Pacific Salmon, seabirds and marine mammals as bioindicators of organochlorine contamination on Northwestern Pacific
Organochlorine pesticides (OCPs) are toxic lipophilic anthropogenic substances, resistant to photolytic, chemical and biological degradation. In the XX century, hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) were used mostly. At the end of 1970, the productions of these two substances were officially banned in several countries. The Stockholm Convention has compiled a list of particularly dangerous toxicants ("dirty dozen"), which included DDT and its metabolites (DDD and DDE) (UNEP 2005) in 2001. In 2009, nine compounds, which include HCH extended the list. DDT was widely used to protect people from malaria and other diseases. After the World War II, DDT was widely used in agriculture as an insecticide, which has led to widespread pollution of water and soil and to a serious deterioration in the human and animal health.
The term “bioindicators” is used for organisms or organism associations which respond to pollutant load with changes in vital functions, or which accumulate pollutants. The most important reasons for using bioindicators are the direct assessment of biological effects, the determination of synergetic and antagonistic effects of multiple pollutants, the early recognition of pollutant damage to living organisms and relatively low cost compared to technical measuring methods. Intensive research over the last decades has resulted in the availability of numerous bioindicators which satisfy the requirements of convenience, standardization, cost, and evaluative capability. Bioindicators are commonly grouped as accumulative indicators and response indicators. Accumulative indicators store pollutants without any evident changes in their metabolisms. Response indicators react with physiological changes or visible symptoms of damage after the influence of toxic substances in low amounts (Markett et al. 2003; Holt and Miller 2010).
Fish inhabit almost the all aquatic environment of the planet. Most fish species are good OCPs accumulators. The many species of fish correspond to required criteria of bioindicators for the assessment of aquatic ecosystems. Therefore, fish are considered as one of the best organisms for the study of bioaccumulation characteristics and effects of pollutants on the ecosystem (Lukyanova et al. 2016). Bioindicators are provided the basis for biomonitoring.
Seabirds are useful bioindicators for organochlorine pollutants monitoring because they often are at the top of the food pyramid. Non-migrating birds can reflect the background contamination of their habitat. If there are no local pollution sources, birds reflect the global pollution resulting from the trans-boundary transfer of pollutants (Kunisue et al. 2003; Tsygankov et al. 2016).
Marine mammals can be considered key species for monitoring of persistent organic pollutants (POPs) in the marine environment all over the world. They can be used as bioindicators of global pollution and also as biomonitors of modern trends in anthropogenic pollution of the biosphere (Tanabe and Subramanian 2006; Tsygankov et al. 2015b).
Therefore, the purpose of the study is to assess environmental status of the Sea of Okhotsk and the Bering Sea using marine organisms – Pacific salmon, seabirds and marine mammals.
Marine organisms have been collected in various parts of the Sea of Okhotsk and the Bering Sea in 2010-2013.
Pacific salmon. Samples of organs from fish of four Oncorhynchus species – pink (O. gorbuscha), chum (O. keta), sockeye (O. nerka), and chinook (O. tshawytscha) – were analyzed. The samples were collected during expeditions organized by Pacific Research Fisheries Centre (TINRO-Center): pink and chum were caught in the southern Sea of Okhotsk, off the Kuril Islands, in June 2012 and 2013, during pre-spawning migrations; sockeye and Chinook were caught in the western Bering Sea and in the Sea of Okhotsk in October and November 2010 and 2011, during feeding ground. The fish were dissected; their organs were separated from the body. In pink and chum, the organs subjected to analysis were muscles, liver, male gonads, eggs, and whole fish; in chinook and sockeye, muscles and liver.
The seabirds (Pacific gull Larus schistisagus, crested auklet Aethia cristatella, auklet crumb Aethia pusilla, northern fulmar Fulmarus glacialis, and grey petrel Oceanodroma furcata) were collected in June and October 2012 from the Sea of Okhotsk. The samples were collected during expeditions organized by Pacific Research Fisheries Centre (TINRO-Center). Various organs, depending on the size of the birds, were analyzed: feathers, the feathers with the skin, liver, muscle, and whole bird.
Marine mammals. The liver and muscles of gray whales (Eschrichtius robustus; 4 males and 3 females) of different ages, and Pacific walrus (Odobenus rosmarus divergens; 5 males and 3 females) caught by the indigenous people in summer 2010-2011 from the coast waters (Mechigmensky Bay) of the Bering Sea were studied. The International Whaling Commission (IWC) has allowed exclusive harvesting rights for these gray whales to the indigenous peoples of Chukotka and Alaska as a means of supporting their traditional lifestyle.
Frozen samples (–20°C) were transported to laboratory. Before chemical analysis, separate organs and tissues were homogenized mechanically. Lipids were extracted from homogenized tissues (20 g) by means of n-hexane extraction, with subsequent disintegration of the fat components by concentrated sulphuric acid (Tsygankov and Boyarova 2015). Concentrations of organochlorine pesticides (HCH isomers (α-, β-, γ-HCH), DDT and its metabolites (DDD, DDE)) in samples were measured by a gas chromatograph Shimadzu GC-2010 Plus with an ECD (electron capture detector) (capillary column Shimadzu HiCap CBP5). Column temperature – 210°C, injector − 250°C, and detector − 280°C. Carrier gas is argon, inlet pressure: 2 kg/cm2, 1:60 flow divider, and flow rate of carrier gas through the column: 0.5 ml/min.
Laboratory blank samples were extracted and analyzed on a regular basis. Retention times for the standard samples were constant and were therefore relied upon for component identification. To identify individual substances, standard working solutions of OCPs in the concentration range of 1–100 mg/ml were applied. The calibration lines showed excellent linearity in the range of the concentrations of interest. To determine the quality of the methodology, a recovery study was performed using standard addition methods. Seven fish tissue samples were spiked with the mixture of pesticides standards. The spiked samples were extracted and analyzed as described in the method above. The results revealed that the mean recovery values ranged from 85.1 to 98.6%. This indicates that the analytical procedures outlined for the OCPs determination in this study were reliable, reproducible and efficient.
The statistical analysis of the results was performed in the software package IBM SPSS Statistics for Mac OS X. Significance of the obtained data was evaluated by using the Mann-Whitney U test with the significance level of p ≤ 0.05.
HCH isomers and DDE were found in all analyzed samples. The total content of pollutants in various organs varied within a wide range, from 41 to 7103 ng/g lipids. In general, the pesticide concentration increased in the following order: muscles < liver < eggs < male gonads. The maximum OCPs concentration in individual fish was recorded from sockeye liver (7103 ng/g lipids), where HCHs constituted 6453 ng/g that was also the maximum value for the studied salmon. The highest concentration of DDE was found in chinook liver (3022 ng/g). DDE in all the samples was the only registered DDT metabolite that indicates destruction of initial DDT, i.e. long-term presence of this pesticide in the ecosystem (Tanabe and Subramanian 2006). All three HCH isomers were detected in pink and chum; the total content of α- and β-HCH was higher than the level of γ-HCH. α- and β-HCH are the most stable isomer and typically constitute the major portion of the total HCHs content in living organisms (Wu et al. 1997).
The total concentration of HCH isomers in all the species was generally higher than the DDE concentration. As we showed earlier, the total concentration of HCHs in marine organisms from the Sea of Japan, the Sea of Okhotsk and the Bering Sea, as a rule, is higher than the DDT content (Lukyanova 2013; Lukyanova et al. 2014; 2015; 2016; Tsygankov et al. 2014; 2015a; 2015b; 2016). In muscles and liver of chinook and sockeye, only two (α- and γ-) of three HCH isomers were detected in all the analyzed samples; the value of γ-isomer was the highest. The high concentration of these isomers in species that spend several years in ocean indicates the recent input of technical HCH and lindane into marine ecosystems (Lukyanova et al. 2016). The same difference was observed for salmon from the Sea of Okhotsk and the Bering Sea. HCHs, as compared to DDT, are subject to atmospheric transfer to a greater degree (Bidleman 1999); as a result, HCHs is spread northward along the Asian coast and accumulates in the Arctic region (Wania and Mackay 1993).
A comparison of the total OCPs amount in muscles and liver of all four fish species showed that the mean values did not differ significantly between pink and chum, but they were significantly lower (p ≤ 0.05) than in chinook, in which the value was even lower than in sockeye (Fig. 2) (Lukyanova et al. 2016). The concentration increases in the following sequence: chum ≤ pink < chinook < sockeye; for instance, the total concentration in muscles ranged within 78.8–174.1, 89.3–222.8, 265.0–2435.4, and 165.7–3020.1 ng/g lipids, respectively.
The total concentrations of pesticides in various organs of the seabirds ranged from 13 to 16095 ng/g lipids. The OCP concentrations in feathers ranged from 29 to 8289 ng/g lipids, in feathers with skin – from 1568 to 16 095 ng/g lipids, in the liver – from 1680 to 2478 ng/g lipids, in muscles – from 2230 to 3000 ng/g lipids, in whole body – from 13 to 15113 ng/g lipids.
DDT was found in the fulmars feathers only, 975-1978 ng/g lipids in each individual. DDE was present in all specimens ranging from 28 to 15276 ng/g lipids. DDD was not detected at all samples. Maximum OCPs concentrations in the whole body were observed in fulmars (5816 ng/g lipids), minimum – in the gray petrel (1705 ng/g lipids). Maximum total OCPs concentration in the feathers was found in the Pacific gull – 8289 ng/g lipids, the minimum – in fulmar, 29 ng/g lipids. The maximum total OCPs concentrations in feathers with the skin and the total DDTs were found in crested auklet (16095 and 15276 ng/g lipids, respectively), the lowest concentrations – in feathers with the skin of the Pacific gull (1568 and 1016 ng/g lipids, respectively). In the liver, the total OCPs concentration in fulmar (2478 ng/g lipids) and total DDTs (1923 ng/g lipids) exceeded those in Pacific gull (1680 and 1377 ng/g lipids, respectively). OCPs concentration in muscle of Pacific gull (3000 ng/g of lipids) and the amount of DDTs (2775 ng/g lipids) were higher than in fulmar (2230 and 2030 ng/g lipids, respectively) (Tsygankov et al. 2016).
Features of nutrition, migratory behavior and bird’s life strategy define species peculiarities in the pesticide accumulation. The studied seabirds are a highly abundant species found primarily in subarctic regions of the North Atlantic and the North Pacific oceans. On the northern part of the Sea of Okhotsk bird reaches the Kurile Islands. Transoceanic migration is not typical for studied seabirds (Shuntov, 1998). In our study seabirds were collected from the south-western coast of Kamchatka and the Kuril Islands, where the most significant bird’s concentrations are formed. Detection of γ-HCH and DDT on the feathers of birds enables estimation of the presence of “fresh” contamination. However, there are no local pollution sources of marine environment and the air in the Sea of Okhotsk areas; the atmospheric transport from areas of application, such as Southeast Asia, appears as the most probable source.
Pesticides were found in all the analyzed specimens of gray whales. The total content of pesticides (∑HCH+∑DDT) in liver was higher than that in muscles. The concentration of pesticides in muscles ranged from 297 to 3581 ng/g lipids; in liver, from 769 to 13808 ng/g lipids (Tsygankov et al. 2015b). No statistically significant sex-dependent differences in the content of OCPs in muscles were observed; nevertheless, the concentration of xenobiotics in males (except for DDT and DDD, which were not found) tended to increase. In liver of males, only concentration of α-HCH had statistically significant higher values (p = 0.05), as compared to females. Here we may only note the tendency of growing pesticide content in liver of males. The low statistical significance of the obtained results is probably related to the small number of studied individuals.
The analysis of total OCP content (∑HCH+DDT) in muscles and liver of gray whale showed that statistically significant differences between muscles and liver existed only for β-HCH (p = 0.002). As for other pollutants, statistically insignificant increases of the total concentration of DDT in liver and that of HCH in muscles were observed.
Pesticides were found in all the studied specimens of Pacific walrus. The total OCP (ΣHCH + ΣDDT) content in liver varied within 4900–90300 ng/g lipids. These values substantially exceeded the range in muscles, which were 200–5700 ng/g lipids (Tsygankov et al. 2015b). In muscles, all isomers of HCH and DDT were detected; in liver, isomers of HCH, DDT, and DDE.
There was no statistically significant difference between muscles of males and females, although concentrations of all the pollutants, except for α-HCH, were higher in females. As for liver, concentrations of all pesticides were higher in females (except for β-HCH, which was higher in males), but these differences were also insignificant statistically.
The total content of various OCPs in muscles and liver of Pacific walrus is showed that statistically significant results of comparison of the organs were obtained only for two compounds, α-HCH (p = 0.016) and DDT (p = 0.021), the concentration of which proved to be higher in liver. For the other compounds, the differences were statistically insignificant: the γ-HCH and DDE concentrations were higher in liver, whereas the β-HCH concentration was higher in muscles.
The different levels of accumulation of pesticides in certain species indicate firstly the different degrees of pollution of their habitats by these compounds. The species-specific pattern of accumulation of lipophilic xenobiotics is determined to a great extent by the total fat content in the subcutaneous tissue and in some organs. Degree of sexual maturity of individuals is also of great importance. Gray whale and Pacific walrus inhabit similar geographical ranges, and the fat content in their organs differs insignificantly, amounting to 8–10%. Substantial differences in pesticide contents may be related also to the stage of reproductive cycle and are determined mostly by feeding habits. Gray whales feed predominantly on benthic crustaceans and other small-sized organisms that live both on and under the surface of soft bottom sediments (infauna). The major portion of walrus’ diet comprises benthic invertebrates: bivalves, some species of shrimps, lobsters, polychaetes, priapulids, octopuses, holothurians, and also some fish species. Moreover, walruses may sometimes prey on spotted seals and harp seal pups (Burdin et al. 2009). Thus, items of walrus’ food accumulate more pesticides in their bodies than gray whale’s food items do, since the coefficients of pollutant accumulation for mollusks and fish are higher than those for crustaceans (Li et al. 2007). The different rates of pesticide biomagnification in gray whale and Pacific walrus are caused to a great extent by the difference in their feeding habits and daily rations (Tsygankov et al. 2015b).
The use of bioindicators organisms facilitates the monitoring of the aquatic environment and indicates the degree of ecosystems contamination. In our study, Pacific salmon, seabirds and marine mammals are used as bioindicators for assessment of the ecological status of the Sea of Okhotsk and the Bering Sea. The presence of considerable concentrations of pesticides in marine organisms from the Sea of Okhotsk and the Bering Sea, which areas are very far from the regions of industrial activities and pesticides application, is not a surprise, but demonstrate and confirm general global pesticides background existing in the world today. The ocean became natural reservoir of contaminants from the various sources. It is determined the need for regular monitoring of the marine environment and biota in this region.
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This work was supported by the Russian Science Foundation (project No. 14-50-00034).
Pacific Salmon, seabirds and marine mammals as bioindicators of organochlorine contamination on Northwestern Pacific
Vasiliy Yu. Tsygankov1, Margarita D. Boyarova1, Olga N. Lukyanova1,2, Nadezhda K. Khristoforova1,3
1 Far Eastern Federal University, 690091, 8 Sukhanova str., Vladivostok, Russia;
2 Pacific Research Fisheries Centre (TINRO-Centre), 690091, 4 Shevchenko Alley, Vladivostok, Russia
3 Pacific Geographical Institute FEB RAS, 690000, 7 Radio str., Vladivostok, Russia
Abstract: Organochlorine pesticides (OCPs) (HCHs and DDT) are still used as pesticides in the Southern Hemisphere and can reach the North Pacific due to atmospheric transfer. Marine mammals (Pacific walrus Odobenus rosmarus divergens, gray whale Eschrichtius robustus), the seabirds (Pacific gull Larus schistisagus, crested auklet Aethia cristatella, auklet crumb Aethia pusilla, northern fulmar Fulmarus glacialis, and grey petrel Oceanodroma furcata) and Pacific salmon (pink (Oncorhynchus gorbuscha), chum (O. keta), chinook (O. tshawytscha), and sockeye (O. nerka)) were collected near the Kuril Islands (the northern-western part of the Pacific Ocean), in the Sea of Okhotsk and the Bering Sea. The total OCPs concentration (HCHs+DDTs) was found in each organism: in the Pacific walrus liver 90263 ng/g lipids, in the seabird tissues – from 29 ng/g lipids to 16095 ng/g lipids; and in the salmon — from from 41 to 7103 ng/g lipids. The concentrations and possible sources of OCPs in marine organisms are discussed.