Eutrophication in histopathology
Eutrophication is the term used to define the process by which some habitats such as lakes, reservoirs, streams or bays become overloaded with nutrient-rich water.
This process can occur in both freshwater and saltwater habitats. When this occurs, large blooms of algae and aquatic plants grow as a result of an excess of nitrogen and phosphorus. Excess phosphorus often causes eutrophication in freshwater, whereas nitrogen is responsible for this phenomenon in saltwater. The sources of these excess nutrients in these habitats include agricultural runoff, overuse of synthetic fertilisers, and sewage leaks, among others. Additionally, certain climatic conditions such as high temperatures and low rain may also promote eutrophication.
In histopathology laboratories, tap water is utilised for different purposes, such as tissue flotation baths, tissue processors, and certain staining techniques, such as staining with haematoxylin and eosin, Masson’s trichrome, Oil-red O, and Gomori methenamine-silver. However, tap water may be contaminated by freshwater algae and other microorganisms, owing to the eutrophication of the habitats that provide freshwater to the population.
In fact, algal contamination by a member of the Staurastrum genus of the Chlorophyta (a green alga) on histological sections stained with the periodic acid–Schiff reagent and the Grocott silver method has been reported, the most probable source being the main water supply common to both cytopathology and histopathology laboratories.
Herein, we report our experience with this form of contamination, and describe some examples of histological slides that were contaminated by freshwater algae because of their presence in the tap water used in the laboratory.
Figure 1A shows the presence, in a kidney histological section, of a filamentous structure formed by a single row of several rectangular/cuboidal blue cells (Σ7 μm in width) arranged end to end. On the basis of the morphology, this structure was catalogued as a member of the Cyanobacteria (blue-green fresh algae), belonging to the genus Oscillatoria, family Oscillatoraceae, class Chroobacteria.
Figure 1B shows the presence, in a skeletal muscle histological section, of a non-branched filamentous structure of a blackish hue formed by a chain of cylindrical barrel-shaped cells (4～6μm in length) with a gelatinous sheath of reddish hue. On the basis of the morphology, this structure was catalogued as a member of the Cyanobacteria, belonging to the genus Anabaena, order Nostocales, class Homogoneae.
Figure 1C shows the presence, in a uterine cervix histological section, of a non-branched elongated structure with thick walls, formed by numerous cuboidal cells (7～12μm in width). Each cell possesses one chloroplast located at the margin. Slight narrowings along the side walls can also be observed. On the basis of the morphology, this structure was catalogued as a green fresh alga, belonging to the genus Ulothrix, class Ulvophyceae, division Chlorophyta.
Figure 1D shows the presence, in a brain histological section, of six non-branched filamentous structures, slightly twisted, of a darkish hue, each formed by a row of cuboidal cells (0.8～2μm in length) with clear cytoplasm and with narrow intercellular spaces. The cells are surrounded by a thin gelatinous sheath. On the basis of the morphology, this structure was catalogued as a member of the Cyanobacteria, belonging to the genus Phormidium, family Oscillatoraceae, class Cyanophyceae.
Similarly, in cytological smears, the presence of diverse types of freshwater algae as contaminants has been reported, the cause also being contamination of tap water.
Eutrophication is one of the causes of the deterioration of water quality. Thus, the contamination of reservoirs by freshwater algae might explain the presence of these microorganisms in the tap water used not only in laboratories, but also in hospitals as drinking water. Consequently, the significance of this finding is two-fold.
Some species of freshwater algae (mainly members of the Cyanobacteria) can produce powerful toxins, such as neurotoxic alkaloids (anatoxins), peptide hepatotoxins (microcystins), and cytotoxic alkaloids (cylindrospermopsins), which present a risk to human health. On the other hand, and because of their morphology, freshwater algae such as those described in this article may be misidentified as filamentous fungi or larvae of certain parasitic worms (e.g. filarial and rhabditiform nematodes).
As is the case with other types of contaminant (‘floaters’), that may arise during tissue processing and slide preparation and be a potential cause of misdiagnosis in surgical pathology, we think that the presence of freshwater algae in histopathological slides because of eutrophication and their consequent presence in laboratory tap water, should also be of concern to, and recognised by, cellular pathologists.
 Eutrophication in histopathology.Histopathology,2019,75,137-138.