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 communities and ecosystems.[1] Aquatic toxicology is a multidisciplinary field which integrates toxicology, aquatic ecology and aquatic chemistry.[1]

This field of study includes freshwater, marine water and sediment environments. Common tests include standardized acute and chronic toxicity tests lasting 24–96 hours (acute test) to 7 days or more (chronic tests). These tests measure endpoints such as survival, growth, reproduction, that are measured at each concentration in a gradient, along with a control test.[2] Typically using selected organisms with ecologically relevant sensitivity to toxicants and a well-established literature background. These organisms can be easily acquired or cultured in lab and are easy to handle.[3]

Sea urchin test method - water pollution - EPA
A purple sea urchin being tested for pollution using a whole effluent toxicity method.

History

While basic research in toxicology began in multiple countries in the 1800s, it was not until around the 1930s that the use of acute toxicity testing, especially on fish, was established. Over the next two decades, the effects of chemicals and wastes on non-human species became more of a public issue and the era of the pickle-jar bioassays began as efforts increased to standardize toxicity testing techniques.[1]

In the United States, the passage of the Federal Water Pollution Control Act of 1947 marked the first comprehensive legislation for the control of water pollution and was followed by the Federal Water Pollution Control Act in 1956.[4] In 1962, public and governmental interests were renewed, in large part due to the publication of Rachel Carson’s Silent Spring, and three years later the Water Quality Act of 1965 was passed, which directed states to develop water quality standards.[1] Public awareness, as well as scientific and governmental concern, continued to grow throughout the 1970s and by the end of the decade research had expanded to include hazard evaluation and risk analysis.[1] In the subsequent decades, aquatic toxicology has continued to expand and internationalize so that there is now a strong application of toxicity testing for environmental protection.

Aquatic toxicity tests

Aquatic toxicology tests (assays): toxicity tests are used to provide qualitative and quantitative data on adverse (deleterious) effects on aquatic organisms from a toxicant. Toxicity tests can be used to assess the potential for damage to an aquatic environment and provide a database that can be used to assess the risk associated within a situation for a specific toxicant. Aquatic toxicology tests can be performed in the field or in the laboratory. Field experiments generally refer to multiple species exposure and laboratory experiments generally refer to single species exposure. A dose–response relationship is most commonly used with a sigmoidal curve to quantify the toxic effects at a selected end-point or criteria for effect (i.e. death or other adverse effect to the organism). Concentration is on the x-axis and percent inhibition or response is on the y-axis.[1]

The criteria for effects, or endpoints tested for, can include lethal and sublethal effects (see Toxicological effects).[1]

There are different types of toxicity tests that can be performed on various test species. Different species differ in their susceptibility to chemicals, most likely due to differences in accessibility, metabolic rate, excretion rate, genetic factors, dietary factors, age, sex, health and stress level of the organism. Common standard test species are the fathead minnow (Pimephales promelas), daphnids (Daphnia magna, D. pulex, D. pulicaria, Ceriodaphnia dubia), midge (Chironomus tentans, C. ruparius), rainbow trout (Oncorhynchus mykiss), sheepshead minnow (Cyprinodon variegatu)[5], zebra fish (Danio rerio)[6], mysids (Mysidopsis), oyster (Crassotreas), scud (Hyalalla Azteca), grass shrimp (Palaemonetes pugio) and mussels (Mytilus galloprovincialis)[7]. As defined by ASTM, these species are routinely selected on the basis of availability, commercial, recreational, and ecological importance, past successful use, and regulatory use.[1]

A variety of acceptable standardized test methods have been published. Some of the more widely accepted agencies to publish methods are: the American Public Health Association, US Environmental Protection Agency (EPA), ASTM International, International Organization for Standardization, Environment and Climate Change Canada, and Organisation for Economic Co-operation and Development. Standardized tests offer the ability to compare results between laboratories.[1]

There are many kinds of toxicity tests widely accepted in the scientific literature and regulatory agencies. The type of test used depends on many factors: Specific regulatory agency conducting the test, resources available, physical and chemical characteristics of the environment, type of toxicant, test species available, laboratory vs. field testing, end-point selection, and time and resources available to conduct the assays are some of the most common influencing factors on test design.[1]

Exposure systems

Exposure systems are four general techniques the controls and test organisms are exposed to the dealing with treated and diluted water or the test solutions.

  • Static. A static test exposes the organism in still water. The toxicant is added to the water in order to obtain the correct concentrations to be tested. The control and test organisms are placed in the test solutions and the water is not changed for the entirety of the test.
  • Recirculation. A recirculation test exposes the organism to the toxicant in a similar manner as the static test, except that the test solutions are pumped through an apparatus (i.e. filter) to maintain water quality, but not reduce the concentration of the toxicant in the water. The water is circulated through the test chamber continuously, similar to an aerated fish tank. This type of test is expensive and it is unclear whether or not the filter or aerator has an effect on the toxicant.
  • Renewal. A renewal test also exposes the organism to the toxicant in a similar manner as the static test because it is in still water. However, in a renewal test the test solution is renewed periodically (constant intervals) by transferring the organism to a fresh test chamber with the same concentration of toxicant.
  • Flow-through. A flow-through test exposes the organism to the toxicant with a flow into the test chambers and then out of the test chambers. The once-through flow can either be intermittent or continuous. A stock solution of the correct concentrations of contaminant must be previously prepared. Metering pumps or diluters will control the flow and the volume of the test solution, and the proper proportions of water and contaminant will be mixed.[1]

Types of tests

Acute tests are short-term exposure tests (hours or days) and generally use lethality as an endpoint. In acute exposures, organisms come into contact with higher doses of the toxicant in a single event or in multiple events over a short period of time and usually produce immediate effects, depending on absorption time of the toxicant. These tests are generally conducted on organisms during a specific time period of the organism’s life cycle, and are considered partial life cycle tests. Acute tests are not valid if mortality in the control sample is greater than 10%. Results are reported in EC50, or concentration that will affect fifty percent of the sample size.[1]

Chronic tests are long-term tests (weeks, months years), relative to the test organism’s life span (>10% of life span), and generally use sub-lethal endpoints. In chronic exposures, organisms come into contact with low, continuous doses of a toxicant. Chronic exposures may induce effects to acute exposure, but can also result in effects that develop slowly. Chronic tests are generally considered full life cycle tests and cover an entire generation time or reproductive life cycle (“egg to egg”). Chronic tests are not considered valid if mortality in the control sample is greater than 20%. These results are generally reported in NOECs (No observed effects level) and LOECs (Lowest observed effects level).

Early life stage tests are considered as subchronic exposures that are less than a complete reproductive life cycle and include exposure during early, sensitive life stages of an organism. These exposures are also called critical life stage, embryo-larval, or egg-fry tests. Early life stage tests are not considered valid if mortality in the control sample is greater than 30%.[1]

Short-term sublethal tests are used to evaluate the toxicity of effluents to aquatic organisms. These methods are developed by the EPA, and only focus on the most sensitive life stages. Endpoints for these test include changes in growth, reproduction and survival. NOECs, LOECs and EC50s are reported in these tests.

Bioaccumulation tests are toxicity tests that can be used for hydrophobic chemicals that may accumulated in the fatty tissue of aquatic organisms. Toxicants with low solubilities in water generally can be stored in the fatty tissue due to the high lipid content in this tissue. The storage of these toxicants within the organism may lead to cumulative toxicity. Bioaccumulation tests use bioconcentration factors (BCF) to predict concentrations of hydrophobic contaminants in organisms. The BCF is the ratio of the average concentration of test chemical accumulated in the tissue of the test organism (under steady state conditions) to the average measured concentration in the water.

Freshwater tests and saltwater tests have different standard methods, especially as set by the regulatory agencies. However, these tests generally include a control (negative and/or positive), a geometric dilution series or other appropriate logarithmic dilution series, test chambers and equal numbers of replicates, and a test organism. Exact exposure time and test duration will depend on type of test (acute vs. chronic) and organism type. Temperature, water quality parameters and light will depend on regulator requirements and organism type.[1]

In the US, many wastewater dischargers (e.g., factories, power plants, refineries, mines, municipal sewage treatment plants) are required to conduct periodic whole effluent toxicity (WET) tests under the National Pollutant Discharge Elimination System (NPDES) permit program, pursuant to the Clean Water Act. For facilities discharging to freshwater, effluent is used to perform static-acute multi-concentration toxicity tests with Ceriodaphnia dubia (water flea) and Pimephales promelas (fathead minnow), among other species. The test organisms are exposed for 48 hours under static conditions with five concentrations of the effluent. The major deviation in the short-term chronic effluent toxicity tests and the acute effluent toxicity tests is that the short-term chronic test lasts for seven days and the acute test lasts for 48 hours. For discharges to marine and estuarine waters, the test species used are sheepshead minnow (Cyprinodon variegatus), inland silverside (Menidia beryllina), Americamysis bahia, and purple sea urchin (Strongylocentrotus purpuratus).[8][9]

Sediment tests

At some point most chemicals originating from both anthropogenic and natural sources accumulate in sediment. For this reason, sediment toxicity can play a major role in the adverse biological effects seen in aquatic organisms, especially those inhabiting benthic habitats. A recommended approach for sediment testing is to apply the Sediment Quality Triad (SQT) which involves simultaneously examining sediment chemistry, toxicity, and field alterations so that more complete information can be gathered. Collection, handling, and storage of sediment can have an effect on bioavailability and for this reason standard methods have been developed to suit this purpose.[1]

Toxicological effects

Toxicity can be broken down into two broad categories of direct and indirect toxicity. Direct toxicity results from a toxicant acting at the site of action in or on the organism. Indirect toxicity occurs with a change in the physical, chemical, or biological environment.

Lethality is most common effect used in toxicology and used as an endpoint for acute toxicity tests. While conducting chronic toxicity tests sublethal effects are endpoints that are looked at. These endpoints include behavioral, physiological, biochemical, histological changes.[1]

There are a number of effects that occur when an organism is simultaneously exposed to two or more toxicants. These effects include additive effects, synergistic effects, potentiation effects, and antagonistic effects. An additive effect occurs when combined effect is equal to a combination or sum of the individual effects. A synergistic effect occurs when the combination of effects is much greater than the two individual effects added together. Potentiation is an effect that occurs when an individual chemical has no effect is added to a toxicant and the combination has a greater effect than just the toxicant alone. Finally, an antagonistic effect occurs when a combination of chemicals has less of an effect than the sum of their individual effects.[1]

Important aquatic toxicology resources

  • ASTM International (formerly American Society for Testing and Materials). A consensus-based organization, representing 135 countries, that develops and delivers international voluntary standard methods for aquatic toxicity testing.[10]
  • Standard Methods for the Examination of Water and Wastewater. A compilation of techniques for water analysis, jointly published by the American Public Health Association (APHA), the American Water Works Association (AWWA), and the Water Environment Federation.[11]
  • "Ecotox." A database maintained by EPA that offers single chemical toxicity information for both aquatic and terrestrial purposes.[12]
  • Society of Environmental Toxicology and Chemistry (SETAC). A nonprofit, worldwide society working to promote scientific research to further our understanding of environmental stressors, environmental education, and the use of science in environmental policy.[13]
  • US EPA publishes guidance manuals outlining aquatic toxicity test procedures.[8][9]
  • Organisation for Economic Co-operation and Development (OECD). A forum for governments to work together to promote policies for the betterment of people’s social and economic well-being around the world. One way in which they accomplish this is through the development of aquatic toxicity test guidelines.[14]
  • Environment and Climate Change Canada. Canada's lead federal agency for environmental protection.[15]

Terminology

  • Median Lethal Concentration (LC50) – The chemical concentration that is expected to kill 50% of a group of organisms.
  • Median Effective Concentration (EC50) – The chemical concentration that is expected to have one or more specified effects in 50% of a group of organisms.
  • Critical Body Residue (CBR) – An approach that routinely examines whole-body chemical concentrations of an exposed organism that is associated with an adverse biological response.
  • Baseline toxicity – Refers to narcosis which is a depression in biological activity due to toxicants being present in the organism.
  • Biomagnification – The process by which the concentration of a chemical in the tissues of an organism increases as it passes through several levels in the food web.
  • Lowest Observed Effect Concentration (LOEC) – The lowest test concentration that has a statistically significant effect over a specified exposure time.
  • No Observed Effect Concentration (NOEC) – The highest test concentration for which no effect is observed relative to a control over a specified exposure time.
  • Maximum Acceptable Toxicant Concentration (MATC) – An estimated value that represents the highest “no-effect” concentration of a specific substance within the range including the NOEC and LOEC.
  • Application Factor (AF) – An empirically derived “safe” concentration of a chemical.
  • Biomonitoring – The consistent use of living organisms to analyze environmental changes over time.
  • Effluent – Liquid, industrial discharge that usually contain varying chemical toxicants.
  • Quantitative Structure-Activity Relationship (QSAR) – A method of modeling the relationship between biological activity and the structure of organic chemicals.
  • Mode of Action – A set of common behavioral or physiological signs that represent a type of adverse response.
  • Mechanism of Action – The detailed events that take place at the molecular level during an adverse biological response.
  • KOW – The octanol-water partition coefficient which represents the ratio of the concentration of octanol to the concentration of chemical in the water.
  • Bioconcentration Factor (BCF) – The ratio of the average chemical concentration in the tissues of the organism under steady-state conditions to the average chemical concentration measured in the water to which the organisms are exposed.

All terms were derived from Rand.[1]

Significance in regulatory context

In the United States, aquatic toxicology plays an important role in the NPDES wastewater permit program. While most wastewater dischargers typically conduct analytical chemistry testing for known pollutants, whole effluent toxicity tests have been standardized and are performed routinely as a tool for evaluating the potential harmful effects of other pollutants not specifically regulated in the discharge permits.[8]

EPA's water quality program has published water quality criteria (for individual pollutants) and water quality standards (for water bodies) that were derived from aquatic toxicity tests.[16]

Sediment quality guidelines

While sediment quality guidelines are not meant for regulation, they provide a way to rank and compare sediment quality developed by National Oceanic and Atmospheric Administration(NOAA).[17] These sediment quality guidelines are summarized in NOAA's Screening Quick Reference Tables (SQuiRT) for many different chemicals.[18]

See also

References

  1. ^ a b c d e f g h i j k l m n o p q r Rand, Gary M.; Petrocelli, Sam R. (1985). Fundamentals of aquatic toxicology: Methods and applications. Washington: Hemisphere Publishing. ISBN 978-0-89116-382-4.
  2. ^ Final Report: Interlaboratory Variability Study of EPA Short-term Chronic and Acute Whole Effluent Toxicity Test Methods, Vol 1 (Report). Washington, DC: U.S. Environmental Protection Agency (EPA). September 2001. EPA 821-B-01-004.
  3. ^ "Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms, Fifth Edition". EPA. October 2002. EPA 821-R-02-012.
  4. ^ "Water Quality Standards History" EPA. Received 2012-06-06 Archived 2012-06-28 at the Wayback Machine
  5. ^ Calow, Peter P (2009). Handbook of Ecotoxicology. John Wiley & Sons. p. 900. ISBN 978-1444313505.
  6. ^ Liu, Fu-Jun; Wang, Jia-Sheng; Theodorakis, Chris W. (May 2006). "Thyrotoxicity of Sodium Arsenate, Sodium Perchlorate, and Their Mixture in ZebrafishDanio rerio". Environmental Science & Technology. 40 (10): 3429–3436. doi:10.1021/es052538g. ISSN 0013-936X.
  7. ^ Vidal-Liñán, Leticia; Bellas, Juan; Campillo, Juan Antonio; Beiras, Ricardo (January 2010). "Integrated use of antioxidant enzymes in mussels, Mytilus galloprovincialis, for monitoring pollution in highly productive coastal areas of Galicia (NW Spain)". Chemosphere. 78 (3): 265–272. doi:10.1016/j.chemosphere.2009.10.060. PMID 19954813.
  8. ^ a b c "Whole Effluent Toxicity (WET)". National Pollutant Discharge Elimination System (NPDES). EPA. 2017-10-10.
  9. ^ a b "Whole Effluent Toxicity Methods". EPA. 2018-04-19.
  10. ^ "About ASTM International". West Conshohocken, Pennsylvania. Retrieved 2018-12-24.
  11. ^ Baird, Rodger B.; Clesceri, Leonore S.; Eaton, Andrew D.; et al., eds. (2012). Standard Methods for the Examination of Water and Wastewater (22nd ed.). Washington, DC: American Public Health Association. ISBN 978-0875530130.
  12. ^ "ECOTOX Knowledgebase" EPA. Accessed 2018-12-13.
  13. ^ "Society of Environmental Toxicology and Chemistry". Pensacola, Florida. Retrieved 2018-12-24.
  14. ^ "About the Organisation for Economic Co-operation and Development". Paris, France. Retrieved 2018-12-24.
  15. ^ "Environment and Climate Change Canada's Mandate". Ottawa, Ontario. 2018-12-10.
  16. ^ Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses (Report). EPA. 1985. PB85-227049.
  17. ^ "Sediment Quality Guidelines developed for the National Status and Trends Program" Archived June 12, 2013, at the Wayback Machine National Status & Trends, 1999
  18. ^ "SQuiRT" National Oceanic and Atmospheric Administration, 2008
Aquatic toxicology databases

Toxicological databases are large compilations of data derived from aquatic and environmental toxicity studies. Data is aggregated from a large number of individual studies in which toxic effects upon aquatic and terrestrial organisms have been determined for different chemicals. These databases are then used by toxicologists, chemists, regulatory agencies and scientists to investigate and predict the likelihood that an organic or inorganic chemical will cause an adverse effect (i.e. toxicity) on exposed organisms.

Several such databases have been compiled relating specifically to aquatic toxicology.

Bioconcentration

Bioconcentration is the accumulation of a chemical in or on an organism when the source of chemical is solely water. Bioconcentration is a term that was created for use in the field of aquatic toxicology. Bioconcentration can also be defined as the process by which a chemical concentration in an aquatic organism exceeds that in water as a result of exposure to a waterborne chemical.There are several ways in which to measure and assess bioaccumulation and bioconcentration. These include: octanol-water partition coefficients (KOW), bioconcentration factors (BCF), bioaccumulation factors (BAF) and biota-sediment accumulation factor (BSAF). Each of these can be calculated using either empirical data or measurements as well as from mathematical models. One of these mathematical models is a fugacity-based BCF model developed by Don Mackay.Bioconcentration factor can also be expressed as the ratio of the concentration of a chemical in an organism to the concentration of the chemical in the surrounding environment. The BCF is a measure of the extent of chemical sharing between an organism and the surrounding environment.In surface water, the BCF is the ratio of a chemical's concentration in an organism to the chemical's aqueous concentration. BCF is often expressed in units of liter per kilogram (ratio of mg of chemical per kg of organism to mg of chemical per liter of water). BCF can simply be an observed ratio, or it can be the prediction of a partitioning model. A partitioning model is based on assumptions that chemicals partition between water and aquatic organisms as well as the idea that chemical equilibrium exists between the organisms and the aquatic environment in which it is found

Biotic Ligand Model

The Biotic Ligand Model (BLM) is a tool used in aquatic toxicology that examines the bioavailability of metals in the aquatic environment and the affinity of these metals to accumulate on gill surfaces of organisms. BLM depends on the site-specific water quality including such parameters as pH, hardness, and dissolved organic carbon. In this model, lethal accumulation values (accumulation of metal on the gill surface, in the case of fish, that cause mortality in 50% of the population) are used to be predictive of lethal concentration values that are more universal for aquatic toxicology and the development of standards. Collection of water chemistry parameters for a given site, incorporation of the data into the BLM computer model and analysis of the output data is used to accomplish BLM analysis. Comparison of these values derived from the model, have repeatedly been found to be comparable to the results of lethal tissue concentrations from acute toxicity tests (Arnold et al. 2005). The BLM was developed from the gill surface interaction model (GSIM) and the free ion activity model (FIAM). Both of these models also address how metals interact with organisms and aquatic environments. Currently, the Environmental Protection Agency (EPA) uses the BLM as a tool to outline Ambient Water Quality Criteria (AWQC) for surface water. Because BLM is so useful for investigation of metals in surface water, there are developmental plans to expand BLM for use in marine and estuarine environments.

Christopher Wood (biologist)

Christopher M. Wood FRSC is currently an Adjunct Professor of Zoology at the University of British Columbia and a Lifetime Distinguished University Professor, and Emeritus Professor of Biology at McMaster University. He is also a Research Professor at the University of Miami. His research is primarily concerned with Fish physiology and aquatic toxicology.

He was educated at the University of British Columbia (BSc, 1968; MSc, 1971) and the University of East Anglia (PhD, 1974). He joined the faculty of McMaster University in 1976 where he was a Canada Research Chair in Environment and Health from 2001-2014. In 2014 he retired from McMaster University and moved to the University of British Columbia, where his research program is now based. He was made a Fellow of the Royal Society of Canada in 2003, and was awarded the 2007 Miroslaw Romanowski Medal. He was also awarded the Fry Medal of the Canadian Society of Zoologists in 1999.

Chronic toxicity

Chronic toxicity, the development of adverse effects as a result of long term exposure to a contaminant or other stressor, is an important aspect of aquatic toxicology. Adverse effects associated with chronic toxicity can be directly lethal but are more commonly sublethal, including changes in growth, reproduction, or behavior. Chronic toxicity is in contrast to acute toxicity, which occurs over a shorter period of time to higher concentrations. Various toxicity tests can be performed to assess the chronic toxicity of different contaminants, and usually last at least 10% of an organism’s lifespan. Results of aquatic chronic toxicity tests can be used to determine water quality guidelines and regulations for protection of aquatic organisms.

Cyanopeptolin

Cyanopeptolins are a class of oligopeptides produced by Microcystis and Planktothrix algae strains, and can be neurotoxic. The production of cyanopeptolins occurs through nonribosomal peptides synthases (NRPS).

Early Life Stage test

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. 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, particularly with fish. Growth and survival are the typically measured endpoints, for which a Maximum Acceptable Toxicant Concentration (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 (EPA) and Environment Canada, as well as the Organisation for Economic Co-operation and Development (OECD).

Ecological death

Ecological death is the inability of an organism to function in an ecological context, leading to death. This term can be used in many fields of biology to describe any species. In the context of aquatic toxicology, a toxic chemical, or toxicant, directly affects an aquatic organism but does not immediately kill it; instead it impairs an organism’s normal ecological functions which then lead to death or lack of offspring. The toxicant makes the organism unable to function ecologically in some way, even though it does not suffer obviously from the toxicant. Ecological death may be caused by sublethal toxicological effects that can be behavioral, physiological, biochemical, or histological.

Fisheries and Illinois Aquaculture Center

The Fisheries and Illinois Aquaculture Center at Southern Illinois University Carbondale (SIUC) was founded by Dr. William M. Lewis, Senior in 1950. The Center is administratively housed in the Graduate School. Faculty have joint appointments in the Center and the Department of Zoology within the College of Science or in the Department of Animal Science, Food and Nutrition in the College of Agricultural Sciences.

Research faculty in the Center have diverse capabilities including molecular genetics, aquatic toxicology, aquatic ecology, bioenergetics, fish nutrition, fish physiology, fisheries policy and management, and aquaculture technology.

Facilities include several research laboratories, an experimental pond facility (90 ponds), a large wet laboratory, research boats (including a 27-foot (8.2 m) research vessel with advanced hydroacoustics), and offices.

The Center generates many peer-reviewed publications and garners grant support from many state and federal agencies as well as foundations.

Fluoxetine

Fluoxetine, sold under the brand names Prozac and Sarafem among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. It is used for the treatment of major depressive disorder, obsessive–compulsive disorder (OCD), bulimia nervosa, panic disorder, and premenstrual dysphoric disorder. It may decrease the risk of suicide in those over the age of 65. It has also been used to treat premature ejaculation. Fluoxetine is taken by mouth.Common side effects include trouble sleeping, sexual dysfunction, loss of appetite, dry mouth, rash, and abnormal dreams. Serious side effects include serotonin syndrome, mania, seizures, an increased risk of suicidal behavior in people under 25 years old, and an increased risk of bleeding. If stopped suddenly, a withdrawal syndrome may occur with anxiety, dizziness, and changes in sensation. It is unclear if it is safe in pregnancy. If already on the medication, it may be reasonable to continue during breastfeeding. Its mechanism of action is not entirely clear but believed to be related to increasing serotonin activity in the brain.Fluoxetine was discovered by Eli Lilly and Company in 1972, and entered medical use in 1986. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world is between US$0.01 and US$0.04 per day as of 2014. In the United States, it costs about US$0.85 per day. In 2016 it was the 29th most prescribed medication in the United States with more than 23 million prescriptions.

Jörundur Svavarsson

Jörundur Svavarsson is a professor in marine biology at the University of Iceland. His fields of research are marine invertebrates, marine biodiversity and ecotoxicology. According to Web of Science Prof. Svavarsson has published 49 papers in peer-reviewed journals, with 13 or them being cited more than 11 times. He is currently the head of the department of Biology at University of Iceland. Professor Svavarsson has spearheaded several cultural and historic projects, one of which was the establishment of an exhibition dedicated to the explorations of Jean-Baptiste Charcot whose ship Pourquoi pas ? was lost on the west coast of Iceland in 1936. In 2012 Professor Svavarsson was awarded the title of "Chevalier des Palmes académiques" for this work, a title which was created by Napoleon in 1808.

The most widely referred to are:

Stephensen E, Svavarsson J, Sturve J, et al. "Biochemical indicators of pollution exposure in shorthorn sculpin (Myoxocephalus scorpius), caught in four harbours on the southwest coast of Iceland" Aquatic Toxicology 48 (4): 431-442 Apr 2000 Times Cited: 39

Fricke, H, Giere O, Steter K, Alfredsson, GA., Kristjansson JK, Stoffers P, and Svavarsson S "Hydrothermal vent communities at the shallow subpolar mid-atlantic Ridge." Marine Biology 102 (3): 425-429 1989 Times cited: 37

Svavarsson S, Brattegard T, Stromberg JO. "Distribution and diversity patterns of asellote isopods (Crustacea) in the deep Norwegian and Greenland seas." Progress in Oceanography 24 (1-4): 297-310 1990. Times cited: 33

Svavarsson S, Gudmundsson G, Brattegard T,"Feeding by assellote isopods (Crustacea) on Foraminifers (Protozoa) in the deep sea. Deep-Sea Research Part I: Oceangraphic Research Papers 40 (6): 1225-1239 JUN 1993 Times cited: 29

LT50

LT50 is the median Lethal Time (time until death) after exposure of an organism to a toxic substance or stressful condition. LT50 is commonly used in toxicology studies to quantify amount of a stressor necessary to kill an organism. LT50 can be used in conjunction with EC50 (median Exposure Concentration) for even more precise quantification.

Modes of toxic action

A mode of toxic action is a common set of physiological and behavioral signs that characterize a type of adverse biological response. A mode of action should not be confused with mechanism of action, which refer to the biochemical processes underlying a given mode of action. Modes of toxic action are important, widely used tools in ecotoxicology and aquatic toxicology because they classify toxicants or pollutants according to their type of toxic action. There are two major types of modes of toxic action: non-specific acting toxicants and specific acting toxicants. Non-specific acting toxicants are those that produce narcosis, while specific acting toxicants are those that are non-narcotic and that produce a specific action at a specific target site.

Olanike Adeyemo

Olanike Kudirat Adeyemo is a Nigerian professor of Veterinary Public Health and Preventive Medicine at University of Ibadan. She is the current Deputy Vice Chancellor (research, innovation and strategic partnership), the first person to attain the role. Her research areas are on Aquatic toxicology, Aquatic veterinary medicine and fish food safety.

Olfactory toxicity in fish

The olfactory system is the system related to the sense of smell (olfaction). Many fish activities are dependent on olfaction, such as: mating, discriminating kin, avoiding predators, locating food, contaminant avoidance, imprinting and homing. These activities are referred to as “olfactory-mediated.” Impairment of the olfactory system threatens survival and has been used as an ecologically relevant sub-lethal toxicological endpoint for fish within studies. Olfactory information is received by sensory neurons, like the olfactory nerve, that are in a covered cavity separated from the aquatic environment by mucus. Since they are in almost direct contact with the surrounding environment, these neurons are vulnerable to environmental changes. Fish can detect natural chemical cues in aquatic environments at concentrations as low as parts per billion (ppb) or parts per trillion (ppt).Studies have shown that exposures to metals, pesticides, or surfactants can disrupt fish olfaction, which can impact their survival and reproductive success. Many studies have indicated copper as a source of olfactory toxicity in fishes, among other common substances. Olfactory toxicity can occur by multiple, complex Modes of Toxic Action.

Poisonous fish

Poisonous fish are fish that are poisonous to eat. They contain toxins which are not destroyed by the digestive systems of animals that eat the fish. Venomous fish also contain toxins, but do not necessarily cause poisoning if they are eaten, since the digestive system often destroys their venom.

Simultaneously extracted metals and Acid-volatile sulfide

Simultaneously extracted metals/Acid-volatile sulfide (SEM-AVS) is an approach used in the field of aquatic toxicology to assess the potential for metal ions found in sediment to cause toxic effects in organisms dwelling in the sediment. In this approach, the amounts of several heavy metals in a sediment sample are measured in a laboratory; at the same time, the amount of acid-volatile sulfide (sulfide which can be liberated from the sediment by treatment with hydrochloric acid) is determined. Based on the chemical interactions between heavy metals (SEM) and acid-volatile sulfide (AVS), the concentrations of these two components can be used to assess the potential for toxicity to sediment-dwelling organisms.

Tissue residue

Tissue residue is the concentration of a chemical or compound in an organism’s tissue, or a portion of an organism’s tissue. Tissue residue is used in aquatic toxicology to help determine the fate of chemicals in aquatic systems, bioaccumulation of a substance, bioavailability of a substance, account for multiple routes of exposure (ingestion, absorption, inhalation), and address an organism’s exposure to chemical mixtures. A Tissue residue approach to toxicity testing is considered a more direct and less variable measure of chemical exposure and is less dependent on external environmental factors than measuring the concentration of a chemical in the exposure media.In general, tissue residue approaches are used for chemicals that bioaccumulate or for bioaccumulative chemicals. The majority of these substances are organic compounds that are not easily metabolized by organisms and have long environmental persistence. Examples of these chemicals include: polychlorinated dibenzodioxins, furans, biphenyls, DDT and its metabolites, and dieldrin.The use of tissue residues in assessing toxicity and bioaccumulation may also be referred to as the tissue residue-effects approach (TRA), critical body residue (CBR) or tissue residue-based toxicity tests.

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