Further description:-  Exposure pathways 

Glossary Entry
The path from sources of pollutants via, soil, water, or food to man and other species or settings. 
Further description: Recycling, Reuse

Further description: exposure / pathways

 

How a contaminant or a chemical will be dangerous including the transfer within environmental medias and the intake possibilities for the receptor.

 

Further Information

 

1. Preface

Chemicals can be released into the soil, water or air from spilled or leaking containers, leaking landfills or dumps, through spraying, or released from smokestacks. These chemicals follow a pathway, or a route from the time of release to the point of human contact. When a substance enters the ecosystem where it is not normally found, it is called a contaminant. Humans become exposed to these contaminants by touching, breathing, or ingesting substances that contains the chemical (ATSDR, 1993, http://www.atsdr.cdc.gov).

To determine if human health is at risk of disease from contaminants, two things must occur:

§         There must be an exposure to a contaminant;

§         And the contaminant must be toxic.

A complete exposure pathway must be present for disease to occur. The elements of an exposure pathway are:

  1. The transport media - how the contaminant moves through the environment
  2. The exposure point - how people came in contact with the contaminant
  3. The exposure route - how the contaminant entered the body
  4. The receptor population - how susceptible the population is to the contaminant (adapted from ATSDR, 1994, http://www.atsdr.cdc.gov).

This is one of the main tasks, which has to be realised within a risk assessment. Nevertheless this means also a chance to reduce risks while interrupting, or reducing relevant or changing pathways and exposure scenarios.

Before starting a risk assessment an exposure assessment is required. Assessing how much of a substance people are exposed to is often difficult and based partially on assumptions.

2. Exposure

The matter of kind how a contaminant or a chemical will be dangerous for human, animals’ plants, water and air.

Intake scenarios are:

  • Inhalation
  • Soil ingestion
  • Dermal ingestion
  • Water ingestion
  • Food ingestion and mother milk

 

Exposure assessment is a major component of risk assessment.

Exposure may be long-term or short-term and occupational or environmental. Exposure is most frequently assessed by environmental exposure studies. These studies:

  • Estimate how much of a substance is/was present in the environment and how much of it people actually come/came into contact with.
  • Are usually conducted to assess long-term exposures. ** Exposure can also be assessed by personal exposure studies. These studies analyse bodily fluids or tissues to calculate how much of a substance people are exposed to.

Other components are toxicity assessment and problem identification and risk characterization.

 

Exposure Classifications

  • Occupational exposures are generally easier to measure, because they occur in a confined space during known lengths of time.
  • Environmental exposures involve greater uncertainty. The individual may be exposed to a chemical in a variety of locations-home, traffic, and shopping-and for varying amounts of time. The great mobility of people in modern society adds to the complexity of this determination.

Examples of exposures:

  • Long-term, occupational exposure: A factory worker inhales a chemical eight hours a day, five days a week, over several years.
  • Short-term, occupational exposure: A plant explosion creates fumes that workers inhale for a few minutes.
  • Long-term, environmental exposure: People in a community drink water from wells contaminated by seepage from an industrial disposal site.
  • Short-term environmental exposure:
    • A child eats 10 aspirin in 5 minutes.
    • People in several city blocks breathe fumes for a few hours after a train tank car spills a hazardous substance.

Measuring Exposure

Exposure can be estimated in two ways.

  • Personal exposure studies measure the amounts of a substance in the body. This method is usually appropriate after a short-term exposure, when the full amount of the substance taken in may still be in the body.
  • Environmental exposure studies measure amounts of a substance in the environment, determine the route of exposure (inhalation, ingestion, or skin contact), and estimate how much is in contact with the population. This method is usually appropriate for measuring long-term exposures to substances that the human body breaks down and excretes. However, variability over time in the concentration of the substance in the environment may lead to uncertainty in this type of study.

Amount Of Substance In Environment

 

Measuring the amount of a substance in the environment is usually straightforward for short-term exposures. Estimating long-term past exposures is usually more complex.

Long-term estimates are difficult when:

  • All the sources are hard to identify.
  • The exact emissions of all sources over time may not be known.
  • Movement of the substance is difficult to assess. For example, wind direction, rainfall, or groundwater seepage may be difficult to measure over time.
  • The sources vary over time. For example, if the substance is in a food item, the amount may vary according to maturity, season, or other factors.

Examples of measuring long-term exposures:

  • Substances in drinking water can be measured, and if past measurements are available, scientists will know the amount present over time.
  • If measurements were not made previously, scientists must estimate the amount that was present. Commonly they determine the source of the substance, and estimate how much was emitted and for how long. Then they use mathematical models to calculate how much entered the medium (drinking water, air, soil, food) that people were exposed to.
  • There may be many sources. For mercury in fish, there may be both local and distant sources, such as different industries. Scientists identify the sources and use mathematical models to calculate transport and estimate the amount present in fish over time.

Models

The mathematical models used to calculate the movement of chemicals are based on the properties of the chemical in question. These properties include:

  • Vapour pressure-how easily it evaporates.
  • Solubility-how easily it dissolves in different mediums, such as water or animal fat.
  • Adsorption-how strongly it attaches to soil.
  • Persistence-how rapidly it is broken down in the environment.

 

3. Pathways

Way from sources of pollutants via, soil, water, or food to human and other species or settings.

 

After the amount of the substance in the environment is assessed, the pathway of exposure must be determined.

Incomplete knowledge of human behaviour requires that assumptions must be made to estimate how much of the chemical is taken in. Scientists must make assumptions about such things as:

  • how much water or a specific food do people drink or eat each day.
  • whether people filter their water/how they prepare their food.
  • how much time people spend indoors/outdoors.
  • whether behaviours vary with age, socio-economic class, or ethnic group.

Soil related pathways are:
- soil – human (direct pathway)
- soil – food plant  - human
- soil - food plant – farm animal - human
- soil - (leachate-) groundwater (- drinking water - human)
- soil - (leachate -) (groundwater -) surface water (- human)
- soil – soil air  - indoor air  - human
- soil - (leachate -) groundwater – soil air – indoor air  - human.

Concerning these pathways we have to assess emissions caused by abandoned sites within:

- soil
- leachate / groundwater
- surface water
- soil air and
- indoor air and ambient air.

 

Role of Exposure Assessment in Risk Assessment

In the end, an exposure assessment provides information on how much of a substance a population has been or will be exposed to.

An exposure assessment enables the results of toxicity assessments to be applied to the real world. That is, once the exposure assessment has estimated the amount of a substance the population of interest has actually been exposed to, then the results of the toxicity assessments can be used to estimate the degree of harm to that population.

 

4. Cross link to European risk modelling

 

Within Europe During the 80th and 90th the responses of governments, industry and the public to the problems posed by contaminated land have differed from country to country, both in nature and in relative timing.

A condensed description of CONTAMINATED LAND APPROACHES IN 16 EUROPEAN COUNTRIES you will find under http://www.clarinet.at/.

In two key documents a comparison between existing risk models.

Recommendation concerning exposure and pathways are:

 

§         Identification of which elements of the human exposure calculation, i.e. boundary conditions, model concepts/algorithms, input parameters should be standardised throughout Europe.

§         To use fixed model concepts/algorithms and input parameters, when these are suitable for standardisation and harmonisation (“fixed model tools and input parameters”).

§         To use options for model concepts/algorithms and input parameters, where some – but not total – standardisation is sensible (“model options”).

§         To use flexible model concepts and input parameters, where standardisation and harmonisation is not suitable for political, geographical or ethnological reasons, and where choice is desirable (“flexible model tools and input parameters”).

§         To develop a procedure on assessing human exposure, including documentation of the sensitivity of calculated human exposure to the input parameters and a guideline on when and how to measure concentrations in contact media.

§         To provide information on the uncertainty/ reliability of the calculated human exposure.

 

§         To begin studies to compare modelled and measured exposures to move from assumed conservatism to quantitative data on levels of conservatism, to decrease the conservatism of models where possible and the bias toward overly high safety factors.

 

5. Author

 Jörg Frauenstein, German Federal Environmental Agency, http://www.umweltbundeamt.de

 

6. Acknowledgement

Extracted from:

http://www.envirotools.org/exposurepathways.shtml

http://www.facsnet.org/tools/ref_tutor/risk/ch2expos.php3

http://www.clarinet.at/library/rivm_rep.pdf

Review of the "NICOLE/ISG Risk Assessment Comparison Study" http://www.consoil.de/consoil/review.html

Assessing Risks from Contaminated Sites: Policy and Practice in 16 European Countries, Colin C Ferguson, http://www.clarinet.at/library/Ferguson_Paper_Policies.PDF

 

 


Key Documents

 

“Variation in calculated human exposure. Comparison of calculations with seven European human exposure models,” CLARINET, 2002, http://www.clarinet.at/library/rivm_rep.pdf

Review of the "NICOLE/ISG Risk Assessment Comparison Study" http://www.consoil.de/consoil/review.html

 

NICOLE / ISG Risk Assessment Comparison Study. FINAL REPORT., Arcadis Geraghty & Miller International, Inc., Newmarket, UK, Arcadis GMI, July 2003.

 

“Variation in calculated human exposure: Comparison of calculations with seven European human exposure models.” RIVM report 711701030, March 2001. RIVM, Bilthoven, The Netherlands. Swartjes, F.A. 2002

 

“Risk assessment for contaminated sites in Europe” – Colin Ferguson, Chapter in Risk Assessment For Contaminated Sites In Europe - Vol. 1 Scientific Basis, First printed 1998, LQM Press, Nottingham. ISBN 0953 309010.

 

Dieter,H.H., Konietzka,R.: Which multiple of safe body dose derived on the basis of default factors would probably be unsafe? regulatory Toxicology and Pharmacology 22, 1995, 262 - 267.

Bockting,G.J.M., Swartjes, F.A., Koolenbrander, J.G.M. and van den Berg,R.: Beoordelingssyste­matiek bodemkwaliteit ten behoeve van bouwvergunningsaanvragen. RIVM Report No. 715810001, 1994.

US-EPA: Soil Screening Guidance: User's Guide, July 1996, http://www.epa.gov/superfund/resources/soil/index.htm#user

US-EPA:Exposure Factors Handbook, Volume 1 - 3, Report, August 1997, http://www.epa.gov/ncea/pdfs/efh/front.pdf.

Concerted Action on Risk Assessment for Contaminated Sites in the European Union. CARACAS-Newsletter No.1 / 96, 1996.

 

Useful Web Links

http://www.consoil.de/consoil/review.html

 

http://www.clarinet.at/library/rivm_rep.pdf

http://www.atsdr.cdc.gov

http://www.envirotools.org/exposurepathways.shtml

http://www.facsnet.org/tools/ref_tutor/risk/ch2expos.php3

http://www.epa.gov/ncea/pdfs/efh/front.pdf

http://www.epa.gov/superfund/resources/soil/index.htm#user

 

List of Abbreviations

 

Abbreviation

Description

DIR

daily intake rate

IR

user specific intake rate of contact media (e.g. soil, dust)

EFR

site and user specific exposure frequency

BW

user specific body weight

PDI or PD

potential daily intake

CEP

completed exposure pathway

ATSDR

Agency for Toxic Substances and Disease Registry

CCM

pollutant concentration

AV

biological availability for the exposure pathway soil oral

R

resorption factor

RI

risk indices

TRD

tolerable doses rates for humans derived from toxicological data

 

List of Key Technical Terms

 

Term

Description

pathway

Way from sources of pollutants via, soil, water, or food to human and other species or settings.

exposure

The matter of kind how a contaminant or a chemical will be dangerous for human, animals’ plants, water and air.

Exposure assessment

An exposure assessment evaluates how much of a substance people come into contact with, how often, and for how long a period.

Measuring Exposure

Exposures are estimated in two ways -- directly by measuring body fluids or tissues or indirectly by analyzing environmental levels of contaminants.

Amount of Exposure

scenarios have to characterize people's behavior to estimate exposure

 

 

Authors
Jörg Frauenstein
German Federal Environmental Agency, Germany

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