Select One Of The Following Major Contaminants As The Topic

Selectone Of The Following Major Contaminants As The Topic Of This Ass

Select one of the following major contaminants as the topic of this assignment: benzene, lead, chromium, mercury, arsenic. Write a 700- to 1,050-word paper addressing the following regarding your chosen contaminant: the contaminant, the sources of the contaminant, physical properties of the contaminant, the routes of exposure and absorption, the pathway of distribution and transport, and the uptake across the cell wall or membrane.

Paper For Above instruction

The selected contaminant for this assignment is mercury. Mercury is a highly toxic element with a long history of environmental and health concerns due to its widespread use and release into the environment. This paper provides a comprehensive overview of mercury, covering its nature, sources, physical properties, exposure routes, mechanisms of distribution within the body, and cellular uptake processes.

The Contaminant: Mercury

Mercury (Hg) is a heavy metal that exists in various chemical forms, including elemental mercury (metallic mercury), inorganic mercury compounds, and organic mercury compounds such as methylmercury. It is widely recognized for its toxicity and ability to bioaccumulate in ecosystems. Its environmental prevalence and health risk potential make it a significant contaminant of concern worldwide.

Sources of Mercury

Mercury enters the environment through both natural and anthropogenic sources. Natural sources include volcanic eruptions, erosion of mercury-containing rocks, and weathering processes. However, human activities have significantly amplified mercury emissions. Major anthropogenic sources encompass coal combustion in power plants, artisanal and small-scale gold mining, chlor-alkali industry, waste incineration, and the disposal of mercury-containing products such as thermometers and fluorescent lamps. Once released, mercury can travel long distances in the atmosphere, depositing into water bodies, soil, and biota.

Physical Properties of Mercury

Mercury exhibits unique physical properties among metals. It is a dense, silvery-white liquid at room temperature with a melting point of -38.83°C and a boiling point of 356.73°C. Mercury has a high surface tension, high density (13.6 g/cm³), and excellent electrical conductivity. These physical features influence its environmental behavior, ease of vaporization, and bioavailability. Its liquid state at room temperature also facilitates its release into the environment through spills or evaporation.

Routes of Exposure and Absorption

Individuals can be exposed to mercury through various routes, including inhalation, ingestion, and dermal contact. The primary concern is inhalation of mercury vapor, especially in occupational settings or environments with contaminated air. Organic mercury compounds like methylmercury are predominantly ingested via contaminated fish and seafood, leading to oral exposure. Dermal exposure, though less concerning compared to inhalation and ingestion, can occur during handling of mercury-contaminated materials.

Absorption efficiency varies depending on the chemical form: approximately 80% of inhaled mercury vapor is absorbed through the lungs, whereas mercury salts and methylmercury are about 7-15% absorbed via gastrointestinal tract. Once absorbed, mercury can enter systemic circulation and distribute throughout the body.

Pathway of Distribution and Transport

After absorption, mercury binds to proteins such as metallothioneins and serum albumin, facilitating its transport via the bloodstream. Elemental mercury vapor, once inhaled, crosses the alveolar-capillary barrier rapidly because of its lipophilicity, entering systemic circulation. Methylmercury readily crosses biological membranes, including the blood-brain barrier and the placental barrier, leading to widespread distribution. Mercury tends to accumulate in tissues like the brain, kidneys, liver, and muscles, with methylmercury showing a propensity to bioaccumulate in aquatic food chains.

The transport mechanisms involve passive diffusion for mercury vapor and active transport processes for methylmercury, often mimicking amino acids to enter cells via amino acid transporters. The extent of distribution influences the toxicological outcomes associated with mercury exposure.

Uptake of Mercury Across Cell Walls or Membranes

The cellular uptake of mercury varies with its chemical form. Elemental mercury vapor diffuses passively across cell membranes due to its lipophilicity once in the bloodstream. Methylmercury, being a lipophilic organic compound, crosses cell membranes efficiently through facilitated diffusion, often utilizing amino acid transporters because of structural similarities to amino acids like methionine. Inorganic mercury compounds may require active transport mechanisms or endocytosis to penetrate cells.

This uptake ultimately leads to accumulation within cells, particularly in neural tissues, contributing to neurotoxic effects. The ability of methylmercury to cross the blood-brain barrier exemplifies the efficiency of its cellular entry and distribution within sensitive tissues.

Once inside cells, mercury can bind to sulfhydryl groups in proteins and enzymes, disrupting cellular functions and leading to toxicity. The cellular uptake process is critical in understanding the mechanism of mercury toxicity and implications for human health.

Conclusion

Mercury's toxic nature, diverse sources, physical properties, and pathways of exposure and distribution highlight the complexity of managing its risks. Understanding its mechanisms of cellular uptake and transport is essential for developing preventative strategies and treatment options for mercury poisoning. Continued research and regulation are vital in reducing human and environmental exposure to this hazardous contaminant.

References

  • Amin, Z., & Farooq, S. (2019). Mercury exposure and its health impacts. Journal of Environmental Science and Health, Part C, 37(4), 339–359.
  • Bloom, N. S. (2006). Mercury risk assessment and from methylmercury in fish. Environmental Toxicology and Chemistry, 25(1), 4–10.
  • Donald, J., & Swaddle, J. P. (2020). Environmental mercury pollution and human health. Environmental Research, 183, 109233.
  • Fitzgerald, W. F., & Lamborg, C. H. (2011). Geochemistry of mercury in the environment. Chemical Reviews, 111(10), 1340–1373.
  • Halbach, S., et al. (2019). Cell membrane transport of methylmercury and inorganic mercury: mechanisms and implications. Toxicology and Applied Pharmacology, 360, 138–148.
  • Lindqvist, O., et al. (1992). Atmospheric mercury. A review. Atmospheric Environment. Part A. General Topics, 26(11), 2173–2188.
  • Mason, R. P., et al. (2012). Mercury in the aquatic environment. Elsevier.
  • Pasquier, G., et al. (2015). Biokinetics of mercury in humans and implications for health risk assessment. Journal of Applied Toxicology, 35(9), 998–1012.
  • U.S. EPA. (2022). Mercury Study Report to Congress. United States Environmental Protection Agency.
  • Werner, D., et al. (2016). Cellular mechanisms of mercury toxicity. Journal of Cellular Physiology, 231(2), 297–308.

Related Assignments