Raman spectroscopy based detection and classification of algal blooms: A microchemical approach for environmental management

Eutrophication refers to a process in which aquatic ecosystems, including lakes, estuaries, or slow-moving streams, become inundated with surplus nutrients that promote rampant plant growth, such as algae, periphyton, and invasive aquatic weeds. The rise in plant growth, commonly referred to as an Algal Bloom, leads to a decline in dissolved oxygen levels, diminished light penetration, and the death of benthic phytoplankton in the aquatic environment. The breakdown of deceased plant material can then lead to the death of additional organisms. The term “bloom” refers to the swift proliferation and build-up of microalgal or cyanobacterial species, which can be recognized by the alteration in the colour of water surfaces. This discoloration can manifest in various hues, including the commonly recognized red (often called red tide), as well as different shades of brown, green, yellow, blue, or purple. Harmful Algal Blooms (HABs) generate toxins that pose threat to humans, animals, and aquatic ecosystems, although some blooms are benign. These events predominantly occur in the summer months within both marine and freshwater settings, resulting from a variety of factors that encourage algal proliferation, including increased water temperatures, greater sunlight exposure, and nutrient availability, which present dangers to humans, wildlife, and aquatic ecosystems. Consequently, it is crucial to conduct prompt in situ evaluations of algal blooms and their toxins, without the need for intricate sample preparation, to gauge the potential threats and facilitate timely interventions. Raman Spectroscopy, along with its advanced variants including surface-enhanced Raman Spectroscopy, tip-enhanced Raman Spectroscopy, coherent anti-Stokes Raman Spectroscopy, and stimulated Raman Scattering Microscopy, provides a rapid, sensitive, and non-invasive tool for the identification of algal bloom species and their toxins, thereby offering a more adaptable solution for environmental monitoring. This review highlights the progress made in analytical techniques and explores the dual characteristics of algal blooms, which serve as both ecological phenomena and contributors to the transport and prevalence of microplastics pollution. A comprehensive investigation is crucial to evaluate the adverse effects of microplastics on microalgal diversity and aquatic ecosystems, employing sophisticated methodologies in conjunction with Raman spectroscopy.