Questions: Environmental Health and Exposure Assessment

Question 1

A non-threshold dose-response model is used for carcinogens because:

• A. Carcinogens are always detectable at any concentration
• B. Any level of exposure is assumed to carry some risk of harm
• C. Carcinogens follow a linear dose-response up to a safe threshold
• D. Risk drops to zero below the regulatory action level

Answer: (B)

Non-threshold models assume that even a single molecule of a carcinogen can initiate cellular damage that leads to cancer. This is why regulatory limits for carcinogens aim to minimize exposure rather than identify a 'safe' dose, in contrast to threshold models used for most non-carcinogenic toxicants.

Question 2

The principle 'the dose makes the poison' applies universally to most chemical hazards, including endocrine disruptors.

• T. True
• F. False

Answer: False

Endocrine disruptors can show non-monotonic dose-response relationships — for example, a very low dose may trigger a larger hormonal effect than a moderate dose because receptor saturation and feedback loops behave differently across dose ranges. This violates the classical toxicological assumption and is why standard high-dose animal testing can miss low-dose effects.

Question 3

What is an exposure pathway, and why is identifying each step along the pathway important for public health intervention?

Model answer: An exposure pathway is the route a contaminant travels from its source to a human receptor — typically: source → environmental medium (air, water, soil) → point of contact → route of entry (inhalation, ingestion, dermal) → target tissue. Identifying each step matters because interventions can break the chain at any point: removing the source, treating the medium, blocking the contact route, or using personal protective equipment.

Effective environmental health interventions rarely eliminate the source directly; more often they interrupt exposure at a feasible point in the pathway. Exposure assessment maps this chain quantitatively so that risk managers can estimate which intervention produces the largest reduction in dose.