46 THE ROLE OF ALGAE AND PLANKTON IN MEDICINE 



sal. Odors and tastes may arise from the oils of living algae; from prod- 

 ucts of active photosynthesis; from products of decomposition; and from 

 the death of fish and other aquatic organisms. The oils of living algae 

 are often unpleasantly odorous, each oil being characteristic of the gene- 

 rative organism. The smells may be fishy, aromatic, or grassy. Their 

 disagreeable character may be heightened after planktonic death, when 

 the frail oil globules are more widely dispersed. The odorous photo- 

 synthetic substances liberated during very rapid growth are ill-defined, 

 but the offending materials present after algal decomposition are better 

 known. They include hydrogen sulfide and other sulfurous compounds, 

 phosphorous and nitrogenous substances, methane, ethereal sulfates, and 

 other volatile gases. Fish and other aquatic organisms may die from 

 suffocation, or from toxic substances such as hydroxylamine resulting from 

 the breakdown of algal proteins. These dead animals contribute a liberal 

 stench to the already odoriferous situation. Often enough, the chemical 

 treatments applied to kill off offending algae aggravate the situation even 

 further. The treatment, such as chlorination, kills the organism and liber- 

 ates the taste and odor-producing materials, and chemical combination 

 with chlorine may favor the formation of additional smelly compounds. 



The most troublesome algae in lakes and reservoirs are the blue-green 

 ones, which grow rapidly and float high in the water, forming surface 

 scums. Greatest growth takes place in waters which are shallow and 

 warm, and in those rich in nitrogen, phosphorus, and loosely-bound carbo- 

 hydrates. The principal causes of bad odors and tastes are the Myxophy- 

 ceae and Diatomales, which are less potent oxygenators than are other 

 algae. 



When unpleasant odors affect ordinary lakes or ponds they merely 

 detract from the beauty of nature. But when they occur in reservoirs of 

 water intended for daily drinking, they present a trenchant problem. Even 

 mild alterations in smell or taste may be psychologically unacceptable to 

 the average person. As Howard and Berry 238 have pointed out, odors 

 caused directly or indirectly by living plankton or by the decomposition 

 of vegetable growths are immediately ascribed by the layman to con- 

 tamination with sewage. This is not too strange, since the decomposing 

 plankton floats on the water, then is thrown onto the shore, where it forms 

 odorous, blackish, discolored masses. It is difficult to convince people that 

 the odor itself signifies no health hazard. When living algae are present 

 in the drinking water, there may be a mild initial taste, but a bitter after- 

 taste ; when the organisms are dead, there is a strong first taste, but practi- 



