(2) An increase in dissolved solids — especially 

 nutrient materials such as nitrogen, phos- 

 phorus, and simple carbohydrates. 



(3) An increase in suspended solids — espe- 

 cially organic materials. 



(4) A shift from a diatom-dominated plankton 

 population to one dominated by blue-green 

 and/or green algae, associated with in- 

 creases in amounts and changes in relative 

 abundance of nutrients. 



(5) A steady though slow decrease in light 

 penetration. 



(6) An increase in organic materials and nu- 

 trients, especially phosphorus, in bottom 

 deposits. 



Recommendation: The Subcommittee wishes to stress 

 that the concentrations set forth are suggested solely as 

 guidelines and the maintenance of these may or may 

 not prevent undesirable blooms. All the factors causing 

 nuisance plant growths and the level of each which 

 should not be exceeded are not known. 



( 1 ) In order to limit nuisance growths, the addition 

 of all organic wastes such as sewage, food processing, 

 cannery, and industrial wastes containing nutrients, 

 vitamins, trace elements, and growth stimulants should 

 be carefully controlled. Furthermore, it should be 

 pointed out that the addition of sulfates or manganese 

 oxide to a lake should be limited if iron is present in 

 the hypolimnion as they may increase the quantity of 

 available phosphorus. 



(2) Nothing should be added that causes an in- 

 creased zone of anaerobic decomposition of a lake or 

 reservoir. 



(3) The naturally occurring ratios and amounts of 

 nitrogen (particularly NOn and NHi) to total phos- 

 phorus should not be radically changed by the addition 

 of materials. As a guideline, the concentration of total 

 phosphorus should not be increased to levels exceeding 

 100 Mg/1 in flowing streams or 50 |Ug/l where streams 

 enter lakes or reservoirs. 



(4) Because of our present limited knowledge of 

 conditions promoting nuisance growth, we must have a 

 biological monitoring program to determine the effec- 

 tiveness of the control measure put into operation. A 

 monitoring program can detect in their early stages the 

 development of undesirable changes in amounts and 

 kinds of rooted aquatics and the condition of algal 

 growths. With periodic monitoring such undesirable 

 trends can be detected and corrected by more stringent 

 regulation of added organics. 



Toxic substances 



Aquatic life too frequently is considered only 

 in terms of harvestable species. The fact that nu- 

 merous other organisms are essential to produce 

 a crop of fishes often is overlooked or given litde 

 attention. To produce a harvestable crop of fish, 

 it is essential to have supporting plants and ani- 

 mals for food. Requirements are established on 



the basis that the needed criteria are those that 

 will protect fish, the harvested crop, and the food 

 organisms necessary to support that crop. At this 

 time, it is believed that every important species 

 should be protected. One can appreciate that un- 

 important organisms may be sacrificed if the 

 following criteria are adopted. Fish too often 

 are considered as a single species instead of a 

 multitude of species. Many are distinctly and 

 greatly different from other related species and 

 have their own distinctive requirements. Because 

 of this, and because the important species, essen- 

 tial food organisms, and water quality will be 

 different in different habitats, a single value or 

 concentration has very limited applicability unless 

 appropriate margins of safety are incorporated. 



For these reasons, the bioassay approach de- 

 scribed later in this section is favored. It is believed 

 that bioassays are the best method for determining 

 safe concentrations of toxicants for the species 

 of local importance. Bioassays are essential also 

 to determine safe concentrations for food orga- 

 nisms of those species and the effect of existing 

 water quality, including environmental variables 

 as well as existing pollution. Pertinent to this 

 stance is the fact that the majority of specific pol- 

 lution problems are ones involving discharges of 

 unknown and variable composition. Almost with- 

 out exception, more than one toxicant or stress is 

 present. Further, suggested safe concentrations 

 probably will not be adequate in instances where 

 more than one adverse factor exists. It is believed 

 that these recommended levels will be adequate 

 for a particular pollutant if dissolved oxygen, 

 temperature, and pH are within the limits recom- 

 mended. If the latter parameters are outside 

 recommended limits, appropriate alterations in the 

 criteria for toxicants must be made. 



Most of the available toxicity data are reported 

 as the median tolerance limit (TLm), the concen- 

 tration that kills 50 percent of the test organisms 

 within a specified time span, usually in 96 hours 

 or less. This system of reporting has been mis- 

 applied by some who have erroneously inferred 

 that a TLm value is a safe value, whereas it is 

 merely the level at which half the test organisms 

 are killed. In many cases, the differences are great 

 between TL,,, concentrations and concentrations 

 that are low enough to permit reproduction and 

 growth. 



Substantial data on long-term effects and safe 

 levels are available for only a few toxicants, per- 

 haps 10. The effect of toxicants on reproduction 

 is nearly unknown, yet this is a very important 

 aspect of all long-term toxicity tests. In chronic 

 tests with six different toxicants, there were three 



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