RISK5002 Chap.9 Environmental and Toxicological Risk
Environmental and Toxicological Risk
Toxicological risk assessment estimates risks to people, animals, plants and ecosystems from physical, chemical and biological hazards. The lecture stresses that everything is made of chemicals, so the question is never whether a substance is natural but how exposure turns a hazard into harm.
The assessment runs in five steps: problem formulation with susceptible groups, hazard identification, dose-response assessment on a logarithmic dose scale, exposure assessment through pathway analysis and conceptual site models, and risk characterisation that combines every pathway.
This chapter applies the steps to arsenic near a former sheep dip, explains the no observed effect level, and evaluates the method's strengths and limits. The worked case follows arsenic in soil from problem formulation to characterisation, showing which groups count as susceptible and which pathways connect the source to people.
The lecture's examples, from an oil spill to contaminated milk, illustrate the range of physical, chemical and biological hazards, and its Western Sydney Airport example shows the method used for noise in an environmental impact statement. The chapter also explains why the method's outputs are estimates that carry substantial uncertainty.
What this chapter covers
- 01
Physical, chemical and biological hazards
- 02
Problem formulation and susceptible groups
- 03
Dose-response curves and NOEL
- 04
Exposure pathways and site models
- 05
Risk characterisation across pathways
- 06
Strengths and limits of the method
Worked example · free
Read a dose-response curve for an exposure limit
- +1The NOEL is the highest tested dose with no observed effect, here about 0.4 units.
- +1The 50% response near 16 units sits about forty times above the NOEL, showing how steep the curve becomes.
- +1A logarithmic axis spreads doses across several orders of magnitude so the whole curve fits on one chart.
- +1The regulator uses the NOEL as an input to acceptable limits, then compares it with exposure estimated through pathway analysis.
Key terms
- Dose-response curve
- A curve showing the response of a population as a function of dose or exposure.
- Exposure pathway
- The route a hazard takes from its source to the target population.
- NOEL
- The no observed effect level, the highest dose at which no effect is seen.
- Risk characterisation
- The final step that combines all pathways into an estimate of the likelihood of harm.
Environmental and Toxicological Risk FAQ
What are the five steps of an environmental risk assessment?
Problem formulation sets the purpose, target population and regulatory context; hazard identification finds the sources of harm; dose-response assessment relates exposure to effect; exposure assessment estimates the dose actually received through each pathway; risk characterisation combines all of this into the likelihood of harm.
Why do susceptible groups matter in problem formulation?
Some people are more sensitive to environmental chemicals because of age, sex, nutrition, pregnancy or other inherent and acquired factors. Defining these groups early ensures the exposure and risk estimates protect the people most at risk.
What limits the reliability of toxicological assessment?
It needs good data that may not exist, a high level of expertise, and it carries considerable uncertainty in dose-response curves and in the models used to build them, so conclusions should state that uncertainty.
What is a conceptual site model?
A conceptual site model is a diagram of how contamination at a site could reach people or the environment. It shows the source, each potential pathway through soil, air, water or food, any barriers, and the receptors. Drawing it during exposure assessment helps ensure that no pathway is missed when the risks are combined in the final step.
Exam move
Choose two cases from the news, such as a chemical spill and a noisy development, and write the five steps for each in a few lines. Practise drawing a source, pathway, barrier and receptor chain for every case. Learn the hazard categories with two examples each, and prepare a balanced paragraph on why an assessment estimates risk rather than proving safety.
Practise writing each step's output in one line for a new case, so that the five steps become a reliable answer plan, and keep two hazard examples per category ready for definition questions.
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