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What is a contaminated site?

Who does what?

Why is it important?

What is risk management?

Risk assessment fundamentals

Risk assessment methods

Limitations of risk assessment

What are RA tiers?


Problem Identification

Receptor Characterisation

Exposure Assessment

Toxicity Assessment

Risk Characterisation

RM Decisions





Application factor 

A value applied to toxicity values (i.e. LC50 or LOEC) to provide an estimate of the concentration that will cause no detrimental effect on an organism. Sometimes referred to as an extrapolation factor or a safety factor.

AS/NZS 4360

AS/NZS 4360: Risk Management is the Australian and New Zealand joint Risk Management Standard.

It was published originally in November 1995 and substantially revised and republished in April 1999.

Risk management is the culture, processes and structures that are directed towards the effective management of potential opportunities and adverse effects.



Benchmark species 

Refers to common internationally used test species, such as rainbow trout or cladoceran ‘water fleas’ for fresh waters, or earthworms for soil.

Benchmark values 

Benchmark values are sometimes applied where regulatory guidelines or standards to protect ecological receptors are not available


The degree to which a contaminant in environmental media can be assimilated by an organism.

The bioavailability of a chemical to the receptor will depend upon its chemical and physical characteristics, and the characteristics of the media it is in. For example, hydrophobic compounds tend to bind to organic matter present in the soil or water, making them less ‘bioavailable’ to the receptor. Reduced bioavailability means a lower exposure of the chemical to the ecological receptor. To a certain degree, bioavailability also depends upon the physiology of the receptor of concern and the route of exposure. For example, if contaminated soil is ingested by a bird, its subsequent bioavailability will be dependent upon its uptake through the gut wall of the bird. In Level 1 ERA it is assumed that the total amount of chemical is bioavailable, which in most cases adds considerable conservatism into the assessment.


An abbreviation of benzene, toluene, ethylbenzene and xylene: volatile hydrocarbons that are present as components of petroleum-based fuels but are also common contaminants at a range of contaminated sites.

For more information on testing in New Zealand related to BTEX follow this link.


An abbreviation of copper, chromium and arsenic. The first two are metals and the last is a metalloid.  They are commonly used together in the treatment of timber. Arsenic was historically also widely used as part of a sheep and cattle dipping solution.


The outcome of an event or situation expressed qualitatively or quantitatively, being a loss, injury, disadvantage or gain.


RMA definition

"Any substance(including gases, liquids,solids and micro-organisms) or energy (excluding noise), or heat, that either by itself or in combination, with the same, or similar or other substances, energy, or heat - 

(a) when discharged into water, changes or is likely to change the physical, chemical, or biological condition of water, or

(b) when discharged onto or into land or into air, changes or is likely to change the physical, chemical, or biological condition of the land, or air onto or into which it is discharged.

Contaminated site

A contaminated site is a site where concentrations of contaminants are above background concentrations, and an assessment suggests that the substances pose a risk to human health or the environment.

Criteria (singular, criterion). 

In the area of risk assessment, and more specifically, for the setting of protective levels for contaminants in the environment, the term ‘criteria’ is often used in two separate, but related ways. How the term ‘criteria’ is applied appears to be dependent upon both the discipline (i.e. aquatic or terrestrial toxicity) and the country. The word ‘criteria’ in the context of water quality in Australia and in Canada, for example in the ANZECC (2000) guideline and in the Canadian water quality guidelines (CCREM, 1987), refers to scientific findings that are used to derive guidelines or standards for water use. For example, the finding that ‘half of a sample of test organisms dies after a given time of exposure to a certain concentration of a toxicant’, is a criterion. In the U.S. however, water quality criteria refer to values that reflect available scientific information on the maximum acceptable concentrations of chemicals in water that will protect aquatic life and human health. This is similar to how the term ‘criteria’ is employed for soil quality purposes, i.e. it is used to describe a protective level for a particular soil contaminant based on the available scientific data.

Ecological receptor

Ecosystems, habitats, communities, populations and individual organisms that can be exposed directly or indirectly to a stressor.

Ecological risk assessment

Ecological risk assessment is the application of risk assessment techniques to assessing risks to plants, animals, and ecosystems.

Ecological values

Plants, animals, or ecosytems that are identified and considered to be of significant societal relevance, ecological or economical significance. Ecological values may be generic or specific to a particular site or habitat.

EIL (ecological impact level)

The concentration of a contaminant which, if exceeded, may adversely affect ecological values.

End point:

Assessment end points are identified during initial discussions between the risk manager and the risk assessor, and are ecologically-relevant receptor/s at risk.

Measurement end point is a measurable response to a stressor (measure, metric or index) that is quantifiably related to the assessment end point. A measurement end point is also known as an ‘effects measure’.

Although assessment and measurement end points may appear to be the same thing, they are not necessarily so.  

Measurement end points are usually more easily measured than an assessment endpoint. An assessment end point must have ecological relevance, for example, an impact at a population or community level. However, due to the high cost of obtaining measurements of end point at this level, most toxicity tests measure an end point at the level of the individual organism. Generally, measurement end point data are extrapolated into corresponding assessment end point values. Therefore, it is very important that the measurement end point is related to a biologically significant response such as survival or fecundity of a population. An example (from ASTM E 1848) is given below

  • Assessment end point: Population-level effects on resident earthworms living in metal-contaminated soils
  • Measurement end point: Toxic effects of site soils to surrogate species of earthworms in standard toxicity tests.

Relationship between assessment and measurement end point: The higher frequency of death of earthworms in site soils compared to control soils or soils from reference sites in the standard earthworm bioassay indicates that mortality is likely to be elevated in populations of earthworms in the metal- contaminated areas of the site.

Environmental standards 

Guidelines that have statutory force to maintain a desired quality of some part of the environment, such as ‘drinking water standards’ or ‘soil quality standards’ Standards should be based on sound scientific data, however the desired level of ‘quality’ is also a political and social decision. Therefore, environmental standards provide the foundation for achieving the objectives of environmental legislation.

Exposure assessment

Exposure assessment is used to estimate the magnitude, duration and frequency of exposure of plants, animals or ecosytems to contaminants of concern.  Includes determining mechanisms or pathways of exposure.

Exposure pathway 

Route by which contaminants enter an organism, e.g., via water and/or food.

Extrapolation factors

Toxicity tests are conducted under specified and controlled conditions that are not the same as the conditions that occur at contaminated sites. For example, the test species may not be the species of concern, or the test concentrations may be a lot higher than the likely environmental concentrations. Extrapolation factors are applied to the toxicity data to ensure protection of the ecological receptor under field conditions. These ‘factors’ are applied to take into account such things as:

  • Extrapolating from a response at a high test concentration / short duration exposure to a lower environmental concentration / longer duration of exposure
  • Extrapolating from laboratory to field data
  • Extrapolating from a test species to the species of concern (factor may be higher if species is threatened or endangered)
  • Allowing for interindividual variation in sensitivity within a population
  • Adding conservatism to poor-quality data
  • Extrapolating from an effect level concentration (EC50, LC50 or LOEC) to a NOEC.

Individual extrapolation factors are often a number between 0 and 10, and the value is usually determined according to a set of given criteria. For example, to convert a LOEC to a NOEC for screening level (Level 1) assessments, a standard safety factor of 10 is commonly used. In ERA, where the total amount of uncertainty can be very high, overuse of application factors can lead to highly unrealistic estimates of investigation levels or benchmark concentrations. It is quite useful to have an understanding and knowledge of the extrapolation factors (if any) that have been used to derive the benchmark or regulatory values for particular contaminants.


Numerical or narrative statements whose application should maintain a certain environmental use, for example a stated degree of protection for aquatic biota. Numerical guidelines should be based on sound scientific data. In effect, a guideline translates (eco) toxicity data into a form from which a standard could, or should, be written. This may call for a value judgement on acceptable risks or requirements.


The concentration of all metallic cations, except those of alkali metals, present in water. In general, hardness is a measure of the concentration of calcium and magnesium in water.

Hazard and hazard identification

A hazard is a source of potential harm or a situation with a potential to cause adverse effect. Hazard identification looks at the source of the risk,or the characteristics of the site that might lead to risk. 

Human health risk assessment

Application of risk assessment techniques to assessing risks to human health and safety.

Likelihood, Probability and Frequency

Likelihood is a qualitative description of probability or frequency.

Probability is measured by the ratio of specific outcomes to the total number of possible outcomes. It is expressed as a number between 0 and 1, with 0 indicating an impossible outcome and 1 indicating an outcome is certain.

Frequency is the number of items occurring in a given category. Often frequency is linked to time, for example, the number of events in a year.

Mechanism of action

Understanding the toxic mechanism of a contaminant helps evaluate the importance of potential exposure pathways and selection of sensitive ecological receptors. For example, a contaminant (like a vertebrate pesticide) may selectively affect higher vertebrates by interfering with organ systems not found in invertebrates, or a contaminant may be present at a level that may not be toxic to most organisms, but which will threaten top predators through food chain biomagnification.

Qualitative risk assessment

Qualitative risk assessment is where the likelihood or the magnitude of the consequences are expressed in qualitative terms (i.e. not quantified).

Quantitative risk assessment

Quantitative risk assessment is risk assessment where the probability or frequency of the outcomes can be estimated and the magnitude of consequences is quantified so that risk is calculated in terms of probable extent of harm or damage over a given period.


A plant, animal, or ecosystem exposed to a stressor.

Reference toxicant 

A standard chemical used to measure the sensitivity of the test organisms in order to establish confidence in the toxicity data obtained from the test material. In most instances a toxicity test with a reference toxicant is performed to assess the sensitivity of the test organisms at the time the test material is evaluated, and the precision of results obtained by the laboratory for that chemical.


Risk is defined as the chance of something happening that will have a (generally adverse) impact on plants, animals, or ecosystems. It may be an event, action, or lack of action. It is measured in terms of consequences and likelihood.

Risk identification

Risk identification is the process of determining what can happen, why and how. Identifying risks requires looking at all possible sources of risk and the elements at risk.


A physical, chemical or biological entity that induces an adverse response in a plant, animal or ecosystem.


Mechanism of exposure of a receptor to a stressor.


Toxicity to plants

Probit analysis

A statistical procedure used to analyse data from toxicity tests.

Toxicity assessment

The overall process of evaluating the type and magnitude of toxicity caused by a hazardous substance. It involves determining the toxicity of the contaminants, and establishes the sensitivity of the ecological receptor(s).

Toxicity of mixtures:

Additive toxicity is where the toxicity of a mixture of contaminants equals the summation of the toxicities of the individual component; e.g. for a mixture of compounds A + B: if the toxicity of compound A = 1, and toxicity of compound B = 1, then the additive toxicity would be 1 + 1 = 2.

Antagonistic toxicity is where the toxicity of a mixture of contaminants is significantly less than the summation of the toxicities of the individual components, e.g. 1 + 1 = 1.

Synergistic toxicity is where the toxicity of a mixture of contaminants results in a potentiation of toxicity where the total toxicity is far greater than the summation of the toxicities of the individual components, e.g. 1 + 1 = 10.

Toxicity tests

Toxicity tests are used to determine the toxicity of contaminants to one or more species. A toxicity test measures the degree of response produced by exposure to a specific level of contaminant (i.e. concentration or dose) compared to an unexposed control. 

Acute toxicity tests are most commonly used in risk assessment. An acute test generally involves an exposure to a single chemical at a high concentration over a short time duration. A ‘short time’ is defined relative to the life-span of the test organism. The types of effects or ‘end points’ which are measured in an acute test are lethality (e.g. the LC50). However, sub-lethal end points that illustrate adverse effects (e.g. the EC50), such as changes in the behaviour of physiology of the test organism can also be reported.

In aquatic toxicity tests, an acute test will usually have a duration of between 48 and 96 hours. The test duration should always be reported with the ecotoxicity value (e.g. 96-hour EC50). In soil toxicity tests the terminology ‘acute’ and ‘chronic’ are infrequently used. Standard test durations may vary between 4 and 28 days.

Acute toxicity values are often converted to estimates of chronic toxicity values using extrapolation factors.

Chronic toxicity tests are usually low-level exposures and conducted over a longer time interval. For example, they may be conducted over the entire life cycle of an organism. Chronic toxicity tests are more realistic reflections of a real environmental exposure. Longer-term tests tend to be more complicated and hence more expensive than acute tests. The types of effects generally measured include reduced growth or reproductive changes. Ecotoxicity values such as the NOEC and the LOEC are mainly generated from chronic data. Where chronic data are not available, LOECs are sometimes derived by applying extrapolation factors to an acute end point such as the LC50. When scanning the toxicity literature for ecotoxicity values, the risk assessor should take care to understand exactly how the values were obtained.

Toxicity Values

Measures of the level (i.e.concentration or dose) of a chemical stressor at which a specific level of toxicity is observed in a receptor (e.g. LC50). Click here for more information.

LD or LC Lethal Dose or Lethal Concentration 

The dose or concentration that produces a specified level of mortality in the test population within a specified time, e.g. LC50 is the median lethal concentration or the concentration of a substance at which 50% of the test population are killed. Typical levels are LC10, LC25, LC50, LC75, LC100.

ED or EC Effective Dose or Effective Concentration  

The dose or concentration that produces a specified level of effect in the test population within a specifed time, e.g. EC50 is the median effective concentration or the concentration of a substance at which 50% of the test population are affected. Typical levels are EC10, EC25, EC50, EC75, EC100.


No observable effect concentration


Lowest observable effect concentration


Uptake, distribution, metabolism and excretion of toxic chemicals within living organisms.

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