海洋科学: 研究開発

抽象的な

Determining the Health Risks of Heavy Metals on Freshwater Dolphin (Finless Porpoise) in Poyang Lake

Areej Sabir, Wang Hua

Globally, heavy metal pollution in the lake ecosystem is a major concern, especially in developing countries. Water is a significant portion of the ecosystem and has ecological, social and economic importance, providing habitat and nutritional resources for many aquatic species. These lake ecosystems have, however, been rapidly destroyed by anthropogenic activities. Industrial runoff, agriculture, transportation, atmospheric deposition, etc. contribute thousands of known and unknown hazardous contaminants to rivers, estuaries and lakes. In recent years, there has been an increase in concern over heavy metal accumulating in China. Dolphins are well-known and highly respected residents of Chinese seas, where they play a vital part in the marine ecology. Humans have had a huge influence on dolphins and their surroundings over the years. The impact of heavy metals is particularly concerning due to the possible harmful consequences on marine life as well as the overall health and productivity of the ecosystem. Dolphins are at the top of the food chain, making them vulnerable to contaminants like heavy metals that may accumulate throughout the food chain.

Heavy metals, which may have accumulated through the food chain, are a particular concern because dolphins are long lived and at the top of the food chain and are therefore susceptible to such pollutants. The effects of heavy metals on marine life may be acute or long-term and may have a significant impact on the health and productivity of the entire ecosystem.

In this study, Poyang Lake, a largest river connected lake and China's largest freshwater lake, in the middle reaches of the Yangtze River was chosen as the research field. We investigated the heavy metals coming from four the sites; Kangshan, Benghu, Xingzi and Duchang to the Poyang Lake. The water of poyang lake was tested in the year 2018 where the amounts of arsenic, selenium and zinc were present at higher levels. The Poyang lake water was then tested in 2020 which showed high level of heavy metals added up in the coming years which were mercury, chromium, selenium and arsenic this was a matter of concern as heavy metals load has increased therefore in order to identify the sources that might be adding the potential load, Kangshan, Benghu, Xingzi and Duchang were selected.

Water transparency decreased in the months December>April>September>March>August>October, November>June, July>May. The transparency of water was being affected by the presence of algal blooms which result due to the excessive amounts of nitrogen and phosphorous in the water. The presence of algal structures was identified by measuring chlorophyll-a, which was highest in July>August>May>October>September> December>November>March>June>April i.e., (0.0071>0.00688>0.00641>0.00617>0.00604>0.00578>0.00400> 0.00348>0.00301>0.00276).

Temperature of a waterway is significant because it affects the amount of dissolved oxygen in the water. As the water temperature increases, the chemical oxygen demand increases. Chemical Oxygen Demand (COD) are the organics and inorganics in the water. This means that the periods of extreme rainfalls i.e. April-June receive a large amount of chemicals through runoffs of agriculture and industrial sites thus leading to the accumulation of heavy metals and production of algal blooms. Chemical oxygen demand was observed the lowest in the months of April and October followed by September and May, March and July, November and December i.e. (13.00, 16.00, 18.00, 20.00, 23.00) and was observed highest in the month of June i.e., (24.00).

The tissue distribution of heavy metals accumulated in the finless porpoise an endangered species was taken from a secondary study. When comparing the proportion/percentage of Hg present in different tissues of FP, we found that Liver has the highest amount of mercury and copper as compared to other major tissues of the FP. 33.35 mg/kg of Hg of found in the major tissues of FP, out of which 73% was present in the liver, Zn was the dominant element in all tissues with a maximum mean concentration of 177.85 mg kg^-1 dw in the liver. Overall, health risk assessment of trace elements in finless porpoises suggested that greater attention should be given to Hg, As, Cd and Se.

These metals are quint essential to maintain various biochemical and physiological functions in living organisms in very low concentrations only. These metals prove to be noxious when they exceed certain threshold concentrations. Heavy metals are significant environmental pollutants and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional and environmental reasons. The most commonly found heavy metals in waste water include copper, nickel, zinc, cobalt and cadmium all of which cause risks for human health and environment. Heavy metal toxicity can lower energy levels and damage the functioning of brain, lungs, kidney, liver and blood composition and other important organs. Long term exposure to high concentrations lead to gradual and progressive physical, muscular and neurological degenerative processes that initiate disease like multiple sclerosis, parkinson’s, alzheimer’s and muscular dystrophy. Repeated long term exposure of some metals and their compounds may cause cancer.