1. POPs Risk
Assessment

2. 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

3. 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

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 compounds
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.

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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).
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

11. RISK ASSESSMENT Quantitative Risk Assessment CSM – Example QRA CSM
Using the example shown in the picture below, an example CSM is as follows:
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

12. RISK ASSESSMENT Quantitative Risk Assessment: CSM – Example QRA CSM
Source
Pathway
Receptor
Primary
Secondary
Transport
Exposure
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
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

14. 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

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 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

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 Assessment
Toxicity Assessment
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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 contamination
environmental media data e.g. surface soils, groundwater, air etc…
points of exposure
routes of exposure e.g. taking into account transport
receptor population
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

18. RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment
Key steps involved are:
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

19. 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

20. RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment
Important Chemical and Physical Parameters
Chemical 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, Flammability
Toxicological Properties: e.g. Acute Toxicity, Genotoxicity,
Ecotoxicological Properties: Acute Toxicity, Chronic Toxicity, Sub-Chronic Toxicity
Bioaccumulation potential
Carcinogenic potency
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

22. RISK ASSESSMENT QRA: Tiers 2 & 3: Exposure Assessment
Exposure Data Example
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

23. 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

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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)
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

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’.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity

27. 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:
A Human Carcinogen
B Probable Human Carcinogen
B1 indicates limited human evidence.
B2 sufficient evidence in animals, inadequate or no evidence in humans.
C Possible Human Carcinogen
D Not Classified as a Human Carcinogen
E Evidence 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

28. 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

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.
QRA
CSM
Tier 1
Tiers 2 & 3
Exposure Assessment
Toxicity