The predicted no-effect concentration (PNEC) is the concentration of a chemical which marks the limit at which below no

adverse effect An adverse effect is an undesired harmful effect resulting from a medication or other intervention, such as surgery. An adverse effect may be termed a " side effect", when judged to be secondary to a main or therapeutic effect. The term compl ...

s of exposure in an

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

are measured. PNEC values are intended to be conservative and predict the concentration at which a chemical will likely have no

toxic 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 subs ...

effect. They are not intended to predict the upper limit of concentration of a chemical that has a toxic effect.European Chemicals Bureau. 2003. Technical Guidance Document on Risk Assessment. European Communities. Available online at: https://echa.europa.eu/documents/10162/16960216/tgdpart2_2ed_en.pdf Predicted No Effect Concentration. 2015. Greenfacts. Available online at: http://www.greenfacts.org/glossary/pqrs/PNEC-predicted-no-effect-concentration.htmLei BL, Huang SB, Jin XW, Wang Z. 2010. Deriving the aquatic predicted no-effect concentrations (PNECs) of three chlorophenols for the Taihu Lake, China. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering. 45(14):1823-31 PNEC values are often used in environmental risk assessment as a tool in

ecotoxicology 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 ...

.Manuilova, A. 2003. Methods and Tools Available for Assessment of Environmental Risk. Dantes. Available online at: http://www.dantes.info/Publications/Publication-doc/An%20overview%20of%20ERA%20-methods%20and%20tools.pdf A PNEC for a chemical can be calculated with

acute toxicity Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as ''acute'' toxicity, the adverse effect ...

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 ...

single-species data, Species Sensitivity Distribution (SSD) multi-species data, field data or model ecosystems data. Depending on 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.http://echa.europa.eu/documents/10162/0645f0cb-7880-4d23-acea-27b05ed7de39

Calculation methods

Assessment factor

The use of assessment factors allows for laboratory, single-species and short term toxicity data to be extrapolated to conservatively predict ecosystem effects and accounts for the uncertainty in the extrapolation. The value of the assessment factor is dependent on the uncertainty of the available data and ranges from 1-1000.Van Sprang, P. 2011. Data compilation, selection and derivation of PNEC values for the aquatic compartment Zinc example. OECD. Available online at: http://www.oecd.org/chemicalsafety/risk-assessment/48720427.pdfThe Edinburgh Centre for Toxicology. Accessed 2015. Environmental Risk Assessment. UNEP/IPCS Training Module No. 3. Section B. Available online at:

Acute toxicity data

Acute toxicity Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as ''acute'' toxicity, the adverse effect ...

data includes

LC50 In toxicology, the median lethal dose, LD50 (abbreviation for " lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is ...

and

EC50 ] Half maximal effective concentration (EC50) is a measure of the concentration of a drug, antibody or toxicant which induces a Stimulus%E2%80%93response_model, response halfway between the baseline and maximum after a specified exposure time. Mo ...

data. This data is frequently screened for quality, relevancy and ideally contains data for species in multiple trophic level, trophic levels and/or taxonomic groups. The lowest

in the compiled database is then divided by the assessment factor to calculate the PNEC for that data. The assessment factor applied to acute toxicity data is typically 1000.

Chronic toxicity data

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 ...

data includes NOEC data. The lowest NOEC value in the test dataset is divided by an assessment factor between 10 and 100 dependent on the diversity of test organisms and the amount of data available. If there are more species or data, the assessment factor is lower.

Species sensitivity data

A PNEC may also be statistically derived from a SSD which is a model of the variability in the sensitivity of multiple species to a single toxicant or other stressor.Jin, Xiaowei, J. Zha, Y. Xu, J. P. Giesy, K. L. Richardson, Z. Wang. 2011. Derivation of predicted no effect concentrations (PNEC) for 2,4,6-throchlorophenol base on Chinese resident species. Chemosphere. 86:17-23. Available online at: https://www.usask.ca/toxicology/jgiesy/pdf/publications/JA-624.pdfShaw-Allen, P. and G. W. Suter II. 2012. Species Sensitivity Distributions (SSDs). CADDIS Volume 4: Data Analysis. EPA. Available online at: http://www.epa.gov/caddis/da_advanced_2.html The hazardous concentration for five percent of the species (HC5) in the SSD is used to derive the PNEC. The HC5 is the concentration at which five percent of the species in the SSD exhibit an effect.Wheeler, J. R., E. P. M. Grist, K. M. Y. Leung, D. Morritt, M. Crane. 2002. Species sensitivity distributions: data and model choice. Marine Pollution Bulletin. 45:192-202. Available online at: http://www.biosch.hku.hk/ecology/staffhp/kl/SSD%20model%20data.pdf The HC5 is typically divided by an assessment factor of 1-5. In many cases, SSDs may not exist due to the lack of data on a large number of species. In these cases, the assessment factor approach to derivation of a PNEC should be used.

Field data or model ecosystems

Field data or model ecosystems data includes field toxicity data and

mesocosm thumb , Diagram of a small form closed system mesocosm. A mesocosm (''meso-'' or 'medium' and ''-cosm'' 'world') is any outdoor experimental system that examines the natural environment under controlled conditions. In this way mesocosm studie ...

toxicity. The magnitude of the assessment factor is study-specific in these types of studies.

Applications

Environmental risk assessment

PNEC is used extensively in Europe by the

European Chemicals Agency The European Chemicals Agency (ECHA; ) is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation, Authorisation and Restrict ...

, the

Registration, Evaluation, Authorisation and Restriction of Chemicals Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) is a European Union regulation dating from 18 December 2006. REACH addresses the production and use of chemical substances, and their potential impacts on both human he ...

program and other

toxicology 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 e ...

agencies to assess environmental risk.European Chemicals Agency. 2009. Guidance in a nutshell Chemical safety assessment. Available online at: https://echa.europa.eu/documents/10162/13632/nutshell_guidance_csa_en.pdf European Chemicals Agency. 2008. Guidance on information requirements and chemical safety assessment. Chapter R.10: Characterisation of dose oncentrationresponse for environment. Available online at: https://echa.europa.eu/documents/10162/13632/information_requirements_r10_en.pdf PNEC values can be used in conjunction with

predicted environmental concentration Calculated value of a chemical in the environment on the basis of exposure models such as the European Union System for the Evaluation of Substances (EUSES). Used in the context of Chemical Safety Assessments (CSA) and referenced in Chemical Safet ...

values to calculate a risk characterization ratio (RCR), also called a Risk Quotient (RQ). RCR is equal to the PEC divided by the PNEC for a specific chemical and is a deterministic approach to estimating environmental risk at local or regional scales.MERAG. 2007. Risk characterization: general aspects. Metals Environmental Risk Assessment Guidance. Available online at: https://www.icmm.com/document/253 If the PNEC exceeds the PEC, the conclusion is that the chemical poses no environmental risk.

ECETOC The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) is a scientific, non-profit, non-commercial and non-governmental association. Established in 1978, ECETOC's main objective is to identify, evaluate, and through such knowled ...

. 1993. Environmental Hazard Assessment of Substances. European Centre for Ecotoxicology and Toxicology of Chemicals. Available online at: http://www.ecetoc.org/index.php?mact=MCSoap,cntnt01,details,0&cntnt01by_category=5&cntnt01template=display_list_v2&cntnt01order_by=Number%20Desc&cntnt01display_template=display_details_v2&cntnt01document_id=229&cntnt01returnid=89

Assumptions

Derivation of PNEC for use in environmental risk lacks some scientific validity because the assessment factors are derived empirically. Additionally, PNECs derived from single-species toxicity data also assume that ecosystems are as sensitive as the most sensitive species and that the ecosystem function is dependent on the ecosystem structure.

References

{{reflist Chemical safety Concentration indicators Environmental toxicology