No effect concentration
Encyclopedia
Measures of pollutant concentration are used to determine risk assessment in public health.
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:
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
.
There is not much debate on the existence of an NEC 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 and it was concluded that the NOEC should be abandoned .
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 . In addition ECx values do depend on the exposure time . ECx values for survival decrease for increasing exposure time, until equilibrium has been established. This is because effects depend on internal concentrations , 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
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).
theory to incorporate multiple stressor
s (e.g. effects of food restriction, temperature ), and quite a few processes that are active under field conditions (e.g. adaptation
, population dynamics, species interactions, life cycle
phenomena ). 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 .
Industry
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
is continually synthesizing
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
new chemicals, the regulation of which requires evaluation of the potential danger for human
Human
Humans are the only living species in the Homo genus...
health
Health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...
and the environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
. Risk assessment is nowadays considered essential for making these decisions on a scientifically sound basis.
Measures or defined limits include:
- No effect concentration (NEC) or No Observed Effect Concentration (NOEC)
- Acceptable Operator Exposure Level (AOEL)
- ECx (in percent)
No effect concentration
No effect concentration (NEC) is a risk assessmentRisk assessment
Risk assessment is a step in a risk management procedure. Risk assessment is the determination of quantitative or qualitative value of risk related to a concrete situation and a recognized threat...
parameter that represents the concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
of a pollutant
Pollutant
A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...
that will not harm the species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
involved, with respect to the effect that is studied. It is often the starting point for environmental policy
Environmental policy
Environmental policy is any [course of] action deliberately taken [or not taken] to manage human activities with a view to prevent, reduce, or mitigate harmful effects on nature and natural resources, and ensuring that man-made changes to the environment do not have harmful effects on...
.
There is not much debate on the existence of an NEC 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
Noel
Noel is a masculine French given name derived from noël . The actual feminine form is Noelle, but in English-speaking regions Noel is sometimes used for females as well...
). This NOEC has been severely criticized on statistical grounds by several authors and it was concluded that the NOEC should be abandoned .
ECx
A proposed alternative is the use of so called ECx –concentrations, or the concentrating showing x % Effect (e.g. an EC50EC50
The term half maximal effective concentration refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after some specified exposure time...
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 . In addition ECx values do depend on the exposure time . ECx values for survival decrease for increasing exposure time, until equilibrium has been established. This is because effects depend on internal concentrations , 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
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 toxico-kinetics, 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 is, 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 BudgetDynamic energy budget
The Dynamic Energy Budget theory aims to identify simple quantitative rules for the organization of metabolism of individual organisms that can be understood from basic first principles...
theory to incorporate multiple stressor
Stressor
Stressor is a chemical or biological agent, environmental condition, an external stimulus or an event that causes stress to an organism. An event that triggers the stress response may include for example:...
s (e.g. effects of food restriction, temperature ), and quite a few processes that are active under field conditions (e.g. adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
, population dynamics, species interactions, life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
phenomena ). 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 .