Aquatic toxicology

thumb|A [[Strongylocentrotus purpuratus|purple sea urchin being tested for pollution using a whole effluent toxicity method.]]

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. Aquatic toxicology is a multidisciplinary field which integrates toxicology, aquatic ecology and aquatic chemistry.

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. 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.

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. Due to the wide use of the organochlorine pesticide DDT and its linkage to causing fish death, the field of aquatic toxicology grew. At first, studies focused mainly on oysters and mussels, as they could not move away from the toxic environment. The results of these studies eventually led to the implementation of programs that monitor concentrations of aquatic pollutants in oysters and mussels, such as the Mussel Watch program of the National Oceanic and Atmospheric Administration (NOAA). 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. for the control of water pollution and was followed by the Federal Water Pollution Control Act in 1956. 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. 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. zebra fish (Danio rerio), mysids (Mysidopsis), oyster (Crassotreas), scud (Hyalalla Azteca), grass shrimp (Palaemonetes pugio) and mussels (Mytilus galloprovincialis). As defined by ASTM International, these species are routinely selected on the basis of availability, commercial, recreational, and ecological importance, past successful use, and regulatory use. 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. 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%. However, this control acceptability criterion is dependent upon the species and the duration of the test. Results are reported in EC50, or concentration that will affect fifty percent of the sample size. (>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 have generally been reported in NOECs (No observed effects level) and LOECs (Lowest observed effects level). However, NOECs and LOECs are becoming less common as endpoints are dependent on the concentration series chosen for the test. These reports are starting to become a topic of debate in the field because of the way it may alter the results of the tests. For example, if the concentration rate of the NOEC is 100, 50, 25, 11.25, 6.25 and the toxicology is reported at 2%, the NOEC would report the concentration as 6.25.

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%.

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, field alterations, bioaccumulation, and bioavailability assessments that can be used in a laboratory or in the field. Due to the expansion of SQTs, it is now more commonly referred to as "Sediment Assessment Framework." 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.

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.
"Ecotox." A database maintained by EPA that offers single chemical toxicity information for both aquatic and terrestrial purposes.
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.
EPA publishes guidance manuals outlining aquatic toxicity test procedures.
Environment and Climate Change Canada. Canada's lead federal agency for environmental protection.

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.
K<sub>OW</sub> – 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.

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). These sediment quality guidelines are summarized in NOAA's Screening Quick Reference Tables (SQuiRT) for many different chemicals.

Aquatic toxicology

History

Sediment tests

Terminology

Sediment quality guidelines

See also

References