Microtox bioassay

[2] When exposed to a toxic substance, the respiratory process of the bacteria is disrupted, reducing light output.

[2] Microtox was developed by Azur Environmental (formerly Microbics Corporation) in 1979 as a cost-effective alternative to toxicity tests available at the time.

[3][4] Prior to Microtox, the majority of toxicity tests available for water specifically focused on fish and daphnids.

[3][4] Since its inception, Microtox has become a standard method for testing the toxicity of water as well as other substrates such as soils and sediments.

In 2011, Microtox and related technologies was acquired by Modern Water from Strategic Diagnostics Incorporated (SDIX) for approximately $4.5 million.

[3] Microtox utilizes a bioluminescent bacteria (Allivibrio fischeri) to determine the toxicity of a particular substance and/or substrate.

[3] Both solid phase (soils and sediment) and aqueous acute toxicity testing (described below) can be conducted using this technology.

[9] The DeltaTox II is a portable instrument that can be used to conduct acute toxicity and adenosine triphosphate (ATP) testing.

[11] Microtox Acute Reagent is a freeze-dried culture of Allivibrio fischeri that is reconstituted prior to testing.

This solution is used for diluting the sample and the reagent, and also provides osmotic protection that is required by Allivibrio fischeri.

[11][12] Microtox can be applied to a variety of matrices including drinking water, stormwater runoff, effluent, industrial discharges, soils and sediments.

[3] Particulate matter in the sample can interfere with bioluminescence by absorbing light and give misleading test results.

The samples can be de-chlorinated using a sodium thiosulphate and deionized water solution that does not affect test results.

For example, smaller particles such as clay tend to tightly bind to chemicals, acting like ion exchange resins.

[12][13] Microtox tests for sediment and soil differ in the way the matrix is prepared for contact with Allivibrio fischeri.

Corrections are made for salinity and particulate matter, then the bacteria are exposed to the sample solution depending on the methods of the particular test.

[12] The light measured directly correlates to the toxicity of the sample, producing data that allows for the calculation of EC50 or IC50s, or other ECxx and ICxx values.

[15] This test is used for samples that are expected to have a low level of toxicity and is generally used as an environmental screening tool.

Common applications are for testing the toxicity of both marine and freshwater, as well as sediments for pesticides and other inorganic and organic chemicals.

Microtox data may be used to establish apparent effects threshold (AET), sediment quality standards and used for NPDES permits, as well as Superfund cleanup levels.

Microtox can also be applied as an early warning system (EWS) and aid in detecting the presence of toxic materials, as well as predict the outcomes of other bioassays and tests.

[citation needed] Numerous studies and published data comparing Microtox results with toxicity values for fish, crustaceans and algae have found a positive correlation.