2 RISK ASSESSMENT Module 2 – Risk Assessment Overview of the course This module introduces POPs Risk Assessment, including Quantitative Risk Assessment and tiered methodologies.ContentsRisk Assessment (RA)Quantitative Risk Assessment (QRA)Conceptual Site Model (CSM)Tier 1Tiers 2 & 3Exposure AssessmentToxicity AssessmentRisk CharacterisationLearning outcomesUnderstand how risk assessment methodologies can be applied to POPs.Appreciate how a tiered system can be used to understand risk to a population.Pre-requisitesIntroduction to POPs – Chapter 1 of the manual or e-learning Module 1Follow-on CourseRehabilitation and RemediationDownload the course as a pdfRelated informationChapter 5 of the ManualApproximate time for this module45 mins – 1 hour
3 RISK ASSESSMENT Introduction As you learnt in module 1, the principle exposure routes are:bio-accumulationinhalation of dust or vapourdermal contactdrinking polluted water
4 RISK ASSESSMENT Introduction Therefore there is a limited set of exposure mechanisms of POPs to humans. The risk assessment approach has 2 stages:To quantify the tolerable intake of POPs from an individual compound and from multiple compoundsTo assess the amount of POPs that an individual, within a population, is exposed to from various sources.This Risk Assessment methodology can be applied to the quantification of health and environmental risks from POPs. On the basis of the risk assessment a rehabilitation strategy and programme of works may be initiated.
5 RISK ASSESSMENT Risk Assessment – Introduction There are various methodologies, backed by modelling systems, available to assess the risks from exposure to contaminants.These mainly rely on assessing toxic and excess carcinogenic risk to a theoretical population as a result of a source concentration migrating via a potential exposure pathway. The mechanism is termed Source-Pathway-Receptor.The complete link between the source, pathway and receptor is known as a ‘pollutant linkage’.
6 RISK ASSESSMENT Risk Assessment – Methodology The modelling of environmental and human population risk is termed Quantified Risk Assessment (QRA) and can be undertaken at a number of levels or Tiers, depending on how complex or site specific the modelling is.International practice is:Tier 1 – using simple scientific or economic/political screening values.Tier 2 – a theoretical, generic, population predictive level.Tier 3 – a single at risk population predictive level.
7 RISK ASSESSMENT Risk Assessment – Main Problems The main problems are: That only a very limited spectrum of the possible exposure pathways can actually be modelled.Food chain uptake of POPs is the most sensitive pathway, but modelling population bio-accumulation is not advanced and experimental data is sparse.The movement of POPs contaminated soils and sediments on both a local and regional scale occurs making it a diffuse rather than a point source. Careful attention is needed from a modelling perspective.
8 RISK ASSESSMENT Quantitative Risk Assessment (QRA) Quantified Risk Assessment offers a repeatable, reproducible and widely available methodology to assess the environmental risks associated with exposure to POPs.Some widely used tools are:US EPA approved - Risk Based Corrective Action Toolkit for Chemical Releases (E )For source contaminant migration within fractured and porous media, soils and rocks, an applicable tool is MODFLOW 2000.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
9 RISK ASSESSMENT Quantitative Risk Assessment: Conceptual Site Model (CSM)A conceptual site model is the first stage, the preliminary stage, of risk assessment.This determines whether there are any potentially unacceptable risks associated with an area of land.It involves the first qualitative assessment encompassing hazard identification and assessment, where a hazard is any property or situation, in this case a POP, which may lead to harm, of human health, ecosystems, etc.Example: US EPA SCEM Builder (the Site Conceptual Exposure Model Builder).QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
10 RISK ASSESSMENT Quantitative Risk Assessment CSM – Methodology For a specific site data can/should be collected:Identify hazards posed by the POPs sources.Any field or literature evidence of pathways and potential receptors.This information is put together and forms the Conceptual Site Model.The hazard can then be assessed.This overview is a simplification of reality that aims to identify the key potential sources, pathways and receptors and their interactions or linkages.It may be a text description, a table, a drawing or a computer model.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
11 RISK ASSESSMENT Quantitative Risk Assessment CSM – Example QRA CSM Using the example shown in the picture below, an example CSM is as follows:QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
12 RISK ASSESSMENT Quantitative Risk Assessment: CSM – Example QRA CSM SourcePathwayReceptorPrimarySecondaryTransportExposureUnderground petrol tankSoil plumeLeaching to water tableAquiferLeaching, groundwater transportInhalation of vapoursResidential offsite propertyDrum store of pesticideSurface soilParticulates by windInhalation of dustComm. onsiteWind & direct contactSoil Ingestion, dermalQRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
13 RISK ASSESSMENT Quantitative Rik Assessment CSM – Pollutant Linkages Pertinent questions to ask:Do sources identified in the Conceptual Site Model link through an identified path, to a receptor?Is there the potential for the pathway to exist and thus link the source and receptor?At this stage these are potential pollutant linkages.These will require modelling to see if they become potential relevant or significant pollutant linkages.The pollutant linkages can be sorted as posing an unacceptable or acceptable risk.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
14 RISK ASSESSMENT Quantitative Risk Assessment: CSM – Unacceptable PollutantLinkagesSignificant Pollutant Linkages can be input into a Tier 1 screening. They become Unacceptable Pollutant Linkages, i.e. pose a risk to the population, when the exposure exceeds the screening values set at Tier 1.Tier 2 or 3 assessments can be undertaken where Unacceptable Pollutant Linkages can be found.This identification of linkages will help the definition of intrusive investigation, sampling and analyses, and will therefore determine the financial costs.Receptors identified within the Conceptual Site Model will determine the sensitivity of further assessment.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
15 RISK ASSESSMENT Quantitative Risk Assessment Tier 1 The identified hazard, in this case the source concentration, is compared against a national or international standard or guideline value e.g.EU Drinking Water StandardsWorld Health Organisation Guidelines for Drinking Water QualityExample: The source concentration of POPs in soil, air or water being compared against a standard protective of human health or possibly aquatic life/livestock drinking waters.Note: Many POPs are banned internationally so no standards or guideline values have been set.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
16 RISK ASSESSMENT Quantitative Risk Assessment: Tiers 2 & 3 The procedure for Tiers 2 and 3 is identical, but the populations are different. See definition of tiers.Site characterisation is carried out, and data collected for the CSM, the pollutant linkages can be quantified in detail. This involves:Exposure AssessmentToxicity AssessmentQRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
17 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Analysis of laboratory and field data will allow identification of the potential POPs hazards at the site in question, in terms of human health or ecological effects. The hazard will not constitute a risk unless the population is exposed and the duration of exposure identified.Therefore the data required are:source of contaminationenvironmental media data e.g. surface soils, groundwater, air etc…points of exposureroutes of exposure e.g. taking into account transportreceptor populationQRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
19 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Chemical and Physical ParametersThe chemical and physical properties of contaminants (POPs) can be assessed and identified, which determine the transport, bioaccumulation or environmental fate of POPs.Online databases can be used, e.g.EPA Superfund Chemical Data MatrixFor physical and toxicological informationEPA CHEMFATE databaseFor mobility informationQRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
20 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Important Chemical and Physical ParametersChemical Name Including CAS No.Concentration and what the chemical is used for.Physical Properties: e.g. Solubility, Vapour Pressure, Melting Point, etc…Chemical Properties: Flash Point, FlammabilityToxicological Properties: e.g. Acute Toxicity, Genotoxicity,Ecotoxicological Properties: Acute Toxicity, Chronic Toxicity, Sub-Chronic ToxicityBioaccumulation potentialCarcinogenic potencyQRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
21 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Exposure Data The routes of exposure are considered at this point. This is the consideration of all intake pathways. As stated previously this may involve drinking water, food chain uptake via meat and crops, direct ingestion of soil and dermal contact.The example on the next page shows the exposure pathways for bio-accumulation.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
23 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Transport mechanismsHaving thoroughly identified the primary source media, e.g. air, soil, groundwater, surface water, which will contribute to transport of contaminants, it is necessary to determine the transport mechanisms.The main transport pathways are:Migration of dust in air dependant on particle size and wind speedMigration of suspended solids/sediments in surface runoffMigration of suspended solid/sediments in surface waterMigration of colloids to groundwater and laterally in groundwaterAttenuation to sediments, soil matrix.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
24 RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment The previous steps are normally input to a model to determine the variation of concentration over time at the receptors, e.g. groundwater, air, etc…This leads to the identification of the Exposure Factors:Exposure frequency - the amount of time an individual or organism is in contact with POPs contaminated medium.Exposure duration – how long the population has been exposed to POPs or is likely to be exposed.Contact Rate – this is the amount of POPs contaminated material contacted or ingested per unit time.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
25 RISK ASSESSMENT QRA: Tiers 2 & 3: Toxicity Assessment From the determined exposures the toxicity assessment is undertaken to calculate the lifetime excess risk.This step involves assessing the potential harm to human health from the identified contaminants (POPs) in soil by comparing exposure information against health criteria, which is a threshold value, e.g.In the UK – Tolerable Daily Intakes (TDIs)Elsewhere – Acceptable Daily Intake (ADI)QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
26 RISK ASSESSMENT QRA: Tiers 2 & 3: Toxicity Assessment Tolerable daily intake is an estimate of the amount of a contaminant, expressed on a body weight basis, that can be ingested daily over a lifetime without appreciable health risk.In this definition ‘tolerable’ should be taken to mean ‘permissible’ rather than ‘satisfactory’.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
27 RISK ASSESSMENT QRA: Tiers 2 & 3: Toxicity Assessment Non-threshold substancesIn the case of carcinogens or non-threshold substances, they are first classified on a weight-of–evidence approach.The result is that each chemical is placed into one of the following five categories:A Human CarcinogenB Probable Human CarcinogenB1 indicates limited human evidence.B2 sufficient evidence in animals, inadequate or no evidence in humans.C Possible Human CarcinogenD Not Classified as a Human CarcinogenE Evidence of Non-carcinogenicity in HumansThe excess lifetime risk is calculated based upon dose-response relationship.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
28 RISK ASSESSMENTRisk CharacterisationTier 2 and 3 assessment quantifies the risk in terms of excess risk to health. Example, a 1% average increase in risk over a lifetime for a population.Once the risk of the POP has been calculated, its impact on the population under risk can be evaluated.This process involves an assessment of the pollutant linkages, the amount that the risk is exceeded and the possible measures that could be put in place given the concentration of the source POP and the calculated risk level.The level of risk that is considered acceptable may be based on socio-political judgements. For excess cancer risk values of between 10-4 and 10-6 are generally considered.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity
29 RISK ASSESSMENT Limitations in Risk Assessment Modelling Most models make assumptions which give rise to highly conservative predictions. This precautionary approach can lead to unnecessary actions using up scarce resources that could be better applied elsewhere.The use of risk modelling must be seen as an attempt to quantify environmental risk and as an aid to decision making, rather than a definitive process of measuring likely risks and quantifying effects.True assessment of risks of POPs (or any other contaminant), on a population requires a detailed medical study and long term monitoring.QRACSMTier 1Tiers 2 & 3Exposure AssessmentToxicity