Toxicity to aquatic life
How does the aquatic ecosystem react on pollutants?
The harmful effects that chemicals have upon individual organisms depend on many different factors. Not only the difference between the freshwater species, but also the form in which pollutants occur, and if the pollutant shows up in lentic or lotic systems. To measure the toxicity there has to get done some toxicity tests. Then there is clarity what the dose is of a chemical that a type of specie will die, which will be expressed in a LC50 or LD50.
The effects of pollution on freshwater species are registered in the loss of some species, with maybe some profits for some of them. There normally is a reduction in diversity but not necessarily numbers of individual species, and a change in the balance of such processes as predation, competition and materials cycling. Because of the complexity of pollution, the effects of take-up in the aquatic life are also depended on the pollutants characteristic feature. If two or more poisons are present together in an effluent they may exert a combined effect to an organism, which can be additive, antagonistic or synergistic.