7.6.4 Biological Toxins

Algae Blooms

An algae bloom is a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. Typically only one or a few species are involved and the bloom is recognized by discoloration of the water resulting from the high density of pigmented cells. Although there is no officially recognized threshold level, algae are unlikely to be considered to be blooming unless more than 10,000 cells per milliliter occur. Algal bloom concentrations may reach millions of cells per milliliter. Colors observed are green, yellowish-brown, or red.

The excessive growth of algae may disrupt higher links of the local food web. Algae that die and sink to the bottom stimulate growth of decomposers, especially bacteria. Decomposition can result in the depletion of oxygen in the deeper water layers, and these conditions may result in fish kills or replacement with less valuable species more tolerant of higher phosphorus and lower oxygen levels. Deoxygenating also may cause chemical changes in the mud on the bottom, lowering the redox value of the sediment, releasing chemicals and toxic gases. All these changes further accelerate the eutrophication of the aquatic ecosystem.

Algal blooms may also be of concern as some species of algae produce neurotoxins. At the high concentrations reached during blooms, these may cause death if affected water is ingested.

Algal blooms are monitored using biomass measurements coupled with the examination of species present. A widely-used measure of algal and cyanobacterial biomass is the chlorophyll concentration. Peak values of chlorophyll a for an oligotrophic lake are about 1-10 µg/l, while in a eutrophic lake they can reach 300 µg/l. In cases of hypereutrophy, maxima of chlorophyll a can be as high as 3,000 µg/l.

Fecal Coliform Bacteria

Escherichia coli (usually abbreviated to E. coli ) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. Its presence in groundwater is a common indicator of fecal contamination. ("Enteric" is the adjective that describes organisms that live in the intestines. "Fecal" is the adjective for organisms that live in feces, so it is often a synonym for "enteric.") The name comes from its discoverer, Theodor Escherich. It belongs among the Enterobacteriaceae, and is commonly used as a model organism for bacteria in general.

The number of individual E. coli bacteria in the feces that one human passes in one day averages between 100 billion and 10 trillion. All the different kinds of fecal coli bacteria and all the very similar bacteria that live in the ground (in soil or decaying plants, of which the most common is Enterobacter aerogenes ) are grouped together under the name "coliform" (meaning "like coli ") bacteria. Technically, the "coliform group" is defined to be all the aerobic and facultative anaerobic, non-spore-forming, Gram-negative, rod-shaped bacteria that ferment lactose with the production of gas within 48 hours at 35°C (in the body, this gas is released as flatulence).

In the fields of water purification and sewage treatment, E. coli was chosen very early in the development of the technology as an "indicator" of the pollution level of water, meaning the amount of human fecal matter in it, measured using the Coliform Index. The main reasons for using E. coli are that there are a lot more coliforms in human feces than there are pathogens (such as Salmonella typhi , which causes typhoid), and E. coli is usually harmless, so it can't "get loose" in the lab and hurt anyone. It can be misleading to use E. coli as an indicator of human fecal contamination because there are other environments in which E. coli grows well, such as paper mills.

There are, however, three situations where the otherwise harmless E. coli can cause illness:

1. When the bacteria get out of the intestinal tract and into the urinary tract, they can cause an infection sometimes referred to as "honeymoon cystitis" because intercourse can lead to introduction of bacteria into the bladder. Although it is more common in females, urinary tract infection is seen in both males and females. It is found in roughly equal proportions in elderly men and women. Since bacteria invariably enter the urinary tract through the urethra, poor toilet hygiene can predispose to infection but other factors are also important (pregnancy in women, prostate enlargement in men) and in many cases the initiating event is unclear.
2. When the bacteria get out of the intestinal tract through a perforation (a hole or tear, which could be caused by an ulcer, for example) and into the abdomen, they usually cause an infection called "peritonitis" that can be fatal. However, E. coli are extremely sensitive to antibiotics such as streptomycin or gentamycin, so treatment with antibiotics is usually effective.
3. Certain strains of E.coli are toxigenic (some produce a toxin very similar to that seen in dysentery) and can cause food-poisoning usually associated with eating contaminated meat (contaminated during or shortly after slaughter or during storage or display). Severity of the illness varies considerably; it can be fatal, particularly to young children, the elderly or the immune compromised, but is more often mild. E. coli can harbor both heat-stable and heat-labile enterotoxins. The latter, termed LT, is highly similar in structure and function to Cholera toxin. It contains one 'A' subunit and five 'B' subunits arranged into one holotoxin. The B subunits assist in adherence and entry of the toxin into host intestinal cells, where the A subunit is cleaved and stimulates the cells to release water, causing diarrhea.

Fecal coliform lives for 24 hours. And its presence in concentrations of over 200 colonies per 100 milliliters is considered recreationally impaired. It can indicate a pollution source most likely a faulty septic system or animal feed lot. Generally fecal coliform is not a pollution risk because of its short life and it usually does not directly enter a water source. Fecal coliform is monitored for every sampling site around Pelican Lake.

Next page: Chapter 7.7 Trophic State Index