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livello medio.
ARGOMENTO: EMERGENZE AMBIENTALI
PERIODO: XXI SECOLO
AREA: DIDATTICA
parole chiave: rischio ambientale marino
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Environmental risk assessment of marine activities – part III
credit to Jan-Bart Calewaert et alii. Original article published by www.coastalwiki.org
Risk Characterisation and Estimation
Risk characterisation consists of integrating the results from the release assessment, exposure assessment and the consequence assessment to produce measures of environmental risks. This may include an estimate of the numbers of measures indicating environmental damage, and the uncertainty involved in these estimates.[4]
In the risk characterisation as described above, PEC incorporates the results of the release and the exposure assessment step while PNEC incorporates the results of the consequence assessment step. Current risk assessment practice compares the PEC with the PNEC for the relevant ecosystem using data from representative species. Implicit in this approach is the assumption that there is a tolerable threshold of any chemical substance in the environment (via the PNEC). An element of precaution is built into the approach via the use of conservative/worse-case assumptions within exposure and effects assessments.[6] The EU practice on risk characterisation involves the calculation of a quotient – the PEC/PNEC ratio. This PEC/PNEC ratio should be calculated for all relevant endpoints. If the PEC/PNEC is less than 1, the substance of concern is considered to present no risk to the environment and there is no need for further testing or risk reduction measures. If the ratio cannot be reduced to below 1 by refinement of the ratio (by gathering of further information and further testing), risk reduction measures are necessary.[4]The PEC/PNEC ratio risk characterisation method does not allow us to assess the effective risk expressed in e.g. terms of number of affected individuals or reduced population density in a specific region resulting from a particular activity.
An overall estimation of risk can be defined as the multiplication of the consequence for each damage-causing event with the frequency of that event. The frequency of an event is a result of the hazard identification and release step (e.g. frequency of collisions, powered grounding, etc. within a particular area).
The consequence of a damage-causing event is usually defined as casualty probabilities. This is presented in the PECs (e.g. amount of fuel oil spilled due to collisions at the receptor site), taking into account the relevant PNECs representing the thresholds below which no damage exists for the investigated species (e.g. no effect concentrations of fuel oil in the different relevant marine ecosystem compartments for seagulls).
The population of the species under investigation (e.g. seagulls) present in the areas covered by each probability band is multiplied by the appropriate casualty probability producing the total number of the population predicted to be affected by each event. When combined with the frequency for each event, a risk estimate can be produced for this specific species. This process can be repeated for a number of key species in order to have an overall idea about the risks for the whole ecosystem. Although a quantitative risk assessment approach is preferred, there may be cases where this can not be carried out (e.g. no PEC or PNEC can be properly calculated). Qualitative risk assessment can be used as an alternative. In this case, the risk characterisation shall entail a qualitative evaluation of the likelihood that an effect will occur under the expected conditions of exposure.
The results of the qualitative risk characterisation can be used as a base to prioritise risk reduction measures.
Risk Evaluation
It is the examination of what the characterised risks actually means in practice. What is the significance or value of the identified hazards and estimated risks? Risk evaluation deals with the trade-off between the perceived risks and benefits. This includes acknowledgement of the public perception of the risk and the influence that this will have on the acceptability of risk and risk decisions.
On its turn, the public perception of risk depends on the economic, social, legal and political context in which the affected and/or concerned population lives.[4]The risk evaluation may take account of these perceived risks and benefits and incorporate them in the final risk assessment. The results from this risk evaluation may serve as an input to the risk management process. Based on the acceptable level of risk eventual choices of action are determined needed to achieve the desired level of risk. If a system has a risk value above the risk acceptance level, actions should be taken to address concerned risks and to improve the system though risk reduction measures.
Major approaches to evaluate risks are:
– Professional judgement:
technical experts most knowledgeable in their fields examine the risks and make conclusions based on ‘best judgement’.
– Expert judgement
may be used to estimate probability (step 3 and 4, see 1.3.2 and 1.3.3) and consequence (step 5, see 1.3.5). Based on a ranking of the probability and consequences of the concerned risk, experts may define acceptance levels.
– Formal analysis: Cost-benefit, cost-risk-benefit and decision analysis are the most common of formal analysis techniques for alternative risk management options. In cost benefit analysis and cost-risk-benefit analysis, benefits (e.g. avoided pollution, risk) and costs (cost of pollution reduction or risk reduction measures) associated with a particular risk management option are evaluated against each other.
– Bootstrapping (a resampling technique used to obtain estimates of summary statistics) identify and continue policies that have evolved over time.
– Decision analysis is an axiomatic theory for making choices in uncertain conditions.
Professional judgement is a qualitative approach, while Formal analysis and Bootstrapping are both defined as quantitative approaches. For each of these approaches different methods exist. It is argued that society achieves a reasonable balance between risks and benefits only through experience.
The safety levels achieved with old risks provide the best guide as to how to manage new risks.
UNCERTAINTY
Uncertainty is inherent to all risk assessments. It is important to assess the magnitude of the uncertainty to determine the “relevance” of the quantified risk.
Risks associated with a specific risk source and receptor and under pre-specified surrounding conditions will be expressed in terms of a range (with a lower and upper bound) rather than a single figure. The best estimate of risk is situated between the upper and lower bound. Comparing the magnitude of this range with the best estimate gives an idea about its relevance or value. Knowing the uncertainty is also important to ensure that the input of the results into the risk evaluation step is realistic (i.e. using cost benefit analysis methods) and thus to ensure that appropriate risk management decisions are made.[1] (MCA, 2003).
Sources of uncertainty
There are several potential sources of uncertainty. These include:
– Uncertainty inherent to the used methods in each of the ERA steps (e.g. choice of model, assumptions made in used models);
– Uncertainty related to the collected data and parameters (e.g. gaps in historic/recent data, use of data from other situations and extrapolations to fill out gaps);
– Idiosyncrasies of the analyst: interpretation of ambiguous or incomplete information , human error;
– Uncertainty about the future (e.g. improved techniques and management to prevent and control pollution: improved ship structure, training of crew, adaptation of shipment routes according to pollution sensitivity areas, improved emergency plans, etc.).
The applicability of historical data to the current situation
The net result is often a lowering of the risk over a period of time. However such changes are usually very slow to occur and often have a minimal impact on accident statistics. In the shipping industry in particular there is unlikely to be a sudden step-change in overall risk levels as vessels are likely to trade for over 20 years and practices evolve rather than being replaced by entirely novel methods. It is thus expected that this will have a small impact on the uncertainty inherent in the analysis (MCA, 2003).
Uncertainty in the completeness of the data
Hazard identification
It is extremely unlikely that every accident will be reported. This will lead to an historical risk level that is lower than the risk in reality. This is expected to be the major cause of uncertainty in the estimation of the base case risk levels. The shipping industry is very diverse, and there is no central body to which all accidents must be reported. However, there are a number of organisations which do collect shipping accident data and it is very likely that major accidents, particularly those involving loss of life, or major pollution will be known by those organisations. It is thus expected that, whilst there will be some uncertainty in the results, the high risk areas will have been adequately identified (MCA, 2003).
Exposure and Consequence assessment
The consequence and exposure steps are one of the most important areas in which completeness of data are problematic. An example is the need of extrapolation from laboratory experiments to the field, acute to chronic effects and for inter and intra species variations because of lacking data, especially in risks assessment in marine environments. These extrapolations entail additional uncertainty which is dealt with by the introduction of assessment or safety factors.
Methods to assess uncertainty
Quantifying all sources of uncertainty is difficult (especially idiosyncrasies of the analyst). Methods for estimating the uncertainty are for example statistical analysis (for uncertainty related to data and parameters and models), expert judgement (for uncertainty related to models) and sensitivity analysis (for uncertainty related to future trends). Uncertainty should be assessed for each of the ERA steps. When passing on results to other steps in the methodology, it is important that the uncertainty bounds are passed also, along with information on the key areas of uncertainty and what effect they might have on the risk levels.
References
- Wilcox R. LT. Burrows M. CDR. Ghosh S. and Ayyub B. M. (2000). Risk-based Technology for the Safety Assessment of Marine Compressed Natural Gas Fuel Systems. International Cooperation on Marine Engineering Systems/The Society of Naval Architects and Marine Engineers. Paper presented at the 8th ICMES/SNAME New York Metropolitan Section Symposium in New York, May 22-23, 2000.
- Stern P. C. and Fineberg H. V. (eds.) (1996). Understanding Risk – Informing Decisions in a Democratic Society. Committee on Risk Characterization, Commission on Behavioural and Social Sciences and Education – National Research Council.
- Covello, V.T. and Merkhofer, M.W. (1993). Risk Assessment Methods Approaches for Assessing Health and Environmental Risks. Plenum, New York
- Fairman R., Mead C. D. and Williams W. P. (1999). Environmental Risk Assessment – Approaches, Experiences and Information Sources. Monitoring and Assessment Research centre, King’s College, London. Published by European Environment Agency – EEA Environmental issue report No 4.[1]
- MacDonald A., McGeehan C., Cain M., Beattie J., Holt H., Zhou R. and Farquhar, D. (1999). Identification of Marine Environmental High Risk Areas (MEHRA’s) in the UK. Department of the Environment, Transport and the Regions, ST-87639-MI-1-Rev 01, London, UK.
- ECOTOC (2001). Risk Assessment in Marine Environments. Technical Report No. 82. ISSN -0773- 8072-82. European Centre For Ecotoxicology and Toxicology of Chemicals, Brussels.
See also
- References for environmental risk assessment
- Case study risk analysis of marine activities in the Belgian part of the North Sea
Le Roy D., Volckaert A., Vermoote S., De Wachter B., Maes F., Coene J. and Calewaert JB. (2006). Risk analysis of marine activities in the Belgian Part of the North Sea (RAMA). Research in the framework of the BELSPO Global change, ecosystems and biodiversity – SPSDII, April 2006, 107 pp + Annexes. Available at [2]
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