Microcystis is a widespread freshwater cyanobacterium, often called blue-green algae, found globally in lakes, ponds, and slow-moving rivers. This photosynthetic bacteria can proliferate under certain conditions, forming visible masses known as blooms that cover large water areas.
Understanding Microcystis Blooms
Microcystis is a colonial bacterium with cells containing gas vesicles for buoyancy regulation. These cells aggregate into colonies that can appear spherical or irregularly shaped. During a bloom, Microcystis creates a thick, unsightly scum on the water surface, often described as having a pea-soup or paint-like consistency and a green or blue-green color.
The rapid growth of Microcystis blooms is linked to specific environmental factors. Nutrient pollution, particularly high levels of nitrogen and phosphorus from agricultural runoff and wastewater, fuels their proliferation. Warm water temperatures, generally exceeding 15°C, also promote Microcystis growth, with optimal bloom formation around 25°C. Stagnant or slow-moving water bodies further contribute by allowing cyanobacteria to accumulate at the surface and outcompete other organisms for light.
The Dangers of Microcystins
The primary danger of Microcystis blooms comes from potent toxins called microcystins. These are hepatotoxins, meaning they primarily affect the liver. Over 250 forms exist, with microcystin-LR being the most common and one of the most studied due to its toxicity.
These toxins are contained within Microcystis cells and released into the water when cells die or are damaged. Cell death can be triggered by environmental changes or management strategies like algaecide application. Microcystins are remarkably stable in water, resisting degradation from chemical breakdown, boiling, and microwave treatments, contributing to their prolonged presence and risk in affected water bodies. These toxins can then enter the food chain, accumulating in aquatic invertebrates, mussels, fish, and other animals consuming contaminated water or organisms.
Health Impacts on Humans and Animals
Exposure to Microcystis toxins affects both humans and animals. For humans, direct skin contact with bloom-affected water can cause rashes, irritation, and blisters. Ingesting contaminated water may result in gastrointestinal issues like nausea, vomiting, diarrhea, and abdominal pain. Inhaling aerosols from contaminated water can cause respiratory irritation, sore throat, dry cough, and sometimes pneumonia.
More severe human impacts from higher or prolonged exposure include liver damage, manifesting as hepatitis, cirrhosis, and potentially liver cancer. While human fatalities from microcystin ingestion are rare, long-term exposure to low doses is a concern. Vulnerable populations include those consuming contaminated drinking water, engaging in recreational activities, or eating contaminated food.
Animals, especially pets and livestock, are susceptible to microcystin poisoning due to drinking large quantities of contaminated water. This can lead to severe illness or death, primarily from liver failure. Symptoms in animals include diarrhea, vomiting, weakness, and collapse. Wildlife is also at risk, with fatalities of birds, fish, and other animals linked to microcystin exposure.
Detecting and Managing Microcystis
Detecting Microcystis blooms often begins with visual identification, as discolored water or surface scums indicate their presence. However, visual cues alone are not sufficient to confirm toxins. Laboratory testing provides confirmation through microscopy for cell counts and chemical tests like ELISA or LC-MS to quantify toxin levels. Public advisories and warning signs then alert people to potential dangers.
Preventing Microcystis blooms involves reducing nutrient influx into water bodies. This includes better agricultural practices to minimize fertilizer runoff and upgrading wastewater treatment facilities to reduce phosphorus and nitrogen discharges. Promoting healthy aquatic ecosystems and maintaining riparian buffers also help absorb excess nutrients.
Management strategies for existing blooms focus on avoiding contact with contaminated water and public education. Advanced water treatment processes are necessary for drinking water supplies to remove microcystins. While physical removal or algaecides can be considered, caution is required with algaecides. They can cause Microcystis cells to rupture and release stored toxins, potentially increasing immediate risk.