Ecotoxicological biotests

Unicellular algae and cyanobacteria

Algae and cyanobacteria, as the representatives of primary producers in aquatic ecosystems, play a significant role in ecotoxicogical testing. The principle of the test is to determine a growth inhibition of experimental microorganisms exposed to the substance tested. Experimental organisms are exposed/incubated for 72 or 96 hours in liquid growth media under specific defined conditions. Growth inhibition is measured as a change in optical density and/or chlorophyll fluorescence compared to the control culture under the same conditions. Cyanobacterium Synechococcus elongatus and green algae Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum or Raphidocellis subcapitata) and Desmodesmus subspicatus (Scenedesmus subspicatus) represent the species the most commonly used in ecotoxicity testing.

• OECD 201/1984, ISO 8692:1989 Water quality - Fresh water algal growth inhibition test with Scenedesmus subspicatus and Selenastrum capricornutum

Common duckweed (Lemna minor)

Biotest using duckweed (Lemna minor) is designed for testing the ecotoxicity of substances dissolved in water or in extract (ISO and OECD standards) and after modification it can be used for assessing the toxicity of sediments and soils as well. The purpose of this assay is determination of sample toxicity on duckweed growth. We determine growth inhibition by selected parameters such as the number of bracts, bract area, fresh and dry weight and chlorophyll amount. Test duration is 168 hours (7 days).

• ISO 20079, (2001): Water quality - Determination of the toxic effect of water constituents and waste water to duckweed Lemna minor - Duckweed growth inhibition test.
• OECD 221 (2002): Lemna sp. Growth inhibition test, guideline for testing chemicals. International Standard

White mustard (Sinapis alba) - germination and root growth test in higher plants

This test is designed to determine the effect of test substances on the germination and root growth of White mustard, but using other species of plants such as Garden cress (Lepidium sativum) or lettuce (Lactuca sativa) is also possible. The principle of the test is the cultivation of seeds on filter paper saturated with different concentrations of tested substance in comparison with seeds growing on a substrate saturated with dilution water. After 72 hours, a length of the root of each plant is measured, and a dry weight is determined.

• OECD 208/1984 Terrestrial plants, growth test

Water flea (Daphnia magna) - Immobilization and reproduction test

Water fleas are an important part of the aquatic environment. They occupy a central position in the freshwater food chain. They represent a preferred prey for predators (vertebrates and invertebrates) but they are also considered as the efficient consumers of planktonic algae. Their presence or absence in water bodies can have a significant impact on entire ecosystem. The acute toxicity test is designed to determine the immobilization of Daphnia in various concentrations of the tested substance after 24 or 48 hours of exposure. For this type of test daphnids younger than 24 hours should be used, since they have the highest sensitivity to toxic substances. The chronic toxicity test determines the effect of tested compounds on the daphnids life cycle and development. Daphnids younger than 24 hours are exposed to chemicals for 21 days. Surviving of parent organisms and number of offspring is recorded and compared with the control organisms.

• OECD 202/1984 Daphnia sp. acute immobilisation test and reproduction test
• ISO 6341:1996 Water quality - Determination of the inhibition of the mobility of Daphnia magna - Acute toxicity test

Toxicity testing in heterotrophic bacteria Escherichia coli and Bacillus subtilis

Representatives of Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis) bacteria are exposed to a dilution series of the tested substance and, after 24 hours, counts and the physiological state of the cells are determined by flow cytometry.

Other organisms

We are also able to perform other ecotoxicological bioassays using the so-called toxkits, commercially available sets containing all necessary materials, chemicals as well as experimental (micro)organisms.

• Ostracodtoxkit F - chronic direct contact freshwater sediment toxicity test with ostracod crustacean Heterocypris incongruens.
• Thamnotoxkit - a test organism, crustacean Thamnocephalus platyurus hatched from the resting stages (cysts) is used for acute toxicity testing of waters.
• Protoxkit F - Protoxkit is the 24h multigenerational chronic bioassay with the freshwater protozoan Tetrahymena thermophila, which is an important member of the benthic microfauna.
• Rotoxkit F - Rotoxkit is a two-day chronic test with freshwater rotifer Brachionus calyciflorus. Mortality and growth inhibition (compared to non-exposed control) is determined.