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УДК 57.044:574.2 DOI: 10.24412/1816-1863-2023-4-10-15
CHARACTERISTICS OF MERCURY BIOACCUMULATION BY FISH IN THE ESTUARY AREA OF THE RED RIVER
Н. Т. Т. Нгуен, магистр, ФГБОУ ВО Астраханский государственный технический университет; преподаватель, Вьетнамский морской университет, [email protected], г. Хайфон, Вьетнам,
И. В. Волкова, д-р биол. наук, профессор, ФГБОУ ВО Астраханский государственный технический университет, Каспийский институт морского и речного транспорта им. ген.-адм. Ф. М. Апраксина, [email protected], г. Астрахань, Россия
В работе рассматривается содержание ртути в мышечной ткани рыб и его корреляция с биотическими и абиотическими показателями водной экосистемы в районе устья Красной реки (Вьетнам). Исследование проводилось в районе устья Красной реки в течение 6 лет. Превышение вьетнамских санитарных норм по содержанию ртути в пищевых продуктах наблюдалось у пресноводного сома (Clarias batrachus), змееголова (Channa Striata), восточного тунца (Euthynnus affinis), красного окуня (Lutjanus vitta) и восточной рыбы-мухоловки (Dactyloptena orientalis) (в 1,7; 1,2; 1,8; 1,3 и 1,1 раза соответственно). Приведены зависимости содержания ртути в мышечной ткани рыб от их массы, продуктов питания и трофического положения в пищевой цепи. Ведущую роль в накоплении ртути в организме рыб играет тип рациона. Было показано, что в трофической сети экосистемы района устья Красной реки, на более высоком трофическом уровне пищевой цепи уровень накопления ртути был выше. Хищники характеризуются более интенсивным накоплением ртути (в 4—13 раз) в м ышечной ткани по сравнению с м ирными видами рыб. Описаны положительные достоверные корреляции между содержанием ртути в рыбе и концентрациями ртути в воде района устья Красной реки. Содержание ртути в м ышечной ткани морских рыб имеет значительную и положительную корреляцию с концентрацией взвешенной ртути.
The content of mercury in fish muscle tissue and its correlation with biotic and abiotic indicators of the aquatic ecosystem in the estuary area of the Red River (Vietnam) are discussed in the work. The study was carried out in the estuary area of the Red River for 6 years. Exceeding Vietnamese health standards for mercury in food products was observed in the freshwater catfish (Clarias batrachus), snakehead (Channa Striata), eastern tuna (Euthynnus affinis), red snapper (Lutjanus vitta) and eastern flyfish (Dactyloptena orientalis) (1,7; 1,2; 1,8; 1,3 and 1,1 times, respectively). The dependences of the mercury content in fish muscle tissue on their mass, food items and trophic position in the food chain are given. The leading role in the accumulation of mercury in the body of fish is played by the type of diet. It was shown that in the trophic network of the ecosystem of the estuary region of the Red River, at a higher trophic level of the food chain, the level of mercury accumulation was higher. Predators are characterized by a more intense accumulation of mercury (4—13 times) in muscle tissue compared to peaceful fish species. Positive reliable correlations between mercury content in fish and mercury concentrations in the water of the estuary area of the Red River are described. The content of mercury in the muscle tissue of marine fish has a significant and positive correlation with the concentration of suspended mercury.
Ключевые слова: ртуть, район устья Красной реки, биоаккумуляция, корреляция. Keywords: mercury, estuary area of the Red River, bioaccumulation, correlation.
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Introduction
The Red River is the longest river flowing in Vietnam [1]. The water resources of river system play an important role in meeting the water needs of the population and economy in most areas of northern Vietnam over a long historical period [2]. In the estuary area of the Red River, there are potential sources of mercury compounds: both local — industrial enterprises (at water transport and industrial
centers in the north of Vietnam based on the cities of Hanoi, Viet Tri, Haiphong), waste incineration and disposal, wastewater, and regional and global emissions mercury (from Europe, America and North Asia) [3].
Mercury is a highly toxic element (first level of danger). The accumulation of mercury in living organisms is the most urgent issue related to the rising level of mercury pollution in water bodies. Fish occupy different links in the trophic network of the aquatic ecosystem
and have a high ability to accumulate microelements, including mercury. Mercury in fish can accumulate in the greatest quantities in the liver and muscle tissue [4]. According to research by V. T. Komova, the deposition of mercury in muscle tissue was higher than in the liver [5]. By inspecting the mercury content of fish muscles at the Red River's estuary, it can be determined if these water bodies are contaminated with hydrotoxins.
The study was conducted to assess mercury levels in fish muscles located in the estuary area of the Red River, taking into account their weight, diet, and mercury concentration in water.
Research method
The study was carried out on delta watercourses (on the Red River and its channels) and in the seaside area in 2016—2021 years.
The atomic — absorption method [6] was used to determine mercury content in fish muscle tissue. The results were processed in the form of average values and their errors (x ± mx) in the STATGRAPHICS Centurion XVIII program environment:
The sanitary and hygienic standards were compared to evaluate the mercury content in fish muscle in the estuary area of the Red River. The Vietnamese sanitary and hygienic standard for mercury content in fish for food products is 0,5 mg/kg wet weight [7].
Results and discussion
The estuary of the Red River was the location where the gross mercury content in the muscle tissue of 6 freshwater fish species that reside there and its channels was assessed (Table 1).
From Table 1, it can be seen that the maximum values of average mercury content
(0,855 ± 0,112 mg/kg) were observed in freshwater catfish (Clarias batrachus), the minimum (0,045 ± 0,011 mg/kg) — in freshwater herring (Sardinella tawilis). The mercury content in food products in Vietnam is more than 1,8 and 1,2 times, respectively, higher than what is allowed by the Vietnamese sanitary and hygienic standards for freshwater catfish (Clarias batrachus) and snakehead fish (Channa Striata).
The mercury content in the muscle tissue of marine fish is presented in Table. 2. The maximum mercury content in muscle tissue of marine fish species caught in the coastal estuary and Bac Bo Bay was found in the Eastern tuna Euthynnus affinis, with a maximum value of 0,836 ± 0,053 mg/kg, while the minimum value was found in the planktivore (Pa-rupeneus barberinus) at 0,287 ± 0,011 mg/kg. Exceeding Vietnamese health standards for mercury content in food products was observed in Eastern tuna (Euthynnus affinis), red snapper (Lutjanus vitta) and Eastern flyfish Dactyloptena orientalis (1,8, 1,3 and 1,1 times, respectively).
In an aquatic ecosystem, the factors influencing the accumulation of mercury in the body of aquatic organisms belong to the group of both abiotic (physicochemical parameters of the aquatic ecosystem) and biotic (functional state of the organism and indicators of the structure of the aquatic community) [4].
Biotic factors contributing to the accumulation of mercury in fish tissues include larger size and weight, low growth rate of fish, and high life expectancy [5]. The mercury content in the muscle tissue of fish depends on morphological parameters, namely on the body weight and length of the fish.
Mercury content in muscle tissue of 4 species of freshwater fish (Anabas testudineus,
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Table 1
Mercury content in the muscle tissue of freshwater fish living in the estuary area
of the Red River
Species n Length, cm Weight, g Hg, mg/kg
Anabas testudineus 35 8,1 ± 0,2 17,9 ± 2,1 0,192 ± 0,003
Channa striata 75 21,8 ± 0,4 116,2 ± 20,5 0,584 ± 0,031
Clarias batrachus 70 22,3 ± 0,5 141,5 ± 11,2 0,855 ± 0,112
Cyprinus carpio 25 42,1 ± 1,9 968,2 ± 5,8 0,482 ± 0,032
Oreochromis niloticus 72 15,8 ± 0,4 108,2 ± 1,8 0,153 ± 0,006
Sardinella tawilis 84 10,3 ± 1,2 21,2 ± 7,8 0,045 ± 0,011
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Table 2
x Mercury content in muscle tissue of marine fish living in the estuary area
o of the Red River
№ Species n Weight, g Length, cm Hg, mg/kg
1 Dactyloptena orientalis 25 512,37 ± 21,75 38,03 ± 1,45 0,552 ± 0,081
2 Lutjanus vitta 30 355,19 ± 17,87 21,60 ± 0,59 0,649 ± 0,037
3 Harpadon nehereus 22 202,83 ± 7,72 32,89 ± 0,48 0,367 ± 0,008
4 Parupeneus barberinus 35 38,27 ± 1,17 12,08 ± 0,57 0,287 ± 0,011
5 Euthynnus affinis 22 1551,06 ± 59,23 68,06 ± 7,32 0,836 ± 0,053
6 Epinephelus areolatus 24 464,16 ± 22,94 20,24 ± 1,68 0,369 ± 0,027
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Clarias batrachus, Sardinella tawilis and Ore-ochromis niloticus) (r = 0,695; 0,508; 0,614 and 0,684, respectively, p < 0,05) and 6 species of marine fish (r = 0,872; 0,705; 0,611; 0,911; 0,832 and 0,837, respectively, p < 0,05) of the 12 studied fish species living in the estuary area of the Red River, revealed a positive and significant correlation with body weight, i.e. For these fish species, the level of mercury accumulation in muscle tissue increases with increasing body weight. The mercury content in the muscle tissue of the snake-head Channa striata and the carp Cyprinus carpio have a significant but weak correlation with their body weight, since the correlation coefficient is less than 0,5.
All studied marine fish have a significant and positive correlation between mercury accumulation in muscles and their body length. Such dependencies were observed in 2 freshwater fish species (Anabas testudineus and Oreochromis niloticus).
In addition to interspecific differences, in all studied fish species from the estuary area of the Red River, intraspecific differences were noted for individuals caught in the middle and lower reaches of the river.
Mercury content in the muscle tissue of fish in 4 species (Anabas testudineus, Clarias batrachus, Oreochromis niloticus, Cyprinus carpio and Sardinella tawilis) caught in the lower reaches of the river is higher than in the same species caught on average the flow of the Red River at 1,26; 1,15; 1,05; 1,05 and 1,22 times, respectively. This fact is associated with an increase in the mass and body length of ichthy-objects in the lower part of the river. Furthermore, in the river's lower and middle areas, the mercury content in fish food items (small and major invertebrates, small fish) also in-
creases with an increase in mercury concentration in the water and sediments.
The snakehead Channa striata had a slightly different appearance. The mercury content in muscle tissue has an inverse relationship with body weight and length, as demonstrated by fish caught in the lower reaches of the Red River, who were larger and heavier, but had less mercury in their muscle tissue compared to those caught in the middle reaches. Growth rate and lifespan are the two main factors that determine mercury accumulation in the muscle of this fish in this case. In the lower part of the river, a high concentration of food items in the water and in bottom sediments leads to an increase in the growth rate of predators. According to N. T. Komova et al. [5], the low growth rate of fish with a long life expectancy is the reason for the accumulation of mercury in large quantities, fish with a low growth rate but a long lifespan are able to accumulate mercury in their muscles more than fish with a high growth rate. This is confirmed by the fact that fish in the estuary area of the Red River, as well as in various water bodies of tropical regions, which have a faster growth rate, accumulate mercury in smaller quantities than in other regions of the world.
The level of mercury accumulation in the muscle tissue of fish living at the estuary area of the Red River reflects their nutritional differentiation. According to the type of nutrition, the studied fish species differed in:
— planktivores: Sardinella tawilis, Parupe-neus barberinus
— benthophages: Oreochromis niloticus, Dactyloptena orientalis
— predators: Cyprinus carpio, Channa striata, Lutjanus vitta, Euthynnus affinis, Epine-phelus areolatus, Harpadon nehereus
Hg 1000,0
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Fig. 1. Mercury content in muscle tissue of fish
with different types of nutrition: 1 — plactophages; 2 — betophages; 3 — zoophages (facultative predators); 4 — euryphages
— euryphages: Anabas testudineus, Clarias batrachus
The grouping of fish species from the Red River according to trophological characteristics indicates that the mercury accumulation in muscle tissue depends on nutrition (fig. 1).
From fig. 1 it was noted that as the position of a fish species in the trophic chain increased, there was a significant increase in the mercury content in their muscle tissue. A study by A. G. Heath, 2002 [8] noted that mercury concentrations in the main food of fish are in the order: from phytoplankton,
small invertebrates, large invertebrates to fish. In the estuary region of the Red River, freshwater herring (Sardinella tawilis) have the lowest muscle mercury concentrations. This is explained by the fact that freshwater herring in the ecosystem are planktivores with a short life span. Predatory feeding contributes to a more intense accumulation of mercury, since their food (small fish, invertebrates) contains more mercury than plankton and aquatic plants. Mercury levels in the muscle tissue of predators are 4—13 times higher than that of peaceful fish species. Compared to fish from other types of food, euryphages have the highest variation in mercury content in muscle tissue, which is attributed to their diverse food types. In addition, the mercury content in the muscle tissue of euryphage fish increases with age, because euryphages that are large enough come from feeding on invertebrates to actively prey on small fish.
Abiotic factors contributing to the mercury accumulation in fish tissues include water parameters and mercury concentrations in water. Correlations between mercury content in fish muscle tissue and mercury concentrations in the aquatic environment are presented in Table. 3.
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Table 3
Correlation coefficient between mercury content in fish muscle tissue and its concentration in the aquatic of the estuary area of the Red River
№ Species n Correlation of mercury content in fish muscles and dissolved mercury Correlation of mercury content in fish muscles and suspended mercury
r P r P
1 Anabas testudineus 35 0,802* 0,000 -0,429 0,010
2 Channa striata 72 0,809* 0,000 -0,004 0,974
3 Clarias batrachus 71 0,326 0,000 0,053 0,664
4 Cyprinus carpio 25 0,942* 0,000 -0,153 0,467
5 Sardinella tawilis 84 0,584* 0,000 -0,057 0,634
6 Oreochromis niloticus 72 0,349 0,000 0,14 0,23
7 Dactyloptena orientalis 25 0,217 0,217 0,117 0,577
8 Lutjanus vitta 30 0,717* 0,000 0,607* 0,000
9 Harpadon nehereus 22 0,872* 0,000 0,746* 0,000
10 Parupeneus barberinus 35 0,885* 0,000 0,523* 0,003
11 Euthynnus affinis 22 0,715* 0,000 0,752* 0,000
12 Epinephelus areolatus 24 0,839* 0,000 0,702* 0,000
Note: r — correlation coefficient; p — reliability;
* — the relationship is statistically significant (at p < 0,05). 1 3
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Mercury content in muscle tissue of 3 species of freshwater fish (Anabas testudineus Channa striata, Cyprinus carpio and Sardinella tawilis) (r = 0,802; 0,809; 0,942 and 0,584, respectively, p < 0,05) and 5 species of marine fish (Lutjanus vitta, Harpadon nehereus, Paru-peneus barberinus, Euthynnus affinis and Epine-phelus areolatus) (r = 0,714; 0,872; 0,885; 0,715 and 0,839 respectively, p < 0,05) from 12 studied fish species, living in the estuary area of the Red River, showed a positive and significant correlation with the concentration of dissolved mercury in water. For these fish species, the level of mercury accumulation in muscle tissue increases as the concentration of dissolved mercury in the water increases.
The content of mercury in the muscle tissue of Oreochromis niloticus and Dactyloptena orientalis does not have a significant correlation dependence on the concentrations of dissolved and suspended mercury in water (correlation coefficient less than 0,5 and reliability p > 0,05), and do not have a significant positive correlation dependence on mercury content in bottom sediments (r = 0,782; 0,769, respectively, p < 0,05). On the other hand, the Oreochromis nilticus and Dactyloptena orientalis are benthophages in the ecosystem. Thus, in an ecosystem, the mercury content in the muscle tissue of benthophagous fish does not depend on the concentration of dissolved and suspended mercury in water, but increases with increasing mercury content in bottom sediments.
The mercury content in the muscle tissue of marine fish has a significant and positive
correlation with the concentration of suspended mercury. This is explained by an increase in suspended mercury in water and in fish food due to the processes of mercury adsorption in the seashore, especially in the marginal filter zone.
Thus, the uptake of mercury by fish depends on their body weight, migration patterns, types of nutrition, their trophic position in the food chain, and mercury content in water and bottom sediments.
Conclusions
In the estuary area of the Red River, the average mercury content in the muscle tissue of freshwater fish varies from 0,045 ± 0,011 mg/kg in freshwater herring (Sardinella tawilis) to 0,851 ± 0,105 mg/kg in freshwater catfish (Clarias batrachus). Exceeding Vietnamese health standards for mercury in food products was observed in freshwater catfish (Clarias batrachus), snakehead (Channa striata), eastern tuna (Euthynnus affinis), red snapper (Lutjanus vitta) and eastern flyfish (Dactyloptena orientalis) (1,7; 1,2; 1,8; 1,3 and 1,1 times, respectively). The mercury content in the muscle tissue of fish has significant, positive correlations with body weight, body length, as well as with the concentrations of dissolved and suspended mercury in water. The predator promotes a more intense accumulation of mercury in muscle tissue; the greatest variations in mercury content in muscle tissue are observed in euryphages due to the diversity of their food types.
Библиографический список
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CHARACTERISTICS OF MERCURY BIOACCUMULATION BY FISH IN THE ESTUARY
AREA OF THE RED RIVER ^
N. T. T. Nguyen, master student, Astrakhan State Technical University; Lecturer, Vietnam Maritime University, [email protected], Haiphong, Vietnam,
I. V. Volkova, Dr. Habil. (Biological Sciences), professor, Astrakhan State Technical University, Caspian institute of maritime and river transport, [email protected], Astrakhan, Russia
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