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What is the impact of mercury pollution on aquatic life and human health?

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For decades mercury pollution has been a global issue affecting human health. I was watching one of the documentaries that had highlighted details of the extent to which mercury pollution can affect human health through the consumption of fish and wildlife. It raised several questions in my mind: what are the sources of mercury pollution? What is the extent of its impact? How can humans play a part in addressing this global problem? All of these led me to the inquiry question: What is the impact of mercury pollution on aquatic life and human health? I progressed through this project using fish as the organism under test and analysed using biology, environmental science, and health sciences.

In this paper, I have taken mercury chloride (one of the vital ingredient in pesticides), as the pollutant and conducted my experiment. This paper aims to identify the impact by exposing fishes to an LD50 environment over a 96-hour period and studying the changes in their mobility and survival rate. The results clearly revealed that aquatic life is impacted substantially by mercury pollution and I’ve listed my proposals to address this global issue to save aquatic life and human life. It is hoped that this study will be able to educate readers about how we are polluting our environment that affects our own health.

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Mercury Pollution

An introduction For several decades since the 1950’s it has been established that mercury emissions to the environment has threatened human health. These early studies showed that fish and other wildlife from various ecosystems generally attain toxic levels of mercury which in turn affects human health when they consume fish and wildlife from these various ecosystems. Point-source deposition and atmospheric deposition are the 2 ways the aquatic ecosystem gets polluted. Humans usually obtain mercury in two ways: as methylmercury from fish consumption, or by breathing in mercury oxide. Methylmercury mainly affects the brain and the spine (central nervous system), and in severe cases irreversibly affects parts of the brain.

Mercury contamination in water bodies Scientists pay special attention to oceanic mercury because this is where mercury is converted into the toxic, carbon-containing form, methylmercury. Eating seafood is the primary way humans are exposed to the heavy metal. According to a study published earlier this year in the journal, Nature Geoscience, majority of methylmercury is produced by microbes, especially in darker conditions. In the aquatic environment, mercury occurs in many forms which depend on the oxidation-reduction conditions. The forms mercury chloride and mercury hydroxide form readily in the good oxidation conditions, whereas sulfur-related forms prevail in the good reduction conditions. All the different forms of mercury are quite harmful, with each form exhibiting its unique health impacts. One of the more harmful forms of mercury, mercuric chloride, is still being utilised as a disinfectant and pesticide as it is more effective than other mercury compounds. It is also an anti-fungal agent which is why it is preferred to be used as a seed surface sterilizer. However, if used in excess, leaching may occur which will cause eutrophication and pollution in water bodies.

Mercury and Aquatic Health

When mercury enters a water body, naturally occurring bacteria absorb it and change it into a form called methyl mercury. This change is especially serious for humans, who readily ingest methylmercury and are particularly susceptible to its effects. Mercury then travels up the food chain as large fish consume smaller fish contaminated with mercury. Rather than dissolving or decomposing, mercury aggregates at consistently rising levels. 2.4 Mercury and Human Health People have higher chances of ingesting toxic levels of mercury when they consume contaminated fish on a regular basis. Mercury has neither any smell nor any colour and accumulates in the flesh of the fish. Thus, it cannot be removed by cutting off the skin or other parts of the fish. Mercury acts as a neurotoxin when it enters the body and hinders the nervous system and the brain. If exposed to mercury, pregnant women and young children face a hazard. Mercury might impede the development of young children and babies. It will result in delayed walking, talking, short attention span and learning disabilities. In unborn children, exposure to mercury may cause mental retardation, cerebral palsy, deafness and blindness. Adults are also in the risk of mercury poisoning which might result in memory loss, tremors, vision loss, numbness in fingers and toes, nonoptimal blood pressure, infertility and heart disease.

Ways to reduce the impact on humans One step people can take to reduce their exposure to mercury is to eat smaller fish or those with a short lifespan like sardines. These fish tend to accumulate lesser mercury than bigger predators and those with longer lifespans. Methylmercury gradually travels up the food chain (Figure.3) and is most prevalent in large, old carnivorous fish.

When mercury is deposited in lakes or waterways, bacteria convert it to methyl mercury. Methyl mercury accumulates in algae which are eaten by small fishes. These smaller fishes are then eaten by larger fish and the cycle continues. Predators at the top of the food chain, such as the walleye, may contain methyl mercury concentrations as high as 130,000 times that of the surrounding water.5 This could result in serious human health issues if contaminated fish are consumed frequently. Figure 3: Mercury biomagnifies from the bottom to the top of the food chain.

Preventing mercury pollution Manufacturers, government programmes and solid waste management facilities have taken several efforts to reduce the amount of mercury emissions. These have significantly reduced mercury from entering the environment from products that contain it. For instance, Hennepin County in Minnesota, USA has programmes which aim to keep mercury out of water bodies. These programmes, together with the pollution control equipment in the county’s waste-to-energy plant, have brought down mercury emission levels from 496 pounds to around 21 pounds in less than ten years, a reduction of over 95%. 3. Experiment and Data Analysis The aquatic organisms have a concentration limit to which it can survive in the polluted environment. The scientific term for that is known as the median lethal concentration. LD 50 is the amount of substance required to kill at least 50% of the test population using the acute toxicity test. Acute toxicity test is used to determine the concentration of a substance required to produce a toxic effect on a specific percentage of the test organisms. 96 hours is the general guideline.

Hypothesis

While the concentration of mercury chloride increases, the survival rate of the fishes decreases, and/or the fishes normal function is impacted. Materials required

  • 5 litres capacity of test chambers
  • Guppy fishes
  • Test solution (Mercury chloride)
  • 1000ppm (Stock solution)
  • Measuring cylinder (100 ml)
  • Funnel Materials needed to prepare the test solution
  • Pipette (10ml)
  • Standard Measuring Flask (SMF) (100ml)
  • Distilled water (1000ml)
  • Mercury chloride powder (500g)
  • Digital weighing scale.

Formulas and Calculations for preparation of stock solution

  • Calculate the mass of mercury in mercury chloride (HgCl2)
  • Mass of mercury= Formula weight (FW) of Salt (HgCl2)/Atomic weight of element 271.40/200.59= 1.353
  • If 1.353g of mercury chloride is taken and dissolved with 1000ml of distilled water, 1000ppm will be gotten.

To reduce the amount of mass and volume used, but to have the same ppm, divide the mass (g) by ten and the ml by 10, it will leave us with 0.13g rounded off to the nearest 2 decimal place which will be dissolved in 100ml of water leaving us with the same ppm in reduced amount of material used. Procedure to prepare the stock solution and final solution

  • Make sure the 6 SMFs are washed thoroughly with distilled water. Label the SMFs as 1000ppm, 0ppm, 10ppm, 20ppm, 30ppm, 40ppm and 50ppm respectively using a marker on the outside of the flask.
  • Weigh 0.13g of mercury chloride powder using a digital weighing scale.
  • Mix this powder with pour 100ml of distilled water to get the stock solution.
  • Ensure that the mercury chloride powder is fully dissolved.
  • Add 1ml of stock solution to 100ml of distilled water, to obtain 10 ppm.
  • Add 2 ml, 3 ml, 4 ml and 5 ml of stock solution to the respective SMFs and then add 100 ml of distilled water to get the other ppms.

Results:

  • Control Tub: All 5 fishes were alive, and movement was not impeded. Responded to stimuli such as light and touch.
  • Tub 1: All 5 fishes were alive, and movement was not impeded. Responded to stimuli such as light and touch.
  • Tub 2: All 5 fishes were alive, but movement was impeded. Their response to stimuli was slower than before.
  • Tub 3: 4 fishes were alive while one was dead. Movement was impeded and their response to stimuli was slower than before.
  • Tub 4: 2 fishes were alive while the other 3 were dead. Movement was impeded and their response to stimuli was much slower than before.
  • Tub 5: 1 fish was alive while the other 4 were dead. Movement was greatly impeded, responded to touch but not to light.

From the experimental results, it is clearly observed that mercury pollution reduces the survival rate of fishes and impacts their functioning. As the concentration of mercury chloride increases, the survival rate of fishes decreases. All the fishes in Tub 1 survived due to the low concentration of mercury chloride in the water. Unfortunately, as the concentration of mercury chloride increased, the fishes’ response to stimuli was impacted and they eventually died. In Tub 5, where there was 50 ppm of mercury chloride, almost all the fishes had died during the 96-hour period. This shows how devastating the effects of mercury pollution are on aquatic life. Additionally, it can be seen from the data that the presence of mercury impacts the health of the fishes and when humans consume them it affects their nervous system, muscular system and results in many other ailments. Hence it is crucial for the government, organizations and environmental science agencies to focus on.

  • Creating awareness among people and communities on mercury pollution through flyers, seminars and TV shows
  • Collaborate with companies / industries that produce mercury containing waste and encourage them to reduce mercury usage.
  • Government to put ban on consumption of the specific fish and wildlife from mercury polluted areas.

The entire journey of doing this project was a fulfilling one and I gained a lot of knowledge on a new topic. Least did I know that mercury pollution can pose such an impact to living organisms until I dived deep through the literature. I can’t believe how a casual chat with my uncle the head of the department of social work department expressing my interest in doing a study on mercury pollution led, to him getting the permission from biology and chemistry department to do the experiment in their lab. Handling the fishes, preparing the medium and monitoring/recording the observations was a very valuable experience and I hope through these results, I have highlighted the importance of ensuring mercury-free water bodies globally for the wellbeing of both the aquatic and human life.

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