An early life stage (ELS) test is a chronic toxicity test using sensitive early life stages like embryos or larvae to predict the effects of toxicants on organisms.McKim JM. 1985. Early life stage toxicity tests. In Rand GM (1995). Fundamentals of Aquatic Toxicology: Effects, Environmental Fate, and Risk Assessment (2nd ed.). Boca Raton: CRC Press. pp 974–1010. . ELS tests were developed to be quicker and more cost-efficient than full life-cycle tests, taking on average 1–5 months to complete compared to 6–12 months for a life-cycle test. They are commonly used in

aquatic toxicology Aquatic toxicology is the study of the effects of manufactured chemicals and other anthropogenic and natural materials and activities on aquatic organisms at various levels of organization, from subcellular through individual organisms to commu ...

, particularly with fish. Growth and survival are the typically measured endpoints, for which a

Maximum Acceptable Toxicant Concentration The maximum acceptable toxicant concentration (MATC) is a value that is calculated through aquatic toxicity tests to help set water quality regulations for the protection of aquatic life. Using the results of a partial life-cycle chronic toxicity ...

(MATC) can be estimated. ELS tests allow for the testing of fish species that otherwise could not be studied due to length of life, spawning requirements, or size. ELS tests are used as part of environmental risk assessments by regulatory agencies including the

U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

(EPA) and

Environment Canada Environment and Climate Change Canada (ECCC; )Environment and Climate Change Canada is the applied title under the Federal Identity Program; the legal title is Department of the Environment (). is the Ministry (government department), department ...

, as well as the

Organisation for Economic Co-operation and Development The Organisation for Economic Co-operation and Development (OECD; , OCDE) is an international organization, intergovernmental organization with 38 member countries, founded in 1961 to stimulate economic progress and international trade, wor ...

(OECD).Technical Overview of Ecological Risk Assessment Analysis Phase: Ecological Effects Characterization.
US EPA.Organisation for Economic Co-operation and Development. 1992. Guideline 210: Fish early-life stage toxicity test. ''OECD Guidelines for the Testing of Chemicals''. Paris, France.

Development

ELS tests were adapted from full life-cycle toxicity tests, chronic tests that expose an organism to a contaminant for its entire life-cycle. These are widely considered to be the best tests for estimating long-term "safe" concentrations of toxicants in aquatic organisms. The first full life-cycle tests on fish were developed for the

fathead minnow Fathead minnow (''Pimephales promelas''), also known as fathead or tuffy, is a species of freshwater Actinopterygii, ray-finned fish belonging to the Family (biology), family Leuciscidae, the shiners, daces and minnows. The natural geographic ra ...

(''Pimephales promelas''),Mount DI, Stephan CE. 1967. A method for establishing acceptable limits for fish-Malathion and the butoxyethanol ester of 2,4-D. ''Trans Am Fish Soc'' 96:185-193. and later for

bluegill The bluegill (''Lepomis macrochirus''), sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose", is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and wetlands ea ...

(''Lepomis macrochirus''),

brook trout The brook trout (''Salvelinus fontinalis'') is a species of freshwater fish in the char genus ''Salvelinus'' of the salmon family Salmonidae native to Eastern North America in the United States and Canada. Two ecological forms of brook trout h ...

(''Salvelinus fontinalis''),

flagfish The flagfish (''Jordanella floridae''), also known as the American flagfish or Florida flagfish, is a species of pupfish, a type of killifish from the family Cyprinodontidae which is endemic to Florida. It is found in the aquarium trade. Its ...

(''Jordanella floridae''), and

sheepshead minnow The sheepshead minnow (''Cyprinodon variegatus''), also known as sheepshead pupfish, is a species of ray-finned fish in the family Cyprinodontidae, the pupfishes. It is found in salt marsh and estuary environments and is native to the eastern co ...

(''Cyprinodon variegatus''). While useful, full life-cycle tests require a high number of test organisms and extensive exposure time in the lab, especially for vertebrates. Typically, life-cycle tests take 6–12 months for

and 30 months for

. Following the passage of the

Toxic Substances Control Act The Toxic Substances Control Act (TSCA) is a United States law, passed by the Congress in 1976 and administered by the United States Environmental Protection Agency (EPA), that regulates chemicals not regulated by other U.S. federal statutes, ...

(TSCA) in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

in 1976, there was an increased need for quicker, more efficient vertebrate toxicity tests. The EPA was now required to assess the environmental effects of new chemicals before they could be commercially produced. Less costly and time-intensive tests were needed to evaluate a multitude of new chemicals. Researchers began developing toxicity tests that focused on early life stages, since these have been shown to be more sensitive to environmental stressors than later life stages. Many critical events occur in a short period of time in the early stages of development.McKim JM. 1977. Evaluation of tests with early life stages of fish for predicting long-term toxicity. ''J Fish Res Board Can'' 34:1148–1154. If a stressor disrupts developmental events (including their timing), it could result in adverse effects that reduce the organism's chances of survival. Meta-analysis has found that early life-cycle portions of full life-cycle tests usually estimate an MATC within a factor of 2 of full life-cycle estimates in saltwater and freshwater fish. In 83% of 72 tests, the ELS portion resulted in the same MATC as the full life-cycle estimate, and the remaining 17% were within a factor of 2.

Limitations

There remain some limitations with early life stage toxicity testing. Although ELS tests are quicker and more cost-efficient than full life cycle tests, they remain resource- and time-intensive. Fish early life stage (FELS) tests require hundreds of fish and 1 to 5 months to complete.Villeneuve D, Volz DC, Embry MR, Ankley GT, Belanger SE, Léonard M, Schirmer K, Tanguay R, Truong L, Wehmas L. 2014. Investigating alternatives to the fish early-life stage test: a strategy for discovering and annotating adverse outcome pathways for early fish development. ''Environ Toxicol Chem'' 33:158-69. Other issues include the lack of mechanistic information, differing sensitivities between species, and insensitivity to parental exposure. ELS tests don't provide information on the toxicant's

mechanism of action In pharmacology, the term mechanism of action (MOA) refers to the specific biochemical Drug interaction, interaction through which a Medication, drug substance produces its pharmacological effect. A mechanism of action usually includes mention o ...

. Sensitivity to specific toxicants varies with species, so the most sensitive or most important species should be tested in each case. ELS tests appear to be insensitive to parental exposure, and MATCs are generally the same for embryos of both exposed and unexposed parents. This could be due to the

mode of action In pharmacology and biochemistry, mode of action (MoA) describes a functional or anatomical change, resulting from the exposure of a living organism to a substance. In comparison, a mechanism of action (MOA) describes such changes at the molecul ...

of the toxicant or the variability and insensitivity of ELS test design. Additionally, growth response has been found to be an insensitive endpoint in ELS tests with fish, having little bearing on the estimation of an MATC. Growth response could be omitted to reduce the duration and cost of screening tests.

Methodology

In a typical early life stage toxicity test, a flow-through dilutor system administers different concentrations of a toxicant to different test chambers. At least five different concentrations of a toxicant are tested, plus controls, with at least two exposure chambers for each treatment. The length of the exposure depends on the test species. For example,

tests are 1–2 months long, while

tests are around 5 months long. Growth and survival are the typical endpoints, for which an MATC can be found. Standard methods for ELS tests have been established by the

OECD The Organisation for Economic Co-operation and Development (OECD; , OCDE) is an international organization, intergovernmental organization with 38 member countries, founded in 1961 to stimulate economic progress and international trade, wor ...

ASTM International ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

, the EPA, and

Regulatory uses

* The FELS guideline of the

OECD Guidelines for the Testing of Chemicals OECD Guidelines for the Testing of Chemicals (OECD TG) are a set of internationally accepted specifications for the testing of chemicals decided on by the Organisation for Economic Co-operation and Development (OECD). They were first published in ...

is the primary test used internationally to estimate chronic fish toxicity. * FELS tests are part of a suite of sublethal toxicity tests for effluent used by

in environmental effects monitoring. * A FELS test is required or recommended by the

US EPA The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

for testing and monitoring chemicals released into aquatic systems.

Current developments

An extended ELS test has been examined as a potential surrogate for a fish full life-cycle test to detect weak environmental estrogens.Panter GH, Hutchinson TH, Hurd KS, Bamforth J, Stanley RD, Duffell S, Hargreaves A, Gimeno S, Tyler CR. 2006. Development of chronic tests for endocrine active chemicals: Part 1. An extended fish early-life stage test for oestrogenic active chemicals in the fathead minnow (''Pimephales promelas'') ''Aquat Toxicol'' 77:279-290. Endocrine active chemicals (EACs) are ubiquitous in the environment, prompting the need for better screening assays to predict their effects, especially in aquatic species. Slightly longer ELS tests could be used instead of full life-cycle tests, taking into account sensitive windows of exposure like sexual differentiation and early gonadal development. Extended ELS tests have proven successful in detecting the effects of weak estrogens in

s. Additionally, adverse outcome pathways (AOPs) are being used to develop an alternative to FELS testing. Industry and regulatory agencies are increasingly interested in an animal-free, cost-efficient surrogate.Knapen D, Vergauwen L, Verstraelen S, Dardenne F, Witters H, Blust R, Villeneuve DL, Ankley GT. 2013. Development of an alternative testing strategy for the fish early life-stage for predicting chronic toxicity." ''Toxicology Letters'' 221: S104. Researchers are developing FELS-related AOPs to create a high-throughput, less costly screening strategy for toxicants that takes the

into account.

References

{{reflist Environmental toxicology Toxicology tests