Algae are microscopic organisms that use photosynthesis to produce energy from sunlight, just like plants, and live in aquatic environments, i.e. all types of natural waters, including saltwater, freshwater, and brackish water (a mixture of salt and freshwater).
Eutrophication
The term comes from the Greek word ‘eutros’ meaning ‘well-nourished’ and refers to the excess input of inorganic nutrients (from human activities), mainly nitrogen and phosphorus, into an aquatic system, leading to an uncontrolled proliferation of phytoplanktonic algae and causing adverse effects on the affected water bodies, such as the covering of the water surface.
The main causes of eutrophication are human activities that affect nearby waters such as rivers, streams or groundwater and thus the seas and oceans. These are:
- Agriculture. Nitrogen fertilizers are used to fertilize crops, seeping into the soil and reaching rivers and groundwater.
- Livestock farming. Animal excrement is rich in nutrients, especially nitrogen. If not properly managed, they can end up in nearby water sources.
- Urban waste. Mainly detergents with phosphates end up in wastewater that flows into rivers, seas, and oceans.
- Industrial activity. Dumping of both nitrogenous and phosphate products can occur, among many other toxic products, such as those used in textile manufacturing.
- Atmospheric pollution. Emissions of nitrogen and sulphur oxides react in the atmosphere to produce acid rain, thus carrying nutrients to water bodies.
- Forestry activity. The forestry residues left in the waters degrade, providing all the nitrogen and other nutrients that the plant has.
Eutrophication has a number of consequences:
- Algal blooms cause the water to become cloudy, preventing light from penetrating the bottom of the ecosystem. As a result, the marine flora is unable to photosynthesize, dies and during their putrefaction and the growth of algae, a large amount of dissolved oxygen is consumed and they provide an abundance of organic matter (sludge).
- It affects water quality because as rotting increases and oxygen is depleted, the water becomes foul-smelling. The smell of these waters can cause economic losses (tourism, areas that lose value...), and respiratory problems and their consumption can cause health problems for people in the area.
- Affect the fish production of an area, either by extraction or by cultivation.
- The increased presence of algae can cause a previously navigable waterway to become non-navigable.
- Some of the algal blooms are toxic. These substances can kill animals when consumed. Affected animals can act as a vector affecting other species and reach humans.
- The anoxic bottom conditions give rise to the growth of bacteria that produce toxins lethal to birds and mammals and invasive species take advantage of the new conditions and displace local organisms.
Harmful algal blooms (HAB or FAN, by its acronym in Spanish)
Some types of algae produce toxins and their concentration can vary as environmental factors such as light, temperature, salinity, pH and nutrient levels can stimulate toxin production, so climate change is posing a real challenge to prevent their proliferation. Algal toxins released into the surrounding water or air can seriously harm people, animals, fish and other parts of the ecosystem.
HABs occur when toxin-producing algae bloom excessively in a body of water. Depending on the type of algae, this effect is sometimes visible to the naked eye as foam, slime, mats or paint with green, blue-green, red or brown colours, and sometimes difficult to see because they grow close to the bottom.
Because of their aglga nature, they can, by their abundance, overgrowth and surface coverage, deplete oxygen in the water, which can lead to the death of fish and other living creatures. This is not only an environmental or health problem but also an economic problem if it occurs in fishing and recreational areas.
With the emergence of HABs, people can be exposed to toxins from the fish they catch and eat, from swimming or drinking the water and from the air they breathe, and become ill. It is important to note that cooking contaminated shellfish or boiling contaminated water does not destroy the toxins but this situation rarely happens when eating commercial seafood because state regulators monitor fishing activity for HABs and shut it down during blooms.
Depending on the type of HAB, a range of health effects can occur. For example, eating shellfish contaminated with toxins from algae called Alexandrium can lead to paralytic shellfish poisoning, which in turn can cause paralysis and even death; Pseudo-nitzschia algae produce a toxin called domoic acid that can cause vomiting, diarrhoea, confusion, convulsions, permanent short-term memory loss or death, when consumed at high levels and FANs that occur in freshwater, such as that of the Great Lakes and other drinking water sources, are dominated by cyanobacteria called microcystin. This type of organism produces a liver toxin that can cause gastrointestinal disease as well as liver damage.
What can nuclear technology do?
Having indicated the above, in the case of Eutrophication, there is the fact that there are aquatic systems, such as estuaries, that naturally tend to have high concentrations of these substances, so that increases of anthropogenic origin are not easily detected, at least in the initial stages of the problem. They only become evident when long-term monitoring is carried out and can be compared with the conditions of the system before it was disturbed or when there are periodic events of overpopulation of organisms such as macroalgae or microalgae.
In order to reduce this problem, governments and others have worked to improve the management of fertilisers, as well as to increase the capacity to collect and treat discharges, and legislation has been introduced to regulate the concentration of pollutants that are discharged from dischargers. In many places, long-term monitoring plans have been designed, using modern tools, to provide clarity on the changes occurring in aquatic systems and, above all, what actions can be taken to reverse or avoid such damage.
One example of this is the Marine-Coastal Stressors Research Network in Latin America and the Caribbean (REMARCO), which uses nuclear and isotopic techniques to obtain scientific information and help define policies that serve as a focus for action.
The aim is to have a tool to diagnose the state of health of aquatic environments, focusing on coastal environments. This requires a series of steps, including sample collection, laboratory analysis and comparison of results, for the quantification of each of the variables (phosphate, nitrate, silicate and chlorophyll are routinely quantified) used in the calculation of the eutrophication index.
Silicate is included because, in marine systems, most of the primary producers are phytoplankton, which in turn are made up of organisms such as diatoms, which build their structure from silicate, hence for these organisms this chemical species is a nutrient.
In the case of chlorophyll, it is quantified as an indicator of primary production, and the relevance lies in monitoring the concentration of chlorophyll in the water, because it is a reflection of the population of primary producers; the higher the amount of chlorophyll, the more active the community of organisms, which in turn is an indication of possible affectation by excess nutrients. The process of chlorophyll quantification requires not only conventional laboratory analysis, but also non-invasive techniques such as spectral analysis of satellite images, which allow data to be obtained from large coastal regions, using specialised algorithms, as well as monitoring over time in specific regions.
On the other hand, REMARCO carries out the study of HABs by monitoring microalgae, toxins and sediments.
The identification and quantification of microalgae uses optical and electron microscopy methods such as the Receptor Binding Assay (RBA). It aims to quantify paralysing toxins and those that cause ciguatera, a disease caused by the consumption of contaminated fish products about which little is known and which can manifest up to 175 different symptoms that can last for months or even decades, making diagnosis and treatment difficult. Other conventional methods such as biological assays and liquid chromatography (HPLC) also allow the quantification of other types of toxins.
For the historical reconstruction of FANs over the last hundred years, scientists use the nuclear method of geochronology (Pb-210).
Another agency working along these lines is the International Atomic Energy Agency (IAEA) to develop the ability to detect and measure biotoxins in seafood. Using nuclear and isotopic techniques, researchers can accurately measure biotoxins and study how they pass from one organism to another, moving up the food chain and possibly ending up on our tables.
Radioligand binding analysis is one of the nuclear techniques used. It is based on the specific interaction between toxins and the receptor to which they bind (the drug target), where an isotope-labelled toxin competes with the toxin in the sample being analysed for a limited number of receptor binding sites, allowing the toxicity of the sample to be quantified.
