Measures of pollutant concentration

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Measures of pollutant concentration are used to determine risk assessment in public health.

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Industry is continually synthesizing new chemicals, the regulation of which requires evaluation of the potential danger for human health and the environment. Risk assessment is nowadays considered essential for making these decisions on a scientifically sound basis.

Measures or defined limits include:

No effect concentration

No effect concentration (NEC) is a risk assessment parameter that represents the concentration of a pollutant that will not harm the species involved, with respect to the effect that is studied. It is often the starting point for environmental policy. [2]

There is not much debate on the existence of an NEC [3] but the assignment of a value is another matter. Current practice consists of the use of standard tests. In the standard tests groups of animals are exposed to different concentrations of chemicals and different effects such as survival, growth or reproduction are monitored. These toxicity tests typically result in a No Observed Effect Concentration (NOEC, also called a No Observable Effect Level or NOEL). This NOEC has been severely criticized on statistical grounds by several authors [4] and it was concluded that the NOEC should be abandoned. [5]

ECx

A proposed alternative is the use of so-called ECx – the concentration(s) showing x% effect (e.g. an EC50 in a survival experiment indicates the concentration where 50% of the test animals would die in that experiment). ECx concentrations also have their problems in applying them to risk assessment. Any other value for x other than zero may give the impression that an effect is accepted, and this is in conflict with the aim of maximally protecting the environment. [6] In addition ECx values do depend on the exposure time. [7] ECx values for survival decrease for increasing exposure time, until equilibrium has been established. This is because effects depend on internal concentrations, [8] and that it takes time for the compound to penetrate the body of test organisms. However, sub-lethal endpoints (e.g., body size, reproductive output) may reveal less predictable effect patterns in time. [9]

The shape of the effect patterns over time depends on properties of the test compound, properties of the organism, the endpoint considered and the dimensions in which the endpoint is expressed (e.g., body size or body weight; reproduction rate or cumulative reproduction).

Biology-based

Biology-based methods not only aim to describe observed effects, but also to understand them in terms of underlying processes such as toxicokinetics, mortality, feeding, growth and reproduction (Kooijman 1997). This type of approach starts with the description of the uptake and elimination of a compound by an organism, as an effect can only be expected if the compound is inside the organism, and where the No Effect Concentration is one of the modeling parameters. As the approach is biologically based it is also possible by using Dynamic Energy Budget theory [10] to incorporate multiple stressors (e.g. effects of food restriction, temperature, etc.) [11] and processes that are active under field conditions (e.g. adaptation, population dynamics, species interactions, life cycle phenomena, etc.). [12] The effects of these multiple stressors are excluded in the standard test procedures by keeping the local environment in the test constant. It is also possible to use these parameter values to predict effects at longer exposure times, or effects when the concentration in the medium is not constant. If the observed effects include those on survival and reproduction of individuals, these parameters can also be used to predict effects on growing populations in the field. [13]

Related Research Articles

Toxicology Branch of biology, chemistry, and medicine

Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating exposures to toxins and toxicants. The relationship between dose and its effects on the exposed organism is of high significance in toxicology. Factors that influence chemical toxicity include the dosage, duration of exposure, route of exposure, species, age, sex, and environment. Toxicologists are experts on poisons and poisoning. There is a movement for evidence-based toxicology as part of the larger movement towards evidence-based practices. Toxicology is currently contributing to the field of Cancer research, since some toxins can be used as drugs for killing tumor cells. One prime example of this is Ribosome Inactivating Proteins, tested in the treatment of Leukemia.

Toxicity The ability of a chemical to cause damage to life

Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as the liver (hepatotoxicity). By extension, the word may be metaphorically used to describe toxic effects on larger and more complex groups, such as the family unit or society at large. Sometimes the word is more or less synonymous with poisoning in everyday usage.

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.

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

Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology.

The dynamic energy budget (DEB) theory is a formal metabolic theory which provides a single quantitative framework to dynamically describe the aspects of metabolism of all living organisms at the individual level, based on assumptions about energy uptake, storage, and utilization of various substances. The DEB theory adheres to stringent thermodynamic principles, is motivated by universally observed patterns, is non-species specific, and links different levels of biological organization as prescribed by the implications of energetics. Models based on the DEB theory have been successfully applied to over a 1000 species with real-life applications ranging from conservation, aquaculture, general ecology, and ecotoxicology. The theory is contributing to the theoretical underpinning of the emerging field of metabolic ecology.

Dose–response relationship change on an organism caused by differing levels of exposure (or doses) to a stressor after a certain exposure time

The dose–response relationship, or exposure–response relationship, describes the magnitude of the response of an organism, as a function of exposure to a stimulus or stressor after a certain exposure time. Dose–response relationships can be described by dose–response curves. This is explained further in the following sections. A stimulus response function or stimulus response curve is defined more broadly as the response from any type of stimulus, not limited to chemicals.

The no-observed-adverse-effect level (NOAEL) denotes the level of exposure of an organism, found by experiment or observation, at which there is no biologically or statistically significant increase in the frequency or severity of any adverse effects of the tested protocol. In drug development, the NOAEL of a new drug is assessed in laboratory animals, such as mice, prior to initiation of human trials in order to establish a safe clinical starting dose in humans. The OECD publishes guidelines for Preclinical Safety Assessments, in order to help scientists discover the NOAEL.

Ecotoxicity potential for biological, chemical or physical stressors to affect ecosystems

Ecotoxicity, the subject of study of the field of ecotoxicology, refers to the potential for biological, chemical or physical stressors to affect ecosystems. Such stressors might occur in the natural environment at densities, concentrations or levels high enough to disrupt the natural biochemistry, physiology, behavior and interactions of the living organisms that comprise the ecosystem.

Biomarkers are chemicals, metabolites, susceptibility characteristics, or changes in the body that relate to the exposure of an organism to a chemical. They have the ability to identify if an exposure has occurred, the route of exposure, the pathway of exposure, and the resulting effects of the exposure. The use of biomarkers in exposure studies is also referred to as biomonitoring. When dealing with exposure assessment, there are three types of biomarkers that can be useful, biomarkers of susceptibility, biomarkers of exposure, and biomarkers of effect. Biomarkers of exposure are the most widely used because they can provide information on the route, pathway, and sometimes, even the source of exposure.

Toxic equivalency factor (TEF) expresses the toxicity of dioxins, furans and PCBs in terms of the most toxic form of dioxin, 2,3,7,8-TCDD. The toxicity of the individual congeners may vary by orders of magnitude.

In environmental toxicology, effects range low (ERL) and effects range median (ERM) are measures of toxicity in marine sediment. They are used by public agencies in the United States in formulating guidelines in assessing toxicity hazards, in particular from trace metals or organic contaminants.

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.

Toxicodynamics, termed pharmacodynamics in pharmacology, describes the dynamic interactions of a toxicant with a biological target and its biological effects. A biological target, also known as the site of action, can be binding proteins, ion channels, DNA, or a variety of other receptors. When a toxicant enters an organism, it can interact with these receptors and produce structural or functional alterations. The mechanism of action of the toxicant, as determined by a toxicant’s chemical properties, will determine what receptors are targeted and the overall toxic effect at the cellular level and organismal level.

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.

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).

Equilibrium partitioning Sediment Benchmarks (ESBs) are a type of Sediment Quality Guideline (SQG) derived by the US Environmental Protection Agency (EPA) for the protection of benthic organisms. ESBs are based on the bioavailable concentration of contaminants in sediments rather than the dry-weight concentration. It has been demonstrated that sediment concentrations on a dry-weight basis often do not predict biological effects. Interstitial water concentrations, however, predict biological effects much better. This is true because the chemical present in the interstitial water is the uncomplexed/free phase of the chemical that is bioavailable and toxic to benthic organisms. Other phases of the chemical are bound to sediment particles like organic carbon (OC) or acid volatile sulfides (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms.

The Predicted No Effect Concentration (PNEC) is the concentration of a chemical which marks the limit at which below no adverse effects of exposure in an ecosystem are measured. PNEC values are intended to be conservative and predict the concentration at which a chemical will likely have no toxic effect. They are not intended to predict the upper limit of concentration of a chemical that has a toxic effect. PNEC values are often used in environmental risk assessment as a tool in ecotoxicology. A PNEC for a chemical can be calculated with acute toxicity or chronic toxicity single-species data, Species Sensitivity Distribution (SSD) multi-species data, field data or model ecosystems data. Depending of the type of data used, an assessment factor is used to account for the confidence of the toxicity data being extrapolated to an entire ecosystem.

In aquatic toxicology, the sediment quality triad (SQT) approach has been used as an assessment tool to evaluate the extent of sediment degradation resulting from contaminants released due to human activity present in aquatic environments. This evaluation focuses on three main components: 1.) sediment chemistry, 2.) sediment toxicity tests using aquatic organisms, and 3.) the field effects on the benthic organisms. Often used in risk assessment, the combination of three lines of evidence can lead to a comprehensive understanding of the possible effects to the aquatic community. Although the SQT approach does not provide a cause-and-effect relationship linking concentrations of individual chemicals to adverse biological effects, it does provide an assessment of sediment quality commonly used to explain sediment characteristics quantitatively. The information provided by each portion of the SQT is unique and complementary, and the combination of these portions is necessary because no single characteristic provides comprehensive information regarding a specific site

The acute to chronic ratio (ACR) uses acute toxicity data to gauge the chronic toxicity (MATC) of a chemical of interest to an organism. The science behind determining a safe concentration to the environment is imperfect, statistically limited, and resource intensive. There is an unfilled demand for the rapid assessment of different chemical toxicity to many different organisms. The ACR is a proposed solution to this demand.

References

Inline

  1. ↑ thefreedictionary.com/AOEL Retrieved on June 19, 2009
  2. ↑ Bruijn et al., 1997, Chen & Selleck 1969
  3. ↑ Van Straalen 1997, Crane and Newman 2000
  4. ↑ Suter 1996, Laskowski 1995, Kooijman 1996, Van der Hoeven 1997
  5. ↑ OECD Document No 54 of "Series on Testing Assessment", 2006
  6. ↑ Bruijn et al. 1997
  7. ↑ Kooijman 1981, Jager et al. 2006
  8. ↑ Kooijman 1981, Péry et al. 2001a
  9. ↑ Alda Alvarez et al. 2006
  10. ↑ Kooijman, 2000
  11. ↑ Heugens, 2001, 2003
  12. ↑ Sibly and Calow (1989)
  13. ↑ Kooijman 1997, Hallam et al. 1989

Bibliography

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