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Samenvatting Environmental Risk Assessment
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Summary of the course 'Environmental Risk Assessment' (1st Ma IMMITE, Ghent University)
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1. Introduction2. Environmental exposure assessment
2.1. Introduction
2.1.1. Aim of exposure assessment
- Estimate concentration in environmental compartments
- Retrospective: estimation in the past or current → measurements for existing chemicals
- Prospective: estimation in the future → with model predictions
2.1.2. Origin of chemical substances
- Xenobiotic: man-made substances
- Most exposure assessment methods developed for man-made organic substances not e.g., metals
2.1.3. Emission, distribution, exposure and protection targets (compartments)
- Populations and ecosystems on water, soil, sediment and air
- Functioning of STP (sewage waste plant) itself
2.1.4. Processes determining exposure
- External exposure assessment:
• Concentration in water, air, soil, sediment
- Internal exposure assessment:
• Bioconcentration bioaccumulation and biomagnification: concentrations in biota
2.2. Emission
2.2.1. Anthropogenic emissions and sources
- Possible emissions during entire life cycle
• Production, formulation, use, waste phases
- Water treatment as point source to aquatic environment:
• Public STP collect diffuse emissions from private & professional use
• Companies with own wastewater treatment plants (WWTP) → ‘industrial setting’
2.2.2. Exposure scenarios and emission estimation (REACH)
- Exposure scenario (ES):
• Set of conditions that describe how substance is manufactured or used and how exposure to
human and environment is controlled
- ES under REACH: sets out how it can be used in a way that risks are adequately controlled:
• Process descriptions
▪ Including quantity used
• Operational conditions
▪ Including frequency and duration of specified operations
• Risk management measures:
▪ Process and emission control
▪ Personal protective equipment
▪ Good hygiene
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, • Other information relevant for safe use
- Dual role of ES:
1) Provide information for exposure estimation
2) Communication tool to users → safety data sheets (SDS)
- Aim:
• Estimate emission rate of substance to each compartment [kg/day]
- Data needs:
• Quantities produced/ used at each stage of life cycle
• Exposure scenarios (~release factors)
- CSR: chemical safety report
2.2.3. Position of emission estimation in exposure
assessment
- Local scenario 1: industrial settling
• All emission is treated by STP (=WWTP)
• Dilution model: waste to river (adsorption)
• ER = daily use or production*RF
- Local scenario 2: wide dispersive uses
• Emission produced by a town
• ER = daily use or production*RF
- Regional scenario:
• 80% of emission is treated by WWTP, 20% is released into environment without treatment
• Multi-media model: consider multiple compartments
• ER to compartment = daily use or production * RF
2.3. Equilibrium partitioning
2.3.1. Principle
- In systems of more than one phase chemicals migrate until thermodynamic equilibrium
𝐶1
Described with equilibrium partition coefficient: 𝐾12 =
𝐶2
Constant if concentrations are sufficiently low
- Important coefficients:
• Air-water (𝐾𝑎𝑤 )
• Solid-water (𝐾𝑝 or 𝐾𝑑 )
• Octanol water (𝐾𝑜𝑤 )
2.3.2. Equilibrium partitioning: air-water
𝑃𝑠 𝑃𝑎∙𝑚3
- Henry constant: 𝐻 = [ ] with
𝑆 𝑚𝑜𝑙
• 𝑃 𝑠 = vapor pressure [Pa]
• 𝑆 = aqueous solubility [mol/m3]
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, 𝐶𝑎 𝐻
𝐾𝑎𝑤 = =
𝐶𝑤 𝑅∙𝑇
• Ca, Cw = concentration in air, water [mol/L]
• R = gas constant = 8,314 Pa m3 mol-1 K-1
• T = temperature at air-water interface [K]
2.3.3. Equilibrium partitioning: solids-water
𝐶𝑠
- 𝐾𝑝 = = 𝐾𝑑 [L/kg]
𝐶𝑤
- Often assumed that organic carbon (without charge) is dominant sorption phase of solids
𝐶𝑂𝐶
𝐾𝑝 = 𝐾𝑜𝑐 ∙ 𝑓𝑂𝐶 with 𝐾𝑂𝐶 =
𝐶𝑤
• 𝐾𝑂𝐶 = organic carbon-water partition coefficient [L/kg OC]
• 𝑓𝑂𝐶 = organic carbon fraction
• 𝐶𝑂𝐶 = concentration sorbet to OC [mol/kg OC]
- Fraction chemical in dissolved phase in aquatic compartment:
𝐶𝑤 1
𝐹𝑅𝑤𝑎𝑡𝑒𝑟 = =
𝐶𝑡𝑜𝑡 1 + 𝐾𝑝 ∙ 𝐶𝑠𝑠
• 𝐶𝑤 = dissolved concentration in water [mol/L]
• 𝐶𝑡𝑜𝑡 = total concentration in aqueous system (in water + solid phase) [mol/L]
• 𝐶𝑠𝑠 = concentration of suspended solids in aqueous system [kg SS/L]
Formula determined by mass balance:
𝐶𝑡𝑜𝑡 = 𝐶𝑤 + 𝐶𝑠 ∗ 𝐶𝑠𝑠 = 𝐶𝑊 + 𝐾𝑝 ∗ 𝐶𝑠𝑠
2.3.4. Equilibrium partitioning: octanol-water
- Higher 𝐾𝑜𝑤 means: more hydrophobic, more lipophilic = more lipid-soluble
• Lower water solubility
• High log Kow means bio-accumulative (usually not more than 4)
- Relation with water solubility:
log10 𝑆 = − log10 𝐾𝑜𝑤 − 0.01 ∙ (𝑀𝑃 − 25) + 0.5
• With 𝑀𝑃 = melting point [°C]
2.3.5. Physicochemical QSAR’s (quantitative structure activity relationships) based on 𝐾𝑜𝑤
𝐶𝑠 𝐶𝑜𝑐
- 𝐾𝑑 = = 𝑓𝑜𝑐 ∙ = 𝑓𝑜𝑐 ∙ 𝐾𝑜𝑐
𝐶𝑤 𝐶𝑤
𝐶𝑠 = 𝑓𝑂𝐶 ∙ 𝐾𝑜𝑐 ∙ 𝐶𝑤
- Organic carbon has a high capacity to absorb lipophilic components, but not as high as lipids or fats
Compensate: 𝐾𝑜𝑐 = 0.41 ∙ 𝐾𝑜𝑤 → 𝐶𝑠 = 𝑓𝑂𝐶 ∙ 0.41 ∙ 𝐾𝑜𝑤 ∙ 𝐶𝑤
Reduce testing needs and costs
- 𝐵𝐶𝐹 = 𝐾𝑜𝑤
- Disadvantage: always have some degree of uncertainty and extrapolation
- QSAR = acceptable alternatives to experimental data for REACH
OECD (economic co-operation and development) set up principles that should be reaches:
1) Defined endpoint
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, • KOC
2) Unambiguous algorithm
• For example: linear regression
3) Defined domain of applicability
• For example: log KOW = 2-8
4) Appropriate measures of goodness-of-fit, robustness and predictivity
• R2
5) Mechanistic interpretation
• Hydrophobic molecules interacts with hydrophobic phase of the sediments
2.4. Intra- and inter-media transport
2.4.1. Intra- vs inter-media transport
- Intra-media = transport within compartments
• Chemical carried downwind and diluted in air
- Inter-media = transport between compartments
• Atmospheric deposition carries chemical from air to water and soil
- Transport rates ~ properties of the chemical & environmental conditions
2.4.2. Inter-media transport
2.4.2.1. Water-sediment transport
- Figure:
• 1) diffusion 2) settling 3) resuspension
- Net sedimentation = settling – resuspension:
• The higher the Kp, the higher sedimentation rate, and thus higher net sedimentation
▪ More chemicals are bound to the particles, and then they settle
• The higher settling rate and the lower resuspension rate, the higher net sedimentation
▪ Chemicals will settle fast and are less likely to go back to aqueous phase
• The higher the turbulence, the lower the net sedimentation
▪ Turbulence decreases settling rate and increase resuspension rate
• The higher particle concentration (Css), the higher the net sedimentation
▪ More particles for chemicals to sorb to means higher settling rate
2.4.2.2. Soil-leaching
- Soil-leaching depends on:
• Rainfall and water fraction of soil (+)
▪ More rain, means more water (& more chemical) that moves down to the soil
• Partition coefficient, Kp (-)
▪ More chemicals bound to particles, so less leaching
• Water (+) and solid (-) fraction of soil
▪ More water means more leaching
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