Copper and Copper Nanoparticles: Poison for the Marine Organisms

 

Copper plays a vital role in enzymic activities in humans and fishes. Copper in small quantity is needed for survival and growth. But if the concentration of copper increases then it acts as a poison. Generally, ocean water has very little concentration of copper, but with increasing industrialization and on-surface activities, its concentration is also increasing. This copper can also react with other gaseous molecules or organic molecules, eventually making ocean water toxic and unsuitable for the growth of marine animals. Ocean Acidification is reducing the carbonate concentration, making it an even more suitable environment for copper to react with organic ligands (L) like thiols, exopolysaccharides etc. 

It is predicted that by the end of this century the concentration of free copper ions in the ocean will increase by 50%. This will greatly change the chemistry of the ocean and will affect the physiological processes of marine species. By 2100, environmental factors will damage the temperature and pH of polar regions far more than expected.

Copper is used in almost every industry. Copper is used in agricultural products, anti-fouling paints for ships, industrial products and catalyst. All these human practices are increasing the copper concentration in the ocean. Fishes tend to grow well and healthy with a diet containing balanced copper quantity. Hence, in almost every country in the world, for large scale fishing, these copper-containing diets are fed to fishes. Eventually adding more copper to water. Fishes grown with a copper diet might be more profitable, but this practice will show adverse effects after few decades.

Many photosynthetic organisms can counteract the increased copper concentration by producing certain ligands. These ligands will bind with copper, reducing its free ionic form and eventually its toxicity. But these organisms can act only up to a certain concentration. Seaweed or Macroalgae will the most affected species from increasing copper. The excess of copper directly affects their reproductive capability and growth rate. According to a study, the growth of seaweed is reduced by about 24% in excess of copper. Seaweed usually shows a significant growth in 9 to 10 days. But when they were grown in copper concentrated water, the time was increased to 12 to 15 days. Even after 12 days, the growth was very less than expected. This will directly affect the population of seaweed.   

They are also affected by increasing water temperature. Increasing copper will disturb the life cycle of many organisms, mainly seaweeds. Increasing copper, increasing temperature and reducing pH, this three factors will have long term effects on the marine ecosystem. 

In fishes, copper is mostly found in the kidney, gills, liver and muscles. Copper plays a vital role in maintaining RBC count and the immune system in the fishes. In most fishes, the copper imbalance leads to serious diseases like Alzheimer's disease and Menkes disease. Small aquatic organisms of lakes, rivers, seas are even more sensitive to metallic pollution. Copper concentration is increasing more in consumable fishes. Different studies have shown that many fishes sold in markets of different countries are contaminated with heavy metals (like copper). Hence today fishes are examined and studied before exporting or selling to check any possible contamination. 

Humans have almost 50 to 100 times more tolerance to heavy metals than fishes. Hence we cannot witness any harmful effects of copper in humans today. But if these heavy metals continue to pass on in the food chain then in few years it will be almost impossible to remove them. Fishes are more sensitive to change in metallic concentration than the change in temperature or pH. 

Effects of Copper, its oxides and Copper Nanoparticles (CuNPs) on different organs of fishes:  

(1) Gills: The gills plays an important role to detect and study the possible effects of copper on fishes. Some species when exposed to higher Copper concentrations, shows dysregulation in protein, glucose and cortisol levels. Effect on gills depends on pH and hardness of the water. Fishes in some conditions have shown a positive response to copper. Also, the effects of copper level on gills depend on age, sex and mass of the fish. CuNPs have fewer effects on gills than dissolved copper ions. In fishes like Caspian Roach, excess of CuPN resulted in cellular degeneration of gills and lowered cellular thickness. CuPN is also found to be toxic for many edible fishes.   

(2) Liver: Metallothionein is a low weight protein found in the liver. When fishes were exposed to excess copper, after some time they showed a notable decrease of metallothionein in the liver. In one amazing study, Roach fishes were exposed to copper for 7 days. It was noted that after the 7th day, these fishes were starved to death. The reason for death was the accumulation of copper in their liver. In another study, Zebrafish was exposed to copper for 14 days and was kept in freshwater for another 14 days. It was found out that even when returning to their normal environment, their body cannot counteract the accumulated copper. Hence copper will now be remained deposited in their body for a lifetime.

(3) Kidneys: Exposure of CuPN to Caspian Roach shows very drastic effects. The excess of CuPN leads to degeneration of tubule cells and interstitial tissues of the kidney. As the concentration of CuPN was increasing, the kidney cells were showing more and more damage. CuPN is also found to be accumulated in the kidneys. Exposure to copper ions reduced the functioning of kidney in these fishes.