Methodology for Exposure and Risk Assessment in Complex Environmental Pollution Situations
Summary (5 min read)
1. Introduction
- Environmental risk assessment refers to the quantitative and qualitative evaluation of the risk posed to human health and/or to the environment by the actual or potential presence and exposure to particular pollutants.
- An accurate site-specific assessment requires knowledge of contaminant form and how it enters in the environment; environmental conditions affecting contaminant (meteorological conditions, soil chemistry, water and sediment chemistry, etc.); presence of plants or animals contaminant bioaccumulation; pathways and routes of exposure to human or ecological receptors and the effects of the contaminant in the target receptor (EPA, 2007).
- Risk assessments vary widely in scope and application.
- It includes human health risk assessments, ecological risk assessments and specific industrial applications of risk assessment that analyze identified endpoints in people, biota or ecosystems (Fairman et al., 1998).
- Applied industrial applications have been separated as many of these assessments do not look in isolation at people or ecological systems.
2. Risk Assessment Methodology
- More specifically, an environmental risk assessment is an analysis of the potential for adverse effects caused by contaminants of concern from a site to determine the need for remedial action or to develop target levels where remedial action is required.
- It involves analyzing the sources of a release, the mechanisms of chemical transport and the potential health risks to receptors.
- Often the methodology for exposure and risk assessment to environmental pollution is translated into sets of assessment questions throughout the several stages of risk assessment (planning and problem formulation, exposure analysis and interpretation and risk characterization) (EPA, 2007).
- These questions are used to meet the needs of assessment, particular important in focusing the assessment during the problem formulation.
- Each one of this step will be discussed in detail in the following sections.
2.1. PROBLEM FORMULATION
- In the first step the problem must be formulated and certain tasks must be clear before the assessment proceeds.
- The risk source will generate hazards that may be released into the environment contributing to the transport, transfer and fate processes through the atmosphere, subsoil, underground and superficial aquatic systems, leading to the contamination of new environmental sub-compartments.
- During the problem formulation stage the following planning and scoping activities should also be included (EPA, 2007): Define the geographic scale and scope of the assessment; Identify potentially exposed populations and sensitive subpopulations; Characterize exposure pathways and exposure routes that will represent the conceptual model; Describe how exposure will be assessed;.
- Determine how the hazard and the receptor’s dose-response will be assessed; Describe how risks will be characterized.
2.2. HAZARD IDENTIFICATION
- Hazard identification involves the identification of those agents that could possibly cause harm to the receptor (people, organisms or ecosystems), specifying how this harm could occur.
- The methods by which hazards are identified depend on the nature of the hazard and may include toxicological testing, examination of accident rates and epidemiological studies.
- Brainstorming examinations of a process or a procedure, carried out in a small team with a chairman asking questions, also known as What if technique.
- Fault trees analyses: diagram that illustrates combinations of failures that will cause one specific failure or interest, the “top event”; the root is the main event and possible causes of the event are traced back to several initiating events;.
- For the conceptual model several inputs will be needed in order to gather information about the transport of contaminants and chemicals, the target exposed population and the way exposure changes in time.
2.3. RELEASE ASSESSMENT
- A release assessment involves the identification of the risk potential source to introduce hazardous agents into the environment.
- This may be descriptive or involve the quantification of the release.
- It should identify the types of releases, its mechanism, the amount released, timings and probabilities of the release occurrence and a description of how these attributes might change in space and in time as a result of various actions or events (Fairman et al., 1998).
- The likelihood or probability of a release of hazards in a non-quantitative way may be given by “Expert judgment”; based on the results of the hazard identification.
- The likelihood is divided in different categories in terms of expressions such as: likely, may occur, not likely and very unlikely (Wilcox et al., 2000).
2.4. EXPOSURE ASSESSMENT
- Exposure assessment is probably the most variable aspect of the risk assessment process.
- The exposure assessment step requires the use of monitoring data, exposure modelling techniques and also mapping models.
- The aim of this stage is to produce a complete picture of how, when, and where the exposure occurs or has occurred, by evaluating sources and releases and the extent and pattern of contaminant contact with humans or ecologically relevant biota.
- (days per year and the number of years exposed).
2.5. CONSEQUENCE OR EFFECTS ASSESSMENT
- A consequence assessment analyzes the effects of the release or the production of the hazards to the specified receptors, and it involves quantifying the relationship between specified exposures to the hazard, health and the environmental effects of those exposures.
- The effects observed in ecological systems are much more varied and few defined end-points exist at present.
- The consequence assessment should describe how the effects are elicited, link them to the receptor at greatest risk and evaluate how they change with varying exposure levels.
- Ecotoxicity tests will generate the PNEC values.
- As a check procedure during this step, the authors should be able to answer to these questions:.
2.6. RISK CHARACTERIZATION AND ESTIMATION
- Risk characterization and estimation consists of integrating the results from the release assessment, exposure assessment and consequence assessment to produce measures of environmental risks.
- But if this 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 (Fairman et al., 1998).
- Sometimes a quantitative risk assessment approach can not be carried out (no PEC or PNEC can be properly calculated).
- In these cases, a qualitative risk assessment can be used as an alternative in which the risk characterization shall include a qualitative evaluation of the likelihood that an effect will occur under the expected conditions of exposure.
2.7. RISK EVALUATION
- Risk evaluation represents the evaluation of what risk assessment actually means in practice.
- Risk evaluation deals with the trade-off between the perceived risks and benefits.
- 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 (Fairman et al., 1998).
- Based on the acceptable level of risk, eventual choices of action are determined 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.
2.8. UNCERTAINTY
- Uncertainty is inherent to all risk assessments.
- Risks associated with a specific risk source and receptor, under pre-specified surrounding conditions, will be expressed in terms of a range (with a lower and upper bound) rather than a single figure.
- Knowing the uncertainty is also important to ensure that the input of the results into the risk evaluation step is realistic and thus to ensure that appropriate risk management decisions are made (Calewaert, 2006).
- Quantifying all sources of uncertainty is difficult.
- Uncertainty should be assessed for each one of the ERA steps.
3.1. APPROACH OVERVIEW
- This section describes the methodology applied to calculate lifetime cancer incidence risk and non-carcinogenic health effects resulting from exposure to radionuclides and chemicals released from a contaminated site during a certain period of time.
- Food crops (leafy and non-leafy, vegetables, grains, fruits); viii) Vegetation (mainly pasture grass) and ix) Animal products (milk, meet, eggs, etc.) (EPA, 1998).
- Models developed previously were used to estimate radionuclide or chemical concentrations in soil and biota, as well as concentrations in vegetation and in milk, from radionuclide or chemical concentration in air, surface water and groundwater.
- Intake and exposures implicit refer to the various locations of exposure as well as to the fraction of time spent at each location.
- Risks are also summed separately for radionuclides, carcinogenic chemicals and non-carcinogenic chemicals.
3.2. SITE CHARACTERIZATION
- As a reference site to apply the risk assessment methodology, a contaminated site from a former Portuguese uranium mine was selected.
- This mine was located in the central part of Portugal and it was exploited for almost a century, first for radium production (1913-1944) and then for uranium concentrates production (1951-2000).
- The mine is surrounded by small houses and country houses, with most of the local population living in a village within about 2 km from the mine.
- A tailing disposal is located near the mine; the liquid effluents, after neutralization and decantation, were discharged into a streamlet flowing to the Mondego river (Bettencourt et al., 1990).
- The contaminated site represents an area of 13,3 ha and until a very recent past radionuclides and chemicals have been released to the air, soil, surface water and indirectly to groundwater as a result of routine operations, accidents and waste disposal practices.
3.3. ENVIRONMENTAL MEDIA CONSIDERED
- An environmental medium is defined as a discrete portion of the total environment that may be sampled or measured directly such as soil, sediment, groundwater, surface water or air (Rood, 2003).
- Environmental media considered in this study that humans may be exposed or consume are: Air; Groundwater; Soil; Food crops; Animal products.
3.4. EXPOSURE ROUTES
- An exposure route is the manner through which a material of concern comes into contact with a human receptor (Rood, 2003).
- Exposure routes that may be considered in this methodology are: Inhalation; Ingestion; Dermal contact with soil and water; Irradiation from air; water, soil and dry sediments (radionuclides only).
3.5. EXPOSURE PATHWAYS
- An exposure pathway is the course that a substance of concern takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it.
- Air (physical transport as advection and dispersion); transfer between media can occur – transport media; Surface soils (transfer between media can occur but transport within the medium is not considered – static medium); Animal products (environmental medium for biota; transport within the media is not considered), also known as Environmental media.
- Ingestion; Inhalation; External radiation; Immersion; Dermal contact, also known as Human exposure routes.
- The intake or exposure from each exposure route is multiplied by an appropriate factor relating intake or exposure to risk.
3.6. CONCENTRATIONS AT POINTS OF EXPOSURE IN EACH ENVIRONMENTAL MEDIA AND EXPOSURE SCENARIO DEFINITION
- As a starting point it is assumed that there are measured or modeled concentrations of radionuclides and chemicals in environmental media.
- Concentrations in air, surface water or groundwater transport media are required.
- The receptor may consume water from a private well; groundwater or surface water may also be used to irrigate crops and livestock; Specific health-effects estimates include: incremental lifetime cancer incidence risk from radionuclides; incremental lifetime cancer incidence risk from chemicals and non-carcinogenic effects from chemicals.
3.7. RISK CALCULATION
- For each of one of these cases the authors will consider only the internal exposure by inhalation and ingestion.
- For internal exposure the total risk will be the sum of the risk by inhalation, soil ingestion, water ingestion and foodstuff ingestion.
- The resulting annual cancer risk from indoor radon inhalation is 2,42 x 10 -4 .
- For a long-term chronic ingestion of radium-226 during 75 years the incremental lifetime cancer risk is of 3,42 x 10 -4 which means an incremental risk of one in ten thousand.
- Inhalation of beryllium may result in rhinitis, tracheobronchitis, pneumonitis and death due pulmonary edema or heart failure.
4. Discussion and Conclusions
- The focus of this study was to exemplify how to apply a risk assessment in some of its components.
- A life expectancy of 75 years was assumed to carcinogenesis effects.
- Radionuclide and chemical concentration in soil, air and groundwater, were needed along with parameters describing the exposure scenario.
- The exposure pathways included in this risk assessment represent some of the exposure pathways that may be present in a contaminated site with radioactive materials and heavy metals; however is not an exhaustive list of potential exposure pathways.
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6 citations
"Methodology for Exposure and Risk A..." refers background or methods in this paper
...Transfer of radionuclides and chemicals from a transport media to static media (soil and biota) were performed in the modeling work developed before and published (Dinis and Fiúza, 2007)....
[...]
...…as for leafy vegetables consumption with the following inputs: milk concentration, Cmilk = 0,029 Bq/L (modeled for a similar contaminated site) (Dinis and Fiúza, 2007); milk ingestion rate, Umilk,ing = 0,615 L/d (EPA, 1997); risk coefficient for milk ingestion, RCfood,ing = 1,38919 x 10 -8 Bq…...
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...This example intends to focus on the risk assessment methodology; the exposure models have been developed and published already (Dinis and Fiúza, 2005; 2006; 2007)....
[...]
...The risk is estimated by the same expression as for leafy vegetables consumption with the following inputs: milk concentration, Cmilk = 0,029 Bq/L (modeled for a similar contaminated site) (Dinis and Fiúza, 2007); milk ingestion rate, Umilk,ing = 0,615 L/d (EPA, 1997); risk coefficient for milk ingestion, RCfood,ing = 1,38919 x 10 -8 Bq -1 (EPA, 1995); exposure frequency, Ef = 365 d/year and considering that all ingested milk comes from the farm cows and is contaminated, fmilk = 1....
[...]
...Radionuclide in leafy vegetables was measure but cow’s milk concentration was modeled from pasture ingestion contaminated by soil, air and groundwater in an appropriate exposure scenario (Dinis and Fiúza, 2007)....
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6 citations
6 citations
"Methodology for Exposure and Risk A..." refers methods in this paper
...This example intends to focus on the risk assessment methodology; the exposure models have been developed and published already (Dinis and Fiúza, 2005; 2006; 2007)....
[...]
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Frequently Asked Questions (9)
Q2. What were the parameters needed to describe the exposure scenario?
Radionuclide and chemical concentration in soil, air and groundwater, were needed along with parameters describing the exposure scenario.
Q3. How many ha of contaminated soil are there?
The contaminated site represents an area of 13,3 ha and until a very recent past radionuclides and chemicals have been released to the air, soil, surface water and indirectly to groundwater as a result of routine operations, accidents and waste disposal practices.
Q4. What is the current plan for a tailings reclamation scheme?
a rehabilitation plan based on an in-situ reclamation scheme to promote the confinement of the tailings materials is under implementation as well as a wastewater treatment system implemented in the mining area (Nero et al., 2005).
Q5. How many people are affected by contaminated leafy vegetables?
The total incremental cancer risk incurred by the ingestion of contaminated soil, water, leafy vegetables and milk is 1,81 x 10 -3 , which means an excess risk of one in one thousand mainly due to leafy vegetable ingestion and water ingestion.
Q6. What is the definition of a release assessment?
A release assessment involves the identification of the risk potential source to introduce hazardous agents into the environment.
Q7. What are the main sources of uncertainty in the ERA?
Uncertainty can arise from several potential sources (Calewaert, 2006): Uncertainty inherent to methods used in each of the ERA steps: choice ofmodel, assumptions made in used models, uncertainties related to the model structure itself as the lack of confidence that the mathematical model is an adequate representation of the assessment problem; Uncertainty related to the collected data and parameters: gaps inhistoric/recent data, use of data from other situations and extrapolations to fill out gaps, variability of a model parameter from its true heterogeneity over space and time, uncertainty of a model parameter resulting from the lack of information or knowledge about its true value; Uncertainty of the analyst: interpretation of ambiguous or incompleteinformation, human error, uncertainty of how an assessor translates a real or forecasted situation in a given model.
Q8. What is the hazard quotient for beryllium exposure?
The resulting hazard quotient to quantify the noncarcinogenic health effects incurred by beryllium inhalation is HQ = 0,05 which is inferior to one; the exposure to beryllium in this scenario does not pose any risk.
Q9. What is the effect of the public perception of risk?
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 (Fairman et al., 1998).