Toxicity
English (en) svenska (sv)
If a substance is toxic (toxicity) is determined by tests for various organisms. The most expensive but best method is to use fish as "guinea pigs". In other methods one can use water fleas or algae. Normally one investigates at what concentration of the substance half of the organisms die at. The trial period can be 48 hours.
One way to test a substance's toxicity with fish can be formulated as follows: One takes x number of zebra fish, adding a certain amount of test substance to a concentration of 100 mg / liter. If more than 50 percent of the fish died within 48 hours, the LC50 for Zebrafish is less than 100 mg / liter. The next attempt is to repeat the test at a concentration of the substance of 10 mg / l. If less than 50 percent of the fish dies the LC50 value is between 10 to 100mg / liter. If wastewater from an industrial discharge is put into municipal sewage treatment plants, it may be advisable to check the toxicity against the plant's biological treatments. An absolute requirement for the dump wastewater that flows to a treatment plant is that the discharge does not affect the bacteria present in the biological treatment stage or in nitrogen removal processes. If the discharge affects the bacteria at the plant, it means that industrial emissions could reduce the plant's capacity. This may mean that even other "good" wastewater can’t be treated and purified. This toxicity data is thus very important to know. In Sweden, virtually all the textile wastewater is led (make link) to municipal treatment plants, where an effective high-grade purification takes place.
