04 - episuite - physical-chemical properties and environmental fate

Sustainable Futures Hands-On Training in the P2 Framework & PBT Profiler ModelsPhysical-Chemical Properties – EPISuite

1

EPISuite™: Physical -Chemical Properties and

Environmental Fate Assessments

Physical/Chemical Properties Assessment

• Provides characteristics used throughout the risk assessment process Physical state

EPI Suite™: Physical - Chemical Properties and Environmental Fate Assessments 2

Physical state

Environmental fate

Toxicity

Routes of exposure• Human and environmental

Physical/Chemical Properties Assesment

• Common Properties Melting point (MP) Boiling point (BP) Vapor Pressure (VP)


p ( ) Water Solubility (WSol)

• Less Common Properties Octanol/water partition coefficient (Kow or P) Henry’s Law Constant (HLC) Dissociation constant (pKA or pKB)


2

Overview of Presentation

• Introduction to EPI Suite™ estimation methods

• Discussion of each physical property What it is


What it is What it can tell the assessor Interpreting the results

• Hands on session for three sample chemicals after completion of Fate Properties

Predictive and Experimental Data

• Reliable experimental data are always preferred over estimated data

EPI S it TM i t l d t t


• EPI SuiteTM can use experimental data to improve the estimations of the other properties

• A list of sources for experimental data is provided in the P2 Framework Manual, Appendix B

EPI Suite™ - Introduction

• P2 Framework tool developed over the past 25 years to screen new chemicals lacking experimental data

• New Version EPIWEB 4.1 Released February 2011


• Provides 3 types of results Physical/chemical (P/Chem) properties Environmental fate properties Environmental fate models

• Free!! (http://www.epa.gov/oppt/sf/tools/methods.htm )


3

EPI Suite™ - V 4.1 Updates

• New version includes many updates User interface updates

Enhanced QSARs for many modules

Additional classes for hydrolysis predictions Additional classes for hydrolysis predictions• Including additional classes and data in the help section

Structure drawing program• Structure searchable data files

Link to pKa calculation (SPARC)

Links to additional data sources• Including Fate and Ecotoxicity data resources


EPI Suite™ - Built in Databases

• EPI Interface is linked to SRC’s PHYSPROP Database Contains >25,000 chemicals with experimental data:

• MP 10,800 • VP 2,837• BP 6,629 • pKA 1,652• WS 6,340 • HLC 1,713


• Kow 13,500

Available experimental data are automatically retrieved if available in the built in database

Identified data can be automatically added to assessment or entered manually

• Databases now searchable by structure• For liquids with unknown MP, enter an MP of 20 °C

EPI Suite™ - Modules

• EPI – Estimation Programs Interface

EPI SuiteTM is a computer platform that houses 13 different predictive modules plus


houses 13 different predictive modules, plus link to ECOSAR.

A user can run EPI Suite and retrieve predictions for ALL modules

Or, modules can be run individually


4

Physical / Chemical Physical / Chemical Property AssessmentsProperty Assessments


p yp y

Physical/Chemical Properties

• Provides Basic information on the nature and characteristics

of a chemical substance


• Which gives insight into: Partitioning in the environment

Potential for environmental exposure

Potential routes of human exposure

Toxicity and biological effects

EPI Suite™ P/Chem Modules

• EPI – Estimation Programs Interface MPBPVP© - Melting point, boiling point, and

vapor pressure


LOGKOW© - Octanol/water partition coefficient

WS/KOW© - Water solubility from Kow

Henry's Law Constant Program© - Air/water partition coefficient

Link to pKa prediction


5

Melting Point and Boiling Point

• Provides physical state MP

• > 25 °C – solid• < 25 °C – liquid


25 C liquid

BP• < 25 °C – gas

• Indicates Environmental partitioning Environmental fate Worker and general population exposure

MP and BP - Interpreting Results

• Environmental partitioning Gases are volatilized in the atmosphere Solids are present in the atmosphere as particulates (dusts) Liquids tend to dissolve more rapidly and have higher water

solubility than high melting organic solids


• Worker and general population exposure Gases through inhalation Liquids through dermal contact

• Lower MP tends to increase absorption through the skin, digestive tract, and lungs

Solids through dermal contact and inhalation of dust Liquids and solids through ingestion

Vapor Pressure

• Vapor Pressure

Provides information on volatility of a substance from dry surfaces


Indicates the physical state in the atmosphere

Can influence other properties (Henry’s Law constant)


6

VP – Interpreting Results

• Environmental Partitioning High VP means more likely to be present in the atmosphere

as vapor VP determines the phase in the atmosphere

• > 10-4 mm Hg - vapor phase


• 10-4 - 10-8 mm Hg – vapor/particulate mixture• < 10-8 mm Hg – particulate

Can be used to gauge the rate of volatilization from soil, plants, and other dry surfaces (see HLC for wet surfaces)

• Exposure < 10-6 mm Hg – lower limit of concern for human inhalation

exposure for vapors (≈ BP of 400 °C)

Octanol/Water Partition Coefficient(Kow or P)

• Provides partitioning between octanol and water Concentration in octanol / concentration in water


Covers a wide range of values• Typically reported in log units (i.e., log Kow)

• Indicates Partitioning in biological systems

Absorption through membranes

Log Kow (cont.)

• Important parameter used by EPI to estimate numerous other properties Water solubility

Bi t ti /Bi l ti


Bioconcentration/Bioaccumulation

Soil adsorption

Aquatic toxicity


7

Log Kow Rules of Thumb

Log Kow Indicates to the Assessor

<1 Highly soluble in water (hydrophilic)

>4 Not very soluble in water (hydrophobic)


>4 Not very soluble in water (hydrophobic)

>8 Not readily bioavailable

>10 Difficult to measure experimentally.

Essentially insoluble in water.

Not bioavailable.

Interpreting Log Kow Results

• Kow indicates partitioning across biological membranes Octanol is used to mimic fat in biological organisms The higher the Kow, the more likely a chemical will partition to

octanol and, therefore, be present in fat The lower the Kow, the more likely a chemical will partition to


e o e t e ow, t e o e e y a c e ca pa t t o towater and, therefore, be present in the body tissues

• Kow indicates absorption through biological membranes Dermal Exposure: Liquids with a log Kow of 2-4 tend to absorb

well through the skin Food/Water Ingestion Exposure: Chemicals with a log Kow of

5-6 tend to bioconcentrate

Water Solubility (WS)

• Provides Degree to which a chemical will dissolve in 1 liter of

water


• Indicates to the assessor Distribution between environmental compartments

Potential for environmental exposure through release to aquatic compartment

Human exposure through ingestion of drinking water


8

Water Solubility (WS)

• Two QSAR models WSKOW

• Accepts experimental Log Kow and MP values


• Accuracy greatly improved if an experimental MP is provided!

WATERNT• Fragment Based Method

• Estimate Accuracy influenced by fragment coverage Fragments are listed for review

WS Rules of Thumb

Water solubility (mg/L) Classification

>10,000 Very soluble


>1,000 – 10,000 Soluble

>100 – 1,000 Moderately soluble

>0.1 – 100 Slightly soluble

<0.1 Insoluble

Interpreting WS Results

• Chemicals with high WS Greater possibility of human and aquatic exposure More likely to be absorbed through GI tract or lungs

Ch i l ith l WS


• Chemicals with low WS Higher potential to bioconcentrate

• Distribution between environmental compartments Higher water solubility indicates partitioning to water

• Possible removal from soil into ground water by rain run-off• Possible removal from atmospheric into ground water by rain

washout


9

Interpreting WS Results

• Potential for exposure Environmental exposure due to presence in

surface water Human exposure through ingestion of drinking

water


water <10-6 g/L (1 ppb) – lower limit of concern for

adverse affects, aquatic exposure, and general population exposure

• Degradation potential Insoluble chemicals may not degrade in the

environment• Microorganisms may be unable to absorb them

Henry’s Law Constant (HLC)

• The ratio of a chemical's equilibrium concentration in the gas phase to that in the aqueous phase


q p Units

• atm-m3/mole (EPI)

• Pa-m3/mole

• Dimensionless (1/40.9 * atm-m3/mole)


• Provides An indication of a chemical’s volatility from

water


• Indicates to the assessor Environmental partitioning Amount removed by stripping in a sewage

treatment plant Environmental exposure


10


• HLC Model/Method Hierarchy Vapor pressure / water solubility estimate

• Best method, but only using experimental VP and WS


Group method estimate• Preferred method (if no VP/WS), but not always provided• Smaller set of fragments, no estimates for many structure

types

Bond contribution method estimate• Larger set of fragments, estimates for many more structure

types

Interpreting HLC Results

• >10-3 atm-m3/mol Rapid volatilization from water to air

• Stripped from sewage treatment plants


• Volatilizes readily from environmental waters

• 10-7 atm-m3/mol is the HLC of water Values <10-7 indicate negligible volatilization

from water to air• Not stripped from sewage treatment plants• Does not volatilize from environmental waters

HLC Rules of Thumb

HLC Classification(Volatility from Water)

≥ 10-1 Very volatile


10-1 – 10-3 Volatile

10-3 – 10-5 Moderately volatile

10-5 – 10-7 Slightly volatile

< 10-7 Nonvolatile


11

Dissociation Constants – pKa/pKb

• Indicates the concentration of the dissociated (ionized) and undissociated (neutral) forms of an acid, base, or organic salt in water

HA H+ + A-


HA H + A

• Indicates to the assessor Many properties - WS, VP, log Kow and HLC trend

as a function of pH

• EPI Web 4.1 Linked to SPARC online calculator

Interpreting pKa/pKb Results

• As the percent ionization increases: Water solubility increases

• Salts tend to be more soluble


Vapor pressure decreases• Salts tend to be less volatile

Henry’s Law constant decreases

Log Kow decreases• Increased partitioning toward water

Environmental FateEnvironmental FateAssessmentsAssessments



12

Environmental Fate Assessment

• How will the chemical behave in the environment? Once released, will the chemical go to air,


Once released, will the chemical go to air, water, soil, sediment

How long will it persist in the environment

How might humans and the environment be exposed to the chemical

Steps in Fate Assessment

• Collect physical/chemical properties Addressed in first portion of talk

• Collect environmental fate properties


Collect environmental fate properties

• Perform environmental fate assessment Distribution in the environment (transport)

Persistence (degradation)

Bioaccumulation (bioconcentration)

Modeling exercises

Transport

• Qualitative assessment based on Chemical Properties Physical/chemical properties (addressed previously)

• Octanol/water partition coefficient (Log Kow)• Water solubility


Water solubility• Vapor pressure• Henry’s Law constant

Fate properties (addressed here)• Soil adsorption coefficient (Koc)• Bioconcentration factor (BCF)

• Quantitative assessment using multi-media (fugacity) model


13

Soil Adsorption Coefficient (Koc)

• Provides A measure of the ability of a chemical to sorb to the

organic portion of soil and sediment

• Indicates to the assessor


Indicates to the assessor The potential for the chemical to leach through soil and

be introduced into ground water The potential for partitioning of the chemical between

water and suspended solids and sediment

• Strong adsorption will impact other fate properties• Often expressed as log Koc

Log Koc Classifications

Adsorption Classifications

Predicted log Koc

Values

Very Strong 4.5


y g

Strong 3.5 – 4.4

Moderate 2.5 – 3.4

Low 1.5 – 2.4

Negligible < 1.5

Interpreting Koc Results

• Low Koc (not tightly bound to soil) Leaching into the soil

• Reduces surface level concentration

• Potential contamination of groundwater


Contamination of surface water with storm runoff

• High Koc (tightly bound to soil) Removal from water column via sorption to

sediment and particulate matter

May reduce rate of degradation because the chemical is not available to microorganisms


14

Interpreting Koc - Other Factors

• pH Soil adsorption decrease as ionization increases

• High clay content


Some chemicals may absorb very strongly to high-clay content soils

• Bond formation with humic matter Some chemicals, most notably aromatic amines,

may form chemicals bonds with organic matter, decreasing the potential for leaching

Persistence

• Removal in the Atmosphere Oxidation (AOP) Photolysis


• Removal in Soil and Water Hydrolysis (KHydro) Biodegradation (Biodeg) Photolysis Chemical decomposition

Atmospheric Oxidation

• Provides The atmospheric persistence of a

compound


p

• Indicates to the assessor How long the chemical may reside in the

atmosphere

Potential to travel long distances from the original point of release


15

Atmospheric Oxidation Processes

• Hydroxyl radicals (OH• radicals) The dominant atmospheric oxidant Produced by UV radiation in sunlight

• Ozone (O )


• Ozone (O3) Selective oxidant

• Nitrate radicals (NO3) Only important at night Limited primarily to urban areas Model not included in EPI v4.1

Interpreting Results

Classification Half-lifeRapid 2 hrs

Moderate 2 hrs - 1 day

Slow > 1 day - 10 days

Negligible > 10 days


Negligible 10 days

Half-life >2 days• Persistence criteria for New Chemicals

May be used to determine the potential for long-range transport

• Traveling large distances in air from the original point of release; crossing international boundaries

Hydrolysis

• Provides Reaction of a compound with water

• Indicates to the assessor


• Indicates to the assessor Persistence of a chemical substance

When hydrolysis products also need to be considered in the assessment

• Parent, hydrolysis product(s), both


16

Hydrolysis Process

• pH sensitive Typical environmental pHs range from

5-9


• Acid or base catalyzed Half-life can be calculated from the rate

constant and the pH

Hydrolysis Estimation

• HYDROWIN Converts acid, neutral, and base rate

constants to half-lives at pH 7 & 8


p

EPI V 4.1 has increased coverage for hydrolysis estimations

• See help section for a list of covered classes

• Additional classes identified

• Experimental data provided when available

Hydrolysis Rules of Thumb

• Some classes of chemicals hydrolyze extremely rapidly (i.e., in hours) Knowledge of rate constant not important


• Acid chlorides, epoxides, and siloxanes

• Changes in temperature can dramatically change the rate of the reaction 10 degree change = 250% change in rate

• Besides natural bodies of water, hydrolysis may also occur in clouds, fog, or moist soil, and effluent


17

Assessment for Hydrolysis

Hydrolysis Half-Life Species to Assess

1 h H d l i d t


<1 hour Hydrolysis product

1 hour – 14 daysParent compound & hydrolysis product

>14 days Parent compound

Biodegradation

• Provides The degradation of a chemical substance by

the action of microorganisms


• Indicates to the assessor Persistence in soil, water, and sediment

The amount of a chemical that may be removed in sewage treatment plants

Biodegradation Introduction

• Aerobic Occurs in oxygenated environments

• Surface water and soil

• Anaerobic


Occurs in oxygen-free systems• Sediment and groundwater• Generally much slower than aerobic degradation

• Primary Initial step in degradation process – forms a new

compound• Ultimate Complete mineralization to CO2 and water


18

Biodegradation Models - BIOWIN

• Probability of Rapid Biodegradation Uses 6 fragment-based models

• Linear and non-linear models


Linear and non linear models >0.5 – likely to biodegrade fast

<0.5 – not likely to biodegrade fast

• Expert Survey • Ultimate and Primary degradation

Linear and Non-Linear Models

1

Likely


0

0.5

Linear Non-Linear

Not Likely

y

Survey Models

• Fragment-based QSAR based on the results of an expert survey on the biodegradability of 200 substances

• Ultimate biodegradation model Semi-quantitative estimate of rate of aerobic ultimate biodegradation

• Primary Biodegradation Survey Model


• Primary Biodegradation Survey Model Semi-quantitative estimate of rate of aerobic primary biodegradation

• Result can be converted to a relative time frame

Result Time Result Time5.0 hours 3.0 weeks4.5 hours – days 2.5 weeks – months4.0 days 2.0 months3.5 days – weeks 1.0 longer


19

Biodegradation Results as Half-life

BIOWIN Output Half-Life (days)

Hours 0.17

Hours to Days 1 25


Hours to Days 1.25

Days 2.33

Days to Weeks 8.67

Weeks 15

Weeks to Months 37.5

Months 60

Recalcitrant 180

Ready Biodegradability Model

• Fragment method developed using data on 884 chemicals from the Japanese MITI protocol


• Provides pass/no pass results>0.50 Ready biodegradable

<0.50 Not Ready biodegradable

• Stringent test – a chemical giving a positive response is expected to biodegrade in the environment

Persistence Assessment

• Criteria

> 2 d< 2 dAir> 180 d> 60 d< 60 dWater, soil, sediment

Persistent ConcernLow Persistence


• Other considerations If the half-life is not known precisely, but it is known to

be rapid (<<60 days), then chemical is of low persistence concern

• Includes hydrolysis, chemical degradation, and photolysis where applicable

> 2 d< 2 dAir


20

Bioaccumulation

Bioaccumulation = Biomagnification & Bioconcentration

• Bioconcentration


The increase in the concentration of a chemical over that in an organism’s surroundings (e.g., water)

• Biomagnification The increase in the concentration of a chemical over that in an

organism’s diet

• Bioaccumulation The increase in the concentration of a chemical through all routes of

exposure

Bioaccumulation

• Bioconcentration often used as a surrogate for Bioaccumulation Provides the ratio of a chemical’s concentration in

the tissue of an aquatic organism to the concentration in the ambient water


concentration in the ambient water Indicates to the assessor

• The potential for a chemical to bioconcentrate in lipids (fatty tissue) of aquatic organisms

• The potential to bioaccumulate in higher trophic levels

Newer methods provide Bioaccumulation Factor (BAF) estimates as well

BCF Estimation – BCF & BAF

• Two QSAR methods – BCFWIN and BCFBAF

• BCFWIN method does not account for


metabolism under field conditions Compounds that metabolize may have a lower

BCF than predicted

• BCFBAF Draft method that adds additional factors

Used in conjunction with BCFWIN for the assessment of certain classes


21

BCF/BAF Criteria

BioaccumulationBioaccumulationLowLow

BioaccumulationBioaccumulation

ConcernConcern

BioaccumulationBioaccumulation

ConcernConcern


Fish BCFFish BCF <1000<1000 >>10001000 >>50005000

Fish Log BCFFish Log BCF <3<3 >>33 >>3.73.7

Volatilization from Water Model

• Volatilization model predicts half-life (in days) for volatilization from Model Lake (still water)


Model River (moving water)

• Based on Henry’s Law Constant• Indicates Partitioning in the environment

Removal in Wastewater Treatment

• The amount of a compound removed in a model sewage treatment plant Sometimes expressed as POTW removal


Sometimes expressed as POTW removal

• Indicates to the assessor How much of the chemical is discharged to

surface water• The residual may affect aquatic life or humans

through ingestion of fish or drinking water


22

STP Model

• Determines losses from physical processes Sludge adsorption Air stripping Biodegradation


Biodegradation• Allows for multiple biodegradation scenarios Degradation half-lives of 10,000 hrs (no

biodegradation) BIOWIN output half-lives User entered biodegradation half-lives

Multi-Media (Fugacity) Model

• Provides quantitative estimates for a model system the size of Ohio Based on estimated and inputted properties from

other modules


Can model multiple release scenarios Provides partition to Air, Water, Soil, and Sediment Provides estimated half-life for the chemical is each

media• Indicates to the assessor Gives a quantitative assessment of partitioning and

fate based on EPI SuiteTM estimates

HandsHands--OnOn


HandsHands OnOnSessionSession

04 - episuite - physical-chemical properties and environmental fate

Documents