Algae's Adversaries: Unveiling Pollutants' Impact On Aquatic Life

Algae are photosynthetic organisms that play a crucial role in aquatic ecosystems. However, certain pollutants can significantly impact their growth and survival. Nutrient pollution, particularly from excess nitrogen and phosphorus, can fuel the rapid growth of algae, leading to harmful algal blooms. These blooms have detrimental effects on aquatic life and ecosystems, blocking sunlight, clogging fish gills, and reducing oxygen levels in the water, creating dead zones where aquatic life cannot survive. Additionally, some types of algae produce toxins that are harmful to both humans and animals, posing risks to public health and local economies. Other pollutants, such as pesticides, metals, engineered nanomaterials, pharmaceuticals, and personal care products, can also interfere with algal-bacterial interactions and affect the physiological and ecological functions of algae. Understanding the impact of these pollutants is essential for managing and protecting aquatic ecosystems and developing effective wastewater treatment technologies.

Nutrient pollution

In water, excess nitrogen and phosphorus cause an overgrowth of algae, known as an algae bloom. This overgrowth of algae has several detrimental effects on the aquatic environment. Firstly, the dense population of algae consumes oxygen, leaving little for other aquatic life forms, leading to the creation of dead zones where aquatic life cannot survive due to low oxygen levels. Additionally, the algae block sunlight from reaching underwater plants, disrupting the food web and causing further ecological imbalances.

When the algae eventually die, their decomposition consumes the remaining oxygen in the water, exacerbating the oxygen depletion and creating hypoxic conditions. The frequency and duration of these dead zones have increased over time, impacting water bodies like the Chesapeake Bay and the Gulf of Mexico. The Gulf of Mexico dead zone, caused by nutrient pollution from the Mississippi River Basin, is the largest in the United States, spanning an area of about 6,500 square miles.

Harmful algal blooms can produce toxins that are dangerous to humans and other organisms. These toxins can accumulate in shellfish, crustaceans, and the internal organs of fish, posing risks to both human and animal health. Direct contact with harmful algae can cause skin and eye irritation, while inhalation of fine spray or droplets from affected water can lead to mild respiratory issues. Consumption of contaminated water or seafood can result in gastroenteritis, vomiting, diarrhoea, fevers, and headaches. In more severe cases, algal toxins may affect the liver or nervous system.

To mitigate the impacts of nutrient pollution and reduce the occurrence of harmful algal blooms, it is essential to implement better farming practices and improve regulations to reduce nutrient runoff into water bodies. This includes adopting regenerative farming practices, improving soil health, and reducing the use of chemical fertilisers and animal manure. By addressing these issues, we can protect aquatic ecosystems, safeguard human and animal health, and minimise the economic toll of harmful algal blooms.

Acid rain

Corallina sp., a type of coralline algae, has been shown to survive extremely low pH conditions (pH 3) and can regulate the pH of its ambient seawater through the dissolution of CaCO3. In contrast, other macro-algae species, such as Ulva conglobata, have been negatively impacted by low pH conditions, with their photosynthetic properties decreasing drastically and their thalli irreversibly damaged.

The increase in atmospheric CO2 and acid rain precipitation are serious global environmental issues that have damaged biodiversity in various ecosystems.

Pesticides

Types of pesticides

Effects of pesticides on algae

Direct effects

Insecticides, herbicides, and fungicides have been found to have adverse direct effects on algal species. These effects include growth inhibition, reduced photosynthesis, and decreased chlorophyll production. The specific effects depend on the type of pesticide, its concentration, and the species of algae. For example, organophosphates and carbamates have been shown to inhibit the growth of various algal species, while pyrethroids have received less attention in terms of their direct effects.

Indirect effects

Factors influencing pesticide effects

The effects of pesticides on algae can be influenced by various factors, including the specific type and concentration of the pesticide, the species of algae, and the environmental conditions. For example, warm water gives certain types of algae a competitive advantage, and slow-moving or stagnant water can create conditions favorable for algal blooms.

Biodegradation and bioaccumulation

It is important to note that microorganisms, including algae, can play a role in the biodegradation of pesticides. However, the effects of pesticides on algae are complex and challenging to predict due to the variety of factors involved.

Furthermore, algae have been shown to bioaccumulate certain pesticides, which can have implications for the transfer of these chemicals to higher trophic levels in the food chain.

In conclusion, pesticides can have significant effects on algae, both directly and indirectly. While the direct effects of pesticides on algae are often negative, the indirect effects within ecosystems can be more complex and may even favor algal growth in some cases. Understanding the ecological effects of pesticides is crucial for safeguarding aquatic ecosystems and human health.

Metals

Algae can be used as a phycoremediator of heavy metals and they show high resistance towards them. Microalgae show various self-defence mechanisms against heavy metal toxicity. The removal of heavy metals is performed by microalgal species through different extracellular and intracellular mechanisms.

The following are the different mechanisms in use for the extraction of heavy metals using algae:

• Physical adsorption
• Ion exchange
• Complexation
• Precipitation
• Phycoremediation
• Bioaccumulation

Algae can be modified using chemical or physical means to enhance the efficiency and specificity of heavy metal removal. These include:

• Algal pre-treatment
• Immobilization
• Genetic modification

Engineered nanomaterials

ENMs may adversely affect algae's gene expression, metabolites, photosynthesis, nitrogen fixation, and growth rate. The major mechanisms of ENM-induced inhibition are attributed to oxidative stress, mechanical damage, released metal ions, and light-shielding effects. Oxidative stress refers to an imbalance in the oxidation system and antioxidant system within an organism, eventually leading to tissue damage. Oxidative stress can be caused by reactive oxygen species (ROS), which are elevated by ENMs. ENMs can also induce the production of intracellular ROS, which can damage intracellular lipid, carbohydrate, protein, DNA, and other biological macromolecules, leading to inflammation and oxidative stress.

ENMs can enter algal cells and spread to various parts, including chloroplasts, vacuoles, endoplasmic reticulum, Golgi apparatus, and mitochondria, causing significant damage or altering their function and structure. ENMs can also enter the nucleus, leading to abnormal nuclear effects, such as DNA damage, which can inhibit the process of cell division.

The toxicity of ENMs on algae is influenced by various factors, including water chemistry, light, and water temperature. The toxicity of ENMs can also differ depending on the characteristics of the algae, such as cell wall thickness, cell volume, and the presence of polysaccharides and other organic matter.

Overall, ENMs can have both positive and negative effects on algae. While ENMs may adversely affect algal growth and function, the rational application of ENM-algae interactions can promote the production of valuable bioactive substances and control biological and chemical pollutants.

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