The influence of oil pollution When the water body is slightly polluted by oil, the mucus secreted by fish can remove oil from the body, but it cannot be removed when it is seriously polluted. Oil and oil film adhere to the epidermal cells of fish gill, which affects the normal breathing of fish. Oil and oil film can also cover algae, destroy chlorophyll of algae, reduce its photosynthetic capacity, and make some plankton die. Oil can also pollute sediments, affect the reproduction of benthos and even kill them. When oil is swallowed by fish or inhaled through gills, it will make fish taste strange and lose its edible value. When the oil pollution is serious, the oil film covers the water surface, which hinders the reoxygenation of the water body, resulting in serious hypoxia of the water body, affecting the photosynthesis of phytoplankton and reducing the primary biological productivity of the aquatic ecosystem; Aquatic animals can't inhale oxygen and discharge carbon dioxide from water smoothly; The biodegradation of organic matter at the bottom of water body will also be affected. In addition, oil pollution will also cause migratory fish to be unable to lay eggs upstream and destroy fish resources.
The influence of chemical pollution There are many kinds and huge quantities of synthetic compounds, and the scope of pollution is expanding day by day, from local pollution to global pollution. Such as penguins in the Antarctic, white bears in the Arctic and reindeer in the tundra, pesticides can be detected from their bodies. Organochlorine pesticides are easily soluble in fat, so they are easy to accumulate, pass through and gradually spread in animal tissues, which brings harm to aquatic organisms and waterfowl. For example, DDT and PCBs have killed nearly 654.38 million+seabirds in Irish waters.
Domestic sewage, industrial wastewater and farmland drainage bring a large number of nitrogen and phosphorus compounds into the water body, which will cause water pollution and threaten the survival and even death of aquatic animals. [Comparison between abnormal crucian carp caused by organophosphorus pesticides (Ⅰ) and normal crucian carp (Ⅱ)]
The influence of heavy metal pollution will also cause great harm to aquatic organisms. Mercury and mercury compounds can be transferred and accumulated along the food chain in aquatic ecosystems. Among them, organic mercury is the most toxic to aquatic organisms. For example, the accumulation of methylmercury in fish nervous system and red blood cells can lead to neurological symptoms, unbalanced activities, abnormal periodic swimming, reduced food intake, weakened breathing and even death. Cadmium will accumulate in fish, damage gill tissue, intestinal mucus and renal tubular cells, and affect liver enzyme activity and blood function. Some people think that cadmium can also cause fish body distortion, which has a bad effect on the nervous system of fish and makes fish body abnormal. In addition, cadmium can also inhibit the respiration of mussels. Other heavy metals such as zinc and chromium are also toxic to aquatic organisms.
The influence of radioactive material pollution radioactive materials (such as strontium (cesium)) pollute water bodies. Because of its long half-life and similar chemical properties to calcium and potassium, fish scales, fish bones and aquatic plants can absorb other substances, such as phosphorus, which can also be absorbed by fish and accumulated in fish scales and fish bones, thus increasing the radiation dose to fish. X-ray irradiation will damage the gonads of fish, cause damage to the primary spermatocytes and nuclear damage in the testis of male fish, greatly delay the sexual maturity of the primary oocytes in the ovary of female fish, and lead to the decline of fertility. Under the chronic action of uranium, the ovaries of some female fish degenerate and are neutral.
The influence of thermal pollution will discharge waste hot water or other "waste heat" into the water body, which will increase the water temperature and decrease the dissolved oxygen, thus affecting the life and survival of aquatic organisms. Generally, when the temperature of fresh water exceeds 32℃, the population and community structure of aquatic organisms will change dramatically and many species will disappear. Rivers at 20℃ are the dominant species, green algae at 30℃ are the dominant species, and cyanobacteria multiply at 35 ~ 40℃. Generally, when the water temperature rises by about 5℃, the survival of fish will be threatened, and even fish will die.
The factors affecting the toxicity mainly include: water quality conditions, exposure time of poisons, and comprehensive effects of various poisons.
Water quality conditions include water temperature, hydrogen ion concentration, hardness, dissolved oxygen in water and other dissolved gases. One of the most important is temperature. Generally speaking, higher temperature will obviously increase the toxicity of pollutants; With the increase of temperature, dissolved oxygen decreases and toxicity increases. The hydrogen ion concentration (pH value) also has a great influence on the toxicity of some pollutants. For example, non-ionic ammonia (NH) formed by ammonia under alkaline conditions has obvious toxicity to aquatic organisms, while ammonium ion (NH) formed under acidic conditions has no obvious toxicity to aquatic organisms. However, heavy metals such as zinc and copper are the opposite, because the number of toxic ions formed at low pH value is greatly increased. Carbon dioxide is a gas dissolved in water, which will affect the toxicity of pollutants. If the concentration of carbon dioxide in water increases, the toxicity of ammonia will decrease. The hardness of water will also affect the toxicity of some pollutants. The toxicity of general cationic detergents to fish increases with the increase of water hardness. However, the toxicity test results of zinc sulfate to fish are the opposite. The higher the hardness of water, the longer the survival time of fish.
Generally speaking, the longer the exposure to toxic substances, the greater the toxic effect. However, if some individuals have been exposed to the same poison at a low concentration in the past, they will show greater tolerance to this poison in the acute toxicity test.
When considering the factors affecting toxicity, we should not only consider the interaction of various factors in water quality, but also consider the interaction between different poisons. When some poisons are mixed together, their toxicity is only additive; When some poisons are mixed together, the toxicity is obviously aggravated, and the so-called multiplication effect appears; The toxicity of some poisons decreases when they coexist, which is the antagonism between poisons. Rivers bring a lot of pollutants into the bay during the rainy season, which leads to the death of fish.