deionized water in the 50 mL volumetric flask. In this stage, Mercury concentration was measured in each sample by using atomic absorption tool, Perkin-Elmer model (AA 700) according to method of cold vapor technique.
Statistical analyses were carried out using SPSS ver. 18.0. Results have been expressed in µg/g-1 ww with SD.
The results showed, that the highest mercury levels were observed in the liver of both species (0.34±0.16 µg/g-1 ww in Common coot and 0.28±0.11 µg/g-1 ww in Common teal). After the liver, the amount of mercury in the kidneys of both species was higher (0.22±0.08 µg/g-1 ww in Common coot and 0.25±0.13 µg/g-1 ww in Common teal). There was a significant difference in mercury concentrations among different tissues (between liver with two other tissues), (P < 0.01). Also, there was no significant difference in mercury concentrations among different tissues of Common teal. In this study, liver and kidney of two both species teal had greater amount of mercury than their breast muscle. Because in animals, liver is the most important part for de-poisoning processes that metabolically transforming these harmful compounds to especial methyl mercury, so it is transferring these harmful components to metabolites, that is directly discharged to bile in order to de- poisoning. Also, mercury salts are excreted through the kidneys and liver, so that the most important excretion route is urine and stool. Also, it seems that the most important of being less of mercury level in breast muscle of Common teal and Common coot than the other tissues is that physiologic conformity with around environment are simultaneously occur with bird growth, that is effective on omitting or neutralizing mercury. Therefore, after increasing weight and length of bird and then its consistency with environment, the concentration of these metals is declined in muscles and increased in intestine and gut. Therefore, these stated issues can be important reason for the high levels of mercury in liver and kidney than breast muscle of birds in the present study.
We also compared differences of mercury concentrations in two both species according to effects of sex. The results showed, there was no significant difference in mercury concentration between tissues of male and female of two species. This case can be the reason for that a female bird can excreted out 58% of the mercury in a breeding season from its body. But this amount is equal to 49% for a male bird in a breeding season that is, with a difference equals to 9%. Therefore, although the female birds can excrete out some mercury during laying eggs from the body, but this amount of mercury which excreted out from body by this way is negligible than mercury excreted out during molting. Then, considering to this subject, it can be concluded that male birds sometimes has same or less mercury concentration than female birds. In addition, it may be because both sexes of both species have a similar strategy to find food, which these subjects are true for the birds of this research.
In addition, we compared differences of mercury concentrations in two both species by effects of Age. There was no significant difference in mercury concentration between tissues of adult and juvenile of two species. In spite of mercury as a food is an unnecessary element for the body and has a such long biological half-life, so its accumulation in body will increase along with growing and pollution level in environment, molting system of Common coot (60 days, completely) and Common teal (182 days, completely) could be partly due to the above reason. Because considering to the sampling season (autumn, the end of molting for both species) more amount of mercury have been excreted out from the adult body of both species. Also, molting of tow both species is long term and they completely lose their feather, then they excrete out more mercury from their body than other birds in a short period. Therefore, above mentioned instances has been the reason for similarity in mercury level in adult and young birds of both species.
Also, the results of comparing effects of species on mercury concentrations shows, there was no significant difference in mercury concentration between tissues of two species. It seems, presence of two both species in similar food level, same environment and using similar food can be due to this subject. Common coot and Common teals studied had similar size and additionally, using same food caused that they have almost equivalent metabolic rate, so it can be the reason of high similarity of mercury concentrations in organs of both species. In addition, simultaneous of migration in Common coot and Common teal and using same fly path during the migration and the same time of sampling can almost be the reason of similarity in mercury concentration in these two species.
The results of correlation of mercury concentrations in various organs with biometric data showed, there was no any statistical correlation for the amounts of mercury in Common coot various organs. This result was the same for Common teal. Just there was negligible statistically significant correlation between the amounts of existing mercury in the liver of Common coot with the length of total body (P < 0.05). But there was not any statistical relationship between other organs of Common coot with body weight and the length of total body. This result was the same for the different organs of Common teal with weight and length of the total body. Therefore, it can be concluded that large body is not necessarily a reason for high levels of mercury concentration in birds’ tissues. Because, it is possible that an individual with larger body do not feed on larger prey.
Reports showed, increasing mercury concentrations up to 5000 µg/kg in birds' body cause negative effects on reproduction and the birds’ behavior. Also, increasing mercury concentrations to this amount provides fatal symptoms (limit that damage to the animal, but it does not cause death) and even be fatal for the birds. According to the results of this study, mercury concentration was lower than from threshold affecting on normal behavior and breeding.