Presentation on theme: "POPs Risk Assessment. RISK ASSESSMENT Module 2 – Risk Assessment Overview of the course This module introduces POPs Risk Assessment, including Quantitative."— Presentation transcript:
POPs Risk Assessment
RISK ASSESSMENT Module 2 – Risk Assessment Overview of the course This module introduces POPs Risk Assessment, including Quantitative Risk Assessment and tiered methodologies. Contents Risk Assessment (RA) Quantitative Risk Assessment (QRA) Conceptual Site Model (CSM) Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity Assessment Risk Characterisation Learning outcomes Understand how risk assessment methodologies can be applied to POPs. Appreciate how a tiered system can be used to understand risk to a population. Pre-requisites Introduction to POPs – Chapter 1 of the manual or e-learning Module 1 Follow-on Course Rehabilitation and Remediation Download the course as a pdf Related information Chapter 5 of the Manual Approximate time for this module 45 mins – 1 hour
RISK ASSESSMENT Introduction As you learnt in module 1, the principle exposure routes are: bio-accumulation inhalation of dust or vapour dermal contact drinking polluted water
RISK ASSESSMENT Introduction Therefore there is a limited set of exposure mechanisms of POPs to humans. The risk assessment approach has 2 stages: 1. To quantify the tolerable intake of POPs from an individual compound and from multiple compounds 2. To 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.
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’.
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.
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.
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 QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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). QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT Quantitative Risk Assessment CSM – Example Using the example shown in the picture below, an example CSM is as follows: QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT Quantitative Risk Assessment: CSM – Example SourcePathwayReceptor PrimarySecondaryTransportExposure Underground petrol tank Soil plume Leaching to water table Aquifer Leaching, groundwater transport Inhalation of vapours Residential offsite property Drum store of pesticide Surface soil Particulates by wind Inhalation of dust Comm. onsite Wind & direct contact Soil Ingestion, dermal Comm. onsite QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT Quantitative Risk Assessment: CSM – Unacceptable Pollutant Linkages Significant 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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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 Standards World Health Organisation Guidelines for Drinking Water Quality Example: 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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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 Assessment Toxicity Assessment QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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: I. source of contamination II. environmental media data e.g. surface soils, groundwater, air etc… III. points of exposure IV. routes of exposure e.g. taking into account transport V. receptor population QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Chemical and Physical Parameters The 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 Matrix For physical and toxicological information EPA CHEMFATE database For mobility information QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Important Chemical and Physical Parameters I. Chemical Name Including CAS No. II. Concentration and what the chemical is used for. III. Physical Properties: e.g. Solubility, Vapour Pressure, Melting Point, etc… IV. Chemical Properties: Flash Point, Flammability V. Toxicological Properties: e.g. Acute Toxicity, Genotoxicity, VI. Ecotoxicological Properties: Acute Toxicity, Chronic Toxicity, Sub-Chronic Toxicity VII. Bioaccumulation potential VIII. Carcinogenic potency QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment Transport mechanisms Having 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 speed Migration of suspended solids/sediments in surface runoff Migration of suspended solid/sediments in surface water Migration of colloids to groundwater and laterally in groundwater Attenuation to sediments, soil matrix. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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) QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. 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’. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT QRA: Tiers 2 & 3: Toxicity Assessment Non-threshold substances In 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: The result is that each chemical is placed into one of the following five categories: AHuman Carcinogen BProbable Human Carcinogen B1indicates limited human evidence. B2sufficient evidence in animals, inadequate or no evidence in humans. CPossible Human Carcinogen DNot Classified as a Human Carcinogen EEvidence of Non- carcinogenicity in Humans The excess lifetime risk is calculated based upon dose- response relationship. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
RISK ASSESSMENT Risk Characterisation Tier 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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity
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. QRA CSM Tier 1 Tiers 2 & 3 Exposure Assessment Toxicity