Background information
Heavy metals such as lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd), and chromium (Cr) are naturally present in the Earth’s crust. They enter aquatic environments through human activities like industrial waste, mining, agricultural runoff, and improper waste management (Balali-Mood et al., 2021). Although small amounts of some heavy metals are biologically beneficial, elevated concentrations pose risks to both human health and marine ecosystems. Unlike organic pollutants, heavy metals do not degrade over time but instead accumulate in sediments and aquatic life, eventually entering the human food chain. High-level exposure to these metals can have serious health consequences. For example, mercury accumulates in fish, and when consumed by humans, can lead to mercury poisoning, negatively impacting neurological functions and cognitive development, particularly in children. Lead exposure can cause developmental and cognitive issues, while cadmium can result in kidney damage and bone demineralization (Tchounwou et al., 2021). Additionally, heavy metals alter water chemistry, affecting aquatic ecosystems by reducing species diversity and impairing the reproductive and metabolic functions of aquatic organisms (Ali et al., 2019).
Activity: Removing Heavy Metals from Water
1. Dissolve a small amount of zinc chloride in water to create a heavy metal solution.
2. Take three beakers and fill each with a different type of soil—sandy, clay, and organic-rich—placing a filter at the bottom of each to hold the soil in place.
3. Pour the same amount of the zinc chloride solution into each beaker, allowing it to filter through the soil into a collection container below.
4. Collect the filtered water that passes through each type of soil in separate beakers placed under the soil columns.
5. Use pH strips to test the filtered water from each sample.
6. Record and compare the pH results to observe how each soil type affects the water’s pH after filtration.
Note: The pH testing may not directly measure heavy metal removal but can indicate how different soil types affect water acidity, which in turn can influence heavy metal retention or mobility. For more accurate results on heavy metal removal, further testing methods like atomic absorption spectroscopy (AAS) would be required.
Case study into how heavy metals degrade with water and time
The Flint Water Crisis in Flint, Michigan, USA, is a well-documented example of how heavy metal contamination can affect water quality and human health over time. The crisis began in 2014 when the city’s water supply was switched from Lake Huron, via Detroit’s system, to the Flint River as a cost-saving measure. The river’s water, being more corrosive, required additional treatment to prevent the leaching of lead from aging pipes into the water supply. However, due to inadequate corrosion control, lead from the old pipes began leaching into the drinking water, resulting in widespread contamination. This led to serious public health concerns, particularly affecting children and vulnerable populations, as lead exposure is linked to developmental and cognitive impairments in children. The crisis highlighted systemic failures in infrastructure management and regulatory oversight, illustrating how poorly maintained infrastructure can lead to severe heavy metal pollution with lasting impacts on human health. Importantly, the Flint River itself is not a source of marine life, so while the crisis severely affected human health, it did not have a direct impact on marine ecosystems.
How Do the Effects of Heavy Metals Vary and Affect Water and Marine Life?
Heavy metals significantly impact both water quality and marine life health. Toxic metals such as lead, mercury, cadmium, and arsenic can cause ecological imbalance even in trace amounts. These metals alter the chemical composition of water, affecting parameters like pH, oxygen levels, and nutrient availability. As a result, water contaminated with heavy metals becomes toxic to most aquatic organisms, leading to reduced biodiversity. For instance, high concentrations of heavy metals can lower dissolved oxygen levels, which are crucial for the survival of fish and other aquatic organisms. Under acidic conditions, metals like aluminum and mercury become more soluble, increasing their bioavailability and toxicity to marine life.
Heavy metals also cause bioaccumulation and biomagnification within aquatic ecosystems. Once absorbed by smaller organisms like plankton, heavy metals move up the food chain, becoming more concentrated in larger predatory species such as large fish, marine mammals, and eventually humans who consume seafood. For example, mercury bioaccumulates in fish like tuna and swordfish, posing health risks to humans when ingested in high amounts. Mercury exposure is particularly dangerous, as it can cause neurological and cognitive issues in both marine animals and humans.
Moreover, heavy metals interfere with the physiological processes of marine organisms. They disrupt essential biological functions, such as the nervous systems of fish and invertebrates, leading to reproductive challenges, slower growth rates, and even death. Mercury, being neurotoxic, causes neurological and behavioral issues in fish. Similarly, cadmium exposure in marine animals has been linked to kidney damage and bone demineralization.
In summary, heavy metals can alter water chemistry, reduce biodiversity, cause bioaccumulation and biomagnification, and disrupt the biological functions of marine life, creating widespread environmental and health concerns.
How Can We Prevent Heavy Metal Contamination in the Future?
Preventing heavy metal contamination in the future will require a combination of strengthened regulatory policies and advanced technological solutions. One of the most important steps is the enforcement of stricter government regulations that limit the discharge of heavy metals into water bodies. Industrial plants, mining operations, and agricultural activities must comply with environmental standards that regulate effluent discharge to reduce pollution.
Industries should adopt advanced wastewater treatment technologies before releasing any potentially contaminated water into the environment. Techniques such as chemical precipitation, reverse osmosis, membrane filtration, and ion exchange have proven effective in reducing heavy metal concentrations to safe levels. In some cases, these processes also allow for the recovery and reuse of heavy metals, which not only reduces pollution but also provides economic benefits by turning waste into valuable resources.
In mining, reforms are crucial to minimize environmental impact. Sustainable mining practices, including proper waste management, can significantly reduce the risk of heavy metal contamination by preventing leaching into groundwater. These best practices should be mandatory and consistently enforced.
Agricultural practices also play a key role in preventing heavy metal contamination. The use of low-metal-content fertilizers and pesticides can reduce the input of toxic metals into the soil and water systems. Additionally, controlled irrigation and precision fertilizer application can minimize excess chemical use, thereby reducing the likelihood of metal leaching into nearby water bodies.
Establishing buffer zones of vegetation around water bodies can help absorb runoff and prevent contaminants, including heavy metals, from reaching aquatic ecosystems. Such natural barriers are effective in mitigating the spread of pollutants.
Finally, shifting reliance from mineral resources to renewable energy sources—such as solar, wind, and hydropower—can significantly reduce the need for mining and industrial processes that contribute to heavy metal contamination. This transition to cleaner energy can be a long-term solution to reducing the overall environmental impact, including the protection of water quality and marine life.
In conclusion, a combination of policy reforms, technological advancements, and sustainable practices across industries can help mitigate and prevent heavy metal contamination, protecting both the environment and human health in the future.
References
Ali, H., Khan, E., & Ilahi, I. (2019). Environmental Chemistry and Ecotoxicology of Hazardous Heavy Metals: Environmental Persistence, Toxicity, and Bioaccumulation. Journal of Chemistry, 2019, 1–14. https://doi.org/10.1155/2019/6730305
Balali-Mood, M., Naseri, K., Tahergorabi, Z., Khazdair, M. R., & Sadeghi, M. (2021). Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic. Frontiers in Pharmacology, 12(643972). https://doi.org/10.3389/fphar.2021.643972
Tchounwou, P. B., Yedjou, C. G., Patlolla, A. K., & Sutton, D. J. (2021). Heavy Metal Toxicity and the Environment. Experientia Supplementum, 101(1), 133–164. https://doi.org/10.1007/978-3-7643-8340-4_6
